Polishing composition with excellent storage stability and method for producing the same

Abstract

[Problem] To provide a polishing composition which is used for polishing a silicon wafer and can improve polishing speed and storage stability. [Solution] Provided is a polishing composition that contains an aqueous dispersion of silica particles, wherein the Rsp value, which is derived from relaxation times determined from pulse NMR measurements of the aqueous dispersion of silica particles and pure water, is not less than 0.01 and less than 0.15. Rsp=(Rav-Rb) / (Rb) Rsp is an indicator that indicates the affinity of silica particles for water. Rav is the inverse of the relaxation time for an aqueous dispersion of silica particles in which the silica concentration is 5 mass%. Rb is the inverse of the relaxation time for pure water.

Description

[Technical Field]

[0001] The present invention relates to a polishing composition using silica-based abrasive grains and a method for producing the same. [Background technology]

[0002] Polishing compositions using silica-based abrasive grains are used for polishing silicon wafers. The polishing composition generally contains silica-based abrasive grains in an aqueous medium such as water, and may further contain an alkaline compound, a water-soluble compound, a chelating agent, an oxidizing agent, a metal corrosion inhibitor, etc. Aiming to shorten polishing time by achieving a high polishing rate, a polishing composition has been disclosed that is defined using a function indicating affinity with water, which is calculated from the relationship between the inverse of the relaxation time of pulse NMR in a dispersed state of silica abrasive grains and the total surface area of ​​the silica abrasive grains (see Patent Document 1). Also disclosed is a polishing composition in which the relationship between the BET specific surface area of ​​silica particles contained as abrasive grains and the specific surface area measured by pulsed NMR is defined (see Patent Document 2). Furthermore, a polishing composition has been disclosed in which the NMR relaxation time is evaluated using the solvent affinity of the abrasive grains (see Patent Documents 3 and 4). A polishing composition has been disclosed in which the pulse NMR measurement value Rsp=(Rav-Rb) / (Rb) of a dispersion of silica particles is 0.15 to 0.7, and the shape factor SF1 of the silica particles is SF1=(area of ​​a circle whose diameter is the maximum diameter of the particle) / (projected area) of 1.20 to 1.80, thereby improving the polishing rate and producing a good polished surface (see Patent Document 5). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 116890 [Patent Document 2] International Publication No. 2015 / 152151 [Patent Document 3] JP 2017-117894 A [Patent Document 4] International Publication No. 2018 / 012174 [Patent Document 5] International Publication No. 2020 / 091000 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a polishing composition which achieves a high removal rate when used to polish silicon wafers and has improved storage stability during storage or transportation. The inventors focused on the amount of water molecules bound to the surface of silica particles, using the Rsp value derived from the relaxation time obtained by pulse NMR measurement as an indicator, and discovered that by using silica particles with an Rsp value within a predetermined range as abrasive grains, the storage stability of the polishing composition can be improved while maintaining high polishing performance. [Means for solving the problem]

[0005] A first aspect of the present invention is a polishing composition containing an aqueous dispersion of silica particles, wherein the polishing composition has the following Rsp value, which is derived from relaxation times obtained by pulse NMR measurement of the aqueous dispersion of silica particles and pure water, of 0.01 or more and less than 0.15: Rsp = (Rav - Rb) / (Rb) where Rav is the reciprocal of the relaxation time of an aqueous dispersion of silica particles with a silica concentration of 5 mass%, and Rb is the reciprocal of the relaxation time of pure water. According to a second aspect, the polishing composition according to the first aspect, wherein the silica particles have an average secondary particle diameter of 40 to 200 nm as measured by a dynamic light scattering method and an average primary particle diameter of 20 to 100 nm as measured by a nitrogen gas adsorption method. As a third aspect, the polishing composition according to the first aspect, wherein a treatment liquid obtained by contacting the silica particle aqueous dispersion with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange is frozen at −70° C. to −80° C., and further freeze-dried at room temperature under a pressure of 5 Pa or less to remove the dispersing medium, and the resulting silica particle powder has a silanol group content of 0.1 to 1.5 mmol / g as calculated by the following formula from the mass loss when heated from room temperature to 700° C. and the molecular weight of water molecules in thermogravimetric analysis: Amount of silanol groups (mmol / g) = 2 × (M2 - M1) ÷ M H2O ÷(M0-M1)×1000 where M0 is the mass of the silica particle powder subjected to thermogravimetric analysis before heating, M1 is the mass loss amount when it reached 200°C, M2 is the mass loss amount when it reached 700°C, and M H2O represents the molecular weight of a water molecule, As a fourth aspect, a silica particle powder obtained by contacting the silica particles with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange is frozen at −70° C. to −80° C., and then freeze-dried at room temperature under a pressure of 5 Pa or less to remove the dispersant has a density of 2.20 to 2.35 g / cm as measured by dry density measurement. 3 The polishing composition according to the first aspect, As a fifth aspect, the silica particle powder obtained by contacting the silica particle aqueous dispersion with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange is heated at 140°C for 2 hours and then heated at 290°C for 1 hour to remove the dispersion medium. The specific surface area (S N2 ) based on the water vapor adsorption method (S H2O ) ratio (S H2O / S N2 ) is 0.10 to 0.65; As a sixth aspect, the polishing composition according to any one of the first to fourth aspects, in which the silica particle aqueous dispersion has been subjected to a heat history at a temperature of 140° C. or higher and lower than 260° C. As a seventh aspect, the polishing composition according to any one of the first to fifth aspects, in which the concentration of the silica particles is 1 to 40 mass %. According to an eighth aspect, the polishing composition according to any one of the first to seventh aspects further contains at least one additive selected from the group consisting of an acidic compound, a basic compound, a water-soluble compound, a chelating agent, an oxidizing agent, and a metal corrosion inhibitor. According to a ninth aspect, the polishing composition according to the eighth aspect, wherein the basic compound is at least one basic compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates, and nitrogen-containing basic compounds. According to a tenth aspect, the polishing composition according to the eighth aspect, in which the chelating agent is an aminocarboxylic acid chelating agent or a phosphonic acid chelating agent. According to an eleventh aspect, the polishing composition according to any one of the first to tenth aspects, wherein the polishing composition has a pH of 1 to 12. As a twelfth aspect, in a test in which the polishing composition was heated and stored at 50°C for 28 days, With respect to the average secondary particle diameter measured by dynamic light scattering of the polishing composition before heating and storing at 50°C for 28 days, The polishing composition according to any one of the first to eleventh aspects, wherein the polishing composition has an average secondary particle diameter increase rate of less than 5% after heat storage at 50°C for 28 days as measured by a dynamic light scattering method. According to a thirteenth aspect, the polishing composition according to any one of the first to twelfth aspects is used for polishing a silicon wafer or a device wafer. As a fourteenth aspect, a step of preparing a colloidal silica dispersion as a precursor; The method for producing the polishing composition according to any one of the first to thirteenth aspects includes a step of heating the precursor at a temperature of 140°C or higher but lower than 260°C to obtain the silica particle aqueous dispersion. As a fifteenth aspect, a silica particle dispersion containing a solvent and silica particles, wherein the following Rsp value derived from relaxation times obtained by pulse NMR measurement of the silica particle dispersion and a blank solution is 0.01 or more and less than 0.15: Rsp = (Rav - Rb) / (Rb) where Rav is the reciprocal of the relaxation time of a silica particle dispersion with a silica concentration of 5 mass%, and Rb is the reciprocal of the relaxation time of a blank solution. According to a sixteenth aspect, the silica particle dispersion according to the fifteenth aspect, wherein the solvent contains water. According to a seventeenth aspect, the silica particle dispersion liquid according to the fifteenth aspect, in which the silica particles have an average secondary particle diameter of 40 to 200 nm as measured by a dynamic light scattering method and an average primary particle diameter of 20 to 100 nm as measured by a nitrogen gas adsorption method. As an eighteenth aspect, the silica particle dispersion according to the fifteenth aspect, wherein a treatment liquid obtained by bringing the silica particle dispersion into contact with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange is frozen at −70° C. to −80° C., and the treatment liquid is further freeze-dried at room temperature under a pressure of 5 Pa or less to remove the dispersion medium, and the silica particle powder obtained has a silanol group amount of 0.1 to 1.5 mmol / g as calculated by the following formula from the mass loss when heated from room temperature to 700° C. and the molecular weight of water molecules in thermogravimetric analysis: Amount of silanol groups (mmol / g) = 2 × (M2 - M1) ÷ M H2O ÷(M0-M1)×1000 where M0 is the mass of the silica particle powder subjected to thermogravimetric analysis before heating, M1 is the mass loss amount when it reached 200°C, M2 is the mass loss amount when it reached 700°C, and M H2O represents the molecular weight of a water molecule, In a nineteenth aspect, a silica particle powder obtained by contacting the silica particle dispersion with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange is frozen at −70° C. to −80° C., and then freeze-dried at room temperature under a pressure of 5 Pa or less to remove the dispersion medium, has a density of 2.20 to 2.35 g / cm as measured by dry density measurement. 3The silica particle dispersion according to a fifteenth aspect, As a twentieth aspect, the silica particle powder obtained by contacting the silica particle dispersion with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange is heated at 140°C for 2 hours and then heated at 290°C for 1 hour to remove the dispersion medium, and the specific surface area (S N2 ) based on the water vapor adsorption method (S H2O ) ratio (S H2O / S N2 ) is 0.10 to 0.65. According to a twenty-first aspect, the silica particle dispersion according to any one of the fifteenth to twentieth aspects is a silica particle dispersion that has undergone a thermal history at a temperature of 140° C. or higher and lower than 260° C. According to a twenty-second aspect, the silica particle dispersion liquid according to any one of the fifteenth to twentieth aspects, in which the concentration of the silica particles is 1 to 40 mass %. As a 23rd aspect, a step of preparing a colloidal silica dispersion as a precursor; a step of heating the precursor at a temperature of 140°C or higher and lower than 260°C to obtain the silica particle dispersion liquid, The method for producing a silica particle dispersion liquid according to any one of the fifteenth to twenty-second aspects is provided. [Effects of the Invention]

[0006] The present invention focuses on the amount of water molecules bound to the surface of silica particles used as abrasive grains, using the Rsp value derived from the relaxation time obtained by pulse NMR measurement of a dispersion of silica particles used as abrasive grains in an aqueous medium and pure water, as an indicator, and has discovered that by achieving a specific Rsp value, a high polishing rate can be achieved and the storage stability of the polishing composition can be improved. Since a high (fast) removal rate leads to an improvement in wafer production efficiency, a polishing composition is required to be able to realize a high removal rate. In addition, if the storage stability of the silica particles contained in the polishing composition is poor, the silica particles will aggregate during storage or transportation, generating minute foreign matter, which may cause a decrease in the removal rate and the occurrence and increase of defects during polishing, so high storage stability is also required.

[0007] The polishing composition contains silica particles as abrasive grains. The interaction between the surface of the silica particles and the aqueous medium in the polishing composition changes depending on the surface condition of the silica particles, and this change in interaction affects the removal rate and storage stability of the polishing composition. In silica particles used as abrasive grains in polishing compositions, the water present on or around the particle surface is classified into bound water and free water depending on its state. Free water refers to water that exists around the silica particles but exists in a free state without interacting with the silica particles. On the other hand, bound water refers to water that is hydrogen-bonded to the silica particles via silanol groups on the silica particle surface. This bound water plays an important role in ensuring good contact between the silica particles and water.

[0008] The state (behavior) of water molecules can be determined from the relaxation time of the protons in water molecules measured by pulsed NMR. The relaxation mechanism in nuclear magnetic resonance (NMR) consists of the process of releasing absorbed energy and the process of the precession of aligned nuclear spins becoming unbalanced. The former is called spin-lattice relaxation (longitudinal relaxation) and its relaxation time is called T1, while the latter is called spin-spin relaxation (transverse relaxation) and its relaxation time is called T2. In T1 relaxation, relaxation is most likely to occur when the speed of molecular motion is approximately the same as the resonance frequency. For example, free water molecules that are not in contact with silica particles (free water) and water molecules that are in contact with silica particles (bound water) have different response times to magnetic field changes, i.e., different relaxation times. In this case, a short relaxation time is thought to indicate that the particle surface in contact with water is large and the particles are highly dispersible. In addition, T2 relaxation occurs due to magnetic interactions. Measurement of relaxation time by pulsed NMR can be said to be a measurement method that utilizes the difference in T2 relaxation. The presence of this bound water in a specific range effectively improves the polishing rate and storage stability during polishing.

[0009] In the present invention, by highly controlling the affinity between silica particles as abrasive grains and the aqueous medium in the polishing composition, it is possible to achieve both improved polishing rate and improved storage stability, particularly in polishing silicon wafers. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below. In the present invention, the silica particle dispersion is a dispersion of silica particles in water or an organic solvent, or a mixed solvent of water and an organic solvent, and a silica particle aqueous dispersion in which silica particles are dispersed in water, a silica particle organic solvent dispersion in which silica particles are dispersed in an organic solvent, and a silica particle mixed solvent dispersion in which silica particles are dispersed in a mixed solvent of water and an organic solvent are sometimes referred to as a colloidal silica dispersion or silica sol, and silica particles are sometimes referred to as colloidal silica (colloidal silica).

[0011] <Rsp value> The present invention relates to a polishing composition containing an aqueous dispersion of silica particles, wherein the polishing composition has an Rsp value of 0.01 or more and less than 0.15, as shown below, derived from the relaxation times obtained by pulse NMR measurement of the aqueous dispersion of silica particles and pure water. The present invention also relates to a silica particle dispersion containing a solvent and silica particles, wherein the Rsp value of 0.01 or more and less than 0.15, as shown below, derived from the relaxation times obtained by pulse NMR measurement of the silica particle dispersion and the solvent (e.g., pure water). Rsp = (Rav - Rb) / (Rb) The Rsp value is an index showing the affinity of silica particles to a solvent, particularly to water molecules, and Rav is the reciprocal of the relaxation time of a silica particle dispersion (e.g., a silica particle aqueous dispersion) with a silica concentration of 5% by mass, and Rb is the reciprocal of the relaxation time of a solvent (e.g., pure water). The Rsp value can be, for example, 0.03 to less than 0.15, 0.05 to less than 0.15, 0.01 to 0.14, 0.03 to 0.14, 0.05 to 0.14, or 0.07 to 0.14. When the Rsp value is 0.01 or more, the silica particles have a moderate water affinity, and can maintain dispersibility in a solvent or a polishing composition. In addition, when the Rsp is less than 0.15, the hydroxyl groups (OH) of water molecules bound near the surface of the silica particles can be easily dispersible. - ) and can suppress excessive dissolution of the silica particle surfaces due to the hydroxy groups when the polishing composition is prepared. As a result, aggregation of the silica particles in an aqueous medium (water) is suppressed, and when a polishing composition containing the silica particles is used for polishing a silicon wafer, the polishing rate is improved and the storage stability of the polishing composition is also improved.

[0012] The measurement principle of this technique (pulse NMR) is based on the fact that solvent molecules in contact with or adsorbed on the particle surface and solvent molecules in the bulk solvent (solvent molecules in a free state that are not in contact with the particle surface) respond differently to changes in magnetic field. When a magnetic field is applied to liquid molecules, energy transfer occurs when they transition from an excited state to a ground state. Generally, energy transfer occurs between liquid molecules (solvent molecules) adsorbed on particle surfaces via the particles, whereas energy transfer is less likely to occur between liquid molecules (solvent molecules) in bulk liquids because there is no intermediary between them. As a result, the NMR relaxation time of liquid molecules (solvent molecules) adsorbed on particle surfaces is shorter than that of molecules in bulk liquids.

[0013] Furthermore, the relaxation time measured in a silica particle dispersion (e.g., a silica particle aqueous dispersion) is the average of two relaxation times reflecting the liquid volume concentration on the silica particle surface and the liquid volume concentration in the free state (liquid in the bulk liquid but not adsorbed on the particle surface). Here, the relaxation time constant R is the reciprocal of the relaxation time T, Rav=(Ps*Rs)+(Pb*Rb) It is calculated by: Rav: average relaxation time constant, that is, the reciprocal of the relaxation time of a silica particle dispersion (for example, an aqueous silica particle dispersion). Ps: the volume concentration of the liquid on the particle surface, that is, the volume concentration of the silica particle dispersion (for example, the silica particle aqueous dispersion). Rs: the relaxation time constant of the liquid molecules adsorbed on the particle surface, that is, the reciprocal of the relaxation time of the liquid molecules adsorbed on the particle surface. Pb: The volume concentration of the bulk liquid, i.e., the volume concentration of a blank solution obtained by removing silica particles from a silica particle dispersion (e.g., an aqueous silica particle dispersion) (in the present invention, for example, pure water is used in the case of an aqueous dispersion, and a solvent with the same composition ratio as the contained solvents is used in the case of an organic solvent dispersion or a dispersion in a mixed solvent of water and an organic solvent). Rb: the relaxation time constant of the bulk liquid molecule, i.e., the reciprocal of the relaxation time of a blank solution (e.g., pure water).

[0014] The pulse NMR measurement value of the silica particle dispersion (for example, silica particle aqueous dispersion) is calculated as Rsp=(Rav-Rb) / (Rb). Rav and Rb are the reciprocals of the relaxation times (transverse relaxation time T2, specifically, the NMR relaxation time after dispersing silica abrasive grains and the NMR relaxation time of a blank solution (e.g., pure water)) measured using a pulsed NMR apparatus (trade name) Acorn area manufactured by Xigo nanotools. Measurement conditions: magnetic field: 0.3T, measurement frequency: 13MHz, measurement nucleus: 1 1 H NMR, measurement method: CPMG pulse sequence method, sample volume 0.77 mL, temperature: 30°C. Rsp is an index of the affinity of the particle surface with the solvent. Note that, for silica particles with the same specific surface area, the larger this value (Rsp) the higher the affinity with the solvent, and particularly when the solvent is aqueous, the higher the hydrophilicity.

[0015] <Particle size (average primary particle size, average secondary particle size)> The average primary particle size of the colloidal silica dispersion refers to the average primary particle size of silica particles, which are the dispersoid. In the present invention, unless otherwise specified, the average primary particle size of the colloidal silica dispersion (silica particles) refers to the particle size converted from the specific surface area obtained by measurement using a nitrogen gas adsorption method (BET method). The specific surface area diameter (average particle diameter (specific surface area diameter) D (nm)) measured by the nitrogen gas adsorption method (BET method) is calculated by the specific surface area S (m 2 / g), D(nm) = 2720 / S. In the present invention, the average primary particle diameter of the silica particles is, for example, 20 to 100 nm, and can also be, for example, 20 to 85 nm, 30 to 70 nm, or 35 to 60 nm. When the average primary particle diameter of the silica particles is 20 nm or more, the silica particles contact both the silicon wafer and the polishing pad when used to polish a silicon wafer, thereby improving the polishing rate. Furthermore, the movement distance of the silica particles due to Brownian motion can be prevented from becoming excessively large, thereby reducing the frequency of contact between silica particles in the polishing composition and improving storage stability. When the average primary particle diameter of the silica particles is 100 nm or less, the occurrence of defects due to scratches caused by rubbing the silica particles against the silicon wafer surface when used to polish a silicon wafer can be reduced. Furthermore, the silica particles settle in the polishing composition, preventing adhesion of the silica particles to each other at the bottom of the storage container, thereby improving the storage stability of the polishing composition.

[0016] The average secondary particle diameter and the dispersion state (whether the silica particles are dispersed or aggregated) of the silica particles in the silica particle dispersion or the polishing composition can be determined by measuring them using a dynamic light scattering method. The average secondary particle size represents the average value of the secondary particle size (dispersed particle size), and the average secondary particle size in a completely dispersed state is said to be about 1.2 to 2 times the average primary particle size (the specific surface area diameter obtained by measurement using the nitrogen gas adsorption method (BET method) or the Sears method, and represents the average value of the primary particle size).The larger the value of the average secondary particle size / average primary particle size, the more it can be determined that the silica particles in the medium are in an agglomerated state. In the present invention, the average secondary particle diameter of silica particles, i.e., for example, colloidal silica dispersion (colloidal silica particles), as measured by dynamic light scattering is, for example, 40 to 200 nm, or may be 40 to 150 nm, 40 to 100 nm, or 50 to 80 nm. Having an average secondary particle diameter within the above range can suppress aggregation of silica particles in the polishing composition. As a result, the polishing rate when used to polish silicon wafers can be further improved, and the storage stability of the polishing composition can be improved. In the present invention, the average secondary particle diameter of the silica particles as measured by dynamic light scattering is measured using a Zetasizer Nano (trade name, manufactured by Malvern Panalytical) in accordance with ISO 22412:2017. The average secondary particle diameter refers to the Z-average particle diameter measured by dynamic light scattering.

[0017] <Polyvalent metal impurities> The polishing composition containing the silica particle aqueous dispersion of the present invention can have a polyvalent metal impurity content of 1 to 100 ppm / SiO2, 1 to 50 ppm / SiO2, or 1 to 40 ppm / SiO2. The silica particle dispersion of the present invention may contain polyvalent metal impurities in an amount of 1 to 100 ppm / SiO2, 1 to 50 ppm / SiO2, or 1 to 40 ppm / SiO2. By keeping the amount of polyvalent metal impurities contained in the polishing composition within the above range, it is possible to suppress changes in the pH or electrolyte concentration of the polishing composition due to the leaching of polyvalent metal impurities from the silica particles, or deterioration in the dispersion stability of the silica particles due to the cationized polyvalent metals in the polishing composition acting as aggregating agents for the silica particles. By ensuring that the amount of polyvalent metal impurities contained in the silica particle dispersion is within the above range, it is possible to suppress changes in the pH or electrolyte concentration of the silica particle dispersion due to elution of the polyvalent metal impurities from within the silica particles, or deterioration in the dispersion stability of the silica particles due to the cationized polyvalent metal in the silica particle dispersion acting as an aggregating agent for the silica particles. In addition, by making the amount of polyvalent metal impurities contained in the silica particle dispersion liquid within the above range, the amount of polyvalent metal impurities contained in the silica particles can be controlled, the network of Si-O-Si bonds constituting the skeleton of the silica particles becomes dense, and the excessive dissolution of the silica particle surface caused by hydroxyl groups can be suppressed.As a result, when used in polishing silicon wafers, the polishing rate can be further improved, and the storage stability of the polishing composition can be improved.

[0018] Examples of the polyvalent metal impurities include iron, aluminum, calcium, magnesium, titanium, zirconium, copper, nickel, chromium, zinc, lead, etc. The amount of polyvalent metal impurities can be analyzed by pretreating the polishing composition or silica particle dispersion to completely dissolve the silica particles contained in the composition or dispersion, and then by inductively coupled plasma optical emission spectroscopy (ICP-OES), inductively coupled plasma mass spectroscopy (ICP-MS), atomic absorption spectroscopy (AA), or the like. Pretreatment for dissolving silica particles can be carried out, for example, by the following process. 36 mL of 38% by weight hydrofluoric acid aqueous solution, 6 mL of 61% by weight nitric acid, and 0.3 mL of 96% by weight sulfuric acid are added to 1 g of silica particles contained in the polishing composition or silica particle dispersion. The resulting mixed solution is treated at 210°C for 15 minutes using a microwave sample pretreatment device to dissolve the silica particles, and the decomposition liquid is then recovered. The recovered decomposition liquid is heated at 120°C under atmospheric pressure until the solvent evaporates and the mixture is dried to obtain a dried product. 0.3 mL of 61% by weight nitric acid is added to the dried product, and then pure water is added so that the total mass of the dried product, nitric acid, and pure water becomes 3 g, thereby obtaining a sample for metal impurity analysis.

[0019] <Silanol group amount> The silica particles contained in the polishing composition or silica particle dispersion of the present invention can have a predetermined amount of silanol groups. That is, the silica particle powder obtained by freeze-drying the colloidal silica dispersion containing the silica particles at room temperature under a pressure of 5 Pa or less to remove the dispersing medium can have a silanol group amount calculated by the following formula from the mass loss when heated from room temperature to 700°C in thermogravimetric analysis and the molecular weight of water molecules, for example, of 0.1 to 1.5 mmol / g, 0.3 to 1.5 mmol / g, 0.5 to 1.5 mmol / g, 0.3 to 1.4 mmol / g, 0.5 to 1.4 mmol / g, 0.3 to 1.3 mmol / g, or 0.3 to 1.3 mmol / g. Amount of silanol groups (mmol / g) = 2 × (M2 - M1) ÷ M H2O ÷(M0-M1)×1000 where M0 is the mass of the silica particle powder subjected to thermogravimetric analysis before heating, M1 is the mass loss amount when it reached 200°C, M2 is the mass loss amount when it reached 700°C, and M H2O represents the molecular weight of a water molecule.

[0020] To obtain a silica particle powder by the freeze-drying method, the target silica particle dispersion is first contacted with a cation exchange resin, an anion exchange resin, and a cation exchange resin in that order to obtain an ion-exchanged solution, which is then frozen at −70° C. to −80° C. and freeze-dried at room temperature under a pressure of 5 Pa or less to remove the dispersant, thereby obtaining the desired silica particle powder.

[0021] Silica particles have silanol groups on their surfaces, which easily adsorb water through hydrogen bonds. Therefore, to quantify the amount of silanol groups on silica particles from the mass loss due to heating, it is preferable to heat the particles to approximately 200°C, at which point the adsorbed water is desorbed, as described above. Furthermore, if the amount of silanol groups on the silica particles is greater than the above, for example, 1.5 mmol / g, bonding between particles is likely to occur when two silica particles come into contact, and the stability of the polishing composition or silica particle dispersion is deteriorated.If the amount of silanol groups on the silica particles is less than the above, for example, 0.1 mmol / g, the silica particle surfaces are not sufficiently solvated in the polar solvent, and therefore the silica particles cannot maintain their dispersibility and aggregate and precipitate, and the stability of the polishing composition or silica particle dispersion is deteriorated.

[0022] <density> The silica particles contained in the polishing composition or silica particle dispersion of the present invention can have a predetermined density. That is, the silica particle powder obtained by freeze-drying the colloidal silica dispersion containing the silica particles at room temperature under a pressure of 5 Pa or less to remove the dispersion medium has a density measured by dry density measurement of, for example, 2.20 to 2.35 g / cm. 3 , 2.22~2.35g / cm 3 , 2.25~2.35g / cm 3 , 2.27~2.35g / cm 3 , 2.25~2.33g / cm 3 , 2.25~2.30g / cm 3 , or 2.27 to 2.30 g / cm 3 It can be said that: The procedure for obtaining silica particle powder by freeze-drying is the same as that described for the determination of the amount of silanol groups.

[0023] The density of the silica particles contained in the polishing composition or silica particle dispersion is 2.20 g / cm 3 or more, or 2.25 g / cm 3 By satisfying the above conditions, the network of Si-O-Si bonds constituting the skeleton of the silica particles becomes dense, and the adsorption and desorption of impurities such as metal ions is suppressed, thereby preventing deterioration of the dispersibility of the silica particles due to fluctuations in the pH, electrolyte concentration or composition balance of the polishing composition or silica particle dispersion. 3By satisfying the following conditions, it is possible to prevent the silica particles from settling in the polishing composition or silica particle dispersion, bonding to each other, and adhesion to a container, thereby further improving the polishing rate when used for polishing silicon wafers and improving the storage stability of the polishing composition.

[0024] <Ratio of specific surface area based on water vapor adsorption method to specific surface area based on nitrogen gas adsorption method> The silica particles contained in the polishing composition or silica particle dispersion of the present invention can have a predetermined ratio of the specific surface area based on the water vapor adsorption method to the specific surface area based on the nitrogen gas adsorption method. That is, the silica particle powder obtained by heating and drying the colloidal silica dispersion containing the silica particles under the atmosphere to remove the dispersing medium can be determined by the specific surface area (S) based on the nitrogen gas adsorption method (BET method) described in "Particle diameter (average primary particle diameter, average secondary particle diameter)". N2 ) is the specific surface area (S H2O ) ratio (S H2O / S N2 ) can be, for example, 0.10 to 0.65, 0.15 to 0.65, 0.20 to 0.65, 0.10 to 0.60, 0.10 to 0.50, 0.10 to 0.40, 0.20 to 0.60, 0.25 to 0.60, 0.25 to 0.50, or 0.25 to 0.40. H2O ) can be determined by measuring the amount of water vapor adsorption of silica particles using a water vapor adsorption / desorption measuring device and performing BET analysis on the relative humidity in the range of relative humidity 0.20 to 0.35.

[0025] To obtain silica particle powder by the heat drying method, the target silica particle dispersion is first contacted with a cation exchange resin, an anion exchange resin, and a cation exchange resin in that order to obtain an ion-exchanged solution. The ion-exchanged solution is heated at 140°C for 2 hours to remove most of the dispersant, then heated at 290°C for 1 hour to completely remove the dispersant, and then ground in a mortar for 10 minutes to obtain the desired silica particle powder.

[0026] As with the quantification of <silanol group amount>, silanol groups are present on the surface of silica particles, and these silanol groups tend to adsorb water through hydrogen bonds. Therefore, when quantifying the specific surface area based on the water vapor adsorption method, it is preferable to remove the adsorbed water by heating at 200°C for 1 hour immediately before measurement, at which point the adsorbed water is desorbed, as described above. Furthermore, when the ratio of the specific surface area based on the water vapor adsorption method to the specific surface area based on the nitrogen gas adsorption method is greater than the above-mentioned value, for example, 0.65, the hydrophilicity of the silica particle surface is high and the hydroxyl groups (OH) in the composition are easily absorbed. ― ) adsorbs to the particle surface, which may cleave the silanol bonds on the silica particle surface and promote dissolution. As the dissolution of the silica particles progresses, the highly active silanol groups inside the silica particles are exposed to the silica particle surface, promoting aggregation of the silica particles, which may deteriorate the storage stability of the polishing composition or silica particle dispersion. On the other hand, if the ratio is less than the above value, for example, 0.10, the hydrophilicity of the silica particle surface is low and the silica particles are not sufficiently solvated in the polar solvent, which prevents them from maintaining dispersibility and causes aggregation and precipitation, which may deteriorate the stability of the polishing composition or silica particle dispersion.

[0027] <Production of Silica Particle Dispersion> The method for producing the colloidal silica dispersion (silica sol) used in the present invention can be roughly divided into the following steps: (I) obtaining active silicic acid; (II) preparing a precursor silica sol; (III) further heating the precursor silica sol; and (IV) concentrating the obtained silica sol.

[0028] 《Process (I)》 The step (I) of obtaining activated silicic acid is divided into a step (a1) of obtaining activated silicic acid and a step (a2) of purifying it. Of the above, the step (a1) is essential, and the step (a2) is not essential but may be performed as desired.

[0029] For example, steps (a1) and (a2) can be carried out as follows. Step (a1): An aqueous solution of alkali metal silicate containing 300 to 10,000 ppm of metal oxides other than silica relative to silica is diluted with pure water to a concentration of 1 to 6 mass% of SiO2 derived from silicate, and then brought into contact with a hydrogen-type strongly acidic cation exchange resin to obtain an aqueous solution of activated silicic acid with an SiO2 concentration of 1 to 6 mass%. Step (a2): To the aqueous activated silicic acid solution obtained in step (a1), an acid selected from mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid is added to adjust the pH to 1 to 2, and the solution is left to stand for 12 hours or more. As a result, metal oxides other than silica are dissolved and ionized, and the solution is then contacted with a hydrogen-type strongly acidic cation exchange resin to remove the dissolved metal ions, and then contacted with a hydroxide-type strongly basic anion exchange resin to remove the anions, thereby obtaining purified activated silicic acid with an SiO2 concentration of 1 to 6 mass%.

[0030] In the above step (a1), it is preferable to use, as the alkali metal silicate, sodium water glass, which is an inexpensive industrial product and has an SiO2 / Na2O molar ratio of about 2 to 4. As impurities contained in the water glass, the main polyvalent metals contained in relatively large amounts are aluminum, iron, calcium, magnesium, etc. The alkali metal silicate aqueous solution can be brought into contact with the hydrogen-type strongly acidic cation exchange resin by passing the alkali metal silicate aqueous solution through a column packed with the ion exchange resin. The column effluent is recovered as an aqueous solution of active silicic acid having an SiO2 concentration of 1 to 6 mass %, preferably 2 to 6 mass %. The amount of hydrogen ion exchange resin used may be an amount sufficient to exchange all of the alkali metal ions in the aqueous alkali metal silicate solution with hydrogen ions, and specifically, the amount is preferably such that the exchange capacity of the hydrogen ion exchange resin is 1 to 5 times, 1 to 3 times, or 1 to 2 times the total amount of alkali metal ions contained in the aqueous alkali metal silicate solution on an equivalent basis. The speed at which the resin is passed through the column is preferably a space velocity of about 1 to 10 per hour.

[0031] 《Process (II)》 The step (II) of preparing a precursor silica sol is, for example, a step of carrying out the following steps (b) and (c), or a step of preparing a commercially available silica sol. Step (b): To the aqueous solution of activated silicic acid obtained in step (I), an aqueous solution of sodium or potassium hydroxide is added to obtain a stabilized aqueous solution of activated silicic acid adjusted to an SiO2 concentration of 1 to 6 mass% and a pH of 7 to 10. Step (c): The aqueous solution of activated silicic acid recovered in step (b) is heated with sufficient stirring for 0.5 to 30 hours at a temperature maintained at 110 to less than 160°C, 110 to 150°C, 120 to 150°C, or 130 to 150°C, to obtain a precursor silica sol.

[0032] The aqueous solution of sodium hydroxide or potassium hydroxide used in step (b) is preferably obtained by dissolving commercially available industrial sodium hydroxide or potassium hydroxide with a purity of 95% by mass or more in industrial water or ion-exchanged water from which cations have been removed, to a concentration of preferably 2 to 20% by mass.

[0033] The equipment used in step (c) may be a conventional acid-resistant, alkali-resistant, and pressure-resistant vessel equipped with a stirrer, a temperature control device, a liquid level sensor, a pressure reducing device, a liquid supply device, the above-mentioned cooling device, etc. In step (c), the liquid temperature inside the container is kept at 110 to less than 160°C.

[0034] 《Process (III)》 The step (III) of further heating the precursor silica sol includes the following steps (d), (e), and (f). Of the above steps, step (f) is essential, while steps (d) and (e) are not essential but are carried out as desired.

[0035] Step (d) or step (e) can be performed before step (f). Either step (d) or step (e) may be performed, or both may be performed, or neither may be performed. When both are performed, either step (d) or step (e) may be performed first. Step (d): The precursor silica sol obtained in step (II) or the precursor silica sol with adjusted pH obtained in the following step (e) is concentrated to an SiO2 concentration of 10 to 40 mass % using a known concentrating device such as a concentrator equipped with an ultrafiltration membrane or a vacuum concentrator. Step (e): The precursor silica sol obtained in step (II) or the precursor silica sol with an adjusted SiO2 concentration obtained in step (d) is brought into contact with a hydrogen-type strongly acidic cation exchange resin to obtain a product liquid, and a basic compound is added to the product liquid to adjust the pH to 7 to 10.

[0036] Step (f): The precursor silica sol obtained in step (II), the precursor silica sol with an adjusted SiO concentration obtained in step (d), or the precursor silica sol with an adjusted pH obtained in step (e) is heated with sufficient stirring at a temperature maintained at, for example, 140 to less than 300°C, 160 to 280°C, 160 to 260°C, 160 to 240°C, 170 to 240°C, 180 to 240°C, or 190 to 240°C for 0.5 to 30 hours to obtain a silica sol. In step (f), the liquid temperature inside the container is kept at 160 to less than 300°C.

[0037] 《Process (IV)》 The step (IV) of further concentrating the obtained silica sol is a step of concentrating the silica sol obtained in the step (III) to 10 to 50 mass %. This step (IV) is not essential but is performed as desired. For the concentration, a known concentrating device such as a concentrator equipped with an ultrafiltration membrane or a vacuum concentrator can be used.

[0038] <Additives> The polishing composition of the present invention may contain, in addition to silica particles as abrasive grains and water as an aqueous medium, at least one additive selected from the group consisting of acidic compounds, basic compounds, water-soluble compounds, chelating agents, oxidizing agents, and metal corrosion inhibitors. The silica particle dispersion of the present invention may contain, in addition to silica particles and water or an organic solvent, or a mixed solvent of water and an organic solvent, at least one additive selected from the group consisting of acidic compounds and basic compounds.

[0039] The mass percentage of the solid content of the polishing composition excluding water as the aqueous medium can be, for example, 0.01 to 40 mass%, 0.01 to 30 mass%, 0.01 to 20 mass%, 0.1 to 40 mass%, 0.1 to 20 mass%, or 0.1 to 15 mass%, and the mass percentage of silica particles in the solid content can be 80 to 100 mass%, or 85 to 99.9 mass%. The mass percentage of silica particles in the polishing composition or silica particle dispersion can be 1 to 40 mass%, 1 to 30 mass%, 1 to 20 mass%, or 3 to 30 mass%. By setting the solid content of the polishing composition excluding the aqueous medium to 0.01% by mass or more, excessive dissolution of the silica particle surface by hydroxy groups can be suppressed. By setting the solid content of the polishing composition excluding the aqueous medium to 40% by mass or less, an increase in the number of silica particles in the polishing composition and an increase in the frequency of contact between silica particles due to a decrease in the amount of solvent can be prevented, and aggregation can be suppressed. In addition, excessive viscosity of the polishing composition can be suppressed, making it easier to handle. As a result, the storage stability of the polishing composition is improved, making it easier to store or transport. The amount of solids in the polishing composition or silica particle dispersion can be measured, for example, by heating the composition in an electric furnace at 1000° C. for 1 hour and weighing the residue.

[0040] Examples of the acidic compound include mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and organic acids such as formic acid, oxalic acid, citric acid, acetic acid, lactic acid, malic acid, malonic acid, succinic acid, tartaric acid, butyric acid, fumaric acid, benzoic acid, glycolic acid, propionic acid, and ascorbic acid. The acidic compound may be used alone or in combination of two or more thereof.

[0041] Examples of the basic compound include alkali metal hydroxides, alkali metal carbonates, alkali metal hydrogencarbonates, nitrogen-containing basic compounds, etc. The basic compound may be used alone or in combination of two or more thereof. Among the basic compounds, the alkali metal hydroxide is preferably sodium hydroxide or potassium hydroxide. The alkali metal bicarbonate is preferably sodium bicarbonate or potassium bicarbonate. The alkali metal carbonate is preferably sodium carbonate or potassium carbonate. The nitrogen-containing basic compound is preferably ammonia or a quaternary ammonium salt, and more preferably a quaternary ammonium compound from the viewpoint of achieving a high polishing rate. The quaternary ammonium compound may be tetramethylammonium hydroxide, ethyltrimethylammonium hydroxide, diethyldimethylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium hydroxide, or a salt thereof. Among these, tetraethylammonium hydroxide or a salt thereof is preferably used, and tetramethylammonium hydroxide or a salt thereof is more preferably used. The basic compound can be blended into the polishing composition in an amount of, for example, 0.1 to 50 mass%, 0.1 to 30 mass%, 0.1 to 10 mass%, 1 to 50 mass%, 1 to 30 mass%, or 1 to 10 mass% relative to the silica particles. By blending the amount of the basic compound within the above range, the pH of the polishing composition can be prevented from excessively increasing or decreasing, thereby improving the stability of the polishing composition.

[0042] By adding these acidic or basic compounds, the pH of the polishing composition according to the present invention can be adjusted to within the range of 1 to 12, 1 to 6, 3 to 6, 7 to 12, 7 to 10, 8 to 11, or 10 to 12. By adjusting the pH of the polishing composition to within the above range, when the polishing composition is used to polish a silicon wafer, the Si bonds on the silicon wafer surface are cleaved by the acid or base, making it easier for the silica particles to scrape the silicon wafer surface, thereby improving the removal rate. Furthermore, by adding these acidic or basic compounds, the pH of the silica particle dispersion according to the present invention can be adjusted to the range of 8 to 11, 8 to 10, or 9 to 10. By adjusting the pH to the above range, the dispersibility of the silica particles can be improved, and aggregation of the silica particles in the solvent can be suppressed.

[0043] Any water-soluble compound can be used as the water-soluble compound. Examples include monomers having a carboxylic acid group, such as acrylic acid, methacrylic acid, and maleic acid, and their polymers, such as polyacrylic acid and polymethacrylic acid, and their salts, such as ammonium polyacrylate, potassium polyacrylate, ammonium polymethacrylate, and potassium polymethacrylate. Other examples include alginic acid, pectinic acid, carboxymethyl cellulose, polyaspartic acid, polyglutamic acid, polyamic acid, ammonium polyamic acid, polyvinylpyrrolidone, hydroxyethyl cellulose, hydroxypropyl cellulose, glycerin, polyglycerin, polyvinyl alcohol, polyacrylamide and its derivatives, polymethacrylamide and its derivatives, and carboxyl- or sulfonic-acid-modified polyvinyl alcohol. The water-soluble compound can be blended into the polishing composition in an amount of, for example, 0.01 to 10 mass%, 0.01 to 5 mass%, 0.01 to 3 mass%, 0.05 to 10 mass%, 0.1 to 10 mass%, or 0.05 to 5 mass% relative to the silica particles. By blending the amount of the water-soluble compound within the above range, the dispersion stability of the silica particles contained in the polishing composition can be improved, and the flatness of the silicon wafer can be improved by protecting the silicon wafer surface except for the convex portions on which the load is concentrated when the silicon wafer is polished.

[0044] As the chelating agent, an aminocarboxylic acid chelating agent or a phosphonic acid chelating agent can be used. Examples of the aminocarboxylic acid chelating agent include ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, triethylenetetraminehexaacetic acid, 1,3-propanediaminetetraacetic acid, 1,3-diamine-2-hydroxypropanetetraacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethylglycine, glycol ether diaminetetraacetic acid, dicarboxymethylglutamic acid, and ethylenediamine-N,N'-disuccinic acid. Examples of the phosphonic acid chelating agent include hydroxyethylidene diphosphonic acid, nitrilotris(methylenephosphonic acid), phosphonobutanetricarboxylic acid, and ethylenediaminetetra(methylenephosphonic acid). The chelating agent can be blended into the polishing composition in an amount of, for example, 0.01 to 10 mass%, 0.01 to 5 mass%, 0.01 to 3 mass%, 0.05 to 10 mass%, 0.1 to 10 mass%, or 0.05 to 5 mass% relative to the silica particles. By blending the amount of the chelating agent within the above range, contamination of the silicon wafer with metal impurities can be reduced, while the dispersion stability of the silica particles contained in the polishing composition can be improved.

[0045] Examples of the oxidizing agent include hydrogen peroxide, potassium permanganate, potassium periodate, hypochlorous acid, and ozone water. The oxidizing agent can be blended into the polishing composition in an amount of, for example, 0.01 to 10 mass%, 0.01 to 5 mass%, 0.01 to 3 mass%, 0.05 to 10 mass%, 0.1 to 10 mass%, or 0.05 to 5 mass% relative to the silica particles. By blending the amount of oxidizing agent within the above range, when the polishing composition is used to polish a silicon wafer, the silicon wafer surface is oxidized, making it easier to scrape off with the silica particles, and the removal rate is improved.

[0046] Examples of the metal corrosion inhibitor include triazole compounds, pyridine compounds, pyrazole compounds, pyrimidine compounds, imidazole compounds, guanidine compounds, thiazole compounds, tetrazole compounds, triazine compounds, and hexamethylenetetramine.

[0047] Examples of the triazole compound include 1,2,3-triazole, 1,2,4-triazole, 3-amino-1H-1,2,4-triazole, benzotriazole (BTA), 1-hydroxybenzotriazole, 1-hydroxypropylbenzotriazole, 2,3-dicarboxypropylbenzotriazole, 4-hydroxybenzotriazole, 4-carboxy-1H-benzotriazole, 4-carboxy-1H-benzotriazole methyl ester (methyl 1H-benzotriazole-4-carboxylate), 4-carboxy-1H-benzotriazole butyl ester (butyl 1H-benzotriazole-4-carboxylate), 4-carboxy-1H-benzotriazole octyl ester (octyl 1H-benzotriazole-4-carboxylate), 5-hexylbenzotriazole, (1,2,3-benzotriazolyl-1-methyl)(1,2,4-triazole), Azolyl-1-methyl)(2-ethylhexyl)amine, tolyltriazole, naphthotriazole, bis[(1-benzotriazolyl)methyl]phosphonic acid, 3H-1,2,3-triazolo[4,5-b]pyridin-3-ol, 1H-1,2,3-triazolo[4,5-b]pyridine, 1-acetyl-1H-1,2,3-triazolo[4,5-b]pyridine, 3-hydroxypyridine, 1,2,4-triazolo[1,5-a]pyridine pyrimidine, 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, 2-methyl-5,7-diphenyl-[1,2,4]triazolo[1,5-a]pyrimidine, 2-methylsulfanyl-5,7-diphenyl-[1,2,4]triazolo[1,5-a]pyrimidine, 2-methylsulfanyl-5,7-diphenyl-4,7-dihydro-[1,2,4]triazolo[1,5-a]pyrimidine, and the like.

[0048] Examples of the pyridine compound include pyridine, 8-hydroxyquinoline, prothionamide, 2-nitropyridin-3-ol, pyridoxamine, nicotinamide, iproniazid, isonicotinic acid, benzo[f]quinoline, 2,5-pyridinedicarboxylic acid, 4-styrylpyridine, anabasine, 4-nitropyridine-1-oxide, ethyl pyridine-3-acetate, quinoline, 2-ethylpyridine, quinolinic acid, arecoline, citrazinic acid, pyridine-3-methanol, 2-methyl-5-ethylpyridine, 2-fluoropyridine, pentafluoropyridine, 6-methylpyridin-3-ol, and ethyl pyridine-2-acetate.

[0049] Examples of the pyrazole compound include pyrazole, 1-allyl-3,5-dimethylpyrazole, 3,5-di(2-pyridyl)pyrazole, 3,5-diisopropylpyrazole, 3,5-dimethyl-1-hydroxymethylpyrazole, 3,5-dimethyl-1-phenylpyrazole, 3,5-dimethylpyrazole, 3-amino-5-hydroxypyrazole, 4-methylpyrazole, N-methylpyrazole, 3-aminopyrazole, and 3-aminopyrazole.

[0050] Examples of the pyrimidine compound include pyrimidine, 1,3-diphenyl-pyrimidine-2,4,6-trione, 1,4,5,6-tetrahydropyrimidine, 2,4,5,6-tetraaminopyrimidine sulfate, 2,4,5-trihydroxypyrimidine, 2,4,6-triaminopyrimidine, 2,4,6-trichloropyrimidine, 2,4,6-trimethoxypyrimidine, 2,4,6-triphenylpyrimidine, 2,4-diamino-6-hydroxylpyrimidine, 2,4-diaminopyrimidine, 2-acetamidopyrimidine, 2-aminopyrimidine, and 4-aminopyrazolo[3,4-d]pyrimidine.

[0051] Examples of the imidazole compound include imidazole, 1,1'-carbonylbis-1H-imidazole, 1,1'-oxalyldiimidazole, 1,2,4,5-tetramethylimidazole, 1,2-dimethyl-5-nitroimidazole, 1,2-dimethylimidazole, 1-(3-aminopropyl)imidazole, 1-butylimidazole, 1-ethylimidazole, 1-methylimidazole, and benzimidazole.

[0052] Examples of the guanidine compound include guanidine, 1,1,3,3-tetramethylguanidine, 1,2,3-triphenylguanidine, 1,3-di-o-tolylguanidine, and 1,3-diphenylguanidine.

[0053] Examples of the thiazole compound include thiazole, 2-mercaptobenzothiazole, and 2,4-dimethylthiazole.

[0054] Examples of the tetrazole compound include tetrazole, 5-methyltetrazole, 5-amino-1H-tetrazole, and 1-(2-dimethylaminoethyl)-5-mercaptotetrazole.

[0055] Examples of the triazine compound include triazine and 3,4-dihydro-3-hydroxy-4-oxo-1,2,4-triazine.

[0056] The metal corrosion inhibitor can be blended into the polishing composition in an amount of, for example, 0.0001 to 10% by mass relative to the silica particles. By blending the amount of the metal corrosion inhibitor within the above range, the stability of the polishing composition can be improved while maintaining the anticorrosive effect.

[0057] <Stability of Polishing Composition: Heat Storage Test> In a test in which the polishing composition of the present invention is heated and stored at 50°C for 28 days, it is desirable that the rate of increase in the average secondary particle diameter, measured by dynamic light scattering, of the polishing composition after heated storage at 50°C for 28 days compared to the average secondary particle diameter, measured by dynamic light scattering, of the polishing composition before heated storage is low (particle diameter remains unchanged), and the rate of increase can be, for example, less than 5%, or can be 4% or less, 0 to less than 5%, 0 to 4%, or 0 to 3%. A polishing composition that satisfies the above-mentioned increase rate exhibits almost no change in particle size or shape of the silica particles contained in the polishing composition even after transportation or storage, and therefore does not produce coarse particles due to aggregation of silica particles or reduce the amount of active ingredient due to sedimentation of silica particles, thereby achieving the desired polishing performance.

[0058] The polishing composition of the present invention can be produced, stored, and transported in the form of a concentrated liquid. The silica concentration in the concentrated liquid is not particularly limited as long as it satisfies the rate of increase in average secondary particle diameter in the 28-day heat storage test at 50°C, and can be, for example, 1 to 30% by mass, 5 to 30% by mass, 5 to 25% by mass, or 10 to 25% by mass. Producing, storing, and transporting the polishing composition in the form of a concentrated liquid can reduce transportation costs and save storage space. The concentrated liquid can be diluted with any solvent, such as pure water, immediately before use to adjust the SiO2 concentration to a predetermined value, for example, 0.1 to 10% by mass, before being used for polishing. Furthermore, by setting the SiO2 concentration of the concentrated liquid within a range that satisfies the rate of increase, deterioration of polishing performance due to aggregation of silica particles contained in the concentrated liquid can be suppressed. The pH of the concentrate can be adjusted to the range of 1-12, 1-6, 3-6, 7-12, 7-10, 8-12, 9-12, 10-12, or 11-12.

[0059] The polishing composition of the present invention can be used for polishing silicon wafers or device wafers. Polishing machines are available for single-side polishing and double-side polishing, and the polishing composition of the present invention can be used to polish silicon wafers in either type of machine. The polishing process for silicon wafers typically involves multiple polishing stages, including a primary polishing step performed at the beginning of the polishing process and a finish polishing step performed after the primary polishing step. The primary polishing and finish polishing may each be performed in two stages. The polishing composition of the present invention may be used for both the primary polishing and the finish polishing, or the polishing composition of the present invention may be used for only one of the primary polishing and the finish polishing. The polishing composition of the present invention may be circulated within the polishing machine during each polishing step, or may be used as a single-use flow-through solution. The polishing composition of the present invention can also be used for CMP polishing of device wafers. The silica particle dispersion of the present invention can be suitably used in a polishing composition. [Example]

[0060] The present invention will be described in more detail below with reference to examples, although the present invention is not limited thereto.

[0061] 1) Synthesis of colloidal silica dispersion (Synthesis Example 1) Synthesis of colloidal silica dispersion A As the raw material water-soluble alkali metal silicate, a sodium silicate aqueous solution conforming to JIS No. 3 was prepared. The main components of this sodium silicate aqueous solution other than water were an SiO2 concentration of 28.8 mass% and an Na2O concentration of 9.47 mass%.

[0062] The above sodium silicate aqueous solution was diluted with pure water to prepare a sodium silicate aqueous solution (a) having an SiO2 concentration of 4 mass %. Next, the sodium silicate aqueous solution (a) was passed through a column packed with hydrogen-type strongly acidic cation exchange resin (trade name) Amberlite IR-120B at a space velocity of 4.5 per hour to remove cations, thereby producing an activated silicic acid aqueous solution.

[0063] A 10% by mass aqueous solution of sodium hydroxide was added to the obtained aqueous solution of activated silicic acid to adjust the pH to 8.5 to 9.5, thereby obtaining a stabilized aqueous solution of activated silicic acid. The SiO2 concentration of the obtained stabilized aqueous solution of activated silicic acid was 3.2% by mass. 2400 g of the stabilized activated silicic acid aqueous solution obtained above was placed in a 3 L stainless steel pressure vessel equipped with a stirrer, a heater, etc., and the liquid temperature in the vessel was adjusted to 130-150°C by heating. After the temperature in the vessel reached 130-150°C, the vessel was heated for 2 hours and 30 minutes while maintaining the temperature at 130-150°C, thereby obtaining a colloidal silica dispersion (precursor silica sol) having an average primary particle size of 10-15 nm.

[0064] The obtained colloidal silica dispersion was concentrated at room temperature using a commercially available ultrafiltration device equipped with a polysulfone ultrafiltration membrane with a molecular weight cutoff of 200,000 (Advantec Co., Ltd. (trade name) Q2000 150E) to an SiO2 concentration of 33 mass%, thereby obtaining a precursor silica sol with an adjusted SiO2 concentration. The precursor silica sol with the adjusted SiO2 concentration was passed through a column packed with a hydrogen-type strongly acidic cation exchange resin (trade name) Amberlite IR-120B at a space velocity of 10 per hour to remove cations, and the resulting dispersion was adjusted to pH 7 to 8 by adding a 10 mass % aqueous sodium hydroxide solution, thereby obtaining a precursor silica sol with an adjusted pH. The precursor silica sol obtained above with adjusted SiO2 concentration and pH was placed in a reactor equipped with a 3 L stainless steel pressure vessel, a stirrer, a heater, etc., and the liquid temperature in the vessel was adjusted to 220-240°C by heating. After the temperature in the vessel reached 220-240°C, the vessel was heated for 2 hours and 20 minutes while maintaining the temperature at 220-240°C, thereby obtaining colloidal silica dispersion A.

[0065] (Synthesis Example 2) Synthesis of colloidal silica dispersion B Colloidal silica dispersion B was obtained in the same manner as in Synthesis Example 1, except that the precursor silica sol with adjusted SiO2 concentration and pH was heated at 210 to 230°C using a SUS pressure vessel.

[0066] (Synthesis Example 3) Synthesis of colloidal silica dispersion C The colloidal silica dispersion B obtained in Synthesis Example 2 was passed through a column packed with a hydrogen-type strongly acidic cation exchange resin (trade name) Amberlite IR-120B at a space velocity of 10 per hour to remove cations, and a 10% by mass aqueous solution of sodium hydroxide was added to the resulting dispersion to adjust the pH to 9 to 10. 2400 g of colloidal silica dispersion B adjusted to pH 9-10 was placed in a reaction apparatus equipped with a stirrer, a heater, etc., in a 3 L stainless steel pressure vessel, and the liquid temperature in the vessel was adjusted to 190-210°C by heating. After the temperature in the vessel reached 190-210°C, the vessel was heated for 12 hours while maintaining the temperature at 190-210°C, thereby obtaining colloidal silica dispersion C.

[0067] (Synthesis Example 4) Synthesis of colloidal silica dispersion D Colloidal silica dispersion D was obtained in the same manner as in Synthesis Example 3, except that colloidal silica dispersion B adjusted to pH 9 to 10 was heated at 170 to 190°C for 72 hours in a SUS pressure vessel.

[0068] (Synthesis Example 5) Synthesis of colloidal silica dispersion E Colloidal silica dispersion E was obtained in the same manner as in Synthesis Example 1, except that the precursor silica sol with adjusted SiO2 concentration and pH was heated at 230 to 250°C for 6 hours in a SUS pressure vessel.

[0069] (Synthesis Example 6) Synthesis of colloidal silica dispersion F Colloidal silica dispersion F was obtained in the same manner as in Synthesis Example 1, except that the precursor silica sol with adjusted SiO2 concentration and pH was heated at 240 to 260°C for 9 hours in a SUS pressure vessel.

[0070] (Synthesis Example 7) Synthesis of colloidal silica dispersion G Colloidal silica dispersion G was synthesized in the same manner as described in Synthesis Example 4 of WO 2020 / 091000. Specifically, an aqueous solution of activated silicic acid stabilized with sulfuric acid was obtained by adding 8% by mass of sulfuric acid to the aqueous solution of activated silicic acid obtained by the same procedure as in Synthesis Example 1 above to adjust the pH to 2-3. Pure water was added to the aqueous solution of activated silicic acid stabilized with sulfuric acid obtained above under stirring, and then a 10% by mass aqueous solution of potassium hydroxide was added to adjust the SiO2 concentration to 3.2% by mass and the pH to 12.0. The liquid temperature in the vessel was then adjusted to 110-130°C using a reactor equipped with a stirrer, heater, etc., in a 3 L stainless steel pressure vessel. After the temperature in the vessel reached 110-130°C, the aqueous solution of activated silicic acid stabilized with sulfuric acid obtained above was continuously fed as a feed liquid while maintaining the vessel at 110-130°C until the pH of the reaction liquid reached 11.4. After the supply of the aqueous solution of activated silicic acid stabilized with sulfuric acid, the temperature inside the vessel was kept at 110°C and the reaction was carried out for 1 hour. Then, the aqueous solution of activated silicic acid stabilized with sulfuric acid was continuously supplied as a feed solution until the pH of the reaction solution reached 11.1. After the supply of the aqueous solution of activated silicic acid stabilized with sulfuric acid, the temperature inside the vessel was kept at 110-130°C and the reaction solution was further heated for 2 hours to obtain a reaction solution.

[0071] The resulting reaction solution was concentrated at room temperature using a commercially available ultrafiltration device equipped with a polysulfone ultrafiltration membrane with a molecular weight cutoff of 200,000 (Advantec Co., Ltd. (trade name) Q2000 150E) to an SiO2 concentration of 40 mass %, thereby obtaining colloidal silica dispersion G.

[0072] (Synthesis Example 8) Synthesis of colloidal silica dispersion H 2400 g of colloidal silica dispersion (product name PL-3) manufactured by Fuso Chemical Co., Ltd. was placed in a reactor equipped with a stirrer, a heater, etc., in a 3 L stainless steel pressure vessel, and the temperature was adjusted to 190 to 210°C. After the temperature inside the vessel reached 190 to 210°C, the vessel was heated for 1 hour while maintaining the temperature at 190 to 210°C, thereby obtaining colloidal silica dispersion H.

[0073] (Synthesis Example 9) Synthesis of colloidal silica dispersion I The temperature in the container was kept at 190-210°C and the heating time was set to 5 hours. 8 Colloidal silica dispersion I was obtained by the same procedure as above.

[0074] 2) Analysis of colloidal silica dispersions and silica particles The colloidal silica dispersions A to I prepared above, as well as a colloidal silica dispersion manufactured by Nissan Chemical Industries, Ltd. (trade name: Snowtex XL) and a colloidal silica dispersion manufactured by Fuso Chemical Industries, Ltd. (trade name: PL-3) were analyzed as follows.

[0075] 2-1) Particle size measurement method The average primary particle size of the silica particles was measured by a nitrogen gas adsorption method. Pure water was added to each colloidal silica dispersion to prepare a sample with an SiO2 concentration adjusted to 10% by mass. Next, 10 mL of Amberlite (trade name) IR-120B hydrogen-type strong acid cation exchange resin was added to 5 g of the obtained sample and stirred for 30 minutes to obtain a sample from which cations had been removed. The obtained sample was filtered through a nylon mesh to remove the cation exchange resin, and then heated in an electric furnace (product name DX302, manufactured by Yamato Scientific Co., Ltd.) at 290°C for 1 hour in an air atmosphere to remove the solvent, yielding a dried product, which was then ground in an agate mortar for 10 minutes to obtain a heat-dried powder. The above heat-dried powder was used as a measurement sample, and the specific surface area value S based on nitrogen gas of the measurement sample was measured by the nitrogen gas adsorption method (BET method) using a specific surface area measurement device (product name: Monosorb (manufactured by Quantachrome Instruments Japan LLC)). N2 The average primary particle size was calculated from the specific surface area obtained. The average secondary particle size of silica particles was measured by dynamic light scattering (DLS) using a Zetasizer Nano (trade name, manufactured by Malvern Panalytical) as follows: 0.1 g of colloidal silica dispersion was dispensed into a polystyrene cell with an optical path length of 10 mm, and a 0.15 mass% aqueous sodium chloride solution was added to obtain a colloidal silica dispersion with a silica concentration adjusted so that the count rate at an attenuator setting of 7 was 200 to 400 kcps. The amount of the prepared colloidal silica dispersion introduced into the cell was adjusted so that the height of the liquid surface from the bottom of the cell was approximately 1 cm, and the average secondary particle size of silica was measured under conditions of an attenuator setting of 7 and a temperature of 22.0°C.

[0076] 2-2) Pulsed NMR analysis method Pure water was added to each colloidal silica dispersion to prepare a sample with an SiO2 concentration of 5% by mass. 0.77 mL of the sample was placed in a glass NMR tube, and the relaxation time of the sample was measured using a pulsed NMR device (product name) Acorn Area manufactured by Xigo Nanotools under the following conditions. Magnetic field: 0.3T Measurement frequency: 13MHz Measurement nuclei: 1 H NMR Measurement method: CPMG pulse sequence method Temperature: 30℃ The reciprocal of the relaxation time of the colloidal silica dispersion obtained by measurement under the above conditions was defined as Rav, and the reciprocal of the relaxation time of pure water obtained by measurement under the same conditions was defined as Rb. The Rsp value of each colloidal silica dispersion was calculated using the following formula. Rsp = (Rav - Rb) / (Rb)

[0077] 2-3) Quantitative method for silanol group amount Pure water was added to each colloidal silica dispersion to prepare a sample with an SiO2 concentration adjusted to 10% by mass. Next, 20 mL of hydrogen-type strongly acidic cation exchange resin Amberlite (trade name) IR-120B was added to 100 g of the resulting sample and stirred for 30 minutes to remove cations. The resulting sample was filtered through a nylon mesh to remove the cation exchange resin, and then 20 mL of hydroxyl-type strongly basic anion exchange resin Amberlite (trade name) IRA-410 was added and stirred for 30 minutes to remove anions. The resulting sample was filtered through a nylon mesh to remove the anion exchange resin, and then 20 mL of hydrogen-type strongly acidic cation exchange resin Amberlite (trade name) IR-120B was added again and stirred for 30 minutes to remove cations. The resulting sample was filtered through a nylon mesh to remove the cation exchange resin, yielding a dispersion from which both cations and anions had been removed. The dispersion from which the ions had been removed was placed in a 300 mL recovery flask. The recovery flask containing the dispersion was immersed for 10 minutes in ethanol cooled to -70°C to -80°C using dry ice, yielding a frozen dispersion. The frozen dispersion was left standing at room temperature under a vacuum of 5 Pa or less using a freeze-drying apparatus (product name FDU-2100, manufactured by Tokyo Rikakikai Co., Ltd.) to sublimate the frozen water and obtain a freeze-dried sample. The freeze-dried sample was ground in an agate mortar for 10 minutes, yielding a freeze-dried powder.

[0078] The freeze-dried powder was heated using a thermogravimetric differential thermal analyzer (product name TG-DTA2000SA, manufactured by Bruker) from room temperature to 700°C, and the amount of mass loss was measured. Specifically, 5 to 10 mg of the freeze-dried powder was placed in a platinum container, and the initial sample mass was designated M0. The platinum container containing the freeze-dried powder was placed in a thermogravimetric differential thermal analyzer and heated in a nitrogen gas atmosphere from room temperature to 700°C at a heating rate of 10°C / min. The flow rate of the nitrogen gas was 100 cc / min. The mass loss M1 at the time the temperature inside the analyzer reached 200°C was defined as the mass loss due to the removal of water adsorbed on the surface of the silica particles contained in the freeze-dried powder. The mass loss M2 at the time the temperature inside the analyzer reached 700°C minus M1 was defined as the mass loss due to the removal of water generated by dehydration condensation of silanol groups. The amount of silanol groups in the silica particles was calculated using the following formula: Amount of silanol groups (mmol / g) = 2 × (M2 - M1) ÷ 18 ÷ (M0 - M1) × 1000

[0079] 2-4) Dry density measurement method The freeze-dried powder of the colloidal silica dispersion prepared in the same manner as in 2-3) was used as a sample for measuring the dry density. Using a dry automatic density measuring device (product name AccuPyc II TEC, manufactured by Micromeritics), the above measurement sample was measured at 1 cm 3 The aluminum cell was filled to 80% capacity, and the dry density of the silica particles was measured by the gas substitution method using He gas at 25°C.

[0080] 2-5) Measurement method for the ratio of specific surface area based on water vapor adsorption method to specific surface area based on nitrogen gas adsorption method Pure water was added to each colloidal silica dispersion to prepare a sample with an SiO2 concentration adjusted to 10% by mass. Next, 20 mL of hydrogen-type strongly acidic cation exchange resin Amberlite (trade name) IR-120B was added to 100 g of the resulting sample and stirred for 30 minutes to remove cations. The resulting sample was filtered through a nylon mesh to remove the cation exchange resin, and then 20 mL of hydroxyl-type strongly basic anion exchange resin Amberlite (trade name) IRA-410 was added and stirred for 30 minutes to remove anions. The resulting sample was filtered through a nylon mesh to remove the anion exchange resin, and then 20 mL of hydrogen-type strongly acidic cation exchange resin Amberlite (trade name) IR-120B was added again and stirred for 30 minutes to remove cations. The resulting sample was filtered through a nylon mesh to remove the cation exchange resin, yielding a dispersion from which both cations and anions had been removed. 20 g of the dispersion was weighed into an alumina dish and heated on a hot plate at 140°C for 2 hours to remove moisture. The resulting silica powder was then heated in an electric furnace at 290°C for 1 hour to completely dry it. The resulting silica powder was ground in an agate mortar for 10 minutes to obtain a heat-dried powder. The water vapor adsorption of the heat-dried powder was measured under the following conditions using a water vapor adsorption / desorption analyzer (TA Instruments Japan, product name Q5000 SA) in an environment where the relative humidity varied from 10% to 90%. The nitrogen gas flow rate was 200 mL / min, and the measurement temperature was 25°C. Immediately before measurement, the heat-dried powder was dried in an electric furnace at 200°C for 1 hour to remove adsorbed water. Within 5 minutes, 10 mg of the sample powder was weighed into a platinum container and used for measurement. A BET plot is created from the relationship between the amount of water vapor adsorption and the relative humidity, and an approximate line is found in the range of relative humidity 0.20 to 0.35. The slope of the line, W M is the water vapor adsorption weight per 1 g of the measurement sample, and the specific surface area S based on the water vapor adsorption method of the measurement sample is calculated using the following formula: H2O was calculated. S H2O =W M ×N A ×AM ÷M H2O =W M x6.02x10 23 x10.8x10 ―20 ÷18 =W M ×3612 where N A is Avogadro's number, A M is the cross section occupied by one water molecule, M H2O represents the molecular weight of water. The specific surface area S measured above using the water vapor adsorption method H2O , and the specific surface area S obtained in 2-1) based on the nitrogen gas adsorption method N2 From the ratio S H2O / S N2 was calculated.

[0081] 3) Preparation of polishing composition Example 1 Using colloidal silica dispersion A obtained in Synthesis Example 1, the various reagents and pure water were added so that the silica particles derived from colloidal silica dispersion A were 20.5 mass%, ethylenediaminetetraacetic acid tetrasodium salt was 0.65 mass%, tetramethylammonium hydroxide (TMAH) was 1.0 mass%, and potassium carbonate was 1.5 mass%, and the mixture was stirred for 30 minutes to obtain the polishing composition of Example 1. Example 2 A polishing composition of Example 2 was prepared in the same manner as in Example 1, except that colloidal silica dispersion B obtained in Synthesis Example 2 was used. Example 3 A polishing composition of Example 3 was prepared in the same manner as in Example 1, except that the colloidal silica dispersion C obtained in Synthesis Example 3 was used. Example 4 A polishing composition of Example 4 was prepared in the same manner as in Example 1, except that colloidal silica dispersion D obtained in Synthesis Example 4 was used. Example 5 A polishing composition of Example 5 was prepared in the same manner as in Example 1, except that colloidal silica dispersion E obtained in Synthesis Example 5 was used. Example 6 A polishing composition of Example 6 was prepared in the same manner as in Example 1, except that the colloidal silica dispersion F obtained in Synthesis Example 6 was used.

[0082] (Comparative Example 1) A polishing composition of Comparative Example 1 was prepared in the same manner as in Example 1, except that a colloidal silica dispersion (trade name: Snowtex XL) manufactured by Nissan Chemical Industries, Ltd. was used as the colloidal silica dispersion. (Comparative Example 2) A polishing composition of Comparative Example 2 was prepared in the same manner as in Example 1, except that the colloidal silica dispersion G obtained in Synthesis Example 7 was used. (Comparative Example 3) A polishing composition of Comparative Example 3 was prepared in the same manner as in Example 1, except that a colloidal silica dispersion (trade name PL-3) manufactured by Fuso Chemical Co., Ltd. was used as the colloidal silica dispersion. Comparative Example 4 A polishing composition of Comparative Example 4 was prepared in the same manner as in Example 1, except that the colloidal silica dispersion H obtained in Synthesis Example 8 was used. (Comparative Example 5) A polishing composition of Comparative Example 5 was prepared in the same manner as in Example 1, except that the colloidal silica dispersion I obtained in Synthesis Example 9 was used.

[0083] <Evaluation> (Storage stability test) The average secondary particle diameter of silica particles was measured immediately after preparation of the polishing compositions of Examples 1 to 6 and Comparative Examples 1 to 5. Each polishing composition was stored in a commercially available thermostatic chamber set at 50°C, and the average secondary particle diameter was measured after 28 days. The average secondary particle diameter was measured according to the procedure described in 2-1) Particle diameter measurement method in the aforementioned 2) Analysis of colloidal silica dispersion and silica particles. The storage stability was judged to be good if the rate of change (rate of increase) in the average secondary particle diameter after storage at 50°C was less than 5% compared to the average secondary particle diameter immediately after preparation of each polishing composition (before storage at 50°C).

[0084] (Polishing test) The polishing compositions of Examples 1 to 6 and Comparative Examples 1 to 5 were diluted 20 times by mass with pure water to obtain polishing test compositions. A polishing test was conducted using the above polishing test composition under the polishing conditions shown below. The wafer to be polished was a single-crystal silicon wafer with a diameter of 200 mm, a conductivity type of P-type, a crystal orientation of Miller index <100>, and a resistivity of 100 Ω·cm or less. The polishing test composition was supplied by a circulation system, and the liquid temperature was 23 to 25°C. The polishing time per batch was 60 minutes, and three batches of polishing were performed using the same polishing pad. The amount of polishing liquid was 25 kg, and new polishing liquid was not replenished or pH adjusted between batches.

[0085] (polishing conditions) Polishing machine: Hamai Sangyo Co., Ltd. Product name: Double-sided polishing machine 13BF Polishing pad: JH-RHODES Co., Ltd., product name LP-57, groove width 2 mm, groove pitch 20 mm Polishing load: 150g / cm 2 Lower surface plate rotation speed: 6.6rpm Upper surface plate rotation speed: 20 rpm Rotation ratio: 3.3 Number of wafers polished: 3 sets of 1 wafer / carrier are prepared, and a total of 3 wafers are polished simultaneously Supply rate of polishing test composition: 6.4 L / min Polishing time: 60min Carrier: Epoxy glass carrier (thickness 0.70 mm)

[0086] (Evaluation conditions for polished wafers) The polishing rate was calculated by measuring the wafer thickness before and after polishing using a laser displacement meter manufactured by Keyence Corporation (Keyence Corporation, product name SI-F1000), subtracting the wafer thickness after polishing from the wafer thickness before polishing, and dividing the result by the polishing time of 60 min. The surface roughness was measured by measuring the root mean square height in a 111 μm square area in the center of the wafer using a 100x objective lens with an optical interference microscope system (trade name) BW-M7000 manufactured by Nikon Solutions Corporation.

[0087] (result) Table 1 shows the physical properties of the colloidal silica dispersions used in Examples 1 to 6 and Comparative Examples 1 to 5, and Table 2 shows the results of the polishing test and the storage stability test of each polishing composition.

[0088] [Table 1]

[0089] [Table 2]

[0090] As shown in Table 2, the polishing speed was 0.32 to 0.34 μm / min in Examples 1 to 6 and 0.32 to 0.33 μm / min in Comparative Examples 1 to 5, showing comparable performance. The surface roughness was 1.09 to 1.16 nm in Examples 1 to 6 and 1.13 to 1.17 nm in Comparative Examples 1 to 5, also showing comparable performance. This is thought to be because the silica particles based on colloidal silica dispersions A to F, which have Rsp values ​​of 0.07 to 0.14, have sufficient water affinity to maintain the dispersibility of the silica particles in the polishing composition, and therefore were able to uniformly and efficiently remove the silicon wafer surface that had been altered by alkaline components such as TMAH and potassium carbonate in the polishing test, thereby achieving the desired polishing rate and surface roughness.

[0091] On the other hand, in the storage stability test, in Examples 1 to 6, where the Rsp value of the colloidal silica dispersion used to prepare the polishing composition was within a certain range, the rate of change in the average secondary particle diameter was 0 to 2%, which was a good result. This is because, in silica particles based on a colloidal silica dispersion with an Rsp value of 0.07 to 0.14, hydroxy groups (OH - ) and excessive dissolution of the silica particle surface by hydroxy groups is suppressed, which is thought to suppress aggregation of silica particles and provide excellent storage stability. On the other hand, in the polishing compositions of Comparative Examples 1 to 5, which use silica particles based on colloidal silica dispersions whose Rsp values ​​are not within a specific range, it is believed that many hydroxy groups are present near the silica particle surfaces, which makes the silica particles more likely to dissolve, and the Si-O-Si bonds on the silica particle surfaces are broken, resulting in an activated state, which makes the silica particles more likely to aggregate together, and thus reduces storage stability.

[0092] The examples of the present invention have confirmed that by using silica particles in a silica sol used in a polishing composition, whose Rsp value obtained by pulse NMR measurement has a specific numerical range, when used as a polishing composition to polish silicon wafers, a high polishing rate can be obtained and storage stability can be improved. Therefore, the polishing composition of the present invention can be used not only as an abrasive for silicon wafers, but also as an abrasive for CMP of device wafers because of its high removal rate and storage stability. [Industrial Applicability]

[0093] In the silica sol used in the polishing composition, by using silica particles having a specific Rsp value obtained by pulse NMR, a high polishing rate can be obtained when used to polish silicon wafers, and the storage stability of the polishing composition can be improved.

Claims

1. A polishing composition comprising an aqueous dispersion of silica particles, wherein the Rsp value as follows, derived from relaxation times obtained by pulse NMR measurement of the aqueous dispersion of silica particles and pure water, is 0.01 or more and less than 0.

15. Rsp=(Rav-Rb) / (Rb) Here, Rav is the reciprocal of the relaxation time of an aqueous dispersion of silica particles having a silica concentration of 5 mass %, and Rb is the reciprocal of the relaxation time of pure water.

2. 2. The polishing composition according to claim 1, wherein the silica particles have an average secondary particle diameter of 40 to 200 nm as measured by a dynamic light scattering method and an average primary particle diameter of 20 to 100 nm as measured by a nitrogen gas adsorption method.

3. 2. The polishing composition according to claim 1, wherein the silica particle aqueous dispersion is brought into contact with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange, the treatment liquid is frozen at −70° C. to −80° C., and the dispersion medium is removed by freeze-drying the treatment liquid at room temperature under a pressure of 5 Pa or less to obtain a silica particle powder. The silica particle powder has a silanol group content of 0.1 to 1.5 mmol / g, as calculated by the following formula from the mass loss when heated from room temperature to 700° C. and the molecular weight of water molecules in thermogravimetric analysis: Amount of silanol groups (mmol / g) = 2 × (M2 - M1) ÷ M Ｈ２Ｏ ÷(M0-M1)×1000 where M0 is the mass of the silica particle powder subjected to thermogravimetric analysis before heating, M1 is the mass loss amount when the temperature reached 200°C, M2 is the mass loss amount when the temperature reached 700°C, and M Ｈ２Ｏ represents the molecular weight of a water molecule.

4. The silica particle dispersion is brought into contact with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange, and the resulting treated liquid is frozen at −70° C. to −80° C., and then freeze-dried at room temperature under a pressure of 5 Pa or less to remove the dispersion medium. The resulting silica particle powder has a density of 2.20 to 2.35 g / cm as measured by dry density measurement. ３ 2. The compound according to claim 1, Polishing composition.

5. The silica particle aqueous dispersion was brought into contact with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to exchange ions, and the treated liquid was heated at 140°C for 2 hours and then at 290°C for 1 hour to remove the dispersing medium. The silica particle powder obtained was measured for its specific surface area (S Ｎ２ ) based on the water vapor adsorption method (S Ｈ２Ｏ ) ratio (S Ｈ２Ｏ / S Ｎ２ 2. The polishing composition according to claim 1, wherein σ is 0.10 to 0.

65.

6. 5. The polishing composition according to claim 1, wherein the aqueous dispersion of silica particles has been subjected to a heat history at a temperature of 140°C or higher and lower than 260°C.

7. 6. The polishing composition according to claim 1, wherein the concentration of the silica particles is 1 to 40 mass %.

8. The polishing composition according to claim 1, further comprising at least one additive selected from the group consisting of an acidic compound, a basic compound, a water-soluble compound, a chelating agent, an oxidizing agent, and a metal corrosion inhibitor.

9. 9. The polishing composition according to claim 8, wherein the basic compound is at least one basic compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates, and nitrogen-containing basic compounds.

10. The polishing composition according to claim 8 , wherein the chelating agent is an aminocarboxylic acid-based chelating agent or a phosphonic acid-based chelating agent.

11. 2. The polishing composition according to claim 1, wherein the polishing composition has a pH of 1 to 12.

12. In a test in which the polishing composition was heated and stored at 50°C for 28 days, With respect to the average secondary particle diameter measured by dynamic light scattering of the polishing composition before heating and storing at 50°C for 28 days, 2. The polishing composition according to claim 1, wherein the increase rate of the average secondary particle diameter of the polishing composition measured by dynamic light scattering after heating and storage at 50°C for 28 days is less than 5%.

13. 2. The polishing composition according to claim 1, which is used for polishing silicon wafers or device wafers.

14. providing a precursor colloidal silica dispersion; and a step of heating the precursor at a temperature of 140° C. or higher and lower than 260° C. to obtain the silica particle aqueous dispersion, A method for producing the polishing composition according to claim 1.

15. A silica particle dispersion comprising a solvent and silica particles, wherein the following Rsp value derived from relaxation times obtained by pulse NMR measurement of the silica particle dispersion and a blank solution is 0.01 or more and less than 0.15: Rsp=(Rav-Rb) / (Rb) Here, Rav is the reciprocal of the relaxation time of a silica particle dispersion liquid having a silica concentration of 5 mass %, and Rb is the reciprocal of the relaxation time of a blank solution.

16. The silica particle dispersion of claim 15 , wherein the solvent comprises water.

17. 16. The silica particle dispersion according to claim 15, wherein the silica particles have an average secondary particle diameter of 40 to 200 nm as measured by a dynamic light scattering method and an average primary particle diameter of 20 to 100 nm as measured by a nitrogen gas adsorption method.

18. 16. The silica particle dispersion according to claim 15, wherein a treatment liquid obtained by bringing the silica particle dispersion into contact with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange, is frozen at −70° C. to −80° C., and further freeze-dried at room temperature under a pressure of 5 Pa or less to remove the dispersion medium, to obtain a silica particle powder. The silica particle powder has a silanol group content of 0.1 to 1.5 mmol / g as calculated by the following formula from the mass loss when heated from room temperature to 700° C. and the molecular weight of water molecules in thermogravimetric analysis: Amount of silanol groups (mmol / g) = 2 × (M2 - M1) ÷ M Ｈ２Ｏ ÷(M0-M1)×1000 where M0 is the mass of the silica particle powder subjected to thermogravimetric analysis before heating, M1 is the mass loss amount when the temperature reached 200°C, M2 is the mass loss amount when the temperature reached 700°C, and M Ｈ２Ｏ represents the molecular weight of a water molecule.

19. The silica particle dispersion is brought into contact with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange, and the resulting treated liquid is frozen at −70° C. to −80° C., and then freeze-dried at room temperature under a pressure of 5 Pa or less to remove the dispersion medium. The resulting silica particle powder has a density of 2.20 to 2.35 g / cm as measured by dry density measurement. ３ The silica particle dispersion according to claim 15, wherein

20. The silica particle dispersion is brought into contact with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to exchange ions, and the treated liquid is heated at 140°C for 2 hours and then at 290°C for 1 hour to remove the dispersing medium. The silica particle powder obtained by the treatment liquid is measured for a specific surface area (S Ｎ２ ) based on the water vapor adsorption method (S Ｈ２Ｏ ) ratio (S Ｈ２Ｏ / S Ｎ２ 16. The silica particle dispersion according to claim 15, wherein the σ is 0.10 to 0.

65.

21. 21. The silica particle dispersion according to claim 15, wherein the silica particle dispersion has been subjected to a thermal history at a temperature of 140°C or higher and lower than 260°C.

22. 21. The silica particle dispersion according to claim 15, wherein the concentration of the silica particles is 1 to 40 mass %.

23. providing a precursor colloidal silica dispersion; and a step of heating the precursor at a temperature of 140° C. or higher and lower than 260° C. to obtain the silica particle dispersion liquid, The method for producing the silica particle dispersion liquid according to claim 15 .

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