JP2024111808A - Hollow silica particle dispersion and method for producing same - Google Patents

Abstract

[Problem] To provide a dispersion of hollow silica particles that has a low refractive index and exhibits excellent anti-reflective performance when used on a coated substrate, and a method for producing the same. [Solution] The particles have a silicon-containing shell and a cavity inside, and the volume of the sediment obtained by centrifuging a dispersion adjusted to 15% by volume of the particles at 1,000,000 G is 25% or less of the volume of the dispersion before centrifugation. When a dispersion containing these particles is used on a coated substrate, it exhibits excellent anti-reflective performance. In particular, when used in a resist material, it exhibits excellent developability. [Selected Figure] None

Description

The present invention relates to a dispersion of hollow silica particles and a method for producing the same.

In recent years, photolithography, which is used in the manufacture of semiconductor elements, printed circuit boards, liquid crystal display panels, organic EL display panels, etc., has become widespread as a processing technique in which a photosensitive substance is applied to a substrate, and then exposed and developed in a pattern. The photosensitive material (resist material) used in this photolithography is a material that forms a functional film, such as a low refractive index film (or a high refractive index film) or an insulating film, in a pattern on the substrate surface. For this reason, high sensitivity, high resolution, and high transparency are required. Such functional films are formed by patterning into the desired shape using the resist material. This resist material is composed of components such as a resin component, a polymerization initiator, and a solvent.

To date, it has been known that hollow silica particles or low-refractive-index particles with a porous interior are used in coating solutions as a means of lowering the refractive index of films. For example, JP 2019-119848 A (Patent Document 1) and JP 2020-166156 A (Patent Document 2) disclose the use of silica particles containing gas in the particles as a photosensitive resin composition to lower the refractive index of the film. In addition, JP 2018-123043 A (Patent Document 3) discloses a method for producing a silica-based hollow particle dispersion having an average particle size of less than 50 nm. Furthermore, JP 2009-020520 A (Patent Document 4) discloses a photosensitive resin composition that is excellent in low dielectric properties, adhesive strength, heat resistance, etc., and discloses the use of colloidal inorganic nanoparticles that have been surface-treated with an organic silane.

JP 2019-119848 A JP 2020-166156 A JP 2018-123043 A JP 2009-020520 A

In recent years, with the increasing density of circuits, fine pitches with a pitch width of about 100 nm are required. To achieve this fine pitch, the pattern portion is required to have high linearity, high smoothness, and little residue on the substrate, and it is necessary to achieve high developability as a resist film. In addition, as a means of lowering the refractive index of the resist film, hollow particles with a high ratio of cavities to the particle (porosity), that is, hollow particles with a large particle diameter, can be blended. However, when hollow particles with a large particle diameter are blended, the surface unevenness of the pattern portion increases, making it difficult to obtain a sharp pattern. On the other hand, when hollow particles with a small particle diameter are blended to suppress the surface unevenness of the pattern portion, the hollow particles have a low porosity and a high refractive index compared to hollow particles with a large particle diameter, so the reduction in the refractive index of the film is insufficient. Thus, there is a correlation between the particle diameter and porosity of the hollow particles. In addition, even if the amount of hollow particles blended is increased to lower the refractive index of the film, the surface unevenness increases due to the small amount of resin components that can exist between the particles, making it difficult to obtain a sharp pattern. In other words, there is a trade-off between refractive index and surface roughness.

When the particles described in Patent Document 1 and Patent Document 2 are used in a resist material requiring a pitch width of about 100 nm, it is expected that a film with a low refractive index can be obtained, but since the particle diameter is large relative to the pitch width, it is difficult to obtain a sharp pattern. In addition, since the particle packing rate in the film is low, the refractive index of the resist film is insufficient. Conversely, if the particle diameter is made small, the porosity of the particles is low and the refractive index is high, so there is a problem that the desired refractive index of the film cannot be obtained. Furthermore, since the compatibility with an alkaline developer is low, it is difficult to form a sharp pattern, and there is a problem that particle-derived residues are generated on the substrate. When the particles described in Patent Document 3 are used, it is easy to obtain a sharp pattern because the particle diameter is small relative to the pitch width, but since the particle packing rate in the film is low, there is a problem that the refractive index of the resist film is high. In addition, since the number density of the silanol groups on the particle surface is low, there is a problem that the compatibility with an alkaline developer is low, making it difficult to form a sharp pattern, and there is a problem that particle-derived residues are generated on the substrate. In Patent Document 4, the particles are surface-treated with an organic silane, so the dispersibility in the resist film is high, but the particle packing rate is low. In addition, it has low compatibility with alkaline developers, which makes it difficult to form sharp patterns and can cause particle-derived residues to appear on the substrate.

To solve these problems, we have discovered the following dispersion of hollow silica particles. These hollow silica particles have an outer shell containing silicon and a cavity inside. The volume of the sediment obtained by centrifuging a dispersion adjusted to 15% by volume of particles at 1,000,000 G is 25% or less of the volume of the dispersion before centrifugation.

Hereinafter, these hollow silica particles may be simply referred to as "particles" or "particles in dispersion liquid."

These particles have a low refractive index and exhibit excellent anti-reflection performance when used on coated substrates. In particular, when used in resist materials, they exhibit excellent developability.

To obtain these particles, we discovered the following manufacturing method.

First, an alkaline aqueous solution containing an element other than silicon that can be an amphoteric oxide is prepared (first step). At this time, the amount of the element that can be an amphoteric oxide in the alkaline aqueous solution is adjusted to be _5.0 mass% or more based on the oxide. A solution of a compound containing silicon and an aqueous solution of an alkali-soluble compound of an inorganic element other than silicon are simultaneously added to the alkaline aqueous solution so that the molar ratio (MOx/SiO ₂ ) of the reaction solution at the end of the addition is 0.5 to 25, where the oxide of silicon is represented as SiO 2 and the oxide of the inorganic element other than silicon is represented as MOx, to prepare a dispersion of composite oxide particles a (second step). Next, a solution of a compound containing silicon and an aqueous solution of the alkali-soluble compound of an inorganic element other than silicon are added at a molar ratio (MOx/SiO ₂ ) smaller than the molar ratio in the second step to prepare a dispersion of composite oxide particles b (third step). Next, an acid is added to the dispersion liquid of the composite oxide particles b to remove at least a part of the elements other than silicon that constitute the composite oxide particles b, thereby preparing a dispersion liquid of silica-based particles (fourth step). The dispersion liquid of the silica-based particles is heated to 60 to 200°C at a heating rate of 3.0°C/min or less, and then cooled to less than 50°C (fifth step).

The properties of the particles in the dispersion obtained by this manufacturing method are similar to those of the particles in the dispersion described above.

When the dispersion of the particles of the present invention is used in a resist material, high developability can be achieved during pattern formation. The resist film obtained here has a low refractive index, low haze, high resolution, and a high density of patterns (fine pitch).

[Particle Dispersion]
The particle dispersion according to the present invention (hereinafter, this may be simply referred to as "dispersion") will be described.

The dispersion of the present invention contains particles having a silicon-containing shell with a cavity inside the shell, and a dispersion medium. The volume of the sediment obtained by centrifuging a dispersion adjusted to 15% by volume of the particles at 1,000,000 G is 25% or less of the volume of the dispersion before centrifugation.

The volume of the sediment obtained by centrifuging a dispersion adjusted to 15% by volume of particles at 1,000,000 G is 25% or less of the volume of the dispersion before centrifugation. If this ratio is within this range, the particles are densely packed in the film, making it possible to form a resist film with a low refractive index.

If this ratio exceeds 25%, the particle filling rate in the film will be low, and it may be difficult to obtain a resist film with a low refractive index. There is no particular lower limit for this ratio, but it is, for example, 20%. This value is more preferably 20 to 24%, and even more preferably 20 to 23%.

The particles preferably have a particle size coefficient of variation (CV value) of 20 to 55%. When the CV value is in this range, a sharp pattern with a low refractive index can be formed. This is because the presence of particles with a correspondingly small diameter in the gaps between the particles allows the particles to be packed more densely in the film than particles with a smaller CV value, resulting in a resist film with a lower refractive index while suppressing unevenness on the film surface.

If the CV value is less than 20%, the particle filling rate in the film will be low, and it may be difficult to obtain a resist film with a low refractive index. Conversely, if the CV value exceeds 55%, a resist film with a low refractive index will be obtained, but the film surface irregularities will be large, and it may be difficult to form a sharp pattern. This CV value is more preferably 22 to 45%, and even more preferably 25 to 35%.

The number density of silanol groups on the particle surface, calculated by the Sears measurement method, is preferably 0.5 to 2.5/ ^nm2 . When the number density of silanol groups is within this range, compatibility with an alkaline developer is high, and therefore a resist film with excellent developability can be obtained.

Here, if the number density of silanol groups is less than 0.5/ ^nm2 , the compatibility with the alkaline developer is low, which may make it difficult to form a sharp pattern or may cause particle-derived residues on the substrate. Conversely, if the number density exceeds 2.5/ ^nm2 , the bond with the photosensitive resin becomes insufficient, and the bond with the resin is weak, which may make it difficult to form a pattern. The silanol group density is preferably 0.8 to 2.2/ ^nm2 , more preferably 1.0 to 2.0/ ^nm2 .

The number density of silanol groups of the particles is calculated from the Sears number and the specific surface area. The Sears number is measured by titration with sodium hydroxide according to the description in Analytical Chemistry 28 (1956), 12, 1981-1983 by Sears. Specifically, 30 g of sodium chloride is added to 150 g of silica particles diluted with pure water to a concentration of 1% by mass, and the pH is adjusted to 4.0 with hydrochloric acid. Then, 0.1 N aqueous sodium hydroxide solution is titrated at 0.1 ml/sec. The Sears number is expressed by the amount (Q) of aqueous sodium hydroxide solution required to reach a pH of 9.0. In other words, the Sears number (A) is the amount of 0.1 N aqueous NaOH solution required to titrate 1.5 g of particles, and is expressed by the following formula (1).

A=(Q×f×100×1.5)/(W×C)...(1)
(In the formula, f represents the titer of the 0.1 N aqueous sodium hydroxide solution used, C represents the particle concentration (mass%) in the dispersion, and W represents the amount (g) of the dispersion collected. )

The number density (ρ) of silanol groups is expressed by the following formula (2):

ρ=(B× _NA )/( ¹⁰¹⁸ ×M×S _BET )...(2)
(In the formula, B is the amount (mol) of sodium hydroxide required to change the pH from 4.0 to 9.0 per 1.5 g of particles calculated from the Sears number (A), and _N is the Avogadro number ( particles/mol), M is the particle amount (1.5 g), and S _BET is the specific surface area (m ² /g) measured using the BET method by nitrogen adsorption.

The refractive index of the particles is preferably 1.12 to 1.35. If the refractive index is within this range, a resist film with a low refractive index can be obtained by using these particles in a resist material. However, it is difficult to obtain particles with a refractive index of less than 1.12. Conversely, if the refractive index exceeds 1.35, the refractive index of the resist film may not be sufficiently low. This refractive index is preferably 1.12 to 1.30, and more preferably 1.12 to 1.25.

The average particle diameter of the particles is not particularly limited, as it depends on the application of the coated substrate and the thickness of the coating, but when used as a resist material, 15 to 55 nm is preferable. This is the average value of the equivalent circle diameter calculated from the area of 300 random particles taken at a specified magnification using a transmission electron microscope (TEM) and then processed to determine the particle area.

Here, particles with an average particle size of less than 15 nm have a low porosity and an insufficient refractive index, so the refractive index of the resist film may not be sufficiently low. Conversely, if the particle size exceeds 55 nm, it may be difficult to obtain a sharp pattern, depending on the content. The average particle size is preferably 20 to 50 nm, and more preferably 25 to 45 nm.

The thickness of the particle shell is preferably 3 to 7 nm. As with the average particle diameter described above, this is the average value of 300 random particles in a TEM photograph, image processing is performed to determine the area of the cavity of the particle, the circle equivalent diameter is calculated from this area, this is subtracted from each particle diameter, and the result is divided by 2.

Here, particles with a shell thickness of less than 3 nm may have difficulty in obtaining the strength necessary to maintain the particle shape. Conversely, if it exceeds 7 nm, the particle refractive index is high, so it may be difficult to obtain a resist film with a low refractive index. The thickness of this shell is preferably 3 to 6 nm, and more preferably 3 to 5 nm.

The difference between the density of the particles in helium gas and the density in nitrogen gas is preferably 0.2 to 1.0 g/cm ^3. When the density difference is in this range, a resist film with a low refractive index can be obtained by blending the particles.

Here, if the density difference is less than 0.2 g/ ^cm3 , the porosity of the particles will be low, and it may be difficult to obtain a resist film with a low refractive index. Conversely, it is difficult to obtain particles with a density difference exceeding 1.0 g/ ^cm3 . The difference in these densities is more preferably 0.3 to 1.0 g/ ^cm3 , and even more preferably 0.4 to 1.0 g/ ^cm3 .

The shape of the particles is not particularly limited. Examples include spherical, ellipsoidal (rugby ball), cocoon, confetti, chain, and dice shapes. Among these, spherical particles are preferred because they have high dispersibility and can be uniformly dispersed in the film.

The sphericity of the particles is preferably 0.80 to 1.00. If the sphericity is in this range, a sharp pattern can be formed.

Here, if the sphericity is less than 0.80, the surface irregularities of the film will become large, and it may become difficult to form a sharp pattern. This sphericity is more preferably 0.85 to 1.00, even more preferably 0.90 to 1.00, and particularly preferably 0.95 to 1.00.

The ratio of the shell thickness to the particle diameter of the particles is preferably 5 to 25%. If this ratio is within this range, a resist film with a low refractive index can be obtained.

If this ratio is less than 5%, it may be difficult to obtain the strength required to maintain the particle shape, and therefore difficult to obtain the particles themselves. Conversely, if the ratio exceeds 25%, the refractive index may not be sufficiently low, and it may be difficult to obtain the desired resist film. This ratio is more preferably 7 to 20%, and even more preferably 7 to 15%.

The cavity inside the outer shell of the particle preferably has a shape that follows the outer shape of the particle. This is because, although it depends on the thickness of the outer shell, it is easy to obtain the strength required to maintain the particle shape when stress is applied to the particle, as the outer shell has a uniform thickness. Furthermore, it is preferable that the cavity is also spherical, similar to the shape of the spherical particle.

In order to reduce the refractive index and obtain a transparent film, it is preferable that the cavity is substantially one cavity. Here, "substantially one cavity" means that although some particles may have "multiple cavities inside the outer shell" due to particle coalescence or the like, the "proportion of particles with one cavity inside the outer shell" is 90% or more. The "number proportion of particles with one cavity inside the outer shell" is more preferably 95% or more, even more preferably 98% or more, particularly preferably 99% or more, and most preferably 100%.

The porosity of the particles is preferably 10 to 70%. If the porosity is in this range, a resist film with a low refractive index can be obtained.

Here, if the porosity is less than 10%, the refractive index will not be sufficiently low, and it may be difficult to obtain the desired resist film. Conversely, if the porosity is more than 70%, it may be difficult to obtain the strength required to maintain the particle shape, and it may be difficult to obtain the particles themselves. This porosity is more preferably 20 to 65%, and even more preferably 30 to 60%.

The specific surface area of the particles, as determined by the BET method using nitrogen gas adsorption, is preferably 90 to 400 m ² /g. If the specific surface area is in this range, a resist film with a low refractive index and a sharp pattern can be obtained.

If the specific surface area is less than 90 m ² /g, it may be difficult to obtain a sharp pattern, although this depends on the content. Conversely, if it exceeds 400 m ² /g, the porosity is low, so the refractive index of the resist film may not be sufficiently low. This specific surface area is more preferably 100 to 300 m ² /g, and even more preferably 110 to 200 m ² /g.

The content of silicon in the particle is preferably 98 parts by mass or more of silicon as silica (SiO ₂ ) when the total amount of metal elements constituting the particle is expressed as 100 parts by mass based on oxide. If the SiO ₂ content is 98 parts by mass or more, a film with a low refractive index is easily obtained. Such particles are preferably used for resist films. The SiO ₂ content is more preferably 99 parts by mass or more, even more preferably 99.5 parts by mass or more, and particularly preferably substantially 100 parts by mass.

Here, substantially 100 parts by mass means that metal elements other than silicon may be contained as impurities, but the total amount of metal elements other than silicon is less than 0.05 parts by mass on an oxide basis. Such high-purity particles are suitable for use in resist films used in semiconductor circuits such as highly integrated logic and memory, and optical sensors, etc.

As such, it is preferable that the constituent components of the particles contain silicon (Si) as the main element. Here, the constituent components of the particles may be any of the following elements (a) to (c). These elements are derived from materials that are preferably used in preparing the particles.

(a) _SiO2
(b) An oxide containing Si and at least one element selected from Al, As, B, Bi, Cd, Co, Fe, Ga, Ge, In, Pb, Sb, Sn, Ti, V, Zn, and Zr. The oxide containing these elements may be a mixture or a composite oxide.
(c) A mixture of the above (a) and (b).

The content of elements other than Si in the particles in the above item (b) is preferably less than 2 parts by mass on an oxide basis when the total amount of metal elements constituting the particles is expressed as 100 parts by mass on an oxide basis. Here, if this content is 2 parts by mass or more, there is a risk that the refractive index of the particles will increase, or it may become difficult to obtain a transparent film due to coloring or the like. This content is more preferably less than 1 part by mass, even more preferably less than 0.5 parts by mass, and particularly preferably substantially 0 parts by mass. Here, substantially 0 parts by mass means that the total amount of metal elements other than silicon is less than 0.05 parts by mass on an oxide basis. Such high-purity particles are suitable for use in resist films used in semiconductor circuits such as highly integrated logic and memory, optical sensors, etc.

In addition, in addition to the particles listed in (a) to (c) above, "particles having a shell and a cavity inside it" and so-called "solid particles" that do not have a cavity inside the particle may be present, so long as the refractive index range of the above-mentioned particles is not exceeded. The ratio of these particles other than the particles of the present invention also varies depending on the type and composition ratio of the elements constituting the particles. For example, in the case of "solid particles" that contain 98 parts by mass or more of silicon as SiO ₂ and have the same average particle size as the particles of the present invention, the ratio of the number of solid particles to the total number of particles is preferably less than 20%. This ratio can be determined, for example, by counting the number of particles of the present invention and solid particles in a predetermined field of view of a TEM photograph. If this ratio is 20% or more, the refractive index will be higher than the desired range, and it may be difficult to obtain the desired resist film. In the case of such solid particles, the ratio of the number is more preferably less than 10%, even more preferably less than 5%, particularly preferably less than 1%, and most preferably 0%. If particles of different element types are present, the ratio of the particles of the present invention to other particles can be determined, for example, by mapping the particles in a specified field of view using energy dispersive X-ray analysis (EDS) and counting the number of particles of the present invention and particles of different element types.

The ratio (A1/A2) of the specific surface area (A1) determined from pulse NMR measurement of an aqueous dispersion of particles to the specific surface area (A2) of the particles determined from the average particle diameter (D) by image analysis of the particles is preferably 0.60 or more. The upper limit of the ratio (A1/A2) is 1.00. The ratio (A1/A2) being in this range indicates high compatibility with an alkaline developer. When such particles are used in a resist material, a resist film with excellent developability is obtained.

Here, if the ratio (A1/A2) is less than 0.60, it may be difficult to obtain a sharp pattern. This ratio (A1/A2) is more preferably 0.65 or more, and even more preferably 0.70 or more.

Pulsed NMR is a measurement method in which magnetization in a thermal equilibrium state in a static magnetic field is excited by irradiating it with pulsed radio waves of several tens of MHz, and the phenomenon in which the excited magnetization returns to its original thermal equilibrium state over time is observed. Liquid molecules in contact with or adsorbed to the particle surface and free liquid molecules not in contact with the particle surface respond differently to changes in the magnetic field.

In general, the movement of liquid molecules adsorbed to particle surfaces is restricted, while liquid molecules not adsorbed to particle surfaces can move freely. As a result, the relaxation time of liquid molecules adsorbed to particle surfaces is shorter than the relaxation time of other liquid molecules. The relaxation time observed in a liquid with dispersed particles is the average value of two relaxation times reflecting the liquid volume concentration on the particle surfaces and the liquid volume concentration in the free state.

Incidentally, the specific surface area (A1) of particles in a dispersion liquid determined from pulsed NMR measurement indicates the specific surface area of the particle in the portion wetted by the dispersion medium. Particles that have been surface-treated with an organosilicon compound have fewer silanol groups on the particle surface than the original particles due to the reaction between the organosilicon compound and the silanol groups on the particle surface, so the specific surface area of the particle in the portion wetted by the hydrophilic dispersion medium is smaller. For this reason, the value of this specific surface area (A1) changes depending on the degree of surface treatment of the particles with an organosilicon compound. The value of the specific surface area (A1) also changes depending on the type of dispersion medium used during measurement.

Therefore, the ratio (A1/A2) is an indicator of the amount of organosilicon compound contained in the surface-treated particles.

The specific surface area (A1) of the particles is calculated by the following formula (4) using the particle volume concentration (Ψp) calculated by the following formula (3):

Ψp=(Sc/Sd)/[(1-Sc)/Td]...Formula (3)
(In the formula, Sc is the solid concentration (mass %) of the particles in the dispersion, Sd is the density of the particles (g/cm ³ ), and Td is the density of the dispersion medium at 25° C. (g/cm ³ ). show.)

Here, the solid content concentration is the concentration of the particles converted into the solid content in the dispersion liquid (hereinafter the same). Sd is the sum of the value obtained by multiplying the density of the constituent components of the particle by their volume ratio and the value obtained by multiplying the density of the constituent components inside the particle by their volume ratio. For example, when the particle is a component of silica, 2.2 is used, when it is alumina, 3.9 is used, when it is arsenic oxide (III), 3.7 is used, when it is boron oxide, 1.9 is used, when it is bismuth oxide (III), 8.9 is used, when it is cadmium oxide, 8.2 is used, when it is cobalt oxide (II), 6.1 is used, when it is iron oxide (III), 5.2 is used, when it is gallium oxide (III), 5.9 is used, when it is germanium oxide (II), 4.2 is used, when it is indium oxide, 7.2 is used, when it is lead oxide (II), 9.5 is used, when it is antimony oxide (V), 5.2 is used, when it is tin oxide, 3.0 is used, when it is titania (anatase), 4.3 is used, when it is titania (rutile), 5.8 is used, when it is vanadium oxide (II), 5.6 is used, and when it is zirconia, 6.0 is used (unit: g/cm ³ ). In addition, when the particle is a composite oxide particle, a particle in which oxides are mixed, or a mixture of oxide particles, Sd can be obtained according to the ratio of the oxides. In addition, when the constituent component inside the particle is air, 0.0 g/cm ³ is used, and in the case of other gases or liquids, the density corresponding thereto is used. For example, in the case of the particles of the present invention, the porosity is used as the volume ratio of the cavity. The porosity of a particle is defined as the ratio of the cavity in the particle to the total volume of the particle. Specifically, first, a TEM photograph of the particle is taken. At this time, the cavity part of the particle has a low density, so the contrast of that part is low. Conversely, the outer shell part has a high density, so the contrast of that part is high. The cavity part and the outer shell part of the particle can be confirmed by this contrast difference. More specifically, image processing is performed on any 300 particles in the TEM photograph to determine the area of the cavity part, and the circle equivalent diameter is calculated from the area, which is taken as the average diameter of the cavity part. The shape of the particle at this time is assumed to be a perfect sphere, and the average volume of the primary particles and the average volume of the cavity part are calculated. The porosity is expressed as the ratio of the average volume of the cavity part to the average volume of the primary particles. Furthermore, for example, when the dispersion medium is water, 1.00 g/cm ³ is used as Td. If other types of dispersion media or mixtures of dispersion media are used, the appropriate densities should be used.

A1={[(Ra/Rb)-1]×Rb}/(Ka×Ψp) ...Formula (4)
(wherein, A1 is the specific surface area (m ² /g) of the particles, Ra is the inverse of the pulse NMR relaxation time in the measurement of the dispersion, and Rb is the inverse of the pulse NMR relaxation time in the measurement of the dispersion medium. Ka indicates a coefficient depending on the dispersion medium and particles used.)

The coefficient Ka is calculated assuming that the specific surface area (A2) obtained from the average particle diameter (D) of the particles is the same as the specific surface area (A3) obtained by pulse NMR measurement of a dispersion of particles that have not been surface-treated.

The specific surface area (A2) of the particles can be calculated using the average particle diameter (D) of the particles according to the following formula (5):

A2=6000/Sd/D...Formula (5)
(In the formula, Sd represents the density of the particles (g/cm ³ ).)

The specific surface area (A3) of particles that have not been surface-treated can be calculated using the particle volume concentration (Ψp) calculated using equation (3) using equation (6).

A3={[(Rc/Rd)-1]×Rd}/(Ka×Ψp) ...Formula (6)
(In the formula, A3 is the specific surface area (m ² /g) of the particles, Rc is the inverse of the pulse NMR relaxation time in the measurement of the particle dispersion, and Rd is the inverse of the pulse NMR relaxation time in the measurement of the dispersion medium.) The reciprocal, Ka, is a coefficient depending on the dispersion medium and particles used.)

Here, the coefficient Ka is set so that the specific surface area (A2) and the specific surface area (A3) have the same value. Therefore, from the formulas (5) and (6),
Ka={[(Rc/Rd)-1]×Rd}/(Ψp×A2) ...Equation (7)
It can be calculated as:

In ^the area _Q1 of the peak appearing at a chemical shift of -78 to -88 ppm, the area _Q2 of the peak appearing at a chemical shift of -88 to -98 ppm, the area _Q3 of the peak appearing at a chemical shift of -98 to -108 ppm, and the area _Q4 of the peak appearing at a chemical shift of -108 to -120 ppm in the 29Si-NMR spectroscopy of the particles, it is preferable that ( _Q4 /ΣQ)×100 is less than 90%, where ΣQ= _Q1 + _Q2 + _Q3 + _Q4 .

The peak assigned to _Q1 is one in which one (--OSi) group and three (--OH) groups are bonded to a Si atom, the peak assigned to _Q2 is one in which two (--OSi) groups and two (--OH) groups are bonded to a Si atom, the peak assigned to _Q3 is one in which three (--OSi) groups and one (--OH) group are bonded to a Si atom, and the peak assigned to _Q4 is one in which four (--OSi) groups are bonded to a Si atom. If the ratio of ( _Q4 /ΣQ) is within this range, the amount of silanol groups is large and compatibility with an alkaline developer is high, resulting in a resist film with excellent developability.

Here, if the ratio of ( _Q4 /ΣQ) is 90% or more, the number of silanol groups is small, so that the compatibility with an alkaline developer is low, and it may be difficult to form a sharp pattern or particle-derived residues may be generated on the substrate. The ratio of ( _Q4 /ΣQ) is more preferably less than 85%.

As mentioned above, the particles have a given number density of silanol groups.

In addition to the silanol groups, the particle shell preferably contains at least one functional group selected from an alkyl group, an acryloyl group, a (meth)acryloyl group, a vinyl group, a mercapto group, and an epoxy group. The presence of these functional groups in the particles improves dispersibility in the dispersion liquid, the coating liquid for forming the resist film, and the resin, and also improves bonding with the resin. Among these, the alkyl group, the epoxy group, the acryloyl group, and the (meth)acryloyl group are preferred because of their high bonding with the resin.

Furthermore, it is preferable that the particle shell contains at least one functional group selected from hydroxyl groups, carboxyl groups, and amino groups. Here, the hydroxyl group may be derived from a silanol group or may be something other than hydroxyl groups. When these functional groups are present in the particles, the compatibility of the particles with the alkaline developer is improved. Among these, hydroxyl groups and carboxyl groups are more preferable in terms of the ease of introducing functional groups into the particle shell.

These functional groups can be identified by measuring and analyzing the dry powder of the particles using a Fourier transform infrared spectrometer (FT-IR).

The particles may be surface-treated with an organosilicon compound. The organosilicon compound is preferably one having the functional group described above. For example, one represented by the following formula (8) can be mentioned. When the particles are surface-treated with such an organosilicon compound, they exhibit high dispersibility in the particle dispersion, the coating liquid for forming a resist film, or in the resin, and a sharp pattern can be obtained.

R _n -SiX _4-n ...Formula (8)
(In the formula, R is an unsubstituted or substituted hydrocarbon group having 1 to 10 carbon atoms, and may be the same or different. Examples of the substituent include an alkyl group, a vinyl group, an epoxy group, an acryloyl group, and the like.) X is an alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, or a hydrogen atom. , n represents an integer of 0 to 4.

Specific examples include the organosilicon compounds shown in Table 1 below. Among these, organosilicon compounds containing at least one of an alkyl group, an epoxy group, an acryloyl group, and a (meth)acryloyl group are more preferred because of their strong bonding strength with resins.

The carbon content of the particles can be measured using a carbon-sulfur analyzer. For example, the particles that have been surface-treated with an organosilicon compound are separated from the unreacted organosilicon compound by centrifugal separation. Only the particles that have been surface-treated with the organosilicon compound are then taken out and dried. The carbon content of the particles can be determined by measuring the particle powder obtained in this way.

The carbon content of the particles is preferably 3% by mass or less. When the carbon content is within this range, the particles have good dispersibility in the dispersion liquid and high compatibility with the alkaline developer, making it possible to obtain a resist film with excellent developability.

Here, even if the carbon content exceeds 3% by mass, there is no further improvement in dispersibility or stability, and no tendency to obtain a sharp pattern. Rather, excessive bonding with the resin may make development difficult, or compatibility with the alkaline developer may decrease, resulting in particle-derived residues on the substrate. There is no particular lower limit for the carbon content, but it is, for example, 0.1% by mass. If the carbon content is less than 0.1% by mass, it may be difficult to obtain sufficient dispersibility and stability in the coating liquid for forming the resist film or in the resin. When such particles are used in a resist film, bonding with the resin may be insufficient, making it difficult to form a sharp pattern. This carbon content is more preferably 0.1 to 2.5% by mass, and even more preferably 0.1 to 2.0% by mass.

This carbon content varies depending on the structure and amount of the surface-treated organosilicon compound. This carbon content is preferably derived from the functional group contained in the particle shell. Here, for example, when the raw material used to prepare the "original particles" before surface treatment with the organosilicon compound is not dependent on the organosilicon compound, and the organosilicon compound of formula (8) is used as a surface treatment agent for the original particles, the above-mentioned preferred carbon content of 0.1 to 3 mass% is contained in the surface-treated particles in an amount of about 0.2 to 7.5 parts by mass of the organosilicon compound as a solid content (R _n -SiO _(4-n)/2 ) per 100 parts by mass of the original particles. Incidentally, examples of the organosilicon compound raw material for preparing the "original particles" include alkoxysilanes such as tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), and phenyltrimethoxysilane.

Here, if the amount of the organosilicon compound contained in the surface-treated particles is less than 0.2 parts by mass relative to 100 parts by mass of the original particles, sufficient dispersibility and stability cannot be obtained, and when the particles are used in a resist film, the bonding with the resin becomes insufficient, and it may be difficult to form a sharp pattern. Conversely, even if the amount of the above-mentioned organosilicon compound exceeds 7.5 parts by mass, the dispersibility and stability are not further improved, and sharp patterns are not easily obtained. Rather, excessive bonding with the resin may make development difficult, or the compatibility with the alkaline developer may decrease, causing particle-derived residues to occur on the substrate. The amount of this surface treatment is more preferably 0.2 to 6.0 parts by mass, and even more preferably 0.2 to 4.5 parts by mass. Incidentally, when the "original particles" are prepared using an organosilicon compound as a raw material, the "original particles" contain carbon, so that the solid content of the organosilicon compound introduced into the particles as a surface treatment to obtain the target carbon content of the particles of the present invention is reduced according to the carbon content of the "original particles" compared to the case of surface treating "original particles not containing carbon".

If the carbon content of the particles is R _A and the number density of silanol groups on the particle surface calculated by the Sears measurement method described above is R _B , then the value of (R _B /R _A ) is preferably 0.2 to 25. If this value is within this range, high dispersibility in the particle dispersion, in the coating liquid for forming a resist film, and in the resin, high binding property with the resin, and high compatibility of the particles with the alkaline developer can be obtained without excess or deficiency.

If this value is less than 0.2, the compatibility with the alkaline developer is low, which may make it difficult to form a sharp pattern or may result in particle-derived residues on the substrate. Conversely, if this value exceeds 25, the bond with the resin is insufficient, so the bond with the resin is weak and the formation of the pattern itself may be difficult. This value is more preferably 0.5 to 15, and even more preferably 1.0 to 10.

The particles may contain elements belonging to alkali metals and alkaline earth metals and ammonia as impurities. If any one of these elements is present in a large amount, the particles may coalesce, and the stability of the dispersion or coating liquid may decrease. Therefore, it may be difficult to obtain a sharp pattern as a resist film. The content of each element belonging to alkali metals and alkaline earth metals, when the element is expressed as an oxide, is preferably less than 100 ppm, more preferably less than 10 ppm, relative to the particles. In addition, ammonia, as NH ₃ , is preferably less than 1000 ppm, more preferably less than 100 ppm, relative to the particles. The alkali metals represent Li, Na, K, Rb, Cs, and Fr, and the alkaline earth metals represent Be, Mg, Ca, Sr, Ba, and Ra.

The particles may contain U, Th, Pd, Ag, Mn, Mo, Ni, and Cr as impurities. If the content of these elements is high, the dispersion may become colored, and it may be difficult to obtain the desired refractive index of the resist film or a sharp pattern. Of these elements, it is preferable that the content of each of U and Th is less than 0.3 ppb, and the content of each of the other elements is less than 100 ppm.

In addition, when the particles are used in semiconductor circuits such as highly integrated logic and memory, which require high purity, or optical sensors, the content of these elements belonging to the alkali metals and alkaline earth metals, as well as elements such as Pd, Ag, Mn, Mo, Ni, and Cr, as well as the above-mentioned elements such as Al, As, B, Bi, Cd, Co, Fe, Ga, Ge, In, Pb, Sb, Sn, Ti, V, Zn, and Zr that are not fixed in the particles, is preferably less than 0.1 ppm. If the content of these elements is 0.1 ppm or more, the metal elements may cause poor insulation of the circuit, short the circuit, or reduce the light transmittance. This may cause a decrease in the dielectric constant of the insulating film, an increase in the impedance of the metal wiring, a delay in the response speed, an increase in power consumption, etc. In particular, U and Th are not preferable because they generate radioactivity and, even if present in small amounts, may cause semiconductors to malfunction due to radioactivity.

To obtain particles with low content of such elements, it is preferable to use equipment that does not contain these elements and has high chemical resistance when manufacturing the particles. Specifically, plastics such as Teflon (registered trademark), FRP, and carbon fiber, and alkali-free glass are preferable. In addition, it is preferable to refine the raw materials used by distillation, ion exchange, and filter removal.

As mentioned above, methods for obtaining high-purity particles include preparing raw materials with low levels of these elements in advance and preventing contamination from the equipment used to manufacture the particles. It is also possible to reduce the levels of these elements in particles manufactured without taking sufficient measures.

There are no particular limitations on the dispersion medium and concentration of the dispersion liquid, so long as the particles are stably dispersed in the liquid without aggregation or precipitation.

Examples of the dispersion medium include water, alcohols, esters, glycols, ethers, ketones, and aprotic polar solvents. These may be used alone or in combination of two or more. In particular, for resist materials, the dispersion medium should have a solubility parameter (SP value) of 10 or more and contain at least one organic solvent with a boiling point of over 100°C at atmospheric pressure, taking into account the workability of the resist material. If the SP value is less than 10, the particles will have low dispersibility and may aggregate. In addition, if the organic solvent has a boiling point of 100°C or less, the particles will dry quickly during application and form a film before leveling, which may cause defects such as particle-derived aggregates in the coating film.

Examples of organic solvents with an SP value of 10 or more and a boiling point exceeding 100°C include propylene glycol monomethyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-normal butyl ether, acetylacetone, ethylene glycol, diphenyl ether, glycerol, formamide, benzyl alcohol, N-methylpyrrolidone, glycerin, cyclohexanone, diethylene glycol monoethyl ether, ethylene glycol monophenyl ether, γ-butyrolactone, diethyl phthalate, dimethyl phthalate, dimethyl sulfoxide, 4-hydroxy-4-methyl-2-pentanone (DAA), 1-butanol, 2-butanol, 1,3-butanediol, 1,4-butanediol, and 1,4-dioxane. Among these, propylene glycol monomethyl ether (PGME) and propylene glycol monomethyl ether acetate (PGMEA) are preferred for resist applications.

The concentration of the dispersion liquid is preferably such that the solid content of the particles is 1 to 40% by mass. If the solid content is less than 1% by mass, the processing time required for producing the coating liquid may be long. Conversely, if the solid content exceeds 40% by mass, the stability of the dispersion liquid may decrease. The concentration of the dispersion liquid is more preferably 5 to 35% by mass, and even more preferably 10 to 30% by mass.

[Method for producing particle dispersion]
The method for producing a particle dispersion according to the present invention includes a first step of preparing an alkaline aqueous solution containing 5.0 mass % or more of an element that becomes an amphoteric oxide based on the oxide, a second step of preparing a dispersion of composite oxide particles a by simultaneously adding a solution of a silicon-containing compound and an aqueous solution of an alkali-soluble compound of an inorganic element other than silicon to the first step such that the molar ratio (MOx/SiO2) of the reaction solution at the end of the addition is 0.5 to 25, where the oxide of silicon is represented as _SiO2 and the oxide of the inorganic element other than silicon is represented as MOx, and the molar ratio (MOx/ _SiO2 ) of the reaction solution at the end of the addition is 0.5 to 25, and a third step of preparing a dispersion of composite oxide particles a by simultaneously adding a solution of a silicon-containing compound and an aqueous solution of an alkali-soluble compound of an inorganic element other than silicon to the first step such that the molar ratio (MOx/SiO2 ₎ of the reaction solution at the end of the addition is 0.5 to 25. a third step of adding a solution of a silicon-containing compound and an aqueous solution of an alkali-soluble compound of an inorganic element other than silicon to prepare a dispersion of composite oxide particles b, a fourth step of adding an acid to the dispersion of composite oxide particles b to remove at least a portion of the elements other than silicon that constitute composite oxide particles b to prepare a dispersion of silica-based particles, and a fifth step of heating the dispersion of silica-based particles to 60 to 200° C. at a heating rate of 3.0° C./min or less, and then cooling to less than 50° C. This results in a dispersion of hollow silica particles.

The particles produced in this way have a low refractive index and the number density of silanol groups on the particle surface is within a specific range, so when used in a resist film, high developability can be achieved during pattern formation. Each process is described below.

[First step]
First, an alkaline aqueous solution containing an element other than silicon that will become an amphoteric oxide is prepared.

Here, "an element other than silicon that can form an amphoteric oxide" means that an oxide containing that element dissolves in an acid with a pH of 3 or less, and dissolves in an alkali with a pH of 10 or more. More specifically, it includes at least one element selected from Al, As, B, Bi, Cd, Co, Fe, Ga, Ge, In, Pb, Sb, Sn, Ti, V, Zn, and Zr.

Among these elements, Al is preferred because it reacts easily with silicon-containing compounds to form composite oxide particles. Examples of the alkaline aqueous solution include aqueous solutions of sodium aluminate and aluminum hydroxide.

The concentration of "elements other than silicon that become amphoteric oxides" in the alkaline aqueous solution is 5.0% by mass or more based on the oxide. At this concentration, particles with a relatively high CV value can be obtained. There is no upper limit to the concentration, so long as the solution can be mixed sufficiently when added in the subsequent second step and a dispersion of the desired particles is obtained. However, for example, to obtain particles with high sphericity, it is preferable to set the concentration to about 20.0% by mass based on the oxide.

If the concentration is less than 5.0% by mass, the particles may not have the volume of the sediment obtained by centrifuging a dispersion adjusted to 15% by volume of particles at 1,000,000 G, which is 25% or less of the volume of the dispersion before centrifugation. This concentration is preferably 5.0 to 15.0% by mass, and more preferably 5.0 to 10.0% by mass.

The proportion of "elements other than silicon that become amphoteric oxides" in the composite oxide particles a prepared in the second step is preferably 20 to 95 parts by mass on an oxide basis when the composite oxide particles a are taken as 100 parts by mass. If the proportion of elements that become amphoteric oxides in the alkaline aqueous solution prepared in the first step is within this range, the formation of particle cavities and thinning of the outer shell becomes easier in the acid treatment in the fourth step described below, making it possible to obtain particles with a low refractive index and particles with a relatively high CV value.

If this ratio is less than 20 parts by mass, it may be difficult to thin the outer shell, making it difficult to obtain particles with a low refractive index. Conversely, if it exceeds 95 parts by mass, particle growth in the second step may be insufficient. This ratio is more preferably 25 to 80 parts by mass, and even more preferably 30 to 65 parts by mass.

In addition, elements that are treated as impurities, such as alkali metals and alkaline earth metals, and are not "elements that become amphoteric oxides" and are not "elements that constitute particles", will not be counted in the 100 parts by mass of the above composite oxide particles a.

Incidentally, silicon is one of the elements that become amphoteric oxides. However, it is not preferable that the "element that becomes an amphoteric oxide" in the alkaline aqueous solution in the first step is silicon alone, or that silicon is present in excess relative to the "elements that become amphoteric oxides other than silicon". If a large amount of silicon is present in this step, the refractive index of the particles finally obtained may be too high. Therefore, when the oxide of silicon contained in this alkaline aqueous solution is expressed as SiO ₂ and the oxide of the amphoteric element other than silicon is expressed as MOx, it is preferable that the molar ratio (MOx/SiO ₂ ) is 10 or more. Since there are cases where this alkaline aqueous solution does not contain silicon, no upper limit is set for the molar ratio (MOx/SiO ₂ ).

The pH of this alkaline aqueous solution is preferably 10 or higher. A pH of 10 or higher is preferable because the amphoteric element is dissolved and present. The pH is more preferably 11 or higher, and even more preferably 12 or higher.

[Second step]
A solution of a compound containing silicon and an aqueous solution of an alkali-soluble compound of an inorganic element other than silicon are simultaneously added to the "alkaline aqueous solution containing an element other than silicon that can become an amphoteric oxide" prepared in the first step so that the molar ratio (MOx/ _SiO2 ) of the reaction solution at the end of the addition is 0.5 to 25, where _SiO2 is the oxide of silicon and MOx is the oxide of an inorganic element other than silicon, to prepare a dispersion of composite oxide particles a.

Here, examples of compounds containing silicon include at least one selected from silicates, acidic silicic acid solutions, and organic silicon compounds.

The silicate is preferably one or more silicates selected from alkali metal silicates, ammonium silicates, and silicates of organic bases. Examples of the alkali metal silicate include sodium silicate and potassium silicate. Examples of the organic base include quaternary ammonium salts such as tetraethylammonium salts, and amines such as monoethanolamine, diethanolamine, and triethanolamine. Examples of ammonium silicates or silicates of organic bases include alkaline solutions in which ammonia, quaternary ammonium hydroxide, amine compounds, etc. are added to a silicic acid solution.

As an acidic silicic acid solution, a silicic acid solution obtained by removing the alkali by treating an aqueous alkali silicate solution with a cation exchange resin, etc., can be used, and an acidic silicic acid solution with a pH of 2 to 4 is particularly preferred.

As the organosilicon compound, an organosilicon compound represented by the above formula (8) in which n is 0 to 3 is preferred.

In the organosilicon compound of formula (8), compounds where n is 1 to 3 are poorly hydrophilic, so it is preferable to hydrolyze them in advance so that they can be mixed uniformly in the reaction system. Well-known methods can be used for the hydrolysis. When a basic catalyst such as an alkali metal hydroxide, aqueous ammonia, or amine is used as a hydrolysis catalyst, the basic catalyst can be removed after hydrolysis and the solution can be used as an acidic solution. When an acidic catalyst such as an organic acid or inorganic acid is used to prepare a hydrolyzate, it is preferable to remove the acidic catalyst by ion exchange or the like after hydrolysis. The obtained hydrolyzate of the organosilicon compound is preferably used in the form of an aqueous solution. Here, an aqueous solution means that the hydrolyzate is not in a cloudy gel state but is transparent.

Examples of the organosilicon compound include organosilicon compounds in which n is 0 to 3 as shown in Table 1. Among them, for example, tetramethoxysilane, tetraethoxysilane, 3-methacryloxypropyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, and 8-methacryloxyoctyltrimethoxysilane are preferred, in that the value (R _B /R _A ) between the carbon content of the particles and the number density of silanol groups on the particle surface can be easily adjusted to a desired range.

Alkali-soluble compounds of inorganic elements other than silicon include alkali metal salts or alkaline earth metal salts, ammonium salts, and quaternary ammonium salts of metal or nonmetallic oxoacids that form oxides of inorganic elements other than silicon. Specific examples include sodium aluminate, sodium tetraborate, ammonium zirconyl carbonate, potassium antimonate, potassium stannate, sodium aluminosilicate, sodium molybdate, ammonium cerium nitrate, and sodium phosphate.

"Compounds containing silicon" and "compounds of inorganic elements other than silicon" have high solubility on the alkaline side. However, when the two are mixed in this high-solubility pH range, the solubility of oxoacid ions such as silicate ions and aluminate ions decreases, and these compounds precipitate to form colloidal particles.

Next, the molar ratio (MOx/SiO ₂ ) will be described.

When the aforementioned "alkali-soluble compound of inorganic elements other than silicon" is expressed as an oxide, suitable examples include _one or _more of _Al2O3 , _{As2O3 , B2O3 , Bi2O3} , CdO, CoO, _Fe2O3 , _Ga2O3 , _GeO2 , _In2O3 , _PbO , _{Sb2O3 , SnO2 , TiO2} , VO, _ZnO2 , and _ZrO2 . In addition, examples of composite oxides of inorganic elements other _than silicon include zinc alumina oxide _and indium tin oxide. These oxides are referred to as MOx, and the number of moles is used to calculate the molar ratio. If multiple types of these oxides are present in the reaction system, the total number of moles of each oxide is used. In addition, the number of moles of the aforementioned "silicon-containing compound" expressed as _SiO2 is used in calculating the molar ratio here.

The molar ratio calculation in the second step includes the "elements that become amphoteric oxides" used in the first step.

Alkali metals and alkaline earth metals are not "elements that make up particles" but are treated as impurities, so they will not be counted in the above MOx.

These matters will also be covered in the third step described below.

When the molar ratio (MOx/ _SiO2 ) in the second step is within this range, the structure of the composite oxide particles is mainly a structure in which silicon and elements other than silicon are alternately bonded with oxygen interposed therebetween. That is, many structures are produced in which oxygen atoms are bonded to the four bonds of a silicon atom, and an element M other than silicon is bonded to these oxygen atoms. As a result, when the element M other than silicon is removed in the fourth step described below, the silicon atoms can also be removed as silicic acid monomers or oligomers accompanying the element M without destroying the shape of the composite oxide particles.

If the molar ratio is less than 0.5, the proportion of "elements other than silicon" removed in the fourth step described below is small, and the porosity of the final particles may not be sufficiently high. Conversely, if the molar ratio exceeds 25, particle growth is suppressed, and the production efficiency until the desired average particle size of the composite oxide particles a is satisfied may decrease. This molar ratio is preferably 0.9 to 8.0, and more preferably 1.2 to 4.0.

In this way, the composite oxide particles a obtained in the second step are removed by acid treatment in the fourth step described below, forming a cavity inside the outer shell of the finally obtained particles. Therefore, it is preferable that the composite oxide particles a are in a form that is easily removed by acid treatment.

For example, when "a solution of a compound containing silicon" and "a solution of _an inorganic element other than silicon that is alkali-soluble" are added in the second step to an "alkali aqueous solution that becomes an amphoteric oxide" having a molar ratio (MOx/SiO 2 ) of 10 or more in the first step, the molar ratio (MOx/SiO ₂ ) in the reaction solution can be reduced as the addition proceeds. By reducing the molar ratio (MOx/SiO ₂ ) in the reaction solution in this way, the molar ratio (MOx/SiO ₂ ) of the resulting composite oxide particles a can also be reduced from the center of the particles toward the outside. If there is a gradient in the molar ratio in the particles in this way, when at least a part of the elements other than silicon that constitute the composite oxide particles b is removed in the acid treatment in the fourth step described later, the part corresponding to the composite oxide particles a can be efficiently removed, which is preferable because it facilitates the formation of particle cavities and the thinning of the outer shell, and particles with a low refractive index can be obtained.

The concentration of the solution of the "silicon-containing compound" and the concentration of the aqueous solution of the "alkali-soluble compound of inorganic elements other than silicon" are preferably 0.05 to 2.0 mass % as _SiO2 and MOx, respectively. When the concentrations are within this range, adhesion and aggregation of particles are suppressed, and particles with large sphericity and a desired CV value can be obtained.

Here, if the concentration of the solution of the "silicon-containing compound" and the concentration of the aqueous solution of the "alkali-soluble compound of inorganic elements other than silicon" are less than 0.05 mass% as _SiO2 and MOx, respectively, the particle growth rate will be slow, and the production efficiency until the desired average particle size of the composite oxide particles a is satisfied may be low, or the particles may have a small CV value. Conversely, if the concentration exceeds 2.0 mass%, the particles may coalesce with each other, resulting in irregular particle shapes or aggregation of the particles. This concentration is more preferably 0.1 to 2.0 mass%, and even more preferably 0.3 to 2.0 mass%.

When adding the solutions in this step, it is preferable that the pH of the reaction system is 10 or higher, and the temperature is 50 to 98°C. If the pH and temperature are within these ranges, the addition of the "solution of a compound containing silicon" and the "aqueous solution of an alkali-soluble compound of an inorganic element other than silicon" allows the composite oxide particles a to grow efficiently. The pH is more preferably 10.5 or higher, and even more preferably 10.5 to 13. The temperature is more preferably 65 to 98°C, and even more preferably 80 to 98°C.

It is preferable to adjust the average particle diameter (Da) of the composite oxide particles a to be approximately 10 to 50 nm.

Here, if the average particle diameter (Da) is less than 10 nm, the outer shell of the final particle may be thick and the porosity of the particle may not be sufficiently high. Conversely, if it exceeds 50 nm, the particle diameter may become too large and it may become difficult to form a sharp pattern. The average particle diameter (Da) is more preferably 15 to 45 nm, and even more preferably 20 to 40 nm.

[Third step]
In this step, a solution of a silicon-containing compound and an aqueous solution of an alkali-soluble compound of an inorganic element other than silicon are added to the dispersion of composite oxide particles a in a molar ratio (MOx/ _SiO2 ) smaller than that in the second step, thereby growing the composite oxide particles a and preparing a dispersion of composite oxide particles b.

In the composite oxide particles b, a layer having a lower molar ratio (MOx/ _SiO2 ) than that of the composite oxide particles a is formed around the composite oxide particles a. This layer is less susceptible to acid attack than the composite oxide particles a, and therefore forms the outer shell of the final particles.

The silicon-containing compound and the alkali-soluble compound of an inorganic element other than silicon used in the third step are selected from those exemplified in the second step. These compounds may be the same type as those used in the second step, or may be a different type from those exemplified in the second step.

If the molar ratio (MOx/SiO ₂ ) in the second step is A and the molar ratio (MOx/SiO ₂ ) in the third step is B, it is preferable to set the ratio (B/A) to less than 0.25. If the ratio (B/A) is less than 0.25, the silica component in the surface layer of the composite oxide particles increases, and the formation of the outer shell becomes easy. As a result, even if elements other than silicon are removed in the fourth step described below, the shape of the composite oxide particles is not destroyed, and hollow silica particles can be stably obtained. If the ratio (B/A) is 0.25 or more, it is difficult to form an outer shell containing a large amount of silica components, so that the composite oxide particles are destroyed when elements other than silicon are removed in the fourth step, making it difficult to maintain the particle shape. For this reason, there is a risk that it may be difficult to obtain hollow silica particles. The ratio (B/A) is more preferably 0.20 or less, and even more preferably 0.15 or less.

The average particle diameter of the composite oxide particles b prepared in the third step is not particularly limited. However, if the final particles are to be used as a resist material, it is preferable to prepare the average particle diameter (Db) to be 15 to 55 nm. By preparing the particles in this range, it is easy to adjust the average particle diameter of the particles to the desired size.

Here, if the average particle size (Db) is less than 15 nm, the porosity of the particles will be low, and it may be difficult to obtain a resist film with a low refractive index. Conversely, if it exceeds 55 nm, the particle size will be large, and it may be difficult to form a sharp pattern. The average particle size (Db) is preferably 20 to 50 nm, and more preferably 25 to 45 nm.

In addition, it is preferable to prepare the value (Dc) obtained by subtracting the average particle diameter (Da) of the composite oxide particles a from the average particle diameter (Db) of the composite oxide particles b prepared in the third step and dividing the result by 2 to be 3 to 9 nm. By preparing it in such a range, it becomes easy to adjust the thickness of the outer shell of the desired particles.

Here, if the value (Dc) is less than 3 nm, the resulting shell may be too thin, making it difficult to maintain the particle shape. Conversely, if the particle is more than 9 nm, the refractive index may not be sufficiently low, making it difficult to obtain the desired resist film. The value (Dc) is more preferably 3 to 7 nm, and even more preferably 3 to 6 nm.

The ratio (Dc/Db) is preferably 0.05 to 0.35. If this ratio is in this range, a resist film with a low refractive index can be obtained.

If this ratio is less than 0.05, it may be difficult to obtain the strength required to maintain the particle shape, and therefore difficult to obtain the particles themselves. Conversely, if the ratio exceeds 0.35, the refractive index may not be sufficiently low, and it may be difficult to obtain the desired resist film. The ratio (Dc/Db) is more preferably 0.06 to 0.28, and even more preferably 0.07 to 0.20.

In the third step, an electrolyte salt may be added to the dispersion of composite oxide particles a.

Specific examples of electrolyte salts include water-soluble electrolyte salts such as sodium chloride, potassium chloride, sodium nitrate, potassium nitrate, sodium sulfate, potassium sulfate, ammonium nitrate, ammonium sulfate, magnesium chloride, and magnesium nitrate.

By adding the electrolyte salt, it becomes easier for an outer shell to form when elements other than silicon are removed in the fourth step. The mechanism by which this effect is achieved is unclear, but it is thought that silica increases on the surface of the grown composite oxide particles, and that the acid-insoluble silica acts as a protective film for the composite oxide particles.

The amount of electrolyte salt added is preferably such that the ratio (ME/MS) is 10 or less, where _ME is the number of moles of the electrolyte salt and _MS is the number of moles of the _silicon -containing compound used in the third _step expressed as _SiO2 .

Here, even if the ratio ( _ME / _MS ) is made larger than 10, the effect of adding the electrolyte salt is not improved, and the electrolyte salt acts as a buffer, which may impair particle growth in the third step or require time to remove elements other than silicon in the fourth step, resulting in a risk of reduced production efficiency. Although the lower limit of the ratio ( _ME / _MS ) is not particularly set, in order to obtain the effect of adding the electrolyte salt, it is preferable that the ratio ( _ME / _MS ) is 0.1 or more. The electrolyte salt may be added in its entirety at the start of the third step, or may be added continuously or intermittently while adding the solution of the compound containing silicon and the aqueous solution of the compound of an inorganic element other than silicon that is alkali-soluble.

The dispersion of composite oxide particles a used in this process preferably has a pH of 10 or higher.

The concentration of the solution of the "silicon-containing compound" and the concentration of the aqueous solution of the "alkali-soluble compound of inorganic elements other than silicon" are preferably 0.05 to 3.0 mass % as SiO ₂ and MOx, respectively. When the concentrations are within this range, adhesion and aggregation of particles are suppressed, and monodisperse particles can be obtained.

When adding the solutions in this step, it is preferable that the pH of the reaction system is 10 or higher, and the temperature is 50 to 98°C. If the pH and temperature are within this range, the addition of the "solution of a compound containing silicon" and the "aqueous solution of an alkali-soluble compound of an inorganic element other than silicon" allows the composite oxide particles b to grow efficiently. The pH is more preferably 10.5 or higher, and even more preferably 10.5 to 13. The temperature is more preferably 65 to 98°C, and even more preferably 80 to 98°C.

[Fourth step]
In this step, an acid is added to the dispersion of composite oxide particles b to remove at least a portion of the elements other than silicon that constitute the composite oxide particles b, thereby preparing a dispersion of silica-based particles. The elements are removed, for example, by dissolving them using a mineral acid or an organic acid, by contacting them with a cation exchange resin to remove them by ion exchange, or by a combination of these methods.

The concentration of the dispersion of composite oxide particles b varies depending on the treatment temperature, but is preferably 0.1 to 30 mass % of composite oxide particles b converted into oxide.

Here, if the concentration is less than 0.1% by mass, the amount of dissolved silica will be large, which may make it difficult to maintain the shape of the composite oxide particles. In addition, the low concentration will result in low processing efficiency. Conversely, if the concentration is higher than 30% by mass, the particles may not be sufficiently dispersible. In addition, in composite oxide particles that contain a large amount of elements other than silicon, it may be difficult to remove elements other than silicon uniformly or efficiently. The concentration of the dispersion of composite oxide particles b is more preferably 0.5 to 25% by mass.

The removal of the above elements is preferably carried out until the molar ratio (MOx/SiO ₂ ) of the resulting particles becomes 0.03 or less.

Here, if the molar ratio (MOx/ _SiO2 ) is greater than 0.03, the refractive index of the hollow silica particles finally obtained may not be sufficiently low, or it may be difficult to obtain the strength required to maintain the particle shape. The molar ratio (MOx/ _SiO2 ) is more preferably 0.01 or less.

In this step, an electrolyte salt may be added in the same manner as in the third step. The amount of the electrolyte salt added is preferably 10 or less as a ratio (M _E /M _S ) in the same manner as in the third step. The electrolyte salt may be added in its entirety at the start of the fourth step, or may be added continuously or intermittently when removing at least a part of the elements other than silicon. However, the amount of electrolyte salt added in the fourth step is such that the total amount of the third and fourth steps is within the above range unless the electrolyte salt is removed in the third step.

The dispersion of silica-based particles from which at least some of the elements other than silicon have been removed can be washed by a known washing method such as ultrafiltration as necessary. At least some of the dissolved elements other than silicon are removed by washing. In this case, if some of the alkali metal ions, etc. in the dispersion are first removed before ultrafiltration, a dispersion of silica-based particles with high dispersion stability can be obtained.

This dispersion "from which at least some of the elements other than silicon have been removed" can also be contacted with at least one of a cation exchange resin and an anion exchange resin to remove some of the dissolved elements other than silicon or alkali metal ions, etc. When washing, heating the solution can be used for effective washing.

By washing in this manner, the content of impurities such as alkali metals in the particles obtained by heat treating the silica-based particles in the fifth step can be effectively reduced. The content of these impurities corresponds to the content of the impurities in the particles described above.

If the impurity content in the silica-based particles is within the range of impurities in the particles described above, there is no need to perform washing in this process.

[Fifth step]
In this step, the dispersion liquid of the silica-based particles is heated to 60 to 200°C at a heating rate of 3.0°C/min or less, and then cooled to less than 50°C.

In this way, the dispersion of silica-based particles is heated to dissolve the silicon from the silica-based particles. The dispersion is then cooled to fix the dissolved silicon to the silica-based particles, thereby obtaining the particles of the present invention. The rate of heating, the heating temperature, and the cooling temperature are some of the major factors in obtaining the desired "refractive index" and "number density of silanol groups on the particle surface calculated by the Sears measurement method" of the particles of the present invention.

Here, if the heating rate is faster than 3.0°C/min, the silicon content on the particle surface may dissolve rapidly, causing the hollow particle shape to collapse and making it difficult to obtain low refractive index particles. There is no particular lower limit for the heating rate, but it is, for example, 0.3°C/min. If the heating rate is extremely slow, it may take too long to heat up to the target temperature, resulting in low production efficiency. The heating rate is preferably 0.5 to 2.8°C/min, more preferably 0.8 to 2.5°C/min.

Next, if the heating temperature is less than 60°C, the silicon content in the particles will not dissolve sufficiently, and the particles may not be fixed in their hollow particle shape. Conversely, if the temperature exceeds 200°C, the silicon content in the particles will dissolve excessively, and the hollow shape may collapse as the outer shell is reduced, or the number density of silanol groups on the particle surface may become insufficient. After heating to the target temperature, the temperature may be lowered, but for stable production, it is preferable to maintain that temperature for 30 minutes or more. Heating is preferably performed at 70 to 180°C, more preferably 80 to 160°C.

After heating the dispersion liquid, the temperature is lowered to less than 50°C. Lowering the temperature to less than 50°C makes it easier to fix the dissolved silicon to the silica-based particles. The temperature may be lowered to room temperature to make handling easier.

The particle dispersion thus obtained satisfies the particle properties described above. Furthermore, when these particles are used in a resist film, a low refractive index and excellent developability can be achieved.

[Surface treatment of particles]
In the present invention, after the fifth step, an organosilicon compound may be added to surface-treat the particles. As the organosilicon compound to be used, it is preferable to use an organosilicon compound represented by the above formula (8) in which n is 1 to 3. Here, when an organosilicon compound in which n is 0 is used, it is preferable to use a partial hydrolyzate of the organosilicon compound. This allows the number density of silanol groups on the particle surface calculated by the Sears measurement method to be adjusted. In addition, the introduction of a functional group improves the compatibility between the particles and the resin component, which is preferable in terms of obtaining particles with high dispersibility in the coating solution and film. The organosilicon compounds may be used alone or in combination.

The method of surface treatment of particles is to first prepare a dispersion liquid of particles. As the dispersion medium, it is preferable to use alcohols such as methanol and ethanol. A predetermined amount of an organosilicon compound represented by formula (8) is added to the dispersion liquid, and the organosilicon compound is hydrolyzed. Water can be added to this hydrolysis as necessary. It is preferable that the ratio (Mw/Mo) of the number of moles of water (Mw) to the number of moles of the organosilicon compound (Mo) used is 1 or more.

Here, if the ratio (Mw/Mo) is less than 1, hydrolysis will be insufficient, and the transparency and haze of the coating may be insufficient. There is no particular upper limit to this ratio, but if this ratio exceeds 500, the hydrolysis reaction will become intense, and the organosilicon compounds may polymerize with each other, making it difficult to efficiently treat the particle surfaces. This ratio is more preferably 1 to 100.

In this hydrolysis, an acid or alkali can be used as a hydrolysis catalyst, if necessary. Among these, ammonia is preferred. This is because if ammonia is used, it is easy to remove even if it remains in the dispersion, and the stability of the dispersion is easily maintained. The ratio (M _N /Mo) of the number of moles of ammonia used (M _N ) to the number of moles of the organosilicon compound (Mo) is preferably in the range of 0.05 to 50.

If the ratio (M _N /Mo) is less than 0.05, the hydrolysis will be insufficient, and the transparency and haze of the coating may be insufficient. If this ratio exceeds 50, the hydrolysis reaction will be so vigorous that the organosilicon compounds may polymerize with each other, making it difficult to efficiently treat the particle surfaces. This ratio is more preferably 0.1 to 10.

The surface treatment is preferably carried out in a homogeneous system, and in order to promote the reaction between the particles and the organosilicon compound, it is preferable to heat the particles for 0.5 to 48 hours at a temperature below the boiling point of the dispersion medium (for example, room temperature to 120°C).

When particles whose surfaces have been chemically bonded to an organosilicon compound by this surface treatment are used in resist materials, the particles are highly dispersible in the film, making it easier to obtain sharp patterns.

Examples of organosilicon compounds include those shown in Table 1 above. These organosilicon compounds may be contained alone or in combination in the particles. In surface treatment, these organosilicon compounds can be used alone or in combination, and it is also possible to treat in stages with the same type, a mixture of multiple types, or multiple types separately.

The amount of this organosilicon compound is preferably 0.2 to 7.5 parts by mass in terms of solid content (R _n —SiO _(4−n)/2 ) per 100 parts by mass of the “original particles” before surface treatment.

If the amount is less than 0.2 parts by mass, it may be difficult to obtain the full effect of the addition. Conversely, if the amount is more than 7.5 parts by mass, the refractive index of the particles may increase, making it difficult to obtain particles with the desired refractive index. The amount of the organosilicon compound is more preferably 0.2 to 6.0 parts by mass, and even more preferably 0.2 to 4.5 parts by mass.

The amount of surface treatment is sufficient if the desired amount of organosilicon compound is reacted with the particle surface and the range of the carbon content of the finally obtained particles is satisfied. This carbon content varies depending on the structure and amount of the chemically bonded organosilicon compound. Here, when the raw material used to prepare the "original particles" before surface treatment does not depend on the organosilicon compound, and the organosilicon compound of formula (8) is used as a surface treatment agent for the "original particles", the above-mentioned carbon content of 0.1 to 3 mass% is approximately 0.2 to 7.5 parts by mass of the organosilicon compound as solid content (R _n -SiO _{(4-n) / 2} ) per 100 parts by mass of the "original particles". Of course, when an organosilicon compound is used to prepare the "original particles" and the carbon content is present in the "original particles", the carbon content is also added to the carbon content of the finally obtained particles. Therefore, the solid content amount of the organosilicon compound to be surface-treated to obtain the target carbon content of the particles of the present invention is reduced according to the carbon content of the "original particles" compared to the case of surface-treating "original particles not containing carbon".

The physical properties and preferred ranges of the final particles and their dispersion are the same as those of the particles and their dispersion described above.

[Coating liquid for film formation]
The particles of the present invention can be applied to a coating liquid for forming a film. The coating liquid contains the particles, a matrix-forming component, and a dispersion medium. The dispersion medium contains at least one of water and an organic dispersion medium. In addition, the composition may contain additives such as a polymerization initiator, a leveling agent, and a surfactant.

The concentration of particles in the coating solution is preferably 5 to 95% by mass as solids based on the total amount of solids such as the particles and matrix-forming components contained. If the particle concentration is less than 5% by mass, it may be difficult to sufficiently reduce the refractive index of the coating. Conversely, if it is more than 95% by mass, cracks may occur in the coating, the surface irregularities may become large, it may be difficult to obtain a sharp pattern, and transparency and haze may deteriorate. The particle concentration is more preferably 20 to 90% by mass, and even more preferably 35 to 85% by mass.

The matrix-forming component preferably contains an alkali-soluble group.

Examples of such alkali-soluble groups include hydroxyl groups, phenolic hydroxyl groups, carboxyl groups, fluorinated alcohol groups, sulfonimide groups, bis(alkylcarbonyl)methylene groups, and alkylene oxide groups.

Matrix-forming components containing alkali-soluble groups include, for example, polycondensates of organosilicon compounds, ultraviolet-curable resins, thermosetting resins, and thermoplastic resins.

Here, examples of UV-curable resins include (meth)acrylic resins, urethane resins, vinyl resins, etc.

Thermosetting resins include urethane resin, melamine resin, silicon resin, butyral resin, reactive silicone resin, phenolic resin, epoxy resin, unsaturated polyester resin, and thermosetting acrylic resin.

Thermoplastic resins include polyester resin, polycarbonate resin, polyamide resin, polyphenylene oxide resin, thermoplastic acrylic resin, polyvinyl chloride resin, fluororesin, vinyl acetate resin, silicone rubber, etc.

These resins may be copolymers or modified products of two or more kinds, or may be used in combination. These resins may also be emulsion resins, water-soluble resins, or hydrophilic resins.

The components that form these resins are preferably monomers or oligomers, due to their particle dispersibility and ease of coating.

The concentration of the matrix-forming components in the coating solution is preferably 5 to 95% by mass in terms of solid content relative to the total amount of solid content, such as the particles and matrix-forming components, contained therein.

Here, if the concentration of the matrix-forming component is less than 5% by mass, it is difficult to form a coating. Even if a coating is obtained, there is a risk that cracks will occur in the coating, the surface irregularities will become large, it will be difficult to obtain a sharp pattern, and the transparency and haze will deteriorate. Conversely, if it is more than 95% by mass, the amount of particles will be small, making it difficult to sufficiently reduce the refractive index. The concentration of this matrix-forming component is more preferably 10 to 80% by mass, and even more preferably 15 to 65% by mass.

As the organic dispersion medium, one that can disperse particles uniformly and dissolve or disperse additives such as matrix-forming components and polymerization initiators is used. Among them, hydrophilic dispersion media and polar dispersion media are preferred. As shown in Table 2, examples of hydrophilic dispersion media include alcohols, esters, glycols, and ethers. Examples of polar dispersion media include esters, ketones, and aprotic dispersion media. These may be used alone or in a mixture of two or more.

Any additive that can be used conventionally for film formation can be used. For example, polymerization initiators, leveling agents, etc. are used to promote polymerization of the matrix-forming components and improve film-forming properties.

Examples of polymerization initiators include those shown in Table 3.

Examples of leveling agents include acrylic leveling agents, silicone leveling agents, fluorine-based leveling agents, nonionic leveling agents, cationic leveling agents, and anionic leveling agents. These may be used alone or in combination of two or more. The content of the leveling agent is preferably 0.001 to 1.0 mass% based on 100 mass% of the nonvolatile components of the dispersion. By containing a leveling agent in this range, it becomes easier to obtain a film with excellent coatability and small surface unevenness.

For the sake of convenience, the concentrations of these additives in the coating solution that are contained as solids when the coating is formed are counted as matrix-forming components, and after coating, they are counted as the matrix.

The solids concentration of the coating solution (the ratio of the total solids of the particles and the matrix-forming components to the coating solution) is preferably 0.1 to 60% by mass.

If the solids concentration of the coating solution is less than 0.1% by mass, it may be difficult to obtain the desired film thickness, or the production of the coated substrate may take time, resulting in reduced productivity. Conversely, if it is more than 60% by mass, the stability of the coating solution may decrease. In addition, the viscosity of the coating solution may increase, resulting in reduced applicability. The solids concentration of the coating solution is more preferably 1 to 50% by mass.

[Coated substrate]
The coating solution is used to form a coating on a substrate.

Specifically, the coating liquid is applied onto a substrate, and then dried to form a film on the substrate. This film is then irradiated (exposed) to ultraviolet light or the like, and developed to form a pattern in the desired shape. For pattern formation, a wet etching process is preferably used.

There are no particular limitations on the method of applying the coating liquid, so long as it can form a coating on the substrate. For example, well-known methods such as spraying, spin coating, roll coating, dip coating, and bar coating can be used. Drying is performed by heating to, for example, about 50 to 150°C, and evaporating and removing the dispersion medium. Exposure is performed through a mask. Examples of actinic rays or radiation that can be used for this exposure include infrared light, g-rays, h-rays, i-rays, KrF light, ArF light, X-rays, and electron beams. Thereafter, a pattern is formed on the exposed parts of the coating using an alkaline developer. The coating is mainly formed of particles and a matrix.

In the case of a coating, the ratio of particles to solids of the matrix-forming components in the coating liquid is the same as the ratio of particles to matrix in the coating. As mentioned above, any additives in the coating liquid that remain as solids are counted as matrix.

For example, the thickness of the coating is preferably 50 to 250 nm for an anti-reflective coating, and 500 nm to 5 μm for a resist coating.

The alkaline developer may be either an inorganic or organic alkaline compound.

Examples of inorganic alkaline compounds include sodium hydroxide, potassium hydroxide, sodium silicate, potassium silicate, sodium carbonate, potassium carbonate, and ammonia. Examples of organic alkaline compounds include tetramethylammonium hydroxide, 2-hydroxyethyltrimethylammonium hydroxide, monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoisopropylamine, diisopropylamine, and ethanolamine. These inorganic and organic alkaline compounds may be used alone or in combination of two or more. The concentration of the alkaline compound in the alkaline developer is preferably 0.01 to 5% by mass.

The refractive index of the coating is preferably 1.15 to 1.38.

Here, it is difficult to obtain a coating with a refractive index of less than 1.15. Conversely, if the refractive index exceeds 1.38, the coating may not achieve a sufficiently low refractive index, although this will depend on the refractive index of the substrate or the refractive index of other films formed below the coating if necessary. The refractive index of the coating is more preferably 1.15 to 1.34, and even more preferably 1.15 to 1.30.

The light transmittance of the coated substrate is preferably 80.0% or more. If the light transmittance is less than 80.0%, the coating may harden unevenly or insufficiently, making it difficult to obtain high developability during pattern formation. This light transmittance is more preferably 85.0% or more, and even more preferably 90.0% or more.

The haze of the coated substrate is preferably 1.5% or less, more preferably 1.2% or less, and even more preferably 0.8% or less.

In addition, the surface irregularities of the pattern on the coated substrate are preferably less than 5 nm.

Here, if the surface unevenness is 5 nm or more, it may be difficult to obtain a sharp pattern by development. This surface unevenness is more preferably less than 4 nm, and even more preferably less than 3 nm.

In addition, it is preferable that the linearity of the pattern on the coated substrate is such that no jagged edges are observed at the pattern edges. Here, if jagged edges are present at the pattern edges, this may adversely affect the circuit pattern in subsequent processes or cause crosstalk between patterns.

It is also preferable that there be no residue from the silica particles on the coated substrate. If residue is present on the substrate, it may adversely affect the circuit pattern in a later process or cause crosstalk between patterns.

The following describes an embodiment of the present invention.

[Example 1]
<Preparation of Particle Dispersion>
A sodium aluminate aqueous solution having an _Al2O3 concentration of 22 mass% was added to pure water to prepare 10.0 kg of a _sodium aluminate aqueous solution having _{an Al2O3} concentration of 6.0 mass% and a pH of 12.6. (First Step)

Next, this was heated to 80°C, and 30.0 kg of a sodium silicate aqueous solution having a _SiO2 concentration of 1.5 mass% and 30.0 _kg of a sodium aluminate aqueous solution having an _Al2O3 concentration of 0.5 mass% were added simultaneously. After that, washing was performed by centrifugal sedimentation to obtain a dispersion of composite oxide particles (a1). The average particle diameter of the composite oxide particles was 32 nm. (Second step)

The dispersion of the composite oxide particles (a1) was heated to 95°C, and 120.0 kg of an aqueous sodium silicate solution having a _SiO2 concentration of 1.5 mass% and 40.0 kg of an aqueous sodium _{aluminate solution having an Al2O3 concentration} of 0.5 mass% were added simultaneously. The mixture was then washed using an ultrafiltration membrane to adjust the solid content to 13 mass%. The mixture was then filtered using a capsule filter with a mesh size of 1 μm to obtain a dispersion of the composite oxide particles (b1). The average particle size of the composite oxide particles was 42 nm. (Third step)

11,250 g of pure water was added to 5,000 g of the dispersion of composite oxide particles (b1), and concentrated hydrochloric acid (concentration 35.5% by mass) was added dropwise to adjust the pH to 1.0. 10 L of an aqueous hydrochloric acid solution with a pH of 3 and 5 L of pure water were added to the dispersion, and the dissolved aluminum salt was separated and washed using an ultrafiltration membrane to obtain silica-based particles (c1) with a concentration of 10% by mass. (Fourth step)

Next, ammonia water was added to 500 g of the dispersion of silica-based particles (c1) to adjust the pH of the dispersion to 10.5, and the dispersion was transferred to a pressure-resistant container. Next, the dispersion was heated to 140°C at a heating rate of 1.5°C/min and held for 10 hours, and then cooled to 25°C. (Fifth step)

Then, ion exchange was performed for 3 hours using 800 g of a cation exchange resin (Diaion SK1B, manufactured by Mitsubishi Chemical Corporation), and then ion exchange was performed for 3 hours using 400 g of anion exchange resin (Diaion SA20A, manufactured by Mitsubishi Chemical Corporation). After that, ion exchange was further performed for 3 hours at 80°C using 400 g of a cation exchange resin (Diaion SK1B, manufactured by Mitsubishi Chemical Corporation) and washing was performed to obtain an aqueous dispersion of particles (d1).

The solvent in the aqueous dispersion of particles (d1) was replaced with methanol using an ultrafiltration membrane to produce a methanol dispersion of particles (P1) with a solids concentration of 20% by mass.

<Surface treatment of particles with organosilicon compounds>
To 200 g of the methanol dispersion of the particles (P1), 0.4 g of 28% by mass ammonia water and 4.0 g of pure water were added, and the mixture was stirred at room temperature for 0.5 hours.

Next, 1.2 g of γ-methacryloxypropyltrimethoxysilane (KBM-503, manufactured by Shin-Etsu Chemical Co., Ltd.) was added as an organic silicon compound and stirred at 50°C for 6 hours to obtain a dispersion of particles (S1) in which the particles (P1) were surface-treated. The solvent was replaced with methanol using an ultrafiltration membrane to produce a methanol dispersion of particles (S1) with a solids concentration of 20% by mass.

The dispersion medium of the methanol dispersion of the particles (S1) was replaced with propylene glycol monomethyl ether (PGME) in an evaporator to obtain a PGME dispersion of the particles (S1) with a solid content concentration of 20.5% by mass. This was used to manufacture a coating liquid for forming a resist film, which will be described later.

The particles and their dispersions were measured using the following methods.

The characteristics of each manufacturing process of the particles, and the properties of the particles and dispersion liquid are shown in Tables 4 to 7 (the same applies to the following examples and comparative examples).

(1) Volume of sediment obtained by centrifugation The particle dispersion was heated to 110°C and held for 3 hours to dry. The particle density (ρ _P ) of 3.0 g of the obtained powder was measured using a dry automatic density meter (AccuPic II 1340, manufactured by Micromeritics Co., Ltd.). N ₂ was used as the measurement gas. The mass % concentration (W _P %) of the particles in a 15 volume % dispersion of the particles is calculated by the formula (12).

V _P = W _P %/ρ _P ...Formula (9)
V _S = W _S %/ρ _S = (100-W _P %)/ρ _S ...Formula (10)
V _P %=V _P /(V _P +V _S )×100...Formula (11)
(In the formula, _Vp is the volume of the particles ( ^cm3 /g), _Vs is the volume of the dispersion medium ( ^cm3 /g), and _Ws % is the mass of the dispersion medium that provides a 15% by volume dispersion of the particles. % concentration (=85) (g), and _ρS indicates the density of the dispersion medium (g/cm ³ ).

From the formulas (9), (10), and (11), if V _P %=15,
W _P %=-(1500/ρ _S )/{[(-85)/ρ _P ]-(15/ρ _S )}...Equation (12)

A particle dispersion was prepared so as to have a mass % concentration ( _WP %) of the particles obtained by formula (12). The obtained dispersion was centrifuged for 30 minutes using a small ultracentrifuge (CS150GXL manufactured by Hitachi Koki Co., Ltd.) at a temperature of 10°C and a rotation speed of 1,370,000 rpm (1,000,000 G). The volume of the sediment in the treatment liquid was measured, and the ratio of the volume of the sediment to the volume of the particles in the dispersion before centrifugation was calculated.

(2) Average particle diameter (D), shell thickness, average particle diameter (Da) of composite oxide particles a, and average particle diameter (Db) of composite oxide particles b
The particle dispersion was diluted to 0.01% by mass, and then dried on a collodion film of a copper cell for an electron microscope. Then, the dispersion was photographed at a predetermined magnification using a field emission transmission electron microscope (HF5000 manufactured by Hitachi High-Technologies Corporation). The particle area of 300 random particles in the obtained photographic projection (TEM photograph) was calculated by image processing, and the circle equivalent diameter was calculated from the area. The average value of the circle equivalent diameters was taken as the average particle diameter (D) of the particles.

In addition, for these 300 randomly selected particles, image processing was performed to determine the area of the cavity of the particle, and the equivalent circle diameter was calculated from the area. This was then subtracted from each particle diameter, and the average value obtained by dividing by 2 was used as the thickness of the outer shell.

Furthermore, the average particle diameter (Da) of composite oxide particles a and the average particle diameter (Db) of composite oxide particles b were determined in the same manner as the average particle diameter (D) of the particles.

(3) Particle size coefficient of variation (CV value)
It was determined from the following formula: The individual particle sizes and average particle size used in determining the CV value were those determined from the TEM photographs taken when determining the average particle size (D) of the particles described above.

(4) Number Density of Silanol Groups on Particle Surface The number density of silanol groups on a particle is calculated from the Sears number and the specific surface area. Specifically, it is determined by the above-mentioned formulas (1) and (2).

The Sears number is measured by titration with sodium hydroxide according to the description in Analytical Chemistry 28 (1956), 12, 1981-1983 by Sears. Specifically, the methanol dispersion of the particles is solvent-substituted with water using an evaporator, and the aqueous dispersion of the particles is diluted with pure water so that the silica particle concentration becomes 1% by mass. 30 g of sodium chloride is added to 150 g of the diluted solution, and the pH is adjusted to 4.0 with hydrochloric acid. Then, 0.1 N aqueous sodium hydroxide solution is titrated at 0.1 ml/sec., and the amount of aqueous sodium hydroxide required to reach a pH of 9.0 is expressed (i.e., the Sears number is the amount of 0.1 N aqueous NaOH solution titrated to 1.5 g of particles). The titration of the 0.1 N aqueous NaOH solution was performed using an automatic titrator with a fixed titration speed of 0.1 ml/sec.

The specific surface area is measured using the BET method with nitrogen adsorption. The measurement sample was a powder made by drying an aqueous dispersion of particles at 105°C.

(5) Refractive index The particle dispersion liquid was taken in an evaporator and the dispersion medium was evaporated. Next, this was vacuum dried at 120°C for 24 hours to obtain a particle powder. A few drops of a standard refractive index liquid with a known refractive index were dropped onto a glass plate, and the above powder was mixed therein. This operation was performed with various standard refractive index liquids, and the refractive index of the standard refractive index liquid when the mixed liquid became transparent was taken as the refractive index of the particles.

(6) Density of particles by helium gas and density by nitrogen gas The particle dispersion was heated to 110°C and kept for 3 hours to dry. The density of 3.0 g of the obtained powder was measured using a dry automatic density meter (AccuPic II 1340, manufactured by Micromeritics Co., Ltd.). At this time, He and _N2 were used as the measurement gas, and the density in each measurement gas was measured.

(7) Particle Shape The appearance of 300 randomly selected particles in the TEM photograph taken when determining the average particle diameter (D) of the above-mentioned particles was observed.

(8) Sphericity of Particles For 300 randomly selected particles in the TEM photograph taken when determining the average particle diameter (D) of the above-mentioned particles, the ratio of the maximum diameter of each particle to the minor axis perpendicular thereto was determined, and the average value thereof was regarded as the sphericity of the particles.

(9) Cavity shape inside the particle shell, the number ratio of particles with one cavity, and the number ratio of solid particles The shape of the cavity inside the particle shell was observed for 300 random particles in the TEM photograph taken when determining the average particle diameter (D) of the above-mentioned particles, and the number ratio of particles with one cavity was calculated. The number ratio of solid particles was also calculated.

(10) Particle porosity and density (Sd)
The area of the hollow part of the particle was determined for 300 arbitrary hollow particles in the TEM photograph taken when determining the average particle diameter (D) of the above-mentioned particles, and the circle equivalent diameter was calculated from the area, and the average value of the circle equivalent diameter was taken as the average cavity diameter. The shape of the particle and the cavity was assumed to be a perfect sphere, and the average volume of the particle and the average volume of the cavity were determined, and the porosity was calculated as the ratio of the average volume of the cavity to the average volume of the particle. In addition, the density of the particle (Sd) was determined from the obtained porosity, the ratio of the constituent components of the particle, and its density.

(11) Specific Surface Area by BET Method The specific surface area was calculated from the amount of adsorbed nitrogen by the BET method using a specific surface area measuring device (Multisorb 12, manufactured by Yuasa Ionics Co., Ltd.).

(12) Specific surface area (A1) by pulsed NMR
The methanol dispersion of the particles was subjected to solvent replacement with water using an evaporator to prepare an aqueous dispersion with a silica particle concentration of 10.0% by mass. The relaxation times of the dispersion and the dispersion medium were measured using a pulse NMR (Acorn Area manufactured by Xigo nanotools), and the specific surface area (A1) was calculated from the above-mentioned formulas (3) and (4). The measurement conditions were a magnetic field of 0.3 T, a measurement frequency of 13 MHz, a measurement nucleus of ¹ H NMR, a measurement method of CPMG pulse sequence method, a sample amount of 1 ml, a Ka value of 0.000027, and a temperature of 25 ° C. Here, the Ka value was calculated by performing a pulse NMR measurement at 25 ° C. for the aqueous dispersion and the aqueous dispersion medium in which the solid content concentration was adjusted to 10.0% by mass by replacing the solvent of the methanol dispersion of the particles (P1) with water using an evaporator, and calculating the Ka value according to the above-mentioned formulas (5) to (7).

(13) Specific surface area (A2)
The specific surface area (A2) was calculated using the average particle diameter (D) and density (Sd) of the particles according to the above formula (5).

(14) Ratio of the area of the peak representing the Q4 structure by ^29Si -NMR analysis of particles A dispersion of particles is placed in a dedicated zirconia sample tube, and measured by a single pulse non-decoupling method using a probe for a solid 6 mmφ sample tube of an NMR device (VNMRS-600, manufactured by Agilent Corp.) without sample rotation. Polydimethylsiloxane is used as a secondary standard, and the chemical shift is set to -34.44 ppm. The spectrum obtained is subjected to waveform separation using analysis software Origin, and the area of each peak is calculated. More specifically, (Q4/ΣQ) ^{×100 was calculated} for the areas of the peaks appearing at chemical shifts of −78 to −88 ppm ( _Q1 ), −88 to −98 ppm ( _Q2 ), −98 to −108 ppm ( _Q3 ), and −108 to −120 ppm ( _Q4 ) in _29Si -NMR spectroscopy, where ΣQ= _Q1 + _Q2 + _Q3 + _Q4 .

(15) Functional Groups Contained in the Outer Shell of Particles The presence or absence of functional groups contained in the outer shell of particles and the types thereof were determined by the following method.

First, the dispersion was dried in an evaporator and then dried at 150 ° C. The dried powder was measured by a diffuse reflectance method using a Fourier transform infrared spectrometer (FT-IR) (FT / IR-6100 manufactured by JASCO Corporation) in a wave number region of 700 cm ^-1 to 4000 cm ^-1 , a TGS detector, a resolution of 4.0 cm ^-1 , and an accumulation count of 50 times, and the peak was detected. The functional group was identified by referring to the organic compound spectrum database SDBS (https://sdbs.db.aist.go.jp (National Institute of Advanced Industrial Science and Technology, 2021.01)).

(16) Carbon Content The dispersion was centrifuged for 30 minutes using a small ultracentrifuge (CS150GXL manufactured by Hitachi Koki Co., Ltd.) at a temperature of 10° C. and a rotation speed of 1,370,000 rpm (1,000,000 G). The precipitate in the treatment solution was collected and vacuum dried at 120° C. for 24 hours to obtain a particle powder. The carbon content of the particles in this powder was measured using a carbon-sulfur analyzer (CS844 manufactured by LECO Japan Co., Ltd.).

(17) Content of metal elements, alkali metals, and alkaline earth metals The content of metal elements (Si, Al, As, B, Bi, Cd, Co, Fe, Ga, Ge, In, Pb, Sb, Sn, Ti, V, Zn, and Zr) in the particles, and the content of impurity elements such as Pd, Ag, Mn, Mo, Ni, Cr, U, Th, alkali metals, and alkaline earth metals were measured by dissolving the particles in hydrofluoric acid, heating to remove hydrofluoric acid, adding pure water as necessary, and measuring the resulting solution using an ICP inductively coupled plasma optical emission spectrometer (ICPM-8500 manufactured by Shimadzu Corporation). The content of impurity elements in the table is based on the highest content value in each group that specifies the content. Note that, for metal elements other than the above impurity elements, the total amount of metal elements other than carbon contained in the particles was calculated to be 100 parts by mass on an oxide basis.

(18) Solid content of organosilicon compound having functional group The dispersion was centrifuged for 30 minutes using a small ultracentrifuge (CS150GXL manufactured by Hitachi Koki Co., Ltd.) at a temperature of 10°C and a rotation speed of 1,370,000 rpm (1,000,000 G). The precipitate of the treatment liquid was collected and vacuum dried at 120°C for 24 hours to obtain a particle powder. The mass loss of this powder before and after heating at 500°C was measured using a thermogravimetric differential thermal analyzer (TG/DTA EXSTAR6000 MSD manufactured by Hitachi High-Tech Science Co., Ltd.), and the silicon content derived from the organosilicon compound was calculated from the difference with the original particle amount. Next, this was converted from the structure of the organosilicon compound used in the surface treatment into the amount of solid content (R _n -SiO _(4-n)/2 ) derived from the organosilicon compound, and the solid content of the organosilicon compound having a functional group was calculated.

<Production of Coating Solution for Forming Resist Film>
73.4 g of PGME, 3.0 g of an alkali-soluble UV-curable acrylic polymer (Acrit 8KQ-2001, manufactured by Taisei Fine Chemical Co., Ltd., solid content concentration 40.0% by mass), 0.05 g of 2,2-dimethoxy-1,2-diphenylethan-1-one (Omnirad 651, manufactured by IGM RESINS B.V.), 0.05 g of bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Omnirad 819, manufactured by IGM RESINS B.V.), and 0.1 g of a fluorine-based leveling agent (Megafac RS-90, manufactured by DIC Corporation, solid content concentration 10% by mass) were mixed. Next, 23.4 g of the PGME dispersion of the particles (S1) was mixed with this to prepare a coating solution for forming a resist film with a solid content concentration of 6 mass %.

<Production of Resist-Coated Substrate>
The resist film-forming coating liquid was applied to a 2-inch square glass substrate (#1737, manufactured by Corning Incorporated) using a spin coater, dried at 80°C for 1 minute, and then cured by irradiating with an ArF excimer laser (193 nm) through a photomask (5 μm line & space pattern) using an exposure device (NSR-S302, manufactured by Nikon Corporation). Thereafter, a 0.3 mass % aqueous solution of tetramethylammonium hydroxide (TMAH) was sprayed to dissolve and remove the unexposed portions, and the substrate was heated at 150°C for 5 minutes to produce a substrate with a resist coating.

The coated substrates were measured for the following items. The results are shown in Table 8 (the same applies to the following Examples and Comparative Examples). In order to make it easier to compare performance, the type of substrate, the ratio of particles and matrix in the coating, and the coating thickness were the same for each Example and Comparative Example.

(19) Film Thickness and Refractive Index of Coating Film thickness and refractive index of the coated substrate were measured using an ellipsometer (EMS-1 manufactured by ULVAC). The refractive index was evaluated according to the following classification.
Evaluation criteria for refractive index of coating:
◎: 1.30 or less ○: 1.31 to 1.34
△: 1.35-1.38
×: 1.39 or more

(20) Total Light Transmittance and Haze The total light transmittance and haze of the coated substrate were measured using a haze meter (NDH-5000, manufactured by Nippon Denshoku Industries Co., Ltd.) and were evaluated according to the following classification.
Evaluation criteria for total light transmittance:
◎: 90% or more ○: 85-89%
△: 80-84%
×: 79% or less Haze evaluation criteria:
◎: 0.8% or less ○: 0.9-1.2%
△: 1.3-1.5%
×: 1.6% or more

(21) Surface Unevenness of a Pattern of a Coated Substrate The surface unevenness of a pattern of a coated substrate was measured by scanning the surface with an atomic force microscope (Dimension Icon, manufactured by Bruker Japan Co., Ltd.) under the conditions of contact mode, scan speed of 0.50 Hz, and scan size of 20 μm×20 μm. The surface roughness was evaluated by classifying it as follows.
Evaluation criteria:
◎: Less than 3 nm ○: 3 nm or more and less than 4 nm △: 4 nm or more and less than 5 nm ×: 5 nm or more

(22) Linearity of the pattern on the coated substrate and residues The linearity of the pattern edge and residues derived from silica particles on the substrate were evaluated from photographic projection images (SEM images) taken with an optical microscope and a field emission scanning electron microscope (S-5500, manufactured by Hitachi High-Technologies Corporation). These were classified and evaluated as follows:
Pattern linearity evaluation criteria:
⊚: No jagged edges are observed on the pattern edge. ◯: Jagged edges are partially observed on the pattern edge. ×: Jagged edges are observed throughout the pattern edge. Evaluation criteria for residue:
◎: No residue was found on the substrate. ○: Residue was found in some areas on the substrate. ×: Residue was found over the entire substrate.

[Example 2]
A PGME dispersion of particles was produced, and a coating liquid and a coated substrate were produced in the same manner as in Example 1, except that in the second step, 11.1 kg of the sodium silicate aqueous solution and 11.1 kg of the sodium aluminate aqueous solution were used, in the third step, 66.0 kg of the sodium silicate aqueous solution and 22.0 kg of the sodium aluminate aqueous solution were used, and in the fifth step, the temperature was increased to 80° C. at a rate of 0.3° C./min.

[Example 3]
A PGME dispersion of particles was produced, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that the concentration of the sodium _aluminate aqueous solution in terms of _Al2O3 in the first step was 5.0 mass%, the amount of the sodium silicate aqueous solution was 5.3 kg and the amount of the sodium aluminate aqueous solution was 5.3 kg in the second step, and the amount of the sodium silicate aqueous solution was 123.0 kg and the amount of the sodium aluminate aqueous solution was 41.0 kg in the third step.

[Example 4]
A PGME dispersion of particles was produced, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that the concentration of the sodium _aluminate aqueous solution in terms of _Al2O3 in the first step was 5.0 mass%, the amount of the sodium silicate aqueous solution was 1.6 kg and the amount of the sodium aluminate aqueous solution was 1.6 kg in the second step, the amount of the sodium silicate aqueous solution was 48.0 kg and the amount of the sodium aluminate aqueous solution was 16.0 kg in the third step, and the temperature increase rate in the fifth step was 0.3°C/min and the mixture was heated to 80°C.

[Example 5]
A PGME dispersion of particles was prepared, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that in the second step, 78.0 kg of the sodium silicate aqueous solution and 78.0 kg of the sodium aluminate aqueous solution were used, in the third step, 234.0 kg of the sodium silicate aqueous solution and 78.0 kg of the sodium aluminate aqueous solution were used, and in the fifth step, the temperature increase rate was 3.0°C/min, the solution was heated to 200°C, maintained at that temperature for 10 hours, and then cooled to 48°C.

[Example 6]
A PGME dispersion of particles was produced, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that the concentration of the sodium aluminate aqueous solution in terms of Al ₂ O ₃ in the first step was 14.0 mass%, the concentration of the sodium silicate aqueous solution in terms of SiO ₂ in the second step was 0.9 mass%, the addition amounts were 83.5 kg, and the sodium aluminate aqueous solution was 83.5 kg, and the sodium silicate aqueous solution in the third step was 204.0 kg and 68.0 kg, respectively.

[Example 7]
A PGME dispersion of particles was produced, and a coating liquid and a coated substrate were produced in the same manner as in Example 1, except that in the first step, the concentration of the sodium aluminate aqueous solution as Al ₂ O ₃ was 5.0 mass%, in the second step, the concentration of the sodium silicate aqueous solution as SiO ₂ was 0.9 mass% and the amount added was 6.3 kg, in the second step, the concentration of the sodium aluminate aqueous solution as Al ₂ O ₃ was 0.3 mass% and the amount added was 6.3 kg, and in the third step, the amount of the sodium silicate aqueous solution was 93.0 kg and the amount of the sodium aluminate aqueous solution was 31.0 kg.

[Example 8]
A PGME dispersion of particles was produced, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that the concentration of the sodium _aluminate aqueous solution in terms of _Al2O3 in the first step was 9.0 mass%, the amount of the sodium silicate aqueous solution was 50.2 kg and the amount of the sodium aluminate aqueous solution was 50.2 kg in the second step, and the amount of the sodium silicate aqueous solution was 183.0 kg and the amount of the sodium aluminate aqueous solution was 61.0 kg in the third step.

[Example 9]
A PGME dispersion of particles was produced, and a coating liquid and a coated substrate were produced in the same manner as in Example 1, except that in the second step, the amount of the sodium silicate aqueous solution was 89.0 kg, the amount of the sodium aluminate aqueous solution was 89.0 kg, in the third step, the amount of the sodium silicate aqueous solution was 234.0 kg, the amount of the sodium aluminate aqueous solution was 78.0 kg, and in the fifth step, the heating rate was 0.8° C./min.

[Example 10]
A PGME dispersion of particles was produced in the same manner as in Example 1, except that the heating temperature in the fifth step was set to 180°C, 4.0 g of γ-methacryloxypropyltrimethoxysilane was used as the organosilicon compound in the surface treatment of the particles, and stirring was performed at 50°C for 24 hours. A coating solution and a coated substrate were produced in the same manner as in Example 1.

[Example 11]
In the surface treatment of the particles, 3.0 g of γ-methacryloxypropyltrimethoxysilane was used as the organosilicon compound, and the mixture was stirred at 50° C. for 24 hours in the same manner as in Example 1, to produce a PGME dispersion of the particles, and to produce a coating solution and a coated substrate.

[Example 12]
A PGME dispersion of particles was prepared, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that in the fifth step, the heating rate was set to 0.6°C/min, the heating temperature was set to 70°C, and 0.12 g of γ-methacryloxypropyltrimethoxysilane was used as the organosilicon compound in the surface treatment of the particles.

[Example 13]
The concentration of sodium aluminate aqueous solution in the first step as Al ₂ O ₃ is 5.0 mass%, the sodium silicate aqueous solution is 3.1 kg, the sodium aluminate aqueous solution is 3.1 kg, and the sodium silicate aqueous solution is 79.5 kg, and the sodium aluminate aqueous solution is 26.5 kg in the third step. In addition, the pH of the dispersion after the concentrated hydrochloric acid is dropped in the fourth step is adjusted to pH 3.0, and while adding 7.0 L of hydrochloric acid aqueous solution of pH 3 and 3.5 L of pure water, the dissolved aluminum salt is separated and washed using an ultrafiltration membrane, and the heating rate in the fifth step is set to 0.8 ° C. / min and heated to 80 ° C., except that, the PGME dispersion of particles is produced in the same manner as in Example 1, and a coating liquid and a coated substrate are produced.

[Example 14]
A PGME dispersion of particles was prepared, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that tetraethoxysilane (ethyl orthosilicate ES28, manufactured by Tama Chemicals Co., Ltd.) was used as the organosilicon compound in the surface treatment of the particles.

[Example 15]
A PGME dispersion of particles was prepared, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that γ-acryloxypropyltrimethoxysilane (KBM-5103, manufactured by Shin-Etsu Chemical Co., Ltd.) was used as the organosilicon compound in the surface treatment of the particles.

[Example 16]
In the first step, a sodium _aluminate aqueous solution having an _Al2O3 concentration of 22% by mass and a sodium silicate aqueous solution having a _SiO2 concentration of 28% by mass were added to pure water to prepare 10.0 kg of an aqueous solution having _{an Al2O3 concentration} of 5.0% by mass and a _SiO2 concentration of 0.5% by mass. In the second step, the amount of the sodium silicate aqueous solution was 6.3 kg, and the amount of the sodium aluminate aqueous solution was 6.3 kg. In the third step, the amount of the sodium silicate aqueous solution was 150.0 kg, and the amount of the sodium aluminate aqueous solution was 50.0 kg. Except for this, a PGME dispersion of particles was produced, and a coating liquid and a coated substrate were produced in the same manner as in Example 1.

[Example 17]
A PGME dispersion of particles was produced, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that the amount of the sodium silicate aqueous solution in the second step was 1.4 kg, the amount of the sodium aluminate aqueous solution was 2.8 kg, and the amount of the sodium silicate aqueous solution in the third step was 68.0 kg, and the amount of the sodium aluminate aqueous solution was 36.0 kg.

[Example 18]
In the second step, 12.8 kg of sodium silicate aqueous solution and 12.8 kg of sodium aluminate aqueous solution were used to obtain composite oxide particles (a18). In the third step, 12.8 kg of 3 mass% sodium sulfate and sodium hydroxide were added to the dispersion of composite oxide particles (a17) to adjust the pH to 12.0. A PGME dispersion of particles was produced in the same manner as in Example 1, except that 108.0 kg of sodium silicate aqueous solution and 36.0 kg of sodium aluminate aqueous solution were added to this. The ratio (M _E /M _S ) in this step was 0.1.

The coating solution and the coated substrate were produced in the same manner as in Example 1, except that a PGME dispersion of these particles was used.

[Comparative Example 1]
In the first step, only sodium hydroxide was added to pure water to prepare 10.0 kg of an aqueous solution having a pH of 12.6.

Next, a PGME dispersion of particles was produced in the same manner as in Example 1, except that the amount of sodium silicate aqueous solution in the second step was 8.9 kg, the amount of sodium aluminate aqueous solution was 8.9 kg, and the amount of sodium silicate aqueous solution in the third step was 91.5 kg, and the amount of sodium aluminate aqueous solution was 30.5 kg. A coating solution and a coated substrate were produced.

[Comparative Example 2]
In the second step, the amount of the sodium silicate aqueous solution was 6.0 kg, and the amount of the sodium aluminate aqueous solution was 72.0 kg, and in the third step, the amount of the sodium silicate aqueous solution was 165.0 kg, and the amount of the sodium aluminate aqueous solution was 55.0 kg. In addition, in the fourth step, the pH of the dispersion after the dropwise addition of concentrated hydrochloric acid was adjusted to pH 3.0, and while adding 4 L of a hydrochloric acid aqueous solution of pH 3 and 2 L of pure water, the dissolved aluminum salt was separated and washed using an ultrafiltration membrane, in the same manner as in Example 1, a PGME dispersion of particles was produced, and a coating liquid and a coated substrate were produced.

[Comparative Example 3]
A PGME dispersion of particles was produced, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that the amounts of the sodium silicate aqueous solution and the sodium aluminate aqueous solution in the second step were 3.8 kg and 3.8 kg, respectively, and that the amounts of the sodium silicate aqueous solution and the sodium aluminate aqueous solution in the third step were 150.0 kg and 50.0 kg, respectively.

[Comparative Example 4]
A PGME dispersion of particles was produced, and a coating liquid and a coated substrate were produced in the same manner as in Example 1, except that in the second step, 129.0 kg of the sodium silicate aqueous solution and 129.0 kg of the sodium aluminate aqueous solution were used, in the third step, 375.0 kg of the sodium silicate aqueous solution and 125.0 kg of the sodium aluminate aqueous solution were used, and in the fifth step, the temperature increase rate was 3.0°C/min and the mixture was heated to 200°C.

[Comparative Example 5]
A PGME dispersion of particles was produced, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that the concentration of the sodium _aluminate aqueous solution in terms of _Al2O3 in the first step was 1.0 mass%, the amount of the sodium silicate aqueous solution was 123.0 kg, the amount of the sodium aluminate aqueous solution was 20.5 kg in the second step, and the amount of the sodium silicate aqueous solution was 224.0 kg, and the amount of the sodium aluminate aqueous solution was 28.0 kg in the third step.

[Comparative Example 6]
A PGME dispersion of particles was prepared, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that in the surface treatment of the particles, 8.0 g of γ-methacryloxypropyltrimethoxysilane was used as the organosilicon compound and the mixture was stirred at 50° C. for 24 hours.

[Comparative Example 7]
A PGME dispersion of particles was prepared, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that in the fifth step, the heating temperature was set to 50° C. and the surface treatment of the particles with an organosilicon compound was not performed.

[Comparative Example 8]
A PGME dispersion of particles was produced in the same manner as in Example 1, except that the amount of the sodium silicate aqueous solution in the second step was 14.5 kg, the amount of the sodium aluminate aqueous solution was 14.5 kg, the amount of the sodium silicate aqueous solution in the third step was 102.0 kg, and the amount of the sodium aluminate aqueous solution was 34.0 kg, and the heating temperature in the fifth step was raised to 250° C. and maintained for 10 hours. A coating solution and a coated substrate were produced in the same manner as in Example 1.

[Comparative Example 9]
A PGME dispersion of particles was produced, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that the concentration of the sodium _aluminate aqueous solution in terms of _Al2O3 in the first step was 3.0 mass%, the amount of the sodium silicate aqueous solution was 6.0 kg and the amount of the sodium aluminate aqueous solution was 6.0 kg in the second step, and the amount of the sodium silicate aqueous solution was 55.5 kg and the amount of the sodium aluminate aqueous solution was 18.5 kg in the third step.

[Comparative Example 10]
The same procedures as in Example 1 were carried out except that the concentration of the sodium aluminate aqueous solution in the first step was 9.0 mass% as Al ₂ O ₃ , the concentration of the sodium silicate aqueous solution in the second step was 4.5 mass% as SiO ₂ and the amount added was 16.8 kg, and the concentration of the sodium aluminate aqueous solution in the Al ₂ O ₃ was 4.5 mass% and the amount added was 5.6 kg. However, since the composite oxide particles a obtained in the second step became agglomerated particles with an average particle diameter of 100 nm or more, the subsequent steps were not carried out, and neither the production of a coating liquid nor a coated substrate was carried out.

[Comparative Example 11]
In the first step, the sodium aluminate aqueous solution had an _Al2O3 concentration of _5.0 mass%, and 5.0 kg of a sodium aluminate aqueous solution with a pH of 12.6 was prepared; in the second step, the sodium silicate aqueous solution had an _SiO2 concentration of 0.9 mass%, and an added amount of 115.0 kg, and the sodium aluminate aqueous solution had an _Al2O3 concentration of _0.3 mass%, and an added amount of 57.5 kg; in the third step, the sodium silicate aqueous solution was 189.0 kg, and the sodium aluminate aqueous solution was 63.0 kg. Except for this, a PGME dispersion of particles was produced, and a coating liquid and a coated substrate were produced in the same manner as in Example 1.

[Comparative Example 12]
A PGME dispersion of particles was produced, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that the amount of the sodium silicate aqueous solution in the third step was 82.5 kg and the amount of the sodium aluminate aqueous solution was 27.5 kg. However, when a TEM photograph of the particles was observed, it was found that no hollow particles were obtained.

[Comparative Example 13]
A PGME dispersion of particles was produced, and a coating solution and a coated substrate were produced in the same manner as in Example 1, except that the amount of the sodium silicate aqueous solution in the second step was 11.1 kg, the amount of the sodium aluminate aqueous solution was 11.1 kg, the amount of the sodium silicate aqueous solution in the third step was 66.0 kg, the amount of the sodium aluminate aqueous solution was 22.0 kg, and the temperature increase rate in the fifth step was 5.0° C./min, and the mixture was heated to 150° C. A PGME dispersion of particles was produced, and a coating solution and a coated substrate were produced. However, a TEM photograph of the particles was observed, and it was found that no hollow particles were obtained.

[Comparative Example 14]
The concentration of the sodium aluminate aqueous solution as Al ₂ O ₃ in the first step is 5.0 mass%, the sodium silicate aqueous solution in the second step is 39.3 kg, the sodium aluminate aqueous solution is 39.3 kg, and the sodium silicate aqueous solution in the third step is 120.0 kg, and the sodium aluminate aqueous solution is 40.0 kg, except that the aqueous dispersion of silica-based particles (Rd14) is obtained in the same manner as in Example 1. Thereafter, the dispersion is dried by an evaporator, and then heated to 500 ° C. at a heating rate of 3.0 ° C. / min and kept for 3 hours, and then cooled to 25 ° C., and the PGME dispersion of particles is produced in the same manner as in Example 1, except that the surface treatment of particles with an organic silicon compound is not carried out in the surface treatment step.

Claims (15)

A particle having an outer shell containing silicon and a cavity therein,
A dispersion of hollow silica particles, characterized in that the volume of the sediment obtained by centrifuging a dispersion adjusted to 15 volume % of the particles at 1,000,000 G is 25% or less of the volume of the dispersion before centrifugation. The dispersion liquid according to claim 1, characterized in that the coefficient of variation of the particle diameter of the particles is 20 to 55%. 3. The dispersion according to claim 1, wherein the number density of silanol groups on the particle surface calculated by the Sears measurement method is 0.5 to 2.5 groups/ ^nm2 . The dispersion according to claim 1 or 2, characterized in that the refractive index of the particles is 1.12 to 1.35. The dispersion liquid according to claim 1 or 2, characterized in that the average particle size of the particles is 15 to 55 nm. The dispersion liquid described in claim 1, characterized in that the thickness of the outer shell is 3 to 7 nm. 3. The dispersion according to claim 1, wherein the difference between the density of the particles in helium gas and the density in nitrogen gas is 0.2 to 1.0 g/cm ³ . The particles are composed of _SiO2 and
an oxide containing Si and at least one element selected from Al, As, B, Bi, Cd, Co, Fe, Ga, Ge, In, Pb, Sb, Sn, Ti, V, Zn, and Zr;
3. The dispersion according to claim 1, further comprising at least one of the following: 3. The dispersion according to claim 1, wherein the particles contain 98 parts by mass or more of silicon as _SiO2 when the total amount of metal elements constituting the particles is expressed as 100 parts by mass on an oxide basis. The dispersion according to claim 1 or 2, characterized in that the ratio (A1/A2) of the specific surface area (A1) of the particles determined from pulse NMR measurement of the aqueous dispersion of the particles to the specific surface area (A2) of the particles determined from the average particle diameter of the particles is 0.60 or more. The dispersion according to claim ₁ or ² , characterized in that the ratio of the area of the peak representing the _Q4 structure appearing at a chemical shift of -108 to -120 ppm to the total area of each peak representing the Q1 to _Q4 structures of silicon atoms appearing at a chemical shift of -78 to -120 ppm by 29Si-NMR analysis of the particles is less than 90%. the particles have at least one functional group selected from an alkyl group, an acryloyl group, a (meth)acryloyl group, a vinyl group, a mercapto group, and an epoxy group;
at least one functional group selected from a hydroxyl group, a carboxyl group, and an amino group;
3. The dispersion according to claim 1, further comprising: A first step of preparing an alkaline aqueous solution containing 5.0 mass% or more of an element other than silicon that can be an amphoteric oxide, based on the oxide;
a _second step of preparing a dispersion of composite oxide particles a by simultaneously adding a solution of a silicon-containing compound and an aqueous solution of an alkali-soluble compound of an inorganic element other than silicon to the aqueous alkaline solution, the molar ratio (MOx/ _SiO2 ) of the reaction solution at the end of the addition being 0.5 to 25, where SiO2 is an oxide of silicon and MOx is an alkali-soluble oxide of an inorganic element other than silicon;
Next, a third step of preparing a dispersion liquid of composite oxide particles b by adding a solution of a compound containing silicon and an aqueous solution of an alkali-soluble compound of an inorganic element other than silicon in a molar ratio (MOx/SiO ₂ ) smaller than that in the second step;
Next, a fourth step of adding an acid to the dispersion liquid of the composite oxide particles b to remove at least a part of the elements other than silicon constituting the composite oxide particles b, thereby preparing a dispersion liquid of silica-based particles;
a fifth step of heating the dispersion of silica-based particles to 60 to 200° C. at a heating rate of 3.0° C./min or less, and then cooling the dispersion to less than 50° C.;
A method for producing a dispersion of hollow silica particles comprising the steps of: The method for producing a dispersion liquid according to claim 9, characterized in that the solution of the compound containing silicon in the second step has a _SiO2 equivalent concentration of 0.05 to 2.0 mass%, and the aqueous solution of the alkali-soluble compound of an inorganic element other than silicon has a MOx equivalent concentration of 0.05 to 2.0 mass%. 10. The method for producing a dispersion according to claim 9, further comprising the step of adding at least one of an organosilicon compound represented by the following formula (8) and a partial hydrolyzate thereof to the dispersion after the fifth step:
R _n -SiX _4-n (8)
(In the formula, R is an unsubstituted or substituted hydrocarbon group having 1 to 10 carbon atoms, X is an alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, or a hydrogen atom, and n is an integer of 0 to 4.)