JP7620504B2 - Ceria-based composite microparticle dispersion, its manufacturing method and polishing abrasive dispersion containing the ceria-based composite microparticle dispersion - Google Patents

Description

The present invention relates to a ceria-based composite microparticle dispersion suitable as an abrasive used in the manufacture of semiconductor devices, etc., and in particular to a ceria-based 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-based composite microparticle dispersion.

Semiconductor devices such as semiconductor substrates and wiring boards have achieved high performance by increasing the density and miniaturization. In the manufacturing process of these semiconductors, so-called chemical mechanical polishing (CMP) is applied, and specifically, it is an essential technology for shallow trench isolation, planarization of interlayer insulating films, and formation of contact plugs and Cu damascene wiring.

Generally, CMP polishing agents consist of abrasive grains and chemical components, and the chemical components play a role in promoting polishing by oxidizing or corroding the target film. On the other hand, the abrasive grains play a role in polishing by mechanical action, and colloidal silica, fumed silica, and ceria particles are used as abrasive grains. Ceria particles in particular have a uniquely high polishing speed for silicon oxide films, and are therefore used in polishing in the shallow trench isolation process.
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 that of the silicon nitride film is low, and the polishing rate ratio (selectivity) is also important.

Conventionally, the method of polishing such members 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.

For example, Patent Document 1 describes a method for producing ultrafine cerium oxide particles (average particle size 10-80 nm) made of single crystals of cerium oxide, which is characterized by mixing and stirring an aqueous solution of cerous nitrate and a base in a ratio such that the pH is 5-10, followed by rapid heating to 70-100°C and aging at that temperature. It further describes that this production method can provide ultrafine cerium oxide particles with high uniformity in particle size and shape.

Non-Patent Document 1 also discloses a method for producing ceria-coated silica that includes a manufacturing process similar to the manufacturing process for cerium oxide ultrafine particles described in Patent Document 1. This method for producing ceria-coated silica does not include the firing-dispersion process included in the manufacturing process described in Patent Document 1.

In addition, Patent Document 2 describes a silica-based composite particle characterized in that the surface of an amorphous silica particle A has a crystalline oxide layer B containing one or more elements selected from zirconium, titanium, iron, manganese, zinc, cerium, yttrium, calcium, magnesium, fluorine, lanthanum, and strontium. In addition, as a preferred embodiment, the surface of an amorphous silica particle A has an amorphous oxide layer C containing an element such as aluminum, which is different from the amorphous silica layer, and further has a crystalline oxide layer B thereon containing one or more elements selected from zirconium, titanium, iron, manganese, zinc, cerium, yttrium, calcium, magnesium, fluorine, lanthanum, and strontium. It is described that such silica-based composite particles can improve the polishing speed because they have a crystalline oxide layer B on the surface of the amorphous silica particles A, and that by pretreating the silica particles, sintering of the particles during firing can be suppressed and dispersibility in the polishing slurry can be improved, and that since they do not contain cerium oxide or the amount of cerium oxide used can be significantly reduced, an inexpensive abrasive with high polishing performance can be provided. It is also described that those having an amorphous oxide layer C between the silica-based particles A and the oxide layer B are particularly excellent in the effect of suppressing sintering of the particles and the effect of improving the polishing speed.

Furthermore, Patent Document 3 describes a silica-based composite microparticle dispersion liquid containing silica-based composite microparticles having an average particle size of 50 to 350 nm and the following characteristics [1] to [3], in which child particles mainly made of crystalline ceria are present on the surface of mother particles mainly made of amorphous silica, and the surfaces of the child particles are further coated with silica. [1] The silica-based composite microparticles have a mass ratio of silica to ceria of 100:11 to 316. [2] When the silica-based composite microparticles are subjected to X-ray diffraction, only the crystalline phase of ceria is detected. [3] The silica-based composite microparticles have a crystallite size of the (111) plane of the crystalline ceria of 10 to 25 nm, as measured by X-ray diffraction. The article also states that such silica-based composite microparticles can polish silica films, Si wafers, and other difficult-to-process materials at high speeds, while achieving high surface precision (low scratches, low surface roughness (Ra) of the substrate being polished, etc.), and that because they do not contain impurities, they can provide a silica-based composite microparticle dispersion that can be preferably used for polishing the surfaces of semiconductor devices such as semiconductor substrates and wiring substrates.

Patent No. 2,746,861 JP 2013-119131 A International Publication No. 2016/159167

Seung-Ho Lee, Zhenyu Lu, S. V. Babu and Egon Matijevic, "Chemical mechanical polishing of thermal oxide films using silica particles coated with ceria", Journal of Materials Research, Volume 17, Issue 10, 2002, pp2744-2749

However, when the present inventors actually produced and examined the cerium oxide ultrafine particles described in Patent Document 1, it was found that the polishing rate was low and that the particles were prone to cause defects on the surface of the polishing substrate (deterioration of surface accuracy, increase in scratches, and residue of abrasive on the surface of the polishing substrate).
The inventors presume that the main reason for this is that, compared to methods for producing ceria particles that include a calcination step (calcination increases the crystallinity of the ceria particles), the method for producing cerium oxide ultrafine particles described in Patent Document 1 does not include a calcination step and simply crystallizes cerium oxide particles from a liquid phase (an aqueous solution containing cerous nitrate), so that the crystallinity of the cerium oxide particles produced is relatively low; and because no calcination process is performed, the cerium oxide does not adhere to the base particles, and so the cerium oxide remains on the surface of the polishing substrate.

In addition, since the ceria-coated silica described in Non-Patent Document 1 is not fired, the actual polishing speed is thought to be low, and since it is not bonded and integrated with the silica particles, it easily falls off, resulting in a decrease in the polishing speed, a lack of polishing stability, and there is also concern that particles may remain on the surface of the polishing substrate.

Furthermore, the present inventors have found that when polishing is performed using silica-based composite particles having an oxide layer C described in Patent Document 2, impurities such as aluminum may remain on the surface of the semiconductor device, adversely affecting the semiconductor device.
Furthermore, the ceria particles described in these documents are attached to the base particles, but are not strongly fixed and therefore tend to fall off from the base particles.
Furthermore, when polishing is performed using an abrasive having crystalline ceria particles formed on spherical silica base particles as described in Patent Document 2, the removal rate of the silica film is high due to the chemical reaction that occurs simultaneously with the mechanical action of the ceria particles during polishing. However, under high pressure conditions, the ceria crystals may fall off, wear down, or collapse, reducing the contact area between the substrate and the ceria, which may result in a slow removal rate.

The silica-based composite microparticle dispersion described in Patent Document 3 is capable of exhibiting excellent polishing performance (polishing speed, high surface accuracy, etc.) in polishing applications, but with the further increase in density and integration of semiconductor devices, there is a demand for abrasive dispersions that exhibit even better polishing performance for semiconductor substrates.

The present invention aims to solve the above problems. That is, the present invention aims to provide a ceria-based composite microparticle dispersion that can polish even silica films, Si wafers, and difficult-to-process materials at high speeds and that, if it does not contain impurities, can be preferably used to polish the surfaces of semiconductor devices such as semiconductor substrates and wiring substrates, a method for producing the same, and a polishing abrasive dispersion that contains the ceria-based composite microparticle dispersion.

The present inventors have conducted extensive research to solve the above problems and have completed the present invention.
The present invention relates to the following (1) to (10).
(1) A ceria-based composite microparticle dispersion comprising ceria-based composite microparticles having the following characteristics [1] to [3]:
[1] The ceria-based composite microparticles have a mother particle, a cerium-containing silica layer on the surface of the mother particle, and child particles dispersed inside the cerium-containing silica layer, the mother particle being mainly composed of amorphous silica, and the child particles being mainly composed of crystalline ceria.
[2] The ceria-based composite fine particles satisfy the following requirements:
1) On the electron microscope photograph, there is a circle inscribed with the image of the ceria-based composite fine particle, and further, the image of the ceria-based composite fine particle has the following relationship with respect to an arch-shaped figure X consisting of an arc on the circumference of the circle and a chord:
(I) At least partially inscribed in the chord of the arcuate figure X.
(II) It is inscribed in a point D on the arc that bisects the entire length of the arc of the arch-shaped figure X, and is at least partially inscribed in a circular curve on one side of the arc and a circular curve on the opposite side of the arc with the point D as the center.
2) The area of the arch shape X is 1.0 to 1.5 times the area of the image of the ceria-based composite fine particle, the length of the chord is 80 nm or more, and the height of the arrow is 40 nm or more.
[3] The ceria-based composite fine particles have an average particle size of 50 to 350 nm as determined by an image analysis method.
(2) The ceria-based composite microparticle dispersion according to (1) above, wherein the ceria-based composite microparticles are inscribed in at least 20% of the chord of the arch shape X in an electron micrograph.
(3) The ceria-based composite microparticle dispersion according to (1) or (2) above, wherein, in an electron microscope photograph, the ceria-based composite microparticles are at least partially inscribed in two arcuate curves extending along the arc for a length of w/6 (w: total length of the arc) on both sides of a point D on the arc that bisects the total length of the arc, and are also at least partially inscribed in two arcuate curves connecting to both ends of the arcuate curve.
(4) The ceria-based composite microparticle dispersion according to any one of (1) to (3) above, further comprising ceria-based composite microparticles having the following characteristic [4]:
[4] The ceria-based composite fine particles have a coefficient of variation of particle size distribution of child particles in the range of 15 to 50%.
(5) The ceria-based composite microparticle dispersion according to any one of (1) to (4) above, wherein the proportion of the ceria-based composite microparticles to all particles in an electron micrograph is 5 to 20%.
(6) A polishing abrasive dispersion containing the ceria-based composite fine particle dispersion according to (1) or (2) above.
(7) The polishing abrasive dispersion according to (6) above, which is used for planarizing a semiconductor substrate having a silica film formed thereon.
(8) A method for producing a ceria-based composite microparticle dispersion, comprising the steps of: (1) preparing a ceria-based composite microparticle dispersion comprising:
Step 1: A step of stirring a silica-based fine particle dispersion liquid in which silica fine particles satisfying the following conditions 1), 2) and 3) are dispersed in a solvent, and continuously or intermittently adding a metal salt of cerium thereto while maintaining the temperature at 0 to 20°C, the pH at 5.0 to 9.0, and the oxidation-reduction potential at 50 to 500 mV, to obtain a precursor particle dispersion liquid containing precursor particles.
1) On the electron microscope photograph, there is a circle inscribed with the image of the silica fine particles, and further, the image of the silica fine particles has the following relationship with respect to an arch-shaped figure Y consisting of an arc on the circumference of the circle and a chord:
(I) At least partially inscribed in the chord of the arcuate shape Y.
(II) It is inscribed in a point D on the arc that bisects the entire length of the arc of the arch-shaped figure Y, and is at least partially inscribed in a circular curve on one side of the arc and a circular curve on the opposite side of the arc with the point D as the center.
2) The area of the arch shape Y is 1.0 to 1.5 times the area of the image of the silica fine particles, the length of the chord is 80 nm or more, and the height of the arrow is 40 nm or more.
3) The silica fine particles have an average particle size of 50 to 350 nm as determined by image analysis.
Step 2: drying the precursor particle dispersion liquid, calcining the precursor particle dispersion liquid at 850 to 1,100° C., adding a solvent to the calcined product, and subjecting the resulting product to a wet-type disintegration treatment at a pH range of 8.6 to 10.8 to obtain the ceria-based composite microparticle dispersion liquid.
(9) The method for producing a ceria-based composite microparticle dispersion according to (8) above, wherein the step 2 is a step of adding the solvent to the sintered body, subjecting the sintered body to a wet disintegration treatment at a pH range of 8.6 to 10.8, subjecting the sintered body to a centrifugation treatment at a relative centrifugal acceleration of 300 G or more, and then removing sedimentary components to obtain the ceria-based composite microparticle dispersion.
(10) The method for producing a ceria-based composite microparticle dispersion according to (8) or (9) above, wherein the step 1 comprises adjusting a pH of a dispersion containing spherical silica particles to a range of 9.5 to 10.5, and wet-disintegrating the dispersion to obtain the silica microparticles.

When the abrasive dispersion containing the ceria-based composite microparticles of the present invention is used, the target object can be polished at high speed. When the ceria-based composite microparticle dispersion of the present invention is used as an abrasive dispersion for polishing a material difficult to process, such as a silica film or a Si wafer, the target object can be polished at high speed compared to the case of using a conventional abrasive dispersion (e.g., abrasive dispersion containing abrasive particles made of spherical silica particles). The reason for this is not clear, but the inventor presumes that the ceria-based composite microparticles of the present invention have a part of their surface that is flat, and therefore act as a sliding friction against the polished surface. When sliding friction acts on the polished surface in this way, it is considered that the polishing speed is improved compared to the abrasive particles that act by rolling friction.
The method for producing a ceria-based composite microparticle dispersion of the present invention provides a method for efficiently producing a ceria-based composite microparticle dispersion exhibiting such excellent performance.
In the method for producing a ceria-based composite microparticle dispersion of the present invention, it is possible to significantly reduce impurities contained in the ceria-based composite microparticles and achieve high purity.
The highly purified ceria-based composite microparticle dispersion obtained by the preferred embodiment of the method for producing a ceria-based composite microparticle dispersion of the present invention does not contain impurities, and therefore can be particularly preferably used for polishing the surfaces of semiconductor devices such as semiconductor substrates and wiring substrates.
Furthermore, when used as an abrasive dispersion for polishing, the ceria-based composite fine particle dispersion of the present invention is effective for planarizing the surface of a semiconductor device, and is particularly suitable for polishing a substrate on which a silica insulating film is formed.

Photographs and figures for explaining the shape of the composite fine particles of the present invention. 1 is a schematic cross-sectional view of a composite fine particle of the present invention. FIG. 3( a ) is an SEM image (100,000 times magnification) of the silica-based fine particles used in Example 1, and FIG. 3( b ) is a TEM image (100,000 times magnification). 1 is a SEM image (100,000 times) of the ceria-based composite fine particles obtained in Example 1. 1 is an X-ray diffraction pattern of the ceria-based composite fine particles obtained in Example 1. FIG. 6( a ) is an SEM image (100,000 times magnification) of the ceria-based composite fine particles obtained in Comparative Example 1, and FIG. 6( b ) is a TEM image (100,000 times magnification).

The present invention will now be described.
The present invention provides a ceria-based composite microparticle dispersion containing ceria-based composite microparticles having the following characteristics [1] to [3].
[1] The ceria-based composite microparticles have a mother particle, a cerium-containing silica layer on the surface of the mother particle, and child particles dispersed inside the cerium-containing silica layer, the mother particle being mainly composed of amorphous silica, and the child particles being mainly composed of crystalline ceria.
[2] The ceria-based composite fine particles satisfy the following requirements:
1) On the electron microscope photograph, there is a circle inscribed with the image of the ceria-based composite fine particle, and further, the image of the ceria-based composite fine particle has the following relationship with respect to an arch-shaped figure X consisting of an arc on the circumference of the circle and a chord:
(I) At least partially inscribed in the chord of the arcuate figure X.
(II) It is inscribed in a point D on the arc that bisects the entire length of the arc of the arch-shaped figure X, and is at least partially inscribed in a circular curve on one side of the arc and a circular curve on the opposite side of the arc with the point D as the center.
2) The area of the arch shape X is 1.0 to 1.5 times the area of the image of the ceria-based composite fine particle, the length of the chord is 80 nm or more, and the height of the arrow is 40 nm or more.
[3] The ceria-based composite fine particles have an average particle size of 50 to 350 nm as determined by an image analysis method.
Such a ceria-based composite fine particle dispersion is hereinafter also referred to as "the dispersion of the present invention."
Moreover, the ceria-based composite fine particles having the above characteristics [1] to [3] are hereinafter also referred to as "composite fine particles of the present invention."

The present invention also provides a method for producing a ceria-based composite fine particle dispersion, which is characterized by including the following steps 1 and 2, and by which the dispersion of the present invention can be obtained.
Step 1: A step of stirring a silica-based fine particle dispersion liquid in which silica fine particles satisfying the following conditions 1), 2) and 3) are dispersed in a solvent, and continuously or intermittently adding a metal salt of cerium thereto while maintaining the temperature at 0 to 20°C, the pH at 5.0 to 9.0, and the oxidation-reduction potential at 50 to 500 mV, to obtain a precursor particle dispersion liquid containing precursor particles.
1) On the electron microscope photograph, there is a circle inscribed with the image of the silica fine particles, and further, the image of the silica fine particles has the following relationship with respect to an arch-shaped figure Y consisting of an arc on the circumference of the circle and a chord:
(I) At least partially inscribed in the chord of the arcuate shape Y.
(II) It is inscribed in a point D on the arc that bisects the entire length of the arc of the arch-shaped figure Y, and is at least partially inscribed in a circular curve on one side of the arc and a circular curve on the opposite side of the arc with the point D as the center.
2) The area of the arch shape Y is 1.0 to 1.5 times the area of the image of the silica fine particles, the length of the chord is 80 nm or more, and the height of the arrow is 40 nm or more.
3) The silica fine particles have an average particle size of 50 to 350 nm as determined by image analysis.
Step 2: drying the precursor particle dispersion, calcining the precursor particle dispersion at 850 to 1,100° C., adding a solvent to the calcined product, and subjecting the resulting product to a wet-type disintegration treatment at a pH range of 8.6 to 10.8 to obtain the ceria-based composite microparticle dispersion.
Such a production method will be hereinafter referred to as the "production method of the present invention."

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

Hereinafter, when simply referring to "the present invention," this refers to the dispersion liquid of the present invention, the composite microparticles of the present invention, and the manufacturing method of the present invention.

In this specification, the expression "image of ceria-based composite fine particles" means "electron microscope photograph of ceria-based composite fine particles" unless otherwise specified.
Electron micrographs refer to scanning electron micrographs (images) or transmission electron micrographs (images). Note that scanning electron micrographs (images) may be abbreviated as "SEM" and transmission electron micrographs (images) as "TEM."
Similarly, the expressions "image of silica-based fine particles" or "image of silica fine particles" respectively mean "electron microscope photograph of silica-based fine particles" or "electron microscope photograph of silica fine particles".
In addition, unless otherwise specified, the expression "ceria-based composite microparticles in their electron microscope photograph" means "in an electron microscope photograph of ceria-based composite microparticles." Similarly, the expression "silica-based microparticles in their electron microscope photograph" means "in an electron microscope photograph of silica-based microparticles," and the expression "silica microparticles in their electron microscope photograph" means "in an electron microscope photograph of silica microparticles."

<Composite fine particles of the present invention>
The composite fine particles of the present invention are characterized by having a pseudo-defective spherical structure, as will be described later.
The shape of the composite fine particles of the present invention will be described with reference to FIG.
Fig. 1(a) is an SEM image of the composite microparticle of the present invention magnified 100,000 times. Fig. 1(a) also shows a line for specifying an arched figure X inscribed in the composite microparticle of the present invention. Fig. 1(b) shows the arched figure X specified by Fig. 1(a).
(a) 1: Composite particle 5: Chord 3: Circle (b) 7: Arc 9: Arrow height D: Equal division point of arc 7 10: Arc-shaped figure X
L1: Starting point of arc 7 L2: End point of arc 7 S: A point on arc 7 located on the L1 side of equal division point D, equivalent to 1/6 of the total length (w) of arc 7 T: A point on arc 7 located on the L2 side of equal division point D, equivalent to 1/6 of the total length (w) of arc 7 S-T: A circular curve on arc 7 connecting point S and point T

In this specification, all or part of the arc that constitutes the portion of the arch shape other than the chord 5 (from the starting point L1 to the ending point L2) may be referred to as an "arc curve."

1A, a method for identifying an arched figure X will be described. Note that an arched figure Y is also identified by a similar method.
First, an electron microscope photograph (SEM image in the case of FIG. 1) of the composite fine particle 1 of the present invention magnified 100,000 times is prepared.
Then, for one composite particle on the image, a circle 3 is determined in which as much of the periphery of the composite particle as possible is inscribed. Next, a chord 5 is determined in which as much of the periphery of the image of the composite particle as possible is inscribed in the circle 3. By determining the circle 3 and the chord 5, an arch-shaped figure consisting of the chord 5 and an arc 7 is specified.

The specification of the arcuate figure X in the present invention will be described with reference to FIG.
Using the method shown in FIG. 1(a), the circle 3 inscribed in the image of the composite particle 1 and its chord 5 are determined.
The two intersections of the chord 5 and the circle 3 are defined as the start point L1 and the end point L2, respectively, and the curve connecting the start point L1 and the end point L2 on the circumference is defined as the arc 7. Here, an arch-shaped figure consisting of the chord 5 and the arc 7 is specified.
Such an arch-shaped figure is selected such that, in the relationship between the image of the composite microparticle 1 and the arch-shaped figure, the image of the composite microparticle 1 is inscribed in a dividing point D that divides the arc 7 equally, and is at least partially inscribed in both a circular curve (D-L1) extending from the dividing point D in the direction of the starting point L1 of the arc 7 and a circular curve (D-L2) extending from the dividing point D in the direction of the end point L2 of the arc 7, and the length of the arrow height 9 of the arch-shaped figure consisting of the arc 7 and the chord 5, and the area of the arch-shaped figure (referred to as area S _x ) are determined.
When the length of the chord 5 is 80 nm or more, the length of the arrow height 9 is 40 nm or more, and the area _S of the arched figure is 1.0 to 1.5 times (area _S /area _S ) the area of the image of the composite microparticle 1 of the present invention (area _S ), the arched figure formed by the arc 7 and the chord 5 is called arched figure X.
When such an arched figure X is specified, the image of the corresponding composite particle is taken as the image of the composite particle 1 of the present invention.

In this application, the shape of the composite microparticle 1 of the present invention may be referred to as "pseudo-defective" and such particles may be referred to as "pseudo-defective particles" or "pseudo-defective particles." In other words, composite microparticles that can specify the arch-shaped figure X are called pseudo-defective particles. In geometry, a three-dimensional structure obtained by cutting a sphere with one face is sometimes called a "defective".

The composite microparticles of the present invention are those in which the arch-shaped figure X can be identified in an electron microscope photograph, and the image of the composite microparticle and the straight line portion inscribed by the chord 5 substantially correspond to the planar structure of the composite microparticles of the present invention. Such a planar structure is sometimes referred to as "planar structure F."
The composite fine particles of the present invention have such a pseudo-spherical structure, and when used as abrasive grains for polishing, in particular, the sliding friction effect is likely to be exerted, which is believed to contribute to an improvement in the polishing rate.

Here, the method for measuring the area S ₀ of the image of the composite fine particle 1 of the present invention on the electron microscope photograph is not particularly limited. For example, it can be measured using a conventionally known image processing device.

The area S _x of the arch-shaped figure X is 1.0 to 1.5 times the area S ₀ of the image of the composite microparticle 1 of the present invention which is a pseudo-spherical particulate, and this value (area S _x /area S ₀ ) is preferably 1.0 to 1.3, and more preferably 1.0 to 1.1.
The area S _X of the arch-shaped figure X is in the range of 1.0 to 1.5 times the area S ₀ of the image of the composite microparticle 1 of the present invention which is pseudo-spherical, and which satisfies other requirements (range of chord length, range of arrow height length, range of average particle size of the composite microparticle, and the requirements for inscription in the above (I) and (II)), when used as an abrasive grain for polishing, sliding friction easily occurs between the composite microparticle and the substrate to be polished, and this can contribute to an improvement in the polishing rate.

The average particle size of the ceria-based composite fine particles of the present invention measured by image analysis is preferably 50 to 350 nm. When the dispersion of the present invention is used as an abrasive, the occurrence of scratches during polishing is reduced. If the average particle size is less than 50 nm, the particle size is small and the polishing rate may not reach a practical level.
Furthermore, if the average particle size exceeds 350 nm, this may result in a decrease in the surface accuracy of the substrate to be polished.
The average particle size of the composite microparticles of the present invention is measured by the following image analysis method. An electron microscope photograph (transmission electron microscope photograph) of the composite microparticles of the present invention enlarged by 100,000 times is prepared, and for any 50 particles on the image, the maximum diameter of the particle is taken as the major axis, and the length is measured and the value is taken as the major axis (DL). A point is also determined on the major axis that divides the major axis into two equal parts, and two points where a straight line perpendicular to the major axis intersects with the outer edge of the particle are found, and the distance between the two points is measured and taken as the minor axis (DS). Then, the geometric mean value of the major axis (DL) and the minor axis (DS) is calculated and taken as the particle size of the particle.
In this manner, the particle sizes of 50 particles are measured, and the value obtained by simple averaging is regarded as the average particle size.

The arrow height 9 in the arched figure X corresponding to the composite microparticle 1 of the present invention is the distance between the chord 5 on a straight line that passes through the center of the circle 3 and is perpendicular to the chord 5 and the arc 7. Note that the value of the arrow height is necessarily determined to be unique for each arched figure.
The arrow height 9 is preferably 40 nm or more in the arch shape X. The composite fine particles of the present invention which are inscribed in an arch shape having an arrow height of 40 nm or more in an electron micrograph have a sufficient thickness as an abrasive grain, are not easily broken, and are suitable for polishing by sliding friction.
In the case of composite fine particles that inscribe an arch shape with an arrow height of less than 40 nm on an electron micrograph, the composite fine particles may not be thick enough to function as abrasive grains.
More preferably, the composite microparticles of the present invention are inscribed in an arch shape having an arrow height of 50 nm or more on an electron micrograph. The upper limit of the arrow height is about 300 nm, which corresponds to the average particle size range of the composite microparticles of the present invention (50 to 350 nm).

A chord 5 of an arched figure X corresponding to the composite microparticle 1 of the present invention is a line segment with the shortest distance connecting a starting point L1 and an ending point L2 of the circular arc curve of the arched figure X.
The length of the chord 5 in the arched figure X corresponding to the composite fine particle 1 of the present invention is 80 nm or more. The length of the inscribed area of the image of the composite fine particle 1 of the present invention with the chord 5 is preferably 90 nm or more.
Incidentally, the upper limit of the chord is about 430 nm, which corresponds to the average particle size range (50 to 350 nm) of the composite fine particles of the present invention.

To improve the polishing speed, friction caused by contact between the particles and the substrate is important. Dynamic friction can be classified into rolling friction and sliding friction, with sliding friction generally generating a greater frictional force than rolling friction. The ceria-based composite microparticles of the present invention have a pseudo-spherical structure with at least one planar structure, and when used as polishing abrasive grains, the sliding friction effect is more likely to work, which is presumably responsible for improving the polishing speed more than when spherical particles are used as polishing abrasive grains.

The composite microparticles of the present invention include the pseudo-spherical particles described above.
In the composite microparticles of the present invention, an electron microscope photograph of the composite microparticles 1 of the present invention magnified 100,000 times is prepared by the above-mentioned method, and it is judged whether or not all particles in the image correspond to pseudo-defective spheroidal particles in the above-mentioned manner. Then, the number ratio of the pseudo-defective spheroidal particles is calculated. In such composite microparticles of the present invention, it is preferable that 5% or more of the particles are pseudo-defective spheroidal particles in terms of number ratio, and this ratio is more preferably 7% or more. Moreover, the number ratio may be 20% or less.

As described above, the composite fine particles of the present invention, which are an aggregate of a plurality of particles, mainly contain pseudo-spherical particles, but may also contain particles of other shapes.
The image of the composite fine particle of the present invention is at least partially inscribed in the chord of the arcuate figure X, and desirably inscribed in at least 20% of the chord of the arcuate figure X. This proportion is preferably 50% or more, more preferably 75% or more, and most preferably 100%.
It is presumed that the higher the ratio of the image of the composite fine particle of the present invention to the inscribed chord, the wider the area of the planar structure F, and the easier it is to exert the effect of sliding friction.

The image of the composite microparticle of the present invention is inscribed in the point D on the arc that bisects the entire length of the arc 7, and is at least partially inscribed in the arc curve (D-L1) on one side of the arc and the arc curve (D-L2) on the other side of the arc with the point D as the center. More preferably, the image of the composite microparticle of the present invention is at least partially inscribed in the arc curve ST that extends over a length of (w)/6 (w: total length of the arc) on both sides of the point D on the arc that bisects the entire length of the arc 7, and is at least partially inscribed in the two arc curves (S-L1, T-L1) that connect to both ends of the arc curve ST.

Next, the structure of the composite fine particles of the present invention will be described with reference to FIG.
2(a) and 2(b) are schematic diagrams illustrating cross sections of composite microparticles of the present invention, in which (a) shows a type in which some of the child particles are exposed to the outside, and (b) shows a buried type in which none of the child particles are exposed to the outside.
As shown in Fig. 2, a composite microparticle 20 of the present invention has a mother particle 10, a cerium-containing silica layer 12 on the surface of the mother particle 10, and a child particle 14 dispersed inside the cerium-containing silica layer 12. The black triangles in Fig. 2 are examples of measurement points X to Z at which the STEM-EDS analysis described later is performed.

The present inventors speculate as follows about the mechanism by which the cerium-containing silica layer is formed in the composite microparticles of the present invention and the mechanism by which child particles are dispersed and present inside the cerium-containing silica layer.

In the schematic diagram of Figure 2, the mother particle 10, the cerium-containing silica layer 12, and the child particle 14 are clearly distinguished from each other for ease of understanding, but in reality, the composite microparticles of the present invention are integrated together, and it is difficult to clearly distinguish between the mother particle 10, the cerium-containing silica layer 12, and the child particle 14 except by contrast in STEM/SEM images or EDS analysis. However, if STEM-EDS analysis is performed on a cross section of the composite microparticles of the present invention and the elemental concentrations of Ce and Si are measured, it can be confirmed that the structure shown in Figure 2 is present.

That is, when EDS analysis is performed by selectively irradiating an electron beam to a location specified by a scanning transmission electron microscope (STEM) and the elemental concentrations of Ce and Si at measurement point X on the cross section of the composite microparticle of the present invention shown in FIG. 2 are measured, the ratio (percentage) of the Ce molar concentration to the sum of the Ce molar concentration and the Si molar concentration (Ce/(Ce+Si)×100) is less than 3%. When the elemental concentrations of Ce and Si are measured at measurement point Z, the ratio (percentage) of the Ce molar concentration to the sum of the Ce molar concentration and the Si molar concentration (Ce/(Ce+Si)×100) is more than 50%. When the elemental concentrations of Ce and Si are measured at measurement point Y, the ratio (percentage) of the Ce molar concentration to the sum of the Ce molar concentration and the Si molar concentration (Ce/(Ce+Si)×100) is 3 to 50%.
Therefore, in an elemental map obtained by performing STEM-EDS analysis, the mother particle 10 and the cerium-containing silica layer 12 in the composite microparticle of the present invention can be distinguished by a line where the ratio (percentage) of the Ce molar concentration to the sum of the Ce molar concentration and the Si molar concentration (Ce/(Ce+Si)×100) is 3%. Also, in an elemental map obtained by performing STEM-EDS analysis, the cerium-containing silica layer 12 and the child particle 14 in the composite microparticle of the present invention can be distinguished by a line where the ratio (percentage) of the Ce molar concentration to the sum of the Ce molar concentration and the Si molar concentration (Ce/(Ce+Si)×100) is 50%.

In this specification, STEM-EDS analysis is performed at 800,000x magnification.

The composite microparticles of the present invention have the form shown in Figure 2, and when a cross section of the microparticles is subjected to STEM-EDS analysis and elemental mapping, it is often found that there is at least one layer with a relatively high ceria concentration (a layer made of ceria microparticles) on the way from the outermost shell to the central mother particle (mainly composed of amorphous silica).

<Mother particle>
The mother particles in the composite fine particles of the present invention will now be described.
As described above, when STEM-EDS analysis is performed on the composite microparticles of the present invention and the element concentrations of Ce and Si are measured in the cross section of the composite microparticles of the present invention shown in Figure 2, the mother particle is the portion where the ratio (percentage) of the Ce molar concentration to the sum of the Ce molar concentration and the Si molar concentration (Ce/(Ce+Si) x 100) is less than 3%.

The average particle size of the base particles in the composite fine particles of the present invention is preferably 50 to 350 nm, and more preferably 60 to 300 nm.
When the dispersion of the present invention is used as an abrasive, the occurrence of scratches during polishing is reduced. When the average particle size of the base particles is less than 50 nm, the average particle size of the composite fine particles obtained by using such base particles is unlikely to reach 50 nm, and when the dispersion of such composite fine particles is used as an abrasive, the polishing rate may not reach a practical level.
Furthermore, when the average particle diameter of the base particles exceeds 350 nm, the average particle diameter of the composite microparticles obtained using such base particles often exceeds 350 nm. If a dispersion of such composite microparticles is used as an abrasive, the polishing rate may not reach a practical standard, and this may result in a decrease in the surface accuracy of the substrate to be polished.
It is more preferable that the base particles exhibit monodispersity.

The average particle size of the base particles in the composite fine particles of the present invention is measured as follows.
An electron microscope photograph of the base particle of the composite microparticle of the present invention magnified 100,000 times is prepared, and for all particles in the image, the maximum diameter of the base particle is taken as the major axis, and the length is measured and this value is taken as the major axis (DL). A point is determined on the major axis that divides the major axis in half, and two points where a straight line perpendicular to this intersects with the outer edge of the particle are found, and the distance between these two points is measured and taken as the minor axis (DS). The geometric mean value of the major axis (DL) and minor axis (DS) is then calculated and taken as the particle diameter of the base particle.
In this manner, the particle sizes of 50 base particles are measured, and the value obtained by simple averaging is regarded as the average particle size.

The shape of the base particles in the composite fine particles of the present invention is mainly a pseudo-spherical trapezoidal particle.
Specifically, the base particle is identified by observing at 800,000 times magnification using STEM-EDS analysis and identifying the line where the ratio (percentage) of Ce molar concentration to the sum of Ce molar concentration and Si molar concentration (Ce/(Ce+Si)×100) is 3%, and then it can be determined whether or not the base particle is pseudo-trapezoidal by the same method as in the case of determining whether or not the shape of the composite microparticle of the present invention described above is pseudo-trapezoidal.

The base particles are mainly composed of amorphous silica, and are usually silica microparticles or silica-based microparticles. These are preferred because they are easy to prepare with a spherical shape and a uniform particle size, and can also be prepared with a variety of particle sizes.

The fact that the base particles are mainly composed of amorphous silica can be confirmed, for example, by the following method. After drying the dispersion liquid containing the composite fine particles of the present invention, the dispersion liquid is pulverized using a mortar, and an X-ray diffraction pattern is obtained using, for example, a conventionally known X-ray diffraction device (for example, RINT1400 manufactured by Rigaku Denki Co., Ltd.). No peaks of crystalline silica such as Cristobalite appear. From this, it can be confirmed that the silica contained in the base particles is amorphous. In addition, in such a case, the base particles are considered to be mainly composed of amorphous silica.
In addition, the dispersion of the present invention is dried, embedded in resin, and then sputter-coated with Pt, and a cross-sectional sample is prepared using a conventionally known focused ion beam (FIB) device. For example, when the prepared cross-sectional sample is subjected to fast Fourier transform (FFT) analysis using a conventionally known TEM device to obtain an FFT pattern, no diffraction pattern of crystalline silica such as Cristobalite appears. From this, it can be confirmed that the silica contained in the base particles is amorphous. In addition, in such a case, the base particles are mainly composed of amorphous silica.
Another method is to use a conventionally known TEM device to observe the presence or absence of lattice fringes due to the atomic arrangement of the base particles on a cross-sectional sample prepared in a similar manner. If the material is crystalline, lattice fringes according to the crystal structure are observed, and if the material is amorphous, lattice fringes are not observed. From this, it can be confirmed that the silica contained in the base particles is amorphous. In such a case, the base particles are considered to be mainly composed of amorphous silica.

The base particles are mainly composed of amorphous silica and may contain other elements such as La, Ce, and Zr in an amount of 10 mass % or less, and may also contain crystalline silica and impurity elements.
For example, it is desirable that the content of each of the elements Na, Ag, Al, Ca, Cr, Cu, Fe, K, Mg, Ni, Ti, Zn and Zr (hereinafter sometimes referred to as "specific impurity group 1") in the base particles is 5000 ppm or less.
The content of each of the elements U, Th, Cl, NO ₃ , SO ₄ and F (hereinafter sometimes referred to as “specific impurity group 2”) in the base particles is preferably 5 ppm or less.

Here, the content of specific impurities group 1 or specific impurities group 2 in the base particles, the composite fine particles of the present invention described below, and the silica fine particles described below means the content relative to the dry amount.
The content relative to the dry amount means the ratio (percentage) of the weight of the measurement object (specific impurity group 1 or specific impurity group 2) to the mass of the solid content contained in the object (parent particle, composite microparticle of the present invention, or silica microparticle described later). Note that the impurity content of the parent particle is roughly the same as the impurity content of the silica microparticle if there is no contamination due to contamination, etc.

<Child Particle>
In the composite fine particles of the present invention, child particles mainly composed of crystalline ceria (hereinafter also referred to as "ceria child particles") are dispersed in the cerium-containing silica layer disposed on the mother particle.

In the cerium-containing silica layer, the ceria particles may be laminated, and the shape of the particles may be spherical, elliptical, rectangular, or the like, but is not limited thereto. Furthermore, the particle size distribution may be uniform or sharp.
Some of the ceria subparticles are embedded in the cerium-containing silica layer, while others are partially exposed from the cerium-containing silica layer.

As described above, when STEM-EDS analysis is performed on the composite microparticles of the present invention and the elemental concentrations of Ce and Si are measured in the cross section of the composite microparticles of the present invention shown in Figure 2, the child particles are those portions where the ratio (percentage) of the Ce molar concentration to the sum of the Ce molar concentration and the Si molar concentration (Ce/(Ce+Si) x 100) exceeds 50%.

The child particles mainly composed of crystalline ceria in the present invention are dispersed in a cerium-containing silica layer arranged on the mother particle, and the coefficient of variation (CV value) in the particle size distribution of the child particles is preferably 15 to 50%. In other words, it is preferable that the width of the particle size distribution of the child particles is large. When the dispersion of the present invention containing ceria child particles with such a large particle size distribution width is used as an abrasive dispersion for polishing, the child particles with large particle sizes come into contact with the substrate to be polished in the early stages of polishing to perform polishing. Even if the child particles are dislodged or worn or broken due to the polishing pressure, the child particles with small particle sizes will next come into contact with the substrate to be polished, so the contact area can be maintained high. As a result, polishing is performed efficiently and at a stable polishing rate.

In the present invention, the coefficient of variation (CV value) in the particle size distribution of the child particles dispersed in the cerium-containing silica layer is preferably 15 to 50%, more preferably 16 to 35%, and even more preferably 18 to 30%.

The average particle size of the child particles is preferably from 10 to 25 nm, and more preferably from 14 to 23 nm.
When the average particle size of the child particles exceeds 25 nm, the precursor particles having such ceria child particles tend to be sintered or coagulated after firing in step 2, making it difficult to disintegrate them. Furthermore, when such a ceria-based composite microparticle dispersion is used for polishing purposes, it is not preferable because it causes scratches on the object to be polished. When the average particle size of the child particles is less than 10 nm, it tends to be difficult to obtain a polishing rate that is practically sufficient when used for polishing purposes.

Here, the particle size distribution of the child particles is measured as follows.
First, the child particles are identified by observing at 800,000 times magnification using STEM-EDS analysis, and a line is identified where the ratio (percentage) of the Ce molar concentration to the sum of the Ce molar concentration and the Si molar concentration (Ce/(Ce+Si)×100) is 50%. Next, the maximum diameter of the child particle is taken as the major axis, and its length is measured and this value is taken as the major axis (DL). A point is also determined on the major axis that divides the major axis in half, and two points where a straight line perpendicular to this intersects with the outer edge of the particle are found, and the distance between these two points is measured and taken as the minor axis (DS). The geometric average value of the major axis (DL) and minor axis (DS) is then calculated, and this is taken as the particle diameter of the child particle.
In this manner, the particle sizes of 100 or more child particles can be measured to obtain a particle size distribution.

The coefficient of variation (CV value) in the particle size distribution of the child particles is calculated by obtaining the standard deviation and the number average value using the particle size distribution obtained as described above as the population, dividing the standard deviation by the number average value, and multiplying by 100 (i.e., standard deviation/number average value x 100).

The child particles may be stacked in the cerium-containing silica layer, i.e., a plurality of child particles may be present inside the cerium-containing silica layer on radial lines from the center of the mother particle.
Furthermore, the child particles may be embedded in the cerium-containing silica layer or may be partially exposed to the outside of the cerium-containing silica layer. However, when the child particles are embedded in the cerium-containing silica layer, the surface of the ceria-based composite fine particle is closer to the silica surface, improving the storage stability and polishing stability and further reducing the amount of abrasive grains remaining on the substrate after polishing. Therefore, it is preferable that the child particles are embedded in the cerium-containing silica layer.

The shape of the child particles is not particularly limited. For example, they may be spherical, elliptical, or rectangular. When the dispersion of the present invention is used for polishing purposes and a high polishing rate is to be obtained, the child particles are preferably non-spherical, and more preferably rectangular.

The child particles dispersed within the cerium-containing silica layer disposed on the surface of the mother particle may be in a monodisperse state, may be in a layered state (i.e., multiple child particles are stacked in the thickness direction of the cerium-containing silica layer), or may be in a linked state.

In the present invention, the child particles are mainly composed of crystalline ceria.
The fact that the child particles are mainly composed of crystalline ceria can be confirmed, for example, by drying the dispersion of the present invention, grinding the obtained solid matter using a mortar, etc. 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 diffraction device (e.g., RINT1400, manufactured by Rigaku Corporation), and only the crystalline phase of ceria is detected in the obtained X-ray diffraction pattern. In such a case, 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 Ceriaite, etc.

The child particles are mainly composed of crystalline ceria (crystalline Ce oxide), and may contain other elements, for example, elements other than cerium, and may 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.

The average crystallite diameter of the ceria particles is calculated using the full width at half maximum of the maximum peak that appears 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 is 0.86 to 0.34°), and preferably 14 to 23 nm (full width at half maximum is 0.62 to 0.37°). In many cases, the peak intensity of the (111) plane is the greatest, but the peak intensity of another crystal plane, for example the (100) plane, may be the greatest. In that case, the calculation can be performed in the same way, and the size of the average crystallite diameter in that case may be the same as the average crystallite diameter of the (111) plane described above.

The method for measuring the average crystallite size of the child particles will be described below using the (111) plane (2θ=approximately 28 degrees) as an example.
First, the composite fine particles of the present invention are pulverized using 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/β cos θ
D: average crystallite diameter (angstroms)
K: Scherrer constant (K=0.94 in the present invention)
λ: X-ray wavelength (1.5419 angstroms, Cu lamp)
β: full width at half maximum (rad)
θ: reflection angle

The composite fine particles of the present invention preferably have silicon atoms in solid solution in the crystalline ceria, which is the main component of the child particles. In general, a solid solution means that two or more elements (metallic or non-metallic) are dissolved together to form a uniform solid phase, and the solid solutions obtained by solid solution are classified into substitutional solid solutions and interstitial solid solutions. Substitutional solid solutions can easily occur in atoms with similar atomic radii, but since the atomic radii of Ce and Si are significantly different, it is considered that at least substitutional solid solutions are difficult to occur. In addition, in the crystal structure of Cerianit, the coordination number of Ce from the Ce center is 8, but for example, when Si is substituted for Ce in a 1:1 ratio, the coordination number of Ce should be 7. However, in the analysis results of a preferred embodiment of the composite fine particles of the present invention, the average coordination number of Ce from the Ce center is 8.0, and the average coordination number of Si is 1.2, so it is estimated that the preferred embodiment of the composite fine particles of the present invention is an interstitial type. Moreover, from the analysis results of the preferred embodiment of the composite fine particles of the present invention, the interstitial solid solution is presumed to be a preferred embodiment of the composite fine particles of the present invention, since the interatomic distance of Ce-Si is smaller than the interatomic distance of Ce-Ce. That is, it is preferable that the cerium atom and silicon atom contained in the child particle satisfy the relationship R ₁ < R ₂ , where R ₁ is the cerium-silicon atomic distance and R ₂ is the cerium-cerium atomic distance.

It has been known that the use of ceria particles as abrasive grains to polish silica-coated substrates or glass substrates shows a specifically high polishing rate compared to the use of other inorganic oxide particles. One of the reasons that ceria particles show a particularly high polishing rate for silica-coated substrates is that the trivalent cerium contained in the ceria particles has a high chemical reactivity with the silica coating on the substrate being polished.

In the preferred embodiment of the composite microparticles of the present invention, in the child particles (ceria microparticles) present on the outer surface side, Si atoms are considered to be interstitially dissolved in _CeO2 crystals. It is presumed that the solid solution of Si atoms causes crystal distortion of _CeO2 crystals, which increases oxygen defects even when fired at high temperatures, resulting in a large amount of trivalent cerium that is chemically active against _SiO2 , and thus promoting the chemical reactivity of _CeO2 , resulting in the above-mentioned high polishing rate. In addition, La, Zr, etc. may be doped to increase the trivalent cerium content.

<Cerium-containing silica layer>
The composite fine particles of the present invention have a cerium-containing silica layer on the surface of the mother particle, and the child particles are dispersed inside the cerium-containing silica layer.

This structure makes it difficult for child particles to fall off due to the crushing process during manufacturing or the pressure during polishing, and even if some child particles are chipped off, most of the child particles remain in the cerium-containing silica layer without falling off, so the polishing function is not reduced.

As described above, when STEM-EDS analysis is performed on the composite microparticles of the present invention and the elemental concentrations of Ce and Si are measured in the cross section of the composite microparticles of the present invention, the cerium-containing silica layer is the portion where the ratio (percentage) of the Ce molar concentration to the sum of the Ce molar concentration and the Si molar concentration (Ce/(Ce+Si)×100) is 3 to 50%.

In an image (TEM image) obtained by observing the composite microparticles of the present invention using a transmission electron microscope, the images of the child particles appear dark on the surface of the mother particle, but part of the cerium-containing silica layer also appears as a relatively faint image around and outside the child particles, i.e., on the surface side of the composite microparticles of the present invention.
When this portion is subjected to STEM-EDS analysis to determine the Si molar concentration and Ce molar concentration of the portion, it can be confirmed that the Si molar concentration is very high. Specifically, the ratio (percentage) of the Ce molar concentration to the sum of the Ce molar concentration and the Si molar concentration (Ce/(Ce+Si)×100) is 3 to 50%.

The average thickness of the cerium-containing silica layer is not particularly limited, but is preferably 10 to 40 nm, more preferably 12 to 30 nm, and may be in a portion where the cerium-containing silica layer is not present, as described later.
The average thickness of the cerium-containing silica layer is determined by drawing straight lines at any 12 points from the center to the outermost shell of the composite microparticle of the present invention, measuring the distance between the line where the ratio (percentage) of the Ce molar concentration to the sum of the Ce molar concentration and the Si molar concentration (Ce/(Ce+Si)×100) is 3%, which is specified from the element map obtained by performing the STEM-EDS analysis as described above, and the outermost shell of the composite microparticle of the present invention (the distance on the line passing through the center of the mother particle), and taking a simple average of these distances. Note that the center of the mother particle means the intersection point of the major axis and the minor axis described above.

The cerium-containing silica layer in the composite microparticles of the present invention is considered to promote the bonding force between the child particles (ceria microparticles mainly composed of crystalline ceria) dispersed and grown in the cerium-containing silica layer during the firing process and the mother particles. Therefore, for example, in the process of obtaining the dispersion of the present invention, the calcined crushed dispersion obtained by firing is pre-crushed in a dry manner if necessary, then crushed in a wet manner, and further centrifuged as necessary to obtain a ceria-based composite microparticle dispersion, and the cerium-containing silica layer is considered to have the effect of preventing the child particles from coming off the mother particles. In this case, there is no problem with the localized falling off of the child particles, and it is not necessary that the entire surface of the child particles is covered with a part of the cerium-containing silica layer. It is sufficient that the child particles are strong enough not to come off the mother particles during the crushing process.
Due to this structure, it is believed that when the dispersion of the present invention is used as an abrasive, the removal rate is high and deterioration of surface accuracy and scratches are reduced.

In addition, in the composite microparticles of the present invention, at least a portion of the surface of the child particles is covered with a cerium-containing silica layer, so that -OH groups of silica are present on the outermost surface (outermost shell) of the composite microparticles of the present invention. Therefore, when used as an abrasive, the composite microparticles of the present invention repel each other due to the charge of the -OH groups on the polishing substrate surface, and as a result, it is believed that they adhere less to the polishing substrate surface.

In addition, ceria generally has a different potential from silica, polishing substrates, and polishing pads, and as the pH goes from alkaline to near neutral, the negative zeta potential decreases, and in the weak acid region, it has a positive potential. Therefore, at an acidic pH during polishing, ceria adheres to the polishing substrate or polishing pad due to differences in the magnitude of the potential or differences in polarity, and is likely to remain on the polishing substrate or polishing pad. On the other hand, since the composite microparticles of the present invention have silica in the outermost shell as described above, their potential becomes negatively charged due to silica, and therefore they maintain a negative potential from an alkaline to an acidic pH, and as a result, abrasive grains are less likely to remain on the polishing substrate or polishing pad. If the disintegration treatment in step 2 of the manufacturing method of the present invention is performed while maintaining a pH of 8.6 to 10.8, part of the silica (silica in the cerium-containing silica layer) on the surface of the composite microparticles of the present invention is dissolved. If the dispersion of the present invention manufactured under such conditions is adjusted to a pH of <7 when applied to polishing applications, the dissolved silica will deposit on the composite microparticles (abrasive grains) of the present invention, and the surface of the composite microparticles of the present invention will have a negative potential. If the potential is low, silicic acid may be added to adequately reinforce the cerium-containing silica layer.

Other properties of the composite fine particles of the present invention will now be described.
In the composite fine particles of the present invention, the ceria-based composite fine particles typically have a mass ratio of silica to ceria of 100:11-316.

In the composite microparticles of the present invention, the mass ratio of silica (SiO ₂ ) to ceria (CeO ₂ ) is not limited as long as the composite microparticles are used as polishing abrasive grains and exhibit useful polishing speed and surface precision, but is typically 100:11 to 316, preferably 100:30 to 316, more preferably 100:30 to 230, more preferably 100:30 to 150, more preferably 100:60 to 316, and even more preferably 100:60 to 230.
The mass ratio of silica to ceria is generally considered to be the same as the mass ratio of mother particles to child particles. If the amount of child particles relative to the mother particles is too small, the mother particles or composite fine particles may bond to each other, resulting in the generation of coarse particles. In this case, the polishing agent (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. In addition, if the amount of ceria relative to silica is too large, not only will the cost become expensive, 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), scratches will increase, and free ceria will remain on the substrate, and it will also be likely to cause problems such as adhesion to wastewater piping of the polishing device.

The silica to be considered when calculating the mass ratio of silica ( _SiO2 ) to ceria ( _CeO2 ) refers to all silica ( _SiO2 ) contained in the composite microparticles of the present invention, and therefore refers to the total amount of silica components constituting the mother particles, silica components contained in the cerium-containing silica layer disposed on the surface of the mother particles, and silica components that may be contained in the child particles.

The content (mass %) of silica (SiO ₂ ) and ceria (CeO ₂ ) in the composite fine particles of the present invention is determined by first determining the solids concentration of the dispersion of the present invention by subjecting it to ignition loss at 1000° C. and then weighing it.
Next, the content (mass%) of cerium (Ce) contained in a predetermined amount of the composite microparticle of the present invention is determined by ICP plasma emission spectrometry and converted into oxide mass% ( _CeO2 mass% etc.). Then, the components other than _CeO2 constituting the composite microparticle of the present invention are considered to be _SiO2 , and the _SiO2 mass% can be calculated.
In the production method of the present invention, the mass ratio of silica to ceria can also be calculated from the amounts of the silica source material and the ceria source material used when preparing the dispersion of the present invention. This is applicable when the process is not one in which ceria or silica is dissolved and removed, and in such a case, the amounts of ceria or silica used and the analytical values show good agreement.

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 conversion. The number of coarse particles is preferably 100 million particles/cc or less, and more preferably 80 million particles/cc or less. Coarse particles of 0.51 μm or more can cause polishing scratches and can also cause the surface roughness of the polished substrate to deteriorate.

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 is taken and injected into a conventionally known coarse particle number measuring device. The number of coarse particles of 0.51 μm or more is then determined. This measurement is carried out three times to obtain a simple average value, which is then multiplied by 1000 to obtain the number of coarse particles of 0.51 μm or more.

The composite fine particles of the present invention preferably have a specific surface area of 9 to 60 m ² /g, more preferably 10 to 43 m ² /g, although there are no particular limitations thereon.

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 flow at 250° C. for 40 minutes, and then the sample is kept at liquid nitrogen temperature in a mixed gas flow of 30% by volume of nitrogen and 70% by volume of helium to allow the nitrogen to be adsorbed in equilibrium on the sample. Next, the temperature of the sample is gradually raised to room temperature while the mixed gas is being passed through, and the amount of nitrogen desorbed during this period is detected, and the specific surface area of the sample is measured using a calibration curve created in advance.
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 in this manner, unless otherwise specified.

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.
In addition, 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 of the elements in 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 spectrometry 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 chromatography

<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 above-mentioned composite fine particles of the present invention are dispersed in a dispersion solvent.

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 at least one additive selected from the group consisting of a polishing accelerator, a surfactant, a pH adjuster, and a pH buffer as an additive for controlling the polishing performance.

As the dispersion solvent for the dispersion liquid of the present invention, for example, alcohols such as methanol and ethanol; amides such as acetone and 2-butanone; ethers such as diethyl ether and isopropyl ether; glycol ethers such as 2-methoxyethanol and 2-ethoxyethanol; glycol ether acetates such as 2-methoxyethyl acetate and 2-ethoxyethyl acetate; esters such as methyl acetate and ethyl acetate; aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane and heptane; 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 can be used. These may be mixed with water.

The solids concentration in the dispersion of the present invention is preferably in the range of 0.3 to 50% by mass.

<Production Method of the Present Invention>
The manufacturing method of the present invention will now be described.
The manufacturing method of the present invention includes steps 1 and 2 described below.

<Step 1>
In step 1, a silica-based fine particle dispersion liquid in which silica fine particles are dispersed in a solvent is prepared.
In this specification, "Step 1" may also be referred to as "mixing step."

The silica-based fine particle dispersion liquid used as a raw material in step 1 is a silica-based fine particle dispersion liquid in which silica fine particles satisfying the following conditions 1), 2) and 3) are dispersed in a solvent.
1) On the electron microscope photograph, there is a circle inscribed with the image of the silica fine particles, and further, the image of the silica fine particles has the following relationship with respect to an arch-shaped figure Y consisting of an arc on the circumference of the circle and a chord:
(I) At least partially inscribed in the chord of the arcuate shape Y.
(II) It is inscribed in a point D on the arc that bisects the entire length of the arc of the arch-shaped figure Y, and is at least partially inscribed in a circular curve on one side of the arc and a circular curve on the opposite side of the arc with the point D as the center.
2) The area of the arch shape Y is 1.0 to 1.5 times the area of the image of the silica fine particles, the length of the chord is 80 nm or more, and the height of the arrow is 40 nm or more.
3) The silica fine particles have an average particle diameter of 50 to 350 nm as determined by image analysis.

Here, the arched figure Y is defined in the same manner as the arched figure X. The preferred range of the area of the arched figure Y relative to the area of the image of the silica fine particles is also the same as in the case of the arched figure X. Furthermore, the preferred ranges of the chord length and arrow height of the arched figure Y are also the same as in the case of the arched figure X.
Furthermore, the average particle size of the silica fine particles is a value obtained by measuring using the same method as the average particle size of the composite fine particles of the present invention described above.

The silica-based microparticle dispersion liquid used as the raw material may contain pseudo-spherical silica microparticles as well as other silica microparticles. The proportion of pseudo-spherical silica microparticles is not particularly limited, but it is usually desirable for the number ratio to be 5 to 20% by mass.

A silica-based microparticle dispersion liquid containing pseudo-spherical silica microparticles can be obtained, for example, by subjecting a silica-based microparticle dispersion liquid containing known spherical silica microparticles to a wet crushing process at a pH range of 9.5 to 10.5.

The silica fine particles in the silica-based fine particle dispersion used as a raw material in step 1 can be silica fine particles having an average particle size equivalent to that of the ceria-based composite fine particles in the ceria-based composite fine particle dispersion obtained by the manufacturing method of the present invention, but are not particularly limited as long as the composite fine particles of the present invention having the desired average particle size can be obtained.

When preparing the dispersion of the present invention for use in the polishing of semiconductor devices and the like by the manufacturing method of the present invention, it is preferable to use the silica-based microparticle dispersion in which the silica microparticles produced by hydrolysis of alkoxysilane are dispersed in a solvent as the silica-based microparticle dispersion.In addition, when using other conventionally known silica-based microparticle dispersions (such as the silica-based microparticle dispersions prepared from water glass as raw material) as raw material, it is preferable to use the silica-based microparticle dispersion after acid treatment and further deionization treatment.In this case, the content of Na, Ag, Al, Ca, Cr, Cu, Fe, K, Mg, Ni, Ti, Zn, U, Th, Cl, NO ₃ , SO ₄ and F contained in silica microparticles is reduced, specifically, it can be 100 ppm or less.
Specifically, the silica fine particles in the silica-based fine particle dispersion liquid, which is the raw material, preferably satisfy the following conditions (a) and (b).
(a) The content of Na, Ag, Al, Ca, Cr, Cu, Fe, K, Mg, Ni, Ti and Zn is each 100 ppm or less.
(b) The contents of U, Th, Cl, _NO3 , _SO4 and F are each 5 ppm or less.
The method for measuring the content of each of the components (a) and (b) that may be contained in the silica microparticles may be the same as the method for measuring the content of each element in specific impurity group 1 and specific impurity group 2 that may be contained in the composite microparticles of the present invention.

In addition, silica fine particles having a suitable reactivity with cerium (dissolved weight of silica fine particles per weight of ceria) are preferably used. In the preparation step of step 1 in the manufacturing method of the present invention, a metal salt of cerium is added to the silica-based fine particle dispersion, so that part of the silica is dissolved by cerium hydroxide or the like, the size of the silica fine particles is reduced, and a precursor of a cerium-containing silica layer containing microcrystals of cerium is formed on the surface of the dissolved silica fine particles. In this case, if the silica fine particles are made of amorphous silica that is highly reactive with cerium, the precursor of the cerium-containing silica layer becomes thick, and the cerium-containing silica layer formed by firing becomes thick or the silica ratio of the layer becomes excessively high, making it difficult to disintegrate in the disintegration step. In addition, if the silica fine particles are made of amorphous silica that is extremely low in reactivity with cerium, the cerium-containing silica layer is not sufficiently formed, and the ceria child particles are easily dropped off. If the reactivity with cerium is appropriate, the dissolution of excess silica is suppressed, the cerium-containing silica layer has a moderate thickness, which prevents the child particles from falling off, and its strength is thought to be greater than the strength between the composite fine particles, making it easier to crush, which is desirable.

In step 1, a silica-based microparticle dispersion liquid in which silica microparticles are dispersed in a solvent is stirred, and while maintaining the temperature at 0 to 20°C, the pH range at 5.0 to 9.0, and the redox potential at 50 to 500 mV, a metal salt of cerium is added continuously or intermittently to neutralize the metal salt of cerium, thereby obtaining a precursor particle dispersion liquid containing precursor particles.

The dispersion medium in the silica-based microparticle dispersion preferably contains water, and it is preferable to use an aqueous silica-based microparticle dispersion (aqueous sol).

The solid content in the silica-based fine particle dispersion is preferably 1 to 40% by mass in terms of SiO _2. If the solid content is too low, the silica concentration in the production process will be low, which may result in poor productivity.

In the manufacturing method of the present invention, for example, when the reaction temperature between the silica fine particles and the metal salt of cerium in step 1 is set to 40 to 50°C, the reactivity between ceria and silica increases, and the dissolution of the silica fine particles progresses. As a result, the particle diameter of the _CeO2 ultrafine particles in the precursor particles obtained by drying at the intermediate stage of step 2 is less than 2.5 nm. This indicates that when silica reacts with ceria in the liquid phase in such a high temperature range, silica inhibits the particle growth of ceria, and the average particle diameter of ceria after drying becomes small, less than 2.5 nm.
In addition, even with such precursor particles, it is possible to make the average crystallite diameter of the ceria child particles 10 nm or more by setting the firing temperature to more than 1100 ° C., but in this case, a silica coating is formed without forming a cerium-containing silica layer, and this silica coating tends to strongly coat the ceria child particles, which is problematic in that it becomes difficult to disintegrate. Therefore, by keeping the reaction temperature at 0 to 20 ° C. and appropriately suppressing the reaction of silica and ceria in the liquid phase, the average crystallite diameter of the CeO ₂ ultrafine particles in the precursor particles after drying can be made 2.5 nm or more, and the particles become easy to disintegrate. Furthermore, since the average crystallite diameter after drying is large, the firing temperature for making the average crystallite diameter of the ceria child particles 10 nm or more can be lowered, and the thickness of the cerium-containing silica layer formed by firing does not become excessively thick, making it easy to disintegrate.

Impurities can be extracted using a cation exchange resin or anion exchange resin, or a mineral acid, organic acid, etc., and the silica-based microparticle dispersion liquid can be deionized as necessary using an ultrafiltration membrane, etc. Silica-based microparticle dispersion liquid from which impurity ions have been removed by deionization treatment is more preferable because it is easier to form hydroxides containing silicon on the surface. However, deionization treatments are not limited to these.

In the production method of the present invention, for example, if the oxidation-reduction potential during the reaction between the silica fine particles and the metal salt of cerium in step 1 is low, rod-shaped crystals are generated and are difficult to deposit on the silica fine particles.
Furthermore, if the redox potential is not adjusted to a predetermined range, the _CeO2 ultrafine particles produced in the blending process tend not to crystallize easily, and the crystallization of uncrystallized _CeO2 ultrafine particles is not promoted even by heating and aging after blending. Therefore, in order to crystallize to a predetermined size in the firing process in step 2, firing at a high temperature is required, making it difficult to disintegrate.

The type of metal salt of cerium is not limited, but cerium chloride, nitrate, sulfate, acetate, carbonate, metal alkoxide, etc. can be used. Specific examples include cerium (I) nitrate, cerium carbonate, cerium (I) sulfate, and cerium (I) chloride. Among them, trivalent cerium salts such as cerium (I) nitrate, cerium (I) chloride, and cerium carbonate are preferred. This is because crystalline cerium oxide and cerium hydroxide are generated from the solution that becomes supersaturated at the same time as neutralization, and these are rapidly coagulated and deposited on silica fine particles, and finally _CeO2 ultrafine particles are formed in a monodisperse state. Furthermore, trivalent cerium salts react moderately with silica fine particles, and a cerium-containing silica layer is easily formed. In addition, trivalent cerium, which is highly reactive with the silica film formed on the polishing substrate, is easily formed in the ceria crystals, so it is preferred. However, sulfate ions, chloride ions, nitrate ions, etc. contained in these metal salts are corrosive. Therefore, if desired, it is necessary to remove them to 5 ppm or less by washing in a post-process after preparation. On the other hand, carbonates are preferably used because they are released as carbon dioxide gas during preparation, and alkoxides are decomposed to form alcohols.

The amount of cerium metal salt added to the silica-based microparticle dispersion is preferably an amount such that the mass ratio of silica to ceria in the resulting ceria-based composite microparticles is in the range of 100:11 to 316, as in the case of the composite microparticles of the present invention described above.

Before or after adding the metal salt of cerium to the silica-based microparticle dispersion, the temperature during stirring is preferably 0 to 20°C, more preferably 3 to 20°C, and even more preferably 3 to 18°C. If the temperature is too low, the reactivity of ceria with silica decreases, and the solubility of silica decreases significantly, so that the crystallization of ceria is not controlled. As a result, coarse crystalline oxide of ceria is generated, and abnormal growth of _CeO2 ultrafine particles occurs on the surface of the silica microparticles, making them difficult to disintegrate after firing, and the amount of silica dissolved by the cerium compound decreases, so that the amount of silica supplied to the cerium-containing silica layer decreases. This is thought to result in a shortage of silica that serves as a binder between the silica mother particle and the ceria child particle (shortage of silica laminated on the mother particle), making it difficult to fix the ceria child particle to the silica mother particle. On the other hand, if the temperature is too high, the solubility of silica increases significantly, and it is considered that the generation of crystalline ceria oxide is suppressed, but the high temperature required during firing promotes the bonding between particles, which may make it impossible to disintegrate, and further, scale is likely to occur on the reactor wall, which is undesirable. In addition, it is preferable that the silica fine particles are not easily dissolved in cerium compounds (neutralized products of cerium salts). In the case of silica fine particles that are easily dissolved, the crystal growth of ceria is suppressed by silica, and the particle size of the _CeO2 ultrafine particles at the preparation stage is less than 2.5 nm.
If the particle size of the _CeO2 ultrafine particles in the preparation stage is less than 2.5 nm, the firing temperature must be increased to make the ceria particle size after firing 10 nm or more, in which case the cerium-containing silica layer tightly covers the base particles, which may make crushing difficult. The solubility of easily soluble silica fine particles can be suppressed by drying them at 100°C or higher before being used as a raw material.
In step 1, by adding the metal salt of cerium to the silica-based microparticle dispersion and then stirring at a temperature of 0 to 20°C, it is possible to obtain the dispersion of the present invention containing the composite microparticles of the present invention in which the coefficient of variation in the particle size distribution of the child particles is a suitable value.

In addition, after adding the metal salt of cerium to the silica-based fine particle dispersion, the stirring time is preferably 0.5 to 50 hours, more preferably 0.5 to 35 hours. If this time is too short, the _CeO2 ultrafine particles aggregate, making it difficult to react with silica on the surface of the silica fine particles, and it is undesirable in that composite fine particles that are difficult to disintegrate tend to be formed. On the other hand, if this time is too long, the formation of the _CeO2 ultrafine particle-containing layer does not proceed further in the reaction, making it uneconomical. After adding the cerium metal salt, it may be aged at 0 to 80°C as desired. This is because aging has the effect of promoting the reaction of the cerium compound and at the same time, adhering the free _CeO2 ultrafine particles that are not attached to the silica fine particles to the silica fine particles.

In addition, before or after adding the metal salt of cerium to the silica-based microparticle dispersion, the pH range of the silica-based microparticle dispersion during stirring is 5.0 to 9.0, preferably 7.6 to 9.0. At this time, it is preferable to adjust the pH by adding an alkali or the like. Examples of such alkali include known alkalis. Specific examples include, but are not limited to, aqueous ammonia solutions, alkali hydroxides, alkaline earth metals, and aqueous solutions of amines.

In addition, before or after adding the metal salt of cerium to the silica-based microparticle dispersion, the oxidation-reduction potential of the microparticle dispersion during stirring is adjusted to 50 to 500 mV. The oxidation-reduction potential is preferably 100 to 300 mV. This is because when trivalent cerium metal salt is used as a raw material, the acid-reduction potential of the microparticle dispersion decreases during preparation. In addition, by keeping the oxidation-reduction potential within this range, the crystallization of the generated CeO ₂ ultrafine particles is promoted. When the oxidation-reduction potential is 50 mV or less or negative, the cerium compound may not be deposited on the surface of the silica microparticles, and plate-shaped or rod-shaped ceria particles or composite ceria particles may be generated. Furthermore, the reactivity of cerium hydroxide, etc. with the silica microparticles decreases, and the CeO ₂ ultrafine particle-containing layer is not formed, and even if it is formed, the proportion of silica in the CeO ₂ ultrafine particle layer is extremely low. Therefore, after firing, a cerium-containing silica layer containing ceria child particles therein is not formed, and the ceria child particles tend to be exposed and disposed on the surface of the silica mother particle.
Methods for keeping the redox potential within the above range include adding an oxidizing agent such as hydrogen peroxide, or blowing in air, oxygen, or ozone. If these methods are not used, the redox potential tends to be negative or to be 50 mV or less.

By such step 1, a dispersion liquid (precursor particle dispersion liquid) containing particles (precursor particles) which are precursors of the composite fine particles of the present invention is obtained. In this step, it is possible to obtain particles in which the average crystallite diameter of the _CeO2 ultrafine particles contained in the precursor particles is 2.5 nm or more and less than 10 nm. If the reactivity of silica and ceria is too high, the average crystallite diameter of the _CeO2 ultrafine particles contained in the precursor particles tends to be less than 2.5 nm, so that in step 2, excessively high temperature firing is required to make the ceria particles 10 nm or more. As a result, the adhesion between the particles becomes strong, and disintegration may become difficult.

As described above, in step 1, the silica-based fine particle dispersion is stirred and the metal salt of cerium is added thereto continuously or intermittently while maintaining the temperature at 0 to 20° C., the pH at 5.0 to 9.0, and the redox potential at 50 to 500 mV. It is preferable to then add the metal salt of cerium thereto continuously or intermittently while maintaining the temperature at higher than 20° C. and not higher than 98° C., the pH at 5.0 to 9.0, and the redox potential at 50 to 500 mV, to obtain the precursor particle dispersion.
That is, in step 1, the treatment is carried out at a temperature of 0 to 20° C., but it is preferable to subsequently change the temperature to a temperature higher than 20° C. and not higher than 98° C. to carry out the treatment, thereby obtaining the precursor particle dispersion liquid.
By carrying out step 1 in this manner, it becomes easier to obtain the dispersion of the present invention containing the composite fine particles of the present invention in which the coefficient of variation in the particle size distribution of the child particles is a suitable value.
When the treatment temperature is more than 20°C and not more than 98°C, the suitable values and adjustment methods of the pH and the oxidation-reduction potential are the same as those when the treatment temperature is 0 to 20°C.

Conversely, the precursor particle dispersion may be obtained by performing a treatment at a temperature of more than 20° C. and not more than 98° C. before performing a treatment at a temperature of 0 to 20° C. That is, the silica-based fine particle dispersion may be stirred, the cerium metal salt may be added continuously or intermittently while maintaining the temperature at more than 20° C. and not more than 98° C., the pH at 5.0 to 10.0, and the redox potential at 50 to 500 mV, and thereafter the cerium metal salt may be added continuously or intermittently while maintaining the temperature at 0 to 20° C., the pH at 5.0 to 9.0, and the redox potential at 50 to 500 mV, to obtain the precursor particle dispersion.
This is because, even when step 1 is carried out in this manner, it is easier to obtain the dispersion of the present invention containing the composite fine particles of the present invention in which the coefficient of variation in the particle size distribution of the child particles is a suitable value.
When the treatment temperature is more than 20°C and not more than 98°C, the suitable values and adjustment methods of the pH and the oxidation-reduction potential are the same as those when the treatment temperature is 0 to 20°C.
Even when the temperature is changed during mixing in this way, so long as the mixing step is carried out at a temperature of 0 to 20° C., the composite fine particles will be produced by the same mechanism as described above.

When the reaction is carried out in the range of 0 to 20°C, the reactivity of cerium with silica is suppressed, and large-sized _CeO2 ultrafine particles are generated, but when the compounding temperature is then kept between 20°C and 98°C and a metal salt of cerium is added, the reactivity of cerium with silica increases, and the dissolution of silica is promoted, so that silica inhibits the crystal growth of ceria, and small-sized _CeO2 ultrafine particles are generated. In this way, the reaction temperature during the compounding step (step 1) must be 0 to 20°C, and the reaction temperature is changed to between 20°C and 98°C and a metal salt of cerium is added, thereby making it possible to broaden the particle size distribution of _CeO2 ultrafine particles and ceria child particles. Note that, as long as the compounding temperature is in the range of 0 to 20°C and there is a step of adding a metal salt of cerium, the reaction at a temperature between 20°C and 98°C may be carried out before or after the reaction at 0 to 20°C, and the temperature may be changed three or more times.
In the case where the reaction temperature is 2 or more stages, the amount of cerium metal salt added in the step of reacting at 0 to 20°C is preferably in the range of 10 to 90 mass% based on the total amount of cerium metal salt added. If the amount exceeds this range, the proportion of large (or small) _CeO2 ultrafine particles and ceria elementary particles decreases, so that the particle size distribution does not become very wide.

The precursor particle dispersion obtained in step 1 may be further diluted or concentrated using pure water or ion-exchanged water before being subjected to step 2.

It is preferable that the solids concentration in the precursor particle dispersion is 1 to 27% by mass.

If desired, the precursor particle dispersion may be deionized using a cation exchange resin, an anion exchange resin, an ultrafiltration membrane, an ion exchange membrane, centrifugation, or the like.

<Step 2>
In step 2, the precursor particle dispersion liquid is dried and then baked at 850 to 1100°C.

The drying method is not particularly limited. It can be dried using a conventionally known dryer. Specifically, a box dryer, band dryer, spray dryer, etc. can be used.
It is further preferable to set the pH of the precursor particle dispersion liquid before drying to 6.0 to 7.0, because when the pH of the precursor particle dispersion liquid before drying is set to 6.0 to 7.0, the surface activity can be suppressed.

After drying, the firing temperature is 850 to 1100°C, preferably 910 to 1100°C, more preferably 920 to 1090°C, and most preferably 930 to 970°C. Firing in this temperature range allows the crystallization of ceria to proceed sufficiently, and the cerium-containing silica layer in which the ceria child particles are dispersed has an appropriate film thickness, the cerium-containing silica layer is firmly bonded to the mother particle, and the child particles dispersed in the cerium-containing silica layer are less likely to fall off. Furthermore, firing in this temperature range makes it difficult for cerium hydroxide and the like to remain. If this temperature is too high, the ceria crystals may grow abnormally, the cerium-containing silica layer may become too thick, the amorphous silica that constitutes the mother particle may crystallize, or the particles may fuse together.

Although alkali metals, alkaline earth metals, sulfates, etc. can be added as flux components during firing to promote the crystal growth of ceria, the flux components can cause metal contamination and corrosion of the polishing substrate, and therefore the content of the flux components during firing is preferably 100 ppm or less, more preferably 50 ppm or less, and most preferably 40 ppm or less per precursor particle (dry).
The flux component may be carried over from the raw colloidal silica or may be used as an alkali to neutralize the cerium metal salt during preparation, but if an alkali metal or alkaline earth metal is present during preparation, the polymerization of the silica fine particles is promoted and densified, reducing the reactivity between the cerium hydroxide and the silica fine particles. Furthermore, the surface of the silica fine particles is protected by an alkali metal or alkaline earth metal, which suppresses the reactivity with the cerium hydroxide and the like, and tends not to form a cerium-containing silica layer. Furthermore, the dissolution of silica during preparation is suppressed, making it difficult for silicon atoms to form a solid solution in the ceria subparticles.

Furthermore, when the calcination is performed within this temperature range, silicon atoms are dissolved in the crystalline ceria, which is the main component of the child particles, and therefore, the cerium atoms and silicon atoms contained in the child particles can satisfy the relationship R ₁ < R ₂ , where R ₁ is the cerium-silicon atomic distance and R ₂ is the cerium-cerium atomic distance.

In step 2, a solvent is added to the fired product obtained by firing, and the product is subjected to a wet crushing treatment at a pH range of 8.6 to 10.8.
Here, the fired body may be dry-disintegrated before being subjected to the wet disintegration treatment, and then the fired body may be wet-disintegrated.

Conventionally known dry crushing devices can be used, such as attritors, ball mills, vibrating mills, and vibrating ball mills.

As the wet disintegration device, a conventionally known device can be used, for example, a batch type bead mill such as a basket mill, a horizontal, vertical or annular type continuous bead mill, a sand grinder mill, a ball mill, etc., a rotor-stator type homogenizer, an ultrasonic dispersion type homogenizer, a wet medium stirring type mill (wet disintegrator) such as an impact crusher that hits fine particles in a dispersion liquid against each other, etc. Examples of beads used in the wet medium stirring mill include beads made from raw materials such as glass, alumina, zirconia, steel, flint, organic resin, etc.
The solvent used when the fired body is wet-disintegrated is water and/or an organic solvent. For example, it is preferable to use water such as pure water, ultrapure water, or ion-exchanged water. The solid content concentration here is not particularly limited, but is preferably in the range of, for example, 0.3 to 50 mass%.

When the fired body is subjected to wet disintegration, it is preferable to carry out the wet disintegration while maintaining the pH of the solvent at 8.6 to 10.8. By maintaining the pH within this range, it is possible to more easily finally obtain a ceria-based composite microparticle dispersion which, when subjected to cationic colloid titration, gives a streaming potential curve in which the ratio (ΔPCD/V) of the streaming potential change (ΔPCD) to the amount of cationic colloid titrant added at the knick (V), as represented by the above formula (1), is −110.0 to −15.0.
That is, it is preferable to perform disintegration to such an extent that the dispersion of the present invention corresponding to the above-mentioned preferred embodiment is obtained. As described above, when the dispersion of the present invention corresponding to the preferred embodiment is used as an abrasive, the polishing rate is further improved. The present inventor presumes that the polishing rate is further improved and the falling off of the ceria child particles can be controlled by appropriately thinning the cerium-containing silica layer on the surface of the composite fine particle of the present invention and/or by appropriately exposing the child particles to a part of the surface of the composite fine particle. Furthermore, it is presumed that the silica in the cerium-containing silica layer dissolves and is deposited again during disintegration, forming a soft and easily soluble silica layer on the outermost layer, and that this easily soluble silica layer improves the frictional force by adhesion with the substrate, thereby improving the polishing rate. It is also presumed that the child particles are easily detached to some extent during polishing because the cerium-containing silica layer is thin or peeled off. It is more preferable that ΔPCD/V is −100.0 to −15.0, and even more preferably −100.0 to −20.0.
In addition, if the fired powder is merely loosened without going through a wet disintegration step such as step 2, if only dry disintegration/pulverization is performed, or if wet disintegration is performed outside the specified pH range, it is difficult for ΔPCD/V to fall within the range of −100.0 to −15, and furthermore it is difficult to form a soft, easily soluble silica layer.

In step 2, it is preferable to add the above-mentioned solvent to the above-mentioned fired body, perform a wet crushing treatment at a pH range of 8.6 to 10.8, and then perform a centrifugation treatment at a relative centrifugal acceleration of 300 G or more, and subsequently remove the precipitated components, thereby obtaining a ceria-based composite microparticle dispersion.
The classification by centrifugation is preferably carried out at a relative centrifugal acceleration of 300 G or more. After the centrifugation, it is preferable to remove the sedimented components to obtain a ceria-based composite fine particle dispersion. There is no particular upper limit to the relative centrifugal acceleration, but in practice, it is used at 10,000 G or less.
This is because, with such a centrifugal acceleration, coarse particles are less likely to remain in the ceria-based composite microparticle dispersion, and as a result, scratches are less likely to occur when the ceria-based composite microparticle dispersion is used for polishing purposes, such as as an abrasive.

In the present invention, the ceria-based composite microparticle dispersion obtained by the above-mentioned manufacturing method can be further dried to obtain ceria-based composite microparticles. The drying method is not particularly limited, and for example, it can be dried using a conventionally known dryer.

The dispersion of the present invention can be obtained by the manufacturing method of the present invention.

<Polishing abrasive dispersion liquid>
The liquid containing the dispersion of the present invention can be preferably used as a polishing abrasive dispersion (hereinafter also referred to as "polishing abrasive dispersion of the present invention"). In particular, it can be preferably used as a polishing abrasive dispersion for planarizing a semiconductor substrate on which an _SiO2 insulating film is formed. In addition, it can be preferably used as a polishing slurry by adding a chemical component to control polishing performance.

The abrasive dispersion for polishing of the present invention has excellent effects such as a high polishing rate when polishing semiconductor substrates, less scratches on the polished surface, and less abrasive residue on the substrate.

The polishing abrasive 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, by adding one or more additives selected from the group consisting of polishing accelerators, surfactants, heterocyclic compounds, pH adjusters, and pH buffers to the polishing abrasive dispersion of the present invention as additives for controlling the polishing performance, the polishing slurry can be suitably used.

<Polishing accelerator>
The polishing abrasive dispersion of the present invention can be used as polishing slurry by adding a conventionally known polishing accelerator as necessary, depending on the type of polishing material.Examples of such accelerators include hydrogen peroxide, peracetic acid, urea peroxide, and mixtures thereof.When using the polishing agent composition containing such a polishing accelerator as hydrogen peroxide, when the polishing material is metal, the polishing speed can be effectively improved.

Other examples of polishing accelerators include inorganic acids such as sulfuric acid, nitric acid, phosphoric acid, oxalic acid, and hydrofluoric acid, organic acids such as acetic acid, and the sodium, potassium, ammonium, and amine salts of these acids, and mixtures thereof. In the case of polishing compositions containing these polishing accelerators, when polishing a workpiece made of multiple components, the polishing rate of a specific component of the workpiece can be accelerated, ultimately resulting in a flat polished surface.

When the polishing abrasive dispersion of the present invention contains a polishing accelerator, the content is preferably 0.1 to 10 mass %, and more preferably 0.5 to 5 mass %.

<Surfactant and/or hydrophilic compound>
In order to improve the dispersibility and stability of the polishing abrasive dispersion of the present invention, a cationic, anionic, nonionic, or amphoteric surfactant or hydrophilic compound can be added. Both the surfactant and the hydrophilic compound have the effect of reducing the contact angle with the polished surface and promoting uniform polishing. As the surfactant and/or hydrophilic compound, for example, those selected from the following group can be used.

Examples of anionic surfactants include carboxylates, sulfonates, sulfates, and phosphates. Examples of carboxylates include soap, N-acylamino acid salts, polyoxyethylene or polyoxypropylene alkyl ether carboxylates, and acylated peptides. Examples of sulfonates include alkyl sulfonates, alkylbenzene and alkylnaphthalene sulfonates, naphthalene sulfonates, sulfosuccinates, α-olefin sulfonates, and N-acylsulfonates. Examples of sulfates include sulfated oils, alkyl sulfates, alkyl ether sulfates, polyoxyethylene or polyoxypropylene alkyl allyl ether sulfates, and alkylamide sulfates. Examples of phosphates include alkyl phosphates, and polyoxyethylene or polyoxypropylene alkyl allyl ether phosphates.

Examples of cationic surfactants include aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium chloride salts, benzethonium chloride, pyridinium salts, and imidazolinium salts; examples of amphoteric surfactants include carboxybetaine type, sulfobetaine type, aminocarboxylate salts, imidazolinium betaine, lecithin, and alkylamine oxide.

Nonionic surfactants include ether type, ether ester type, ester type, and nitrogen-containing type. Ether types include polyoxyethylene alkyl and alkylphenyl ethers, alkylarylformaldehyde condensed polyoxyethylene ethers, polyoxyethylene polyoxypropylene block polymers, and polyoxyethylene polyoxypropylene alkyl ethers. Ether ester types include polyoxyethylene ethers of glycerin esters, polyoxyethylene ethers of sorbitan esters, and polyoxyethylene ethers of sorbitol esters. Ester types include polyethylene glycol fatty acid esters, glycerin esters, polyglycerin esters, sorbitan esters, propylene glycol esters, and sucrose esters. Nitrogen-containing types include fatty acid alkanolamides, polyoxyethylene fatty acid amides, and polyoxyethylene alkyl amides. Other examples include fluorine-based surfactants.

The surfactant is preferably an anionic surfactant or a nonionic surfactant, and the salt may be an ammonium salt, a potassium salt, or a sodium salt, with the ammonium salt and potassium salt being particularly preferred.

Further, other surfactants, hydrophilic compounds, etc. include esters such as glycerin esters, sorbitan esters, and alanine ethyl esters; ethers such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyethylene glycol alkyl ethers, polyethylene glycol alkenyl ethers, alkyl polyethylene glycols, alkyl polyethylene glycol alkyl ethers, alkyl polyethylene glycol alkenyl ethers, alkenyl polyethylene glycols, alkenyl polyethylene glycol alkyl ethers, alkenyl polyethylene glycol alkenyl ethers, polypropylene glycol alkyl ethers, polypropylene glycol alkenyl ethers, alkyl polypropylene glycols, alkyl polypropylene glycol alkyl ethers, alkyl polypropylene glycol alkenyl ethers, and alkenyl polypropylene glycols; polysaccharides such as alginic acid, pectinic acid, carboxymethylcellulose, curdlan, and pullulan; amino acid salts such as glycine ammonium salt and glycine sodium salt; polyaspartic acid, polyglutamic acid, polylysine polycarboxylic acids and their salts, such as polymalic acid, polymethacrylic acid, ammonium salts of polymethacrylic acid, sodium salts of polymethacrylic acid, polyamic acid, polymaleic acid, polyitaconic acid, polyfumaric acid, poly(p-styrene carboxylic acid), polyacrylic acid, polyacrylamide, aminopolyacrylamide, ammonium salts of polyacrylic acid, sodium salts of polyacrylic acid, polyamic acid, ammonium salts of polyamic acid, sodium salts of polyamic acid, and polyglyoxylic acid; vinyl polymers, such as polyvinyl alcohol, polyvinylpyrrolidone, and polyacrolein; Examples include sulfonic acids and their salts, such as ammonium taurate, sodium methyl taurate, sodium methyl sulfate, ethyl ammonium sulfate, butyl ammonium sulfate, sodium vinyl sulfonate, sodium 1-allyl sulfonate, sodium 2-allyl sulfonate, sodium methoxymethyl sulfonate, ammonium ethoxymethyl sulfonate, and sodium 3-ethoxypropyl sulfonate; and amides, such as propionamide, acrylamide, methyl urea, nicotinamide, succinamide, and sulfanilamide.

When the substrate to be polished is a glass substrate or the like, any surfactant can be used suitably. However, when the substrate is a silicon substrate for semiconductor integrated circuits or the like, and the effects of contamination by alkali metals, alkaline earth metals, halides, or the like must be avoided, it is preferable to use an acid or its ammonium salt surfactant.

When the polishing abrasive dispersion of the present invention contains a surfactant and/or a hydrophilic compound, the total content is preferably 0.001 to 10 g, more preferably 0.01 to 5 g, and particularly preferably 0.1 to 3 g, per 1 L of the polishing abrasive dispersion.

The content of the surfactant and/or hydrophilic compound is preferably 0.001 g or more per liter of the polishing abrasive dispersion in order to obtain a sufficient effect, and is preferably 10 g or less in order to prevent a decrease in the polishing speed.

Only one type of surfactant or hydrophilic compound may be used, or two or more types may be used in combination.

<Heterocyclic compounds>
In the case where the substrate to be polished contains a metal, the abrasive dispersion of the present invention may contain a heterocyclic compound in order to form a passivation layer or a dissolution-suppressing layer on the metal and suppress the erosion of the substrate to be polished. Here, the term "heterocyclic compound" refers to a compound having a heterocycle containing one or more heteroatoms. The term "heteroatom" refers to an atom other than a carbon atom or a hydrogen atom. The term "heterocycle" refers to a cyclic compound having at least one heteroatom. The term "heteroatom" refers only to an atom that forms a part of the ring system of a heterocycle, and does not refer to an atom that is located outside the ring system, that is separated from the ring system by at least one non-conjugated single bond, or that is a part of a further substituent of the ring system. Preferred examples of heteroatoms include, but are not limited to, nitrogen atoms, sulfur atoms, oxygen atoms, selenium atoms, tellurium atoms, phosphorus atoms, silicon atoms, and boron atoms. Examples of heterocyclic compounds that can be used include imidazole, benzotriazole, benzothiazole, and tetrazole. More specific examples include 1,2,3,4-tetrazole, 5-amino-1,2,3,4-tetrazole, 5-methyl-1,2,3,4-tetrazole, 1,2,3-triazole, 4-amino-1,2,3-triazole, 4,5-diamino-1,2,3-triazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, and 3,5-diamino-1,2,4-triazole, but are not limited to these.

When a heterocyclic compound is blended into the polishing abrasive dispersion of the present invention, the content is preferably 0.001 to 1.0 mass%, more preferably 0.001 to 0.7 mass%, and even more preferably 0.002 to 0.4 mass%.

<pH Adjuster>
In order to enhance the effects of the above-mentioned additives, the pH of the polishing composition can be adjusted by adding an acid or a base or a salt compound thereof, if necessary.

When adjusting the pH of the polishing abrasive dispersion of the present invention to 7 or more, an alkaline pH adjuster is used. Preferably, sodium hydroxide, aqueous ammonia, ammonium carbonate, or an amine such as ethylamine, methylamine, triethylamine, or tetramethylamine is used.

When adjusting the pH of the polishing abrasive dispersion of the present invention to less than 7, an acidic pH adjuster is used. For example, mineral acids such as hydrochloric acid and nitric acid, as well as hydroxy acids such as acetic acid, lactic acid, citric acid, malic acid, tartaric acid, and glyceric acid, are used.

<pH Buffer>
In order to keep the pH value of the polishing abrasive dispersion of the present invention constant, a pH buffer may be used. Examples of the pH buffer include phosphates and borates such as ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium tetraborate tetrahydrate, or organic acid salts.

In addition, examples of the dispersion solvent for the abrasive grain 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; 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 be used in combination with water.

The solids concentration in the polishing abrasive dispersion of the present invention is preferably in the range of 0.3 to 50% by mass. If the solids concentration is too low, the required polishing speed may not be achieved. Conversely, if the solids concentration is too high, the polishing speed is rarely improved any further.

The present invention will be described below based on examples. The present invention is not limited to these examples.

<Experiment 1>
First, the details of the measurement and test methods in the examples and comparative examples will be described. The measurement and test results for each of the examples and comparative examples are shown in Table 1.

[Area (S _x ), area (S ₀ ), chord length, arrow height and total arc length (w) of the arched shape X of the ceria-based composite fine particle, and chord length, arrow height and total arc length (w) of the arched shape Y of the silica fine particle]
For the ceria-based composite microparticles obtained in the Examples and Comparative Examples, the area ( _Sx ) of the arched figure X and the area (S0) of the pseudo-spherical decapitated ceria-based composite microparticles were determined by the method described with reference to Fig. ₁ , and the area ratio ( _Sx / _S0 ) was calculated. The chord length, arrow height, and total arc length (w) of the arched figure X were also calculated. Similarly, for the silica microparticles, the chord length, arrow height, and total arc length (w) of the arched figure Y were also calculated.

[Analysis of ingredients]
[Measurement of _SiO2 content and _CeO2 content]
The _SiO2 content in the ceria composite microparticles is measured by performing 1000°C ignition loss on the ceria composite microparticle dispersion, determining the mass of solid content, and then measuring the Ce content by standard addition method using an ICP plasma emission spectrometer (e.g., SPS5520, manufactured by SII) described later to calculate _CeO2 mass%, and the solid content other than _CeO2 is considered to be _SiO2 , and the _SiO2 content is calculated. The _SiO2 content, _CeO2 content, and the mass part of ceria relative to 100 mass parts of silica in the ceria composite microparticles are calculated based on the _CeO2 content and _SiO2 content obtained here. The solid content concentration of the ceria composite microparticle dispersion can also be obtained here.

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, about 1 g of a sample (adjusted to 20% solids by mass) made of ceria-based composite microparticles or ceria-based composite microparticle dispersion is collected 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 in a 100 ml measuring flask, and water is added to make the mixture 100 ml. Next, the operation of collecting 10 ml of the solution from the 100 ml solution in a 20 ml measuring flask is repeated five times to obtain five 10 ml portions. Then, using this, Ce is measured by the standard addition method using an ICP plasma emission analyzer (e.g., SPS5520, manufactured by SII). Here, a blank is also measured in the same manner, and the blank is subtracted to adjust the Ce measurement value.

[X-ray diffraction method, measurement of average crystallite size]
The ceria-based composite microparticle dispersion or silica microparticles obtained in the Examples and Comparative Examples were dried using a conventionally known dryer, and the obtained powder was ground in a mortar for 10 minutes. The X-ray diffraction pattern was obtained using an X-ray diffractometer (Rigaku Corporation, RINT1400) 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 by the above-mentioned method, and the average crystallite size was calculated by Scherrer's formula.

<Average particle size>
(1) For the ceria-based composite microparticle dispersions obtained in the Examples and Comparative Examples, the average particle diameter of the ceria-based composite microparticles contained therein was measured by the above-mentioned image analysis method based on a photographic projection image obtained by photographing the ceria-based composite microparticles using a transmission electron microscope.
An electron microscope photograph (transmission electron microscope photograph) of the composite fine particles of the present invention magnified 100,000 times is prepared, and for any 50 particles on the image, the maximum diameter of the particle is taken as the major axis, and the length is measured and the value is taken as the major axis (DL). In addition, a point is determined on the major axis that divides the major axis in half, and two points where a straight line perpendicular to the major axis intersects with the outer edge of the particle are determined, and the distance between the two points is measured and taken as the minor axis (DS). Then, the geometric mean value of the major axis (DL) and the minor axis (DS) is calculated, and this is taken as the particle diameter of the particle. In this way, the particle diameters of 50 particles are measured, and the value obtained by simply averaging them is taken as the average particle diameter.
(2) The average particle size of the pseudo-defective ceria-based composite microparticles contained in the ceria-based composite microparticle dispersions obtained in the Examples and Comparative Examples was also measured by the above-mentioned image analysis method based on a photographic projection obtained by photographing with a transmission electron microscope. However, in measuring the average particle size of the pseudo-defective ceria-based composite microparticles, 50 pseudo-defective ceria-based composite microparticles were selected from the ceria-based composite microparticles shown in the photographic projection obtained by photographing with a transmission electron microscope, and the measurement and calculation were performed in the same manner as above.
(3) Regarding the average particle size of the base particles of the ceria-based composite microparticles in the ceria-based composite microparticle dispersions obtained in the Examples and Comparative Examples, and the average particle size of the base particles of the pseudo-spherical ceria-based composite microparticles contained in the ceria-based composite microparticle dispersions obtained in the Examples and Comparative Examples, the average particle size of the silica sol (silica microparticle dispersion) used as a raw material for producing the ceria-based composite microparticle dispersions was measured and calculated by the methods (1) and (2) described above.

<Coefficient of variation>
The coefficient of variation was determined by the method described above.

<Specific surface area>
The specific surface area of the ceria-based composite particles obtained in the examples and comparative examples was measured by the above-mentioned method using a surface area measuring device (manufactured by Mountech Co., Ltd., product number: Mascsorb HM-1220).
In the present invention, the specific surface area means a value obtained by measurement in this manner, unless otherwise specified.

[Number ratio of pseudo-spherical particles]
An electron microscope photograph of the composite fine particle dispersion of the present invention magnified 100,000 times is prepared, and 50 particles in the image are judged as to whether they correspond to pseudo-defective particles or not, and the number ratio of the pseudo-defective particles is calculated.
That is, the ratio of pseudo-spherical particles to 50 particles was calculated.

[Polishing test method]
<Polishing of _SiO2 film>
A polishing abrasive dispersion containing the ceria-based composite fine particle dispersion obtained in each of the Examples and Comparative Examples was prepared, in which the solid content concentration was 0.6% by mass and the pH was adjusted to 5.0 by adding nitric acid.
Next, a substrate having a SiO ₂ insulating film (thickness 1 μm) produced by thermal oxidation was prepared as a substrate to be polished.
Next, the substrate to be polished was set in a polishing apparatus (NF300, manufactured by Nano Factors Corporation), and polishing was performed using a polishing pad ("IC-1000/SUBA400 concentric type" manufactured by Nitta Haas Corporation) by supplying a polishing abrasive dispersion liquid for polishing at a rate of 50 ml/min for 1 minute with a substrate load of 0.5 MPa and a table rotation speed of 90 rpm.
The weight change of the substrate before and after polishing was determined, and the polishing rate was calculated.

[Polished substrate surface roughness]
The smoothness (surface roughness Ra) of the surface of the substrate to be polished obtained by the above-mentioned polishing test of the _SiO2 film was measured using an atomic force microscope (AFM, Hitachi High-Tech Science Corporation). Since smoothness and surface roughness are roughly proportional to each other, the surface roughness is shown in Table 1.

An example is given below.

Example 1
[Preparation of silica-based microparticle dispersion containing pseudo-spherical silica microparticles]
A diluted slurry was obtained by adding 451 g of ion-exchanged water to 500 g of silica sol (manufactured by JGC Catalysts and Chemicals Co., Ltd.: Spherica Slurry SS-300, average particle size 341 nm).
Next, an aqueous sodium hydroxide solution was added to this diluted slurry to adjust the pH to 9.6, and then wet-disintegration was carried out for 900 minutes in a wet disintegrator (a batch-type benchtop sand mill manufactured by Kampe Co., Ltd.) using zirconia beads of φ0.05 mm (manufactured by Nikkato Co., Ltd.) Here, an aqueous sodium hydroxide solution was added during the wet disintegration to maintain the pH at 9.5 to 10.5.

After crushing, the beads were separated by passing them through a wire net with a mesh size of 44. An SEM image (100,000 times magnification) of the silica fine particles dispersed in the obtained silica-based fine particle dispersion is shown in FIG. 3(a) and a TEM image (100,000 times magnification) is shown in FIG. 3(b).
As shown in Fig. 3, the silica fine particles were pseudo-defective in shape. That is, when the silica fine particles were inscribed, an arched figure Y was present with an area ratio of 1.0 to 1.5 times, an arrow height of 174 nm, and a chord length of 285 nm.
The average particle size of the silica fine particles was 232 nm, and the average particle size of the pseudo-spherical particles among them was 207 nm.
3, it can be seen that the silica microparticles used in Example 1 are at least partially inscribed in the chord of the arched figure Y. It can also be seen that the silica microparticles are inscribed in a point D on the arc that bisects the entire length of the arc of the arched figure Y, and are at least partially inscribed in both the arc curves on one side and the opposite side of the arc with the point D as the center.
Furthermore, it can be confirmed from FIG. 3 that the silica fine particles used in Example 1 are inscribed in at least 20% of the chord of the arcuate shape Y.
Furthermore, the solid content was 4.6% by mass, and the weight was 1,375 g.

Next, 41 g of a cation exchange resin (manufactured by Mitsubishi Chemical Corporation) was added to 1286 g of the resulting dispersion of pseudo-spherical silica fine particles, and the mixture was stirred for 60 minutes.
After the ion exchange, the resin was separated by passing the mixture through a 44 mesh wire net to obtain a cation exchange liquid having a solid content of 4.0% by mass, a pH of 3.1, and a weight of 1,440 g.
Next, 50 g of anion exchange resin (manufactured by Mitsubishi Chemical Corporation) was added to 1,440 g of the obtained cation exchange liquid, and the mixture was stirred for 60 minutes.
After the ion exchange, the resin was separated by passing the mixture through a 44 mesh wire net to obtain an anion-exchanged liquid having a solid content concentration of 3.0% by mass, a pH of 4.5, and a weight of 1,891 g.
Next, an aqueous ammonia solution was added to the obtained anion-exchanged liquid to adjust the pH to 9.1. The liquid obtained here is hereinafter also referred to as A-1 liquid.

Next, ion-exchanged water was added to cerium nitrate (III) hexahydrate (Kanto Chemical Co., Ltd., 4N high-purity reagent) to obtain an aqueous solution of cerium nitrate with a _CeO2 content of 3.0% by mass (hereinafter also referred to as B-1 solution).
Next, while A-1 solution (1894 g) was kept at 15.5° C. and stirred, B-1 solution (2293 g, CeO ₂ dry 70 g) was added thereto over 27 hours. During this time, the liquid temperature was maintained at 15.5° C., and 3% ammonia water was added as necessary to maintain the pH at 5.0 to 9.0. After the addition was completed, the liquid was aged for 4 hours at a liquid temperature of 15.5° C. During the addition of B-1 solution and aging, the liquid was aged while blowing air into it, and the redox potential was maintained at 50 to 400 mV.
Thereafter, washing was performed while replenishing ion-exchanged water through an ultrafiltration membrane. The precursor particle dispersion obtained after washing had a solid content of 5.0% by mass, a pH of 7.5 (at 25° C.), and an electrical conductivity of 20 μs/cm (at 25° C.).

Next, the resulting precursor particle dispersion was adjusted to pH 6.5 using an aqueous acetic acid solution, dried in a dryer at 120°C for 15 hours, and then calcined in a muffle furnace at 950°C for 2 hours to obtain a powder (calcined body).

Next, 300 g of ion-exchanged water was added to 88 g of the powder (calcined body) obtained after calcination, and the pH was adjusted to 9.2 using a 3% aqueous ammonia solution. After that, wet-grinding was performed for 180 minutes using φ0.25 mm quartz beads (manufactured by Daiken Chemical Industry Co., Ltd.) in a wet-grinding machine (batch-type benchtop sand mill manufactured by Kampe Co., Ltd.).
After the crushing, the beads were separated by passing the mixture through a 44-mesh wire screen. The solid content of the resulting dispersion of the crushed fired body was 7.1% by mass and the weight was 1,090 g. During the crushing, an aqueous ammonia solution was added to keep the pH at 9.2.

Furthermore, the sintered powder dispersion was centrifuged at 1700 G for 102 seconds in a centrifuge (manufactured by Hitachi Koki Co., Ltd., model number "CR21G") to recover the light liquid, which was then diluted to 200 g with ion-exchanged water and dispersed by ultrasonic irradiation for 3 hours to obtain a ceria-based composite microparticle dispersion.
The average particle size of the ceria-based composite fine particles contained in the obtained ceria-based composite fine particle dispersion was 236 nm, and the average particle size of the pseudo-spherical particles among them was 209 nm.
FIG. 4 shows an SEM image (100,000 times magnification) of the obtained ceria-based composite microparticles. As shown in FIG. 4, the ceria-based composite microparticles were pseudo-spherical. That is, an arched figure X was present in which the area ratio when the ceria-based composite microparticles were inscribed was 1.1 times, the arrow height was 156 nm, and the chord length was 275 nm. From FIG. 4, it can be confirmed that the ceria-based composite microparticles obtained in Example 1 were at least partially inscribed in the chord of the arched figure X. It can also be confirmed that the ceria-based composite microparticles are inscribed in the equipartition point D on the arc that bisects the entire length of the arc of the arched figure X, and are at least partially inscribed in the arc curves on one side and the opposite side of the arc with the equipartition point D as the center.
Furthermore, it can be confirmed from FIG. 4 that the ceria-based composite fine particles obtained in Example 1 are inscribed in at least 20% of the chord of the arcuate shape X.

The resulting ceria-based composite microparticle dispersion was then subjected to a polishing test. The results are shown in Table 1.

The ceria-based composite microparticles contained in the ceria-based composite microparticle dispersion obtained in Example 1 were also measured by X-ray diffraction. The obtained X-ray diffraction pattern is shown in Figure 5. As shown in Figure 5, a fairly sharp crystal pattern of ceriaite was observed in the X-ray diffraction pattern.

In addition, STEM-EDS analysis was performed on the ceria-based composite microparticles contained in the ceria-based composite microparticle dispersion obtained in Example 1, and it was confirmed that the ceria-based composite microparticles have a mother particle, a cerium-containing silica layer on the surface of the mother particle, and child particles dispersed inside the cerium-containing silica layer.

Example 2
The same operation as in Example 1 was carried out, and the obtained sintered crushed body dispersion liquid was treated for 102 seconds at 1700 G in a centrifuge (manufactured by Hitachi Koki Co., Ltd., model number "CR21G") to recover the heavy liquid, dilute it to 59 g by adding ion-exchanged water, and then disperse it by ultrasonic irradiation to obtain a ceria-based composite microparticle dispersion liquid.

The average particle size of the ceria-based composite fine particles contained in the obtained ceria-based composite fine particle dispersion was 236 nm, and the average particle size of the pseudo-spherical particles among them was 209 nm.
In addition, an SEM image of the obtained ceria-based composite particles was taken, and it was confirmed that the ceria-based composite particles had a pseudo-spherical shape.
That is, there was an arched figure X in which the area ratio when the ceria-based composite microparticles were inscribed was 1.1 times, the arrow height was 156 nm, and the chord length was 275 nm. From the SEM image of the obtained ceria-based composite microparticles, it was confirmed that the ceria-based composite microparticles obtained in Example 2 were at least partially inscribed in the chord of the arched figure X. It was also confirmed that the ceria-based composite microparticles were inscribed in a point D on an arc that bisects the entire length of the arc of the arched figure X, and were at least partially inscribed in a circular curve on one side and a circular curve on the opposite side of the arc with the point D as the center.
Moreover, from the SEM image of the obtained ceria-based composite particles, it was confirmed that the ceria-based composite particles obtained in Example 2 were inscribed in at least 20% of the chord of the arch shape X.

The resulting ceria-based composite microparticle dispersion was then subjected to a polishing test. The results are shown in Table 1.

The ceria-based composite microparticles contained in the ceria-based composite microparticle dispersion obtained in Example 2 were also measured by X-ray diffraction. The crystal pattern of ceriaite was observed.

<Comparative Example 1>
Preparation of <<Silica Sol (60 nm)>>> 12,090 g of ethanol and 6,363.9 g of ethyl orthosilicate were mixed to obtain mixed solution _a1 .
Next, 6,120 g of ultrapure water and 444.9 g of 29% ammonia water were mixed to prepare a mixed liquid _b1 .
Next, 192.9 g of ultrapure water and 444.9 g of ethanol were mixed to prepare a bed water.
The water bed was adjusted to 75° C. while stirring, and mixed liquid a ₁ and mixed liquid b ₁ were added simultaneously to the water bed so that the addition was completed in 10 hours for each. After the addition was completed, the liquid temperature was kept at 75° C. for 3 hours for aging, and then the solid content was adjusted to obtain 9,646.3 g of silica sol having a SiO ₂ solid content of 19 mass% and an average particle size of 60 nm measured by a laser diffraction/scattering method.

Preparation of <<Silica Fine Particle Dispersion (Average Particle Diameter of Silica Fine Particles: 108 nm)>> 2,733.3 g of methanol and 1,822.2 g of ethyl orthosilicate were mixed to prepare 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 the silica fine particle dispersion obtained in the previous step by dispersing silica fine particles having an average particle size of 60 nm in a solvent was added thereto.
The bed water containing the silica microparticle dispersion was adjusted to 65° C. while stirring, and mixed liquid a ₂ and mixed liquid b ₂ were added simultaneously to the bed water so that the addition was completed within 18 hours for each. After the addition was completed, the liquid temperature was kept at 65° C. for 3 hours for aging, and then the solid concentration (SiO ₂ solid concentration) was adjusted to 19 mass %, and 3,600 g of a high-purity silica microparticle dispersion was obtained.
The silica fine particles contained in this high-purity silica fine particle dispersion had an average particle diameter of 108 nm as measured by a dynamic light scattering method (PAR-III manufactured by Otsuka Electronics Co., Ltd.) The minor axis/major axis ratio of the silica fine particles 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.

Next, 114 g of a cation exchange resin (SK-1BH manufactured by Mitsubishi Chemical Corporation) was gradually added to 1,053 g of this high-purity silica fine particle dispersion (average particle diameter of silica fine particles: 108 nm), 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 fine particle dispersion liquid to obtain 6,000 g of A-2 liquid having a SiO ₂ solid content concentration of 3 mass %.

Next, ion-exchanged water was added to cerium nitrate (III) hexahydrate (Kanto Chemical Co., Ltd., 4N high-purity reagent) to obtain B-2 solution having a _CeO2 content of 2.5% by mass.

Next, the temperature of A-2 liquid (6,000 g) was raised to 50°C, and while stirring, B-2 liquid (8,453 g, equivalent to 117.4 parts by mass of _CeO2 relative to 100 parts by mass of _SiO2 ) was added thereto over 18 hours. During this time, the liquid temperature was maintained at 50°C, and 3% aqueous ammonia was added as necessary to maintain the pH at 7.85. During the addition of B-2 liquid and during aging, the liquid was mixed while blowing air into it, and the redox potential was maintained at a positive value.
After the addition of B-2 liquid was completed, the liquid temperature was raised to 93° C. and aging was performed for 4 hours. After aging, the mixture was left to cool indoors and cooled to room temperature, and then washed while replenishing ion-exchanged water through an ultrafiltration membrane. The precursor particle dispersion obtained after washing had a solids concentration of 7% by mass, a pH of 9.1 (at 25° C.), and an electrical conductivity of 67 μs/cm (at 25° C.).

Next, a 5% by weight aqueous solution of acetic acid was added to the resulting precursor particle dispersion 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 1090°C for 2 hours to obtain a powder.

310 g of the powder obtained after firing and 430 g of ion-exchanged water were placed in a 1 L beaker with a handle, 3% aqueous ammonia solution was added, and ultrasonic waves were irradiated for 10 minutes in an ultrasonic bath while stirring to obtain a suspension with a pH of 10 (temperature: 25°C).

Next, 595g of φ0.25mm quartz beads were put into a crusher (LMZ06, manufactured by Ashizawa Finetech Co., Ltd.) that had been previously cleaned and operated with water, and the above suspension was further filled into the charge tank of the crusher (filling rate 85%). Considering the ion-exchanged water remaining in the crushing chamber and piping of the crusher, the concentration during crushing was 25% by mass. Then, wet crushing and crushing were performed under the conditions of a disk circumferential speed of 12 m/sec, a number of passes of 25, and a residence time per pass of 0.43 minutes. In addition, 3% aqueous ammonia was added for each pass to maintain the pH of the suspension at 10 during crushing and crushing. In this way, a celica-based composite microparticle dispersion with a solid content concentration of 22% by mass was obtained.
The resulting microparticle dispersion was then centrifuged at a relative centrifugal acceleration of 675 G for 1 minute in a centrifugal separator (manufactured by Hitachi Koki Co., Ltd., model number "CR21G") to remove precipitated components, thereby obtaining a celica-based composite microparticle dispersion.

Figure 6(a) shows an SEM image (100,000 times magnification) of the ceria-based composite microparticles obtained in Comparative Example 1, and Figure 6(b) shows a TEM image (100,000 times magnification).

The ceria-based composite microparticles contained in the dispersion of the present invention do not contain coarse particles, and therefore have low scratching and a high polishing rate. Therefore, the polishing abrasive dispersion containing the dispersion of the present invention can be preferably used for polishing the surfaces of semiconductor devices such as semiconductor substrates and wiring substrates. Specifically, it can be preferably used for planarizing semiconductor substrates on which a silica film is formed.

Claims (9)

A ceria-based composite microparticle dispersion comprising ceria-based composite microparticles having the following characteristics [1] to [3], wherein the proportion of the ceria-based composite microparticles in all particles in an electron microscope photograph is 5 to 20% :
[1] The ceria-based composite microparticles have a mother particle, a cerium-containing silica layer on the surface of the mother particle, and child particles dispersed inside the cerium-containing silica layer, the mother particle being mainly composed of amorphous silica, and the child particles being mainly composed of crystalline ceria.
[2] The ceria-based composite fine particles satisfy the following requirements:
1) On the electron microscope photograph, there is a circle inscribed with the image of the ceria-based composite fine particle, and further, the image of the ceria-based composite fine particle has the following relationship with respect to an arch-shaped figure X consisting of an arc on the circumference of the circle and a chord:
(I) At least partially inscribed in the chord of the arcuate figure X.
(II) It is inscribed in a point D on the arc that bisects the entire length of the arc of the arch-shaped figure X, and is at least partially inscribed in a circular curve on one side of the arc and a circular curve on the opposite side of the arc with the point D as the center.
2) The area of the arch shape X is 1.0 to 1.5 times the area of the image of the ceria-based composite fine particle, the length of the chord is 80 nm or more, and the height of the arrow is 40 nm or more.
[3] The ceria-based composite fine particles have an average particle size of 50 to 350 nm as determined by an image analysis method. The ceria-based composite microparticle dispersion according to claim 1, wherein the ceria-based composite microparticles are inscribed in at least 20% of the chord of the arcuate figure X in the electron micrograph. The ceria-based composite microparticle dispersion according to claim 1 or 2, further comprising: an electron microscope photograph in which the ceria-based composite microparticles are at least partially inscribed in an arc curve extending along the arc for a length of w/6 (w: total length of the arc) on both sides of a point D on the arc that bisects the total length of the arc; and the ceria-based composite microparticles are at least partially inscribed in two arc curves connected to both ends of the arc curve. The ceria-based composite microparticle dispersion according to any one of claims 1 to 3, further comprising ceria-based composite microparticles having the following characteristic [4]:
[4] The ceria-based composite fine particles have a coefficient of variation of particle size distribution of child particles in the range of 15 to 50%. A polishing abrasive dispersion containing the ceria-based composite microparticle dispersion according to claim 1 or 2. 6. The polishing abrasive dispersion according to claim 5, which is used for planarizing a semiconductor substrate on which a silica film is formed. A method for producing a ceria-based composite microparticle dispersion, comprising the steps of :
Step 1: A step of stirring a silica-based fine particle dispersion liquid in which silica fine particles satisfying the following conditions 1), 2) and 3) are dispersed in a solvent, and continuously or intermittently adding a metal salt of cerium thereto while maintaining the temperature at 0 to 20°C, the pH at 5.0 to 9.0, and the oxidation-reduction potential at 50 to 500 mV, to obtain a precursor particle dispersion liquid containing precursor particles.
1) On the electron microscope photograph, there is a circle inscribed with the image of the silica fine particles, and further, the image of the silica fine particles has the following relationship with respect to an arch-shaped figure Y consisting of an arc on the circumference of the circle and a chord:
(I) At least partially inscribed in the chord of the arcuate shape Y.
(II) It is inscribed in a point D on the arc that bisects the entire length of the arc of the arch-shaped figure Y, and is at least partially inscribed in a circular curve on one side of the arc and a circular curve on the opposite side of the arc with the point D as the center.
2) The area of the arch shape Y is 1.0 to 1.5 times the area of the image of the silica fine particles, the length of the chord is 80 nm or more, and the height of the arrow is 40 nm or more.
3) The silica fine particles have an average particle size of 50 to 350 nm as determined by image analysis.
Step 2: A step of drying the precursor particle dispersion liquid, calcining the precursor particle dispersion liquid at 850 to 1,100° C., adding a solvent to the calcined body, and subjecting the mixture to a wet crushing treatment at a pH range of 8.6 to 10.8 to obtain the ceria-based composite microparticle dispersion liquid. 8. The method for producing a ceria-based composite microparticle dispersion according to claim 7, wherein the step 2 is a step of adding the solvent to the sintered body, performing a wet crushing treatment at a pH range of 8.6 to 10.8 , performing a centrifugation treatment at a relative centrifugal acceleration of 300 G or more, and then removing sedimentation components to obtain the ceria-based composite microparticle dispersion. 9. The method for producing a ceria-based composite microparticle dispersion according to claim 7 or 8 , wherein the step 1 comprises adjusting a pH of a dispersion containing spherical silica particles to a range of 9.5 to 10.5, and wet-disintegrating the dispersion to obtain the silica microparticles.

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