WO2024106338A1

WO2024106338A1 - Polishing liquid composition

Info

Publication number: WO2024106338A1
Application number: PCT/JP2023/040571
Authority: WO
Inventors: 坂本俊介
Original assignee: 花王株式会社
Priority date: 2022-11-17
Filing date: 2023-11-10
Publication date: 2024-05-23

Abstract

According to one aspect of the present disclosure, provided is a polishing liquid composition capable of reducing silica residues and scratches on a substrate surface after polishing.　In one aspect, the present disclosure pertains to a polishing liquid composition that contains silica particles and an aqueous medium, the silica particles having an ignition loss of 2% or less on a dry weight basis, and, when D90 is the particle diameter at which a cumulative frequency from the small particle diameter side is 90% in a particle size distribution in terms of the weight obtained by a centrifugal sedimentation method, the silica particles having a D90 of 65 nm or less.

Description

Polishing composition

This disclosure relates to a polishing composition, a method for manufacturing a magnetic disk substrate, and a method for polishing a substrate.

In recent years, magnetic disk drives have become smaller and have larger capacities, and there is a demand for higher recording density. To achieve higher recording density, it is necessary to reduce the unit recording area and improve the detection sensitivity of the weakened magnetic signal. For this reason, technological development is being carried out to lower the flying height of the magnetic head. To accommodate the lower flying height of the magnetic head and ensure the recording area, magnetic disk substrates are strictly required to improve smoothness and flatness (reduced surface roughness, waviness, and edge sagging) and reduce surface defects (reduced residual abrasive grains, scratches, protrusions, pits, etc.).

In order to meet such demands and to improve both the surface quality (smoothness and fewer scratches) and productivity, a multi-stage polishing method having two or more polishing steps is often adopted in the manufacturing method of magnetic disk substrates. Generally, to meet the demand for smoothness, an abrasive containing colloidal silica particles is used, and from the viewpoint of improving productivity, a polishing liquid composition containing alumina particles as abrasive particles is used. However, when alumina particles are used as abrasive particles, the alumina particles may penetrate the substrate, causing defects in the magnetic disk substrate or in a magnetic disk having a magnetic layer applied to the magnetic disk substrate.

Therefore, for example, Japanese Patent Application Laid-Open No. 2017-19978 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2021-175774 (Patent Document 2) propose polishing liquid compositions that do not contain alumina particles but contain silica particles as abrasive grains.

In one aspect, the present disclosure relates to a polishing liquid composition that contains silica particles and an aqueous medium, the silica particles having an ignition loss of 2% or less on a dry weight basis, and the silica particles having a particle diameter D90 of 65 nm or less, where D90 is the particle diameter at which the cumulative frequency from the small particle diameter side is 90% in a particle size distribution calculated by weight conversion obtained by centrifugal sedimentation.

In one aspect, the present disclosure relates to a method for manufacturing a magnetic disk substrate, which includes a polishing step of polishing a substrate to be polished using the polishing liquid composition of the present disclosure.

In one aspect, the present disclosure relates to a method for polishing a substrate, comprising polishing a substrate to be polished with the polishing liquid composition of the present disclosure, the substrate to be polished being a substrate used in the manufacture of magnetic disk substrates.

In one aspect, the present disclosure relates to a method for reducing residual silica on a substrate after polishing, the method comprising polishing the substrate to be polished with the polishing liquid composition of the present disclosure.

In one aspect, the present disclosure relates to a method for manufacturing a magnetic disk substrate, comprising the steps of selecting silica particles as abrasive grains having an ignition loss of 2% or less on a dry weight basis and a D90 of 65 nm or less, where D90 is the particle diameter at which the cumulative frequency from the small particle size side is 90% in a particle size distribution calculated by weight conversion obtained by centrifugal sedimentation, and polishing a substrate to be polished using a polishing liquid composition containing the silica particles and an aqueous medium.

In recent years, with the increase in recording density of magnetic disk drives, the read head is now positioned within a few nanometers of the substrate that rotates at high speed. Drive failures have occurred due to the low position of the read head.
As a result of the inventors' investigations, it was found that silica particles remaining on the substrate surface after polishing (hereinafter also referred to as "silica residue") are one of the causes of drive failure. In particular, it was found that even silica residues that cannot be detected by a scanning electron microscope (SEM) after finish polishing are one of the causes of drive failure.
Furthermore, as the capacity of magnetic disk drives increases, the requirements for the surface quality of substrates become more stringent, and there is a demand for the development of a polishing composition that can further reduce scratches on the substrate surface.
In the present disclosure, "silica residue" is a general term for silica particles remaining on the substrate to be polished, and can be expressed as the number of particles per unit area. In one or more embodiments, "silica residue" includes silica particles that are simply in contact with the substrate, silica particles that are electrostatically bonded to the substrate, and silica particles that are partially embedded in the substrate.

In one aspect, the present disclosure provides a polishing composition that can reduce residual silica and scratches on the substrate surface after polishing.

The silica particles (silica residues) remaining on the substrate surface after polishing are time-consuming to measure, and are rarely recognized as an item for evaluating the quality of the substrate surface after polishing, and have not been recognized as a cause of drive failure. Note that the "silica residues" that were considered a problem in the prior art are physical defects such as being embedded in scratches or being pierced, and are relatively easily detectable by model testing using simple cleaning or by using an electron microscope, and therefore have different problems and effects from the "silica residues" in this disclosure.
In Patent Document 1, since heat-treated silica, which generally has a high surface hardness, is used, there is a problem that the substrate surface tends to have many dent defects and punctures. In Patent Document 2, a high polishing rate and excellent substrate surface quality are both achieved, but a further improvement in the polishing rate is desired in terms of improving substrate productivity. However, Patent Documents 1 and 2 do not address the issue of reducing residual silica.
In the present disclosure, by using as an indicator the residual silica that is at a level that cannot be detected by a scanning electron microscope (SEM) and that is detected by inductively coupled plasma mass spectrometry (ICP-MS), in one or a plurality of embodiments, it is possible to reduce the residual silica to a level that is difficult to detect by X-ray fluorescence analysis.
The present disclosure is based in one aspect on the discovery that the amount of residual silica, which is undetectable by scanning electron microscopy (SEM) and detected by inductively coupled plasma mass spectrometry (ICP-MS), correlates with the loss on ignition of silica particles having a given particle size distribution.

In other words, in one aspect, the present disclosure relates to a polishing liquid composition (hereinafter also referred to as the "polishing liquid composition of the present disclosure") that contains silica particles and an aqueous medium, the silica particles having an ignition loss of 2% or less on a dry weight basis, and the silica particles having a particle diameter D90 of 65 nm or less, where D90 is the particle diameter at which the cumulative frequency from the small particle diameter side is 90% in a particle size distribution in weight conversion obtained by centrifugal sedimentation.

The mechanism by which the effects of the present disclosure are manifested is not clear, but is speculated as follows.
As a result of the study by the inventors, it is believed that the residual silica that leads to the failure of the drive is related to D90, which means the ratio of large diameter particles. Large diameter particles have a large force to transmit the polishing load to the substrate to be polished, so they are more likely to remain on the substrate. However, simply reducing D90 reduces the polishing speed, resulting in a trade-off relationship. In addition, it is believed that another factor in the residual silica is the hydrogen bond between the silanol group of the silica particle and the substrate surface. However, the amount of residual silica shows only a weak correlation with the "silanol group density" of the silica particle compared to the ignition loss of the silica particle. It is believed that a further mechanism is involved in the correlation between the amount of residual silica and the ignition loss.
The silanol group density is generally determined by titration, and only the silanol groups on the outermost surface are detected. On the other hand, the ignition loss detects all silanol groups, including those inside the particles. In addition, a high load is applied to the particles during polishing, and it is believed that some particles collapse and the internal silanol groups are exposed. Since these internal silanol groups are also thought to be involved in the silica remaining on the substrate, it is believed that processing to a state where the ignition loss is small (for example, forming a dense particle structure by slowing down the growth rate of silica particles) contributes to reducing the silica remaining.
Furthermore, by decreasing D90, not only can the residual silica be reduced, but also coarse particles that cause localized scratches can be reduced, which is thought to reduce scratches as well.
However, the present disclosure need not be construed as being limited to these mechanisms.

In the present disclosure, unless otherwise specified, the silica residue refers to the amount of silica residue detected by inductively coupled plasma mass spectrometry (ICP-MS). Specifically, it can be evaluated by the method described in the Examples. In one or more embodiments, the silica residue refers to the amount of silica residue detected by inductively coupled plasma mass spectrometry (ICP-MS) that is at a level that cannot be detected by scanning electron microscope (SEM).
In the present disclosure, scratches on the substrate surface can be detected, for example, by an optical defect inspection device and can be quantitatively evaluated as the number of scratches. The number of scratches can be specifically evaluated by the method described in the Examples.

[Silica Particles A (Component A)]
The polishing liquid composition of the present disclosure contains silica particles A (hereinafter also referred to as "component A") as abrasive grains. In one or more embodiments, the silica particles A (component A) are silica particles having an ignition loss of 2% or less on a dry weight basis, and a D90 of 65 nm or less when the particle size D90 is the particle size at which the cumulative frequency from the small particle size side is 90% in the particle size distribution in weight conversion obtained by centrifugal sedimentation. The use form of component A is preferably a slurry-like polishing liquid component. Component A may be used alone or in combination of two or more types.

The particle diameter D10 of component A measured by centrifugal sedimentation in terms of weight is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 11 nm or more, from the viewpoint of improving the polishing rate, and is preferably 35 nm or less, more preferably 25 nm or less, and even more preferably 14 nm or less, from the viewpoint of improving the substrate surface quality. More specifically, the particle diameter D10 of component A measured by centrifugal sedimentation is preferably 5 nm or more and 35 nm or less, more preferably 10 nm or more and 25 nm or less, and even more preferably 11 nm or more and 14 nm or less.

The particle diameter D50 of component A measured by centrifugal sedimentation in terms of weight is preferably 10 nm or more, more preferably 15 nm or more, and even more preferably 17 nm or more, from the viewpoint of improving the polishing rate, and is preferably 40 nm or less, more preferably 30 nm or less, and even more preferably 20 nm or less, from the viewpoint of improving the substrate surface quality. More specifically, the particle diameter D50 of component A measured by centrifugal sedimentation is preferably 10 nm or more and 40 nm or less, more preferably 15 nm or more and 30 nm or less, and even more preferably 17 nm or more and 20 nm or less.

The particle diameter D90 of component A measured by centrifugal sedimentation in terms of weight is 65 nm or less, preferably 60 nm or less, more preferably 55 nm or less, and even more preferably 52 nm or less, from the viewpoint of reducing scratches, and is preferably 30 nm or more, more preferably 35 nm or more, and even more preferably 39 nm or more or 40 nm or more, from the viewpoint of improving the polishing rate. More specifically, the particle diameter D90 of component A measured by centrifugal sedimentation is preferably 30 nm or more and 60 nm or less, more preferably 35 nm or more and 55 nm or less, and even more preferably 39 nm or more and 52 nm or less, or 40 nm or more and 52 nm or less.

In this disclosure, D10, D50, and D90 refer to particle sizes at which the cumulative frequency from the small diameter side is 10%, 50%, and 90%, respectively, in the particle size distribution in weight conversion obtained by centrifugal sedimentation. In this disclosure, the centrifugal sedimentation method, in one or more embodiments, is a method of classifying and detecting particles by size based on the difference in sedimentation velocity (disk centrifugal sedimentation light transmission method). The particle size distribution by centrifugal sedimentation method can be measured, for example, using a disc centrifugal particle size distribution measuring device (CPS Disc Centrifuge). In the following description, the particle size distribution by centrifugal sedimentation method is sometimes referred to as the "particle size distribution by CPS measurement." Specifically, it can be calculated by the measurement method described in the examples.

　Methods for adjusting the particle size distribution of component A by centrifugal sedimentation include, for example, adjusting the particle growth time, particle temperature, particle concentration, etc. during the growth process of the silica particles. Other embodiments of methods for adjusting the particle size distribution of component A by centrifugal sedimentation include, for example, a method of giving a desired particle size distribution by adding new core particles during the particle growth process in the manufacturing stage, and a method of mixing two or more types of silica particles with different particle size distributions to give a desired particle size distribution.

From the viewpoint of improving the polishing rate and reducing scratches, the average secondary particle diameter of component A is preferably 1 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more, and from the same viewpoint, it is preferably 500 nm or less, more preferably 300 nm or less, even more preferably 100 nm or less, even more preferably 70 nm or less, even more preferably 40 nm or less, and even more preferably less than 40 nm. More specifically, the average secondary particle diameter of component A is preferably 1 nm or more and 500 nm or less, more preferably 1 nm or more and 300 nm or less, even more preferably 1 nm or more and 100 nm or less, even more preferably 5 nm or more and 70 nm or less, even more preferably 10 nm or more and 40 nm or less, and even more preferably 10 nm or more and less than 40 nm. In this disclosure, the average secondary particle diameter of component A refers to the average particle diameter based on the scattering intensity distribution measured by dynamic light scattering. In this disclosure, "scattering intensity distribution" refers to the volumetric particle size distribution of particles of submicron or less obtained by dynamic light scattering (DLS) or quasielastic light scattering (QLS). The average secondary particle size of component A in this disclosure can be obtained specifically by the method described in the examples.

The ignition loss of component A on a dry weight basis is 2% or less, preferably 1.9% or less, more preferably 1.6% or less, and even more preferably 1.5% or less, from the viewpoint of reducing residual silica, and is preferably 0% or more, more preferably 0.5% or more, and even more preferably 1.0% or more, from the viewpoint of storage stability. More specifically, the ignition loss of component A on a dry weight basis is preferably 0% or more and 1.9% or less, more preferably 0.5% or more and 1.6% or less, and even more preferably 1.0% or more and 1.5% or less.
In the present disclosure, the ignition loss on a dry weight basis of component A (hereinafter, also simply referred to as "ignition loss") is, in one or more embodiments, a sample is prepared by mixing component A with water to form a silica slurry, drying the mixture at a constant temperature between 105°C and 180°C, leaving the mixture to stand and return to room temperature, and then drying the mixture at a constant temperature between 105°C and 180°C. The loss on drying LOD (wt%) and the loss on ignition LOI (wt%) after the sample is heat-treated at 800°C or higher are measured, and the value is calculated from the following formula. Specifically, it can be calculated by the method described in the examples. It can be evaluated that the smaller the ignition loss, the smaller the total number of silanol groups contained in 1g of component A.
Loss on ignition of component A on a dry weight basis=100×{1−(100−LOI)/(100−LOD)}

Methods for adjusting the ignition loss of component A include, for example, adjusting the dropping speed, reaction temperature, and concentration of the silicic acid liquid during the growth process of the silica particles. Other embodiments of the method for adjusting the ignition loss of component A include, for example, a method for adjusting the desired ignition loss by subjecting existing silica particles to heat treatment, metal modification of surface silanol groups, organic acid modification, and silane coupling treatment, and a method for mixing two or more types of silica particles with different ignition losses to give the desired ignition loss.

An index showing a stronger correlation with the residual silica than the "loss on ignition" is "the value represented by the following formula (I) when the loss on ignition based on the dry weight of component A is WL". From the viewpoint of reducing the residual silica, the value represented by the following formula (I) when the loss on ignition based on the dry weight of component A is WL is preferably 5 or less, more preferably 2.5 or less, and even more preferably 2 or less, and from the viewpoint of maintaining the polishing rate and storage stability, it is preferably 0 or more, more preferably 0.1 or more, and even more preferably 0.5 or more. More specifically, the value represented by the following formula (I) is preferably 0 or more and 5 or less, more preferably 0.1 or more and 2.5 or less, and even more preferably 0.5 or more and 2 or less.
{(WL) ³ x D90}/100 (I)
By setting the value represented by the above formula (I) to a predetermined value or less, it is possible to achieve both a high effect of reducing residual silica and a good removal rate.

Examples of component A include colloidal silica, precipitated silica, fumed silica, pulverized silica, and surface-modified silica thereof. From the viewpoints of improving the polishing rate and easy availability, component A is preferably at least one selected from colloidal silica and precipitated silica, and from the viewpoints of improving the polishing rate and improving the quality of the substrate, such as reducing scratches, colloidal silica, which is less likely to have a sharp surface shape or a localized high surface hardness portion, is more preferable.
The colloidal silica may be obtained, for example, by a method of particle growth using an aqueous solution of alkali silicate as a raw material (hereinafter also referred to as the "water glass method"), or by a method of condensation of a hydrolyzate of an alkoxysilane (hereinafter also referred to as the "sol-gel method"), and from the viewpoint of ease of production and economic efficiency, the silica obtained by the water glass method is preferred. Silica particles obtained by the water glass method and the sol-gel method can be produced by a conventionally known method.
The precipitated silica is silica particles obtained by a precipitation method. Examples of methods for producing precipitated silica particles include known methods such as those described in Tosoh Research and Technology Report, Vol. 45 (2001), pp. 65-69. Specific examples of methods for producing precipitated silica particles include a precipitation method in which silica particles are precipitated by a neutralization reaction between a silicate such as sodium silicate and a mineral acid such as sulfuric acid. The neutralization reaction is preferably carried out under alkaline conditions at a relatively high temperature, whereby the growth of primary silica particles proceeds quickly, and the primary particles are aggregated and precipitated in the form of flocks, which are preferably further pulverized to obtain precipitated silica particles.

The shape of component A may be a so-called spherical shape and/or a so-called cocoon shape, from the viewpoints of improving the removal rate and reducing scratches.
As component A, from the viewpoints of improving the removal rate and reducing scratches, spherical silica is preferably used.

The average aspect ratio of component A is preferably 1.00 or more, more preferably 1.02 or more, from the viewpoint of improving the polishing rate, and is preferably 1.20 or less, more preferably 1.1 or less, and even more preferably 1.06 or less, from the viewpoint of reducing scratches. More specifically, the average aspect ratio of component A is preferably 1.00 or more and 1.20 or less, more preferably 1.02 or more and 1.1 or less, and even more preferably 1.02 or more and 1.06 or less.

The content of component A in the polishing composition of the present disclosure is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and even more preferably 1.5% by mass or more, from the viewpoint of improving the polishing rate and reducing scratches, and is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of economy. More specifically, the content of component A in the polishing composition of the present disclosure is preferably 0.1% by mass or more and 30% by mass or less, more preferably 0.5% by mass or more and 20% by mass or less, even more preferably 1% by mass or more and 15% by mass or less, and even more preferably 1.5% by mass or more and 10% by mass or less. When component A consists of two or more types of silica particles, the content of component A refers to the total content thereof.

[Aqueous medium]
The aqueous medium contained in the polishing liquid composition of the present disclosure includes water such as distilled water, ion-exchanged water, pure water, and ultrapure water, or a mixed solvent of water and a solvent. The above-mentioned solvent includes a solvent that can be mixed with water (e.g., alcohol such as ethanol). When the aqueous medium is a mixed solvent of water and a solvent, the ratio of water to the entire mixed medium is not particularly limited as long as the effect of the present disclosure is not hindered. From the viewpoint of economic efficiency, for example, 95% by mass or more is preferable, 98% by mass or more is more preferable, and substantially 100% by mass is even more preferable.
The content of the aqueous medium in the polishing liquid composition of the present disclosure can be the remainder excluding component A and the optional components described below (component B, component C, component D, and other components) that are blended as necessary.

[Acid (Component B)]
The polishing composition of the present disclosure may contain an acid (hereinafter also referred to as "Component B") from the viewpoint of further improving the polishing rate and further reducing scratches. In the present disclosure, the use of an acid includes the use of an acid and/or a salt thereof. Component B may be one type or a combination of two or more types.
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, polyphosphoric acid, and amidosulfuric acid; organic acids such as organic phosphoric acid and organic phosphonic acid; and the like. Among them, from the viewpoint of further improving the polishing rate and further reducing scratches, component B is preferably at least one selected from phosphoric acid, sulfuric acid, and 1-hydroxyethylidene-1,1-diphosphonic acid, more preferably at least one selected from sulfuric acid and phosphoric acid, and even more preferably phosphoric acid. Examples of salts of these acids include salts of the above acids and at least one selected from metals, ammonia, and alkylamines. Specific examples of the above metals include metals belonging to Groups 1 to 11 of the periodic table. Among them, from the viewpoint of further improving the polishing rate and further reducing scratches, salts of the above acids and metals belonging to Group 1 or ammonia are preferred.

When the polishing composition of the present disclosure contains component B, the content of component B in the polishing composition of the present disclosure is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, from the viewpoint of further improving the polishing rate and further reducing scratches, and from the same viewpoint, it is preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less, and even more preferably 2.5% by mass or less. More specifically, the content of component B in the polishing composition of the present disclosure is preferably 0.001% by mass or more and 5% by mass or less, more preferably 0.01% by mass or more and 4% by mass or less, even more preferably 0.05% by mass or more and 3% by mass or less, and even more preferably 0.1% by mass or more and 2.5% by 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.

[Oxidizing agent (component C)]
The polishing composition of the present disclosure may contain an oxidizing agent (hereinafter also referred to as "Component C") from the viewpoint of further improving the polishing rate and further reducing scratches. Component C may be one type or a combination of two or more types.
From the same viewpoint, examples of component C include peroxides, permanganic acid or its salts, chromic acid or its salts, peroxoacids or its salts, oxyacids or its salts, nitric acids, sulfuric acids, etc. Among these, component C is preferably at least one selected from hydrogen peroxide, iron(III) nitrate, peracetic acid, ammonium peroxodisulfate, iron(III) sulfate, and ammonium iron(III) sulfate, and hydrogen peroxide is more preferable from the viewpoints of increasing the polishing rate, preventing metal ions from adhering to the surface of the substrate to be polished, and ease of availability.

When the polishing liquid composition of the present disclosure contains component C, the content of component C in the polishing liquid 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 further improving the polishing rate, and is preferably 4 mass% or less, more preferably 2 mass% or less, and even more preferably 1.5 mass% or less, from the viewpoint of further improving the polishing rate and further reducing scratches. More specifically, the content of component C in the polishing liquid composition of the present disclosure is preferably 0.01 mass% or more and 4 mass% or less, more preferably 0.05 mass% or more and 2 mass% or less, and even more preferably 0.1 mass% or more and 1.5 mass% or less. When component C is a combination of two or more types, the content of component C refers to the total content thereof.

[Nitrogen-containing compound (component D)]
The polishing liquid composition of the present disclosure may further contain a nitrogen-containing compound (hereinafter also referred to as "component D") from the viewpoint of improving the polishing rate without significantly increasing the silica residue. In one or more embodiments, component D is an organic amine compound having 10 or less nitrogen atoms in the molecule. In terms of improving the polishing rate without significantly increasing the silica residue, component D is preferably one or more compounds having any of primary to tertiary amino groups. In one or more embodiments, component D may have a hydroxyl group from the viewpoint of workability taking into account odor and/or boiling point. Component D may be one type or a combination of two or more types.

The number of nitrogen atoms in the molecule of component D is preferably 10 or less, more preferably 5 or less, even more preferably 4 or less, and even more preferably 2 or less, from the viewpoint of improving the polishing speed without significantly increasing the amount of silica remaining.

From the viewpoint of improving the polishing rate without significantly increasing the amount of residual silica, in one or a plurality of embodiments, Component D may be at least one compound selected from an aliphatic amine compound having 10 or less nitrogen atoms in the molecule and an alicyclic amine compound having 10 or less nitrogen atoms in the molecule.
From the same viewpoint, examples of the aliphatic amine compound include at least one selected from monoethanolamine, ethylenediamine, N,N,N',N'-tetramethylethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,4-diaminobutane, hexamethylenediamine, 3-(diethylamino)propylamine, 3-(dibutylamino)propylamine, 3-(methylamino)propylamine, 3-(dimethylamino)propylamine, N-aminoethylethanolamine, N-(2-aminoethyl)diethanolamine, N-aminoethylisopropanolamine, N-aminoethyl-N-methylethanolamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine. Among these, at least one selected from monoethanolamine (MEA), N-aminoethylethanolamine (AEA), and tetraethylenepentamine (TEPA) is preferred, and monoethanolamine (MEA) and/or N-aminoethylethanolamine (AEA) is more preferred.
From the same viewpoint, examples of the alicyclic amine compound include at least one selected from piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, 1-amino-4-methylpiperazine, N-methylpiperazine, 1-(2-aminoethyl)piperazine, hydroxyethylpiperazine, and piperazine-1,4-bisethanol, and among these, hydroxyethylpiperazine (HEP) is preferred.

In one or more embodiments, the molecular weight of component D is preferably 60 or more and 500 or less, more preferably 60 or more and 300 or less, even more preferably 60 or more and 150 or less, and even more preferably 60 or more and 135 or less, from the viewpoint of improving the polishing rate without significantly increasing the amount of silica remaining.

When the polishing liquid composition of the present disclosure contains component D, the content of component D in the polishing liquid composition of the present disclosure is preferably 0.001 mass% or more, more preferably 0.01 mass% or more, and even more preferably 0.05 mass% or more, from the viewpoint of improving the polishing rate without significantly increasing the amount of silica remaining, and from the same viewpoint, it is preferably 10 mass% or less, more preferably 5 mass% or less, and even more preferably 1 mass% or less. More specifically, the content of component D in the polishing liquid composition of the present disclosure is preferably 0.001 mass% or more and 10 mass% or less, more preferably 0.01 mass% or more and 5 mass% or less, and even more preferably 0.05 mass% or more and 1 mass% or less. When component D is a combination of two or more types, the content of component D refers to the total content thereof.

In one or more embodiments, the mass ratio D/A of the content of component D to the content of component A in the polishing liquid composition of the present disclosure is preferably 0.00018 or more, more preferably 0.0018 or more, and even more preferably 0.0054 or more, from the viewpoint of improving the polishing rate without significantly increasing the amount of silica remaining, and from the same viewpoint, is preferably 0.18 or less, more preferably 0.09 or less, and even more preferably 0.054 or less. More specifically, the mass ratio D/A in the polishing liquid composition of the present disclosure is preferably 0.00018 or more and 0.18 or less, more preferably 0.0018 or more and 0.09 or less, and even more preferably 0.0054 or more and 0.054 or less.

[Other ingredients]
The polishing liquid composition of the present disclosure may contain other components as necessary. Examples of other components include corrosion inhibitors, thickeners, dispersants, rust inhibitors, basic substances, surfactants, water-soluble polymers, etc. The other components are preferably contained in the polishing liquid composition within a range that does not impair the effects of the present disclosure. When the polishing liquid composition of the present disclosure contains other components, the content of the other components in the polishing liquid composition of the present disclosure is preferably more than 0 mass%, more preferably 0.1 mass% or more, and preferably 10 mass% or less, and more preferably 5 mass% or less. More specifically, the content of the other components in the polishing liquid composition of the present disclosure is preferably more than 0 mass% and 10 mass% or less, more preferably 0.1 mass% or more and 10 mass% or less, and even more preferably 0.1 mass% or more and 5 mass% or less.

[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% by mass or less, more preferably 2% by mass or less, even more preferably 1% by mass or less, even more preferably 0.1% by mass or less, even more preferably 0.05% by mass or less, even more preferably 0.02% by mass or less, and even more preferably substantially 0% by mass (i.e., not contained). In addition, in one or more embodiments, the content of alumina particles in the polishing liquid composition of the present disclosure is preferably 2% by mass or less, more preferably 1% by mass or less, even more preferably 0.5% by mass or less, and even more preferably substantially 0% by mass (i.e., not contained), based on the total amount of abrasive grains in the polishing liquid composition.

[pH]
The pH of the polishing composition of the present disclosure is preferably 0.5 or more, more preferably 0.7 or more, even more preferably 0.9 or more, and even more preferably 1 or more, from the viewpoint of improving the polishing rate and reducing scratches, and from the same viewpoint, it is preferably 9 or less, more preferably 6 or less, even more preferably 4 or less, even more preferably 3 or less, even more preferably 2.5 or less, and even more preferably 2 or less. More specifically, the pH of the polishing composition of the present disclosure is preferably 0.5 or more and 9 or less, more preferably 0.5 or more and 6 or less, even more preferably 0.7 or more and 4 or less, even more preferably 1 or more and 3 or less, even more preferably 1 or more and 2.5 or less, and even more preferably 1 or more and 2 or less. The pH can be adjusted using the above-mentioned acid (component B) or a known pH adjuster. The above pH is the pH of the polishing composition at 25 ° C., and can be measured using a pH meter, and is preferably the value 2 minutes after immersing the electrode of the pH meter in the polishing composition.

[Method of manufacturing the polishing composition]
The polishing liquid composition of the present disclosure can be produced, for example, by blending component A, an aqueous medium, and optional components (component B, component C, component D, and other components) as necessary by a known method. Therefore, 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 and an aqueous medium. In the present disclosure, "blending" includes mixing component A, an aqueous medium, and optional components (component B, component C, component D, and other components) as necessary simultaneously or in any order. The blending can be performed using a mixer such as a homomixer, a homogenizer, an ultrasonic disperser, and a wet ball mill. The preferred blending amount of each component in the method for producing a silica slurry and a polishing liquid composition can be the same as the preferred content of each component in the polishing liquid composition according to the present disclosure described above.

In this disclosure, "the content of each component in the polishing liquid composition" refers to the content of each component at the time of use, i.e., at the time when the polishing liquid composition begins to be used for polishing. In one or more embodiments, the content of each component in the polishing liquid composition in this disclosure can be considered to be the blending amount of each component.

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. This is preferable in that production and transportation costs can be further reduced. When used, the concentrated polishing composition of the present disclosure may be appropriately diluted with the above-mentioned water as necessary. The dilution ratio is not particularly limited as long as the above-mentioned content (at the time of use) of each component can be secured after dilution, and may be, for example, 10 to 100 times.

[Polishing liquid kit]
In one aspect, the present disclosure relates to a polishing liquid kit for producing the polishing liquid composition of the present disclosure, the polishing liquid kit including a container-containing silica dispersion containing component A and an aqueous medium contained in a container (hereinafter also referred to as the "polishing liquid kit of the present disclosure"). The polishing liquid kit according to the present disclosure may further include an additive aqueous solution containing component B, and at least one selected from component C and component D, contained in a container separate from the container-containing silica dispersion. According to the present disclosure, in one or more embodiments, a polishing liquid composition capable of reducing silica residue and scratches on the substrate surface after polishing can be obtained.
In one or more embodiments, the polishing liquid kit of the present disclosure may be, for example, a polishing liquid kit (two-liquid type polishing liquid composition) that contains a silica dispersion (slurry) containing component A and an aqueous medium, and an additive aqueous solution containing components B, C, and D as necessary, in a mutually unmixed state, and that is mixed when used and diluted with an aqueous medium as necessary. The aqueous medium contained in the silica dispersion may be the entire amount of the aqueous medium used to prepare the polishing liquid composition, or may be a part of it. The silica dispersion and the additive aqueous solution may each contain the above-mentioned other components as necessary.

[Polished substrate]
In one or more embodiments, the substrate to be polished is a substrate used for manufacturing a magnetic disk substrate. In one or more embodiments, the surface of the substrate to be polished is polished with the polishing composition of the present disclosure, and then a magnetic layer is formed on the substrate surface by sputtering or the like, thereby manufacturing a magnetic disk substrate.

Materials of the substrate to be polished that are suitable for use in this disclosure include, for example, metals or semimetals such as silicon, aluminum, nickel, tungsten, copper, tantalum, and titanium, or alloys thereof; glassy materials such as glass, glassy carbon, and amorphous carbon; ceramic materials such as alumina, silicon dioxide, silicon nitride, tantalum nitride, and titanium carbide; and resins such as polyimide resins. In particular, the substrate to be polished is suitable for use with metals such as aluminum, nickel, tungsten, and copper, and alloys containing these metals as the main components. As the substrate to be polished, for example, Ni-P plated aluminum alloy substrates and glass substrates such as crystallized glass, tempered glass, aluminosilicate glass, and aluminoborosilicate glass are more suitable, and Ni-P plated aluminum alloy substrates are even more suitable. In this disclosure, the term "Ni-P plated aluminum alloy substrate" refers to an aluminum alloy substrate whose surface has been ground and then electrolessly plated with Ni-P.

The shape of the substrate to be polished can be, for example, a disk-like, plate-like, slab-like, prism-like, or other shape with a flat surface, or a lens-like, or other shape with a curved surface, and a disk-like substrate is preferred. In the case of a disk-like substrate to be polished, the outer diameter is, for example, 2 to 100 mm, and the thickness is, for example, 0.4 to 2 mm.

Generally, magnetic disks are manufactured by polishing a substrate that has undergone a grinding process, then polishing it through a rough polishing process and a finish polishing process, and then through a magnetic layer forming process. In one or more embodiments, the polishing composition of the present disclosure is preferably used for polishing in the finish polishing process. In one or more embodiments, the polishing composition of the present disclosure is a polishing composition for magnetic disk substrates.

[Method for reducing residual silica]
In one aspect, the present disclosure relates to a method for reducing residual silica on a substrate after polishing, which comprises polishing a substrate to be polished with the polishing liquid composition of the present disclosure (hereinafter, also referred to as the "method for reducing residual silica of the present disclosure"). The substrate to be polished in the method for reducing residual silica of the present disclosure may be the above-mentioned substrate to be polished.
In one or more embodiments, the method for reducing silica residue according to the present disclosure may further include selecting silica particles A (component A) contained in the polishing liquid composition according to the present disclosure. In the present disclosure, "selecting silica particles A" includes purchasing a product that describes in a catalog, product manual, label, or the like the physical properties of silica particles A (component A) and/or the ability to reduce silica residue.
Therefore, in one or a plurality of embodiments, the method for reducing silica residue of the present disclosure relates to a method for reducing silica residue, comprising selecting silica particles A (component A) and polishing a substrate to be polished using the polishing liquid composition of the present disclosure containing the selected silica particles A (component A).
In another aspect, the present disclosure relates to a method for reducing residual silica, comprising: selecting silica particles as abrasive grains, the ignition loss on a dry weight basis is 2% or less, and when the particle size D90 is the particle size at which the cumulative frequency from the small particle size side is 90% in the particle size distribution in weight conversion obtained by centrifugal sedimentation, the D90 is 65 nm or less; and polishing a substrate to be polished using a polishing liquid composition containing the silica particles and an aqueous medium. The silica particles in the method for reducing residual silica of this aspect include the above-mentioned silica particles A (component A). The polishing liquid composition in the method for reducing residual silica of this aspect includes the above-mentioned polishing liquid composition of the present disclosure.
According to the method for reducing silica residues of the present disclosure, the use of the polishing composition of the present disclosure can reduce silica residues and scratches on the substrate surface after polishing. The specific polishing method and conditions can be the same as those of the substrate manufacturing method of the present disclosure described below.

[Polishing method]
In one aspect, the present disclosure relates to a method for polishing a substrate (hereinafter also referred to as the "polishing method of the present disclosure"), which comprises using the polishing liquid composition of the present disclosure to polish a substrate, and the substrate is a substrate used in the manufacture of a magnetic disk substrate. The substrate to be polished in the polishing method of the present disclosure may be the substrate to be polished described above. The polishing method of the present disclosure may be used, for example, in a finish polishing process.
According to the polishing method of the present disclosure, by using the polishing composition of the present disclosure, the silica residue and scratches on the substrate surface after polishing can be reduced. Therefore, the productivity of the substrate (e.g., magnetic disk substrate) with improved substrate quality can be improved. The specific polishing method and conditions can be the same as the substrate manufacturing method of the present disclosure described later.

[Method of manufacturing magnetic disk substrate]
In one aspect, the present disclosure relates to a method for producing a magnetic disk substrate (hereinafter also referred to as the "substrate production method of the present disclosure"), which includes a polishing step (hereinafter also referred to as the "polishing step") of polishing a substrate to be polished with the polishing liquid composition of the present disclosure. The polishing step in the substrate production method of the present disclosure is, for example, a finish polishing step.
In one or a plurality of embodiments, the substrate manufacturing method of the present disclosure may further include a step of selecting silica particles A (component A) contained in the polishing liquid composition of the present disclosure. In the present disclosure, "selecting silica particles A" includes, as described above, purchasing a product that describes in a catalog, product manual, label, or the like the physical properties of silica particles A (component A) and/or the ability to reduce residual silica.
Therefore, in one or more embodiments, the substrate manufacturing method of the present disclosure relates to a method for manufacturing a magnetic disk substrate, which includes a step of selecting silica particles A (component A) and a step of polishing a substrate to be polished using the polishing liquid composition of the present disclosure containing the selected silica particles A (component A).
In another aspect, the present disclosure relates to a method for manufacturing a magnetic disk substrate, comprising the steps of selecting silica particles as abrasive grains, the ignition loss on a dry weight basis being 2% or less, and the particle diameter D90 being 65 nm or less, where D90 is the particle diameter where the cumulative frequency from the small particle diameter side is 90% in the particle size distribution in weight conversion obtained by centrifugal sedimentation, and polishing a substrate to be polished using a polishing liquid composition containing the silica particles and an aqueous medium.The silica particles in the method for manufacturing a magnetic disk substrate of this aspect include the above-mentioned silica particles (component A).The polishing liquid composition in the method for manufacturing a magnetic disk substrate of this aspect includes the above-mentioned polishing liquid composition of the present disclosure.

In one or more embodiments, the polishing process is a process in which the polishing liquid composition of the present disclosure is supplied to the surface to be polished of a substrate to be polished, a polishing pad is brought into contact with the surface to be polished, and at least one of the polishing pad and the substrate to be polished is moved to perform polishing.
In one or more embodiments, the polishing step is a step in which a substrate to be polished is sandwiched between plates to which a polishing pad such as a nonwoven organic polymer-based abrasive cloth is attached, and the platen and the substrate to be polished are moved while the polishing liquid composition of the present disclosure is supplied to a polishing machine to polish the substrate.

When the polishing process of the substrate to be polished is carried out in multiple stages, the polishing process using the polishing liquid composition of the present disclosure is preferably carried out in the second stage or later, and more preferably in the final polishing process or finish polishing process. In this case, a separate polishing machine may be used for each step to avoid contamination with the abrasive or polishing liquid composition from the previous step, and when separate polishing machines are used, it is preferable to clean the substrate to be polished after each polishing process. Furthermore, the polishing liquid composition of the present disclosure can also be used in circulating polishing in which the used polishing liquid is reused. There are no particular limitations on the polishing machine, and any known polishing machine for substrate polishing can be used.

The polishing pad used in this disclosure is not particularly limited, and may be, for example, a suede type, a nonwoven fabric type, a polyurethane independent foam type, or a two-layer type laminated with these, with suede type polishing pads being preferred from the standpoint of polishing speed.

The polishing load in the polishing process using the polishing composition of the present disclosure is preferably 5.9 kPa or more, more preferably 6.9 kPa or more, and even more preferably 7.5 kPa or more, from the viewpoint of ensuring the polishing rate, and is preferably 20 kPa or less, more preferably 18 kPa or less, and even more preferably 16 kPa or less, from the viewpoint of reducing scratches. In this disclosure, "polishing load" refers to the pressure of the platen applied to the polishing surface of the substrate to be polished during polishing. The polishing load can be adjusted by applying air pressure or a weight to at least one of the platen and the substrate to be polished.

In the polishing step, the amount of polishing per ¹ cm2 of the substrate to be polished is preferably 0.05 mg or more, more preferably 0.1 mg or more, and even more preferably 0.2 mg or more, from the viewpoints of improving the polishing rate and reducing scratches, and from the same viewpoint, it is preferably 2.5 mg or less, more preferably 2 mg or less, and even more preferably 1.6 mg or less. More specifically, the amount of polishing per ¹ cm2 of the substrate to be polished is preferably 0.05 mg or more and 2.5 mg or less, more preferably 0.1 mg or more and 2 mg or less, and even more preferably 0.2 mg or more and 1.6 mg or less.

In a polishing process using the polishing liquid composition of the present disclosure, the supply rate of the polishing liquid composition of the present disclosure is, from the viewpoint of reducing scratches, preferably ^0.05 mL/min or more and 15 mL/min or less, more preferably 0.06 mL/min or more and 10 mL/min or less, even more preferably 0.07 mL/min or more and 1 mL/min or less, and even more preferably 0.07 mL/min or more and 0.5 mL/min or less, per 1 cm2 of the substrate to be polished.

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

According to the substrate manufacturing method disclosed herein, by using the polishing composition disclosed herein, it is possible to reduce residual silica and scratches on the substrate surface after polishing. As a result, substrates (e.g., magnetic disk substrates) with improved substrate quality can be efficiently manufactured.

[Silica particles]
In one aspect, the present disclosure relates to silica particles having an ignition loss of 2% or less on a dry weight basis, and a particle diameter D90 of 65 nm or less when the particle diameter D90 is the particle diameter at which the cumulative frequency from the small particle diameter side is 90% in the particle size distribution in weight conversion obtained by centrifugal sedimentation (hereinafter, the silica particles having the ignition loss and the D90 are also referred to as the "silica particles of the present disclosure"). The silica particles of the present disclosure can be suitably used as abrasive grains for polishing magnetic disk substrates. In one or more embodiments, the silica particles of the present disclosure are the above-mentioned component A.
The ignition loss of the silica particles of the present disclosure based on dry weight is preferably 1.9% or less, more preferably 1.6% or less, even more preferably 1.5% or less from the viewpoint of reducing residual silica when the silica particles of the present disclosure are used as abrasive grains for polishing magnetic disk substrates, and from the viewpoint of storage stability, it is preferably 0% or more, more preferably 0.5% or more, even more preferably 1.0% or more.More specifically, the ignition loss of component A based on dry weight is preferably 0% or more and 1.9% or less, more preferably 0.5% or more and 1.6% or less, even more preferably 1.0% or more and 1.5% or less.
The D90 of the silica particles of the present disclosure is preferably 60nm or less, more preferably 55nm or less, and even more preferably 52nm or less from the viewpoint of reducing scratches when the silica particles of the present disclosure are used as abrasive grains for polishing magnetic disk substrates, and is preferably 30nm or more, more preferably 35nm or more, and even more preferably 40nm or more from the viewpoint of improving polishing speed.More specifically, the D90 of the silica particles of the present disclosure is preferably 30nm or more and 60nm or less, more preferably 35nm or more and 55nm or less, and even more preferably 40nm or more and 52nm or less.
When the ignition loss on dry weight basis of the silica particles of the present disclosure is WL, the value represented by the following formula (II) is preferably 5 or less, more preferably 2.5 or less, and even more preferably 2 or less from the viewpoint of reducing the residual silica when the silica particles of the present disclosure are used as abrasive grains for polishing magnetic disk substrates, and is preferably 0 or more, more preferably 0.1 or more, and even more preferably 0.5 or more from the viewpoint of maintaining the polishing rate and storage stability. More specifically, the value represented by the following formula (II) is preferably 0 or more and 5 or less, more preferably 0.1 or more and 2.5 or less, and even more preferably 0.5 or more and 2 or less.
{(WL) ³ x D90}/100 (II)
The ignition loss on a dry weight basis of the silica particles of the present disclosure, the value represented by formula (II), and D90 are preferably the same as the value represented by formula (I) described for the silica particles (component A) contained in the polishing liquid composition of the present disclosure.

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

1. Preparation of polishing compositions (Examples 1 to 4 and Comparative Examples 1 to 4)
Silica particles (component A or non-component A), acid (component B), oxidizing agent (component C) and water were mixed to prepare the polishing liquid compositions of Examples 1 to 4 and Comparative Examples 1 to 4 shown in Table 1. The content (active content) of each component in the polishing liquid composition was 5.5 mass% for silica particles (component A or non-component A), 1.0 mass% for acid (component B), and 0.3 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 do not contain alumina abrasive grains. The silica particles used as the abrasive grains are colloidal silica produced by a water glass method. The pH of the polishing liquid compositions of Examples 1 to 4 and Comparative Examples 1 to 4 was 1.8.
(Examples 5 to 15 and Reference Examples 1 to 3)
Silica particles (component A), acid (component B), oxidizing agent (component C), nitrogen-containing compound (component D or non-component D) and water were mixed to prepare the polishing liquid compositions of Examples 5 to 15 and Reference Examples 1 to 3 shown in Table 1. The content (active content) of each component in the polishing liquid composition was as follows: silica particles (component A): 5.5 mass %, acid (component B): 1.0 mass %, oxidizing agent (component C): 0.3 mass %, nitrogen-containing compound (component D or non-component D): 0.10 mass %. The content of water is the remainder excluding components A, B, C, and D or non-component D. The polishing liquid compositions of Examples 5 to 15 and Reference Examples 1 to 3 do not contain alumina abrasive grains. The silica particles used as the abrasive grains were manufactured by the water glass method. The pH of the polishing liquid compositions of Examples 5 to 15 and Reference Examples 1 to 3 was 1.8.

The following were used as component A or non-component A, component B, component C, component D or non-component D for preparing the polishing composition.
(Component A)
(Preparation of Silica Particles A1 to A4)
To 500 g of a metal silicate aqueous solution adjusted to pH 10-12 and silica concentration 2%, 7 kg of an acidic silicic acid solution adjusted to a silica concentration of 5% is intermittently added dropwise over 1-24 hours to increase the particle size (build-up). At this time, by adjusting the dropping speed of the dropping liquid, the silicic acid concentration, the reaction temperature, pressure, pH, etc., silica particles having silanol groups in a desired range can be obtained. In particular, by slowing down the dropping speed to allow the particles to grow slowly, a dense surface and internal structure are formed, and the number of siloxane bonds increases, making it possible to adjust the silanol groups and ignition loss.
By the above-mentioned production method, the following silica particles A1 to A4 were prepared.
Silica particles A1: spherical silica particles [colloidal silica (water glass method), aspect ratio 1.04, average secondary particle diameter 21 nm, ignition loss 1.10%]
Silica particles A2: spherical silica particles [colloidal silica (water glass method), aspect ratio 1.06, average secondary particle diameter 17 nm, ignition loss 1.11%]
Silica particles A3: spherical silica particles [colloidal silica (water glass method), aspect ratio 1.05, average secondary particle diameter 18 nm, ignition loss 1.17%]
Silica particles A4: spherical silica particles [colloidal silica (water glass method), aspect ratio 1.04, average secondary particle diameter 25 nm, ignition loss 1.58%]
(Non-Component A)
Silica particles A5: non-spherical silica particles [colloidal silica (water glass method), aspect ratio 1.12, average secondary particle size 142 nm, ignition loss 4.13%, manufactured by JGC Catalysts and Chemicals]
Silica particles A6: mixed silica [a mixture of spherical colloidal silica A1 and spherical colloidal silica A8 in a weight ratio of A1/A8 = 50/50 was used as the mixed silica (aspect ratio 1.03, average secondary particle diameter 27 nm, ignition loss 1.75%).]
Silica particles A7: spherical silica particles [colloidal silica (water glass method), aspect ratio 1.03, average secondary particle size 110 nm, ignition loss 2.38%, manufactured by JGC Catalysts and Chemicals, SI-80]
Silica particles A8: spherical silica particles [colloidal silica (water glass method), aspect ratio 1.03, average secondary particle size 48 nm, ignition loss 1.96%, manufactured by JGC Catalysts and Chemicals, SI-45]
(Component B)
Phosphoric acid [concentration 75%, manufactured by Nippon Chemical Industry Co., Ltd.]
(Component C)
Hydrogen peroxide [concentration 35% by mass, manufactured by ADEKA]
(Component D)
MEA: Monoethanolamine (molecular weight 61, nitrogen atom number 1)
AEA: N-(β-aminoethyl)ethanolamine (molecular weight 104.5, number of nitrogen atoms 2)
TEPA: Tetraethylenepentamine (molecular weight 189.3, number of nitrogen atoms 5)
(Non-Component D)
PEI: Polyethyleneimine (number average molecular weight 600, number of nitrogen atoms approximately 20, "Epomin SP-006" manufactured by Nippon Shokubai Co., Ltd.)

2. Measurement method for each parameter [Method for measuring particle diameters D10, D50 and D90 of silica particles by centrifugal sedimentation method (CPS measurement)]
The silica particles were diluted with ion-exchanged water to prepare a dispersion containing 0.4% by mass of silica particles, which was used as a sample. In Comparative Example 2, the spherical silica particles (A1) and the spherical silica particles (A8) were mixed in a mass ratio of 50/50.
The particle size distribution of the prepared sample was measured by centrifugal sedimentation using the following measuring device. The particle sizes at which the cumulative frequency from the small diameter side in the particle size distribution in weight conversion obtained by centrifugal sedimentation was 10%, 50%, and 90%, respectively, were defined as D10, D50, and D90.
<Measurement conditions>
Measuring device: "CPS DC24000 UHR" manufactured by CPS Instruments
Measurement range: 0.0004 to 1 μm
Particle extinction coefficient: 0.1
Particle shape factor: 1.0
Rotational speed: 20,000 rpm
Standard particle size for calibration: 0.476 μm
Standard particle density: 1.0465 (13%, 34°C)
Density gradient solution: sucrose aqueous solution (8%, 24%)
Solvent viscosity: 1.16 cp (13%, 34° C.)
Refractive index of solvent: 1.3592 (18%, 34°C)
Measurement temperature: 15 to 45°C
Measurement time: 100 to 420 minutes

[Method for measuring particle size D50 (average secondary particle size) of silica particles by DLS measurement]
Silica particles were mixed with phosphoric acid and ion-exchanged water to prepare a 1% by mass silica particle dispersion. In Comparative Example 2, the spherical silica particles (A1) and the spherical silica particles (A8) were mixed so that the mass ratio was 50/50. The prepared 1% by mass silica particle dispersion was placed in the following measuring device and measured under the following conditions. In the obtained particle size distribution, the particle diameter at which the cumulative volume frequency from the small diameter side was 50% was taken as D50. Note that D50 by DLS was taken as the average secondary particle diameter (volume average particle diameter) of the silica particles. The measurement results are shown in Table 1.
<Measurement conditions>
Measurement equipment: Malvern Zetasizer Nano "Nano S"
Sample volume: 1.5mL
Laser: He-Ne, 3.0 mW, 633 nm
Scattered light detection angle: 173°

[Average aspect ratio of silica particles]
Photographs of silica particles observed with a TEM (JEM-2000FX manufactured by JEOL, 80 kV, 10,000 to 50,000 magnifications) were imported into a personal computer as image data using a scanner, and the projected images of 500 silica particles were analyzed using analysis software (WinROOF (Ver. 3.6) manufactured by Mitani Corporation) as described below.
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.
In the case of the mixed silica of Comparative Example 2, the spherical silica particles (A1) and the spherical silica particles (A8) were mixed in a mass ratio of 50/50, dried, and observed under a TEM, and the average aspect ratio was calculated from the minor axis/major axis ratio in image analysis.

[Ignition loss]
The silica particles were mixed with ion-exchanged water to prepare a 40% by mass silica slurry. In Comparative Example 2, the spherical silica particles (A1) and the spherical silica particles (A8) were mixed in a mass ratio of 50/50.
The prepared silica slurry was adjusted to pH = 3.5 with sulfuric acid, and heated at 180 ° C. using a Shimadzu Corporation infrared moisture meter "MOC63u" to remove moisture. After that, it was left to stand for 10 minutes and returned to room temperature to obtain 2 g of sample. Of this, 1 g of sample was again measured for loss on drying LOD (how much moisture it absorbs at room temperature) using the infrared moisture meter. The remaining 1 g of sample was placed in a ceramic crucible and fired in a firing furnace at 1000 ° C. for 2 hours, and then cooled in a desiccator for 30 minutes, after which the loss on ignition LOI (weight lost due to dehydration of silanol groups) was measured. Finally, the loss on ignition WL based on dry weight was calculated using the following formula.
Loss on ignition on a dry weight basis WL=100×{1−(100−LOI)/(100−LOD)}

[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 the electrode in the polishing composition was recorded.

3. Substrate Polishing Using the prepared polishing compositions of Examples 1 to 15, Comparative Examples 1 to 4, and Reference Examples 1 to 3, the following substrates to be polished were finish-polished under the polishing conditions shown below.
[Polished substrate]
The substrate to be polished was an aluminum alloy substrate plated with Ni-P and roughly polished with a polishing composition containing silica abrasive grains. The substrate to be polished had a thickness of 0.6 mm, an outer diameter of 97 mm, an inner diameter of 25 mm, and a center line average roughness Ra of 1 nm measured by an AFM (Digital Instrument NanoScope IIIa Multi Mode AFM). The ratio of Ni to P in the Ni-P plating was 88:12 by mass.
[Finish polishing conditions]
Polishing machine: double-sided polishing machine (9B type double-sided polishing machine, manufactured by SpeedFam)
Number of substrates to be polished: 10 Polishing liquid: Polishing liquid composition Polishing pad: Suede type (foam layer: polyurethane elastomer, thickness 0.9 mm, average pore size 10 μm, manufactured by Fujibo Co., Ltd.)
Rotation speed of the platen: 32.5 rpm
Polishing load: 10.5 kPa (set value)
Amount of polishing solution supplied: 100 mL/min. Supply rate per ^{1 cm2} of substrate to be polished: 0.076 mL/min. Amount polished per ^{1 cm2} of substrate to be polished: 0.23 mg
Polishing time: 6 minutes

4. Evaluation method [Evaluation of removal rate]
The polishing rates of the polishing compositions of Examples 1 to 15, Comparative Examples 1 to 4, and Reference Examples 1 to 3 were evaluated as follows. First, the mass of each substrate was measured before and after polishing (using an electronic balance manufactured by Sartorius, "BP-210S"), and the mass loss was calculated 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 (unit: minutes), and the value was introduced into the following formula to calculate. Then, a relative value was calculated with the polishing rate of Comparative Example 1 taken as 100, and this was used as the evaluation item.
Mass loss (mg)={mass before polishing (mg)−mass after polishing (mg)}
Polishing rate (mg/min)=mass reduction (mg)/polishing time (min)

[Evaluation of residual silica]
The substrate after the polishing is washed using a cleaning machine manufactured by Hikari Co., Ltd., and then one substrate is immersed in 20 mL of ultrapure water and ultrasonically washed for 15 minutes. This operation extracts the silica particles remaining on the substrate surface into the ultrapure water. The substrate is removed, and a solution containing 0.2 g of nitric acid and 0.5 g of hydrofluoric acid in 20 mL of ultrapure water is left to stand for 15 minutes to completely dissolve the silica particles. The solution was then measured for Si intensity under the following measurement conditions using an Agilent inductively coupled plasma mass spectrometry (ICP-MS) device "Agilent 8900". The lower the Si intensity in the solution, the less silica remains. Then, a relative value was calculated with the silica remainder in Comparative Example 1 set at 100, and this was used as an evaluation item.
<ICP-MS measurement conditions>
Measurement element: Si (mass number 28.1)
Gas: Argon (purity 99.99%)
Plasma flow rate: 15 L/min, auxiliary 1.0 L/min, carrier 1.35 mL
Integration time: 0.34 seconds per mass number Integration times: 3 Calibration curve: Calculated from five points of Si standard sample: 0, 0.1, 0.25, and 0.5 ppm The silica residue values shown in Table 1 are average values obtained by carrying out the same operation and analysis using five substrates for each condition.

[Scratch Evaluation]
Measuring equipment: "Candela OSA7100" manufactured by KLA Tencor Corporation
Evaluation: Four of the substrates were randomly selected from those placed in the polishing tester, and each substrate was irradiated with a laser at 10,000 rpm to measure the number of scratches. The total number of scratches on both sides of each of the four substrates was divided by 8 to calculate the number of scratches per substrate surface. The evaluation results of the number of scratches are shown in Table 1 as a relative value with Comparative Example 4 taken as 100.

5. Results The results of each evaluation are shown in Table 1.

As shown in Table 1, it was found that the polishing liquid compositions of Examples 1 to 15, which use the specified silica particles, can reduce silica residue and scratches on the substrate surface after polishing, compared to Comparative Examples 1 to 4. It was also found that Examples 5 to 15, which contain the specified nitrogen-containing compound, can improve the polishing rate without significantly increasing the amount of silica residue, compared to Reference Examples 1 to 3, which do not contain the specified nitrogen-containing compound.

In one aspect, the present disclosure can reduce residual silica and scratches on the substrate surface after polishing, thereby improving the productivity of substrates with improved substrate quality. The present disclosure can be suitably used in the manufacture of magnetic disk substrates.

Claims

Contains silica particles and an aqueous medium,
The silica particles have an ignition loss of 2% or less on a dry weight basis;
The polishing composition, wherein the silica particles have a particle diameter D90 of 65 nm or less, where D90 is the particle diameter at which a cumulative frequency from the small particle diameter side is 90% in a particle size distribution calculated on a weight basis obtained by a centrifugal sedimentation method.
Further comprising a nitrogen-containing compound,
The polishing composition according to claim 1 , wherein the nitrogen-containing compound is an organic amine compound having 10 or less nitrogen atoms in the molecule.
3. The polishing composition according to claim 1, wherein the silica particles have a value represented by the following formula (I) of 5 or less, where WL is an ignition loss on a dry weight basis of the silica particles:
{(WL) 3 x D90}/100 (I)
The polishing composition according to any one of claims 1 to 3, wherein the silica particles have a particle diameter D10 of 5 nm or more and 35 nm or less, where D10 is the particle diameter at which the cumulative frequency from the small particle diameter side in the particle size distribution is 10%.
The polishing composition according to any one of claims 1 to 4, wherein the silica particles have a particle diameter D50 of 10 nm or more and 40 nm or less, where D50 is the particle diameter at which the cumulative frequency from the small particle diameter side in the particle size distribution is 50%.
The polishing composition according to any one of claims 1 to 5, wherein the polishing composition is a polishing composition for magnetic disk substrates.
A method for manufacturing a magnetic disk substrate, comprising a polishing step of polishing a substrate to be polished using the polishing composition according to any one of claims 1 to 6.
The method for manufacturing a magnetic disk substrate according to claim 7, wherein the substrate to be polished is an aluminum alloy substrate plated with Ni-P.
The method for manufacturing a magnetic disk substrate according to claim 7 or 8, wherein the polishing process is a finish polishing process.
A method for polishing a substrate, comprising polishing the substrate to be polished with the polishing composition according to any one of claims 1 to 6, the substrate being a substrate used in the manufacture of magnetic disk substrates.
1. A method for reducing residual silica on a polished substrate, comprising:
A method for reducing residual silica, comprising polishing a substrate to be polished with the polishing composition according to claim 1 .
a step of selecting silica particles as the abrasive grains, the silica particles having an ignition loss of 2% or less on a dry weight basis, and a particle size distribution obtained by centrifugal sedimentation in weight conversion, the particle size being 90% of the cumulative frequency from the small particle size side, and a D90 of 65 nm or less;
A method for producing a magnetic disk substrate, comprising the step of polishing a substrate to be polished with a polishing composition containing the silica particles and an aqueous medium.