Silica-based particle dispersion, polishing slurry for polishing magnetic disk substrates, polishing composition for polishing magnetic disk substrates, and method for producing silica-based particle groups

Abstract

To provide a silica particle dispersion that can reduce undulation and increase polishing speed when used as a polishing slurry.SOLUTION: A silica particle dispersion having the following characteristics is provided. The weight average particle diameter is within a specific range. It has an average aspect ratio of 1.35 or more and includes first, second, and third particles. For each of the first, second, and third particles, the ratio of its projected area to the area of its equiperipheral circle is within a specific range. The ratio of the cumulative 10% particle diameter to the cumulative 90% particle diameter in the weight-equivalent particle diameter distribution is 2 or more. The coefficient of variation of the particle content ratio (mass %) corresponding to each section (S1 to S6) is 100% or less when the cumulative 1% particle diameter (D1) and the cumulative 99% particle diameter (D99), both of which are based on weight-equivalent particle diameter distribution, of the silica particle dispersion are divided into six equal parts using 1 / 6 of the particle diameter difference between the D1 and the D99 as a unit. The section S1 is the largest.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a silica-based particle dispersion, an abrasive slurry for polishing magnetic disk substrates, an abrasive composition for polishing magnetic disk substrates, and a method for producing silica-based particles. [Background technology]

[0002] Conventionally, silica sol, fumed silica, fumed alumina, etc. have been used as polishing particles. In the manufacture of semiconductor integrated circuit-equipped substrates, aluminum wiring is formed on a silicon wafer, and an oxide film such as silica is then formed on top of this as an insulating film. In this case, unevenness is generated by the wiring, so this oxide film is polished to flatten it. In polishing such substrates, the surface after polishing must be flat and free of steps and unevenness, and further, smooth and free of microscopic scratches, and a high polishing rate is required.

[0003] A common method for achieving a high polishing rate is to use large abrasive grains. However, if the particle size of the abrasive grains becomes too large, the flatness of the substrate surface after polishing tends to deteriorate. Therefore, it is known that making the abrasive grains non-spherical, that is, making the abrasive grains irregularly shaped particles (irregular particles), is effective in achieving a high polishing rate without deteriorating the surface flatness. As a method for obtaining large, irregularly shaped particles, as disclosed in Patent Document 1, a method is known in which porous silica gel is pulverized using a bead mill or the like to prepare an irregularly shaped porous gel, and this irregularly shaped gel is then grown using silicic acid or the like to obtain large, irregularly shaped particles with a high degree of irregularity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-177576 Summary of the Invention [Problem to be solved by the invention]

[0005] However, although the polishing composition described in Patent Document 1 has a high polishing rate, if high flatness is to be achieved on the polished substrate surface, it is necessary to prepare the particle size of the irregular-shaped particles smaller. When attempting to reduce the particle size using the method of Patent Document 1, repeated grinding is required to crush the porous silica gel used as the raw material into even smaller sizes. Repeated grinding can reduce the size of the irregular-shaped porous gel, but at the same time, the irregularity of the irregular-shaped porous gel also decreases. As a result, the irregularity of the irregular-shaped silica particles after particle growth using silicic acid or the like also decreases, resulting in a problem of a decrease in the polishing rate. Furthermore, repeated grinding is required to crush the irregular-shaped porous gel to a predetermined size, which is inefficient and uneconomical.

[0006] The present invention aims to provide a silica-based particle dispersion that, when used as a polishing slurry, can reduce waviness and increase the polishing rate, as well as a polishing slurry for polishing magnetic disk substrates, a polishing composition for polishing magnetic disk substrates, and a method for producing silica-based particle groups. [Means for solving the problem]

[0007] The present inventors have conducted extensive research and have completed the present invention, which comprises the following (1) to (8). (1) A silica-based particle dispersion containing a silica-based particle group consisting of irregularly shaped silica-based particles and spherical silica-based particles, the silica-based particle dispersion having the following characteristics [1] to [6]: [1] The silica-based particles have a weight average particle size of 50 nm or more and 600 nm or less. [2] The silica-based particle group has an average aspect ratio of 1.35 or more as measured by image analysis, and further includes first particles having a major axis of 10 nm or more and less than 50 nm, second particles having a major axis of 50 nm or more and less than 100 nm, and third particles having a major axis of 100 nm or more, wherein the average aspect ratio of the first particles is 1.30 or more, the average aspect ratio of the second particles is 1.35 or more, and the average aspect ratio of the third particles is 1.43 or more. [3] The average ranges of the area ratios (F1 / F2) of the projected area (F1) obtained by image analysis for each of the first particles, the second particles, and the third particles to the area (F2) of a circle having a perimeter equal to the projected perimeter are 0.84 or less, 0.77 or less, and 0.66 or less, respectively. [4] In the weight-converted particle size distribution of the silica-based particles, the particle size ratio (D90 / D10) of the cumulative 10% particle size (D10) from the smallest particle size to the cumulative 90% particle size (D90) is 2 or more. [5] In the weight-converted particle size distribution of the silica-based particle group, the range from D1 to D99 is divided into six equal parts, each of which is equal to 1 / 6 of the particle size difference (D99-D1) between the cumulative 1% particle size (D1) and the cumulative 99% particle size (D99) from the smallest particle size. When the corresponding weight-converted particle size distribution regions are designated S1, S2, S3, S4, S5, and S6 from the smallest particle size side, the coefficient of variation of the particle content (mass%) corresponding to each of the regions S1 to S6 is 100% or less. [6] Among the particle contents (mass%) corresponding to the regions S1, S2, S3, S4, S5, and S6, the particle content (mass%) corresponding to the region S1 is the largest. (2) The silica-based particle dispersion liquid according to (1) above, wherein the first particles are particles without a pore structure, and the second particles and the third particles are both particles with a pore structure. (3) A polishing slurry for polishing magnetic disk substrates, comprising the silica-based particle dispersion liquid described in (1) or (2) above. (4) A composition for polishing magnetic disk substrates, comprising the silica-based particle dispersion liquid described in (1) or (2) above. (5) A method for producing silica-based particle groups consisting of irregularly shaped silica-based particles and spherical silica-based particles, comprising the following steps 1 to 3: (Step 1) A silica-based gel having a particle strength of 4 to 16 GPa, represented by the following formula (F1), is wet-crushed under alkaline conditions using media (particle diameter 0.1 to 5 mm) to obtain a solution containing particles made of irregularly shaped silica-based gel. (Step 2) A step of adding a silicic acid liquid under alkaline conditions to a solution containing particles made of the irregular silica-based gel, filling the pores between the primary particles of the particles made of the irregular silica-based gel by reacting with the silicic acid contained in the silicic acid liquid, causing the particles to grow while maintaining their irregular shape, thereby forming irregular silica-based particles, and obtaining a solution containing the irregular silica-based particles. (Step 3) A step of concentrating the solution containing the irregularly shaped silica-based particles and recovering the silica-based particle groups. σ=[(1-ε) / π]·K·H / d 2 ···(F1) σ; particle strength [P] d: Particle diameter converted to specific surface area [m] K: average coordination number of particles ε: Porosity of powder π: Pi H: Adhesion strength [N] (6) In the step 1, the specific surface area of ​​the silica-based gel is 50 m 2 / g or more 800m 2 / g or less, and the weight average particle diameter of the particles made of the irregular shaped silica-based gel is 40 nm or more and 550 nm or less, In the step 3, the silica-based particles have a specific surface area of ​​270 m 2 / g or less and the weight average particle diameter is 50 nm or more and 600 nm or less. (7) In the step 1, the pH during wet grinding is 8 or more and 11.5 or less; The method for producing a silica-based particle group according to (5) or (6) above, wherein in step 2, the pH when adding the silicic acid liquid is 9 or more and 12.5 or less, the SiO2 concentration after adding the silicic acid liquid is 1 mass% or more and 10 mass% or less, and heating is performed to a temperature of 60°C or more and 170°C or less before or after adding the silicic acid liquid. (8) The method for producing a silica-based particle group according to any one of (5) to (7) above, wherein in step 2, the amount of the silicic acid solution added is in a range such that the SiO2 molar concentration of the silicic acid solution is 0.5 to 20 times the SiO2 molar concentration of the solution containing particles made of the irregular silica-based gel. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a silica-based particle dispersion that, when used as a polishing slurry, can reduce waviness and increase the polishing rate, as well as a polishing slurry for polishing magnetic disk substrates, a polishing composition for polishing magnetic disk substrates, and a method for producing silica-based particle groups. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will now be described. The present invention is a silica-based particle dispersion containing a silica-based particle group consisting of irregular silica-based particles and spherical silica-based particles, and has the following characteristics [1] to [6]. [1] The silica-based particles have a weight average particle size of 50 nm or more and 600 nm or less. [2] The silica-based particle group has an average aspect ratio of 1.35 or more as measured by image analysis, and further includes first particles having a major axis of 10 nm or more and less than 50 nm, second particles having a major axis of 50 nm or more and less than 100 nm, and third particles having a major axis of 100 nm or more, wherein the average aspect ratio of the first particles is 1.30 or more, the average aspect ratio of the second particles is 1.35 or more, and the average aspect ratio of the third particles is 1.43 or more. [3] The average ranges of the area ratios (F1 / F2) of the projected area (F1) obtained by image analysis for each of the first particles, the second particles, and the third particles to the area (F2) of a circle having a perimeter equal to the projected perimeter are 0.84 or less, 0.77 or less, and 0.66 or less, respectively. [4] In the weight-converted particle size distribution of the silica-based particles, the particle size ratio (D90 / D10) of the cumulative 10% particle size (D10) from the smallest particle size to the cumulative 90% particle size (D90) is 2 or more. [5] In the weight-converted particle size distribution of the silica-based particle group, the range from D1 to D99 is divided into six equal parts, each of which is equal to 1 / 6 of the particle size difference (D99-D1) between the cumulative 1% particle size (D1) and the cumulative 99% particle size (D99) from the smallest particle size. When the corresponding weight-converted particle size distribution regions are designated S1, S2, S3, S4, S5, and S6 from the smallest particle size side, the coefficient of variation of the particle content (mass%) corresponding to each of the regions S1 to S6 is 100% or less. [6] Among the particle contents (mass%) corresponding to the regions S1, S2, S3, S4, S5, and S6, the particle content (mass%) corresponding to the region S1 is the largest.

[0010] Such a silica-based particle dispersion will be hereinafter referred to as the "dispersion of the present invention."

[0011] The silica-based particles contained in the dispersion of the present invention will also be referred to as "silica-based particles of the present invention" hereinafter. In the present invention, the term "particle group" means an aggregation of a large number of particles.

[0012] The present invention also provides a method for producing silica-based particle groups consisting of irregularly shaped silica-based particles and spherical silica-based particles, the method comprising the following steps 1 to 3: (Step 1) A silica-based gel having a particle strength of 4 to 16 GPa, represented by the following formula (F1), is wet-crushed under alkaline conditions using media (particle diameter 0.1 to 5 mm) to obtain a solution containing particles made of irregularly shaped silica-based gel. (Step 2) A step of adding a silicic acid liquid under alkaline conditions to a solution containing particles made of the irregular silica-based gel, filling the pores between the primary particles of the particles made of the irregular silica-based gel by reacting with the silicic acid contained in the silicic acid liquid, causing the particles to grow while maintaining their irregular shape, thereby forming irregular silica-based particles, and obtaining a solution containing the irregular silica-based particles. (Step 3) A step of concentrating the solution containing the irregularly shaped silica-based particles and recovering the silica-based particle groups. σ=[(1-ε) / π]·K·H / d 2 ···(F1) σ; particle strength [P] d: Particle diameter converted to specific surface area [m] K: average coordination number of particles ε: Porosity of powder π: Pi H: Adhesion strength [N]

[0013] Such a method for producing silica-based particles is hereinafter also referred to as the "production method of the present invention."

[0014] <Spherical silica particles and irregularly shaped silica particles> The silica-based particles of the present invention are composed of irregularly shaped silica-based particles and spherical silica-based particles. Spherical silica-based particles refer to silica-based particles that are spherical in shape. Furthermore, irregularly shaped silica-based particles refer to particles that are irregularly shaped (non-spherical) other than spherical silica-based particles. More specifically, in the present application, images or photographs of silica-based particles obtained from an electron microscope (scanning electron microscope) are analyzed (image analysis method), and particles with an aspect ratio of 1.1 or more are considered irregularly shaped silica-based particles, while particles with an aspect ratio of less than 1.1 are considered spherical silica-based particles.

[0015] The aspect ratio of each particle contained in the silica-based particle group of the present invention means a value obtained by measurement using the method described below.

[0016] Examples of the irregular silica particles include silica microparticles obtained by pulverizing silica particles, and particle-linked silica microparticles in which these silica microparticles are linked together as primary silica microparticles. Here, "linked silica microparticles" refers to the fact that adjacent primary silica microparticles are fixed together by the bond formed between them. Here, the type of bond is not particularly limited, but examples include chemical bonds such as siloxane bonds formed by the condensation reaction between the surface silanol groups of adjacent primary silica microparticles.

[0017] <Weight average particle diameter> The silica-based particles of the present invention have a weight-average particle diameter of 50 nm to 600 nm. When the dispersion of the present invention is used for polishing, a high polishing rate can be achieved, and the abrasive grains can be prevented from remaining on the substrate, thereby preventing scratches on the substrate, smoothing the substrate surface, and suppressing waviness.

[0018] The silica-based particles of the present invention preferably have a weight-average particle diameter of 50 nm or more and 600 nm or less. When the silica-based particles are used as a polishing slurry, if the weight-average particle diameter is within this range, they exhibit an excellent polishing rate, the occurrence of waviness is relatively small, and the occurrence of scratches is also suppressed. When the weight-average particle diameter of the silica-based particles is less than 50 nm, the polishing rate tends to be low when used as a polishing slurry. On the other hand, when the weight-average particle diameter of the silica-based particles is greater than 600 nm, waviness, scratches, etc. tend to worsen. From the same viewpoint, the weight-average particle diameter of the silica-based particles is more preferably 100 nm or more and 500 nm or less, and even more preferably 120 nm or more and 300 nm or less.

[0019] The weight-average particle diameter of the silica-based particle group of the present invention is determined by diluting the dispersion of the present invention with a 0.05% by mass aqueous solution of sodium dodecyl sulfate to a solids concentration of 2% by mass, injecting 0.1 mL of the diluted dispersion into a known disc centrifugal particle size distribution analyzer (e.g., manufactured by CPS Instruments) with a syringe, and measuring it in a density gradient solution of 8% to 24% sucrose at 18,000 rpm to determine the weight-equivalent particle size distribution, and then determining the weight-equivalent particle size distribution from the distribution.

[0020] <Specific surface area equivalent particle diameter> The weight-average particle diameter of the silica-based particles of the present invention is as described above, but the specific surface area-converted particle diameter is preferably in the range of 10 nm to 300 nm.If the specific surface area-converted particle diameter is in this range, when the dispersion of the present invention is applied to polishing, an excellent polishing rate can be obtained, and further, the abrasive grains can be prevented from remaining on the substrate, and the occurrence of scratches on the substrate can also be prevented.

[0021] If the specific surface area converted particle diameter of the silica-based particles of the present invention is less than 10 nm, the polishing rate may be low, and particles may even remain on the substrate. On the other hand, if the specific surface area converted particle diameter of the silica-based particles exceeds 300 nm, scratches may occur or the surface roughness of the substrate after polishing may increase. From the same viewpoint, the specific surface area converted particle diameter of the silica-based particles of the present invention is preferably 15 nm or more and 200 nm or less, more preferably 20 nm or more and 150 nm or less, and particularly preferably 30 nm or more and 100 nm or less.

[0022] In this specification, the particle size converted into specific surface area of ​​silica-based particles or the like mainly means the primary particle size of silica particles, and is a value converted from the specific surface area measured by nitrogen adsorption method or titration method. Specifically, it means the average particle size converted into specific surface area, and in principle, it is the specific surface area (SA:m) measured by the BET method. 2 It is calculated from the formula (DSA) = 6000 / (SA × ρ) using the particle diameter (ρ) (ρ = 2.2 for silica) and the particle diameter (DSA / g). The measurement method is described in detail below.

[0023] <Average aspect ratio of silica-based particles> The silica-based particle group of the present invention is a silica-based particle group consisting of irregularly shaped silica-based particles and spherical silica-based particles, and the average aspect ratio of the silica-based particle group measured by image analysis is 1.35 or more. When the silica-based particle dispersion of the present invention is used for polishing purposes, the average aspect ratio of the silica-based particle group is desirably 1.35 or more. If the average aspect ratio of the silica-based particles of the present invention is 1.35 or more, when the dispersion of the present invention is applied to polishing purposes, a practically sufficient polishing rate can be obtained. From the same viewpoint, the average aspect ratio of the silica-based particles is more preferably 1.4 or more and 7 or less, and particularly preferably 1.42 or more and 5 or less. If the average aspect ratio is more than 7, the polishing rate will be improved, but scratches may occur.

[0024] The average aspect ratio of the silica-based particles of the present invention means a value obtained by the following measurement. A scanning electron microscope (SEM) (for example, an ultra-high resolution field emission scanning electron microscope S-5500 [capable of STEM observation] (manufactured by Hitachi High-Technologies Corporation)) is used to take a planar SEM image (magnification: 200,000 times) of the dispersion of the present invention (silica concentration: 40% by mass). 150 or more particles are identified in the resulting image or photograph, and for each particle, the ratio of the long side to the short side of the circumscribed rectangle (long side / short side) is determined to be the maximum, and this maximum value is taken as the aspect ratio of that particle. The aspect ratios of all the particles obtained are then simply averaged to obtain the average aspect ratio.

[0025] <Average aspect ratio of first particles, second particles, and third particles> The present inventors have found that, when the dispersion of the present invention is applied to polishing applications, the polishing rate can be improved while minimizing the occurrence of "waviness" on the substrate to be polished by further adjusting the average aspect ratio of each of the first particles (small particles) having a major axis of 10 nm or more but less than 50 nm, the second particles (medium particles) having a major axis of 50 nm or more but less than 100 nm, and the third particles (large particles) having a major axis of 100 nm or more to a predetermined value or more. Specifically, it is desirable that the average aspect ratio of the first particles is 1.30 or more, the average aspect ratio of the second particles is 1.35 or more, and the average aspect ratio of the third particles is 1.43 or more. The range of the major axis of the third particles is usually 100 nm or more and less than 500 nm. Furthermore, when the dispersion of the present invention is applied to polishing applications, the polishing rate is determined mainly by the first particles, second particles, and third particles, and therefore the influence of silica-based particles having a major axis of less than 10 nm is considered to be small.

[0026] A method for identifying the first particles, second particles, and third particles in the present invention, and a method for determining the average aspect ratio of each of the identified particles will be described below. First, a planar SEM image (magnification 200,000) of the dispersion of the present invention (silica concentration 40% by mass) is taken using a scanning electron microscope (SEM) (for example, an ultra-high resolution field emission scanning electron microscope S-5500 [STEM observation possible] (manufactured by Hitachi High-Technologies Corporation)), and for any particle selected from the obtained image or photograph, the ratio of the long side to the short side of the circumscribing rectangle (long side / short side) is determined to be maximum, and this maximum value is taken as the aspect ratio of the particle, and the long side of the circumscribing rectangle when the aspect ratio is maximum is taken as the major axis of the particle. Particles with a major axis of 10 nm or more and less than 50 nm are classified as first particles, particles with a major axis of 50 nm or more and less than 100 nm as second particles, and particles with a major axis of 100 nm or more as third particles. This process of classifying each particle into first particles, second particles, third particles, and other particles is repeated until the number of particles classified into each of the first particles, second particles, and third particles reaches 50 or more. Next, the aspect ratios of all particles classified as first particles are simply averaged to determine the average aspect ratio of the first particles. The same process is carried out to determine the average aspect ratios of the second and third particles.

[0027] Generally, it is known that relatively large particles have a high polishing rate, and that the polishing rate increases as the particle irregularity and aspect ratio increase. On the other hand, relatively large particles or particles with a relatively high irregularity and aspect ratio tend to worsen the surface roughness and waviness of the polished substrate. In contrast, relatively small particles tend to have a slower polishing rate but improve the surface roughness and waviness of the substrate. Furthermore, spherical particles are known to have a slower polishing rate than irregularly shaped particles but improve waviness and surface roughness. Based on these findings, it is believed that third particles with a major axis of 100 nm or more have a relatively fast polishing rate but worsen the surface roughness and waviness of the substrate. On the other hand, first particles with a major axis of 10 nm or more but less than 50 nm have a relatively slow polishing rate due to their small size, but improve the surface roughness and waviness of the substrate. Therefore, it is presumed that the first particles play a role in repairing the waviness caused by the third particles. The second particles, which have a major axis of 50 nm or more and less than 100 nm, are considered to have polishing performance intermediate between the first and third particles, and to play a role in contributing to a certain degree of polishing speed and elimination of waviness on the substrate surface.

[0028] As described above, the coexistence of the first, second, and third particles not only increases the polishing rate, but also provides a polished surface that is smooth and has little waviness. In particular, the first particles with a major axis of 10 nm or more but less than 50 nm are irregular particles with an aspect ratio of 1.3 or more, and therefore have a relatively high polishing rate, which is presumably why the repair effect of the first particles is enhanced.

[0029] The first particles, each having a major axis of 10 nm or more but less than 50 nm, serve to reduce waviness caused by polishing the third particles in order to achieve low waviness. Furthermore, by setting the average aspect ratio of the first particles to 1.30 or more, it is possible to maintain a higher polishing rate compared to spherical particles. From the viewpoint of improving the polishing rate while reducing waviness, the average aspect ratio of the first particles is preferably 1.32 or more but 3 or less, and more preferably 1.35 or more but 2 or less. This is because an aspect ratio of less than 1.32 results in an insufficient polishing rate. Furthermore, an aspect ratio of more than 3 tends to worsen waviness.

[0030] The second particles, with a major axis of 50 nm or more but less than 100 nm, play an intermediate role between the first particles and the third particles, compensating for the lack of polishing speed caused by the first particles and partially eliminating the "waviness" caused by the third particles. If the average aspect ratio of the second particles is less than 1.35, the particle shape becomes similar to that of spherical particles, and when used in a polishing slurry, the polishing speed may decrease. In addition, the average aspect ratio of the second particles is preferably 1.4 or more but 3, more preferably 1.45 or more but 2, from the viewpoint of reducing moderate waviness while improving the polishing speed.

[0031] The third particles having a major axis of 100 nm or more have a high degree of irregularity, and therefore play a role in achieving a high polishing rate. That is, a high polishing rate can be achieved by setting the average aspect ratio of the third particles to 1.43 or more. Furthermore, from the viewpoint of improving the polishing rate without excessively worsening the waviness, the average aspect ratio of the third particles is preferably 1.45 or more and 3 or less, and more preferably 1.5 or more and 2 or less.

[0032] <Particle surface smoothness parameter> In the silica-based particle group of the present invention, it is desirable that the ranges of the average values ​​of the area ratios (F1 / F2) of the projected area (F1) obtained by image analysis for each of the first particle, the second particle, and the third particle, to the area (F2) of a circle having a perimeter equal to the projected perimeter (measured for 50 or more particles for each) are 0.84 or less, 0.77 or less, and 0.66 or less, respectively. Here, the projected area (F1) and the area (F2) can be measured using, for example, known image analysis software (for example, RADIUS 2.0 manufactured by Emsis).

[0033] The area ratio (F1 / F2) is a parameter indicating the smoothness of the particle surface. A value of 1 for (F1 / F2) indicates a spherical shape, while values ​​smaller than 1 indicate fine irregularities on the particle surface. When (F1 / F2) is close to 1, the particle is spherical, resulting in a slower polishing rate when the dispersion of the present invention is used for polishing. The smaller (F1 / F2) is, the more likely it is that irregular protrusions will form on the particle surface. When the particle surface is irregular, the protrusions will selectively contact the substrate when used for polishing, resulting in stress concentration on the substrate and a higher polishing rate. However, the presence of irregularities does not significantly affect the waviness of the substrate surface. In the present invention, by setting the average area ratio (F1 / F2) of the first particle (small particle), second particle (medium particle), and third particle (large particle) of the silica-based particle group to a predetermined value or less, we have succeeded in obtaining abrasive grains composed of silica-based particles that exhibit small waviness and a high polishing rate.

[0034] Although primary particles with a major axis of 10 nm or more and less than 50 nm have a low aspect ratio and therefore a slow polishing rate, the polishing rate can be increased to a certain extent by setting the average area ratio to 0.84 or less. From the viewpoint of improving the polishing rate, the average area ratio (F1 / F2) of the primary particles is preferably 0.2 or more and 0.8 or less, and more preferably 0.3 or more and 0.75 or less.

[0035] The second particles having a major axis of 50 nm or more and less than 100 nm have a higher aspect ratio than the first particles, and therefore have a relatively high polishing rate. Furthermore, by setting the average area ratio (F1 / F2) to 0.77 or less, the polishing rate can be further increased. Furthermore, from the viewpoint of improving the polishing rate, the average area ratio (F1 / F2) of the second particles is preferably 0.2 or more and 0.7 or less, and more preferably 0.3 or more and 0.65 or less.

[0036] Third particles with a major axis of 100 nm or more have the highest aspect ratio and are large in size, and therefore exhibit a high polishing rate, but the polishing rate can be further improved when the average area ratio (F1 / F2) is 0.66 or less. From the viewpoint of improving the polishing rate, the average area ratio (F1 / F2) of these third particles is preferably 0.2 or more and 0.64 or less, and more preferably 0.3 or more and 0.6 or less.

[0037] <Particle size ratio (D90 / D10) in weight-equivalent particle size distribution> The silica-based particles of the present invention have a particle size ratio (D90 / D10) of 2 or more between the cumulative 10% particle size (D10) from the smallest particle size and the cumulative 90% particle size (D90) in their weight-equivalent particle size distribution. Here, the particle size ratio (D90 / D10) in the weight-equivalent particle size distribution indicates the breadth of the particle size distribution; the larger the (D90 / D10) value, the broader the particle size distribution. In other words, a high (D90 / D10) value indicates that both small and large particles are present. Therefore, while large particles exhibit a high polishing rate, they also exacerbate waviness, while the small particles present at the same time have the function of repairing the exacerbated waviness. From the perspective of reducing waviness while improving the polishing rate, the particle size ratio (D90 / D10) of the silica-based particle group is preferably 2 to 15, and more preferably 2.5 to 12. If the (D90 / D10) value is too small, the polishing rate will be insufficient due to the small number of large particles, while if it is too large, the small particles will not be able to repair the waviness caused by the large particles. The weight-equivalent particle size distribution of silica-based particles and the like can be measured using a disc centrifugal particle size distribution measuring device (for example, manufactured by CPS Instruments).

[0038] <Particle content by weight conversion particle size distribution region> In the weight-converted particle size distribution of the silica-based particle group of the present invention, when D1 to D99 are divided into six equal parts, each of which is defined as 1 / 6 of the particle size difference (D99-D1) between the cumulative 1% particle size (D1) and the cumulative 99% particle size (D99) from the smallest particle size, and the corresponding particle size regions are designated S1, S2, S3, S4, S5, and S6 from the smallest particle size side, the coefficient of variation of the particle content (mass % of the particles contained in each region) corresponding to each of regions S1 to S6 is 100% or less, and preferably 50% or less. The fact that the coefficient of variation of the particle content corresponding to each of the regions S1 to S6 is 100% or less (preferably 50% or less) means that the variation in the particle content in each region is relatively small, and this particle size distribution generally exhibits a trapezoidal distribution. Since a silica-based particle group having a trapezoidal distribution contains a large amount of both large and small particle components, it is presumed that this indicates that it can exhibit both the effect of improving the polishing rate due to the large particles and the effect of reducing waviness due to the small particles. In the present application, the standard deviation is divided by the average value, and the result is further divided by 100 to obtain the coefficient of variation (%).

[0039] Furthermore, with regard to the particle contents (mass%) corresponding to the regions S1, S2, S3, S4, S5, and S6 in the weight-equivalent particle size distribution of the silica-based particle group of the present invention, it is desirable that the particle content corresponding to region S1 be the largest. Here, region S1 contains the smallest particles, and since small particles are effective in suppressing the occurrence of "waviness" on the substrate to be polished, making the particle content corresponding to region S1 higher than the particle contents corresponding to the other regions can contribute to suppressing the occurrence of "waviness."

[0040] <Pore structure> In the present invention, it is preferable that the first particles are particles that do not have a pore structure, and that both the second particles and the third particles are particles that have a pore structure. Specifically, some of the silica-based particles of the present invention preferably have pores inside the particles. More specifically, they preferably have a gradient pore structure depending on the particle size (major axis). The silica-based particles of the present invention include first particles (small particles) with a major axis of 10 nm or more but less than 50 nm, second particles (medium particles) with a major axis of 50 nm or more but less than 100 nm, and third particles (large particles) with a major axis of 100 nm or more. The small particles do not have pores inside the particles. In contrast, the medium and large particles have a pore structure inside the particles. Furthermore, the number of pores inside the medium and large particles tends to increase as the particle size increases. In this application, the dependence of the presence or absence of pores inside the particles and the number of pores on the particle size is referred to as a gradient pore structure inside the particles.

[0041] The reason why the above-mentioned gradient structure of pores occurs is presumed to be the following mechanism. The silica-based gel (silica powder) that is the raw material for the method for producing silica-based particles of the present invention described later has an outer diameter of the order of microns, for example, several tens to several hundreds of microns. 2 / g and is an agglomerate structure of primary particles ranging in size from a few nanometers to a few tens of nanometers, i.e., a silica-based gel. Agglomerates of this structure have voids between the primary particles. In the method for producing silica-based particles of the present invention, described below, a raw silica-based gel (silica powder) having such a structure is milled to produce an irregular silica-based gel of the desired particle size, while maintaining the structure of the primary particles and their voids. After this milling process, silicic acid is used to fill the pores between the primary particles of the irregular silica-based gel, improving its strength and allowing the particles to grow to the desired size. The irregular silica-based gel before particle growth contains particles of various sizes, ranging from 10 nm to over 100 nm. When these particles are grown using silicic acid, the silicic acid penetrates into the irregular silica gel particles, causing particle growth. The penetration depth of the silicic acid generally reaches a depth of several tens of nanometers, depending on the particle growth conditions, pore size, and particle shape. Therefore, primary particles with a particle size of 10 nm or more but less than 50 nm do not have pores within the particles. On the other hand, when the second particles have a particle size of 50 nm or more but less than 100 nm, if the particle size is relatively small and the pore diameter is relatively large, silicic acid penetrates into the interior of the irregular silica-based gel. Therefore, pores are unlikely to remain inside, but if the particle size is relatively large and the pore diameter is small, pores tend to remain inside. As a result, the number of second particles with pores tends to be smaller than that of the third particles described below. Silica does not penetrate deep into the third particles with a particle size of 100 nm or more. Therefore, the internal pores tend to remain, and the number of pores tends to be greater than that of the first and second particles. Furthermore, due to this mechanism, the pores inside the particles tend to be located at the center of the particles.

[0042] When particles having a gradient structure of pores depending on particle size are used for polishing, the polishing rate tends to improve and waviness and surface roughness tend to be improved. The reason for these improved polishing performances is that the medium and large particles with internal pores have a lower particle density due to the presence of internal pores, and the number of particles per unit weight increases compared to particles without internal pores. On the other hand, because the silicate sufficiently reinforces the spaces between the primary particles, the particles are strong and do not collapse during polishing. Therefore, it is assumed that the increased contact area between the substrate and the particles improves the polishing speed. Furthermore, as the number of particles increases, the load on each particle decreases, mitigating localized stress concentration on the polishing substrate. This reduces excessive digging of the polishing substrate, tending to improve surface roughness and waviness. Furthermore, because small particles do not have internal pores, they are relatively hard, which tends to improve the polishing speed.

[0043] The dispersion of the present invention is prepared by dispersing the silica-based particles of the present invention as described above in a dispersion medium. The dispersion medium is not particularly limited and may be, for example, water or an organic solvent. The amount of the silica-based particles of the present invention contained in the dispersion of the present invention is also not particularly limited, and may be, for example, 1 to 30% by mass, or 2 to 20% by mass.

[0044] The dispersion of the present invention can be prepared, for example, by the production method of the present invention described below.

[0045] [Method of producing silica-based particle dispersion and silica-based particle group] The manufacturing method of the present invention will be described. The manufacturing method of the present invention is a method for manufacturing silica-based particle groups consisting of irregular silica-based particles and spherical silica-based particles. The manufacturing method is characterized by including the following steps 1 to 3. According to this manufacturing method, silica-based particles that satisfy the above conditions [1] to [6] can be produced.

[0046] (Step 1) A step of wet-crushing a silica-based gel having a powder strength of 4 to 16 GPa, represented by the following formula (F1), using media (particle diameter 0.1 to 5 mm) under alkaline conditions to obtain a first solution containing particles made of irregularly shaped silica-based gel. σ=[(1-ε) / π]·K·H / d 2 ···(F1) (where σ, d, K, ε, π and H are: σ: powder strength [Pa], d: Particle diameter converted to specific surface area [m] K: average coordination number of particles, ε: porosity of powder, π: Pi, H: adhesive force of particles [N]

[0047] If the powder is a silica-based gel having a strength of 4 to 16 GPa, it can be made into particles made of irregularly shaped silica-based gel by wet pulverization under alkaline conditions.

[0048] The strength of a powder can be calculated from the Rumpf equation, which indicates the compressive or tensile strength of a powder. According to the Rumpf equation, the strength of a powder can be expressed by equation (F1). The crushing mechanism can be classified into surface crushing, which is performed by frictional and shear forces, and volume crushing, in which powder is broken down by impact and compression forces. However, in actual crushing, these two processes occur simultaneously to some extent, and it is thought that whether surface crushing or volume crushing is predominant depends on the type of raw material and the crushing conditions. Furthermore, volume crushing breaks down the entire powder, so the resulting particles tend to have a high degree of irregularity. In surface crushing, the particles are crushed gradually from the surface, and the convex parts of the surface are easily broken down, so they tend to gradually become more spherical, reducing the degree of irregularity of the particles. At the same time, fine particles are generated by the breaking down of the convex parts of the surface, and these fine particles tend not to have a high degree of irregularity. In wet milling using beads, beads of a predetermined size are used to introduce a suspended slurry into a mill for milling, and the desired size is obtained by selecting the bead diameter and adjusting the residence time inside the mill. In this case, depending on the milling conditions and the type of raw material, it is thought that volumetric milling is likely to occur for materials that rapidly become smaller in size. Furthermore, the silica-based gel obtained as a result of volumetric milling tends to have relatively large particles. On the other hand, if the size change is gradual, it is thought that surface crushing has occurred. In this case, if the strength of the raw material silica-based gel is high, a long residence time is required to crush the material to the desired size, which tends to make surface crushing more likely. For the reasons mentioned above, particles produced by surface crushing tend to be small in size and have a low degree of irregularity. Therefore, by selecting a raw material with a silica-based gel strength of 16 GPa or less and ending the crushing process at a stage where the volumetric crushing mechanism is mainly occurring, particles with a high degree of irregularity can be obtained. Next, regarding the relationship between powder strength and silica-based gel distribution, when powders with a strength of 4 to 16 GPa are wet-milled using beads, adjusting the ratio of surface and volumetric grinding by adjusting the residence time inside the mill tends to easily produce a trapezoidal distribution. When the powder strength is below 4 GPa, the powder strength is too weak, causing volumetric grinding to proceed and reaching the desired size too quickly, making it difficult to adjust the distribution through grinding and resulting in a trapezoidal distribution. On the other hand, when the powder strength is 16 GPa or higher, grinding is difficult, requiring repeated grinding to achieve the desired size and distribution. In this case, surface grinding is promoted, resulting in an increase in small particle components, making it difficult to obtain a trapezoidal distribution.

[0049] Here, the particle diameter (d) converted into specific surface area of ​​the particles is determined by the BET method and is calculated by the following formula (F2). d=6000 / (ρs×SA1) (F2) (where d, ρs and SA1 are: d: Specific surface area equivalent particle diameter [nm], ρs: silica density (= 2.2 [g / mL]), SA1: specific surface area of ​​silica powder [m 2 / g]) Here, SA1 (specific surface area) means a value obtained by measurement using the BET method or titration method, which will be explained in detail later.

[0050] The porosity (ε) of the powder was calculated from the pore volume (PV) and silica volume (SV) of the powder using the following formula (F3). ε=(PV) / (PV+SV)×100...(F3) (where ε, PV, and SV are: ε: Porosity of powder [unitless], PV: pore volume of powder [mL / g], SV: Silica volume, calculated by the following formula: SV = 1 / ρs = 1 / 2.2 = 0.4545 The method for determining the pore volume (PV) of the powder is described later.

[0051] The average coordination number (K) of the particles was calculated using the above-mentioned value of the powder porosity (ε) from the following formula (F4) (known as the Ridgway-Tarbuck formula), which expresses the relationship between the powder porosity (ε) in a random packing of uniform spherical particles and the average coordination number (K) of the primary particles. Of the two solutions obtained, the smaller solution is taken as the average coordination number (K). ε=1.072-0.1192K+0.00431K 2 (F4)

[0052] The adhesive strength (H) was calculated using the following formula (F5) from the theoretical strength (Q) of glass and the cross-sectional area of ​​the adhesion between primary particles in the raw silica powder. The "cross-sectional area of ​​the adhesion portion between primary particles in the raw silica powder" is also referred to as the "cross-sectional area of ​​the adhesion portion between particles." Furthermore, the "length of the adhesion portion between primary particles in the raw silica powder" is also referred to as the "length of the adhesion portion between particles." The theoretical strength of glass (Q) is 20 GN / m according to the literature (NEW GLASS Vol. 23, No. 3, 2008, pp. 11-18, "Introduction: Fracture Science of Glass"). 2 ]. The cross-sectional area of ​​the particle adhesion portion was determined by measuring the length of 50 points where primary particles were attached to each other through image analysis of scanning electron microscope photographs, and the length (L) of the particle adhesion portion was regarded as the diameter of the cross section of the adhesion portion to calculate the area of ​​the circle. The value obtained by multiplying the obtained area of ​​the circle by the theoretical strength (Q) of the glass was used as the cross-sectional area of ​​the particle adhesion portion. The length (L) of the particle-adhered portion in the present invention means a value obtained by the following measurement. A planar SEM image (magnification: 200,000) of the dispersion of the present invention (silica concentration: 40% by mass) is taken using a scanning electron microscope (SEM) (for example, an ultra-high resolution field emission scanning electron microscope S-5500 [STEM observation possible] (manufactured by Hitachi High-Technologies Corporation)), and the lengths of 50 or more locations where primary particles adhere to each other are measured in the obtained image or photograph. The length (L) of the particle-adhered portion is determined by simply averaging the lengths of all the locations obtained. H=(L / 2) 2 ×π×Q (F5) (where H, L, π and Q are: H: Adhesion force [N], L: length of particle adhesion part [nm], π: Pi (=3.14), Q: Theoretical strength of glass (= 20 [GN / m 2 ]))

[0053] In this way, the strength (σ) of the silica-based gel can be calculated from the above-mentioned formula (F1) (and formulas (F2), (F3), (F4), and (F5)). For reasons described below, the strength (σ) of the silica-based gel is preferably 15 GPa or less. Regarding silica-based gel, the porosity of the powder, the specific surface area of ​​the powder, and the length of the particle adhesion part are not particularly limited, but the porosity of the silica-based gel is usually 0.5 to 0.9, and the specific surface area of ​​the silica-based gel is 50 to 800 m 2 / g, and the length of the attached portion is preferably in the range of 5 to 15 nm. Here, the specific surface area of ​​the silica-based gel means a value obtained by measurement using the BET method or titration method, which will be explained in detail later.

[0054] The strength σ of the silica-based gel calculated by the above formula (F1) is preferably 4 to 16 GPa. Within this strength range, volumetric crushing is likely to occur during crushing, making it easier to obtain a highly irregular silica-based gel in step [1], and furthermore, through steps [2] and [3], it becomes easier to produce the silica-based particle groups of the present invention having the aforementioned characteristics in particle size number distribution, weight-equivalent particle size distribution, various aspect ratios, etc. The strength σ of the silica-based gel is more preferably 4 to 15 GPa, even more preferably 4 to 12 GPa, and most preferably 4 to 8 GPa. When the strength of the silica-based gel is within this range, the particle size distribution of the irregular silica-based gel after pulverization is not a normal distribution but a trapezoidal distribution, depending on the pulverization conditions. The irregular silica-based gel undergoes particle growth using silicic acid in the next step, and the trapezoidal distribution remains even after particle growth using silicic acid. When such a trapezoidal distribution is obtained, the coefficient of variation of the area of ​​regions S1 to S6 of the particle size distribution becomes 100% or less (preferably 50% or less).

[0055] The size of the silica gel, which is the raw material, is not particularly limited as long as the strength is 4 to 16 GPa, but from the viewpoint of crushing efficiency, it is preferably 100 μm or less, more preferably 10 μm to 60 μm, and particularly preferably 20 μm to 50 μm. If the size is less than 10 μm, the viscosity of the suspension is high and handling is difficult, and if the size exceeds 100 μm, the large size is likely to cause clogging of the screen or gap of the crusher.

[0056] For wet pulverization, a conventionally known wet pulverizer can be used, such as a ball mill or a bead mill. Examples of media materials used in wet milling include zirconia, glass, and alumina. Among these, zirconia and glass are preferred from the viewpoint of crushing particles more finely. The size (particle size) of the media is not particularly limited as long as it is a size that can produce the desired irregular silica gel. However, to efficiently prepare an irregular silica gel with a particle size of 40 nm to 550 nm, the particle size is in the range of 0.1 to 5 mm, preferably 0.1 to 1 mm.

[0057] Wet milling must be carried out under alkaline conditions. If the conditions are not alkaline, there is a problem in that the crushed particles will re-aggregate. However, if the pH is too high, the irregular silica gel after milling is likely to dissolve or change over time, so the pH during wet milling is preferably 8 to 11.5, more preferably 9 to 10.5. Wet pulverization may be carried out in one stage from the viewpoint of efficiently pulverizing to the desired particle size, or may be carried out in two or more stages by changing the pulverization conditions according to the particle size during the pulverization process.

[0058] In the solution obtained in step 1, the weight average particle size of the particles made of the irregular shaped silica gel is preferably 40 nm or more and 550 nm or less, and more preferably 70 nm or more and 250 nm or less.

[0059] In the solution containing particles made of irregularly shaped silica-based gel obtained in step 1, the shape of the particles made of silica-based gel is usually made irregular (non-spherical) through wet grinding. The degree of irregular shape is not particularly limited here.

[0060] (Step 2) A step of adding a silicic acid liquid under alkaline conditions to a solution containing particles made of the irregular silica-based gel, filling the pores between the primary particles of the particles made of the irregular silica-based gel by reacting with the silicic acid contained in the silicic acid liquid, causing the particles to grow while maintaining their irregular shape, thereby forming irregular silica-based particles, and obtaining a second solution containing the irregular silica-based particles.

[0061] As the silicic acid solution, a conventionally known silicic acid solution can be used. The concentration of the silicic acid solution is preferably 1% by mass or more and 10% by mass or less. The amount of silicic acid solution added is preferably in the range of 0.5 to 20 times the SiO2 molar concentration of the solution containing particles made of irregular silica-based gel. If the amount of silicic acid solution added is more than 20 times, self-nucleation by silicic acid is likely to occur. If the amount is less than 0.5 times, the particles cannot grow to the desired size, and the polishing rate tends to decrease.

[0062] The addition of the silicic acid solution must be carried out under alkaline conditions. If the conditions are not alkaline, the particles cannot grow, and problems such as the generation of small particles due to self-nucleation occur. In addition, from the viewpoint of particle growth, the pH when adding the silicic acid solution is 9 or more and 12.5 or less, and preferably 9 or more and 11 or less.

[0063] Before or after the addition of the silicic acid solution, it is preferable to heat the solution containing particles made of irregular silica-based gel. From the viewpoint of particle growth, the temperature of the solution after heating is preferably 60°C or higher and 170°C or lower, more preferably 80°C or higher and 120°C or lower.

[0064] The SiO2 concentration after the addition of the silicic acid liquid is preferably 1% by mass or more and 10% by mass or less.

[0065] (Step 3) A step of concentrating the second solution containing the irregularly shaped silica-based particles and recovering the silica-based particle group.

[0066] The specific surface area of ​​the silica-based particles obtained in step 3 is 270 m 2 / g or less is preferable, and 2 / g or more 182m 2 It is more preferable that the saturation coefficient is 1 / g or less. Here, the specific surface area of ​​the silica-based particles refers to a value obtained by measurement using the BET method or titration method, which will be described in detail later.

[0067] The weight average particle size of the silica-based particles obtained in step 3 is preferably 50 nm or more and 600 nm or less, and more preferably 100 nm or more and 200 nm or less. The weight average particle size is measured by the same method as that for measuring the weight average particle size of the silica-based particles of the present invention.

[0068] When concentrating the solution containing irregularly shaped silica particles obtained in step 2, known concentration methods such as an ultrafiltration membrane and an evaporator can be used. In this manner, silica-based particles that satisfy the above conditions [1] to [6] can be produced.

[0069] [Polishing slurry and composition for polishing magnetic disk substrates] Next, the polishing slurry and composition for polishing magnetic disk substrates according to this embodiment will be described. The polishing composition for magnetic disk substrates according to this embodiment (also referred to as "polishing composition") contains the silica-based particle dispersion according to this embodiment. The polishing slurry for polishing magnetic disk substrates according to this embodiment can be prepared by diluting this polishing composition with water or the like.

[0070] The polishing composition according to this embodiment may further contain other components. As other components, one or more components selected from a polishing accelerator, a surfactant, a hydrophilic compound, a heterocyclic compound, a pH adjuster, and a pH buffering agent can be used.

[0071] Examples of the polishing accelerator include acids such as sulfuric acid, nitric acid, phosphoric acid, oxalic acid, and hydrofluoric acid, as well as the sodium salts, potassium salts, and ammonium salts of these acids, and mixtures thereof. In the case of a polishing composition containing such a polishing accelerator, when polishing a workpiece made of multiple components, the polishing rate of a specific component of the workpiece can be accelerated, thereby ultimately obtaining a flat polished surface.

[0072] When the polishing composition according to this embodiment contains a polishing accelerator, the content thereof is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less. Surfactant and / or Hydrophilic Compound To improve the dispersibility and stability of the polishing composition, a cationic, anionic, nonionic, or amphoteric surfactant or hydrophilic compound can be added.

[0073] Both the surfactant and the hydrophilic compound have the effect of reducing the contact angle with the polished surface and promoting uniform polishing. The surfactant and / or hydrophilic compound can be selected from the following group, for example:

[0074] Anionic surfactants include carboxylates, sulfonates, sulfates, and phosphates. Carboxylate salts include soaps, N-acylamino acid salts, polyoxyethylene or polyoxypropylene alkyl ether carboxylates, and acylated peptides. Sulfonate salts include alkylsulfonates, alkylbenzene and alkylnaphthalenesulfonates, naphthalenesulfonates, sulfosuccinates, α-olefinsulfonates, and N-acylsulfonates. Examples of sulfate ester salts include sulfated oil, alkyl sulfate, alkyl ether sulfate, polyoxyethylene or polyoxypropylene alkyl allyl ether sulfate, and alkyl amide sulfate. Examples of phosphate ester salts include alkyl phosphate, polyoxyethylene or polyoxypropylene alkyl allyl ether phosphate, and the like.

[0075] Examples of cationic surfactants include aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium chloride salts, benzethonium chloride, pyridinium salts, and imidazolinium salts. Examples of amphoteric surfactants include carboxybetaine type, sulfobetaine type, aminocarboxylate salts, imidazolinium betaine, lecithin, and alkylamine oxide.

[0076] Examples of nonionic surfactants include ether type, ether ester type, ester type, and nitrogen-containing type, and examples of ether type surfactants include polyoxyethylene alkyl and alkylphenyl ethers, alkylarylformaldehyde condensed polyoxyethylene ethers, polyoxyethylene polyoxypropylene block polymers, and polyoxyethylene polyoxypropylene alkyl ethers. Examples of ether ester type surfactants include polyoxyethylene ethers of glycerin esters, polyoxyethylene ethers of sorbitan esters, and polyoxyethylene ethers of sorbitol esters. Examples of ester type surfactants include polyethylene glycol fatty acid esters, glycerin esters, polyglycerin esters, sorbitan esters, propylene glycol esters, and sucrose esters. Examples of nitrogen-containing surfactants include fatty acid alkanolamides, polyoxyethylene fatty acid amides, and polyoxyethylene alkylamides. Other examples include fluorine-based surfactants.

[0077] The surfactant is preferably an anionic surfactant or a nonionic surfactant, and the salt includes ammonium salt, potassium salt, sodium salt, etc., with ammonium salt and potassium salt being particularly preferred.

[0078] Further, other surfactants, hydrophilic compounds, etc. include esters (glycerin esters, sorbitan esters, alanine ethyl esters, etc.), ethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyethylene glycol alkyl ethers, polyethylene glycol alkenyl ethers, alkyl polyethylene glycols, alkyl polyethylene glycol alkyl ethers, alkyl polyethylene glycol alkenyl ethers, alkenyl polyethylene glycols, alkenyl polyethylene glycol alkyl ethers, alkenyl polyethylene glycol alkenyl ethers, polypropylene glycol alkyl ethers, polypropylene glycol alkenyl ethers, alkyl polypropylene glycols, alkyl polypropylene glycol alkyl ethers, alkyl polypropylene glycol alkenyl ethers, and alkenyl polypropylene glycols, etc.), polysaccharides (alginic acid, pectinic acid, carboxymethylcellulose, curdlan, pullulan, etc.), amino acid salts (glycine ammonium salt, glycine sodium salt ... Polycarboxylic acids and their salts (polyaspartic acid, polyglutamic acid, polylysine, polymalic acid, polymethacrylic acid, ammonium polymethacrylate, sodium polymethacrylate, polyamic acid, polymaleic acid, polyitaconic acid, polyfumaric acid, poly(p-styrenecarboxylic acid), polyacrylic acid, polyacrylamide, aminopolyacrylamide, ammonium polyacrylate, sodium polyacrylate, polyamic acid, ammonium polyamic acid, sodium polyamic acid, and polyglyoxylic acid, etc.), vinyl polymers (polyvinyl alcohol, etc.), alcohol, polyvinylpyrrolidone and polyacrolein, etc.), sulfonic acids and their salts (ammonium methyl taurate, sodium methyl taurate, sodium methyl sulfate, ethyl ammonium sulfate, butyl ammonium sulfate, sodium vinyl sulfonate, sodium 1-allylsulfonate, sodium 2-allylsulfonate, sodium methoxymethylsulfonate, ammonium ethoxymethylsulfonate, sodium 3-ethoxypropylsulfonate, etc.), and amides (propionamide, acrylamide,methylurea, nicotinamide, succinamide, sulfanilamide, etc.

[0079] When the substrate to be polished is a glass substrate or the like, any surfactant can be suitably used. However, when the substrate is a silicon substrate for a semiconductor integrated circuit or the like, and the influence of contamination by alkali metals, alkaline earth metals, halides, or the like must be avoided, it is desirable to use an acid or its ammonium salt surfactant.

[0080] When the polishing composition of this embodiment contains a surfactant and / or a hydrophilic compound, the total content thereof is preferably 0.001 g or more and 10 g or less, more preferably 0.01 g or more and 5 g or less, and particularly preferably 0.1 g or more and 3 g or less, per liter of the polishing composition.

[0081] The surfactant or hydrophilic compound may be used alone or in combination with two or more kinds.

[0082] When the polishing composition according to this embodiment contains a metal, a heterocyclic compound may be added to the polishing composition to form a passivation layer or dissolution-inhibiting layer on the metal and thereby inhibit erosion of the substrate. Here, a "heterocyclic compound" refers to a compound having a heterocycle containing one or more heteroatoms. A heteroatom refers to an atom other than a carbon atom or a hydrogen atom. A heterocycle refers to a cyclic compound containing at least one heteroatom. The term "heteroatom" refers only to atoms that form part of the ring system of a heterocycle, and does not refer to atoms that are external to the ring system, separated from the ring system by at least one non-conjugated single bond, or that are part of a further substituent of the ring system. Preferred heteroatoms include, but are not limited to, nitrogen, sulfur, oxygen, selenium, tellurium, phosphorus, silicon, and boron. Examples of heterocyclic compounds that can be used include imidazole, benzotriazole, benzothiazole, and tetrazole. More specific examples include 1,2,3,4-tetrazole, 5-amino-1,2,3,4-tetrazole, 5-methyl-1,2,3,4-tetrazole, 1,2,3-triazole, 4-amino-1,2,3-triazole, 4,5-diamino-1,2,3-triazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, and 3,5-diamino-1,2,4-triazole, but are not limited to these.

[0083] When a heterocyclic compound is blended into the polishing composition of this embodiment, the content is preferably 0.001 mass% or more and 1.0 mass% or less, more preferably 0.001 mass% or more and 0.7 mass% or less, and even more preferably 0.002 mass% or more and 0.4 mass% or less.

[0084] In order to enhance the effects of the above-mentioned additives, the pH of the polishing composition can be adjusted by adding an acid or a base as necessary.

[0085] When the polishing composition according to this embodiment is adjusted to a pH of 7 or higher, an alkaline pH adjuster is used. Preferably, sodium hydroxide, aqueous ammonia, ammonium carbonate, or an amine such as ethylamine, methylamine, triethylamine, or tetramethylamine is used.

[0086] When the polishing composition is adjusted to a pH of less than 7, an acidic pH adjuster is used. For example, hydroxy acids such as lactic acid, citric acid, malic acid, tartaric acid, and glyceric acid are used.

[0087] To maintain the pH value of the polishing composition constant, a pH buffer may be used, such as phosphates and borates such as ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium tetraborate tetrahydrate, or organic acids.

[0088] For the polishing composition according to this embodiment, a solvent can be used as needed. Water is usually used as the solvent, but alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, etc. can be used as needed, and water-soluble organic solvents such as ethers, esters, ketones, etc. can also be used. In addition, a mixed solvent consisting of water and an organic solvent can also be used.

[0089] The concentration of abrasive particles in the polishing composition according to this embodiment is preferably in the range of 0.5% by mass or more and 50% by mass or less, and more preferably 5% by mass or more and 30% by mass or less. If the concentration is less than 0.5% by mass, depending on the type of substrate or insulating film, the concentration may be too low, resulting in a slow polishing rate and productivity problems. If the concentration of abrasive particles exceeds 50% by mass, the stability of the abrasive becomes insufficient, and the polishing rate and polishing efficiency do not improve further. In addition, dried matter may be generated and adhered during the process of supplying the dispersion liquid for the polishing treatment, which may cause scratches. [Example]

[0090] [Evaluation of Silica-Based Gel, Silica-Based Particle Group, and Polishing Composition] The silica-based particles and polishing compositions obtained in each Example and Comparative Example were evaluated as follows. The results are shown in Table 1. The physical properties of the raw materials (silica powder (silica-based gel)) in each Example and Comparative Example are also shown in Table 1.

[0091] (1) Weight-equivalent particle size distribution and weight-average particle size of silica-based particles The silica-based particle dispersion was diluted with a 0.05% by mass aqueous solution of sodium dodecyl sulfate to a solids concentration of 2% by mass, and 0.1 mL of this was injected with a syringe into a known disc centrifugal particle size distribution analyzer (manufactured by CPS Instruments). Measurement was then carried out in a density gradient solution of 8% to 24% sucrose at 18,000 rpm to determine the weight-equivalent particle size distribution and the weight-average particle size [nm]. Furthermore, the cumulative 10% particle size (D10) [nm] and cumulative 90% particle size (D90) [nm] were determined from the weight-equivalent particle size distribution obtained, and the particle size ratio (D90 / D10) was calculated. Furthermore, from the weight-equivalent particle size distribution obtained, the cumulative 1% particle size (D1) [nm], cumulative 99% particle size (D99) [nm], the particle size difference between the cumulative 1% particle size (D1) and the cumulative 99% particle size (D99) (D99-D1), and 1 / 6 of that value were calculated. Furthermore, D1 to D99 were equally divided into six, and the corresponding weight-equivalent particle size distribution regions were designated S1, S2, S3, S4, S5, and S6 from the smallest particle size side, and the particle contents (mass%) corresponding to each of the regions S1 to S6 were calculated. The above measurements and calculations were carried out using the disc centrifugal particle size distribution analyzer. Furthermore, the coefficient of variation (%) of the particle content (mass%) of each of the regions S1 to S6 was calculated from the particle content (mass%) corresponding to each of the regions S1 to S6. The particle content (mass%) values ​​corresponding to each of the regions S1 to S6 were compared to determine the region with the highest particle content.

[0092] (2) Specific surface area and specific surface area equivalent particle diameter of silica-based particles and silica-based gel (purified silica gel) 50 mL of silica particle dispersion liquid (silica concentration 40% by mass) containing silica particle groups was adjusted to pH 3.5 with HNO3, 40 mL of 1-propanol was added, and the sample was dried at 110°C for 16 hours. The sample was then pulverized in a mortar and calcined in a muffle furnace at 500°C for 1 hour to prepare a measurement sample. The specific surface area was then calculated from the amount of nitrogen adsorption using a nitrogen adsorption method (BET method) using a specific surface area measuring device (Yuasa Ionics, Model No. Multisorb 12) using the BET single-point method.

[0093] Specifically, 0.5 g of sample was placed in a measurement cell and degassed at 300°C for 20 minutes in a mixed gas stream of 30% nitrogen and 70% helium. The sample was then maintained at liquid nitrogen temperature in the mixed gas stream to allow equilibrium adsorption of nitrogen onto the sample. Next, the sample temperature was gradually raised to room temperature while the mixed gas was being passed through. The amount of nitrogen desorbed during this process was measured, and the specific surface area of ​​the irregularly shaped silica particles was calculated using a previously prepared calibration curve. The specific surface area (SA) was then substituted into the following formula to determine the specific surface area-equivalent particle diameter D1: Specific surface area equivalent particle diameter D1 (nm) = 6000 / (ρ×SA) (where ρ is the density of silica particles, 2.2 [g / cm 3 ].)

[0094] In addition, the specific surface area of ​​the silica-based particles is 100m 2 / g or more, sintering will progress during firing in the BET method. In this case, the specific surface area (SA) is determined by the titration method, and the particle size converted to specific surface area (DSA) is calculated using the formula (DSA) = 6000 / (SA × ρ).

[0095] Here, the titration method is the following method. First, a sample equivalent to 1.5 g of SiO2 was placed in a beaker and transferred to a thermostatic reactor (25°C). Pure water was added to bring the volume to 90 ml (the following procedure was performed in a thermostatic reactor maintained at 25°C). Next, 0.1 mol / L hydrochloric acid solution was added to the beaker to adjust the pH to 3.6. 30 g of sodium chloride was then added, and the mixture was diluted to 150 ml with pure water and stirred for 10 minutes. A pH electrode was then attached, and 0.1 mol / L sodium hydroxide solution was added dropwise while stirring to adjust the pH to 4.0. The sample adjusted to pH 4.0 was then titrated with 0.1 mol / L sodium hydroxide solution. The titer and pH values ​​were recorded at least four points in the pH range of 8.7 to 9.3. A calibration curve was then created, with the titer of 0.1 mol / L sodium hydroxide solution designated as X and the pH value at that point designated as Y. Then, the consumption amount V (ml) of 0.1 mol / L sodium hydroxide solution required to change the pH from 4.0 to 9.0 per 1.5 g of SiO2 is calculated from the equation V = (A × f × 100 × 1.5) / (W × C), and this is used to calculate the specific surface area according to the equation SA = 29.0V-28. In the above formula, A is the titration amount (ml) of 0.1 mol / L sodium hydroxide solution required per 1.5 g of SiO2 to change the pH from 4.0 to 9.0, f is the titer of the 0.1 mol / L sodium hydroxide solution, C is the SiO2 concentration (%) of the sample, and W is the amount of sample collected (g). The specific surface area and specific surface area converted particle diameter of the silica-based gel (purified silica gel) were measured in the same manner as in the case of the silica-based particles described above.

[0096] (3) Major axis, average aspect ratio, and area ratio (F1 / F2) of silica-based particle groups A planar SEM image (magnification 200,000 times) of the silica-based particle dispersion (silica concentration 40% by mass) was taken using a scanning electron microscope (SEM) (ultra-high resolution field emission scanning electron microscope S-5500 [STEM observation possible] (manufactured by Hitachi High-Technologies Corporation)), and analyzed using image analysis software (RADIUS 2.0 manufactured by emsis). Specifically, for a particle arbitrarily selected in the SEM image, the ratio of the long side to the short side of the circumscribing rectangle (long side / short side) was determined to be maximum, and this maximum value was taken as the aspect ratio of that particle. The long side of the circumscribing rectangle at which the aspect ratio was maximum was taken as the major axis of that particle. Particles with a major axis of 10 nm or more and less than 50 nm were classified as first particles, particles with a major axis of 50 nm or more and less than 100 nm as second particles, and particles with a major axis of 100 nm or more as third particles. This process of classifying each particle into first particles, second particles, third particles, and other particles was repeated until the number of particles classified into each of the first particles, second particles, and third particles reached 50 or more. Next, the aspect ratios of all particles classified as the first particles were simply averaged to determine the average aspect ratio of the first particles. The average aspect ratios of the second particles and the third particles were similarly determined. Furthermore, the aspect ratios of all particles classified into the first particles, second particles, third particles, and other particles were simply averaged to determine the average aspect ratio of the silica-based particle group.

[0097] Furthermore, for a scanning electron microscope photograph (magnification 200,000 times) of the silica-based particle dispersion (silica concentration 40% by mass), the area ratio (F1 / F2) of the projected area (F1) of the first particles, second particles, and third particles to the area (F2) of a circle having a perimeter equal to the projected perimeter was measured using the image analysis software described above. Specifically, the projected area (F1) and the area (F2) of a circle having a perimeter equal to the projected perimeter were measured for 50 first particles, 50 second particles, and 50 third particles, and the individual area ratio (F1 / F2) was calculated for each. The average of the 50 particles was calculated and used as the area ratio (F1 / F2).

[0098] (4) Checking the pores A silica-based particle dispersion (silica concentration 40% by mass) was photographed using an ultra-high-resolution field-emission scanning electron microscope S-5500 [STEM observation possible] (Hitachi High-Technologies Corporation) and transmission electron microscope images (200,000 magnification) were taken of 500 particles. First particles (longest diameter: 10 nm to less than 50 nm), second particles (longest diameter: 50 nm to less than 100 nm), and third particles (longest diameter: 100 nm or more) were selected from the 500 particles. 20 particles were randomly selected for each of the first, second, and third particles. If no pores were visually observed, the first, second, or third particles were determined to have no pores. If one or more pores were observed, the first, second, or third particles were determined to have pores. Regarding the presence or absence of pores, pores were determined to be present if pores with an inner diameter of 1 nm or more were observed. As described above, 20 randomly selected first particles, second particles, and third particles were identified using transmission electron microscope images (200,000 magnifications), and the presence or absence of pores inside the particles was confirmed by visual inspection. If no pores were confirmed in 20 particles of each of the first particles, second particles, and third particles, the first particles, second particles, or third particles were determined to have no pores, and if one or more pores were confirmed, the first particles, second particles, or third particles were determined to have pores. Regarding the presence or absence of pores, if pores with an inner diameter of 1 nm or more were confirmed, they were deemed to be present.

[0099] (5) Polishing test method (polishing speed ratio and waviness ratio) An aluminum substrate coated with nickel plating for hard disks (nickel-plated substrate manufactured by Toyo Kohan Co., Ltd.) was prepared as the substrate to be polished. This substrate to be polished was set in a polishing device (NF300 manufactured by Nanofactor Co., Ltd.) and polished 1 μm using a polishing pad (Bellatrix NO178 manufactured by FILWEL) with a substrate load of 0.05 MPa, a platen rotation speed of 50 rpm, a head rotation speed of 50 rpm, and polishing slurry supplied at a rate of 40 g / min. ·Polishing speed ratio The polishing rate was determined from the difference in weight of the polished substrate before and after polishing and the polishing time, and a relative value was calculated with Comparative Example 1 set to 100. Waviness ratio The amplitude of minute irregularities with a waviness wavelength of several tens to several hundreds of μm was measured at any point that equally bisects the diameter of the outer and inner circles of a polished doughnut-shaped aluminum substrate. Next, the amplitude of minute irregularities with a waviness wavelength of several tens to several hundreds of μm was similarly measured at a point on the straight line connecting the measurement point and the center point of the doughnut-shaped aluminum substrate, where the center point bisects the measurement point. The average of these two values ​​was then calculated as the "waviness value," and the relative value (waviness ratio) was calculated with Comparative Example 1 set to 100. The conditions for measuring the amplitude of the unevenness are as follows. Equipment: ZygoNewView7200 Lens: 2.5x Zoom ratio: 1.0 Filter: 50~500μm Measurement area: 3.75mm x 2.81mm

[0100] (6) Method for measuring pore volume of silica gel 10 g of silica gel sample powder was placed in a crucible and dried at 105°C for 1 hour, then placed in a desiccator and cooled to room temperature. Next, 1 g of the sample was placed in a well-washed cell, and nitrogen was adsorbed using a nitrogen adsorption device. The pore volume was calculated using the following formula. Pore ​​volume (mL / g) = (0.001567 × (V-Vc) / W) In the above formula, V is the adsorption amount (mL) under standard conditions at a pressure of 735 mmHg, Vc is the volume of the cell blank (mL) at a pressure of 735 mmHg, and W is the mass of the sample (g). The density ratio between nitrogen gas and liquid nitrogen was set to 0.001567.

[0101] (7) Length of particle adhesion part of silica gel The length of the particle-adhered portion of the silica-based gel was measured using the method described above.

[0102] Example 1 [Preparation of silica powder (silica-based gel)] Pure water was added to 462.5 g of sodium silicate to prepare a 21% by mass sodium silicate aqueous solution in terms of SiO2, and 25% by mass sulfuric acid was added to adjust the pH to 7.1 to obtain a solution containing silica hydrogel (hereinafter referred to as "silica hydrogel solution"). The silica hydrogel solution was kept at 21°C in a thermostatic chamber and allowed to stand for 3 hours for aging, and then washed with pure water until the sodium sulfate content (content relative to SiO2 contained in the silica hydrogel) became 0.05 mass% to obtain a purified silica hydrogel solution. The content of sodium sulfate relative to SiO2 contained in the silica hydrogel solution was measured using high performance liquid chromatography (HPLC, manufactured by Nippon Dionex Co., Ltd., ICS-1100).

[0103] This purified silica hydrogel solution had an SiO2 concentration of 5.0% by mass. Here, the SiO2 content in the purified silica hydrogel was determined by subjecting 5 g of the purified silica hydrogel to ignition loss at 1000°C, weighing it, and assuming that all of the obtained material was SiO2. The purified silica hydrogel solution was dried at 120°C to obtain silica powder consisting of a silica-based gel. This silica powder was pulverized in a mortar to obtain silica powder (silica-based gel) with a particle size of 13 μm after pulverization. The specific surface area of ​​this silica powder (silica gel) was measured using the method described above and found to be 550 m 2 / g. Furthermore, the average particle size (particle size converted into specific surface area) (d), pore volume, and length of particle adhesion portion of this silica powder (silica-based gel) were measured using the methods described above, and the strength of the silica powder (silica-based gel) was calculated using these values. For convenience, the unit of the average particle diameter (particle diameter converted into specific surface area) (d) of the particles is expressed in "nm" in Table 1. Similarly, the unit of the powder strength (σ) is expressed in "GPa."

[0104] (Step 1) Preparation of a solution containing particles made of irregular silica gel <Particles made of irregularly shaped silica gel> 6.28 kg of water was weighed into a 10 L container, and 87.3 g of an aqueous sodium hydroxide solution (concentration: 48% by mass) was added to prepare an aqueous sodium hydroxide solution with a pH of 9.7. To this aqueous solution, 2.49 kg of the silica powder was added, and then a 48% aqueous sodium hydroxide solution (concentration: 48% by mass) was added to adjust the pH, thereby obtaining a silica powder suspension with a pH of 10.3. This suspension was passed through a mill equipped with 1.0 mmφ zirconia media and milled until the weight average particle diameter became 6.3 μm, to obtain a silica-based fine particle dispersion (1) with an SiO 2 concentration of 25.6%. Next, the silica-based microparticle dispersion (1) was passed through a grinder equipped with 0.5 mmφ glass media and ground until the weight average particle diameter reached 478 nm, yielding a silica-based microparticle dispersion (2) with an SiO2 concentration of 21.8%. The silica-based fine particle dispersion (2) was passed through a grinder equipped with 0.25 mmφ glass media and ground until the weight average particle diameter reached 98 nm, yielding an irregular shaped silica-based fine particle dispersion with an SiO2 concentration of 17.8%.

[0105] (Step 2) Growth of particles made of irregular silica gel and concentration of the preparation 472 g of the obtained irregular shaped silica-based fine particle dispersion was weighed out and diluted with 2044 g of water to obtain 2519 g of irregular shaped silica-based fine particle dispersion with an SiO2 concentration of 3.0 mass %. Next, an aqueous sodium hydroxide solution (concentration: 4.8% by mass) and water were added to adjust the pH to 10.4. The temperature was then raised to 98°C and maintained for 30 minutes. Next, while maintaining the temperature at 98°C, 5,376 g of acidic silicic acid solution (SiO concentration: 4.6% by mass) was added over 16 hours, and stirring was continued for another hour while maintaining the temperature at 98°C to obtain a solution (hereinafter referred to as "prepared solution"). The amount of silicic acid solution added was such that the SiO2 molar concentration of the silicic acid solution was 3.33 times that of the irregular shaped silica microparticle dispersion, and the SiO2 concentration in the prepared solution was 4.0 mass%.

[0106] (Step 3) Collection of silica particles This prepared solution was cooled to room temperature and then concentrated to an SiO2 concentration of 12 mass % using an ultrafiltration membrane (SIP-1013 manufactured by Asahi Kasei Corporation). The mixture was then concentrated using a rotary evaporator to an SiO2 concentration of 50% by mass, yielding a group of silica particles consisting of irregular silica particles and non-irregular silica particles.

[0107] The specific surface area of ​​the obtained silica-based particles is 42 m 2 / g and the weight average particle size was 124 nm.

[0108] The first particles, second particles, and third particles were each checked for the presence or absence of pores using the method described above. As a result, no pores were found in the first particles, but pores were found in both the second particles and the third particles.

[0109] <Comparative Example 1> Preparation of silica powder (silica-based gel) Pure water was added to 462.5 g of sodium silicate to prepare a sodium silicate aqueous solution with a concentration of 24% by mass in terms of SiO2. A sulfuric acid aqueous solution (concentration: 25% by mass) was added to adjust the pH to 7.1, yielding a solution containing silica hydrogel. This solution containing silica hydrogel was maintained at 21°C in a thermostatic chamber and allowed to stand for 5.75 hours for aging. Subsequently, the solution was washed with pure water until the content of sodium sulfate relative to the SiO2 contained in the silica hydrogel was 0.05% by mass, yielding a purified silica hydrogel. This purified silica hydrogel had an SiO2 concentration of 5.0% by mass and a specific surface area of ​​350 m 2 The purified silica hydrogel obtained was dried at 120° C. and pulverized in a mortar to obtain silica powder (silica-based gel) having a volume-based particle size of 12 μm after pulverization. The volumetric particle size (μm) of the dried and pulverized purified silica hydrogel was measured using a HORIBA LA950 laser diffraction / scattering particle size distribution analyzer, adjusting the sample concentration so that the transmittance R was 90±0.5%.

[0110] The average particle size (particle size converted to specific surface area) (d), pore volume, and length of particle adhesion portion of this silica powder (silica-based gel) were measured using the method described above, and the strength of the silica powder (silica-based gel) was calculated using these values. For convenience, the unit of the average particle diameter (particle diameter converted into specific surface area) (d) of the particles is expressed in "nm" in Table 1. Similarly, the unit of the powder strength (σ) is expressed in "GPa."

[0111] (Preparation of a solution containing particles made of irregular silica gel) 5.01 kg of water was weighed into a 10 L container, and 84 g of an aqueous sodium hydroxide solution (concentration: 48% by mass) was added to prepare an aqueous sodium hydroxide solution with a pH of 9.7. To this aqueous sodium hydroxide solution, 1.87 kg of the silica powder (silica-based gel) was added, and then a sodium hydroxide solution (concentration: 48% by mass) was added to adjust the pH, to obtain a silica powder suspension with a pH of 10.3. This silica powder suspension was passed through a mill equipped with 1.0 mmφ zirconia media and milled until the weight average particle diameter reached 800 nm, yielding a solution (11) containing particles made of silica-based gel with an SiO2 concentration of 21.7 mass%. Next, the resulting solution (11) containing particles made of silica-based gel was passed through a grinder equipped with glass media of 0.35 mmφ and ground until the weight average particle diameter reached 98 nm, yielding a solution (12) containing particles made of irregular silica-based gel with an SiO2 concentration of 18.7 mass%.

[0112] (Growth of irregularly shaped silica gel particles and concentration of the formulation) 1.9 kg of the resulting solution (12) containing particles made of irregular silica-based gel was weighed, and 10.5 kg of water was added to obtain 12.4 kg of a solution with an SiO2 concentration of 3.0 mass%. Next, an aqueous sodium hydroxide solution (concentration 48 mass%) and water were added, and the pH was adjusted to 10.4. The temperature was then raised to 98°C and maintained for 30 minutes. Next, while maintaining the temperature at 98°C, 25.7 kg of an acidic silicic acid solution (concentration 4.6 mass%) was added over 16 hours, and stirring was continued for another hour while maintaining the temperature at 98°C to obtain a prepared liquid (hereinafter referred to as prepared liquid B).

[0113] This preparation (B) was cooled to room temperature and concentrated to an SiO2 concentration of 12 mass % using an ultrafiltration membrane ("SIP-1013" manufactured by Asahi Kasei Corporation). Furthermore, the mixture was concentrated to an SiO2 concentration of 50 mass % using a rotary evaporator to obtain a group of silica-based particles consisting of irregularly shaped silica-based particles and spherical silica-based particles. The specific surface area of ​​the obtained silica-based particles is 87m 2 / g and the weight average particle size was 137 nm.

[0114] As in Example 1, the first particles, second particles, and third particles were each checked for the presence or absence of pores. As a result, no pores were found in the first particles, but pores were found in both the second particles and the third particles.

[0115] [Table 1]

[0116] [Table 2]

Claims

1. A silica-based particle dispersion liquid containing a silica-based particle group consisting of irregularly shaped silica-based particles and spherical silica-based particles, the silica-based particle dispersion liquid having the following characteristics [1] to [6]: [1] The silica-based particles have a weight average particle diameter of 50 nm or more and 600 nm or less. [2] The silica-based particle group has an average aspect ratio of 1.35 or more as measured by image analysis, and further includes first particles having a major axis of 10 nm or more and less than 50 nm, second particles having a major axis of 50 nm or more and less than 100 nm, and third particles having a major axis of 100 nm or more, wherein the average aspect ratio of the first particles is 1.30 or more, the average aspect ratio of the second particles is 1.35 or more, and the average aspect ratio of the third particles is 1.43 or more. [3] The average ranges of the area ratios (F1 / F2) of the projected area (F1) obtained by image analysis for each of the first particle, the second particle, and the third particle to the area (F2) of a circle having a perimeter equal to the projected perimeter are 0.84 or less, 0.77 or less, and 0.66 or less, respectively. [4] In the weight-converted particle size distribution of the silica-based particles, the particle size ratio (D90 / D10) of the cumulative 10% particle size (D10) from the smallest particle size to the cumulative 90% particle size (D90) is 2 or more. [5] In the weight-converted particle size distribution of the silica-based particle group, when D1 to D99 are divided into 6 equal parts using 1 / 6 of the particle size difference (D99-D1) between the cumulative 1% particle size (D1) and the cumulative 99% particle size (D99) from the smallest particle size, and the corresponding weight-converted particle size distribution regions are designated S1, S2, S3, S4, S5, and S6 from the smallest particle size side, the coefficient of variation of the particle content (mass%) corresponding to each of the regions S1 to S6 is 100% or less. [6] Among the particle contents (mass%) corresponding to the regions S1, S2, S3, S4, S5, and S6, the particle content (mass%) corresponding to the region S1 is the largest.

2. 2. The silica-based particle dispersion according to claim 1, wherein the first particles are particles having no pore structure, and the second particles and the third particles are particles having a pore structure.

3. 3. A polishing slurry for polishing magnetic disk substrates, comprising the silica-based particle dispersion liquid according to claim 1.

4. 3. A composition for polishing magnetic disk substrates, comprising the silica-based particle dispersion liquid according to claim 1.

5. A method for producing silica-based particle groups consisting of irregularly shaped silica-based particles and spherical silica-based particles, comprising the following steps 1 to 3: (Step 1) A silica-based gel having a particle strength of 4 to 16 GPa, represented by the following mathematical formula (F1), is wet-disintegrated under alkaline conditions using media (particle diameter 0.1 to 5 mm) to obtain a solution containing particles made of irregularly shaped silica-based gel. (Step 2) A step of adding a silicic acid liquid under alkaline conditions to a solution containing particles made of the irregular silica-based gel, filling the pores between the primary particles of the particles made of the irregular silica-based gel by reacting with the silicic acid contained in the silicic acid liquid, causing the particles to grow while maintaining their irregular shape, thereby forming irregular silica-based particles, and obtaining a solution containing the irregular silica-based particles. (Step 3) A step of concentrating the solution containing the irregularly shaped silica-based particles and recovering the silica-based particle groups. σ=[(1-e) / π]・K・H / d 2 ・・・(F1) σ: Particle strength [P] d: Particle diameter converted into specific surface area [m] K: average coordination number of particles ε: Porosity of powder π: pi H: Adhesion [N]

6. In the step 1, the specific surface area of ​​the silica-based gel is 50 m 2 / g or more 800m 2 / g or less, and the weight average particle diameter of the particles made of the irregular shaped silica-based gel is 40 nm or more and 550 nm or less, In the step 3, the silica-based particles have a specific surface area of ​​270 m 2 6. The method for producing silica-based particles according to claim 5, wherein the silica-based particles have a molecular weight of 1000 to 10 ...

7. In the step 1, the pH during wet grinding is 8 or more and 11.5 or less, In the step 2, the pH when the silicic acid solution is added is 9 or more and 12.5 or less, and SiO after the silicic acid solution is added 2 The method for producing silica-based particles according to claim 5 or 6, wherein the concentration is 1% by mass or more and 10% by mass or less, and the silicic acid solution is heated to a temperature of 60°C or more and 170°C or less before or after the addition of the silicic acid solution.

8. In the step 2, the amount of the silicic acid solution added is determined by the SiO 2 The SiO of the silicic acid solution with respect to the molar concentration ２ The method for producing silica-based particles according to claim 5 or 6, wherein the molar concentration is in the range of 0.5 to 20 times by mole.

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