JP7482699B2 - Method for producing irregular silica particle dispersion - Google Patents

Description

The present invention relates to a method for producing a dispersion of irregularly shaped silica particles and a dispersion of irregularly shaped silica particles.

Conventionally, silica sol, fumed silica, fumed alumina, etc. have been used as polishing particles. In the manufacture of semiconductor substrates with integrated circuits, aluminum wiring is formed on a silicon wafer, and an oxide film of silica or the like is provided on top of this as an insulating film. In this case, unevenness is created by the wiring, so this oxide film is polished to flatten it. In polishing such substrates, what is required is a flat surface without steps or unevenness, a smooth surface without microscopic scratches, and a high polishing speed.

The abrasive used in chemical mechanical polishing (CMP) is usually composed of polishing particles, an oxidizing agent, additives such as organic acids, and a solvent such as pure water. The polishing particles are spherical and made of metal oxides such as silica and alumina, with an average particle size of about 200 nm. The oxidizing agent increases the polishing speed of metals for wiring and circuits.
When the surface of the workpiece has steps (unevenness) caused by the wiring groove pattern, it is required to polish the surface to a coplanar surface while mainly removing the convex parts, resulting in a flat polished surface. However, when polishing the part above the coplanar surface with conventional spherical polishing particles, there was a problem (called dishing) in that the metal for the circuit in the wiring groove at the bottom of the concave part was polished to below the coplanar surface. When this dishing (overpolishing) occurs, the thickness of the wiring is reduced, the wiring resistance increases, and the flatness of the insulating film formed on it is reduced. For this reason, it is required to suppress dishing.
In recent years, non-spherical particles have been proposed as abrasive particles in place of conventional spherical particles.

Patent Document 1 discloses a method for producing a silica sol containing irregularly shaped particles, which involves adding a silicic acid liquid to an aqueous solution of an alkali metal silicate containing 0.05 to 5.0% by weight of _SiO2 to adjust the _SiO2 / _M2O (molar ratio, M is an alkali metal or quaternary ammonium) of the mixed solution to 30 to 60, then adding a compound of one or more metals selected from the group consisting of Ca, Mg, Al, In, Ti, Zr, Sn, Si, Sb, Fe, Cu and rare earth metals (the addition may be made before or during the addition of the silicic acid liquid), maintaining this mixed solution at any temperature of 60°C or higher for a certain period of time, and further adding a silicic acid liquid to adjust the _SiO2 / _M2O (molar ratio) in the reaction solution to 60 to 100, thereby producing a sol in which substantially irregularly shaped silica particles are dispersed.

Patent Document 2 discloses a method for producing an elongated silica sol, which comprises adding an aqueous solution of a water-soluble calcium salt, magnesium salt or a mixture thereof to an aqueous colloidal solution of active silicic acid, adding an alkaline substance to the obtained aqueous solution, heating a part of the obtained mixture to 60° C. or higher to prepare a heel liquid, and the remainder to prepare a feed liquid, adding the feed liquid to the heel liquid, and concentrating the _SiO2 concentration to 6 to 30% by weight by evaporating water during the addition.

In Patent Document 3, a colloidal aqueous solution of active silicic acid containing 0.5 to 10% by weight of _SiO2 and having a pH of 2 to ₆ is treated with an aqueous solution containing a water-soluble salt of a divalent or trivalent metal, either alone or in combination, and the aqueous solution is treated with a metal oxide (MO in the case of a salt of a divalent metal, _{and M2O3} in the case of a salt of a trivalent metal, where M represents a divalent or trivalent metal atom, and O represents an oxygen atom) relative to the SiO2 of the colloidal aqueous solution of active silicic acid. The method for producing a beaded silica sol is described in the publication, which comprises adding and mixing an acidic spherical silica sol having an average particle size of 10 to 120 nm and a pH of 2 to 6 to the resulting mixed liquid (1) such that the ratio A/B (weight ratio) of the silica content (A) derived from the acidic spherical silica sol to the silica content (B) derived from this mixed liquid (1) is 5 to 100 and the total silica content (A+B) of the mixed liquid (2) obtained by mixing the acidic spherical silica sol with the mixed liquid (1) is 5 to 40% by weight of _SiO2 in the mixed liquid (2), adding and mixing an alkali metal hydroxide or the like to the mixed liquid (2) such that the pH is 7 to 11, and heating the resulting mixed liquid (3) at 100 to 200°C for 0.5 to 50 hours.

Patent Document 4 describes a method for producing a silica sol in which an alkyl silicate is hydrolyzed with an acid catalyst without using a solvent, with a composition having a SiO ₂ concentration of 1 to 8 mol/L, an acid concentration of 0.0018 to 0.18 mol/L, and a water concentration of 2 to 30 mol/L, and then the SiO ₂ concentration is diluted with water to a range of 0.2 to 1.5 mol/L, and then an alkali catalyst is added so that the pH is 7 or more, and the mixture is heated to proceed with polymerization of silicic acid, and amorphous silica particles having an average diameter in the thickness direction of 5 to 100 nm and a length 1.5 to 50 times that diameter are dispersed in a liquid dispersion.

Patent Document 5 describes a method for adding an alkaline earth metal, such as Ca, Mg, Ba, or the like, to an acidic aqueous solution of active silicic acid having an SiO ₂ concentration of about 2 to 6 mass %, which is obtained by decationizing an aqueous solution of an alkali metal silicate such as water glass, in a weight ratio of 100 to 1500 ppm in terms of its oxide relative to the SiO ₂ of the active silicic acid, and further adding an alkaline substance in an amount such that the SiO ₂ /M ₂ O (M represents an alkali metal atom, NH ₄ , or a quaternary ammonium group) molar ratio in this solution is 20 to 150, to obtain an initial heel liquid, and an active silicic acid aqueous solution obtained in a similar manner and having an SiO ₂ concentration of 2 to 6 mass % and an SiO ₂ /M ₂ O (M is the same as above) molar ratio of 20 to 150 is used as a charge liquid, and the charge liquid is charged into the initial heel liquid at 60 to 150° C. at a rate of charge liquid SiO _{2 /initial heel liquid SiO 2} per hour. This publication describes a method for producing a silica sol having a distorted shape, which is obtained by adding water to a liquid at a weight ratio of _0.05 to 1.0 with or without evaporating water from the liquid.

In Patent Document 6, colloidal silica aqueous solutions produced by (1) a method of neutralizing an aqueous solution of alkali silicate with a mineral acid, adding an alkaline substance, and heat-aging, (2) a method of adding an alkaline substance to an activated silicic acid obtained by cation exchange treatment of an aqueous solution of alkali silicate, and heat-aging, (3) a method of heat-aging an activated silicic acid obtained by hydrolyzing an alkoxysilane such as ethyl silicate, or (4) a method of directly dispersing silica fine powder in an aqueous medium, are usually colloidal silica particles having a particle diameter of 4 to 1,000 nm (nanometers), preferably 7 to 500 nm, dispersed in an aqueous medium, and have a concentration of 0.5 to 50 mass %, preferably 0.5 to 30 mass %, as SiO _2. It is described that the particle shape of the silica particles can be spherical, irregular, flat, plate-like, elongated, fibrous, etc.

Patent Document 7 reports that an abrasive containing spherical, separate silica particles that are not bonded to each other, containing A) 5-95% by weight of silica particles with a size of 5-50 nm, and b) 95-5% by weight of silica particles with a size of 50-200 nm, where the particles as a whole have a bimodal particle size distribution, provides a high removal rate.

Patent Document 8 also discloses that an excellent polishing rate can be achieved by using a polishing silica sol with a degree of irregularity in the range of 1.55 to 4, with peaks in the particle size distribution measured by dynamic light scattering method in the particle size range of 30 to 70 nm and in the particle size range of 71 to 150 nm, and with a particle size difference between the two peaks in the range of 50 to 100 nm.

Furthermore, Patent Document 9 discloses that a polishing composition containing spherical particles with a sphericity of 0.9 or more and non-spherical particles not corresponding to these spherical particles in a specified weight ratio provides a polished surface with excellent flatness even if the polished surface has irregularities, and suppresses deterioration of polishing performance even when polished for a long period of time.

Patent Document 10 discloses colloidal silica useful as an abrasive for electronic materials, which is prepared by contacting an aqueous alkali silicate solution with a cation exchange resin to prepare activated silicic acid, adding a compound that serves as a source of potassium ions and an alkaline agent such as an alkali metal hydroxide or quaternary ammonium hydroxide to the activated silicic acid to make it alkaline, and then heating to form silica particles. Next, while maintaining the alkalinity under heating, an aqueous activated silicic acid solution, an alkaline agent, and a compound that serves as a source of potassium ions are added to grow the silica particles, and a group of irregularly shaped silica particles containing potassium ions with a long axis/short axis ratio of 1.2 to 10 as observed in transmission electron microscope photographs are disclosed.

Patent Document 11 discloses a method for producing silica particles characterized in that at least four or more silica primary particles having an average primary particle diameter (D1) in the range of 20 to 100 nm are clustered together, the average particle diameter (DCL) is in the range of 40 to 300 nm, and the aspect ratio (DL)/(DS) is in the range of 1.5 to 5, which comprises mixing an acidic silicic acid liquid and an alkali halide into an alkali silicate aqueous solution so as to obtain a predetermined molar ratio range to obtain a seed particle precursor dispersion of silica particles, which is then heated and aged, and then the acidic silicic acid liquid is added while stirring at a Reynolds number (Re) represented by the following formula (1) in the range of 2000 to 1,000,000.
Re=nd ² ρ/μ (1)
(where n is the rotation speed of the impeller [S-1], d is the diameter of the impeller [m], ρ is the density of the dispersion [kg/m ³ ], and μ is the viscosity of the dispersion [Pa·s]).

Generally, the following methods are known for producing irregularly shaped silica particles having a relatively large particle size.
1) A method of adding a component serving as a silica source to seed particles of irregular shape and growing the particles to obtain irregular silica particles; 2) A method of bonding spherical particles together to obtain particle-linked silica-based particles or irregular silica particles similar thereto; 3) A method of crushing silica particles to obtain irregular silica particles. Here, the manufacturing method 1) can prepare particles with a high degree of irregularity, but only particles with a small specific surface area converted particle diameter can be obtained, so when applied to polishing purposes, there is a problem that the polishing speed is low. When a silica source such as silicic acid is added to particles with a small specific surface area converted particle diameter and grown to a large size, the irregularity decreases as the particles grow and approaches sphere, so it is not easy to obtain irregular silica particles with the desired degree of irregularity. In addition, when such particles with a low degree of irregularity are used for polishing purposes, there is a problem that the polishing speed is low.
In the manufacturing method of 2), components other than silica are required to connect the particles together (for example, calcium oxide and magnesium oxide in Patent Document 2, alkali catalyst in Patent Document 4, alkaline earth metal in Patent Document 5, potassium chloride in Patent Document 11, etc.), and there is a concern that irregular silica particles containing these components may cause contamination when used for polishing semiconductors. In addition, these components other than silica function as aggregation promoters for silica particles, causing irregular morphology, but on the other hand, when preparing silica particles with a large size and high irregularity, a large amount of aggregation promoter is required, so the aggregation reaction proceeds too much and coarse aggregates are generated in some parts. When such a silica sol is used for polishing, scratches are likely to occur due to the large number of coarse particles, and the polishing performance tends to be unstable due to sedimentation.
In the manufacturing method 3), it is not easy to obtain irregularly shaped silica particles that are uniform in both particle size and shape.

Japanese Patent Application Laid-Open No. 4-187512 Japanese Patent Application Laid-Open No. 7-118008 JP 2001-11433 A JP 2001-48520 A JP 2001-150334 A Japanese Patent Application Laid-Open No. 8-279480 JP 2003-529662 A JP 2007-137972 A JP 2006-80406 A JP 2011-98859 A JP 2015-86102 A

The present invention aims to provide a method for producing an irregular silica particle dispersion liquid containing irregular silica particles with a relatively large particle size and excellent polishing properties, without using any elements other than alkaline earth metals and halogens derived from raw materials such as sodium silicate. Another objective of the present invention is to provide an irregular silica particle dispersion liquid containing irregular silica particles with a relatively large particle size and excellent polishing properties.

According to one aspect of the present invention, there is provided a method for producing a dispersion liquid of irregularly shaped silica particles, comprising the following steps 1 to 3 and satisfying the following condition 1:
Step 1: Mixing a first acidic silicic acid liquid with an alkaline aqueous solution containing an alkaline compound having at least Na or K;
Further, by heating and aging at a temperature in the range of 50° C. or more and less than 100° C., a precursor dispersion liquid having an SiO ₂ concentration of 3 mass % or more and 20 mass % or less and satisfying the condition shown in the following mathematical formula (F1-1) is obtained. Step 2≦SiO ₂ /A ₂ O≦15...(F1-1)
(Here, _SiO2 represents the number of moles of silica in the precursor dispersion, and _A2O represents the total number of moles of _Na2O and _K2O in the precursor dispersion.)
Step 2: A step of adding a second acidic silicic acid liquid to the precursor dispersion liquid obtained in step 1 so that a second addition rate ratio represented by the following mathematical formula (F2-1) is in the range of 0.1 [kg/hr kg] to 0.6 [kg/hr kg], and further heating and aging the mixture at a temperature in the range of 50° C. to 100° C. to obtain a seed particle dispersion liquid. Second addition rate ratio [kg/hr kg]=(silica content in the second acidic silicic acid liquid [kg])/(addition time of the second acidic silicic acid liquid [hr])/(silica content in the precursor dispersion liquid [kg])...(F2-1)
Step 3: A step of adding a third acidic silicic acid liquid to the seed particle dispersion obtained in step 2 so that a third addition speed ratio represented by the following mathematical formula (F3-1) is in the range of 1.1 [kg/hr kg] to 10 [kg/hr kg], and further heating and aging the mixture at a temperature in the range of 50° C. to less than 100° C. to obtain an irregularly shaped silica particle dispersion: Third addition speed ratio [kg/hr kg]=(silica content in the third acidic silicic acid liquid [kg])/(addition time of the third acidic silicic acid liquid [hr])/(silica content in the precursor dispersion [kg]) ...(F3-1)
Condition 1: The condition shown in the following formula (F0-1) is satisfied.
1.9≦[the third addition speed ratio]/[the second addition speed ratio]≦40 (F0-1)

In the method for producing a dispersion liquid of irregular shaped silica particles according to one embodiment of the present invention, it is preferable to include the following step 4 subsequent to the step 3.
Step 4: Concentrating the irregular shaped silica particle dispersion obtained in step 3

In the method for producing a dispersion liquid of irregular shaped silica particles according to one embodiment of the present invention, it is preferable that the following condition 2 is further satisfied.
Condition 2: In the precursor dispersion, the number of moles of halogen elements converted per 1 mole of silica (mol/mol ratio) is 0.5% or less, and the number of moles of alkaline earth metals converted per 1 mole of silica (mol/mol ratio) is 1000 ppm or less.

In the method for producing a dispersion liquid of irregular shaped silica particles according to one aspect of the present invention, it is preferable that the following condition 3 is further satisfied.
Condition 3: The silica content ratio represented by the following formula (F0-2) is in the range of 10 or more and 100 or less.
Silica content ratio={(silica content in the second acidic silicic acid liquid [kg])+(silica content in the third acidic silicic acid liquid [kg])}/(silica content in the precursor dispersion liquid [kg]) (F0-2)

In the method for producing a dispersion liquid of irregular shaped silica particles according to one aspect of the present invention, it is preferable that the following condition 4 is further satisfied.
Condition 4: the SiO ₂ /A ₂ O molar ratio in the irregular shaped silica particle dispersion is in the range of 60 or more and 140 or less.
(Here, _SiO2 represents the number of moles of silica in the irregular silica particle dispersion, and _A2O represents the total number of moles of _Na2O and _K2O in the irregular silica particle dispersion.)

In the method for producing a dispersion of irregularly shaped silica particles according to one aspect of the present invention, the alkaline aqueous solution in step 1 is preferably an aqueous potassium silicate solution.

In the method for producing a dispersion of irregularly shaped silica particles according to one embodiment of the present invention, it is preferable that the alkaline compound in step 1 is potassium hydroxide.

In the manufacturing method of an irregular silica particle dispersion according to one embodiment of the present invention, it is preferable that the obtained irregular silica particles have a specific surface area converted particle diameter (D1) in the range of 10 nm to 200 nm, an average particle diameter (D2) measured by dynamic light scattering in the range of 20 nm to 300 nm, and the value of (D2)/(D1) in the range of 1.2 to 20.

According to one aspect of the present invention, there is provided an irregular silica particle dispersion liquid containing irregular silica particles characterized in that the specific surface area converted particle diameter (D1) is in the range of 10 nm to 200 nm, the average particle diameter (D2) measured by dynamic light scattering is in the range of 20 nm to 300 nm, and the value of (D2)/(D1) is in the range of 1.2 to 20.

In one embodiment of the present invention, the irregular shaped silica particle dispersion preferably contains a potassium compound.

According to the present invention, it is possible to provide a method for producing an irregular silica particle dispersion liquid containing irregular silica particles with a relatively large particle size and excellent polishing properties, and further to provide a method for producing the same without using any elements other than alkaline earth metals and halogens derived from raw materials such as sodium silicate. In addition, according to the present invention, it is possible to provide an irregular silica particle dispersion liquid with a relatively large particle size and excellent polishing properties.

[Method of manufacturing irregular silica particle dispersion]
The method for producing a dispersion of irregular shaped silica particles according to the present invention will be described below.
The method for producing a dispersion liquid of irregular shaped silica particles according to the present invention is characterized by including the following steps 1 to 3 and satisfying the following condition 1.

<Step 1>
In step 1, a first acidic silicic acid liquid is added to an alkaline aqueous solution so as to satisfy the conditions described below, and mixed to obtain a precursor dispersion liquid that satisfies the conditions described below.
The precursor dispersion is preferably prepared, for example, as follows.
That is, an alkaline aqueous solution is added to ultrapure water and stirred until homogeneous, and then a first acidic silicic acid liquid is added and mixed thoroughly. The mixture of the alkaline solution and the first acidic silicic acid liquid is heated to a temperature range of 50°C or more and less than 100°C, and is maintained at that temperature range for 15 minutes to 2 hours to produce a precursor dispersion. When adding the first acidic silicic acid liquid, it is preferable to add the first acidic silicic acid liquid continuously to prevent excessive aggregation.

Alkaline aqueous solution The alkaline aqueous solution contains an alkaline compound having at least Na or K. Examples of the alkaline compound having at least Na or K include sodium silicate, potassium silicate, potassium hydroxide, and sodium hydroxide. As the alkaline silicate compound, sodium silicate or potassium silicate commercially available under the names of No. 1 water glass, No. 2 water glass, No. 3 water glass, etc. are preferable. In addition, an alkaline silicate aqueous solution obtained by hydrolyzing a hydrolyzable organic compound such as tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS) with excess NaOH or KOH, etc. is also preferable.
Examples of the alkaline compound optionally contained in the alkaline aqueous solution include lithium silicate, quaternary ammonium silicate, ammonia, amines, and salts thereof.
The alkaline aqueous solution is preferably a potassium silicate aqueous solution or a potassium hydroxide aqueous solution. In general, in electronic materials, sodium ions, which have a small ionic radius, tend to diffuse into substrates and the like and can cause defects. Therefore, potassium ions, which have a relatively large ionic radius, are desirable.
The concentration of the alkaline compound component in the alkaline aqueous solution is not particularly limited, but is preferably 1% by mass or more and 50% by mass or less, and more preferably 5% by mass or more and 25% by mass or less.
The alkaline aqueous solution preferably does not contain halide ions (such as chloride ions) and alkaline earth metals (such as calcium and magnesium). The alkaline aqueous solution preferably contains 1000 ppm or less of halogen ions and 100 ppm or less of alkaline earth metals (such as magnesium).

- Acidic silicic acid solution As the acidic silicic acid solution, it is preferable to use an acidic silicic acid solution obtained by de-alkalinizing an aqueous solution of an alkali silicate (alkali metal silicate, ammonium silicate, etc.) with a cation exchange resin. The _SiO2 concentration of the acidic silicic acid solution is preferably about 0.1% by mass to 10% by mass, more preferably 1% by mass to 7% by mass. A solution with a pH of about 1 to 5 is preferably used.

Step 1 is a step of preparing a precursor dispersion of the desired irregular seed particles. In step 1, an aqueous alkali silicate solution is added to ultrapure water and stirred until uniform, and then a first acidic silicate liquid is added continuously or intermittently and mixed. After mixing, the temperature is raised to 50°C or higher and lower than 100°C, and maintained for 15 minutes to 2 hours or less for heat aging to obtain a precursor particle dispersion. If the temperature during mixing is within the above range, after steps 2, 3, and, if necessary, step 4, a dispersion of irregular silica particles of the present invention with excellent polishing performance can be obtained.

The SiO ₂ concentration of the obtained precursor dispersion is a parameter that controls the irregularity of the irregular seed particles, and is 3% by mass or more and 20% by mass or less, and more preferably 3% by mass or more and 15% by mass or less as SiO _2. If the SiO ₂ concentration of the precursor dispersion is less than 3% by mass, irregular seed particles with a high irregularity tend to be difficult to obtain. If the SiO ₂ concentration of the precursor dispersion is more than 20% by mass, aggregation and precipitation are likely to occur, and even if aggregation and precipitation do not occur, a large amount of silica is deposited inside the reaction tank, and irregular seed particles of the desired size cannot be obtained. If the SiO ₂ concentration of the precursor dispersion is within the above range, the irregular silica particles of the present invention and their dispersion liquid having excellent polishing performance can be obtained after step 2, step 3, and if necessary, step 4.

The obtained precursor dispersion satisfies the condition represented by the following formula (F1-1).
2≦SiO ₂ /A ₂ O≦15...(F1-1)
Here, _SiO2 represents the number of moles of silica in the precursor dispersion, and _A2O represents the total number of moles of _Na2O and _K2O in the precursor dispersion.
The SiO ₂ /A ₂ O (molar ratio) in the precursor dispersion is preferably from 2 to 5. When the SiO ₂ /A ₂ O (molar ratio) is within this range, it is suitable for generating dispersed seed particles in step 2 without causing aggregation or precipitation.
K ₂ O and Na ₂ O in A ₂ O mean the amounts of K and Na present in the precursor dispersion, respectively, converted into their oxides.
A precursor dispersion having a _SiO2 / _A2O (molar ratio) of less than 2 contains an excessive amount of alkali, and therefore the solubility of silica in the dispersion becomes excessively high, making it unsuitable for producing a seed particle dispersion in step 2. On the other hand, when a precursor dispersion having a _SiO2 / _A2O (molar ratio) of more than 15 is applied to step 2, seed particles are produced in excess, which tends to make it difficult to achieve the desired particle growth.

The pH of the precursor dispersion is preferably in the range of 9 or more and 12.5 or less, and more preferably 10 or more and 12 or less.
If the pH of the precursor dispersion is less than 9, the pH is too low, so that irregular seed particles may not be generated in step 2. Even if seed particles are generated, they may not maintain stability and may aggregate, or the acidic silicic acid liquid added in step 2 may not dissolve or deposit, causing aggregation or gelation.
On the other hand, if the pH of the precursor dispersion exceeds 12.5, the solubility of silica in the dispersion increases significantly, and the ionic strength also increases significantly, so that the seed particles produced in step 2 may aggregate, which may cause precipitation.

<Step 2>
The method for producing an irregular shaped silica particle dispersion of the present invention is characterized in that the irregular shaped silica particle dispersion is prepared in two stages (step 2 and step 3) in which the addition rate of the acidic silicic acid liquid is different.
Step 2 is a step of preparing irregular seed particles having a desired size and irregularity from the precursor prepared in step 1. In step 2, a second acidic silicic acid liquid is added to the precursor dispersion obtained in step 1 so as to satisfy the conditions described below, and the mixture is further heated and aged to obtain a seed particle dispersion.
Here, the precursor dispersion has a _SiO2 concentration of 3 mass% or more and 20 mass% or less, and a _SiO2 / _A2O (molar ratio) of 2 or more and 15 or less ( _SiO2 represents the number of moles of silica in the precursor dispersion, and _A2O represents the total number of moles of _K2O and _Na2O in the precursor dispersion).

The second acidic silicic acid liquid is preferably an acidic silicic acid liquid obtained by de-alkalizing an aqueous alkali silicate solution with a cation exchange resin, similar to the first acidic silicic acid liquid used in step 1. The _SiO2 concentration of the acidic silicic acid liquid is preferably about 0.1% by mass to 10% by mass, more preferably 1% by mass to 7% by mass. The pH of the acidic silicic acid liquid is preferably about 1 to 5.

In step 2, the acidic silicic acid liquid is added to the precursor dispersion liquid continuously or intermittently so that the second addition rate ratio represented by the following formula (F2-1) is in the range of 0.1 [kg/hr kg] to 0.6 [kg/hr kg], and mixed. Then, the mixture is heated and aged at a temperature of 50° C. or higher and lower than 100° C. to prepare a seed particle dispersion liquid.
Second addition speed ratio [kg/hr kg]=(silica content in second acidic silicic acid liquid [kg])/(addition time of second acidic silicic acid liquid [hr])/(silica content in precursor dispersion liquid [kg]) (F2-1)

The second addition speed ratio means the addition speed of silica in the second acidic silicic acid liquid relative to the silica content in the precursor dispersion liquid, and is a parameter that controls the size and irregularity of the irregular seed particles. When the second addition speed ratio is in the range of 0.1 to 0.6, the core particles generated can be moderately aggregated or associated to obtain irregular seed particles with a large average particle size. Furthermore, since the core particles become larger, the specific surface area equivalent diameter of the seed particles becomes larger, which is preferable. When the second addition speed ratio is less than 0.1, the core size generated becomes larger, but the aggregation or association of the core particles progresses too much, resulting in coarse aggregates and a tendency for precipitation to occur. Also, when the second addition speed ratio exceeds 0.6, the aggregation or association of the generated core particles does not progress easily, making it difficult to obtain irregular seed particles. Even if irregular seed particles are obtained, they will be particles with a low degree of irregularity. The second addition speed ratio is preferably 0.1 to 0.5.

As described above, after the second acidic silicic acid liquid is added to the precursor dispersion liquid, the mixture is further heated and aged at a temperature of 50° C. or more and less than 100° C. By aging in this temperature range, the unreacted acidic silicic acid liquid remaining in the reaction liquid can be dissolved and deposited on the particle surface, completing the reaction. As a result, irregular seed particles that have grown to an appropriate size and are dispersed can be obtained.
The temperature of the heat aging is more preferably in the range of 50°C or higher and 99°C or lower, and further preferably in the range of 60°C or higher and 98°C or lower.
If the temperature is less than 50° C., the unreacted acidic silicic acid solution remaining in the reaction solution will not dissolve sufficiently and will remain in the reaction solution, possibly causing particle aggregation in the subsequent steps.
If the temperature during heating and maturation is 100° C. or higher, this is the boiling point of the reaction solution, so the solvent is likely to evaporate and the concentration increases, making it difficult to control the reaction. Even if the reaction can be carried out, the core particles will tend to aggregate excessively, leading to precipitation.
The heat aging period varies depending on the holding temperature and the _SiO2 concentration of the acidic silicic acid solution, but is preferably within about 24 hours.

<Step 3>
Step 3 is a step of growing the irregular seed particles obtained in step 2 to a desired size. In step 3, a third acidic silicic acid liquid is added to the seed particle dispersion obtained in step 2 so that a third addition rate ratio represented by the following mathematical formula (F3-1) is in the range of 1.1 [kg/hr kg] to 10 [kg/hr kg], and the mixture is further heated and aged at a temperature of 50° C. or higher and lower than 100° C. to obtain an irregular silica particle dispersion.
Third addition speed ratio [kg/hr kg]=(silica content in third acidic silicic acid liquid [kg])/(addition time of third acidic silicic acid liquid [hr])/(silica content in precursor dispersion liquid [kg]) (F3-1)
Here, the third addition rate ratio means the addition rate of silica in the third acidic silicic acid liquid relative to the silica content in the precursor dispersion. When the third addition rate ratio is in the range of 1.1 [kg/hr·kg] or more and 10 [kg/hr·kg] or less, an appropriate reaction rate can be achieved. Therefore, dissolution of the added acidic silicic acid liquid and deposition of the dissolved silica on the irregular seed particles occur, and the irregular seed particles obtained in step 2 can be grown to a desired size, which is preferable. When the third addition rate ratio is less than 1.1 [kg/hr·kg], the addition rate of the acidic silicic acid becomes significantly slow. Therefore, although the irregular seed particles can be grown, the production efficiency is poor and the economic efficiency is poor. When the third addition rate ratio exceeds 10 [kg/hr·kg], the addition rate of the acidic silicic acid liquid is significantly high, so that self-nucleation of the acidic silicic acid liquid is likely to occur. It is preferable that the third addition rate ratio is 2 or more and 6 or less.

In step 3, as described above, the seed particle dispersion is heated to 50° C. or more and less than 100° C., the third acidic silicic acid liquid is added, and the mixture is heated and aged by maintaining the mixture at that temperature for 15 minutes to 24 hours. By carrying out such heating and aging, the unreacted silicic acid remaining in the reaction liquid is deposited on the particle surface, and the reaction can be completed.
The heat aging temperature is preferably in the range of 60°C or higher and 98°C or lower.
If the heating and aging temperature is less than 50° C., the added acidic silicic acid solution does not dissolve sufficiently, and self-nucleation by silicic acid is likely to occur.
The retention time varies depending on the retention temperature or the _SiO2 concentration of the acidic silicic acid solution, but is preferably within about 24 hours.
As the third acidic silicic acid liquid, an acidic silicic acid liquid similar to the above-mentioned first acidic silicic acid liquid is used.

<Condition 1>
In the method for producing a dispersion liquid of irregular shaped silica particles of the present invention, it is further necessary to satisfy the following condition 1.
Condition 1 is to satisfy the condition shown in the following formula (F0-1).
1.9≦[third addition speed ratio]/[second addition speed ratio]≦40...(F0-1)
The value of [third addition speed ratio]/[second addition speed ratio] is an index for efficiently obtaining irregularly shaped and large-sized silica particles. When the value is in the range of 1.9 to 40, large-sized irregularly shaped silica particles can be obtained without using elements that are sources of contamination, such as halogens and alkaline earth metals.
When the value of [third addition speed ratio]/[second addition speed ratio] is less than 1.9, it becomes difficult to obtain irregularly shaped silica particles and large-sized particles.
When the value of [third addition speed ratio]/[second addition speed ratio] exceeds 40, irregular silica particles are easily obtained, but silicic acid tends to easily undergo self-nucleation, and it tends to be difficult to obtain silica particles having the desired particle size distribution and size.
The value of [third addition speed ratio]/[second addition speed ratio] is more preferably 5 or more and 20 or less.

<Step 4>
The method for producing a dispersion liquid of irregular shaped silica particles of the present invention may further include the following step 4.
Step 4 is a step of concentrating the irregular shaped silica particle dispersion liquid obtained in step 3.
In step 4, the irregular silica particle dispersion obtained in step 3 can be used as it is for polishing purposes or as a raw material for polishing slurry. If desired, the irregular silica particle dispersion obtained in step 3 can be concentrated before being used for various purposes.
Specifically, for example, the irregular silica particle dispersion obtained in step 3 is cooled to a temperature between room temperature and 40° C. Thereafter, the irregular silica particle dispersion is concentrated using an ultrafiltration membrane or the like, and further concentrated using an evaporator or the like, and the remaining irregular silica particles are recovered. Centrifugation may be used to further remove coarse particles.

In the method for producing silica particles of the present invention, a dispersion of irregularly shaped silica particles is obtained through step 3 or step 4, and can be used as is as an abrasive, etc. If necessary, it can be dried by a conventional method before use, and if necessary, it can be calcined by a conventional method before use.

<Condition 2>
In the method for producing a dispersion liquid of irregular shaped silica particles of the present invention, it is preferable that the following condition 2 is further satisfied.
Condition 2 is that in the precursor dispersion, the number of moles of halogen elements converted per 1 mole of silica (mol/mol ratio) is 0.5% or less, and the number of moles of alkaline earth metals converted per unit mole of silica (mol/mol ratio) is 1000 ppm or less.
Halogen elements and alkaline earth metals are contained in small amounts in silica sand, which is a natural raw material, and are also contained in small amounts in raw materials used to manufacture cullet and sodium silicate. Therefore, when silica sol is manufactured using sodium silicate as a raw material, the content of these elements derived from the raw material is 0.5% or less as halogen elements converted to 1 mole of silica, and 1000 ppm or less as alkaline earth metals converted to 1 mole of silica. However, since the content of these elements derived from the raw material is small, the influence on the generation of core particles, particle growth, or particle shape is small. Therefore, in conventional methods for manufacturing irregular-shaped particles, these elements are added during particle synthesis, and, for example, a method is used in which seed components of silica particles are bonded to each other via an alkaline earth metal (e.g., MgO, CaO, etc.) to form irregular shapes (a method in which an alkaline earth metal is added to a seed particle dispersion liquid and the seed components of silica particles are bonded to each other via an alkaline earth metal), or a method is used in which an alkali halide (e.g., KCl) is added to a seed particle dispersion liquid to adjust the ionic strength to form irregular shapes of seed particles. However, when the irregular shaped silica particle dispersion is used for polishing, these foreign substances such as alkaline earth metals and alkali halides may have adverse effects such as contamination of the substrate depending on the application, so it is preferable that they are not present in the first place.
The method for producing an irregular silica particle dispersion of the present invention is a method for producing an irregular silica particle dispersion without using foreign substances such as halogen elements and alkaline earth metals during particle synthesis, and specifically, the method is characterized in that particle growth is performed by adding an acidic silicic acid liquid to seed particles in two stages with different addition rates of the acidic silicic acid liquid. Therefore, it does not require foreign substances required in the conventional irregular sphericity method.

<Condition 3>
In the method for producing a dispersion liquid of irregular shaped silica particles of the present invention, it is preferable that the following condition 3 is further satisfied.
Condition 3 is that the silica content ratio represented by the following formula (F0-2) is in the range of 10 or more and 100 or less.
Silica content ratio={(silica content in the second acidic silicic acid liquid [kg])+(silica content in the third acidic silicic acid liquid [kg])}/(silica content in the precursor dispersion liquid [kg]) (F0-2)
The silica content ratio shown by the formula (F0-2) is the weight ratio of silicic acid to be grown to a seed precursor, and is an index for efficiently growing seed particles to a desired particle size. When the value is in the range of 10 to 100, the particles can be efficiently grown to a desired size.
When the silica content ratio represented by the formula (F0-2) is less than 10, the amount of silicic acid for growing the generated seed particles becomes insufficient, and large-sized irregularly shaped silica particles cannot be obtained.
When the silica content ratio shown by the formula (F0-2) exceeds 100, the amount of silicic acid that grows the nucleated irregular silica seeds becomes excessive. Therefore, the particle shape becomes closer to a sphere, and irregular silica particles with the desired degree of irregularity cannot be obtained. In addition, the excess silicic acid may cause self-nucleation.
The silica content ratio represented by formula (F0-2) is more preferably 20 or more and 80 or less.

<Condition 4>
In the method for producing a dispersion liquid of irregular shaped silica particles of the present invention, it is preferable that the following condition 4 is further satisfied.
Condition 4 is that the _SiO2 / _A2O molar ratio in the irregular silica particle dispersion at the end of step 3 is in the range of 60 to 140. (Here, _SiO2 represents the number of moles of silica in the irregular silica particle dispersion at the end of step 3, and _A2O represents the total number of moles of _Na2O and _K2O in the irregular silica particle dispersion at the end of step 3.)
Here, K ₂ O and Na ₂ O in A ₂ O mean the amounts of K and Na present in the irregular shaped silica particle dispersion, respectively, converted into oxides.
The _SiO2 / _A2O molar ratio in the irregular silica particle dispersion at the end of step 3 is an index of the pH during particle growth. Although it varies depending on the target size, within this range, the silicic acid used for particle growth can be sufficiently dissolved and deposited on the surfaces of the irregular seed particles, allowing the particles to grow to the desired particle diameter.
When the _SiO2 / _A2O molar ratio in the irregular silica particle dispersion is less than 60, the pH during the reaction is high, so that the particles may aggregate during the reaction. Even if the particles grow without aggregation, the ionic strength of the dispersion after the reaction is high, so that aggregation is likely to occur during concentration in the subsequent process. In order to prevent aggregation and maintain the stability of the particles, it is necessary to lower the ionic strength, and although methods such as ion exchange and washing can be used to lower the ionic strength, this reduces the economic efficiency.
When the SiO ₂ /A ₂ O molar ratio in the irregular shaped silica particle dispersion exceeds 140, the pH during the reaction is low, so that the silicic acid added for particle growth does not dissolve sufficiently, and self-nucleation tends to occur.
The SiO ₂ /A ₂ O molar ratio in the irregular shaped silica particle dispersion is more preferably 80 or more and 120 or less.

[Deformed silica particles]
In the manufacturing method of irregular silica particle dispersion of the present invention, it is preferable that the obtained irregular silica particles have a specific surface area converted particle diameter (D1) in the range of 10 nm to 200 nm, an average particle diameter (D2) measured by dynamic light scattering method in the range of 20 nm to 300 nm, and a value of (D2)/(D1) in the range of 1.2 to 20. Such irregular silica particles have a relatively large particle diameter and excellent polishing properties.

[Irregular shaped silica particle dispersion]
The irregular silica particle dispersion obtained by the manufacturing method of the present invention is preferably formed by dispersing irregular silica particles in water, the irregular silica particles having a specific surface area converted particle diameter (D1) in the range of 10 nm or more and 200 nm or less, an average particle diameter (D2) measured by dynamic light scattering in the range of 20 nm or more and 300 nm or less, and an irregularity [(D2)/(D1)] value in the range of 1.2 or more and 20 or less.
When the irregularity [(D2)/(D1)] is in the range of 1.2 to 20, when used as polishing abrasive grains, it shows a high polishing rate, has few defects, and can obtain a polished surface with low surface roughness. When the irregularity [(D2)/(D1)] is less than 1.2, it becomes close to a spherical particle, and when such an irregular silica particle dispersion is applied to a polishing application, the polishing rate tends to decrease. When the irregularity [(D2)/(D1)] is more than 20, when such an irregular silica particle dispersion is applied to a polishing application, defects such as scratches tend to occur on the polished substrate, and the surface roughness of the polished substrate also tends to deteriorate.
The average particle size (D2) measured by dynamic light scattering is preferably in the range of 20 nm to 300 nm, since it can obtain a high polishing rate. When the irregular silica particle dispersion liquid having an average particle size (D2) of less than 20 nm is used for polishing, the polishing rate is not sufficient in practice. Also, when the irregular silica particle dispersion liquid having an average particle size (D2) of more than 300 nm is used for polishing, the polishing rate decreases, and scratches tend to easily occur on the polished substrate.

The specific surface area converted particle diameter (D1) is preferably in the range of 10 nm or more and 200 nm or less.
When the specific surface area converted particle diameter (D1) is less than 10 nm, the number of particles increases due to the small size, but the polishing speed of each particle is low, so when used for polishing, the polishing speed is significantly reduced. When the specific surface area converted particle diameter (D1) is more than 200 nm, the size is too large, so the number of particles is significantly reduced. Therefore, when used for polishing, the polishing speed tends to decrease. In addition, the size is too large, so that precipitation of silica particles occurs in the dispersion liquid, which may require a lot of effort to redisperse when used, or may not be dispersed sufficiently, resulting in unstable polishing performance.
The specific surface area converted particle diameter (D1) is more preferably 20 or more and 150 or less.

The irregularity value [(D2)/(D1)] is more preferably 1.5 or more and 15 or less, and particularly preferably 1.5 or more and 5 or less.
The average particle size (D2) measured by dynamic light scattering is more preferably 30 nm or more and 250 nm or less.

The _SiO2 concentration of the irregular shaped silica particle dispersion is preferably 10% by mass or more and 50% by mass or less, and more preferably 20% by mass or more and 50% by mass or less.
As the dispersion medium for the irregular shaped silica particle dispersion, water or a mixed solvent of water and a hydrophilic organic solvent can be used.

The irregular silica particle dispersion of the present invention preferably contains a potassium compound. By containing a potassium compound, the dispersion can be kept alkaline, the dissociation of the surface silanol groups of the irregular silica particles progresses, and the irregular silica particles can be kept stable without aggregation.
Examples of the potassium compound include potassium hydroxide, salts of potassium hydroxide, potassium silicate, etc. The potassium compounds may be used alone or in combination of two or more.
The concentration of the potassium compound in the irregular shaped silica particle dispersion is preferably 50 or more and 400 or less, and more preferably 60 or more and 300 or less, in terms of the SiO ₂ /K ₂ O molar ratio.

In the present invention, particles having a particle diameter of 0.51 μm or more contained in the irregular shaped silica particle dispersion are called coarse particles. The ratio of the coarse particles is preferably 500,000 particles/cc or less, and more preferably 120,000 particles/cc or less, when expressed as the number of coarse particles in a silica particle dispersion having a _SiO2 concentration of 1% by mass.
If the number of coarse particles exceeds 500,000/cc, polishing scratches tend to occur easily during polishing.

[1] Method for quantifying _SiO2 The _SiO2 content in the silica microparticle dispersion was determined by subjecting the silica microparticle dispersion to ignition loss at 1000°C to determine the mass of the solid content, and then, in the same manner as in the case of measuring the Na and K contents described below, using an atomic absorption spectrophotometer (Hitachi, Ltd., Z-2310) to calculate the mass% of Na and K by the calibration curve method, converting Na and K to _Na2O and _K2O , and determining the _SiO2 content by assuming that the solid components other than _Na2O and _K2O are _SiO2 .

[2] Method for Quantifying Na and K 1. Preparation of Measurement Sample (1) Approximately 1 g of the irregular shaped silica particle dispersion is weighed out onto a platinum dish.
(2) Add 3 mL of phosphoric acid, 5 mL of nitric acid, and 10 mL of hydrofluoric acid to (1) above and heat on a sand bath.
(3) Once dried, add a small amount of water and 50 mL of nitric acid to dissolve, place in a 100 mL measuring flask, add water to make 100 mL, and use as the measurement sample.
2. Method for Measuring the Contents of Na and K The measurement sample obtained in 1 above was measured using an atomic absorption spectrophotometer (Hitachi, Ltd., Z-2310), and the contents of Na and K were calculated using the calibration curve method.

[3] Method for quantifying alkaline earth metals (1) The measurement sample prepared in the above [2] Method for quantifying Na and K is taken in an amount of 10 mL into a 20 mL measuring flask. This operation is repeated five times to obtain five 10 mL aliquots.
(2) This is used to perform measurements using the standard addition method in an ICP plasma emission spectrometer (manufactured by SII, model number SPS5520).
(3) Measure the blank in the same manner, subtract the blank amount to adjust and obtain the measured value for each element.

[4] Method for Determining Halogen Content 1. Sample Preparation (1) 5 g of a sample made of a dispersion of irregular shaped silica particles is diluted with water to a total volume of 100 ml.
(2) The mixture is centrifuged at 4,000 rpm for 20 minutes using a centrifuge (HIMAC CT06E manufactured by Hitachi) to remove the precipitated components, and the resulting liquid is used as a measurement sample.
2. Method for measuring halogen content The aqueous solution obtained in 1 above was measured using an ion chromatograph, and the halogen content was calculated using a calibration curve method.
System: DIONEX ICS-1100

[5] Measurement method for average particle diameter D2 by dynamic light scattering method The irregular shaped silica particle dispersion liquid is diluted with 0.58% ammonia water to adjust the silica concentration to 1% by mass, and the average particle diameter D2 is measured using a laser particle analyzer.
[Laser particle analyzer]
Manufactured by Otsuka Electronics Co., Ltd., model number "Zeta potential/particle size measurement system ELSZ-1000S" (measurement principle: dynamic light scattering method, light source wavelength: 665.70 nm, cell: 10 mm square plastic cell)

[6] Measurement method of specific surface area converted particle diameter D1 50 mL of irregular silica particle dispersion was adjusted to pH 3.5 with HNO ₃ , 40 mL of 1-propanol was added, and a sample was dried at 110°C for 16 hours. The sample was then pulverized in a mortar and baked at 500°C for 1 hour in a muffle furnace to obtain a measurement sample. The specific surface area was calculated from the amount of adsorbed nitrogen by the BET single point method using a specific surface area measuring device (manufactured by Yuasa Ionics, model number Multisorb 12) and nitrogen adsorption method (BET method).
Specifically, 0.5g of sample is taken into a measuring cell, and degassed at 300°C for 20 minutes in a mixed gas flow of 30v% nitrogen and 70v% helium, and then the sample is kept at liquid nitrogen temperature in the mixed gas flow to allow nitrogen to be equilibrated and adsorbed on the sample.Next, while the mixed gas is flowing, the sample temperature is gradually raised to room temperature, and the amount of nitrogen desorbed during this period is detected, and the specific surface area of the irregular silica particles is calculated using a calibration curve created in advance.Furthermore, the obtained specific surface area (SA) is substituted into the following formula to obtain the specific surface area converted particle diameter D1.
Specific surface area converted particle diameter D1 (nm) = 6000 / (ρ × SA)
(Here, ρ represents the density of the silica particles, 2.2 [g/cm ³ ].)

[7] Measurement method for coarse particles 1. Preparation of measurement sample The silica particle dispersion was diluted with water to 1% by mass to prepare a measurement sample.
2.
5 mL of the measurement sample is injected into a measurement device (Accusizer 780APS manufactured by Particle Sizing System Inc.) and the measurement is performed. The number of coarse particles of 0.51 μm or more is regarded as the number of coarse particles of the measurement sample. The measurement conditions are as follows.
＜System Setup＞
・Stir Speed Control / Low Speed Factor 1600 / High Speed Factor 2500
＜System Menu＞
・Data Collection Time 120 sec.
Syringe Volume 2.5mL
・Sample Line Number: Sum Mode
・Initial 2nd-Stage Dilution Factor 30
・Vessel Fast Flush Time 60 sec.
・System Flush Time / Before Measurement 100 sec. / After Measurement 100 sec.
・Sample Equilibration Time 25 sec./ Sample Flow Time 10 sec.

[Example 1]
- Preparation of potassium silicate solution 2.766 kg of potassium hydroxide aqueous solution (KOH concentration 48.7 mass%) was added to 3.699 kg of ultrapure water and stirred until homogenous. 2.82 kg of silica powder (water content 20 mass%) was added to this potassium hydroxide aqueous solution and mixed. This mixture was heated to 95°C and held for 4 hours to obtain a potassium silicate solution.
In the obtained potassium silicate solution, the _SiO2 concentration was 24.5 mass%, the _K2O concentration was 12.4 mass%, the _SiO2 / _K2O (molar ratio) was 3.10, and the Cl ion concentration was 8 ppm (hereinafter, this potassium silicate solution or an equivalent potassium silicate solution will be referred to as "potassium silicate solution (1)").

- Production of acidic silicic acid solution 15 kg of potassium silicate aqueous solution with a _SiO2 concentration of 5 mass% was passed through 6 L of strong acid cation exchange resin (SK1BH (manufactured by Mitsubishi Chemical Corporation)) at a space velocity of 2.75 (1/hr) to obtain 15 kg of acidic silicic acid solution. In the obtained acidic silicic acid solution, the _SiO2 concentration was 4.6 mass% (hereinafter, this acidic silicic acid solution or an acidic silicic acid solution equivalent thereto will be referred to as "acidic silicic acid solution").

<Preparation of Precursor Dispersion>
0.88 kg of potassium silicate solution (1) was added to 2.344 kg of ultrapure water and stirred until homogenous to obtain an alkaline aqueous solution. 0.15 kg of acidic silicic acid solution was added to this alkaline aqueous solution and mixed.
The mixture was heated to 98.5° C. and maintained at that temperature for 1.3 hours to obtain a precursor dispersion.
The precursor dispersion had a SiO ₂ concentration of 6.6 mass %, and the SiO ₂ /A ₂ O (molar ratio) was 3.2.

<Preparation of seed particle dispersion>
To the entire amount of this precursor particle dispersion, 6.97 kg of acidic silicic acid liquid was added over 4.9 hours (second addition rate ratio = 0.29) at 98.5°C. After completion of the addition, the mixture was left at 98.5°C for 0.5 hours to obtain a seed particle dispersion.
The _SiO2 concentration of this seed particle dispersion was 5.2% by mass, and the _K2O concentration was 1.1% by mass. The average particle size of the seed particles measured by a dynamic light scattering particle size measuring device was 105 nm.

<Production of irregular shaped silica particle dispersion>
0.006 kg of potassium silicate solution (1) was added to 0.113 kg of ultrapure water. 10.34 kg of the seed particle dispersion was added thereto and mixed. The temperature was then raised to 97.5° C. and maintained at that temperature for 0.5 hours.
Thereafter, 142.94 kg of the acidic silicic acid liquid was added over 12 hours (third addition rate ratio=2.5) at 97.5° C. After the addition was completed, the mixture was left at 97.5° C. for 1 hour and then cooled to room temperature to obtain a dispersion of irregular shaped silica particles.
In the obtained irregular silica particle dispersion, the _SiO2 concentration was 4.6 mass% and the _K2O concentration was 0.07 mass%. The average particle diameter D2 of the irregular silica particles measured with a dynamic light scattering particle size measuring device was 131 nm. In addition, when the reaction vessel was checked after the reaction was completed, no precipitation was found at the bottom of the vessel.

The mixture was then concentrated using an ultrafiltration module to prepare a silica particle dispersion having a _SiO2 concentration of 11.7% by mass.
The obtained silica particles had a specific surface area converted particle diameter D1 of 41 nm. When the shape of the obtained silica particles was observed with an electron microscope, the particles were found to have an irregular shape, such as a plurality of particles bonded together.

[Example 2]
Potassium Silicate Solution In this example, a potassium silicate solution prepared in the same manner as in Example 1 was used.
Acidic silicic acid solution In this example, an acidic silicic acid solution prepared in the same manner as in Example 1 was used.

<Preparation of Precursor Dispersion>
0.88 kg of potassium silicate solution (1) was added to 1.989 kg of ultrapure water and stirred until homogenous to obtain an alkaline aqueous solution. 0.137 kg of acidic silicic acid solution was added to this alkaline aqueous solution and mixed.
The mixture was heated to 87.0° C. and maintained at that temperature for 1.3 hours to obtain a precursor dispersion.
In the precursor dispersion, the SiO ₂ concentration was 7.4 mass %, and the SiO ₂ /A ₂ O (molar ratio) was 3.2.

<Preparation of seed particle dispersion>
To this precursor dispersion, 6.993 kg of the acidic silicic acid liquid was added over 4.9 hours (second addition rate ratio=0.30) at 87.0° C. After the addition was completed, the mixture was left at 87.0° C. for 0.5 hours to obtain a seed particle dispersion.
The _SiO2 concentration of this seed particle dispersion was 5.4% by mass, and the _K2O concentration was 1.1% by mass. The average particle size of the seed particles measured by a dynamic light scattering particle size measuring device was 64 nm.

<Production of irregular shaped silica particle dispersion>
0.003 kg of potassium silicate solution (1) was added to 0.461 kg of ultrapure water. 10.00 kg of the seed particle dispersion was added thereto and mixed. Then, the temperature was raised to 87.0° C. and maintained at that temperature for 0.5 hours.
Thereafter, 142.29 kg of the acidic silicic acid liquid was added over 12 hours (third addition rate ratio=2.5) at 87.0° C. After the addition was completed, the mixture was left at 87.0° C. for 1 hour and then cooled to room temperature to obtain a dispersion of irregular shaped silica particles.
In the obtained irregular silica particle dispersion, the _SiO2 concentration was 4.6 mass% and the _K2O concentration was 0.07 mass%. The average particle diameter D2 of the silica particles measured by a dynamic light scattering particle size measuring device was 91 nm. In addition, when the reaction vessel was checked after the reaction was completed, no precipitation was found at the bottom of the vessel.

The mixture was then concentrated using an ultrafiltration module to prepare a dispersion of irregular shaped silica particles with a _SiO2 concentration of 11.8% by mass.
The resulting irregular shaped silica particles had a particle diameter D1 calculated based on a specific surface area of 41 nm. When the shape of the resulting silica particles was observed with an electron microscope, the particles were found to be particles containing irregular shaped particles in which a plurality of particles were bonded together.

[Example 3]
Potassium Silicate Solution In this example, a potassium silicate solution prepared in the same manner as in Example 1 was used.
Acidic silicic acid solution In this example, an acidic silicic acid solution prepared in the same manner as in Example 1 was used.

<Preparation of Precursor Dispersion>
0.88 kg of potassium silicate solution (1) was added to 1.609 kg of ultrapure water and stirred until homogenous to obtain an alkaline aqueous solution. 0.137 kg of acidic silicic acid solution was added to this alkaline aqueous solution and mixed.
The mixture was heated to 87.0° C. and maintained at that temperature for 1.3 hours to obtain a precursor dispersion.
In the precursor dispersion, the SiO ₂ concentration was 8.5 mass %, and the SiO ₂ /A ₂ O (molar ratio) was 3.2.

<Preparation of seed particle dispersion>
To this precursor dispersion, 7.041 kg of the acidic silicic acid liquid was added over 4.9 hours at 87.0° C. (second addition rate ratio=0.30). After the addition was completed, the mixture was left at 87.0° C. for 0.5 hours to obtain a seed particle dispersion.
In this seed particle dispersion, the _SiO2 concentration was 5.7 mass %, and the _K2O concentration was 1.1 mass %. The average particle size of the seed particles measured with a dynamic light scattering particle size measuring device was 73 nm.

<Production of irregular shaped silica particle dispersion>
0.008 kg of potassium silicate solution (1) was added to 0.870 kg of ultrapure water. 9.67 kg of the seed particle dispersion was added thereto and mixed. Then, the temperature was raised to 87.0° C. and maintained at that temperature for 0.5 hours.
Thereafter, 143.07 kg of the acidic silicic acid liquid was added over 12 hours at 87.0° C. (third addition rate ratio=2.5). After the addition was completed, the mixture was left for 1 hour at 87.0° C. Then, it was cooled to room temperature to obtain a dispersion of irregular shaped silica particles.
In the obtained silica particle dispersion, the _SiO2 concentration was 4.6 mass% and the _K2O concentration was 0.07 mass%. The average particle diameter D2 of the irregular silica particles measured by a dynamic light scattering particle size measuring device was 98 nm. In addition, when the reaction vessel was checked after the reaction was completed, no precipitation was confirmed at the bottom of the vessel.

The mixture was then concentrated using an ultrafiltration module to prepare a dispersion of irregular shaped silica particles with a _SiO2 concentration of 11.6% by mass.
The resulting irregular shaped silica particles had a particle diameter D1 calculated based on a specific surface area of 41 nm. When the shape of the resulting silica particles was observed with an electron microscope, the particles were found to be particles containing irregular shaped particles in which a plurality of particles were bonded together.

[Example 4]
Potassium Silicate Solution In this example, a potassium silicate solution prepared in the same manner as in Example 1 was used.
Acidic silicic acid solution In this example, an acidic silicic acid solution prepared in the same manner as in Example 1 was used.

A seed particle dispersion was obtained in the same manner as in Example 3 (SiO ₂ concentration was 5.7% by mass, K ₂ O concentration was 1.1% by mass, and the average particle size of the seed particles was 73 nm).

<Production of irregular shaped silica particle dispersion>
9.67 kg of the seed particle dispersion was added to 0.335 kg of ultrapure water and mixed in. The mixture was then heated to 97.5° C. and held at that temperature for 0.5 hours.
Thereafter, 147.57 kg of the acidic silicic acid liquid was added over 12 hours (third addition rate ratio = 2.4) at 97.5°C. After the addition was completed, the mixture was left at 97.5°C for 1 hour and then cooled to room temperature to obtain a dispersion of irregular shaped silica particles.
In the obtained irregular silica particle dispersion, the _SiO2 concentration was 4.7 mass% and the _K2O concentration was 0.07 mass%. The average particle diameter D2 of the irregular silica particles measured with a dynamic light scattering particle size measuring device was 104 nm. In addition, when the reaction vessel was checked after the reaction was completed, no precipitation was found at the bottom of the vessel.

The mixture was then concentrated using an ultrafiltration module to prepare a dispersion of irregular shaped silica particles with a _SiO2 concentration of 11.9% by mass.
The resulting irregular shaped silica particles had a specific surface area converted particle diameter D1 of 47 nm. When the shape of the resulting silica particles was observed with an electron microscope, the particles were found to be particles containing irregular shaped particles in which a plurality of particles were bonded together.

[Example 5]
Preparation of potassium silicate solution 3.556 kg of potassium hydroxide aqueous solution (KOH concentration 48.7% by mass) was added to 4.757 kg of ultrapure water and stirred until homogenous. 3.62 kg of silica powder (water content 20.0%) was added to this potassium hydroxide aqueous solution and mixed.
The mixture was heated to 95° C. and maintained at that temperature for 4 hours to obtain a potassium silicate solution.
In the obtained potassium silicate solution, the _SiO2 concentration was 24.5 mass%, the _K2O concentration was 12.3 mass%, the _SiO2 / _K2O (molar ratio) was 3.12, and the Cl ion concentration was 4 ppm (hereinafter, this potassium silicate solution or an equivalent potassium silicate solution will be referred to as "potassium silicate solution (2)").
Acidic silicic acid solution In this example, an acidic silicic acid solution prepared in the same manner as in Example 1 was used.

<Preparation of Precursor Dispersion>
0.99 kg of potassium silicate solution (2) was added to 0.672 kg of ultrapure water and stirred until homogenous to obtain an alkaline aqueous solution. 0.132 kg of acidic silicic acid solution was added to this alkaline aqueous solution and mixed.
The mixture was heated to 80.0° C. and maintained at that temperature for 1.3 hours to obtain a precursor dispersion.
In the precursor dispersion, the SiO ₂ concentration was 13.8 mass %, and the SiO ₂ /A ₂ O (molar ratio) was 3.2.

<Preparation of seed particle dispersion>
To this precursor dispersion, 7.840 kg of the acidic silicic acid liquid was added over 4.9 hours at 80.0° C. (second addition rate ratio=0.30). After the addition was completed, the mixture was left at 80.0° C. for 0.5 hours to obtain a seed particle dispersion.
In the obtained seed particle dispersion, the _SiO2 concentration was 6.3 mass %, and the _K2O concentration was 1.3 mass %. The average particle size of the seed particles measured by a dynamic light scattering particle size measuring device was 71 nm.

<Production of irregular shaped silica particle dispersion>
0.001 kg of potassium silicate solution (2) was added to 1.970 kg of ultrapure water. 9.63 kg of the seed particle dispersion was added thereto and mixed. Then, the temperature was raised to 97.5° C. and maintained at that temperature for 0.5 hours.
Thereafter, 160.06 kg of the acidic silicic acid liquid was added over 12 hours (third addition rate ratio = 2.5). After the addition was completed, the mixture was left at 97.5°C for 1 hour. Then, it was cooled to room temperature to obtain a dispersion of irregular shaped silica particles.
In the obtained silica particle dispersion, the _SiO2 concentration was 4.6 mass% and the _K2O concentration was 0.07 mass%. The average particle diameter D2 of the irregular silica particles measured by a dynamic light scattering particle size measuring device was 102 nm. In addition, when the reaction vessel was checked after the reaction was completed, no precipitation was confirmed at the bottom of the vessel.

The mixture was then concentrated using an ultrafiltration module to prepare a dispersion of irregular shaped silica particles with a _SiO2 concentration of 11.7% by mass.
The resulting irregular shaped silica particles had a particle diameter D1 calculated based on a specific surface area of 45 nm. When the shape of the resulting silica particles was observed with an electron microscope, the particles were found to be particles containing irregular shaped particles in which a plurality of particles were bonded together.

[Comparative Example 1]
839.5g of pure water was added to 67.2g of sodium silicate ( _SiO2 concentration 24.28% by mass, _Na2O concentration 8.0% by mass) to prepare 906.7g of sodium silicate aqueous solution with a silica concentration of 1.8% by mass. 264.1g of acidic silicic acid solution ( _SiO2 concentration 4.7% by mass) obtained in the same manner as in Example 1 was added to this sodium silicate aqueous solution, stirred, and then heated to 79°C and held at 79°C for 30 minutes to obtain a precursor dispersion.
Next, 6,122.2 g of acidic silicic acid solution was added continuously over 9 hours. Then, 2,040.6 g of acidic silicic acid solution was added continuously over 2 hours. After the addition was completed, the mixture was kept at 79° C. for 1 hour and then cooled to room temperature. The particle diameter D2 measured by dynamic light scattering was 15 nm. In addition, when the reaction vessel was checked after the reaction was completed, no precipitation was observed at the bottom of the vessel.
The obtained silica sol was concentrated using an ultrafiltration membrane (product name: SIP-1013, manufactured by Asahi Kasei Corporation) until the silica concentration became 12% by mass, and then concentrated to 20% by mass with a rotary evaporator.
The silica sol had a particle diameter D1 calculated based on a specific surface area of 11 nm. When the shape of the particles was observed with an electron microscope, the shape of the particles was found to be almost spherical, and no irregularly shaped particles were obtained.

[Comparative Example 2]
1,126.6 g of pure water was added to 87.84 g of potassium silicate ( _SiO2 concentration 20.5 mass%, _K2O concentration 9.37 mass%), 31.42 g of potassium hydroxide aqueous solution (KOH concentration 3 mass%) was added, and after stirring, the mixture was heated to 83°C and maintained at 83°C for 30 minutes to obtain a precursor dispersion liquid.
Next, 1,493.8 g of acidic silicic acid solution was added continuously over 3 hours. Then, 8,962.8 g of acidic silicic acid solution was added continuously over 12 hours. After the addition was completed, the mixture was kept at 83° C. for 1 hour and then cooled to room temperature. The dynamic light scattering particle diameter D2 was 35 nm. In addition, when the reaction vessel was checked after the reaction was completed, no precipitation was confirmed at the bottom of the vessel.
The obtained silica sol was concentrated using an ultrafiltration membrane (product name: SIP-1013, manufactured by Asahi Kasei Corporation) until the silica concentration became 12% by mass, and then concentrated to 20% by mass with a rotary evaporator.
The silica sol had a particle diameter D1 calculated based on the specific surface area of 25 nm. When the shape of the particles was observed with an electron microscope, the shape of the particles was almost spherical, and no irregular-shaped particles were obtained.

[Comparative Example 3]
9,483 g of pure water was added to 3,294 g of sodium silicate ( _SiO2 concentration 24.3 mass%, _Na2O concentration 8 mass%), 347 g of an acidic silicic acid solution ( _SiO2 concentration 4.6 mass%) obtained in the same manner as in Example 1 was added, and 254 g of an aqueous potassium chloride solution (KCl concentration 20 mass%) was added. After stirring, the mixture was heated to 97°C and held at 97°C for 30 minutes to obtain a precursor dispersion.
Next, 281.8 kg of acidic silicic acid solution was added continuously over 15 hours. After the addition was completed, the mixture was kept at 97° C. for 1 hour and then cooled to room temperature. The dynamic light scattering particle diameter D2 was 155 nm. When the reaction vessel was checked, precipitation due to coarse silica aggregates was confirmed in part of the reaction vessel.
The obtained silica sol was concentrated using an ultrafiltration membrane (product name: SIP-1013, manufactured by Asahi Kasei Corporation) until the silica concentration became 12% by mass, and then concentrated to 20% by mass with a rotary evaporator.
The specific surface area converted particle diameter D1 of the obtained silica sol was 65 nm. When the shape of the particles was observed with an electron microscope, the particles were found to be irregularly shaped. However, as shown in Table 2 below, the number of coarse particles was large, and coarse aggregates and precipitates were partially observed.

[Comparative Example 4]
1,196 g of pure water was added to 3,804 g (4.6 mass%) of the acidic silicic acid liquid, 42.34 g of an aqueous potassium fluoride solution (KF concentration 10 mass%) was further added, and the pH was adjusted to 8.0 using an aqueous sodium hydroxide solution (NaOH concentration 3.0 mass%). The mixture was then kept at 98° C. for 1 hour to obtain a precursor dispersion liquid.
Next, 7,609 g of acidic silicic acid liquid was added over 2 hours, and the pH was maintained at 9-10 with NaOH during the addition, and after the addition was completed, the mixture was aged at 98°C for 1 hour. The specific surface area converted particle diameter D1 of the obtained silica sol was 9 nm, and the dynamic light scattering particle diameter D2 was 54 nm. Furthermore, when the reaction vessel was checked after the reaction was completed, no precipitation or the like was confirmed at the bottom of the vessel. When the particle shape was observed with an electron microscope, it was found to be irregularly shaped particles, but only irregularly shaped particles with small primary and secondary diameters were obtained.

[Comparative Example 5]
Add pure water to 782.6g of acidic silicic acid solution to dilute to 3.6% by mass of _SiO2 concentration, add 5.8g of 10% by mass of calcium nitrate aqueous solution while stirring, add 6.0g of 10% by mass of sodium hydroxide, and further add 188.2g of pure water to prepare a precursor dispersion. The obtained precursor dispersion was put into an autoclave and heated at 120°C for 6 hours while stirring. After heating, it was cooled to room temperature and the silica sol was taken out. In addition, when the reaction vessel was checked after the reaction was completed, no precipitation was confirmed at the bottom of the vessel.
The obtained silica sol was concentrated to 12% by mass using an ultrafiltration membrane. The specific surface area converted particle diameter D1 of the obtained silica sol was 9 nm, and the dynamic light scattering particle diameter D2 was 30 nm. When the particle shape was observed with an electron microscope, it was found to be irregular particles, but only irregular particles with small primary and secondary diameters were obtained.

Table 1 lists the various values in the manufacturing method of the irregular silica particle dispersion. Table 2 lists the average particle size of the irregular silica particles contained in the obtained irregular silica particle dispersion.

According to the manufacturing method of the present invention, irregular silica particles can be obtained without adding components other than silica-based components, such as alkaline earth metal-based raw materials (e.g., CaO and MgO, etc.) or raw materials containing halogen elements (e.g., KCl and KF, etc.).
Therefore, the irregular shaped silica particle dispersion obtained by the manufacturing method of the present invention does not contaminate the substrate to be polished when used for the SiO ₂ oxide film of a semiconductor device or a silicon semiconductor wafer.
Therefore, it is possible to efficiently produce a dispersion of irregular shaped silica particles which does not contain any components other than silica-based components and is suitable for semiconductor-related polishing applications.
Furthermore, according to the manufacturing method of the present invention, it is possible to obtain an irregularly shaped silica particle dispersion in which silica particles having a desired irregularity are dispersed in a solvent, and therefore it is possible to produce a dispersion containing silica particles that exhibits excellent polishing properties for glass hard disks, quartz glass, crystal, aluminum hard disks, _SiO2 oxide films of semiconductor devices, silicon semiconductor wafers, compound semiconductor wafers, etc.

Claims (8)

A method for producing a dispersion of irregular shaped silica particles, comprising the following steps 1 to 3, and satisfying the following condition 1:
Step 1: Mixing a first acidic silicic acid liquid with an alkaline aqueous solution containing an alkaline compound having at least Na or K;
Further, by heating and aging at a temperature in the range of 50° C. or more and less than 100° C., a precursor dispersion liquid having an SiO ₂ concentration of 3 mass % or more and 20 mass % or less and satisfying the condition shown in the following mathematical formula (F1-1) is obtained. Step 2≦SiO ₂ /A ₂ O≦15...(F1-1)
(Here, _SiO2 represents the number of moles of silica in the precursor dispersion, and _A2O represents the total number of moles of _Na2O and _K2O in the precursor dispersion.)
Step 2: A step of adding a second acidic silicic acid liquid to the precursor dispersion liquid obtained in step 1 so that a second addition rate ratio represented by the following mathematical formula (F2-1) is in the range of 0.1 [kg/hr kg] to 0.6 [kg/hr kg], and further heating and aging the mixture at a temperature in the range of 50° C. to 100° C. to obtain a seed particle dispersion liquid. Second addition rate ratio [kg/hr kg]=(silica content in the second acidic silicic acid liquid [kg])/(addition time of the second acidic silicic acid liquid [hr])/(silica content in the precursor dispersion liquid [kg])...(F2-1)
Step 3: A step of adding a third acidic silicic acid liquid to the seed particle dispersion liquid obtained in the step 2 so that a third addition speed ratio represented by the following mathematical formula (F3-1) is in the range of 1.1 [kg/hr kg] to 10 [kg/hr kg], and further heating and aging the mixture at a temperature in the range of 50° C. to less than 100° C. to obtain an irregularly shaped silica particle dispersion liquid. Third addition speed ratio [kg/hr kg]=(silica content in the third acidic silicic acid liquid [kg])/(addition time of the third acidic silicic acid liquid [hr])/(silica content in the precursor dispersion liquid [kg])...(F3-1)
Condition 1: The condition shown in the following formula (F0-1) is satisfied.
1.9≦[the third addition speed ratio]/[the second addition speed ratio]≦40 (F0-1) 2. The method for producing an irregular shaped silica particle dispersion according to claim 1, further comprising the following step 4 subsequent to step 3:
Step 4: Concentrating the irregular shaped silica particle dispersion obtained in step 3 3. The method for producing a dispersion liquid of irregular shaped silica particles according to claim 1, further satisfying the following condition 2:
Condition 2: In the precursor dispersion, the number of moles of halogen elements converted per 1 mole of silica (mol/mol ratio) is 0.5% or less, and the number of moles of alkaline earth metals converted per 1 mole of silica (mol/mol ratio) is 1000 ppm or less. The method for producing a dispersion liquid of irregular shaped silica particles according to any one of claims 1 to 3, further satisfying the following condition 3:
Condition 3: The silica content ratio represented by the following formula (F0-2) is in the range of 10 or more and 100 or less.
Silica content ratio={(silica content in the second acidic silicic acid liquid [kg])+(silica content in the third acidic silicic acid liquid [kg])}/(silica content in the precursor dispersion liquid [kg]) (F0-2) The method for producing a dispersion liquid of irregular shaped silica particles according to any one of claims 1 to 4, further satisfying the following condition 4:
Condition 4: The _SiO2 / _A2O molar ratio in the irregular silica particle dispersion is in the range of 60 to 140. (Here, _SiO2 represents the number of moles of silica in the irregular silica particle dispersion, and _A2O represents the total number of moles of _Na2O and _K2O in the irregular silica particle dispersion.) The method for producing a dispersion of irregular silica particles according to any one of claims 1 to 5, wherein the alkaline aqueous solution in step 1 is an aqueous potassium silicate solution. The method for producing a dispersion liquid of irregular shaped silica particles according to any one of claims 1 to 5, wherein the alkaline compound in the step 1 is potassium hydroxide. The method for producing an irregular silica particle dispersion according to any one of claims 1 to 7, characterized in that the obtained irregular silica particles have a specific surface area converted particle diameter (D1) in the range of 10 nm to 200 nm, an average particle diameter (D2) measured by dynamic light scattering in the range of 20 nm to 300 nm, and a value of (D2)/(D1) in the range of 1.2 to 20.