Polishing liquid composition

Abstract

To provide, in one embodiment, a polishing liquid composition which can satisfy both of polishing speed improvement and waviness reduction.SOLUTION: The present disclosure, in one embodiment, relates to a polishing liquid composition comprising silica particles, an acid, and an oxidizing agent. The silica particles are such that the average particle size A obtained from a BET specific surface area is 60 nm to 90 nm; the number ratio of particles having a particle size equal to or less than the average particle size A, as obtained from an image analysis using a scanning electron microscope (SEM), is 80% or more; the average aspect ratio of particles having a particle size equal to or less than the average particle size A, as obtained from an image analysis using SEM, is 1.10 or more and less than 1.15; and the average aspect ratio of particles having a particle size larger than the average particle size A, as obtained from an image analysis using SEM, is 1.20 or more and less than 1.25.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a polishing composition and a method for manufacturing a magnetic disk substrate using the same. [Background technology]

[0002] In recent years, magnetic disk drives have become smaller and have larger capacities, and higher recording densities are being demanded. To achieve higher recording densities, technological developments are being made to reduce the unit recording area and lower the flying height of the magnetic head in order to improve the detection sensitivity of weakened magnetic signals. In order to reduce the flying height of the magnetic head and ensure the recording area, there are increasingly strict requirements for magnetic disk substrates in terms of improving smoothness and flatness, as typified by reducing surface roughness, waviness, and edge sagging (roll-off), and reducing defects, as typified by reducing scratches, protrusions, pits, etc.

[0003] In response to such demands, for example, Patent Document 1 proposes a polishing composition containing silica abrasive grains and water, in which the abrasive grains have an average aspect ratio of 1 to 1.25 for cumulative 0 to 5% of particles in a cumulative particle size distribution based on the number of particles from the small particle size side, and an average aspect ratio of 1 to 1.30 for all particles. Patent Document 2 proposes a polishing composition containing silica abrasive grains and water, in which the abrasive grains have an average aspect ratio of 1.25 or less for 0 to 20% of the particles in a cumulative volume distribution from the small particle size side, and an average aspect ratio of 1.3 or more for 80 to 100% of the particles in a cumulative volume distribution. Patent Document 3 proposes a polishing composition containing silica abrasive grains and water, in which the abrasive grains have an average aspect ratio of 1.1 or more and a cumulative frequency 99% particle size measured by a light transmission centrifugal sedimentation method of less than 295 nm. Patent Document 4 proposes a polishing composition comprising first silica abrasive grains having an average aspect ratio As1 and second silica abrasive grains having an average aspect ratio As2 larger than that of the first silica abrasive grains, wherein the average minor diameter Dmin1 of the first silica abrasive grains is 30 nm or more and 60 nm or less, and the relationship between the average minor diameter Dmin1 of the first silica abrasive grains and the average minor diameter Dmin2 of the second silica abrasive grains satisfies 1<(Dmin2 / Dmin1)<3. Patent Document 5 proposes a polishing agent having a solid acid amount or solid base amount of 0.01 mmol / g or more, in which inorganic oxide fine particles having an average particle size of 2 μm or less are dispersed in a dispersion medium, and which has a pH of 8 to 11.5. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-174009 A [Patent Document 2] JP 2017-179217 A [Patent Document 3] JP 2020-055914 A [Patent Document 4] JP 2015-203108 A [Patent Document 5] JP 2012-200832 A Summary of the Invention [Problem to be solved by the invention]

[0005] With the increase in capacity of magnetic disk drives, the required characteristics for the surface quality of substrates are becoming more severe, and there is a demand for a polishing composition that can realize not only an improvement in the polishing speed (productivity) but also a reduction in the waviness of the substrate surface (substrate quality). In general, there is a trade-off between the polishing speed and the waviness, and for example, there is a problem that if the polishing speed is improved, the waviness of the substrate surface after polishing worsens.

[0006] In view of this, in one aspect, the present disclosure provides a polishing composition that can achieve both an improvement in the polishing rate and a reduction in waviness. [Means for solving the problem]

[0007] In one aspect, the present disclosure relates to a polishing liquid composition comprising silica particles, an acid, and an oxidizing agent, wherein the silica particles have an average particle size A of 60 nm or more and 90 nm or less, as determined from a BET specific surface area, a number ratio of particles having an average particle size of A or less, as determined from image analysis using a scanning electron microscope (SEM), of 80% or more, an average aspect ratio of particles having an average particle size of A or less, as determined from image analysis using SEM, of 1.10 or more and less than 1.15, and an average aspect ratio of particles having a particle size greater than the average particle size A, as determined from image analysis using SEM, of 1.20 or more and less than 1.25.

[0008] In one aspect, the present disclosure relates to a method for producing a magnetic disk substrate, comprising the step of supplying the polishing liquid composition of the present disclosure between a substrate to be polished and a polishing pad, and polishing the substrate to be polished. Effect of the Invention

[0009] According to the present disclosure, in one or more embodiments, a polishing composition capable of achieving both an improvement in removal rate and a reduction in waviness can be provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present disclosure is based on the discovery that by using a polishing composition containing specific silica particles, an acid, and an oxidizing agent for polishing (e.g., rough polishing), the polishing rate can be improved and waviness of the polished substrate surface after polishing can be reduced.

[0011] That is, in one aspect, the present disclosure relates to a polishing liquid composition comprising silica particles, an acid, and an oxidizing agent, wherein the silica particles have an average particle size A of 60 nm or more and 90 nm or less as determined from a BET specific surface area, the number ratio of particles having an average particle size of A or less is 80% or more as determined from image analysis using a scanning electron microscope (SEM), the average aspect ratio of particles having an average particle size of A or less is 1.10 or more and less than 1.15 as determined from image analysis using SEM, and the average aspect ratio of particles having a particle size greater than the average particle size A is 1.20 or more and less than 1.25 as determined from image analysis using SEM (hereinafter also referred to as the "polishing liquid composition of the present disclosure").

[0012] Although the details of the mechanism by which the effects of the present disclosure are manifested are not clear, it is presumed as follows. Generally, silica particles are dispersed and stable in the polishing region under strong acidity, regardless of the isoelectric point. This is because the water molecules present on the surface of the silica particles are hydrated and repelled. However, if the hydration repulsion is large, the mechanical force that the silica particles exert on the substrate is weakened, and the polishing rate is thought to decrease. In the present disclosure, the silica particles having a specific particle size and a specific aspect ratio, and further a specific particle size ratio, are thought to reduce the hydration repulsion by narrowing the distance between the silica particles, thereby improving the polishing rate. In addition, the waviness, which indicates the quality of the substrate, is thought to improve because the area of ​​the silica particles acting per unit substrate area increases due to the narrowing of the distance between the silica particles, and stress concentration on the substrate is alleviated. However, the present disclosure need not be construed as being limited to these mechanisms.

[0013] In the present disclosure, the "waviness" of a substrate refers to unevenness on the substrate surface having a longer period than the "roughness". In the present disclosure, unevenness with a period of 60 to 160 μm is referred to as "short wavelength waviness", and unevenness with a period of 500 to 5000 μm is referred to as "long wavelength waviness". By reducing the waviness (short wavelength waviness, long wavelength waviness) of the substrate surface after polishing, the flying height of the magnetic head in a magnetic disk drive can be reduced, and the recording density of the magnetic disk can be improved. The waviness (short wavelength waviness, long wavelength waviness) of the substrate surface can be measured, for example, by the method described in the Examples. In the present disclosure, "reduction of waviness" refers to reduction of at least one of the short wavelength waviness and the long wavelength waviness.

[0014] [Silica particles (component A)] The silica particles (hereinafter also referred to as "component A") contained in the polishing liquid composition of the present disclosure may be of one type, or a combination of two or more types.

[0015] In the present disclosure, the average particle size A calculated from the BET specific surface area of ​​component A is 60 nm or more and 90 nm or less, and from the viewpoint of improving the polishing rate, it is 60 nm or more, preferably 62 nm or more, more preferably 63 nm or more, and even more preferably 65 nm or more, and from the viewpoint of reducing waviness, it is 90 nm or less, preferably 85 nm or less, more preferably 80 nm or less, and even more preferably 75 nm or less. In the present disclosure, the average particle size A can be calculated using the BET specific surface area, specifically, by the method described in the Examples.

[0016] The BET specific surface area of ​​component A is set to 45.5 m from the viewpoint of improving the polishing speed and reducing waviness. 2 / g or less is preferable, and 45m 2 / g or less is more preferable, and 44m 2 / g or less is more preferable, 2 / g or less is even more preferable, and from the same viewpoint, 30.3m 2 / g or more is preferable, and 32m 2 / g or more is more preferable, and 34m 2 / g or more is more preferable, and 36m 2 / g or more is even more preferable. In the present disclosure, the BET specific surface area can be calculated by a nitrogen adsorption method.

[0017] In the present disclosure, the number ratio of particles in Component A having an average particle size of A or less, determined by image analysis using a scanning electron microscope (hereinafter also simply referred to as "SEM"), is, from the viewpoints of improving the polishing rate and reducing waviness, 80% or more, preferably 82% or more, and more preferably 84% or more, and from the viewpoints of improving the polishing rate, preferably 90% or less, more preferably 88% or less, even more preferably 86% or less, and even more preferably 85% or less. In the present disclosure, the ratio of the number of particles having an average particle size of A or less obtained from image analysis using SEM can be calculated by observing a predetermined number of particles using SEM, and counting the number of particles having a particle size of A or less and the total number of particles obtained from the BET specific surface area of ​​component A using a known image analysis system. Specifically, it can be calculated by the method described in the Examples.

[0018] In the present disclosure, the average aspect ratio of particles in component A having an average particle size of A or less, as determined by image analysis using SEM, is 1.10 or more and less than 1.15, and from the viewpoint of improving the polishing rate, it is 1.10 or more and preferably 1.105 or more, more preferably 1.11 or more, and even more preferably 1.115 or more, and from the viewpoint of reducing waviness, it is preferably less than 1.15 and 1.145 or less, more preferably 1.14 or less, even more preferably 1.13 or less, and even more preferably 1.125 or less. In the present disclosure, the average aspect ratio of particles having an average particle size A or less obtained by image analysis using SEM is a simple average value obtained by observing a predetermined number of particles having a particle size A or less determined from the BET specific surface area of ​​component A using SEM and calculating the long axis / short axis ratio of the smallest inscribed rectangle of the particles using an image analysis system. Specifically, it can be calculated by the method described in the Examples.

[0019] In the present disclosure, the average aspect ratio of particles in component A having an average particle size greater than A, as determined by image analysis using SEM, is 1.20 or more and less than 1.25; from the viewpoint of improving the polishing rate, it is 1.20 or more, preferably 1.21 or more, more preferably 1.22 or more, and even more preferably 1.225 or more; and from the viewpoint of reducing waviness, it is less than 1.25 and preferably 1.245 or less, more preferably 1.24 or less, and even more preferably 1.235 or less. In the present disclosure, the average aspect ratio of particles having an average particle size greater than A obtained by image analysis using SEM is a simple average value obtained by observing a predetermined number of particles having an average particle size greater than A obtained from the BET specific surface area of ​​component A using SEM and calculating the long axis / short axis ratio of the smallest inscribed rectangle of the particles using an image analysis system. Specifically, it can be calculated by the method described in the Examples.

[0020] In the present disclosure, the average aspect ratio of component A (average aspect ratio of the entire silica particles (component A)) is preferably 1.12 or more, more preferably 1.122 or more, even more preferably 1.124 or more, and even more preferably 1.13 or more, from the viewpoint of improving the polishing rate, and is preferably less than 1.15, more preferably 1.149 or less, even more preferably 1.145 or less, and even more preferably 1.14 or less, from the viewpoint of reducing waviness.

[0021] In the present disclosure, the ammonia adsorption amount of Component A determined by ammonia temperature programmed desorption (NH3-TPD) is preferably 50 mmol / mg or more, more preferably 52 mmol / mg or more, even more preferably 54 mmol / mg or more, and even more preferably 56 mmol / mg or more, from the viewpoint of improving the polishing rate, and is preferably 80 mmol / mg or less, more preferably 78 mmol / mg or less, even more preferably 76 mmol / mg or less, and even more preferably 70 mmol / mg or less. Temperature-programmed desorption is a method that can measure the strength and amount of solid acid and basic sites by adsorbing probe molecules (NH3, CO2, etc.) to a solid sample and measuring the desorbed gas that is generated by continuously increasing the temperature of the sample. NH3, a basic gas, is used to measure the amount and strength of acid sites. At this time, it is thought that NH3 adsorbed to weak acid sites desorbs at low temperatures, and NH3 adsorbed to strong acid sites desorbs at high temperatures. The amount of desorbed NH3 depends on the amount of acid sites. In the present disclosure, the ammonia adsorption amount of silica particles determined by ammonia temperature programmed desorption (NH3-TPD) can be calculated specifically by the method described in the Examples.

[0022] Examples of component A include colloidal silica, wet process silica (precipitated silica), fumed silica, pulverized silica, and surface-modified silica thereof. Among these, component A is preferably colloidal silica having a particle size of 1 nm to 1000 nm and stably dispersed in an aqueous medium, from the viewpoint of improving the polishing rate and reducing waviness. The colloidal silica can be prepared, for example, by a method of particle growth using an aqueous solution of an alkali silicate as a raw material (water glass method), a method of condensation of a hydrolyzate of an alkoxysilane (sol-gel method), or a method of precipitating silica particles by a neutralization reaction between a silicate such as sodium silicate and a mineral acid such as sulfuric acid (precipitation method).

[0023] The shape of component A may be either non-spherical or spherical. Silica particles that satisfy the above average particle size A and the two average aspect ratios (average aspect ratio of particles less than average particle size A, average aspect ratio of particles exceeding average particle size A), and preferably that further satisfy the above average aspect ratio of the entire silica particles, and / or the above ammonia adsorption amount, can be prepared, for example, by using a particle growth method using an aqueous alkali silicate solution as a raw material, and adjusting the reaction temperature and reaction pressure so as to obtain the average particle size A and the two average aspect ratios, and preferably so as to obtain the above average aspect ratio of the entire silica particles, and / or the above ammonia adsorption amount. In one or more embodiments, component A can be obtained as follows. The alkali silicate, which is the raw material of silica particles, is dissolved in water to a concentration of, for example, 2 to 8 mass %. A strong acid (e.g., hydrochloric acid, sulfuric acid, nitric acid, etc.) is added to the aqueous solution to neutralize the silicic acid, thereby forming a silica hydrogel. The pH at this time is preferably about 4 to 6. The hydrogel of the alkali silicate neutralized with the strong acid is allowed to stand for, for example, 1 to 5 hours at a temperature range of 10 to 40°C, for example, to mature the silica. Thereafter, the salt is removed by washing with pure water or alkaline water. After adding an alkaline solution (e.g., sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc.) to the dispersion after washing, the pH of the dispersion is adjusted to a range of 6 to 12. The temperature at this time is preferably 40 to 120°C. The adjusted dispersion is stirred for about 30 minutes to 3 hours to form a colloidal silica hydrogel. Thereafter, the obtained silica sol is subjected to hydrothermal treatment at a temperature of, for example, 100 to 300° C. and a pressure of, for example, 0.1 to 0.3 MPa for about 30 minutes to 6 hours to grow and stabilize the silica particles, thereby obtaining component A.

[0024] The content of Component A in the polishing composition of the present disclosure is preferably 1.5 mass% or more, more preferably 3.0 mass% or more, and even more preferably 4.5 mass% or more from the viewpoint of improving the polishing rate, and is preferably 10.0 mass% or less, more preferably 9.0 mass% or less, and even more preferably 8.0 mass% or less from the viewpoint of reducing waviness. When Component A is a combination of two or more types, the content of Component A refers to the total content thereof.

[0025] [Acid (component B)] The polishing liquid composition of the present disclosure contains an acid (hereinafter also referred to as "Component B"). In the present disclosure, the acid may be in the form of a salt in part or in whole. In the present disclosure, the content of the acid salt in Component B is preferably 50 mass % or less, more preferably 20 mass % or less, even more preferably 10 mass % or less, still more preferably 5 mass % or less, and even more preferably 0 mass %, from the viewpoints of improving the polishing rate and reducing waviness. Component B may be one type or a combination of two or more types.

[0026] Examples of component B include inorganic acids such as nitric acid, sulfuric acid, sulfurous acid, persulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, tripolyphosphoric acid, and amidosulfuric acid; organic acids such as organic phosphoric acid, organic phosphonic acid, and carboxylic acid; and the like. Among them, from the viewpoint of improving the polishing rate and reducing waviness, it is preferable to contain an inorganic acid and an organic phosphonic acid, and it is more preferable to contain an inorganic acid. In the present disclosure, from the same viewpoint, the content of the inorganic acid in component B is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 100% by mass. From the same viewpoint, the inorganic acid is preferably at least one selected from nitric acid, sulfuric acid, hydrochloric acid, perchloric acid and phosphoric acid, more preferably at least one selected from sulfuric acid and phosphoric acid, and even more preferably phosphoric acid. From the same viewpoint, the organic phosphonic acid is preferably at least one selected from 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), aminotrimethylene phosphonic acid, ethylenediaminetetramethylene phosphonic acid, and diethylenetriaminepentamethylene phosphonic acid, and more preferably HEDP. Examples of the salts of these acids include salts of the above acids with at least one selected from metals, ammonia, and alkylamines. Examples of the metals include metals belonging to Groups 1 to 11 of the periodic table. Among these, from the viewpoints of improving the polishing rate and reducing waviness, salts of the above acids with metals belonging to Group 1A or ammonia are preferred.

[0027] From the viewpoints of improving the polishing rate and reducing waviness, the content of Component B in the polishing liquid composition of the present disclosure is preferably 0.01 mass % or more, more preferably 0.1 mass % or more, and even more preferably 0.5 mass % or more, and from the same viewpoints, it is preferably 3 mass % or less, more preferably 2 mass % or less, and even more preferably 1.8 mass % or less. When Component B is a combination of two or more types, the content of Component B refers to the total content thereof.

[0028] [Oxidizing agent (component C)] The polishing composition of the present disclosure contains an oxidizing agent (hereinafter also referred to as "component C") from the viewpoints of improving the polishing rate and reducing waviness. In one or more embodiments, component C is preferably an oxidizing agent that does not contain a halogen atom. Component C may be one type or a combination of two or more types.

[0029] Examples of component C include peroxides, permanganic acid or its salts, chromic acid or its salts, peroxoacid or its salts, oxyacid or its salts, metal salts, nitric acids, and sulfuric acids, from the viewpoints of improving the polishing rate and reducing waviness. Among these, at least one selected from hydrogen peroxide, iron (III) nitrate, peracetic acid, ammonium peroxodisulfate, iron (III) sulfate, and ammonium iron (III) sulfate is preferred, and hydrogen peroxide is more preferred from the viewpoints of improving the polishing rate, preventing metal ions from adhering to the surface of the substrate to be polished, and ease of availability.

[0030] The content of component C in the polishing composition of the present disclosure is preferably 0.01 mass % or more, more preferably 0.05 mass % or more, and even more preferably 0.1 mass % or more from the viewpoint of improving the polishing rate, and is preferably 4 mass % or less, more preferably 3 mass % or less, even more preferably 2 mass % or less, and even more preferably 1 mass % or less from the viewpoint of reducing waviness. When component C is a combination of two or more types, the content of component C refers to the total content thereof.

[0031] [water] The polishing composition of the present disclosure preferably contains water as a medium. Examples of water include distilled water, ion-exchanged water, pure water, and ultrapure water. The content of water in the polishing composition of the present disclosure can be the remainder excluding component A, component B, component C, and any optional components described below.

[0032] [Mass ratio of component B to component A] In the polishing liquid composition of the present disclosure, the mass ratio B / A of component B to component A (content of component B / content of component A) is, from the viewpoints of improving the polishing rate and reducing waviness, preferably 5 mass% or more, more preferably 10 mass% or more, even more preferably 15 mass% or more, even more preferably 20 mass% or more, even more preferably 25 mass% or more, and from the same viewpoints, preferably 50 mass% or less, more preferably 40 mass% or less, even more preferably 35 mass% or less, and even more preferably 30 mass% or less.

[0033] [Mass ratio of component C to component A] In the polishing liquid composition of the present disclosure, the mass ratio C / A of component C to component A (content of component C / content of component A) is, from the viewpoints of improving the polishing rate and reducing waviness, preferably 0.1 mass% or more, more preferably 1 mass% or more, even more preferably 5 mass% or more, even more preferably 10 mass% or more, even more preferably 15 mass% or more, and from the same viewpoints, preferably 40 mass% or less, more preferably 30 mass% or less, even more preferably 25 mass% or less, and even more preferably 20 mass% or less.

[0034] [Other ingredients] In one or more embodiments, the polishing liquid composition of the present disclosure may contain other components as necessary within a range that does not impair the effects of the present disclosure. Examples of other components include corrosion inhibitors, thickeners, dispersants, rust inhibitors, basic substances, surfactants, water-soluble polymers, etc.

[0035] [Alumina abrasive grains] From the viewpoint of reducing protrusion defects, the polishing liquid composition of the present disclosure preferably does not substantially contain alumina abrasive grains. In the present disclosure, "substantially does not contain alumina abrasive grains" may include, in one or more embodiments, not containing alumina particles, not containing an amount of alumina particles that functions as abrasive grains, or not containing an amount of alumina particles that affects the polishing result. Specifically, in one or more embodiments, the content of alumina abrasive grains in the polishing liquid composition of the present disclosure is preferably 5 mass% or less, more preferably 2 mass% or less, even more preferably 1 mass% or less, even more preferably 0.1 mass% or less, even more preferably 0.05 mass% or less, even more preferably 0.02 mass% or less, and even more preferably substantially 0 mass%.

[0036] [pH of polishing composition] The pH of the polishing liquid composition of the present disclosure is preferably 1 or more, more preferably 1.1 or more, and even more preferably 1.2 or more from the viewpoint of reducing waviness, and is preferably 6 or less, more preferably 4 or less, and even more preferably 2 or less from the viewpoint of improving the polishing rate. The pH can be adjusted using the above-mentioned acid (component B) or a known pH adjuster. In the present disclosure, the above pH is the pH of the polishing liquid composition at 25° C., and can be measured using a pH meter. For example, the pH can be the value measured 2 minutes after immersing the electrode of the pH meter in the polishing liquid composition.

[0037] [Method of manufacturing the polishing composition] The polishing liquid composition of the present disclosure can be produced, for example, by blending component A, component B, component C, and water as required, and, if desired, optional components (other components) by a known method. For example, in one or more embodiments, the polishing liquid composition of the present disclosure can be produced by blending at least component A, component B, component C, and water as required. Thus, in one aspect, the present disclosure relates to a method for producing a polishing liquid composition, which includes a step of blending at least component A, component B, component C, and water as required. In the present disclosure, "blending" includes mixing component A, component B, component C, and water as required, and optional components (other components) as required, simultaneously or in any order. Silica particles (component A) may be mixed in the form of a concentrated slurry, or may be mixed after diluting with water or the like. When component A is made of multiple types of silica particles, the multiple types of silica particles can be blended simultaneously or separately. When component B is made of multiple types of acids, the multiple types of acids can be blended simultaneously or separately. When component C is made of multiple types of oxidizing agents, the multiple types of oxidizing agents can be blended simultaneously or separately. The blending can be carried out using a mixer such as a homomixer, a homogenizer, an ultrasonic disperser, a wet ball mill, etc. The preferred blending amount of each component in the method for producing the polishing liquid composition can be the same as the preferred content of each component in the polishing liquid composition of the present disclosure described above.

[0038] An embodiment of the polishing liquid composition of the present disclosure may be a so-called one-component type in which all components are premixed and supplied to the market, or a so-called two-component type in which components are mixed at the time of use.

[0039] In the present disclosure, "the content of each component in the polishing liquid composition" refers to the content of each component at the time of use, that is, at the time when the use of the polishing liquid composition for polishing is started. In one or more embodiments, the content of each component in the polishing composition of the present disclosure can be considered as the blending amount of each component.

[0040] The polishing composition of the present disclosure may be stored and supplied in a concentrated state to the extent that its storage stability is not impaired. In this case, it is preferable in that the manufacturing and transportation costs can be further reduced. The concentrated polishing composition of the present disclosure may be used by diluting it appropriately with the above-mentioned water as necessary when used. The dilution ratio is not particularly limited as long as the content (at the time of use) of each of the above-mentioned components can be secured after dilution, and may be, for example, 10 to 100 times.

[0041] [Polishing liquid kit] In one aspect, the present disclosure relates to a kit for preparing the polishing liquid composition of the present disclosure, the kit including a silica dispersion (first liquid) containing component A and water, and an additive aqueous solution (second liquid) containing components B and C, which are not mixed with each other (hereinafter also referred to as the "polishing liquid kit of the present disclosure"). The first liquid and the second liquid may be mixed at the time of use and diluted with water as necessary. The water contained in the first liquid may be the entire amount of water used in preparing the polishing composition, or may be a part of the amount. The second liquid may contain a part of the water used in preparing the polishing composition. The first liquid and the second liquid may each contain the above-mentioned optional components (other components) as necessary. When the first liquid and the second liquid are mixed, the above-mentioned optional components (other components) may be further mixed. According to the present disclosure, it is possible to obtain a polishing liquid kit that can achieve both an improvement in the polishing rate and a reduction in waviness.

[0042] [Method of manufacturing magnetic disk substrate] In one aspect, the present disclosure relates to a method for manufacturing a magnetic disk substrate (hereinafter also referred to as the "substrate manufacturing method of the present disclosure"), which includes a step of supplying the polishing liquid composition of the present disclosure between a substrate to be polished and a polishing pad, and polishing the substrate to be polished (hereinafter also referred to as the "polishing step"). In general, a magnetic disk is manufactured by polishing a substrate to be polished after a grinding process through a rough polishing process and a finish polishing process, and then through a magnetic layer forming process. The substrate manufacturing method of the present disclosure is preferably one or more selected from a manufacturing method in which the polishing liquid composition of the present disclosure is supplied between a substrate to be polished and a polishing pad in a rough polishing process, a manufacturing method in which the polishing liquid composition of the present disclosure is supplied between a substrate to be polished and a polishing pad in a finish polishing process, and a manufacturing method in which the polishing liquid composition of the present disclosure is supplied between a substrate to be polished and a polishing pad in both the rough polishing process and the finish polishing process. Among them, the manufacturing method in which the polishing liquid composition of the present disclosure is supplied between a substrate to be polished and a polishing pad in a rough polishing process is more preferable. That is, in one or more embodiments, the polishing liquid composition of the present disclosure is preferably for use in a rough polishing process.

[0043] In one or more embodiments, the polishing step includes supplying the polishing liquid composition of the present disclosure to a surface of a substrate to be polished, contacting a polishing pad with the surface to be polished, and moving at least one of the polishing pad and the substrate to be polished to perform polishing. In one or more embodiments, the polishing step includes: clamping the substrate to be polished between plates to which a polishing pad is attached, supplying the polishing liquid composition of the present disclosure to the polishing surface, and polishing the substrate to be polished by moving the polishing pad and the substrate to be polished while applying pressure.

[0044] [Substrate to be polished] In one or more embodiments, the substrate to be polished is a magnetic disk substrate used in the manufacture of a magnetic disk substrate, and examples of such substrates include Ni-P plated aluminum alloy substrates and glass substrates such as crystallized glass, reinforced glass, aluminosilicate glass, and aluminoborosilicate glass, with Ni-P plated aluminum alloy substrates being preferred. That is, the polishing liquid composition of the present disclosure is preferably used for polishing Ni-P plated aluminum alloy substrates. In the present disclosure, the term "Ni-P plated aluminum alloy substrate" refers to an aluminum alloy substrate whose surface is ground and then electroless Ni-P plated. After polishing the surface of the substrate to be polished with the polishing composition of the present disclosure, a magnetic layer is formed on the substrate surface by sputtering or the like, thereby producing a magnetic disk substrate. The shape of the substrate to be polished may be, for example, a shape having a flat surface such as a disk, plate, slab, or prism, or a shape having a curved surface such as a lens, and is preferably a disk-shaped substrate to be polished. In the case of a disk-shaped substrate to be polished, the outer diameter is, for example, 10 to 120 mm, and the thickness is, for example, 0.5 to 2 mm.

[0045] The polishing pad used in the present disclosure is not particularly limited, and for example, a suede type, a nonwoven fabric type, a polyurethane independent foam type, or a two-layer type in which these are laminated may be used. From the viewpoint of improving the polishing rate, a suede type polishing pad is preferred.

[0046] The polishing load in the polishing step is preferably 3 kPa or more, more preferably 5 kPa or more, even more preferably 7 kPa or more, and is preferably 30 kPa or less, more preferably 25 kPa or less, and even more preferably 20 kPa or less, from the viewpoint of maintaining the polishing rate and reducing waviness. In the present disclosure, the "polishing load" refers to the pressure of the platen applied to the polished surface of the substrate during polishing. The polishing load can be adjusted by the air pressure or weight load on the platen, substrate, etc.

[0047] In the polishing process, 2 From the viewpoints of ensuring the polishing rate and reducing waviness, the polishing amount per unit area is preferably 0.2 mg or more, more preferably 0.3 mg or more, and even more preferably 0.4 mg or more, and from the same viewpoints, it is preferably 2.5 mg or less, more preferably 2 mg or less, and even more preferably 1.6 mg or less.

[0048] The polished substrate in the polishing process 2From the viewpoint of economy, the supply rate of the polishing composition per unit time is preferably 2.5 mL / min or less, more preferably 2 mL / min or less, and even more preferably 1.5 mL / min or less, and from the viewpoint of improving the polishing rate, it is preferably 0.01 mL / min or more, more preferably 0.03 mL / min or more, and even more preferably 0.05 mL / min or more.

[0049] The method of supplying the polishing liquid composition of the present disclosure to the polishing machine can be, for example, a method of continuously supplying the composition using a pump or the like. When supplying the polishing liquid composition to the polishing machine, in addition to a method of supplying the composition as a single liquid containing all components, the composition can be divided into a plurality of blending component liquids and supplied as two or more liquids, taking into consideration the storage stability of the polishing liquid composition. In the latter case, the plurality of blending component liquids are mixed, for example, in the supply pipe or on the substrate to be polished, to form the polishing liquid composition of the present disclosure.

[0050] According to the substrate manufacturing method of the present disclosure, by using the polishing liquid composition of the present disclosure, it is possible to improve the polishing rate and reduce waviness on the substrate surface after polishing, so that it is possible to produce high-quality magnetic disk substrates with high yield and good productivity. EXAMPLES

[0051] The present disclosure will be described in more detail below with reference to examples, but these are merely illustrative and the present disclosure is not limited to these examples.

[0052] 1. Preparation of Silica Particles (Examples 1 to 4 and Comparative Examples 1 to 4) The raw material for silica particles, alkali silicate, is dissolved in water to a concentration of 2-8% by mass. A strong acid such as hydrochloric acid, sulfuric acid, or nitric acid is added to the aqueous solution to neutralize the silicic acid, forming a silica hydrogel. The pH at this time is kept at 4-6. The hydrogel of alkali silicate neutralized with a strong acid is left to stand for 1 to 5 hours at a temperature range of 10 to 40°C to allow the silica to mature.Then, the salt is removed by washing with pure water or alkaline water. After adding an alkaline solution such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide to the washed dispersion, the pH of the dispersion is adjusted to a range of 6 to 12. The temperature at this time is 40 to 120°C. The prepared dispersion is stirred for about 30 minutes to 3 hours to convert the silica hydrogel into a colloid. Thereafter, the obtained silica sol is subjected to hydrothermal treatment at a temperature of 100 to 300° C. and a pressure of 0.1 to 0.3 MPa for about 3 to 6 hours to grow and stabilize the silica particles, thereby producing silica particles (colloidal silica). The reaction temperature, reaction pressure, and reaction time are adjusted in various ways so as to obtain the average particle size A and average aspect ratio shown in Table 1, thereby obtaining silica particles of Examples 1 to 4 and Comparative Examples 1 to 4.

[0053] 2. Preparation of Polishing Composition The polishing liquid compositions of Examples 1 to 4 and Comparative Examples 1 to 4 were prepared by mixing silica particles (component A or non-component A), acid (component B), oxidizing agent (component C) and water shown in Table 1. The content (effective amount) of each component in each polishing liquid composition was 6 mass% for silica particles (component A or non-component A), 1.6 mass% for acid (component B), and 1.0 mass% for oxidizing agent (component C). The content of water is the remainder excluding component A or non-component A, component B, and component C. The polishing liquid compositions of Examples 1 to 4 and Comparative Examples 1 to 4 did not contain alumina abrasive grains. The pH of the polishing liquid compositions of Examples 1 to 4 and Comparative Examples 1 to 4 was 1.6. The following components B and C were used in preparing the polishing composition. (Component B) Phosphoric acid [75% phosphoric acid, manufactured by Nippon Chemical Industry Co., Ltd.] (Component C) Hydrogen peroxide [ADEKA Corporation Hydrogen peroxide 35%]

[0054] 3. Measurement of each parameter [Measurement of average particle size A of silica particles] Each silica particle was dried with hot air at 110°C for 12 hours and crushed in an agate mortar as necessary to obtain a powdered silica particle sample. The obtained sample was pre-dried at 200°C for 15 minutes immediately before measuring the BET specific surface area, and the specific surface area S (unit: m) was measured by the BET method (nitrogen adsorption method) using a Micromeritic automatic specific surface area measurement device "Flowsorb III2305" (Shimadzu Corporation). 2 The specific surface area S was then used to calculate the average particle size A of the silica particles according to the following formula: Average particle size A (unit: nm) = 2727 / S

[0055] [Number ratio, average aspect ratio] Using a scanning electron microscope (field emission scanning electron microscope S-4800) manufactured by Hitachi High-Technologies Corporation, images were taken at random from 10 fields of view at a scanning voltage of 10 kV and a magnification of 200 K. As the object to be photographed, copper grit on which a carbon film was vapor-deposited was subjected to hydrophilization treatment, and several drops of an aqueous solution in which the aqueous dispersion of each silica particle was diluted to 0.1 mass % were dropped onto it. After that, the sample was dried overnight at room temperature to obtain a sample. The image data obtained by the above method was analyzed using image analysis software (WinROOF2013) manufactured by Mitani Shoji Co., Ltd., to quantify the particle shapes of 1,000 or more particles as a parameter, and the number ratio and average aspect ratio were calculated. The minor axis and major axis of each silica particle were determined, and the average aspect ratio (average aspect ratio) was calculated by dividing the major axis by the minor axis.

[0056] [NH3 adsorption amount by ammonia temperature programmed desorption method] The amount of NH3 adsorption measured by ammonia temperature programmed desorption (NH3-TPD) was determined as follows. Measuring device: "BELCAT-B" manufactured by Japan Bell Co., Ltd. Measurement method: Each silica solid sample (0.01 mg) was pre-dried for 1 hour at 120°C in a He gas (50 cc / min) atmosphere. Then, it was adsorbed at 100°C for 1 hour in a 5 vol% NH3 / He (30 cc / min) atmosphere, and the temperature was increased at a rate of 10°C / min in a He gas (30 cc / min) atmosphere, up to a maximum temperature of 800°C. A quadrupole mass spectrometer was used as the detector, and the mass numbers were set to 16 and 17 to avoid confusion with water (H2O = mass number 18) when detecting ammonia (NH3 = mass number 17). The amount of adsorbed NH3 (mmol / mg) was calculated from the integral value of the peak area for the obtained spectrum.

[0057] [pH measurement] The pH of the polishing composition was measured at 25° C. using a pH meter (manufactured by DKK-Toa Corporation), and the value measured 2 minutes after immersing an electrode in the polishing composition was recorded.

[0058] 4.Polishing method The following substrates were polished under the polishing conditions shown below using the polishing compositions of Examples 1 to 4 and Comparative Examples 1 to 4. Then, the polishing rate and waviness were measured by the measuring methods described below. The results are shown in Table 1.

[0059] [Substrate to be polished] Substrate to be polished: Ni-P plated aluminum alloy substrate (thickness 0.6-0.8 mm, diameter 95-100 mm)

[0060] [Polishing conditions] Polishing machine: Double-sided polishing machine (9B type double-sided polishing machine, manufactured by SpeedFam Co., Ltd.) Number of boards: 10 Polishing liquid: Polishing liquid composition described in the Examples and Comparative Examples Polishing pad: Suede type (foam layer: polyurethane elastomer, thickness 1.0 mm, average pore size 30 μm, surface layer compression rate 2.5%, Filwel) Plate rotation speed: 40 rpm Polishing load: 9.8kPa (set value) Polishing liquid supply amount: 100mL / min Substrate to be polished 1cm 2 Feed rate per unit: 0.8mL / min Substrate to be polished 1cm 2 Polishing amount per piece: 0.8mg Polishing time: 5 minutes After polishing, the substrate is removed from the double-sided polisher and the surface is cleaned using an automatic cleaner.

[0061] 5. Evaluation [Evaluation of polishing speed] The polishing rate was determined by measuring the mass of each substrate before and after polishing using an electronic balance (manufactured by Sartorius, "BP-210S") and calculating the mass loss from the change in mass of each substrate. The polishing rate was calculated by dividing the average mass loss of all 10 substrates by the polishing time, and was introduced into the following formula. The polishing rate of Comparative Example 1 was set to 100, and a relative value was calculated as the evaluation item. The results are shown in Table 1. Mass loss (g) = {mass before polishing (g) - mass after polishing (g)} Polishing speed (g / min) = mass loss (g) / polishing time (min)

[0062] [Evaluation of short and long wavelength waviness] Two substrates were randomly selected from the 10 substrates after polishing, and both sides of each selected substrate were measured at three random points (total of 12 points) under the following conditions. The average values ​​of the measurements at the 12 points were calculated as the short wavelength waviness and long wavelength waviness of the substrate. Then, relative values ​​were calculated with Comparative Example 1 set to 100, and the results are shown in Table 1. <Measurement conditions> Measuring device: New View 7300 (Zygo) Lens: 2.5x Zoom: 0.5x Short wavelength range: 60~160μm Long wavelength range: 500~5000μm Analysis software: Zygo Metro Pro (Zygo)

[0063] [Table 1]

[0064] As shown in Table 1 above, the polishing liquid compositions of Examples 1 to 4, which used specified silica particles, had improved removal rates and reduced short-wavelength waviness and long-wavelength waviness, compared to the polishing liquid compositions of Comparative Examples 1 to 4, which used silica particles that did not satisfy the specified requirements for any of the average particle size A, the number ratio equal to or less than the average particle size A, the average aspect ratio equal to or less than the average particle size A, and the average aspect ratio exceeding the average particle size A. [Industrial Applicability]

[0065] According to the present disclosure, for example, it is possible to provide a magnetic disk substrate suitable for achieving high recording density.

Claims

1. A polishing liquid composition comprising silica particles, an acid, and an oxidizing agent, The silica particles are The average particle size A, determined from the BET specific surface area, is between 60 nm and 90 nm. The number ratio of particles with an average particle size of A or less, as determined by image analysis using a scanning electron microscope (SEM), is 80% or more. The average aspect ratio of particles with an average particle size of A or less, as determined by image analysis using SEM, is 1.10 or more and less than 1.

15. A polishing liquid composition in which the average aspect ratio of particles with an average particle size greater than A, as determined by image analysis using SEM, is 1.20 or more and less than 1.

25.

2. The ammonia heating desorption method of the silica particles (NH 3 The polishing liquid composition according to claim 1, wherein the ammonia adsorption amount determined by -TPD is 50 mmol / mg or more and 80 mmol / mg or less.

3. The polishing liquid composition according to claim 1 or 2, wherein the average aspect ratio of the silica particles is less than 1.

15.

4. The polishing liquid composition according to claim 1 or 2, wherein the pH is 1 or higher and 6 or lower.

5. The polishing liquid composition according to claim 1 or 2, wherein the silica particles are colloidal silica.

6. A method for manufacturing a magnetic disk substrate, comprising the step of supplying the polishing liquid composition according to claim 1 or 2 between a substrate to be polished and a polishing pad, and polishing the substrate to be polished.