Silica-ceria composite fine particle dispersion and method for producing same

Abstract

To provide a silica-ceria-based composite fine particle dispersion liquid capable of polishing even a silica film, an Si wafer and a hard-to-process material at high speed, achieving high surface accuracy at the same time, and reducing the content of foreign matter causing abrasive grains to remain on a substrate.SOLUTION: A silica-ceria composite fine particle dispersion comprising silica-ceria composite fine particles having the following characteristics, wherein a solid concentration in a supernatant obtained by adjusting the solid concentration to 3% by mass and then subjecting the dispersion to a centrifugal separation treatment in a 000G at 24 °C for 3 minutes is less than 0.04% by mass: The silica-ceria composite particle contains a plurality of ceria particles and has a silica layer on the outermost surface thereof. In the silica-ceria composite particulate, a part of silica is compounded with ceria. The mass ratio of silica to ceria in the silica-ceria composite particle is 100:11 to 300. The silica-ceria composite fine particles have an average particle size of 50 to 350nm as determined by image analysis.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a silica-ceria composite microparticle dispersion suitable as an abrasive used in the manufacture of semiconductor devices and the like, and in particular to a silica-ceria composite microparticle dispersion for planarizing a film to be polished formed on a substrate by chemical mechanical polishing (CMP), a method for producing the same, and a polishing abrasive dispersion containing the ceria composite microparticle dispersion. [Background technology]

[0002] Higher performance is being achieved through increased density and miniaturization of semiconductor devices such as semiconductor substrates and wiring boards. Chemical mechanical polishing (CMP) is used in the semiconductor manufacturing process, and is an essential technology for shallow trench isolation, planarization of interlayer insulating films, and formation of contact plugs and Cu damascene wiring.

[0003] Generally, CMP abrasives consist of abrasive grains and chemical components, with the chemical components accelerating polishing by oxidizing or corroding the target film. Meanwhile, the abrasive grains polish through mechanical action, and colloidal silica, fumed silica, and ceria particles are used as abrasive grains. Ceria particles in particular exhibit a particularly high polishing rate for silicon oxide films, and are therefore used in polishing shallow trench isolation processes. In the shallow trench isolation process, not only the silicon oxide film but also the silicon nitride film is polished. To facilitate isolation, it is desirable that the polishing rate of the silicon oxide film is high and the polishing rate of the silicon nitride film is low, and this polishing rate ratio (selectivity) is also important.

[0004] Conventionally, the polishing method for such components involves a relatively rough primary polishing process followed by a precise secondary polishing process to obtain a smooth surface or an extremely high-precision surface with few scratches or other imperfections. Regarding the abrasive used in the secondary polishing as the finish polishing, the following methods have been proposed.

[0005] Patent Document 1 describes a silica-based composite particle dispersion containing silica-based composite particles having an average particle size of 50 to 350 nm, characterized in that the particles have child particles mainly composed of crystalline ceria on the surface of mother particles mainly composed of amorphous silica, and the child particles further have a silica coating on the surface thereof, and the silica-based composite particles have the following characteristics [1] to [3]: [1] The silica-based composite particles have a silica to ceria mass ratio of 100:11 to 316; [2] When the silica-based composite particles are subjected to X-ray diffraction, only the crystalline phase of ceria is detected; and [3] The silica-based composite particles have a crystallite size of 10 to 25 nm on the (111) plane of the crystalline ceria, as measured by X-ray diffraction. It is also stated that such silica-based composite microparticles can be used to polish even silica films, Si wafers, and other difficult-to-process materials at high speeds, while at the same time achieving high surface precision (low scratches, low surface roughness (Ra) of the substrate to be polished, etc.), and that because they do not contain impurities, a silica-based composite microparticle dispersion can be provided that can be preferably used to polish the surfaces of semiconductor devices such as semiconductor substrates and wiring boards. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6,730,254 Summary of the Invention [Problem to be solved by the invention]

[0007] The silica-based composite microparticle dispersion described in Patent Document 1 exhibits excellent polishing performance (e.g., polishing rate, high surface accuracy) in polishing applications. However, as semiconductor devices become increasingly denser and more integrated, abrasive dispersions with even better polishing performance for semiconductor substrates are needed. While the silica-based composite microparticle dispersion described in Patent Document 1 achieves a high polishing rate due to the mechanical action of the ceria particles during polishing and the simultaneous chemical reaction, under high-pressure conditions, the ceria particles may fall off, wear down, or disintegrate, reducing the contact area between the substrate and the ceria, resulting in a lower polishing rate. Furthermore, the fallen ceria particles may remain on the substrate and cause defects. Patent Publication No. 2019-172533 also proposes composite microparticles in which ceria microparticles are supported on silica host particles and further coated with a silica coating. Such composite microparticles achieve a high polishing rate by exposing the ceria microparticles to a moderate extent due to the peeling of the outermost silica layer during polishing. However, the thickness of the silica layer is insufficient, making the ceria microparticles prone to falling off. On the other hand, if the thickness of the silica coating is too thick, the ceria fine particles are not exposed much or at all during polishing, and therefore a high polishing rate cannot be obtained.

[0008] The present invention aims to solve the above-mentioned problems. That is, the present invention aims to provide a silica-ceria composite microparticle dispersion that can polish even silica films, Si wafers, and other difficult-to-process materials at high speed, achieve high surface precision (low surface roughness), and reduce the amount of foreign matter that causes abrasive grains to remain on the substrate, a method for producing the same, and a polishing abrasive dispersion containing the silica-ceria composite microparticle dispersion. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems and have completed the present invention. The present invention provides a silica-ceria composite microparticle dispersion comprising silica-ceria composite microparticles having the following characteristics [1] to [4], wherein the solid content concentration in the supernatant obtained by adjusting the solid content concentration to 3% by mass and then centrifuging the mixture at 24,000 G for 3 minutes is less than 0.04% by mass. [1] The silica-ceria composite fine particles contain a plurality of ceria fine particles and have a silica layer on the outermost surface thereof. [2] In the silica-ceria composite fine particles, a part of the silica is composited with ceria. [3] The mass ratio of silica to ceria in the silica-ceria composite particles is 100:11-300. [4] The silica-ceria composite fine particles have an average particle diameter of 50 to 350 nm as determined by image analysis. Such a silica-ceria composite fine particle dispersion will hereinafter also be referred to as the "dispersion of the present invention." The silica-ceria composite fine particles contained in the dispersion of the present invention will also be referred to as "composite fine particles of the present invention" hereinafter.

[0010] In the dispersion of the present invention, the silica-ceria composite fine particles have an outermost layer, and the average thickness of the outermost layer is preferably in the range of 7 to 18 nm, for example.

[0011] The dispersion of the present invention is preferably a dispersion of abrasive grains for polishing, and more preferably a dispersion of abrasive grains for polishing for planarizing a semiconductor substrate on which a silica film is formed.

[0012] The present invention provides a method for producing a silica-ceria composite fine particle dispersion, comprising the following steps 1 to 7: Step 1: A step of mixing an alkali with an aqueous solution of a cerium salt, followed by washing to obtain a precursor particle dispersion. Step 2: A step of wet-disintegrating the precursor particle dispersion under alkaline conditions to obtain a dispersion of disintegrated precursor particles containing fine ceria particles. Step 3: A step of adding an acidic silicic acid solution and an alkali to the above-mentioned dispersion of crushed precursor particles under alkaline conditions to obtain a dispersion of silica-ceria composite fine particles (1). Step 4: A step of adding an aqueous cerium salt solution to the dispersion of the silica-ceria composite microparticles (1), washing, wet-pulverizing under alkaline conditions, and adding an acidic silicic acid solution and an alkali under alkaline conditions to obtain a dispersion. Step 4A: A step of performing the same procedure as in the previous step, starting with adding the aqueous cerium salt solution again to the dispersion obtained in the previous step, two or more times to obtain a dispersion of silica-ceria composite fine particles (X). Step 5: A step of heating and drying the dispersion of silica-ceria composite fine particles (X) obtained in step 4A under weakly acidic conditions, followed by calcining to obtain a silica-ceria composite fine particle powder. Step 6: A step of adding water to the silica-ceria composite fine particle powder, stirring, and adjusting the alkalinity to obtain a silica-ceria composite fine particle suspension. Step 7: A step of wet-disintegrating the silica-ceria composite microparticle suspension under alkaline conditions to obtain a silica-ceria composite microparticle dispersion.

[0013] Such a method for producing a silica-ceria composite fine particle dispersion is hereinafter also referred to as the production method of the present invention.

[0014] In the production method of the present invention, the step 1 is a step of preparing the precursor particle dispersion by continuously or intermittently adding the cerium salt aqueous solution to an alkaline aqueous solution while stirring and mixing, and then performing washing (wherein the stirring and mixing of the cerium salt aqueous solution and the alkaline aqueous solution is performed at a liquid temperature of 5 to 30°C, a pH of 4.0 to 8.0, and an oxidation-reduction potential of 50 to 400 mV), The step 2 is a step of wet-disintegrating the precursor particle dispersion liquid under a pH condition of 9.0 to 10.0 to obtain the precursor particle dispersion liquid, The step 3 is a step of adjusting the pH of the precursor particle crushed dispersion liquid to 10.0 to 11.0, maintaining the liquid temperature at 80 to 90°C, subsequently continuously or intermittently simultaneously adding the acidic silicic acid liquid (silica concentration 4 to 5% by mass) and the alkaline aqueous solution, and further maintaining the temperature at 80 to 90°C to obtain the silica-ceria composite microparticle (1) dispersion liquid; Step 4 is a step of continuously or intermittently adding the cerium salt aqueous solution to the silica-ceria composite microparticle (1) dispersion, stirring and mixing the solution while maintaining the temperature of the solution at 5 to 30°C, the pH at 4.0 to 8.0, and the oxidation-reduction potential at 50 to 400 mV, washing the solution, wet-disintegrating the solution under the alkaline conditions of pH 9.0 to 10.0, continuously or intermittently simultaneously adding the acidic silicic acid solution and the alkaline aqueous solution having a silica concentration of 4 to 5% by mass while maintaining the temperature of the solution at 80 to 90°C under alkaline conditions of pH 10.0 to 11.0, and maintaining the temperature at 80 to 90°C, to obtain a dispersion, The step 4A is a step of performing the same operation, starting with adding the cerium salt aqueous solution in the previous step, to the dispersion obtained in the previous step two or more times to obtain a dispersion of silica-ceria composite fine particles (X), The step 5 is a step of adjusting the silica-ceria composite microparticle (X) dispersion obtained in the step 4 under weakly acidic conditions of pH 5.0 to 7.0, drying by heating, and then calcining the dispersion to obtain the silica-ceria composite microparticle powder; Step 6 is a step of adding water to the silica-ceria composite microparticle powder, stirring the mixture, and adjusting the pH to an alkaline condition of 9.0 to 10.0 to obtain the silica-ceria composite microparticle suspension; The step 7 is preferably a step of wet-disintegrating the silica-ceria composite microparticle suspension under alkaline conditions of pH 9.0 to 11.0 to obtain the silica-ceria composite microparticle dispersion.

[0015] The dispersion of the present invention is preferably produced by the production method of the present invention.

[0016] Hereinafter, when simply referring to "the present invention", it means any of the dispersion of the present invention, the composite fine particles of the present invention, and the production method of the present invention. [Effects of the Invention]

[0017] When the silica-ceria composite microparticle dispersion of the present invention is used for polishing purposes, for example, as a polishing abrasive dispersion, it can polish difficult-to-process materials such as silica films and Si wafers at high speed. At the same time, it can achieve high surface precision (e.g., low surface roughness (Ra) of the substrate to be polished). In such applications, the silica-ceria composite microparticle dispersion of the present invention is a silica-ceria composite microparticle dispersion in which the amount of uncomposite free ceria microparticles that cause abrasive residue on the substrate is reduced. The method for producing a silica-ceria composite microparticle dispersion of the present invention provides a method for efficiently producing a silica-ceria composite microparticle dispersion that exhibits such excellent performance. [Brief explanation of the drawings]

[0018] [Figure 1] 1 shows a transmission electron microscope photograph (300,000 times magnification) of the composite fine particles of the present invention, and the results of elemental analysis by STEM-EDS analysis of the silica layer (near the "+" mark). [Figure 2] 1 shows a transmission electron microscope photograph (300,000 times magnification) of the composite fine particles of the present invention, and the results of elemental analysis by STEM-EDS analysis of the ceria fine particles (near the "+" mark). DETAILED DESCRIPTION OF THE INVENTION

[0019] <Composite fine particles of the present invention and dispersion of the present invention> The composite fine particles of the present invention and the dispersion of the present invention will now be described.

[0020] [Effects of composite particles] The silica-ceria composite fine particles of the present invention contain a plurality of ceria fine particles therein, have a silica layer on the outermost surface, and further have part of the silica composited with the ceria. In principle, no ceria particles are present in the outermost silica layer. The plurality of ceria particles are present inside the silica layer, and the ceria particles may appear to be aggregated or may be separated and dispersed. The composite of a portion of the silica and ceria can be confirmed by the presence of silica and ceria in one composite particle, as described later, by elemental mapping of the dispersion of the present invention by SEM-EDS analysis.

[0021] In conventional polishing particle dispersions in which ceria fine particles are supported on base particles, the ceria fine particles present on the particle surfaces tend to fall off during the grinding process or polishing pressure, resulting in a large amount of abrasive particles remaining on the substrate after polishing. On the other hand, for example, in the ceria-based composite particles described in JP 2019-172533 A, the composite particles have a silica layer or a cerium-containing silica layer formed as a fixed layer on the ceria fine particles supported on the base particles. However, because the thickness of this layer is thin, the ceria fine particles also tend to fall off during the grinding process or polishing pressure. The composite particles of the present invention contain ceria fine particles within the composite particles, thereby preventing the ceria fine particles from falling off in the dispersion of the present invention. It is generally known that ceria microparticles exhibit a uniquely high polishing rate for silica-based coatings such as glass. Therefore, to achieve a high polishing rate, the ceria microparticles must be in direct contact with the substrate during polishing. On the other hand, composite microparticles in which ceria is simply supported on silica particles tend to easily shed during polishing. Patent Publication No. 2019-172533 proposes composite microparticles in which ceria microparticles are supported on silica host particles and then coated with a silica coating. Such composite microparticles achieve a high polishing rate by exposing the ceria microparticles adequately due to the peeling of the outermost silica layer during polishing. However, the thickness of the silica layer is insufficient, leading to the ceria microparticles easily falling off. On the other hand, if the silica coating is too thick, the ceria microparticles are not exposed much or at all during polishing, resulting in a low polishing rate. It is presumed that the composite microparticles of the present invention contain ceria microparticles inside thereof, and furthermore, have an appropriate thickness of the silica layer on the surface, which prevents the ceria microparticles from falling off, and furthermore, the silica layer peels off appropriately during polishing, exposing the ceria microparticles, thereby achieving a high polishing rate. Furthermore, if the silica layer peels off during polishing and the ceria microparticles are exposed, there is a concern that the ceria microparticles will fall off. However, although the reason for this is unclear, experimental results show that the composite microparticles of the present invention have a high polishing rate and lower ceria fall-off assessment results than conventional ones. Therefore, it is presumed that the silica layer peels off moderately during polishing, exposing the ceria microparticles, and therefore the ceria microparticles are fixed and will not fall off.

[0022] [Structure of silica-ceria composite particles] The composite fine particles of the present invention are particles having an average particle diameter (measured by image analysis) in the range of 50 to 350 nm in appearance. There are no particular limitations on the particle shape, but they are typically spherical or nearly spherical. The composite fine particles of the present invention contain a plurality of ceria fine particles therein, have a silica layer on the outermost surface, and further have a part of the silica composited with the ceria. In principle, the silica layer does not contain ceria fine particles. A plurality of ceria fine particles are present inside the silica layer, and the ceria fine particles may be aggregated or separated and dispersed, but a highly dispersed state is more preferable. High dispersion of the ceria fine particles is achieved by the manufacturing method of the present invention (including repeated coating of the silica component and the ceria component) described later. As will be described later, the composite of part of the silica and ceria can be confirmed by the presence of silica and ceria in one particle in element mapping by SEM-EDS analysis of the composite fine particles of the present invention.

[0023] [Average particle size of silica-ceria composite particles] The average particle size (image analysis method) of the composite fine particles of the present invention is preferably in the range of 50 to 350 nm. When the average particle size of the composite fine particles of the present invention is in this range, the occurrence of scratches during polishing is reduced. If the average particle size of the composite fine particles of the present invention is less than 50 nm, the particle size is small and the polishing rate may not reach a practical level, which is undesirable. Furthermore, if the average particle size of the composite fine particles of the present invention exceeds 350 nm, the surface precision of the substrate to be polished may be reduced. The average particle size of the composite fine particles of the present invention is preferably in the range of 70 to 300 nm, more preferably in the range of 100 to 250 nm. The method for measuring and calculating the average particle size of the composite fine particles of the present invention will be described later.

[0024] In this specification, when "A to B" (A and B are represented by numerical values) is written, it means "a range of A or more and B or less." For example, "50 to 350" means "a range of 50 to 350," and "50 to 350 nm" means "a range of 50 nm to 350 nm."

[0025] [Inclusion of Multiple Ceria Particles in the Composite Particles of the Present Invention] In the composite particles of the present invention, a plurality of ceria fine particles are encapsulated therein, and further, a silica layer in which no ceria fine particles are present is present on the outermost surface of the composite particles of the present invention in principle. As described above, in conventional particle dispersions in which ceria fine particles are supported on mother particles, the ceria fine particles present on the particle surfaces tend to fall off during the grinding process or due to the polishing pressure, resulting in a large amount of abrasive grains remaining on the substrate after polishing. However, in the composite microparticles of the present invention, the ceria fine particles are encapsulated within the composite microparticles and further have an outermost layer on the outside thereof, which prevents the ceria fine particles from falling off.

[0026] The fact that a plurality of ceria fine particles are encapsulated in the composite fine particles of the present invention will now be described. An image (TEM image, 300,000x magnification) obtained by observing the composite microparticles of the present invention using a transmission electron microscope shows multiple relatively opaque or black particle images covered by a relatively transparent outermost layer. STEM-EDS analysis of such a relatively transparent outermost layer (e.g., near the "+" mark in Figure 1) and the relatively opaque or black particle image covered by the outermost layer (e.g., near the "+" mark in Figure 2) revealed that the relatively transparent outermost layer contains Si (silicon) and O (oxygen) but essentially no Ce (cerium), suggesting the presence of at least SiO2, and the area near the "+" mark can be said to be a silica layer. On the other hand, the area near the relatively opaque or black particle image contains Si, O, and Ce, suggesting the presence of CeO2 in addition to SiO2. Considering that the TEM image was taken from a perpendicular direction of the composite microparticle, the area near the "+" mark can be said to be composed of a silica layer and ceria microparticles encapsulated therein. 1 shows that a plurality of relatively opaque or black particle images (ceria fine particles) are covered with a relatively transparent outermost layer (silica layer), which also suggests that the composite fine particles of the present invention are composed of silica and ceria.

[0027] (Outermost layer silica) The thickness of the silica layer of the composite fine particles of the present invention is not critical as long as the ceria fine particles contained therein are not easily separated from the silica layer, and examples of such thicknesses include a range of 7 to 18 nm.

[0028] [Crystallite diameter of ceria particles] The crystallite diameter of the ceria fine particles is preferably 10 to 25 nm, and more preferably 14 to 23 nm. If the crystallite diameter of the ceria fine particles exceeds 25 nm, the silica-ceria composite fine particles containing such ceria fine particles tend to sinter or coagulate after firing in step 5 of the production method of the present invention, making them difficult to disintegrate. Furthermore, even if such a silica-ceria composite fine particle dispersion is used for polishing purposes, it is undesirable because it causes scratches on the object to be polished. Similarly, if the crystallite diameter of the ceria fine particles is less than 10 nm, it tends to be difficult to achieve a practically sufficient polishing rate when used for polishing purposes. The method for measuring the crystallite size of the ceria fine particles is described in Example "6. X-ray diffraction method, measurement of average crystallite size."

[0029] [Silica-ceria mass ratio] In the composite microparticles of the present invention, the mass ratio of silica (SiO2) to ceria (CeO2) is not limited as long as useful polishing speed and surface precision are exhibited when the composite microparticles of the present invention are used as polishing abrasive grains, but is typically 100:11 to 300, preferably 100:30 to 300, more preferably 100:30 to 210, more preferably 100:30 to 150, more preferably 100:60 to 300, and even more preferably 100:60 to 210. Regarding the mass ratio of silica to ceria, if the amount of ceria relative to silica is too low, the composite fine particles may bond together, resulting in the generation of coarse particles. In this case, the abrasive (polishing slurry) containing the dispersion of the present invention may cause defects (deterioration of surface accuracy, such as an increase in scratches) on the surface of the polishing substrate. Furthermore, if the amount of ceria relative to silica is too high, not only will the cost increase, but resource risks will also increase. Furthermore, fusion between particles will progress. As a result, the roughness of the substrate surface will increase (deterioration of surface roughness Ra), increasing scratches, and further, free ceria may remain on the substrate and may easily cause problems such as adhesion to the waste liquid pipes of the polishing device. The method for measuring the mass ratio of silica to ceria in the composite fine particles of the present invention is described in Example "1. Analysis of silica and ceria and calculation of mass ratio."

[0030] (Ceria dropout decision) It is desirable that the dispersion of the present invention contains as few foreign matters as possible other than the composite fine particles of the present invention. Generally, coarse particles and the like are known as foreign matters contained in silica fine particle dispersions, but in addition to these, ceria fine particles that have fallen off from the composite fine particles have also been a problem. In the dispersion of the present invention, the composite microparticles of the present invention encapsulate ceria microparticles, and the outermost surface is composed of a silica layer, so that the ceria microparticles are less likely to fall off. This is presumably achieved by the production method of the composite microparticle dispersion of the present invention described below (including repeated coating with a silica component and a ceria component), in which the ceria microparticles are encapsulated in the composite microparticles of the present invention, and the outer layer is tightly coated with silica.

[0031] The dispersion of the present invention is a dispersion of silica-ceria composite microparticles adjusted to a solids concentration of 3% by mass (2 g of the dispersion is ignited at 1,000°C to reduce its weight, the mass of the resulting solid matter is determined, and the solids concentration is calculated), and then 300 g of the dispersion is filled into a 500 cc centrifuge tube and centrifuged at 24,000 G for 3 minutes, and 100 g of the supernatant is recovered from the centrifuge tube. The measured solids concentration is less than 0.04% (the method for determining the solids concentration is the same as above). The solid content obtained by this process refers to fine particle components, such as shed ceria and silica particles, that remain on the substrate after polishing and cause problems. A solid content concentration of less than 0.04% by mass is preferred because fewer abrasive particles remain on the substrate after polishing. A solid content concentration of less than 0.03% by mass is recommended, and more preferably 0.02% by mass or less.

[0032] (Ceria fine particles) In the present invention, the ceria fine particles contain crystalline ceria as a main component. The fact that the microparticles are mainly composed of crystalline ceria can be confirmed, for example, by drying the dispersion of the present invention, pulverizing the resulting solid in a mortar, or the like, to obtain the composite microparticles of the present invention, and then subjecting the composite microparticles to X-ray analysis using, for example, a conventionally known X-ray diffractometer (e.g., RINT1400, manufactured by Rigaku Corporation), and finding that only the crystalline phase of ceria is detected in the resulting X-ray diffraction pattern. In such cases, the child particles are considered to be mainly composed of crystalline ceria. The crystalline phase of ceria is not particularly limited, but examples thereof include cerianite.

[0033] The composite fine particles of the present invention contain crystalline ceria (crystalline Ce oxide) as a main component and may contain other elements, such as elements other than cerium, and may also contain a cerium hydrate compound as a polishing promoter. However, as described above, when the composite microparticles of the present invention are subjected to X-ray diffraction, only the crystalline phase of ceria is detected. That is, even if a crystalline phase other than ceria is contained, the content of the crystalline phase other than ceria is low or the crystalline phase is dissolved in the ceria crystal, so that the crystalline phase is outside the detection range by X-ray diffraction.

[0034] The average crystallite diameter of the ceria microparticles is calculated using the full width at half maximum of the maximum peak appearing in a chart obtained by subjecting the composite microparticles of the present invention to X-ray diffraction. For example, the average crystallite diameter of the (111) plane is 10 to 25 nm (full width at half maximum: 0.86 to 0.34°), preferably 14 to 23 nm (full width at half maximum: 0.62 to 0.37°). While the peak intensity of the (111) plane is often the greatest, the peak intensity of another crystal plane, such as the (100) plane, may also be the greatest. In this case, calculations can be made in the same way, and the average crystallite diameter in this case may be the same as the average crystallite diameter of the (111) plane.

[0035] The method for measuring the average crystallite size of ceria fine particles will be described below using the (111) plane (near 2θ=28 degrees) as an example. First, the composite microparticles of the present invention are pulverized in a mortar, and an X-ray diffraction pattern is obtained using, for example, a conventionally known X-ray diffractometer (e.g., RINT1400 manufactured by Rigaku Denki Co., Ltd.). Then, the full width at half maximum of the peak of the (111) plane near 2θ=28 degrees in the obtained X-ray diffraction pattern is measured, and the average crystallite size can be calculated using the following Scherrer formula. D=Kλ / βcosθ D: average crystallite diameter (angstroms) K: Scherrer constant (in the present invention, K=0.94) λ: X-ray wavelength (1.5419 Å, Cu lamp) β: Full width at half maximum (rad) θ: reflection angle

[0036] The number of coarse particles of 0.51 μm or more that can be contained in the dispersion of the present invention is preferably 100 million particles / cc or less in dry equivalent, and more preferably 80 million particles / cc or less. Coarse particles of 0.51 μm or more can cause polishing scratches and further deteriorate the surface roughness of the polished substrate.

[0037] The method for measuring the number of coarse particles that may be contained in the dispersion of the present invention is as follows. After diluting the sample with pure water to 0.1% by mass, 5 ml of the sample was taken and injected into a conventional coarse particle number measuring device. The number of coarse particles of 0.51 μm or larger was then determined. This measurement was carried out three times, and the simple average value was calculated. This value was then multiplied by 1000 to obtain the number of coarse particles of 0.51 μm or larger.

[0038] The specific surface area of ​​the composite fine particles of the present invention is not particularly limited, but it is preferred that the specific surface area is 9 to 60 m 2 / g, and 10 to 43 m 2 / g is more preferred.

[0039] Here, a method for measuring the specific surface area (BET specific surface area) will be described. First, a dried sample (0.2 g) is placed in a measurement cell and degassed in a nitrogen gas stream at 250°C for 40 minutes. The sample is then kept at liquid nitrogen temperature in a mixed gas stream of 30% by volume nitrogen and 70% by volume helium to allow equilibrium adsorption of nitrogen onto the sample. Next, the temperature of the sample is gradually raised to room temperature while the mixed gas is flowing, and the amount of desorbed nitrogen is detected during this process. The specific surface area of ​​the sample is then measured using a previously prepared calibration curve. Such a BET specific surface area measurement method (nitrogen adsorption method) can be carried out using, for example, a conventionally known surface area measurement device. In the present invention, the specific surface area means a value obtained by measurement using such a method, unless otherwise specified.

[0040] In the composite fine particles of the present invention, the content of each element of the specific impurity group 1 is preferably 100 ppm or less, more preferably 50 ppm or less, even more preferably 25 ppm or less, still more preferably 5 ppm or less, and even more preferably 1 ppm or less. Furthermore, the content of each element of specific impurity group 2 in the composite fine particles of the present invention is preferably 5 ppm or less. The method for reducing the content of each element of specific impurity group 1 and specific impurity group 2 in the composite fine particles of the present invention is as described above. The content of each element of the specific impurity group 1 and the specific impurity group 2 in the composite fine particles of the present invention can be measured by the following method. Na and K: Atomic absorption spectroscopy Ag, Al, Ca, Cr, Cu, Fe, Mg, Ni, Ti, Zn, Zr, U and Th: ICP-MS (Inductively Coupled Plasma Atomic Emission Spectroscopy Mass Analysis) ·Cl: Potentiometric titration method NO3, SO4 and F: Ion chromatograph

[0041] The composite microparticles of the present invention are formed by alternately depositing silica and ceria on precursor particles, and have a plurality of ceria microparticles encapsulated within a silica microparticle, with some of the silica being composited with ceria, and the outermost surface consisting of a silica layer.

[0042] (Silica-ceria composite particle dispersion) The outermost layer of the composite fine particle of the present invention is made of a silica layer, and the ceria fine particles are encapsulated therein, so that the ceria fine particles can be prevented from falling off.

[0043] <Dispersion of the Present Invention> The dispersion of the present invention will now be described. The dispersion of the present invention is one in which the composite fine particles of the present invention as described above are dispersed in a dispersion solvent.

[0044] The dispersion of the present invention contains water and / or an organic solvent as a dispersion solvent. It is preferable to use water, such as pure water, ultrapure water, or ion-exchanged water, as the dispersion solvent. Furthermore, the dispersion of the present invention can be suitably used as a polishing slurry by adding one or more additives selected from the group consisting of a polishing accelerator, a surfactant, a pH adjuster, and a pH buffer to control the polishing performance.

[0045] Examples of dispersion solvents that can be used in the dispersion of the present invention include alcohols such as methanol, ethanol, isopropanol, n-butanol, and methyl isocarbinol; ketones such as acetone, 2-butanone, ethyl amyl ketone, diacetone alcohol, isophorone, and cyclohexanone; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; ethers such as diethyl ether, isopropyl ether, tetrahydrofuran, 1,4-dioxane, and 3,4-dihydro-2H-pyran; glycol ethers such as 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, and ethylene glycol dimethyl ether; Examples of organic solvents that can be used include glycol ether acetates such as 2-methoxyethyl acetate, 2-ethoxyethyl acetate, and 2-butoxyethyl acetate; esters such as methyl acetate, ethyl acetate, isobutyl acetate, amyl acetate, ethyl lactate, and ethylene carbonate; aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane, heptane, isooctane, and cyclohexane; halogenated hydrocarbons such as methylene chloride, 1,2-dichloroethane, dichloropropane, and chlorobenzene; sulfoxides such as dimethyl sulfoxide; and pyrrolidones such as N-methyl-2-pyrrolidone and N-octyl-2-pyrrolidone. These may also be used in combination with water.

[0046] (concentration) The solid content concentration in the dispersion of the present invention is preferably in the range of 0.3 to 50% by mass.

[0047] <Production Method of the Present Invention> Next, the production method of the present invention will be described. The production method of the present invention for producing a silica-ceria composite microparticle dispersion is characterized by comprising the following steps 1 to 7. Step 1: A step of mixing an alkali with an aqueous solution of a cerium salt, followed by washing to obtain a precursor particle dispersion. Step 2: A step of wet-disintegrating the precursor particle dispersion under alkaline conditions to obtain a dispersion of disintegrated precursor particles containing fine ceria particles. Step 3: A step of adding an acidic silicic acid solution and an alkali to the above-mentioned dispersion of crushed precursor particles under alkaline conditions to obtain a dispersion of silica-ceria composite fine particles (1). Step 4: A step of adding an aqueous cerium salt solution to the dispersion of the silica-ceria composite microparticles (1), washing, wet-pulverizing under alkaline conditions, and adding an acidic silicic acid solution and an alkali under alkaline conditions to obtain a dispersion. Step 4A: A step of performing the same procedure as in the previous step, starting with adding the aqueous cerium salt solution again to the dispersion obtained in the previous step, two or more times to obtain a dispersion of silica-ceria composite fine particles (X). Step 5: A step of heating and drying the dispersion of silica-ceria composite fine particles (X) obtained in step 4A under weakly acidic conditions, followed by calcining to obtain a silica-ceria composite fine particle powder. Step 6: A step of adding water to the silica-ceria composite fine particle powder, stirring, and adjusting the alkalinity to obtain a silica-ceria composite fine particle suspension. Step 7: A step of wet-disintegrating the silica-ceria composite microparticle suspension under alkaline conditions to obtain a silica-ceria composite microparticle dispersion.

[0048] [Outline of the production method of the present invention and mechanism of action] In the manufacturing method of the present invention, first, an alkali and an aqueous cerium salt solution are mixed, and after washing, a precursor particle dispersion liquid is prepared in which fine ceria particles are aggregated [Step 1]. Next, the precursor particle dispersion is wet-disintegrated under alkaline conditions to prepare a precursor particle dispersion containing ceria fine particles (single particles) [Step 2]. Next, an acidic silicic acid solution and an alkali are added to the precursor particle crushed dispersion under alkaline conditions to prepare silica-ceria composite fine particles (1) having a silica layer on the outermost surface [step 3]. Next, an aqueous cerium salt solution is added to the dispersion of the silica-ceria composite particles (1), and the mixture is washed to prepare silica-ceria composite particles (2) consisting of aggregates of silica-ceria composite particles having an outermost layer made of ceria [step 4-1]. Next, the silica-ceria composite microparticle (2) dispersion is wet-disintegrated under alkaline conditions to obtain a silica-ceria composite microparticle (2) disintegrated dispersion containing silica-ceria composite microparticles (single particles) having an outermost layer made of ceria [step 4-2]. Next, an acidic silicic acid solution and an alkali are added to the crushed dispersion of silica-ceria composite particles (2) under alkaline conditions to prepare a dispersion of silica-ceria composite particles (3) having a silica layer on the outermost surface [step 4-3]. Next, the steps 4-1, 4-2 and 4-3 are repeated in this order at least twice to prepare a silica-ceria composite fine particle dispersion (X) [Step 4A]. Next, the silica-ceria composite fine particle dispersion (X) is heated and dried, and then calcined to obtain a silica-ceria composite fine particle powder [step 5]. Next, water is added to the silica-ceria composite fine particle powder to obtain a silica-ceria composite fine particle suspension under alkaline conditions [Step 6]. Next, the silica-ceria composite microparticle suspension is wet-disintegrated under alkaline conditions to obtain a silica-ceria composite microparticle dispersion (single particles) [Step 7].

[0049] Through steps 1 to 7 of this production method, composite microparticles can be obtained in which ceria microparticles are encapsulated therein and the ceria microparticles are prevented from falling off into the dispersion of the present invention. It is believed that the composite microparticles of the present invention have ceria microparticles encapsulated therein and have a silica layer of an appropriate thickness on the surface, which prevents the ceria microparticles from falling off, and that the silica layer peels off appropriately during polishing, exposing the ceria microparticles, resulting in a high polishing rate.

[0050] [Process 1] Step 1 is a step of mixing an alkali with an aqueous cerium salt solution to obtain a dispersion of precursor particles made of ceria fine particles (which may be aggregates of ceria fine particles).

[0051] The alkali can be a known aqueous alkali solution. A typical example is an aqueous ammonia solution (ammonia water), and other examples include, but are not limited to, aqueous solutions of alkali hydroxides, alkaline earth metals, or amines. The pH of the solution should be alkaline, and an alkaline aqueous solution with a pH of 10.0 to 12.0 is usually used.

[0052] The cerium salt in the cerium salt aqueous solution is not limited, and examples thereof include cerium chloride, cerium nitrate, cerium sulfate, cerium acetate, cerium carbonate, and cerium metal alkoxide. Specific examples include cerous nitrate, cerium carbonate, cerous sulfate, and cerous chloride. Of these, cerous nitrate and cerous chloride are preferred.

[0053] In step 1, the mixing ratio of the alkali and the aqueous cerium salt solution is not particularly limited.

[0054] More specifically, in step 1, the precursor particle dispersion is preferably prepared by continuously or intermittently adding an aqueous cerium salt solution to an aqueous alkaline solution while stirring and mixing, followed by washing. When stirring and mixing the aqueous cerium salt solution and the aqueous alkaline solution, it is desirable to satisfy the following conditions: a liquid temperature of 5 to 30°C, a pH of 4.0 to 8.0, and an oxidation-reduction potential of 50 to 400 mV.

[0055] As mentioned above, the liquid temperature of the prepared solution (prepared solution obtained by adding an aqueous cerium salt solution to an aqueous alkaline solution) when the aqueous cerium salt solution is continuously or intermittently added to the aqueous alkaline solution while stirring and mixing is preferably 5 to 30°C. This temperature range makes it possible to minimize excessive aggregation of precursor microparticles, which are aggregates of ceria microparticles. If the liquid temperature is below 5°C, the reaction does not proceed well and ceria microparticles are difficult to produce. If the liquid temperature exceeds 30°C, aggregation of the precursor microparticles is excessively promoted, which is undesirable. A liquid temperature of 10 to 28°C is preferably recommended.

[0056] When the cerium salt aqueous solution is continuously or intermittently added to the alkaline aqueous solution while stirring and mixing, the pH of the prepared solution (prepared solution obtained by adding the cerium salt aqueous solution to the alkaline aqueous solution) is preferably in the range of pH 4.0 to 8.0, as described above. This pH range can relatively effectively suppress excessive aggregation of precursor microparticles, which are aggregates of ceria microparticles. If the pH is less than 4.0, ceria dissolves in the dispersion, making such deposition less likely to occur. A pH exceeding 8.0 is undesirable because it tends to promote excessive aggregation of the precursor microparticles. A pH range of pH 6.0 to 8.0 is recommended. An alkaline aqueous solution may be added as needed to maintain the pH within this range.

[0057] When the cerium salt aqueous solution is continuously or intermittently added to the alkaline aqueous solution while stirring and mixing, the redox potential of the prepared solution (prepared solution obtained by adding the cerium salt aqueous solution to the alkaline aqueous solution) is preferably in the range of 50 to 400 mV, as described above. This is because when a trivalent cerium metal salt is used as a raw material, the acid-reduction potential of the microparticle dispersion decreases during preparation. Furthermore, maintaining the redox potential in this range promotes crystallization of the resulting CeO2 ultrafine particles. A redox potential of less than 50 mV is undesirable because it tends to produce irregularly shaped ceria microparticles and their aggregates, such as plate-like or rod-like ceria microparticles. A redox potential of approximately 400 mV is sufficient; it is not necessarily necessary to adjust the redox potential to exceed 400 mV. The redox potential is preferably in the range of 100 to 300 mV. The redox potential can be adjusted, for example, by blowing in air using a method such as air bubbling.

[0058] The solid content of the precursor particle dispersion is not particularly limited, but since the precursor particle dispersion is subjected to wet crushing in the next step, the solid content is preferably in the range of 0.1 to 1.0 mass %.

[0059] After stirring and mixing the cerium salt aqueous solution and the alkaline aqueous solution, washing is performed. For example, the preparation (including the generated precursor particles) can be washed using an ultrafiltration membrane while replenishment with ion-exchanged water. Washing the preparation produces the effect of suppressing aggregation by the salt, and a precursor particle dispersion can be obtained.

[0060] After the cerium salt aqueous solution and the alkaline aqueous solution are mixed by stirring, the prepared solution may be aged before washing. The aging condition can be, for example, to maintain the mixture at room temperature for about 30 minutes to 4 hours. Aging increases the tendency for the reaction to reach equilibrium.

[0061] [Process 2] Step 2 is a step of wet-crushing the precursor particles (aggregates of ceria fine particles) obtained in step 1 to obtain a dispersion of crushed precursor particles (a dispersion of monodispersed ceria fine particles).

[0062] In step 2, the precursor particle dispersion obtained in the previous step is preferably subjected to wet disintegration under conditions of pH 9.0 to 10.0. A pH within this range (pH 9.0 to 10.0) is preferred because it facilitates the production of monodispersed ceria microparticles. If the precursor particle dispersion has a pH of less than 9.0, it tends to be difficult to achieve a dispersed state, and if the pH exceeds 10.0, it tends to be difficult to deflocculate the precursor particles and achieve a dispersed state. The recommended pH range for wet disintegration is 9.1 to 9.9. The solids concentration of the precursor particle dispersion when wet disintegrating the precursor particle dispersion is not particularly limited, but is typically in the range of 0.1 to 1.0 mass%.

[0063] As the crushing device for wet crushing, conventionally known devices can be used, including, for example, batch-type bead mills such as basket mills, horizontal, vertical, and annular continuous bead mills, sand grinder mills, ball mills, rotor-stator homogenizers, ultrasonic dispersion homogenizers, wet media agitation mills (wet crushers) such as impact crushers that collide fine particles in a dispersion liquid. Examples of beads used in wet media agitation mills include beads made from raw materials such as glass, alumina, zirconia, steel, and flint.

[0064] [Process 3] Step 3 is a step of adding an acidic silicic acid solution and an alkali to the dispersion of crushed precursor particles (monodispersed ceria particles) obtained in the previous step to obtain a dispersion of silica-ceria composite particles (1). Here, the silica-ceria composite particles (1) are presumed to be ceria particles having a silica layer on the outermost surface.

[0065] More specifically, in step 3, the pH of the precursor particle disintegration dispersion obtained in the previous step is adjusted to 10.0 to 11.0, and the liquid temperature is maintained at 80 to 90°C. Then, an acidic silicic acid solution (silica concentration 4 to 5% by mass) and an alkaline aqueous solution are added continuously or intermittently at the same time, and the temperature is further maintained at 80 to 90°C to prepare a silica-ceria composite microparticle (1) dispersion.

[0066] The pH of the precursor particle dispersion is preferably adjusted to 10.0 to 11.0. This pH range facilitates silica deposition on the surface of the ceria microparticles, which is preferable for forming a silica layer on the outermost surface. If the pH is less than 10.0, such silica deposition is unlikely to occur, which is undesirable. If the pH is greater than 11.0, such silica deposition is also unlikely to occur, which is undesirable. The pH range of the precursor particle dispersion is preferably recommended to be 10.1 to 10.9. The aforementioned aqueous alkaline solution can be used to adjust the pH range. Next, the pH of the precursor particle crushed dispersion liquid is adjusted to 10.0 to 11.0, and the precursor particle crushed dispersion liquid is then maintained at a liquid temperature in the range of 80 to 90°C, preferably for 30 minutes to 5 hours. Maintaining the liquid temperature in this range (80 to 90°C) is desirable to allow the reaction to reach equilibrium. A liquid temperature below 80°C makes it difficult for the reaction to reach equilibrium, while a liquid temperature above 90°C is undesirable because the pH may deviate from the above-mentioned preferred range.

[0067] The pH of the precursor particle crushed dispersion is adjusted to 10.0 to 11.0, and the liquid temperature is maintained at 80 to 90°C. Then, an acidic silicic acid solution (silica concentration 4 to 5% by mass) and an alkaline aqueous solution are added continuously or intermittently to prepare a silica-ceria composite microparticle (1) dispersion. Simultaneous addition of the acidic silicic acid solution and the alkaline aqueous solution promotes silica deposition on the surfaces of the ceria fine particles contained in the precursor particle crushed dispersion. The pH of the alkaline aqueous solution used is preferably in the range of 10.0 to 12.0.

[0068] After the acidic silicic acid solution and the alkaline aqueous solution are simultaneously added to the precursor particle crushed dispersion, the temperature of the prepared solution is preferably maintained at 80 to 90°C for 30 minutes to 5 hours. Maintaining the solution in this temperature range (80 to 90°C) is desirable to allow the reaction to reach equilibrium. If the solution temperature is below 80°C, the reaction will be difficult to reach equilibrium, and if the solution temperature exceeds 90°C, the pH may deviate from the above-mentioned preferred range, which is undesirable. The silica-ceria composite fine particles (1) obtained in step 3 are composite fine particles in which the outermost layer of the ceria fine particles is made of silica, as described above.

[0069] [Step 4] Step 4 includes the following steps 4-1, 4-2, and 4-3.

[0070] [Step 4-1] In step 4-1, an aqueous cerium salt solution is added to the dispersion of silica-ceria composite particles (1), followed by washing to obtain a dispersion of silica-ceria composite particles (2). The silica-ceria composite particles (2) are presumably formed by providing a ceria coating on the surface of silica-ceria composite particles (1), the outermost surface of which is made of silica.

[0071] Specifically, in step 4-1, an aqueous cerium salt solution is continuously or intermittently added to a dispersion of silica-ceria composite microparticles (1) while stirring and mixing, followed by a washing treatment to prepare a dispersion of silica-ceria composite microparticles (2). (However, it is desirable that the mixing conditions for stirring and mixing the aqueous cerium salt solution and the silica-ceria composite microparticles (1) satisfy the following: a liquid temperature of 5 to 30°C, a pH of 4.0 to 8.0, and an oxidation-reduction potential of 50 to 400 mV.)

[0072] As described above, the liquid temperature when the cerium salt aqueous solution is continuously or intermittently added to the silica-ceria composite microparticle (1) dispersion while stirring and mixing is preferably 5 to 30°C. This temperature range facilitates the formation of a crystalline ceria coating (a ceria coating containing fine particulate ceria) on the surface of the silica-ceria composite microparticle (1). The liquid temperature is preferably 10 to 28°C.

[0073] When the cerium salt aqueous solution is continuously or intermittently added to the silica-ceria composite microparticle (1) dispersion while stirring and mixing, the pH is preferably in the range of 4.0 to 8.0. This pH range is preferred because it facilitates ceria deposition on the surface of the silica-ceria composite microparticle (1). If the pH is less than 4.0, ceria dissolves in the dispersion, making deposition less likely. If the pH exceeds 8.0, excessive aggregation tends to be promoted, which is undesirable. The recommended pH range is preferably 4.1 to 7.9. An aqueous alkaline solution may be added as needed to maintain the pH within this range.

[0074] When the cerium salt aqueous solution is continuously or intermittently added to the silica-ceria composite microparticle (1) dispersion while stirring and mixing, the redox potential is preferably in the range of 50 to 400 mV. This range of redox potential is preferred because it promotes crystallization of the ceria microparticles. If the redox potential is less than 50 mV, the cerium compound may not deposit on the surface of the silica microparticles, resulting in the formation of plate-like or rod-like ceria particles or composite ceria particles. If the redox potential exceeds 400 mV, the crystallization effect saturates and is not necessarily required. A range of 100 to 300 mV is recommended for the redox potential. The redox potential can be adjusted, for example, by blowing air into the mixture.

[0075] After stirring and mixing the cerium salt aqueous solution and the alkaline aqueous solution, washing is performed. For example, the preparation (including the generated precursor particles) can be washed using an ultrafiltration membrane while replenishment with ion-exchanged water. Washing the preparation produces the effect of suppressing aggregation by the salt, and a precursor particle dispersion can be obtained.

[0076] After stirring and mixing the aqueous cerium salt solution and the aqueous alkaline solution, the prepared solution may be aged before washing. The aging condition may be, for example, maintaining the solution at room temperature for about 30 minutes to 4 hours. Aging facilitates the reaction to reach equilibrium.

[0077] The solid content of the dispersion of the silica-ceria composite fine particles (2) is not particularly limited, but since the dispersion is subjected to wet crushing in the next step, the solid content is preferably in the range of 6 to 8 mass %. The silica-ceria composite fine particles (2) in the silica-ceria composite fine particle (2) dispersion obtained in step 4-1 are presumed to be aggregates of composite fine particles whose outermost layer is made of ceria.

[0078] [Step 4-2] Step 4-2 is a step of wet-disintegrating the dispersion of silica-ceria composite microparticles (2) to obtain a dispersion of disintegrated silica-ceria composite microparticles (2). The dispersion of disintegrated silica-ceria composite microparticles (2) is presumed to contain composite microparticles whose outermost layer is made of ceria.

[0079] Specifically, in step 4-2, the silica-ceria composite microparticle (2) dispersion obtained in the previous step is preferably wet-disintegrated at a pH of 9.0 to 10.0 to prepare a silica-ceria composite microparticle (2) dispersion. This pH range is preferred because the disintegrated microparticles are easily dispersed. If the pH is less than 9.0, the dispersibility of the disintegrated microparticles is low, and even if the pH exceeds 10.0, the dispersibility of the disintegrated microparticles tends to be low. The pH range recommended for wet-disintegration is preferably 9.0 to 9.9. The solids concentration of the silica-ceria composite microparticle (2) dispersion when wet-disintegrating the silica-ceria composite microparticles (2) is not particularly limited, but is usually preferably in the range of 6 to 8% by mass. As for the wet crushing device, the same crushing device as used in step 2 can be used. The composite fine particles contained in the crushed dispersion of silica-ceria composite fine particles (2) obtained in step 4-2 are presumed to be composite fine particles whose outermost layer is made of ceria.

[0080] [Step 4-3] Step 4-3 is a step of adding an acidic silicic acid solution and an alkaline aqueous solution to the disintegrated dispersion of silica-ceria composite fine particles (2) to obtain a dispersion of silica-ceria composite fine particles (3). Here, the silica-ceria composite particles (3) are composite particles having a silica layer on the outermost surface.

[0081] Specifically, in step 4-3, it is preferable to adjust the pH of the disintegrated dispersion of silica-ceria composite microparticles (2) obtained in the previous step to 10.0 to 11.0, maintain the liquid temperature at 80 to 90°C, and then continuously or intermittently add an acidic silicic acid solution (silica concentration 4 to 5% by mass) and an alkaline aqueous solution simultaneously, and further maintain the temperature at 80 to 90°C to prepare a dispersion of silica-ceria composite microparticles (3).

[0082] In step 4-3, the pH of the disintegrated dispersion of silica-ceria composite microparticles (2) is preferably adjusted to 10.0 to 11.0. If the pH is in this range, silica is likely to deposit on the surface of the ceria microparticles, which is preferable for forming a silica layer. If the pH is less than 10.0, silica deposition is unlikely to occur. If the pH is greater than 11.0, silica deposition is also unlikely to occur. The pH range of the disintegrated dispersion of silica-ceria composite microparticles (2) is preferably recommended to be in the range of 10.1 to 10.9. Here, the aforementioned aqueous alkaline solution can be used to adjust the pH range.

[0083] After adjusting the pH of the silica-ceria composite microparticle (2) dispersion to 10.0 to 11.0, the silica-ceria composite microparticle (2) dispersion is maintained at a liquid temperature in the range of 80 to 90°C, preferably for 30 minutes to 5 hours. Maintaining the liquid temperature in this range (80 to 90°C) is desirable because it facilitates the reaction to reach equilibrium. A liquid temperature below 80°C makes it difficult for the reaction to reach equilibrium, while a liquid temperature above 90°C is undesirable because the pH may deviate from the preferred range.

[0084] The pH of the silica-ceria composite microparticle (2) disintegrated dispersion is adjusted to 10.0 to 11.0, and the liquid temperature is maintained at 80 to 90°C. Then, an acidic silicic acid solution (silica concentration 4 to 5% by mass) and an alkaline aqueous solution are added continuously or intermittently to prepare a silica-ceria composite microparticle (3) dispersion. Simultaneous addition of the acidic silicic acid solution and the alkaline aqueous solution promotes silica deposition on the surfaces of the ceria fine particles contained in the precursor particle crushed dispersion. The pH of the alkaline aqueous solution used is preferably in the range of 10.0 to 12.0.

[0085] After the acidic silicic acid solution and the alkaline aqueous solution are simultaneously added to the disintegrated dispersion of silica-ceria composite microparticles (2), the temperature of the prepared solution is preferably maintained at 80 to 90°C for 30 minutes to 5 hours. Maintaining the solution in this temperature range (80 to 90°C) is desirable because it facilitates the reaction to reach equilibrium. A solution temperature below 80°C makes it difficult for the reaction to reach equilibrium, while a solution temperature above 90°C is undesirable because the pH may deviate from the preferred range. The silica-ceria composite fine particles (3) obtained in step 4-3 are composite fine particles having a silica layer on the outermost surface.

[0086] [Process 4A] Step 4A is a step of repeating steps 4A-1, 4A-2, and 4A-3 consecutively two or more times, where steps 4A-1, 4A-2, and 4A-3 are the same as steps 4-1, 4-2, and 4-3 in step 4, respectively. Specifically, step 4A involves repeating two or more consecutive cycles of treatment with an aqueous cerium salt solution (step 4A-1), wet crushing (step 4A-2), and treatment with an acidic silicic acid solution (and an alkaline aqueous solution) (step 4A-3) to increase the particle size while maintaining the structure of the silica-ceria composite fine particles (3) (composite fine particles having a silica layer on the outermost surface). It is recommended that steps 4A-1, 4A-2, and 4A-3 be repeated three or more times.

[0087] As described above, the details of steps 4A-1, 4A-2, and 4A-3, which are repeatedly performed in step 4A, are the same as steps 4-1, 4-2, and 4-3 in step 4, respectively. By repeatedly performing steps 4A-1, 4A-2, and 4A-3 (twice or more), silica-ceria composite microparticles having silica as the outermost layer (silica-ceria composite microparticles (X) finally obtained in step 4A) can be obtained. The silica-ceria composite microparticle dispersion finally obtained in step 4A is a dispersion of silica-ceria composite microparticles (X) having a silica layer on the outermost surface (silica-ceria composite microparticle (X) dispersion).

[0088] [Step 5] Step 5 is a step of heating and drying the silica-ceria composite fine particle (X) dispersion liquid finally obtained in step 4A, and then calcining it to obtain a silica-ceria composite fine particle powder. Specifically, step 5 is a step in which the silica-ceria composite microparticle (X) dispersion liquid finally obtained in step 4A is adjusted to a weak acidity, heated and dried, and then calcined to obtain a silica-ceria composite microparticle powder.

[0089] In step 5, it is desirable to adjust the pH of the silica-ceria composite fine particle (X) dispersion liquid finally obtained in step 4A to 5.0 to 7.0, which is preferable since the surface activity can be suppressed within this range. The method of heat drying is not particularly limited. Drying can be performed using a conventionally known dryer. Specifically, a box dryer, band dryer, spray dryer, etc. can be used. After heat drying, the firing temperature is 850 to 1100°C, preferably 910 to 1100°C, more preferably 920 to 1090°C, and most preferably 1040 to 1080°C. Firing within this temperature range allows sufficient crystallization of ceria, and firing within this temperature range also makes it difficult for cerium hydroxide and other components to remain. If this temperature is too high, abnormal growth of ceria crystals may occur, the cerium-containing silica layer may become too thick, amorphous silica may crystallize, or particles may fuse together.

[0090] [Step 6] Step 6 is a step of adding water to the silica-ceria composite fine particle powder obtained in the previous step and stirring the mixture to obtain a silica-ceria composite fine particle suspension.

[0091] Specifically, in step 6, it is preferable to add water to the silica-ceria composite fine particle powder obtained in the previous step, stir the mixture, and adjust the pH to 9.0 to 10.0 to obtain a silica-ceria composite fine particle suspension.

[0092] [Step 7] Step 7 is a step of wet-disintegrating the silica-ceria composite microparticle suspension to obtain a silica-ceria composite microparticle dispersion. In step 7, the silica-ceria composite particles are wet-disintegrated to form silica-ceria composite particles in which a plurality of ceria particles are encapsulated in silica particles, a portion of the silica is further composited with ceria, and the outermost surface is composed of a silica layer.

[0093] Specifically, in step 7, the silica-ceria composite microparticle suspension obtained in the previous step is preferably wet-disintegrated under conditions of pH 9.0 to 11.0 to obtain a silica-ceria composite microparticle dispersion. Regarding the pH condition of 9.0 to 11.0 during the disintegration of silica-ceria composite microparticle suspensions, we believe that this range results in a moderately thin silica layer on the surface of the composite microparticles, thereby improving the polishing rate and preventing the shedding of ceria microparticles. Furthermore, we believe that the silica dissolves and re-deposits during disintegration, forming a soft, easily soluble silica layer on the outermost surface. This easily soluble silica layer adheres to the substrate, improving friction and improving the polishing rate. At pH levels below 9.0, the silica layer cannot be adequately thinned, and the easily soluble silica layer is difficult to form. At pH levels above 11.0, the silica layer becomes too thin, leading to the tendency for the ceria microparticles to shedding. We recommend a pH range of 9.0 to 11.0. The crushing device for wet crushing is the same as that used in step 2.

[0094] The silica-ceria composite fine particles obtained in step 7 are composed of silica fine particles containing a plurality of ceria fine particles, with part of the silica being composited with the ceria, and the outermost layer being a silica layer.

[0095] [Example] The present invention will be described below based on examples. The present invention is not limited to these examples. Details of the measurement methods and test methods used in the examples and comparative examples will be described. Furthermore, the following measurement results and test results for each example and comparative example are shown in Table 1.

[0096] 1. Analysis of silica and ceria and calculation of mass ratio [Measurement of SiO2 and CeO2 contents] The SiO2 content in the silica-ceria composite microparticles was determined by subjecting the silica-ceria composite microparticle dispersion to ignition loss at 1000°C, determining the mass of the solids, and then measuring the Ce content by the standard addition method using an ICP plasma emission spectrometer (e.g., SII, SPS5520) described below to calculate the CeO2 mass%. The SiO2 content was determined by assuming that the solid components other than CeO2 were SiO2. The SiO2 content, CeO2 content, and parts by mass of ceria per 100 parts by mass of silica in the silica-ceria composite microparticles were calculated based on the CeO2 content and SiO2 content determined here. The solids concentration of the silica-ceria composite microparticle dispersion can also be determined here.

[0097] A method for measuring the Ce content by the standard addition method using an ICP plasma emission spectrometer (for example, SPS5520 manufactured by SII) will be described. First, approximately 1 g of a sample (adjusted to 20% solids by mass) consisting of silica-ceria composite microparticles or a silica-ceria composite microparticle dispersion is placed on a platinum dish. 3 ml of phosphoric acid, 5 ml of nitric acid, and 10 ml of hydrofluoric acid are added, and the mixture is heated on a sand bath. After drying, a small amount of water and 50 ml of nitric acid are added to dissolve the mixture, and the resulting solution is placed in a 100 ml volumetric flask. Water is then added to the resulting solution to make a 100 ml solution. Next, 10 ml of the resulting solution is aliquoted into a 20 ml volumetric flask five times, yielding five 10 ml aliquots. Ce is then measured using an ICP plasma optical emission spectrometer (e.g., SII, SPS5520) using the standard addition method. A blank is also measured in the same manner, and the measured Ce value is calculated by subtracting the blank.

[0098] 2. Confirmation of the inclusion of ceria particles in composite particles and the presence of silica on the outermost surface First, photographs or images of the silica-ceria composite fine particles contained in the dispersion were obtained at 300,000 magnifications using a transmission electron microscope, as shown in FIGS. 1 and 2. Next, a STEM-EDS analysis (JEM2100 manufactured by JEOL Ltd.) was performed on a relatively black area near the outermost surface and slightly inward from the outermost surface of one randomly selected particle in the obtained photograph or image, and a qualitative analysis was performed. If the outermost surface "contains Si and O, but does not contain Ce in principle," and the relatively black portion "contains Si, O, and Ce," the particle was determined to be "a particle containing ceria microparticles and having a silica layer on its outermost surface." This judgment was made for 50 particles randomly selected from the obtained photograph or image, and if 40 or more particles corresponded to "particles containing ceria microparticles and having a silica layer on the outermost surface," the composite microparticles contained in the dispersion were judged to be "particles containing ceria microparticles and having a silica layer on the outermost surface."

[0099] 3. Confirmation of the composite of silica and ceria The composite particles of the present invention were subjected to SEM-EDS analysis (magnification: 300,000 times), and when it was confirmed that both silica and ceria were present in one particle, it was determined that silica and ceria were composited. In the examples and comparative examples, a "JEM2100" manufactured by JEOL Ltd. was used as the STEM-EDS.

[0100] 4. Measurement of the average particle size of composite particles The average particle size of the composite microparticles of the present invention was determined by image analysis. The image analysis method is as follows: An electron microscope photograph (TEM or SEM, 100,000x magnification) of the dispersion of the present invention (solid content concentration 0.1% by mass) was prepared, and 50 particles were randomly selected from the image. The maximum diameter of the particle was taken as the major axis, and the length was measured and defined as the major axis (DL). A point was determined on the major axis that equally bisects the major axis, and two points where a line perpendicular to this intersects with the outer edge of the particle were found. The distance between these two points was measured and defined as the minor axis (DS). The geometric mean of the major axis (DL) and minor axis (DS) was then calculated and defined as the particle size of the particle. The particle sizes of the 50 particles were measured in this manner, and the arithmetic average was used as the average particle size of the composite microparticles. (In this specification, transmission electron microscope photographs are also referred to as TEM, and scanning electron microscope photographs are also referred to as SEM.)

[0101] 5. Quantification of Debris from Composite Microparticles The dispersion liquid of the present invention was adjusted to a solid content concentration of 3% by mass (2 g was ignited at 1,000°C to reduce its weight, the mass of the resulting solid was determined, and the solid content concentration was calculated). 300 g of the dispersion liquid was then filled into a 500 cc centrifuge tube and centrifuged at 24,000 G for 3 minutes (manufactured by Hitachi Koki Co., Ltd., model number "CR21G"). 100 g of the supernatant was recovered from the centrifuge tube, and the solid content was measured.

[0102] 6. X-ray diffraction method, measurement of average crystallite size The dispersions of the present invention obtained in the examples and comparative examples were dried using a conventional dryer, and the resulting powder was pulverized in a mortar for 10 minutes. An X-ray diffraction pattern was obtained using an X-ray diffractometer (RINT1400, manufactured by Rigaku Denki Co., Ltd.) to identify the crystal type. In addition, the full width at half maximum of the peak of the (111) plane (near 2θ = 28 degrees) in the obtained X-ray diffraction pattern was measured using the method described above, and the average crystallite size was calculated using the Scherrer formula described above.

[0103] 7. Measurement of the specific surface area of ​​composite particles The specific surface area (BET specific surface area) of the composite microparticles obtained in the examples and comparative examples was measured by placing a dried sample (0.2 g) in a measurement cell, degassing it in a nitrogen gas flow at 250°C for 40 minutes, and then maintaining the sample at liquid nitrogen temperature in a mixed gas flow of 30% by volume of nitrogen and 70% by volume of helium to allow equilibrium adsorption of nitrogen onto the sample. Next, the temperature of the sample was gradually raised to room temperature while the mixed gas was flowing, and the amount of desorbed nitrogen was detected during this period, and the specific surface area of ​​the sample was measured using a previously prepared calibration curve. Such a BET specific surface area measurement method (nitrogen adsorption method) can be carried out using, for example, a conventionally known surface area measurement device (for example, manufactured by Mountec Co., Ltd., product number: Mascsorb HM-1220).

[0104] 8. Redox Potential Measurement The redox potential of the composite particle dispersion was measured at 25 °C (unit: mV) using an ORP meter: NOR-6800 manufactured by Nissin and an ORP electrode: CP-101C manufactured by Nissin for the composite particle dispersion.

[0105] [Polishing test method] <Polishing of SiO2 film> A polishing abrasive grain dispersion containing the silica-ceria composite particle dispersion obtained in each of the examples and comparative examples was prepared. Here, the solid content concentration was 0.6% by mass, and nitric acid was added to adjust the pH to 5.0. Next, a substrate having a SiO2 insulating film (thickness 1 μm) formed by a thermal oxidation method was prepared as the polished substrate. Subsequently, this polished substrate was set in a polishing apparatus (NF300 manufactured by Nanofactor Co., Ltd.), and a polishing pad (IC-1000 / SUBA400 concentric circle type manufactured by Nitta Haas Co., Ltd.) was used. Polishing was performed by supplying the polishing abrasive grain dispersion at a rate of 50 ml / min for 1 minute at a substrate load of 0.5 MPa and a table rotation speed of 90 rpm, and the polishing rate was calculated by determining the weight change of the polished substrate before and after polishing.

[0106] [Surface roughness of polished substrate] The smoothness (surface roughness Ra) of the surface of the polished substrate obtained by performing the polishing test of the SiO2 film as described above was measured using an atomic force microscope (AFM, manufactured by Hitachi High-Technologies Corporation). Since the smoothness and the surface roughness are generally in a proportional relationship, the surface roughness is described in Table 1.

[0107] [Synthesis Example 1] <Preparation of acidic silicic acid solution> Pure water was added to an aqueous sodium silicate solution (silica concentration 24.06% by mass, Na2O concentration 7.97% by mass) to obtain an aqueous sodium silicate solution (silica concentration 5% by mass). 18 kg of the obtained aqueous sodium silicate solution was passed through an ion exchange column (volume 6 L, diameter: 11 cm, height: 72 cm) filled with a strongly acidic cation exchange resin (SK1BH, manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.0 h -1The solution was passed through a filter at 100°C, yielding 18 kg (silica concentration 4.5% by mass, pH 2.7). In the following Examples and Comparative Examples, unless otherwise specified, this acidic silicic acid solution or an acidic silicic acid solution equivalent to this acidic silicic acid solution was used as the raw material.

[0108] [Synthesis Example 2] <High-purification treatment of acidic silicic acid solution> 18 kg of the acidic silicic acid solution was again applied to an ion exchange column (volume 1.1 L, diameter: 6 cm, height: 44 cm) packed with a strong acid cation exchange resin SK1BH (manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.1 h -1 A high-purity acidic silicic acid solution with a silica concentration of 4.4 mass % was obtained by passing the solution through the reactor at 100°C. In the following examples and comparative examples, unless otherwise specified, this high-purity acidic silicic acid solution or a high-purity acidic silicic acid solution equivalent to this high-purity acidic silicic acid solution was used as the high-purity acidic silicic acid solution. In this specification, the term "concentration" following the term "ammonia water" refers to the ammonia concentration of the ammonia water.

[0109] [Example 1] The dispersion of the present invention was prepared by the manufacturing method described below. Step 1 (Preparation of precursor particle dispersion) Cerium nitrate (III) hexahydrate (Kanto Chemical Co., Ltd., 4N high-purity reagent) was mixed with ion-exchanged water to obtain an aqueous cerium nitrate solution (1) (CeO concentration: 3.0% by mass). (Unless otherwise specified, the term "aqueous cerium nitrate solution (1)" refers to an aqueous cerium nitrate solution with a CeO concentration of 3.0% by mass.) Next, ammonia water (concentration: 3% by mass) was added to ion-exchanged water (7,583 g) to adjust the pH to 9.1 (at 25°C), and 503 g of an aqueous cerium nitrate solution (1) (containing 15.09 g of CeO2) was added thereto over 1 hour with stirring. During the addition of the cerium nitrate aqueous solution (1), the liquid temperature was maintained at 15.5°C, and ammonia water (concentration: 3% by mass) was added as needed to maintain the pH in the range of 4.0 to 8.0. After the addition was completed, the liquid temperature was maintained at 15.5°C for 2 hours for aging. During the addition of the cerium nitrate aqueous solution (1) and during aging, air was blown into the prepared liquid (composed of the ion-exchanged water, ammonia water, and cerium nitrate aqueous solution (1) mixed in this example) to maintain the redox potential in the range of 50 to 400 mV. The resulting precursor particle dispersion had a solids concentration of 1.0% by mass, a pH of 5.5 (at 25°C), and an electrical conductivity of 140 μs / cm (at 25°C).

[0110] Step 2 (Preparation of Precursor Particle Dispersion) Next, the pH of the obtained precursor particle dispersion was adjusted to 9.2 using ammonia water (concentration: 3% by mass), and then wet-crushing was performed for 150 minutes using zirconia beads (manufactured by Nikkato Corporation) with a wet crusher (a batch-type benchtop sand mill manufactured by Kanpe Co., Ltd.). After crushing, the beads were separated to obtain 1,090 g of precursor particle crushed dispersion (solid concentration: 1.0% by mass). During crushing, ammonia water (concentration: 3% by mass) was added to maintain the pH at 9.2.

[0111] Step 3 (Preparation of silica-ceria composite microparticle (1) dispersion) To 1,010 g of the precursor particle crushed dispersion obtained above, 22 g of ion-exchanged water and 31 g of ammonia water (concentration 1.9% by mass) were added, and the mixture was stirred at room temperature for 10 minutes (pH 10.8 at the end of stirring), and then the liquid temperature was raised to 87° C. and maintained at 87° C. for 30 minutes. Next, after the temperature was raised and maintained, 5,225 g of high-purity silicic acid liquid (silica concentration 4.4% by mass) and 484 g of ammonia water (1.9% by mass) were simultaneously added over 12 hours to the precursor particle crushed dispersion. After the addition was completed, the mixture was maintained at 87° C. for another hour and then cooled to room temperature to obtain a silica-ceria composite microparticle (1) dispersion. The obtained dispersion of silica-ceria composite fine particles (1) was concentrated to a solid concentration of 12% by mass using an ultrafiltration membrane (manufactured by Asahi Kasei Corporation, SIP-1013).

[0112] Step 4 (including Step 4-1, Step 4-2, and Step 4-3) Step 4-1 (Preparation of silica-ceria composite microparticle (2) dispersion) To 3,333 g of a silica-ceria composite microparticle (1) dispersion (solids concentration: 3% by mass) obtained by diluting the silica-ceria composite microparticle (1) dispersion with ion-exchanged water, 4,000 g of a cerium nitrate aqueous solution (1) (containing 120 g of CeO) was added over 18 hours. During the addition of the cerium nitrate aqueous solution (1), the liquid temperature was maintained at 15.5°C, and ammonia water (concentration: 3% by mass) was added as needed to maintain the pH at 4.0 to 8.0. After the addition was completed, the liquid temperature was maintained at 15.5°C for 4 hours for aging. Note that during the addition of the cerium nitrate aqueous solution (1) and aging, air was blown into the mixed solution to maintain the redox potential in the range of 50 to 400 mV. Subsequently, washing was carried out by an ultrafiltration membrane while replenishing ion-exchanged water. After washing, the obtained silica-ceria composite microparticle (2) dispersion had a solids concentration of 7% by mass, a pH of 9.0 (at 25°C), and an electrical conductivity of 67 μs / cm (at 25°C).

[0113] Step 4-2 (Preparation of Dispersion of Silica-Ceria Composite Microparticles (2)) Next, 350 g of 0.25 mm quartz beads (50% loading) were added to a mill (LMZ06, manufactured by Ashizawa Finetech Co., Ltd.), which had been previously cleaned and operated with water. The silica-ceria composite microparticle (2) dispersion was then loaded into the mill's charge tank. Considering the ion-exchanged water remaining in the mill's milling chamber and piping, the concentration at the time of milling was 6% by mass. Wet crushing and grinding were performed under conditions of a disk peripheral speed of 4 m / sec and a residence time per pass of 0.43 minutes. Ammonia water (3% by mass) was added to maintain the pH of the suspension at 9.2 during crushing and grinding. In this way, a crushed silica-ceria composite microparticle (2) dispersion (5.5% by mass solids concentration) was obtained.

[0114] <Step 4-3 (Preparation of Silica-Ceria Composite Microparticle (3) Dispersion> 4,980 g of ion-exchanged water and 180 g of ammonia water (concentration: 1.9% by mass) were added to 1,080 g of the crushed dispersion of silica-ceria composite microparticles (2), and the mixture was stirred at room temperature for 10 minutes (the pH at this point was 10.8), and then the temperature was raised to 87°C and maintained for 30 minutes. To this dispersed dispersion of silica-ceria composite microparticles (2) kept at elevated temperature, 3,199 g of high-purity silicic acid liquid (silica concentration 4.4% by mass) and 296 g of aqueous ammonia (concentration 1.9% by mass) were added simultaneously over 12 hours. After the addition was completed, the mixture was further kept at 87°C for 1 hour, and then cooled to room temperature to obtain a dispersed dispersion of silica-ceria composite microparticles (3). The obtained dispersion of silica-ceria composite fine particles (3) was concentrated to a solid concentration of 12% by mass using an ultrafiltration membrane (manufactured by Asahi Kasei Corporation, SIP-1013).

[0115] Step 4A (repetition of steps 4A-1, 4A-2 and 4A-3) Step 4A-1 (first operation in Step 4A) 3,333 g of silica-ceria composite microparticles (3) (solid content concentration: 3% by mass) obtained by diluting the silica-ceria composite microparticle (3) dispersion with ion-exchanged water was added with stirring to 4,000 g of cerium nitrate aqueous solution (1) (containing 120 g of dry CeO2) over 18 hours. During this time, the liquid temperature was maintained at 15.5°C, and ammonia water (concentration: 3% by mass) was added as needed to maintain the pH at 4.0 to 8.0. After the addition was completed, the liquid temperature was maintained at 15.5°C for 4 hours for aging. During the addition of the cerium nitrate aqueous solution (1) and aging, air was blown into the prepared solution to maintain the redox potential at 50 to 400 mV. After that, washing was carried out by an ultrafiltration membrane while replenishing ion-exchanged water. After washing, the obtained dispersion of silica-ceria composite microparticles (4) had a solid content of 7% by mass, a pH of 9.1 (at 25°C), and an electrical conductivity of 75 μs / cm (at 25°C).

[0116] Step 4A-2 (first operation in Step 4A) Next, 350 g of 0.25 mm diameter quartz beads (50% loading) were added to a mill (LMZ06, manufactured by Ashizawa Finetech Co., Ltd.), which had been previously cleaned and operated with water. The silica-ceria composite microparticle (4) dispersion was then loaded into the mill's charge tank. Considering the ion-exchanged water remaining in the mill's milling chamber and piping, the concentration at the time of milling was 6% by mass. Wet crushing and grinding were performed under conditions of a disk peripheral speed of 4 m / sec and a residence time per pass of 0.43 minutes. Ammonia water (3% by mass concentration) was added to maintain the pH of the suspension at 9.2 during crushing and grinding. In this way, a crushed silica-ceria composite microparticle (4) dispersion (solids concentration: 5.5% by mass) was obtained.

[0117] Step 4A-3 (first operation in Step 4A) To 1,360 g of the silica-ceria composite microparticle (4) disintegrated dispersion, 6,286 g of ion-exchanged water and 228 g of ammonia water (concentration 1.9% by mass) were added and stirred at room temperature for 10 minutes (pH at this point was 10.8), then the temperature was raised to 87°C and maintained for 30 minutes. 1,936 g of high-purity acidic silicic acid solution (silica concentration 4.4% by mass) and 179 g of ammonia water (concentration 1.9% by mass) were simultaneously added to the silica-ceria composite microparticle (4) disintegrated dispersion over 12 hours. After the addition was completed, the mixture was maintained at 87°C for another hour and then cooled to room temperature to obtain a silica-ceria composite microparticle (5) dispersion. The obtained dispersion of silica-ceria composite fine particles (5) was concentrated to a concentration of 12% by mass using an ultrafiltration membrane (manufactured by Asahi Kasei Corporation, SIP-1013).

[0118] Step 4A-1 (Second operation in Step 4A) Next, 4,000 g of cerium nitrate aqueous solution (1) (120 g of dry CeO2) was added over 18 hours while stirring 3,333 g of a dispersion of silica-ceria composite microparticles (5) diluted with ion-exchanged water (solid content concentration: 3% by mass). During the addition of the cerium nitrate aqueous solution (1), the liquid temperature was maintained at 15.5°C, and ammonia water (concentration: 3% by mass) was added as needed to maintain the pH at 4.0 to 8.0. After the addition of the cerium nitrate aqueous solution (1) was completed, the liquid was aged by maintaining the liquid temperature at 15.5°C for 4 hours. During the addition of the cerium nitrate aqueous solution (1) and aging, air was blown into the prepared solution to maintain the redox potential at 50 to 400 mV. After that, washing was carried out by ultrafiltration while replenishment of ion-exchanged water. After washing, the obtained dispersion of silica-ceria composite microparticles (6) had a solid content of 7% by mass, a pH of 9.0 (at 25°C), and an electrical conductivity of 70 μs / cm (at 25°C).

[0119] Step 4A-2 (Second operation in Step 4A) Next, 350 g of 0.25 mm diameter quartz beads (50% loading) were added to a mill (LMZ06, manufactured by Ashizawa Finetech Co., Ltd.) that had been previously cleaned and operated with water. The silica-ceria composite microparticle (6) dispersion was then loaded into the mill's charge tank. Considering the ion-exchanged water remaining in the mill's milling chamber and piping, the concentration during milling was 6% by mass. Wet crushing and milling were performed under conditions of a disk peripheral speed of 4 m / sec and a residence time per pass of 0.43 minutes. Ammonia water (3% by mass) was added to maintain the pH of the suspension at 9.2 during crushing and milling. Thus, a crushed silica-ceria composite microparticle (6) dispersion (5.5% by mass solids concentration) was obtained.

[0120] Step 4A-3 (Second operation in Step 4A) To 1463 g of the silica-ceria composite microparticle (6) disintegrated dispersion, 6763 g of ion-exchanged water and 245 g of ammonia water (concentration 1.9% by mass) were added and stirred at room temperature for 10 minutes (pH at this point was 10.8), then the temperature was raised to 87°C and maintained for 30 minutes. Next, 1353 g of high-purity acidic silicic acid solution (silica concentration 4.4% by mass) and 125 g of ammonia water (concentration 1.9% by mass) were simultaneously added over 6 hours to the silica-ceria composite microparticle (6) disintegrated dispersion, and after the addition was completed, the mixture was maintained at 87°C for another hour and then cooled to room temperature to obtain a silica-ceria composite microparticle (7) dispersion. The obtained dispersion of silica-ceria composite fine particles (7) was concentrated to a solid concentration of 12% by mass using an ultrafiltration membrane (manufactured by Asahi Kasei Corporation, SIP-1013).

[0121] Step 4A-1 (3rd operation in Step 4A) Next, 4000 g of cerium nitrate aqueous solution (1) (containing 120 g of dry CeO2) was added over 18 hours while stirring 3333 g of a silica-ceria composite microparticle (7) dispersion (solid content concentration: 3% by mass) diluted with ion-exchanged water. During the addition of the cerium nitrate aqueous solution (1), the liquid temperature was maintained at 15.5°C, and ammonia water (concentration: 3% by mass) was added as needed to maintain the pH in the range of 4.0 to 8.0. After the addition was completed, the liquid was aged for 4 hours at a liquid temperature of 15.5°C. During the addition of the cerium nitrate aqueous solution (1) and aging, air was blown into the prepared solution to maintain the redox potential at 50 to 400 mV. After that, washing was carried out by an ultrafiltration membrane while replenishing ion-exchanged water. After washing, the obtained dispersion of silica-ceria composite microparticles (8) had a solid content of 7% by mass, a pH of 9.2 (at 25°C), and an electrical conductivity of 75 μs / cm (at 25°C).

[0122] Step 4A-2 (third operation in Step 4A) Next, 350 g of 0.25 mm diameter quartz beads (50% loading) were added to a mill (LMZ06, manufactured by Ashizawa Finetech Co., Ltd.) that had been previously cleaned and operated with water. The silica-ceria composite microparticle (8) dispersion was then loaded into the mill's charge tank. Considering the ion-exchanged water remaining in the mill's milling chamber and piping, the concentration at the time of milling was 6% by mass. Wet crushing and pulverization were performed under conditions of a disk peripheral speed of 4 m / sec and a residence time per pass of 0.43 minutes. Ammonia water (2% by mass concentration) was added to maintain the pH of the suspension at 9.2 during crushing and pulverization. In this way, a crushed silica-ceria composite microparticle (8) dispersion (solids concentration: 5.5% by mass) was obtained.

[0123] Step 4A-3 (third operation in Step 4A) To 1,529 g of the crushed dispersion of silica-ceria composite microparticles (8) obtained above, 7,067 g of ion-exchanged water and 256 g of ammonia water (concentration: 1.9% by mass) were added, and the mixture was stirred at room temperature for 10 minutes (pH at this point was 10.8), and then the temperature was raised to 87°C and maintained for 30 minutes. Subsequently, 1,043 g of high-purity acidic silicic acid solution (silica concentration 4.4% by mass) and 97 g of ammonia water (concentration 1.9% by mass) were simultaneously added to the heated and maintained silica-ceria composite microparticle (8) dispersion over 6 hours. After the addition was completed, the mixture was maintained at 87°C for another hour, and then cooled to room temperature to obtain silica-ceria composite microparticle (X) dispersion. The obtained dispersion of silica-ceria composite fine particles (X) was concentrated using an ultrafiltration membrane (manufactured by Asahi Kasei Corporation, SIP-1013) to a silica concentration of 12% by mass.

[0124] Step 5 (preparation of silica-ceria composite fine particle powder) Next, the obtained silica-ceria composite microparticle (X) dispersion was adjusted to pH 6.5 using an aqueous acetic acid solution (concentration: 3% by mass), dried in a dryer at 120°C for 15 hours, and then calcined in a muffle furnace at 1080°C for 2 hours to obtain a powder (calcined body).

[0125] Step 6 (preparation of silica-ceria composite microparticle suspension) 100 g of the powder obtained after firing and 430 g of ion-exchanged water were placed in a 1 L beaker with a handle, to which a 3% aqueous ammonia solution was added, and the mixture was irradiated with ultrasound for 10 minutes in an ultrasonic bath while stirring to obtain a suspension of silica-ceria composite microparticles (9) with a pH of 9.2 (temperature: 25°C).

[0126] Step 7 (preparation of silica-ceria composite microparticle dispersion) 575 g of 0.25 mm diameter quartz beads (85% loading) were added to a mill (LMZ06, manufactured by Ashizawa Finetech Co., Ltd.) that had been previously cleaned and operated with water. The silica-ceria composite microparticle (9) suspension was then loaded into the mill's charge tank. Taking into account the ion-exchanged water remaining in the mill's milling chamber and piping, the concentration during milling was 20% by mass. Wet crushing and milling were performed under conditions of a disk peripheral speed of 12 m / sec and a residence time per pass of 0.43 minutes. Ammonia water (3% by mass) was added to maintain the pH of the suspension at 9.2 during crushing and milling. In this way, a crushed dispersion of silica-ceria composite microparticles (9) (solids concentration: 15% by mass) was obtained.

[0127] Furthermore, the crushed dispersion of silica-ceria composite microparticles (9) was centrifuged at 1700 G for 102 seconds in a centrifugal separator (manufactured by Hitachi Koki Co., Ltd., model number "CR21G"), and the light liquid was collected to obtain a dispersion of silica-ceria composite microparticles (10).

[0128] The resulting ceria-based composite fine particle dispersion was subjected to a polishing test. The results are shown in Table 1. Furthermore, the ceria-based composite microparticles contained in the ceria-based composite microparticle dispersion obtained in Example 1 were measured by X-ray diffraction. A fairly sharp cerianite crystal pattern was observed in the X-ray diffraction pattern.

[0129] <Example 2> The same operation as in Example 1 was carried out, and the obtained silica-ceria composite microparticle (9) disintegrated dispersion (solid content concentration 15% by mass) was treated at 1700 G for 102 seconds in a centrifuge (manufactured by Hitachi Koki Co., Ltd., model number "CR21G"), and the heavy liquid was recovered and diluted to 59 g with ion-exchanged water, and then dispersed by ultrasonic irradiation to obtain silica-ceria composite microparticle dispersion (11). The resulting ceria-based composite fine particle dispersion was subjected to a polishing test. The results are shown in Table 1.

[0130] Furthermore, the ceria-based composite microparticles contained in the ceria-based composite microparticle dispersion obtained in Example 2 were measured by X-ray diffraction, and the crystal pattern of cerianite could be observed.

[0131] <Comparative Example 1> [Preparation of ceria-coated silica particle dispersion] Process (A) 12,090 g of ethanol and 6,363.9 g of ethyl orthosilicate were mixed to prepare an ethanol solution of ethyl orthosilicate. Next, 6,120 g of ultrapure water and 444.9 g of ammonia water (concentration 29% by mass) were mixed to prepare ammonia water (1). A container was charged with bed water (a mixture of 192.9 g of ultrapure water and 444.9 g of ethanol), and the bed water was adjusted to 75°C while stirring. To this was added an ethanol solution of ethyl orthosilicate and aqueous ammonia (1), each added simultaneously so that the addition would be completed within 10 hours. After the addition was completed, the liquid temperature was maintained at 75°C for 3 hours for aging, and the solids concentration was adjusted to obtain 9,646.3 g of a silica microparticle dispersion (silica sol) with an SiO2 solids concentration of 19% by mass and an average particle diameter of 60 nm as measured by laser diffraction / scattering.

[0132] Process (B) 2,733.3 g of methanol and 1,822.2 g of ethyl orthosilicate were mixed to prepare a methanol / ethanol mixed solution of ethyl orthosilicate. Next, 1,860.7 g of ultrapure water and 40.6 g of ammonia water (concentration 29% by mass) were mixed to prepare ammonia water (2). Next, bed water (a mixture of 59 g of ultrapure water and 1,208.9 g of methanol) was added to the container, and then 922.1 g of the silica fine particle dispersion obtained in step (A) was added to the container. The water containing the silica microparticle dispersion in the container was adjusted to 65°C while stirring, and then the methanol / ethanol mixed solution of ethyl orthosilicate and the ammonia water (2) were simultaneously added so that the addition was completed within 18 hours for each. After the addition was completed, the liquid temperature was maintained at 65°C for 3 hours for aging, and then the silica concentration was adjusted to 19% by mass, and 3,600 g of silica microparticle dispersion (silica concentration 19% by mass) was obtained.

[0133] To 1,053 g of this silica microparticle dispersion (average particle size of silica microparticles (dynamic light scattering method): 108 nm), 114 g of cation exchange resin (SK-1BH manufactured by Mitsubishi Chemical Corporation) was gradually added, and the mixture was stirred for 30 minutes to separate the resin. The pH at this time was 5.1. Ultrapure water was added to the obtained silica microparticle dispersion to obtain 6,000 g of silica microparticle dispersion (silica concentration 3% by mass).

[0134] Process (C) Ion-exchanged water was added to cerium (III) nitrate hexahydrate (Kanto Chemical Co., Ltd., 4N high-purity reagent) to obtain an aqueous cerium nitrate solution (CeO2 concentration: 2.5% by mass).

[0135] Process (D) A silica microparticle dispersion (silica concentration 3% by mass) (6,000 g) was heated to 15.5°C, and an aqueous cerium nitrate solution (CeO concentration 2.5% by mass) (8,453 g, equivalent to 117.4 parts by mass of CeO per 100 parts by mass of SiO) was added thereto over 18 hours while stirring. During the addition of the cerium nitrate aqueous solution, the temperature of the prepared solution (silica microparticle dispersion and cerium nitrate aqueous solution) was maintained at 15.5°C, and ammonia water (concentration 3% by mass) was added as needed to maintain the pH at 4.0 to 8.0. Furthermore, during the addition of the cerium nitrate aqueous solution and aging, air (atmospheric air) was blown into the prepared solution to maintain a positive redox potential. After the addition of the cerium nitrate aqueous solution was completed, the mixture was aged for 4 hours at a liquid temperature of 15.5°C. After aging, the mixture was left to cool indoors until it reached room temperature, after which it was washed with an ultrafiltration membrane while replenishing with ion-exchanged water to obtain a precursor particle dispersion (solid concentration 7% by mass). This precursor particle dispersion had a pH of 9.1 (25°C) and an electrical conductivity of 67 μs / cm (25°C).

[0136] Process (E) An aqueous acetic acid solution (concentration: 5% by mass) was added to the precursor particle dispersion liquid (solid content concentration: 7% by mass) obtained in step (D) to adjust the pH to 6.5, and the mixture was dried in a dryer at 100°C for 16 hours, and then calcined in a muffle furnace at 1040°C for 2 hours to obtain a powder.

[0137] Process (F) 310 g of the powder obtained in step (E) and 430 g of ion-exchanged water were placed in a 1 L beaker with a handle, and an aqueous ammonia solution (concentration: 3% by mass) was added thereto. Ultrasonic waves were irradiated for 10 minutes in an ultrasonic bath while stirring, and a powder suspension with a pH of 10 (temperature: 25°C) was obtained.

[0138] Process (G) The powder suspension obtained in step (F) was filled into the charge tank of a pulverizer (filling rate: 85%). The pulverizer used was an LMZ06 manufactured by Ashizawa Finetech Co., Ltd. The pulverizer had been cleaned and run with water beforehand, and 595 g of 0.25 mm diameter quartz beads were added to the pulverizer. The solid content concentration during pulverization was estimated to be approximately 20% by mass, taking into account the ion-exchanged water remaining in the pulverizer chamber and piping. Wet crushing and pulverization were performed under conditions of a disk peripheral speed of 12 m / sec and a residence time per pass of 0.43 minutes. Aqueous ammonia solution (concentration: 3% by mass) was added after each pass to maintain the pH of the suspension at 10 during crushing and pulverization. In this way, a ceria-coated silica microparticle dispersion (solid content concentration: 15% by mass) was obtained.

[0139] Process (H) The ceria-coated silica microparticle dispersion obtained in step (G) was centrifuged for 1 minute at a relative centrifugal acceleration of 675 G using a centrifugal separator (manufactured by Hitachi Koki Co., Ltd., model number "CR21G") to remove sedimentary components and obtain a ceria-coated silica microparticle dispersion.

[0140] <Comparative Example 2> Preparation of silica sol (average particle size 60 nm) 12,090 g of ethanol and 6,363.9 g of ethyl orthosilicate were mixed to prepare a mixed solution a1. Next, 6,120 g of ultrapure water and 444.9 g of 29% ammonia water were mixed to prepare a mixture b1, and then 192.9 g of ultrapure water and 444.9 g of ethanol were mixed to prepare a bed water. The water bed was then adjusted to 75°C while being stirred, and mixed liquid a1 and mixed liquid b1 were added simultaneously so that the addition would be completed within 10 hours for each. After the addition was completed, the liquid temperature was maintained at 75°C for 3 hours for aging, and then the solid content was adjusted to obtain 9,646.3 g of silica sol with an SiO2 solid content of 19% by mass and an average particle size of 60 nm as measured by laser diffraction / scattering.

[0141] Preparation of silica microparticle dispersion (average particle diameter of silica microparticles: 108 nm) 2,733.3 g of methanol and 1,822.2 g of ethyl orthosilicate were mixed to prepare a mixed solution a2. Next, 1,860.7 g of ultrapure water and 40.6 g of 29% ammonia water were mixed to prepare a mixed liquid b2. Next, 59 g of ultrapure water and 1,208.9 g of methanol were mixed to prepare a bed of water, and 922.1 g of a silica fine particle dispersion liquid obtained in the previous step by dispersing silica fine particles having an average particle size of 60 nm in a solvent was added. The bed water containing the silica microparticle dispersion was then adjusted to 65°C while being stirred, and mixed liquid a2 and mixed liquid b2 were simultaneously added thereto so that the addition would be completed within 18 hours for each. After the addition was completed, the liquid temperature was maintained at 65°C for 3 hours for aging, and then the solid concentration (SiO2 solid concentration) was adjusted to 19 mass% to obtain 3,600 g of a high-purity silica microparticle dispersion. The silica microparticles contained in this high-purity silica microparticle dispersion had an average particle diameter of 108 nm as measured by dynamic light scattering (PAR-III manufactured by Otsuka Electronics Co., Ltd.) The minor axis / major axis ratio of the silica microparticles was also measured based on a transmission electron microscope photograph, and was found to be 1.0. In addition, the contents of Na, Ag, Al, Ca, Cr, Cu, Fe, K, Mg, Ni, Ti, Zn, Zr, U, Th, Cl, NO3, SO4 and F were measured using atomic absorption spectrometry, ICP (inductively coupled plasma atomic emission spectrometry), potentiometric titration or ion chromatography, and all were found to be below 1 ppm.

[0142] [Table 1]

Claims

1. A silica-ceria composite microparticle dispersion comprising silica-ceria composite microparticles having the following characteristics [1] to [4], wherein the solid content concentration of the supernatant obtained by adjusting the solid content concentration to 3% by mass and then subjecting the resultant to centrifugation at 24,000 G for 3 minutes is less than 0.04% by mass. [1] The silica-ceria composite fine particles contain a plurality of ceria fine particles and have a silica layer on the outermost surface thereof. [2] In the silica-ceria composite fine particles, a part of the silica is composited with ceria. [3] The mass ratio of silica to ceria in the silica-ceria composite particles is 100:11 to 300. [4] The silica-ceria composite fine particles have an average particle diameter of 50 to 350 nm as determined by image analysis.

2. 2. A polishing abrasive dispersion comprising the silica-ceria composite fine particle dispersion according to claim 1.

3. 3. The polishing abrasive dispersion according to claim 2, which is used for planarizing a semiconductor substrate on which a silica film is formed.

4. A method for producing a silica-ceria composite fine particle dispersion, comprising the following steps 1 to 7: Step 1: A step of mixing an alkali with an aqueous solution of a cerium salt, followed by washing to obtain a precursor particle dispersion. Step 2: A step of wet-disintegrating the precursor particle dispersion under alkaline conditions to obtain a dispersion of disintegrated precursor particles containing fine ceria particles. Step 3: A step of adding an acidic silicic acid solution and an alkali to the precursor particle crushed dispersion under alkaline conditions to obtain a silica-ceria composite fine particle (1) dispersion. Step 4: A step of adding an aqueous cerium salt solution to the dispersion of the silica-ceria composite fine particles (1), washing, wet-pulverizing under alkaline conditions, and adding an acidic silicic acid solution and an alkali under alkaline conditions to obtain a dispersion. Step 4A: A step of repeating the same procedure, starting with adding the aqueous cerium salt solution to the dispersion obtained in the previous step, two or more times to obtain a dispersion of silica-ceria composite fine particles (X). Step 5: A step of heating and drying the silica-ceria composite fine particle (X) dispersion obtained in step 4A under weakly acidic conditions, followed by calcining to obtain a silica-ceria composite fine particle powder. Step 6: A step of adding water to the silica-ceria composite fine particle powder, stirring, and adjusting the alkalinity to obtain a silica-ceria composite fine particle suspension. Step 7: A step of wet-disintegrating the silica-ceria composite fine particle suspension under alkaline conditions to obtain a silica-ceria composite fine particle dispersion.

5. Step 1 is a step of preparing the precursor particle dispersion liquid by continuously or intermittently adding the cerium salt aqueous solution to an alkaline aqueous solution while stirring and mixing, and then performing washing (wherein the stirring and mixing of the cerium salt aqueous solution and the alkaline aqueous solution is performed at a liquid temperature of 5 to 30° C., a pH of 4.0 to 8.0, and an oxidation-reduction potential of 50 to 400 mV), The step 2 is a step of wet-disintegrating the precursor particle dispersion liquid under a pH condition of 9.0 to 10.0 to obtain the precursor particle dispersion liquid, The step 3 is a step of adjusting the pH of the crushed precursor particle dispersion to 10.0 to 11.0, maintaining the liquid temperature at 80 to 90°C, continuously or intermittently simultaneously adding the acidic silicic acid liquid (silica concentration: 4 to 5% by mass) and the alkaline aqueous solution, and further maintaining the temperature at 80 to 90°C to obtain the silica-ceria composite fine particle (1) dispersion, Step 4 is a step of continuously or intermittently adding the aqueous cerium salt solution to the dispersion of silica-ceria composite microparticles (1), stirring and mixing the solution while maintaining the temperature of the solution at 5 to 30°C, the pH at 4.0 to 8.0, and the oxidation-reduction potential at 50 to 400 mV, washing the solution, wet-disintegrating the solution under the alkaline conditions of pH 9.0 to 10.0, continuously or intermittently simultaneously adding the acidic silicic acid solution and the alkaline aqueous solution having a silica concentration of 4 to 5% by mass while maintaining the temperature of the solution at 80 to 90°C under alkaline conditions of pH 10.0 to 11.0, and maintaining the temperature at 80 to 90°C, thereby obtaining a dispersion; Step 4A is a step of performing the same operation as in the previous step, starting with adding the cerium salt aqueous solution again to the dispersion obtained in the previous step, two or more times to obtain a dispersion of silica-ceria composite fine particles (X), The step 5 is a step of adjusting the silica-ceria composite fine particle (X) dispersion obtained in the step 4A under weakly acidic conditions of pH 5.0 to 7.0, drying by heating, and then calcining the dispersion to obtain the silica-ceria composite fine particle powder; Step 6 is a step of adding water to the silica-ceria composite fine particle powder, stirring the mixture, and adjusting the pH to an alkaline condition of 9.0 to 10.0 to obtain the silica-ceria composite fine particle suspension; The step 7 is a step of wet-disintegrating the silica-ceria composite microparticle suspension under alkaline conditions of pH 9.0 to 11.0 to obtain the silica-ceria composite microparticle dispersion. The method for producing a silica-ceria composite fine particle dispersion according to claim 4.

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