Silica-based particle fluid dispersion for polishing and manufacturing method thereof

Abstract

To provide a silica-based particle fluid dispersion for polishing, capable of simultaneously realizing smoothness, flatness and a high polishing speed when used as polishing slurry for a purpose of finish-polishing of an aluminum hard disk.SOLUTION: A silica-based particle fluid dispersion for polishing includes a silica-based particle group satisfying following conditions: a particle diameter in terms of a specific surface area and an average particle diameter by a dynamic light scattering are within a specific range; an irregular shape degree expressed by a ratio of the particle diameter in terms of a specific surface area and the average particle diameter by a dynamic light scattering is within a specific range; a ratio of silica-based particles having a recessed portion is within a range of less than 5 number%; a ratio of particles having a particle diameter equivalent to a projection area larger by 1.8 times of the particle diameter in terms of a specific surface area and the average particle diameter by a dynamic light scattering is within a range of less than 5 number%; a ratio of particles having an aspect ratio (a ratio of a major axis / a minor axis) of 1.3 or more is within a range of 8 to 20 number%; and when a waveform separation is applied to a volume-based particle size distribution, four separation peaks are detected, with each component ratio within a range of 5 to 40 volume%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a silica particle dispersion for polishing suitable for use in a polishing slurry or a polishing composition for magnetic disk substrates, and to a method for producing the same. [Background technology]

[0002] In finishing abrasives (polishing abrasive dispersions) for aluminum hard disks, in order to meet the demand for low scratching on the substrate surface after polishing, abrasive particles with a spherical shape and a narrow particle size distribution are used. However, it has been pointed out that such abrasive particles have a problem of a relatively slow polishing rate. Therefore, in recent years, there has been a demand for abrasive particles that can achieve high polishing rates and low scratching. Conventionally, silica sol, fumed silica, fumed alumina, etc. have been used as abrasive particles for aluminum hard disks. In the manufacture of aluminum hard disk substrates, the surface after polishing must be flat and free of steps or irregularities, 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, as the particle size of the abrasive grains increases, the smoothness and flatness of the polished substrate surface tend to deteriorate. Therefore, in order to achieve a high polishing rate without deteriorating the surface smoothness and flatness, it is known to be effective to make the abrasive grains non-spherical while maintaining the particle size, that is, to make the abrasive grains irregularly shaped particles (irregular particles). As a method for obtaining 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 porous gel is grown by adding silicic acid or the like to obtain highly irregularly shaped particles.

[0004] Another method for achieving a high polishing rate is known, as disclosed in Patent Document 2, in which an alkali halide is added to an aqueous alkali silicate solution and an acidic silicic acid solution, the molar ratio of the alkali halide to silica is set to 0.01 to 0.5, the solution is heated and stirred, and the acidic silicic acid solution is added while stirring at a Reynolds number in the range of 2000 to 1,000,000, to produce silica particles in which at least four primary particles are clustered together.

[0005] Yet another method for obtaining a high polishing rate is disclosed in Patent Document 3, which involves adding a hydrolyzed liquid obtained by hydrolyzing an alkyl silicate to a liquid containing an alkali catalyst and water, and controlling the pH of the mixed liquid to obtain non-spherical silica particles having a bent and / or branched structure, i.e., irregularly shaped silica particles. Yet another method for obtaining a high polishing rate is disclosed in Patent Document 4, which involves mixing spherical silica particles and associative silica particles. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-177576 [Patent Document 2] Patent No. 6207345 [Patent Document 3] International Publication No. 2010 / 035613 [Patent Document 4] Japanese Patent Application Laid-Open No. 2017-155242 Summary of the Invention [Problem to be solved by the invention]

[0007] However, although the polishing composition described in Patent Document 1 has a high polishing rate, in order to obtain high smoothness and flatness 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. In addition, repeated grinding is required to crush the irregular-shaped porous gel to a predetermined size, which is inefficient and uneconomical.

[0008] The silica particles described in Patent Document 2 have a higher polishing rate than spherical silica particles, but when used for finish polishing of hard disks, there is a problem in that they cannot achieve high smoothness and flatness of the substrate. The colloidal silica described in Patent Document 3 is disclosed as particles having a bent and / or branched structure obtained using a hydrolysis solution obtained by hydrolyzing alkyl silicate, but because the colloidal silica uses alkyl silicate as a raw material, it is very expensive and economically unfeasible, making it unsuitable for hard disk applications. Furthermore, when the authors actually conducted a reproduction experiment, they found that although a bent or branched structure was obtained, the polishing rate was significantly slower than that of irregularly shaped silica particles made from alkali silicate, possibly due to the lack of particle hardness.

[0009] Patent Document 4 discloses a colloidal silica abrasive used in the final polishing process of synthetic quartz glass substrates, comprising a colloidal solution containing spherical colloidal silica abrasive grains and associative colloidal silica abrasive grains. It reports that the polishing rate can be improved by adjusting the degree of association of the associative colloidal silica in the colloidal silica abrasive, resulting in a faster polishing rate than polishing using conventional colloidal silica. However, it has been reported that associative colloidal silica with an average particle size of less than 70 nm tends to have spherical particles, which may not provide sufficient grinding power and make it difficult to improve the polishing rate. Furthermore, in other applications, such as polishing aluminum hard disks, using abrasive particles with an average particle size of 40 nm or more can easily cause scratches on the polished substrate.

[0010] An object of the present invention is to provide a silica-based particle dispersion for polishing that can achieve both smoothness and flatness and a high polishing rate when used as a polishing slurry for finish polishing of aluminum hard disks, and a method for producing the same. [Means for solving the problem]

[0011] The present inventors have conducted extensive research to solve the above problems and have completed the present invention. The present invention includes the following (1) to (4). A silica-based particle dispersion for polishing, comprising a silica-based particle group consisting of irregularly shaped silica-based particles and spherical silica-based particles, wherein the silica-based particle group satisfies the following conditions [1] to [7]: [1] The silica-based particles have an average particle size (Dd) measured by dynamic light scattering method of 10 to 50 nm and a particle size (De) converted into a specific surface area of ​​6 to 35 nm. [2] The irregularity (Dd / De), which is the ratio of the average particle diameter (Dd) measured by dynamic light scattering to the particle diameter converted to specific surface area (De), is within the range of 1.35 to 1.65. [3] In an electron microscope photograph or image of the silica-based particle group, the proportion of silica-based particles having concave recesses is in the range of less than 5% by number. [4] In the silica-based particle group, the proportion of particles whose individual projected area-equivalent particle diameter (DF) of silica-based particles, as measured by image analysis, is greater than 1.8 times the specific surface area-equivalent particle diameter (De), is less than 5% by number. [5] In the silica-based particle group, the proportion of particles having an aspect ratio (ratio of major axis to minor axis) in the range of 1.3 to 2.0 as determined by image analysis is within the range of 8 to 20% by number. [6] Among the individual projected area equivalent particle diameters of the silica-based particles in the silica-based particle group, the range between the minimum particle diameter and the maximum particle diameter is divided into three equal parts, and the three ranges are defined from the smallest particle diameter to the largest particle diameter. The values ​​of the average perimeter (M) / average projected area equivalent perimeter (N) / average projected area equivalent particle diameter (Df) ((M) / (N) / (Df)) for the silica-based particles falling into each particle range are within the ranges of 0.04 to 0.08 for the small particle range, 0.03 to 0.06 for the medium particle range, and 0.02 to 0.05 for the large particle range. [7] When the volume-based particle size distribution of the silica-based particle group is subjected to waveform separation, at least four separated peaks are detected, and the proportion of each component is within the range of 5 to 40% by volume. (2) The dispersion of silica-based particles for polishing according to (1) above, wherein the average long axis / short axis ratio of the silica-based particles in an electron micrograph or image is in the range of 1.15 to 1.25. (3) The dispersion of silica-based particles for polishing according to (1) or (2) above, wherein the average envelopment index of the silica-based particles in an electron micrograph or image is in the range of 0.90 to 0.94. (4) Turbidity is 0.01 cm -1 More than 0.70cm -1 The silica particle dispersion for polishing according to any one of the above (1) to (3) falls within the following ranges: [Effects of the Invention]

[0012] The silica-based particle dispersion of the present invention is a silica-based particle dispersion containing silica-based particles consisting of irregular silica-based particles and spherical silica-based particles, and in particular, the irregular silica-based particles (non-spherical silica-based particles) have a structure in which approximately two primary silica particles are bonded together and the necks formed between the bonded primary silica particles are filled, resulting in no depressions.When such irregular silica-based particles are applied to a polishing process, they have a large contact area with the substrate and can achieve a high polishing rate.

[0013] For example, when the silica-based particle dispersion for polishing of the present invention is used as a polishing slurry or polishing composition for polishing an aluminum substrate for a magnetic disk, a sufficient polishing rate is exhibited and further, the occurrence of "scratches" on the substrate to be polished can be suppressed. The present invention provides such a silica-based particle dispersion for polishing and further provides a method for producing the same. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a conceptual diagram of a photograph or image obtained by observing a dimple-type silica-based particle using an electron microscope (scanning electron microscope or the like). DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will now be described. The present invention is a silica-based particle dispersion for polishing containing a silica-based particle group consisting of irregular silica-based particles and spherical silica-based particles, wherein the silica-based particle group satisfies the following conditions [1] to [7]: [1] The silica-based particles have an average particle size (Dd) measured by dynamic light scattering method of 10 to 50 nm and a particle size (De) converted into a specific surface area of ​​6 to 35 nm. [2] The irregularity (Dd / De), which is the ratio of the average particle diameter (Dd) measured by dynamic light scattering to the particle diameter converted to specific surface area (De), is within the range of 1.35 to 1.65. [3] In an electron microscope photograph or image of the silica-based particle group, the proportion of silica-based particles having concave recesses is in the range of less than 5% by number. [4] In the silica-based particle group, the proportion of particles whose individual projected area-equivalent particle diameter (DF) of silica-based particles, as measured by image analysis, is greater than 1.8 times the specific surface area-equivalent particle diameter (De), is less than 5% by number. [5] In the silica-based particle group, the proportion of particles having an aspect ratio (ratio of major axis to minor axis) in the range of 1.3 to 2.0 as determined by image analysis is within the range of 8 to 20% by number. [6] Among the individual projected area equivalent particle diameters of the silica-based particles in the silica-based particle group, the range between the minimum particle diameter and the maximum particle diameter is divided into three equal parts, and the three ranges are defined from the smallest particle diameter to the largest particle diameter. The values ​​of the average perimeter (M) / average projected area equivalent perimeter (N) / average projected area equivalent particle diameter (Df) ((M) / (N) / (Df)) for the silica-based particles falling into each particle range are within the ranges of 0.04 to 0.08 for the small particle range, 0.03 to 0.06 for the medium particle range, and 0.02 to 0.05 for the large particle range. [7] When the volume-based particle size distribution of the silica-based particle group is subjected to waveform separation, at least four separated peaks are detected, and the proportion of each component is within the range of 5 to 40% by volume. Such a dispersion of silica-based particles for polishing will be referred to as "the dispersion of the present invention" below. The silica-based particles contained in the dispersion of the present invention will hereinafter also be referred to as “particles of the present invention.” In the present invention, the term “particles” means an aggregation of a large number of particles. In this specification, the expression "X to Y" (where X and Y are represented by numerical values) means "a range of not less than X and not more than Y." For example, the expression "0.04 to 0.08" means "a range of not less than 0.04 and not more than 0.08."

[0016] The present invention is characterized in that, in a silica-based particle dispersion containing silica-based particles consisting of irregular silica-based particles (non-spherical silica-based particles) and spherical silica-based particles, the majority of the irregular silica-based particles are in the form of about two primary silica particles bonded together, and the proportion of irregular silica-based particles with a structure that does not have a neck portion consisting of a recessed structure between the bonded primary silica particles is relatively high, and the proportion of irregular silica-based particles with such a neck portion consisting of a recessed structure is relatively low.When applied to a polishing process, the irregular silica-based particles without a neck portion consisting of a recessed structure have a large contact area with a substrate and can achieve a high polishing rate.

[0017] <Mechanism of action> As mentioned above, the silica-based particle dispersion liquid for polishing of the present invention is a silica-based particle dispersion liquid for polishing, which comprises a silica-based particle group consisting of irregular silica-based particles and spherical silica-based particles.Here, irregular silica-based particles essentially include irregular silica-based particles that do not have a neck portion that is made up of a depression structure (non-depression type silica-based particles), and may also include irregular silica-based particles that have a neck portion that is made up of a depression structure (depression type silica-based particles) within a certain range.In addition, the spherical silica-based particles do not have a depression type structure. When non-recessed silica-based particles are used in polishing processes, their irregular shape makes it difficult for the non-recessed silica-based particles to roll on the substrate, which increases the coefficient of dynamic friction between the substrate and the abrasive grains, contributing to an increase in the polishing rate and further causing stress dispersion, which is thought to tend to reduce scratching on the substrate surface. On the other hand, when depression-type silica-based particles are applied to polishing processes, their irregular shape contributes to an increase in the polishing rate as described above, but the depression structure causes local stress concentration, which is the opposite of stress dispersion, and it is thought that they are more likely to cause scratches on the substrate surface than non-depression-type silica-based particles, etc. Furthermore, compared to the stress concentration that occurs in spherical silica fine particles (single particles) when applied to polishing processes, depression-type silica-based particles have a larger individual particle mass, so a larger load is more likely to be applied, and it is presumed that this makes them more likely to cause scratches. The silica-based particle group consisting of the irregular silica-based particles and spherical silica-based particles can exhibit the above-mentioned excellent performance as a silica-based particle dispersion for polishing by specifically satisfying the above-mentioned characteristics [1] to [7].

[0018] The silica-based particle dispersion for polishing of the present invention will be described in detail below. <Silica-based particle dispersion for polishing> The silica-based particle dispersion for polishing of the present invention is a silica-based particle dispersion containing a silica-based particle group in which irregularly shaped silica-based particles (non-spherical silica-based particles) and spherical silica-based particles coexist, and the silica-based particle group has the characteristics [1] to [7] above. In more detail, the irregular silica-based particles essentially include irregular silica-based particles of a type that do not have a concave portion recessed toward the inside of the particle (non-depressed silica-based particles), and may also include irregular silica-based particles of a type that have a concave portion recessed toward the inside of the particle (depressed silica-based particles) in an amount of less than 5% by number (of the silica-based particles in the silica-based particle dispersion for polishing). In the following description of the present application, "% by number" is used as a unit for the proportion of depression-type silica-based particles in the silica-based particle group, the proportion of particles in the silica-based particle group whose individual projected area-equivalent particle diameter (DF) is greater than 1.8 times the specific surface area-equivalent particle diameter (De), the proportion of particles in the silica-based particle group whose aspect ratio (major axis / minor axis ratio) is in the range of 1.3 to 2.0, the proportion of spherical silica-based particles in the silica-based particle group, the proportion of non-spherical silica-based particles in the silica-based particle group, etc.

[0019] <Number ratio of irregular silica particles and spherical silica particles> The spherical silica-based particles contained in the silica-based particle dispersion for polishing of the present invention refer to particles having a major axis / minor axis ratio of less than 1.3, as determined by the method described below in "Measurement of the Content of Irregularly Shaped Silica-Based Particles and Spherical Silica-Based Particles." When the silica-based particle dispersion for polishing of the present invention is used for polishing, these spherical silica-based particles contribute to the planarization of the polished substrate. The recommended proportion of spherical silica-based particles contained in the silica-based particle dispersion for polishing of the present invention is usually 80 to 92% by number, and more preferably 82 to 90% by number. The irregular silica-based particles contained in the silica-based particle dispersion for polishing of the present invention refer to particles having a major axis / minor axis ratio of 1.3 or more, as determined by the method described below in "Measurement of the content of irregular silica-based particles and spherical silica-based particles." Such irregular silica-based particles contribute to improving the polishing rate when the silica-based particle dispersion for polishing of the present invention is used for polishing purposes. The proportion of irregular silica-based particles contained in the silica-based particle dispersion for polishing of the present invention is usually recommended to be in the range of 8 to 20% by number, more preferably 10 to 18% by number.

[0020] <Non-recessed silica particles> The non-depressed silica-based particles will now be described. Non-depressed silica-based particles are silica-based particles that do not have a recessed portion toward the inside of the particle. As described above, non-depressed silica-based particles are the irregularly shaped silica-based particles, and therefore have a major axis / minor axis ratio of 1.3 or more. When the silica-based particle dispersion for polishing of the present invention is used for polishing purposes, the non-depressed silica-based particles have a large contact area with the polishing substrate and do not have a depression structure on the particle surface, so they are less likely to roll, and can make sufficient contact with the polishing substrate, allowing polishing to proceed efficiently.

[0021] <Depression-type silica particles> The depression-type silica particles will now be described. The hollow silica-based particles have hollow portions toward the inside of the particle. The depression-type silica particles will be explained with reference to FIG. FIG. 1 is a conceptual diagram of a photograph or image obtained by observing a dimple-type silica-based particle using an electron microscope (scanning electron microscope or the like). In the present application, as shown in Figure 1, when a tangent line M is drawn that touches two points (points A and B) on the particle contour at the portion of the particle that is concave toward the inside, and a straight line is drawn perpendicular to the tangent line M from the tangent line M to the particle contour, and the length of this line (the length from the tangent line M to the particle contour) is L, particles that satisfy L ≥ 3 [nm] are defined as pitted silica-based particles. Note that for the non-pitched silica-based particles, the relationship L < 3 [nm] applies.

[0022] Depression-type silica-based particles are irregularly shaped silica-based particles (non-spherical silica-based particles), and examples that may fall into this category include non-spherical particles, particle-linked particles, plate-like particles, curved particles, elongated particles, and branched particles.

[0023] The fact that the silica-based particle group is composed of silica can be confirmed, for example, using an ICP (inductively coupled plasma) optical emission spectrometer. 1 g of an aqueous dispersion containing silica-based particle groups is placed in a 30 ml zirconia crucible with a lid, dried (200°C, 20 minutes), and fired (700°C, 5 minutes). Then, 2 g of Na2O2 and 1 g of NaOH are added and melted for 15 minutes. Further, 50 ml of HCl and 200 ml of water are added for dissolution, and the mixture is diluted with pure water to 500 ml to obtain a sample. The silicon content of the obtained sample can be measured using an ICP (Shimadzu Corporation, ICPS-8100, analysis software ICPS-8000). If the silicon content is 90 mass% or more, the particles are determined to be composed of silica.

[0024] Due to their production process, recessed silica particles are inevitably irregularly shaped (non-spherical) or interlocked silica particles. When used as polishing abrasives, these particles have difficulty rolling on the substrate, which increases the coefficient of kinetic friction between the substrate and the abrasive, and tends to contribute to an increase in the polishing rate. However, due to their shape with necks, depression-type silica-based particles are prone to localized stress concentration on the substrate, and further, as mentioned above, their irregular shape gives them a high coefficient of dynamic friction and enables them to achieve a high polishing rate, which results in excessive stress concentration.It is therefore presumed that this is a factor in increasing the surface roughness of the substrate and increasing scratches during polishing treatment, compared to irregular silica-based particles or particle-linked silica particles or spherical silica-based particles that do not have necks with the depression structure.

[0025] <Silica-based particle dispersion> The silica-based particle dispersion of 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 the silica-based particle group satisfies the above conditions [1] to [7]. The silica-based particle dispersion contains silica particles (primary particles) consisting of spherical single particles and irregularly shaped particles in which approximately two of these particles are bonded together. Therefore, when the particle size distribution is subjected to waveform separation, it has a multi-modal distribution in which at least four peaks are detected, and has a broader particle size distribution than, for example, a silica-based particle dispersion containing only spherical single particles. The content of depression-type silica-based particles in the silica-based particle group of the present invention is preferably less than 5% by number.In this case, since the silica-based particle group contains a large number of spherical, small-sized silica-based particles and non-depression-type silica-based particles with a structure without depressions, and the depression-type silica-based particles are relatively small, as described above, when the irregularly shaped silica-based particles or particle-linked silica particles without necks are used in polishing, the irregularly shaped particles have difficulty rolling on the substrate, increasing the coefficient of dynamic friction between the substrate and the abrasive grains, contributing to an increase in the polishing rate, and further causing stress dispersion, thereby reducing scratches on the substrate surface.

[0026] On the other hand, when the content of dimple-type silica-based particles is 5% or more by number, the content of monoparticles and irregularly shaped silica particles with a structure without dimples decreases, and furthermore, because dimple-type particles are formed by bonding primary silica particles and have dimples, they tend to have a larger contact area with the substrate than non-dimple-type silica-based particles without dimples. Furthermore, because the particle diameter is larger than that of monoparticles, stress tends to concentrate on certain parts of the substrate compared to non-dimple-type silica-based particles and monoparticles, which is thought to result in scratches on the substrate and worsen surface roughness.

[0027] Although the particle group of the present invention is composed of silica, it may contain less than 10 mass % of components other than silica, such as Al, Ti, Fe, Ca, Mg, Cr, Ni, Cu, Zn, K, or Na, or oxides thereof. As described above, it can be confirmed that the particle group of the present invention is made of silica using, for example, an ICP apparatus. The content of components other than silica that may be contained in the particle group of the present invention can be identified and quantified, for example, using an inductively coupled plasma optical emission spectrometer. Note that Ni, Cu, K, and Na can be identified and quantified using an atomic absorption spectrophotometer.

[0028] The proportion (content) of the dimple-type silica particles in the particle group of the present invention will be described. The silica-based particle dispersion is observed using an electron microscope (scanning electron microscope photograph, etc.) at a magnification of 50,000 to 100,000 times, and an image is taken so that 200 or more particles are included in the same field of view. The particles in the obtained photograph or image are checked to see if they correspond to depression-type silica-based particles using the method described above with reference to Figure 1. Specifically, 200 particles are randomly selected within the same field of view, and checked to see if they correspond to depression-type silica-based particles, and the number ratio (content ratio) of the 200 particles that correspond to depression-type silica-based particles is calculated.

[0029] The content of dimpled silica-based particles in the particle group of the present invention calculated in this manner is preferably less than 5% by number, and more preferably less than 3.3% by number, as described above. If the content of the dimpled silica particles in the particle group of the present invention is within this range, it is desirable to achieve both scratch prevention and surface roughness and a high polishing rate. Therefore, a content of less than 3.3% by number is optimal and even more desirable in terms of achieving both scratches and surface roughness and a high polishing rate. On the other hand, if the content of dimple-type silica-based particles exceeds 5% by number, scratches and surface roughness tend to worsen. This is presumably because dimple-type silica-based particles, due to their necked shape, tend to cause localized stress concentration on the substrate. Furthermore, as mentioned above, their irregular shape has a high coefficient of dynamic friction, allowing for a high polishing rate, resulting in excessive stress concentration, which is thought to be a factor in increasing the surface roughness and scratches on the substrate during polishing compared to irregularly shaped silica-based particles, particle-linked silica particles, or spherical silica-based particles that do not have necked portions formed by the dimple structure. Among the 200 particles, the number average value of the length (L) of the particles corresponding to the dimple-type silica-based particles is calculated, and this value is designated as the number average value La.

[0030] <Average particle diameter (Dd)> The average particle size (Dd) of the particles of the present invention as measured by dynamic light scattering is preferably 10 to 50 nm, more preferably 12 to 48 nm, even more preferably 15 to 45 nm, and even more preferably 15 to 39 nm. When the average particle size (Dd) is in the range of 10 to 50 nm, when the dispersion of the present invention is used as an abrasive, a high polishing rate can be obtained, and furthermore, the abrasive grains can be prevented from remaining on the object to be polished. In addition, the occurrence of scratches on the object to be polished can be suppressed, and waviness and surface roughness can also be suppressed, resulting in a smoother surface of the object to be polished. If the average particle diameter (Dd) is less than 10 nm, the polishing rate tends to be low when the dispersion of the present invention is used as an abrasive. If the average particle diameter (Dd) is more than 50 nm, waviness and surface roughness tend to worsen, and scratches tend to occur more easily.

[0031] The average particle size (Dd) of the particle group of the present invention means a value obtained by measurement using the dynamic light scattering method described below. Specifically, a silica particle dispersion with a silica concentration of 1% by mass was prepared and measured using a particle size distribution analyzer (Otsuka Electronics' "nanoSAQLA") Ammonia water with a concentration of 0.58% by mass was used as the dispersion medium.

[0032] <Average particle diameter (De)> The particle diameter (De) of the particles of the present invention converted into a specific surface area is preferably 6 to 35 nm, more preferably 10 to 32 nm, and even more preferably 13 to 30 nm. When the average particle size (De) is in the range of 6 to 35 nm, when the dispersion of the present invention is used as an abrasive, a high polishing rate can be obtained, and furthermore, the abrasive grains can be prevented from remaining on the object to be polished. In addition, the occurrence of scratches on the object to be polished can be suppressed, and waviness and surface roughness can also be suppressed, resulting in a smoother surface of the object to be polished. If the average particle diameter (Dd) is less than 6 nm, the polishing rate tends to be low when the dispersion of the present invention is used as an abrasive. If the average particle diameter (De) is more than 35 nm, waviness and surface roughness tend to worsen, and scratches tend to occur more easily. The method for measuring and calculating the particle diameter converted into specific surface area is described in the "Examples" section.

[0033] <Ratio (Dd / De)> In the particles of the present invention, the irregularity (Dd / De) expressed as the ratio of the average particle diameter (Dd) measured by dynamic light scattering to the particle diameter (De) converted into specific surface area is preferably within the range of 1.35 to 1.65. The particle diameter (De) converted into specific surface area of ​​the particle group of the present invention is a value converted from the specific surface area. Specific measurement and calculation methods are described in the "Examples" section of this specification. In the silica-based particle group of the present invention, the ratio (Dd / De) of the average particle diameter (Dd) measured by dynamic light scattering to the particle diameter (De) converted into specific surface area is an index indicating the number or proportion of particles that are bonded together as primary particles. The value of the ratio (Dd / De) is preferably within the range of 1.35 to 1.65. A ratio (Dd / De) value within this range is preferable in terms of achieving both high polishing speed and low scratching. If the ratio (Dd / De) value is less than 1.35, the number and proportion of bonded irregular silica-based particles will be low, which will hinder the polishing speed. If the ratio (Dd / De) value exceeds 1.65, the number and proportion of bonded irregular silica-based particles will be high, which will hinder scratches and surface roughness. In the particle group of the present invention, the value of the ratio (Dd / De) is more preferably from 1.40 to 1.60, and further preferably from 1.43 to 1.58.

[0034] <Proportion of particles whose individual projected area equivalent particle diameter (DF) is greater than 1.8 times the specific surface area equivalent average particle diameter (De)> In the particle group of the present invention, the proportion of particles whose individual projected area equivalent particle diameter (DF) as determined by image analysis method is greater than 1.8 times the specific surface area equivalent particle diameter (De) is in the range of less than 5% by number. The percentage of particles whose individual projected area equivalent particle diameter (DF) is greater than 1.8 times the specific surface area equivalent average particle diameter (De) is an index representing the percentage of irregular silica particles in which three or more primary particles are bonded together. In particular, a value of 1.8 times or greater indicates irregular silica particles in which approximately three primary particles are bonded together. The number of coarse particles is generally considered to be the cause of scratches and defects on polished substrates. Such coarse particles are measured using a so-called coarse particle number measuring device, but the detection limit of such devices is approximately 0.2 μm. In contrast, irregular silica particles of 0.2 μm or less, such as those in which three or more particles are bonded together, cannot be detected, depending on the primary particle diameter. Therefore, the number of such coarse particles is defined by the DF / De ratio. If the percentage is less than 5.0% by number, scratches after polishing can be suppressed. In the particle group of the present invention, when the proportion of particles whose individual projected area-equivalent particle diameter (DF) measured by image analysis is greater than 1.8 times the average particle diameter (De) converted from the average specific surface area is less than 5% by number, a high polishing rate is exhibited while scratches tend to be low, which is desirable. On the other hand, when this proportion exceeds 5% by number, there are many coarse particles of three or more individuals, which tends to worsen scratches.

[0035] <Silica-based particle group particles with specific aspect ratio ranges and their particle ratios> In the particle group of the present invention, the proportion of particles with an aspect ratio (major axis / minor axis ratio) in the range of 1.3 to 2.0 is preferably within the range of 8 to 20% by number. Here, the aspect ratio is measured and calculated by image analysis. The measurement and calculation of aspect ratio and the method for measuring particle proportion are described in the "Examples" section. Furthermore, in this specification, the proportion of particles with an aspect ratio (major axis / minor axis ratio) in the range of 1.3 to 2.0 is also referred to as the "proportion of irregularly shaped particles in a specific aspect ratio range." Meanwhile, particles with an aspect ratio (major axis / minor axis ratio) greater than 2.0 represent coarse irregularly shaped silica-based particles, such as those formed by bonding three or more particles together, and can cause deterioration of scratch resistance. When a silica-based particle dispersion containing silica-based particles with an aspect ratio (major axis / minor axis ratio) of 1.3 to 2.0 in the range of 8 to 20% by number is used for polishing, it exhibits a practical polishing rate and suppresses scratch formation on the polished surface. If the ratio is less than 8% by number, it becomes difficult to achieve a sufficient polishing rate. If the ratio exceeds 20% by number, the polishing rate increases, but the surface roughness of the polished surface tends to deteriorate. The ratio is more preferably 10% to 18% by number, and even more preferably 11% to 17% by number.

[0036] <Average perimeter / Average projected area equivalent perimeter / Average projected area equivalent particle size> In the particle group of the present invention, the range between the minimum particle size and the maximum particle size of the individual projected area equivalent particle sizes of the silica-based particles as determined by image analysis is divided into three equal parts, and the ranges from small to large particle size are designated as small, medium, and large particle ranges, respectively.The value of the average perimeter (M) / average projected area equivalent perimeter (N) / average projected area equivalent particle size (Df) for the silica-based particles falling into each particle range ((M) / (N) / (Df)) is preferably within the range of 0.04 to 0.08 for the small particle range, 0.03 to 0.06 for the medium particle range, and 0.02 to 0.05 for the large particle range. Here, the value of [mean perimeter (M) / mean perimeter equivalent to projected area (N) / mean particle diameter equivalent to projected area (Df)] is an index showing the degree of particle surface roughness normalized by particle diameter, with a larger value indicating a more rough particle surface and a smaller value indicating a smoother surface. If the particle surface is uneven, the load is concentrated on the convex parts during polishing, resulting in a faster polishing rate. On the other hand, the surface roughness of the polished substrate tends to worsen. This tendency becomes more pronounced as the particle size increases. Therefore, to achieve both a good polishing rate and a good substrate surface roughness, it is preferable that larger particles have relatively small surface irregularities, and it is preferable that smaller particles have large surface irregularities. Therefore, the M / N / Df value, which indicates the roughness of the particle surface, is defined as a preferred value for each particle size in the particle size distribution, and when the value of [(M) / (N) / (Df)] is within the range of 0.04 to 0.08 for small particles, 0.03 to 0.06 for medium particles, and 0.02 to 0.05 for large particles, a smooth polished surface is obtained and the polishing rate tends to be improved, which is preferable in terms of achieving both polishing rate and surface roughness. When the value is outside the above range for small, medium, or large particles, the polishing rate tends to decrease if the value is small, and the surface roughness tends to worsen if the value is large. The methods for measuring and calculating the average perimeter (M), average projected area-equivalent perimeter (N), average projected area-equivalent particle diameter (Df), and [(M) / (N) / (Df)] values ​​corresponding to the respective particle ranges of the particle group of the present invention are described in the "Examples" section.

[0037] <Waveform separation peak obtained from volume-based particle size distribution> When the particle group of the present invention is subjected to waveform separation of the volume-based particle size distribution, at least four separation peaks are detected, and it is desirable that the proportion of each component is within the range of 5 to 40 volume %. Here, the method for determining the volume-based particle size distribution and the method for determining waveform separation are described in "Examples". The volumetric particle size distribution of the particle group of the present invention is a multimodal distribution in which four separated peaks are detected. For example, in the case of a particle group with a unimodal distribution, the polishing rate and waviness occur according to the particle size. When the particle size is large, the polishing rate is high but the waviness and surface roughness increase, while when the particle size is small, the waviness and surface roughness improve but the polishing rate decreases. In contrast, in the case of a particle group with a multimodal distribution such as four separated peaks, polishing proceeds while leaving polishing marks according to the particle size of each component, and the sum of these marks represents the waviness and polishing rate. Therefore, if the distribution shows a sufficient polishing rate for both the large particle component and the small particle component (a distribution containing many small and large particles and which shows a multimodal distribution when wave-form separated), a high polishing rate, low waviness, and low surface roughness can be achieved simultaneously. In particular, when the component proportion of each separation peak obtained by waveform separation is in the range of 5% to 40% by volume, each component can efficiently contribute to polishing, which is desirable. When the component proportion of a separation peak is less than 5% by volume at any one point, that component does not contribute much to polishing, and similarly, when the component proportion exceeds 40% by volume at any one point, that component contributes excessively to polishing, which is undesirable. In addition, when the peak areas obtained by waveform separation are designated as S1, S2, S3, and S4 in order from the smallest size, the size of the peak areas is not particularly limited. For example, S1 <S2<S3かつS3> It is preferable to satisfy the relationship S4. In this case, the proportion of large-sized components does not become extremely high, so that in polishing applications, the silica fine particle dispersion of the present invention is more likely to be able to achieve both a high polishing rate and suppress the surface roughness of the substrate to be polished.

[0038] Such a silica-based particle group having a multimodal volume-based particle size distribution has a wide range of particle sizes from large to small (broad distribution), and has more suitable polishing performance. Specifically, the volume fraction of the maximum peak after waveform separation is desirably 40% by volume or less of the total volume. If the volume fraction of the maximum peak is 40% by volume or less, the distribution becomes broad, and waveform separation tends to result in a multi-modal distribution with four or more separated peaks. If the volume fraction of this maximum peak exceeds 40% by volume, the distribution is essentially close to a unimodal distribution, and even if waveform separation is performed on such a volume-based particle size distribution, the number of separated peaks tends to be less than four. The average major axis / minor axis ratio in an electron micrograph or image of the particles of the present invention is preferably in the range of 1.15 or more and 1.25 or less. When the dispersion of the present invention is used for polishing, the average long diameter / short diameter ratio of the silica-based particle group in an electron microscope photograph or image is preferably in the range of 1.15 to 1.25 inclusive, in order to achieve both high polishing speed and low scratching. If the average long diameter / short diameter ratio is less than 1.15, there will be few irregularly shaped silica-based particles in which two or more primary particles are bonded together, which tends to result in a low polishing speed, which is a problem. If the average long diameter / short diameter ratio exceeds 1.25, there will be many irregularly shaped silica-based particles in which three or more primary particles are bonded together, which tends to result in poor scratching. The average long diameter / short diameter ratio of the silica-based particle group in an electron microscope photograph or image is preferably recommended to be in the range of 1.16 to 1.22, and more preferably in the range of 1.18 to 1.20. The method for determining the average value of the long diameter / short diameter ratio in an electron microscope photograph or image of the silica-based particle group is described in the Examples section.

[0039] The average degree of envelopment of the particles of the present invention in an electron microscope photograph or image is preferably in the range of 0.90 to 0.94. Here, the average degree of envelopment of the silica-based particles represents (serves as) an index of the number of depressions on the particle surface and depressions due to necks between particles. When the dispersion of the present invention is used for polishing, it is desirable for the average degree of envelopment of the silica-based particles in an electron microscope photograph or image to be in the range of 0.90 to 0.94, in order to achieve both high polishing speed and low scratching. If the average degree of envelopment is less than 0.90, there will be many depressions on the particle surface and depressions due to necks between particles, i.e., large unevenness on the particle surface, or there will be many depression-shaped silica-based particles, which will easily cause localized stress concentration on the substrate, resulting in a tendency for scratches to worsen, which is problematic. In the case of irregularly shaped silica-based particles, the shape of which is such that two or more primary particles are bonded together inevitably results in a low degree of envelopment. Therefore, if the average degree of envelopment is greater than 0.97, there will be extremely few depressions on the particle surface and very few irregularly shaped silica-based particles, which will result in a tendency for the polishing speed to decrease, which is problematic. The average degree of envelopment in an electron micrograph or image of the silica-based particle group is preferably in the range of 0.91 to 0.94, and more preferably in the range of 0.92 to 0.94. The method for determining the average degree of envelopment in an electron microscope photograph or image of silica-based particle groups is described in the Examples section.

[0040] In the dispersion of the present invention, the turbidity is 0.01 cm -1 More than 0.70cm -1 It is desirable that the range is as follows: Here, turbidity is a parameter that indicates the scattering of light in the dispersion of the present invention, and the scattering intensity tends to increase as the amount of larger particles or particles with higher irregularities increases. Therefore, a high turbidity comprehensively indicates the content of coarse particles and particles with higher irregularities that cause scratches in the dispersion of the present invention. The turbidity of the dispersion of the present invention is 0.01 cm -1 More than 0.70cm -1 When the turbidity of the dispersion is within the range below, there are almost no coarse particles or highly irregular particles that cause scratches, and even if such a dispersion is used for polishing purposes, the occurrence of scratches is almost suppressed. -1 If the turbidity is greater than 0.01 cm, there will be coarse particles or highly irregular particles that will cause scratches, and if such a dispersion is used for polishing purposes, scratches may occur to a degree that will cause practical problems. -1 If the turbidity is less than 0.70 cm, most of the particles in the dispersion will be small in diameter, which may cause a decrease in the polishing rate. -1 If the thickness exceeds 100 μm, scratches tend to worsen and this is problematic. -1 The range of 0.05 to 0.40 cm is recommended. -1 The method for determining the turbidity of the dispersion of the present invention is described in the Examples.

[0041] As described above, the dispersion of the present invention is obtained by dispersing the silica-based particles of the present invention in a solvent. Examples of the solvent include water, alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, and water-soluble organic solvents such as ethers, esters, and silicates. A mixed solvent consisting of water and an organic solvent may also be used.

[0042] The content of the silica-based particles of the present invention contained in the dispersion of the present invention is preferably 1 to 50 mass %, more preferably 10 to 50 mass %. Here, the content of the silica-based particle group of the present invention contained in the dispersion of the present invention was calculated by subjecting the dispersion of the present invention to ignition loss at 1000°C, weighing the obtained solid content, and subtracting the separately calculated alkali content converted into an oxide (e.g., NaO) from the weight, to obtain the content of the silica-based particle group of the present invention.

[0043] <Polishing composition for magnetic disk substrates> The polishing composition for magnetic disk substrates will now be described. The polishing composition for magnetic disk substrates contains the dispersion of the present invention or the silica-based particles of the present invention. The term "polishing composition for magnetic disk substrates" encompasses the concept of "polishing slurry." A polishing composition for magnetic disk substrates with a low solids concentration, or a polishing composition for magnetic disk substrates diluted with water or the like, is usually referred to as a polishing slurry. A polishing composition for magnetic disk substrates containing the dispersion of the present invention is hereinafter also referred to as the "composition of the present invention."

[0044] The composition of the present invention may further contain other components in addition to the dispersion of the present invention. 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.

[0045] 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. When the composition of the present invention contains 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 achieving a flat polished surface.

[0046] When the composition of the present invention contains a polishing accelerator, the content thereof is preferably 0.1 to 10 mass %, more preferably 0.5 to 5 mass %. In order to improve the dispersibility and stability of the polishing composition of the present invention, a cationic, anionic, nonionic or amphoteric surfactant or a hydrophilic compound can be added.

[0047] 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:

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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 alcinyl ethers, alkyl polyethylene glycols, alkyl polyethylene glycol alkyl ethers, alkyl polyethylene glycol alcinyl ethers, alcinyl polyethylene glycols, alcinyl polyethylene glycol alkyl ethers, alcinyl polyethylene glycol alcinyl ethers, polypropylene glycol alkyl ethers, polypropylene glycol alcinyl ethers, alkyl polypropylene glycols, alkyl polypropylene glycol alkyl ethers, alkyl polypropylene glycol alcinyl ethers, alcinyl polypropylene glycols, etc.), polysaccharides (alginic acid, pectinic acid, carboxymethylcellulose, curdlan, pullulan, etc.), amino acid salts (glycine ammonium salt, glycine sodium salt ... polysaccharides), polysaccharides (alginic acid, pectinic acid, polysaccharides), polysaccharides (alginic acid, pectinic acid, polysaccharides), polysaccharides (alginic acid, pectinic acid, polysaccharides), polysaccharides (alginic acid, pectinic acid, polysaccharides), polysaccharides ( 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.

[0053] 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 ammonium salt surfactant.

[0054] When the composition of the present invention 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 composition of the present invention.

[0055] The surfactant or hydrophilic compound may be used alone or in combination with two or more kinds.

[0056] When the substrate to be polished contains a metal, the composition of the present invention may contain a heterocyclic compound 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.

[0057] When the composition of the present invention contains a heterocyclic compound, the content is preferably from 0.001% by mass to 1.0% by mass, more preferably from 0.001% by mass to 0.7% by mass, and even more preferably from 0.002% by mass to 0.4% by mass.

[0058] 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.

[0059] When adjusting the pH of the composition of the present invention to 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.

[0060] 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.

[0061] To maintain a constant pH value of the composition of the present invention, 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.

[0062] The concentration of the abrasive particles in the composition of the present invention is preferably 0.5 to 50% by mass, more preferably 5 to 30% by mass. 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 the 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 products may be generated and adhere during the process of supplying the dispersion liquid for the polishing treatment, which may cause scratches. [Example]

[0063] The silica-based particle dispersions obtained in each of the Examples and Comparative Examples were evaluated as follows, and the results are shown in Table 1.

[0064] <Measurement of the content of irregular silica particles and spherical silica particles> Using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), silica-based particles constituting a silica-based particle group were photographed at 50,000x magnification, and the resulting photographic projection or projected image (limited to those with 500 or more particles displayed on the photograph or image) was used to randomly select 100 particles. A rectangle was then imagined circumscribing each silica-based particle, and the long / short side value of the rectangle with the largest long / short side value was taken as the aspect ratio of each silica-based particle. The number of silica-based particles with an aspect ratio of 1.3 or more was determined, and the percentage (number %) of this ratio out of the total number of particles (100) was calculated to represent the content (A) of irregularly shaped silica-based particles. The value of 100-A was taken as the content (B) of spherical silica-based particles. In the present invention, photographing with a scanning electron microscope (SEM) was performed using a silica-based particle dispersion liquid as a sample, using a scanning electron microscope (for example, S-2000 model manufactured by Hitachi, Ltd.).

[0065] <Measuring the average particle size (Dd) of silica-based particles using dynamic light scattering> The average particle size of silica-based particles was measured by dynamic light scattering using a particle size distribution analyzer (nanoSAQLA manufactured by Otsuka Electronics Co., Ltd.) for a silica-based particle dispersion (silica concentration 1 mass%, solvent: ammonia water [concentration 0.58 mass%]).

[0066] <Specific surface area converted particle diameter (De) of silica-based particles> The particle diameter (De) converted into specific surface area can be calculated by measuring the specific surface area SA of the silica-based particles and using the following formula. De(nm)=6000 / (ρ×SA) (where ρ is the density of silica particles, 2.2 [g / cm 3 ].) Here, the specific surface area SA is determined by the BET method described later. However, when the specific surface area of ​​the silica-based particles determined by the BET method is 100 m 2When it was / g or more, since sintering proceeded during firing in the BET method, in this case, the specific surface area (SA) was determined by the titration method (volumetric titration method) described later, and the particle size in terms of specific surface area (De) was calculated from the formula De = 6000 / (SA×ρ).

[0067] <BET method> For a 50 mL silica-based particle dispersion containing silica-based particles (silica concentration: 40% by mass), the pH was adjusted to 3.5 with HNO3, 40 mL of 1-propanol was added, and the sample was dried at 110 °C for 16 hours. After pulverizing in a mortar, it was fired in a muffler furnace at 500 °C for 1 hour to obtain a measurement sample. Then, using a specific surface area measurement device (manufactured by Yuasa Ionics, model Multi-Sorb 12), the specific surface area was calculated by the BET one-point method from the nitrogen adsorption amount using the nitrogen adsorption method (BET method).

[0068] Specifically, 0.5 g of the measurement sample obtained as described above was placed in a measurement cell, degassed at 300 °C for 20 minutes in a mixed gas stream of 30 v% nitrogen and 70 v% helium, and then the sample was maintained at liquid nitrogen temperature (-196 °C) in the above mixed gas stream, and nitrogen was adsorbed on the sample in equilibrium. Next, while flowing the above mixed gas, the sample temperature was gradually raised to room temperature, and the amount of nitrogen desorbed during that time was detected, and the specific surface area of the silica-based particles was calculated from a calibration curve prepared in advance. Then, the obtained specific surface area (SA) was substituted into the conversion formula from specific surface area to particle size described above to obtain the particle size in terms of specific surface area (De).

[0069] <Titration method (volumetric titration method)> Here, the titration method is as follows. For a silica-based particle dispersion containing silica-based particles (silica concentration: 40% by mass) similar to the case of the BET method above, after collecting a silica-based particle dispersion corresponding to 1.5 g as SiO2 in a beaker, it was transferred to a thermostatic reaction tank (25 °C), and pure water was added to make the liquid volume 90 ml. The following operations were carried out in a thermostatic reaction tank maintained at 25 °C. Next, 0.1 mol / L hydrochloric acid solution was added to this to adjust the pH to 3.6, and then 30 g of sodium chloride was added, and the mixture was diluted with pure water to 150 ml and stirred for 10 minutes. A pH electrode was then set, and 0.1 mol / L sodium hydroxide solution was added dropwise while stirring to adjust the pH to 4.0. The silica-based particle dispersion adjusted to pH 4.0 was then titrated with 0.1 mol / L sodium hydroxide solution, and the titration amount and pH value were recorded at four or more points in the pH range of 8.7 to 9.3. A calibration curve was then created, with the titration amount of 0.1 mol / L sodium hydroxide solution represented as X and the pH value at that time represented as Y. The amount of 0.1 mol / L sodium hydroxide solution V (ml) required to change the pH from 4.0 to 9.0 per 1.5 g of SiO2 was calculated from the equation V = (A × f × 100 × 1.5) / (W × C), and the specific surface area was calculated using 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 SiO to change the pH to 4.0 to 9.0, f is the titer of the 0.1 mol / L sodium hydroxide solution, C is the SiO concentration (mass%) of the silica-based particle dispersion, and W is the amount (g) of the silica-based particle dispersion collected. The value of Dd / De was calculated from the value of the specific surface area converted particle diameter (De) of the silica-based particle group thus obtained and the value of the average particle diameter (Dd) of the silica-based particle group determined by the dynamic light scattering method as described above.

[0070] <Confirmation of dimpled silica particles and calculation of their proportion> A scanning electron microscope photograph (S-2000 model manufactured by Hitachi, Ltd., 200,000x magnification, containing 200 or more particles in the same field of view) of the silica-based particle dispersion was taken, and whether or not the particles in the photograph corresponded to depression-type silica-based particles was confirmed by the following method.

[0071] First, as shown in Figure 1, a tangent line M was drawn at the concave portion of a particle, touching two points (points A and B) on the particle contour that sandwiched the concave portion, and the maximum length of the straight line drawn perpendicular to the tangent line M from the tangent line M to the particle contour was determined. If the length (L) was 3 nm or greater, the particle was determined to be a concave-type silica-based particle. Note that if a particle has multiple concave portions, including multiple concaves with a length L of 3 nm or greater, the length L of the particle will be taken to mean the maximum L. In this way, 200 particles randomly selected within the field of view were investigated to determine whether they were pitted silica-based particles, and the percentage (number %) of particles that were pitted silica-based particles among the 200 particles was calculated.

[0072] <Methods for measuring and calculating the particle diameter equivalent to the individual projected area (DF) of silica-based particles> The particle diameter equivalent to the individual projected area (DF) of silica-based particles is measured and calculated using the following method: First, using a scanning electron microscope (SEM), an arbitrary point on the surface of a silica-based particle constituting a silica-based particle group is measured at a magnification of 3000 times, with a field of view of 1.1 x 10 -3 mm 2 15 fields of view were photographed with an area of ​​15. Then, 300 silica-based particles were randomly selected from the silica-based particles contained in each image photographed in each field of view, and the projected area (S) of each particle was measured by image analysis using an image analysis system, and the particle diameter (circle diameter) of the circular particle corresponding to each of the measured projected areas was calculated, and this was taken as the particle diameter (DF) corresponding to the individual projected area of ​​each silica-based particle.

[0073] <How to determine the percentage of silica-based particles whose individual projected area equivalent particle diameter (DF) value is greater than 1.8 times the specific surface area equivalent particle diameter (De) using image analysis method> The particle diameter (De) converted to a specific surface area of ​​the silica-based particle group was calculated by measuring the specific surface area of ​​the silica-based particle group using the method described above. The individual projected area equivalent particle diameter (DF) values ​​of the 300 silica-based particles were determined by processing the SEM projection images with an image analysis system as described above, and 100 silica-based particles were randomly selected from the 300 silica-based particles. The number ratio of particles whose individual projected area equivalent particle diameter (DF) value was 1.8 times or more the specific surface area equivalent particle diameter (De) was calculated, and this was taken as the proportion of particles whose individual projected area equivalent particle diameter (DF) value was greater than 1.8 times the specific surface area equivalent particle diameter (De).

[0074] <Method for measuring / calculating the proportion of particles with an aspect ratio of 1.3 to 2.0 in silica-based particle groups> The silica-based particles constituting the silica-based particle group were observed at a magnification of 3000 times using a scanning electron microscope (SEM), and the obtained images were processed using an image analyzer to determine the aspect ratio of each of 100 or more silica-based particles. Here, for each silica-based particle, a rectangle was assumed to circumscribe the silica-based particle, and the ratio of the long side to the short side of the rectangle with the largest ratio was taken as the aspect ratio of that silica-based particle.Then, the number ratio of particles with an aspect ratio of 1.3 to 2.0 among 100 or more silica-based particles was calculated.

[0075] <Method of measuring and calculating average circumference (M)> The range from the minimum to maximum particle diameters corresponding to the individual projected area (DF) of 300 silica-based particles determined by the above method was divided into three equal parts, and the range was divided into small particle range, medium particle range, and large particle range from the smallest particle diameter.The perimeter (m) of each silica-based particle falling into each particle range was measured by image analysis using an image analysis system, and the number average for each particle range was determined, and this value was used as the average perimeter (M) for each particle range.

[0076] <Method of measuring and calculating the perimeter equivalent to the average projected area (N)> For the 300 silica-based particles whose individual projected area equivalent particle diameters (DF) were determined using the above method, the range from the minimum value to the maximum value was divided into thirds, and the range was divided into small particle ranges, medium particle ranges, and large particle ranges from the smallest particle diameter.For each silica-based particle falling into each particle range, the projected area (S) of each particle was determined by image analysis using an image analysis system.Furthermore, the projected area equivalent perimeter (n) of each particle was determined using the following formula (1).The number average of the projected area equivalent perimeter (n) for each particle range was determined, and this value was used as the average projected area equivalent perimeter (N) for each particle range. Perimeter length equivalent to projected area (n)=2·(S·π)1 / 2 Equation (1)

[0077] <Methods for measuring and calculating particle diameter equivalent to average projected area (Df)> The individual projected area equivalent particle diameters (DF) of 300 silica-based particles determined by the above method were calculated for the silica-based particles falling within the small particle range, medium particle range, and large particle range, and the number average of the individual projected area equivalent particle diameters (DF) for each particle range was determined, and this was designated as the average projected area equivalent particle diameter (Df) for each particle range.

[0078] The value of [(M) / (N) / (Df)] was calculated from the average perimeter (M), average projected area equivalent perimeter (N), and average projected area equivalent particle diameter (Df) corresponding to each particle range obtained in this way.

[0079] <Volume-based particle size distribution> In the present invention, the volumetric particle size distribution of silica-based particles is measured by centrifugal sedimentation. The silica-based particle dispersion is diluted with a 0.05% by mass aqueous solution of sodium dodecyl sulfate to adjust the solid content to 2% by mass, and the volumetric particle size distribution can be measured using a known disk centrifugal particle size distribution analyzer (for example, manufactured by CPS Instruments).

[0080] <Waveform separation from volume-based particle size distribution> Waveform separation is performed by analyzing the volumetric particle size distribution obtained using the disk centrifugal particle size distribution analyzer using the peak analyzer in Origin (OriginLab Corporation), a graphing and data analysis software. First, the baseline is set to 0, the peak type is set to Gaussian, and the maximum point of the particle size distribution is selected as the peak position. Peak fitting is performed without weighting, and it is confirmed that the calculated peak does not deviate from the following conditions 1 and 2. If it does deviate, the peak position is shifted to any position within the distribution range until conditions 1 and 2 are met, and peak fitting is repeated. Then, if the corrected R-squared value is 0.999 or less, a peak is added to any position within the distribution range, and peak fitting is repeated until the corrected R-squared value is 0.999 or greater. The number of separated peaks at this point is taken as the number of peaks, and the area of ​​each peak is taken as the component proportion. Condition 1: Each calculated peak must not take a value greater than the original distribution. Condition 2: Each calculated peak must not take a negative value.

[0081] <Calculation of the average long diameter / short diameter ratio of silica-based particle groups> The average value of the ratio of the major axis to the minor axis in an electron micrograph or image of the silica-based particle group was determined by the following method. The silica-based particle dispersion of the present invention (concentration 40% by mass) was photographed under a transmission electron microscope at a magnification of 300,000 times (or 500,000 times) to obtain a photographic projection or projected image. For each particle, the maximum diameter was taken as the major axis, and the length was measured, and this value was taken as the major axis (La). A point was determined on the major axis that divided the major axis into two equal parts, and two points where a line perpendicular to this point intersected the outer edge of the particle were found. The distance between these two points was measured, and this was taken as the minor axis (Sh). The minor axis / major axis ratio (Sh / La) was calculated for each particle in this way, and the number average value of 100 of these was calculated, which was taken as the minor axis / major axis ratio of the silica fine particles for polishing.

[0082] <Average envelope degree> A 0.1 ml sample of silica-based particle dispersion (silica concentration: 0.1% by mass) was dried on a STEM grid at room temperature and image data of the STEM image was obtained using a scanning transmission electron microscope (S-5500, Hitachi High-Technologies Corporation). One hundred particles were then randomly selected from the STEM image. The image data (secondary electron image, 100x magnification, jpg image) of the STEM image was then read into SEM image analysis software (e.g., "RADIUS 2.0" manufactured by EMSIS). A specific region of the image was selected as the analysis region (frame), and this analysis region (frame) was then binarized. Specifically, 153 gradations were selected as the lower limit and 255 gradations as the upper limit for each RGB value, and binarization was performed using these two thresholds. Particles within the binarized analysis region were detected, and any clusters of particles detected as a single particle were deleted. For particles recognized as single particles, the perimeter of the particle's projected image was calculated. This procedure is carried out for 100 individual particles. Then, for each individual particle, the degree of envelopment is calculated using the following formula, and the average degree of envelopment is calculated by simply averaging these values. Envelope ratio = [(envelope perimeter [A]) / (actual perimeter [B])] Here, the perimeter when connecting the vertices of the convex parts of the single particle with the shortest distance is defined as the envelope perimeter [A], and the length of the outline of the polishing silica microparticle itself is defined as the actual perimeter [B].

[0083] <Measurement of turbidity of silica-based particle dispersion> Using a spectrophotometer (V-550 manufactured by JEOL Ltd.), the absorbance (log(I / I)) at a wavelength of 500 nm of a silica-based particle dispersion liquid with a solid content adjusted to 3% by mass is measured. Water is used as a control liquid. Then, the turbidity (τ) is calculated using the Lambert's law formula shown below. τ(cm -1 )=(1 / W)×ln(I0 / I)=(1 / W)×2.303×log(I0 / I) Here, W is the cell width (cm), I0 is the incident light intensity (%), and I is the transmitted light intensity (%).

[0084] <Polishing test method (polishing speed 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.

[0085] <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.

[0086] <Scratch> The polished substrate obtained in the polishing test was observed over the entire surface using an ultrafine defect visualization macro device (manufactured by VISION PSYTEC, product name: Micro-Max) at Zoom 15. 2 The number of scratches (linear scratches) present on the polished substrate surface corresponding to the number of scratches was counted and totaled. The number of scratches occurring in Comparative Example 1 was set to 100, and the ratio of the number of scratches occurring in each Example is shown in Table 1.

[0087] [Example] The components and properties of the silica fine particle dispersions (silica concentration 40% by mass) of Examples and Comparative Examples are shown in Table 1. Comparative Examples 1 and 2 are as described below.

[0088] [Comparative Example 1] "SI-40" (manufactured by JGC Catalysts and Chemicals, Ltd.: silica concentration 40% by mass), which is a dispersion liquid in which silica fine particles are dispersed, was used as Comparative Example 1.

[0089] Comparative Example 2 "SI-50" (manufactured by JGC Catalysts and Chemicals, Ltd.: silica concentration 48% by mass), which is a dispersion liquid in which silica fine particles are dispersed, was used as Comparative Example 2.

[0090]

Table 1

Claims

1. A silica-based particle dispersion for polishing containing a silica-based particle group consisting of irregularly shaped silica-based particles and spherical silica-based particles, wherein the silica-based particle group satisfies the following conditions [1] to [7]: [1] The silica-based particles have an average particle size (Dd) of 10 to 50 nm as measured by a dynamic light scattering method, and a particle size (De) converted to a specific surface area within the range of 6 to 35 nm. [2] The irregularity (Dd / De), which is the ratio of the average particle diameter (Dd) measured by dynamic light scattering to the particle diameter (De) converted into specific surface area, is within the range of 1.35 to 1.

65. [3] In an electron microscope photograph or image of the silica-based particle group, the proportion of silica-based particles having concave recesses is in the range of less than 5% by number. [4] In the silica-based particle group, the proportion of particles whose individual projected area-equivalent particle diameter (DF) of the silica-based particles is greater than 1.8 times the specific surface area-equivalent particle diameter (De) as determined by image analysis is less than 5% by number. [5] In the silica-based particle group, the proportion of particles having an aspect ratio (major axis / minor axis ratio) in the range of 1.3 to 2.0 as determined by image analysis is within the range of 8 to 20% by number. [6] Among the individual projected area equivalent particle diameters of the silica-based particles in the silica-based particle group, the range between the minimum particle diameter and the maximum particle diameter is divided into three equal parts, and the three ranges are defined from the smallest particle diameter to the largest particle diameter. The values ​​of the average perimeter (M) / average projected area equivalent perimeter (N) / average projected area equivalent particle diameter (Df) ((M) / (N) / (Df)) for the silica-based particles falling within each particle range are within the ranges of 0.04 to 0.08 in the small particle range, 0.03 to 0.06 in the medium particle range, and 0.02 to 0.05 in the large particle range. [7] When the volume-based particle size distribution of the silica-based particle group is subjected to waveform separation, at least four separated peaks are detected, and the proportion of each component is within the range of 5 to 40% by volume.

2. 2. The silica-based particle dispersion for polishing according to claim 1, wherein the average major axis / minor axis ratio of the silica-based particle group in an electron micrograph or image is in the range of 1.15 to 1.

25.

3. 3. The silica-based particle dispersion for polishing according to claim 1, wherein the average envelopment degree of the silica-based particle group in an electron micrograph or image is in the range of 0.90 to 0.

94.

4. Turbidity is 0.01 cm -1 0.70cm or more -1 3. The silica-based particle dispersion for polishing according to claim 1, wherein the dispersion has the following range:

Images