Polishing slurry composition

Abstract

To provide a polishing liquid composition with superior storage stability, capable of reducing scratches on a substrate surface after polishing, while ensuring the polishing speed.SOLUTION: In one aspect, the present disclosure pertains to a polishing liquid composition for magnetic disk substrates that contains silica particles (component A), an acid (component B), an oxidizer (component C), a quaternary phosphonium salt having at least one hydrocarbon group without any substituent (component D), and an aqueous medium.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, magnetic disk drives have become smaller and their capacities have increased, resulting in a demand for higher recording densities. To achieve higher recording densities, technological developments are underway to reduce the unit recording area and lower the flying height of the magnetic head to improve the detection sensitivity of weakened magnetic signals. To accommodate the lower flying height of the magnetic head and ensure a sufficient recording area, magnetic disk substrates are increasingly being required to improve smoothness and flatness, such as reducing surface roughness, waviness, and edge sagging (roll-off), as well as to reduce defects, such as scratches, protrusions, and pits.

[0003] Polishing solutions that can improve the polishing rate and flatness of substrates other than magnetic disk substrates have also been developed. For example, Patent Document 1 proposes a polishing liquid for CMP (chemical mechanical polishing) used to polish a substrate having a stopper containing polysilicon and a member containing an insulating material (e.g., silicon oxide), the polishing liquid containing abrasive grains containing metal oxide, a quaternary phosphonium cation having a hydrocarbon group with two or more carbon atoms bonded to a phosphorus atom, and a liquid medium. Patent Document 2 proposes a CMP abrasive used for polishing a surface containing cobalt, which contains abrasive grains, a quaternary phosphonium salt, and water and has a pH of more than 4.0. Patent Document 3 proposes a CMP polishing liquid used in a second polishing step of polishing the barrier film to expose the interlayer insulating film after a first polishing step of polishing the conductive material of a substrate having an interlayer insulating film, a barrier film, and a conductive material, in which the barrier film is polished to expose the interlayer insulating film, the polishing liquid containing a specific quaternary phosphonium salt compound, negatively charged abrasive grains, a metal oxide dissolving agent, and an oxidizing agent. Patent Document 4 proposes a chemical mechanical polishing composition for treating tungsten-containing surfaces, which is a polishing liquid containing a liquid carrier, specific silica abrasive particles, and a specific cationic surfactant. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 142292 [Patent Document 2] International Publication No. 2022 / 107217 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-120885 [Patent Document 4] Special Publication No. 2019-501517 Summary of the Invention [Problem to be solved by the invention]

[0005] As the capacity of magnetic disk drives increases, the requirements for the surface quality of substrates become more stringent, and there is a need for the development of a polishing composition that can further reduce scratches on the substrate surface. In addition, there is generally a trade-off between the polishing rate and scratches, and there is a problem that improving one will worsen the other.

[0006] Therefore, the present disclosure provides a polishing composition that can reduce scratches on the substrate surface after polishing while ensuring a satisfactory removal rate, as well as a method for manufacturing a magnetic disk substrate and a method for polishing a substrate using the same. [Means for solving the problem]

[0007] In one aspect, the present disclosure relates to a polishing liquid composition for magnetic disk substrates, which contains silica particles (component A), an acid (component B), an oxidizing agent (component C), a quaternary phosphonium salt having at least one unsubstituted hydrocarbon group (component D), and an aqueous medium.

[0008] In one aspect, the present disclosure relates to a method for producing a magnetic disk substrate, which includes a step of polishing a substrate to be polished using the polishing liquid composition of the present disclosure.

[0009] In one aspect, the present disclosure relates to a method for polishing a substrate, which comprises polishing a substrate to be polished with the polishing liquid composition of the present disclosure, wherein the substrate to be polished is a substrate used in the manufacture of magnetic disk substrates. [Effects of the Invention]

[0010] In one or more embodiments, the polishing composition of the present disclosure can achieve the effect of reducing scratches on the substrate surface after polishing while ensuring a sufficient removal rate. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present disclosure is based on the finding that the use of a polishing composition containing silica particles, an acid, an oxidizing agent, a specific quaternary phosphonium salt, and an aqueous medium makes it possible to reduce scratches on the polished substrate surface while ensuring a satisfactory removal rate.

[0012] That is, in one aspect, the present disclosure relates to a polishing liquid composition for magnetic disk substrates (hereinafter also referred to as "the polishing liquid composition of the present disclosure") containing silica particles (component A), an acid (component B), an oxidizing agent (component C), a quaternary phosphonium salt having at least one unsubstituted hydrocarbon group (component D), and an aqueous medium.

[0013] Although the details of the mechanism by which the effects of the present disclosure are manifested are not clear, it is presumed as follows. A quaternary phosphonium salt (component D) having at least one unsubstituted hydrocarbon group adsorbs onto the surface of a substrate to be polished (e.g., a Ni-P-plated aluminum alloy substrate), imparting hydrophobicity to the substrate surface. It is presumed that imparting hydrophobicity to the substrate surface suppresses excessive chemical reactions, thereby reducing the number of scratches and point defects (LPD). When the quaternary phosphonium salt has a hydrophilic substituent such as a hydroxyl group, its suppression ability is reduced, and therefore its effectiveness in imparting hydrophobicity to the substrate surface is weakened. However, the present disclosure need not be construed as being limited to these mechanisms.

[0014] In the present disclosure, scratches on the substrate surface can be detected, for example, by an optical defect inspection device and quantitatively evaluated as the number of scratches. The number of scratches can be specifically evaluated by the method described in the Examples.

[0015] [Silica particles (component A)] The polishing composition of the present disclosure contains silica particles (hereinafter also referred to as "Component A"). From the viewpoints of improving the polishing rate and reducing scratches, Component A may include colloidal silica, fumed silica, pulverized silica, and surface-modified silica thereof, with colloidal silica being preferred. Component A may be one type or a combination of two or more types.

[0016] From the viewpoint of improving the polishing rate, 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. From the viewpoint of reducing scratches, 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, and even more preferably 40 nm or less. 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, and even more preferably 10 nm or more and 40 nm or less. In the present disclosure, the "average secondary particle diameter of silica particles" refers to a value measured by dynamic light scattering, and can be, for example, the average secondary particle diameter based on the scattering intensity distribution measured at a detection angle of 90° in dynamic light scattering. Specifically, the average secondary particle diameter of silica particles can be determined by the method described in the Examples.

[0017] The content of component A in the polishing liquid composition of the present disclosure is preferably 0.1 mass% or more, more preferably 1 mass% or more, and even more preferably 3 mass% or more, calculated as SiO2, from the viewpoint of improving the removal rate. From the viewpoint of reducing scratches, the content is preferably 20 mass% or less, more preferably 15 mass% or less, and even more preferably 10 mass% or less, calculated as SiO2. More specifically, the content of component A in the polishing liquid composition of the present disclosure is preferably 0.1 mass% or more and 20 mass% or less, more preferably 1 mass% or more and 15 mass% or less, and even more preferably 3 mass% or more and 10 mass% or less, calculated as SiO2. When component A consists of two or more types of silica particles, the content of component A refers to the total content of these particles.

[0018] [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 use of an acid includes the use of an acid or a salt thereof. Component B may be one type, or two or more types may be combined.

[0019] 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; and organic acids such as organic phosphoric acid, organic phosphonic acid, and carboxylic acid. Among these, at least one selected from inorganic acids and organic phosphonic acids is preferred from the viewpoint of ensuring the polishing rate and reducing scratches. 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. The organic phosphonic acid is preferably at least one selected from 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), and diethylenetriaminepenta(methylenephosphonic acid), and HEDP is more preferred. Examples of salts of these acids include salts of the above acids with at least one selected from metals, ammonia, and alkylamines. Examples of the metal include metals belonging to groups 1 to 11 of the periodic table.

[0020] From the viewpoints of ensuring the removal rate and reducing scratches, the content of component B in the polishing liquid composition of the present disclosure is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more. From the same viewpoints, it is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. More specifically, the content of component B in the polishing liquid composition of the present disclosure is preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.1% by mass or more and 4% by mass or less, and even more preferably 1% by mass or more and 3% 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.

[0021] From the viewpoints of improving the removal rate and reducing scratches, the mass ratio A / B of the content of component A to the content of component B in the polishing liquid composition of the present disclosure is preferably 0.2 or more, more preferably 0.5 or more, and even more preferably 1 or more, and from the same viewpoints, it is preferably 10 or less, more preferably 7 or less, and even more preferably 4 or less. More specifically, the mass ratio A / B in the polishing liquid composition of the present disclosure is preferably 0.2 or more and 10 or less, more preferably 0.5 or more and 7 or less, and even more preferably 1 or more and 4 or less.

[0022] [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 scratches. Component C may be one type or a combination of two or more types.

[0023] From the viewpoints of improving the polishing rate and reducing scratches, examples of component C include peroxides, permanganic acid or its salts, chromic acid or its salts, peroxoacids or their salts, oxyacids or their salts, metal salts, nitric acids, sulfuric acids, etc. 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 further improving the polishing rate, preventing metal ions from adhering to the surface of the substrate to be polished, and ease of availability.

[0024] From the viewpoints of improving the removal rate and reducing scratches, the content of component C in the polishing liquid composition of the present disclosure is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, and preferably 4% by mass or less, more preferably 2% by mass or less, and even more preferably 1.5% by mass or less. More specifically, the content of component C in the polishing liquid composition of the present disclosure is preferably 0.01% by mass or more and 4% by mass or less, more preferably 0.05% by mass or more and 2% by mass or less, and even more preferably 0.1% by mass or more and 1.5% by 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.

[0025] [Quaternary phosphonium salt (ingredient D)] The polishing composition of the present disclosure contains a quaternary phosphonium salt having at least one unsubstituted hydrocarbon group (hereinafter also referred to as "Component D"). The hydrocarbon group refers to a group bonded to a phosphorus atom, i.e., a substituent on the phosphorus atom. Furthermore, the "unsubstituted" substituent does not include a group composed only of hydrogen and / or carbon. Component D may be one type or a combination of two or more types. The number of carbon atoms in one group of the hydrocarbon group is preferably 1 or more, more preferably 3 or more, and even more preferably 4 or more, from the viewpoint of improving the polishing rate and reducing scratches, and is preferably 12 or less, more preferably 6 or less, from the viewpoint of suppressing silica aggregation. The hydrocarbon group is preferably an alkyl group, an aryl group, or an aralkyl group, more preferably an alkyl group or an aryl group, from the viewpoints of improving the polishing rate and reducing scratches, and suppressing silica aggregation. The alkyl group is preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 4 to 7 carbon atoms, and even more preferably an alkyl group having 4 to 6 carbon atoms, such as a butyl group, from the viewpoints of improving the polishing rate, reducing scratches, and suppressing silica aggregation, such as a butyl group. The aryl group is preferably an aryl group having 6 to 12 carbon atoms, such as a phenyl group, from the viewpoints of improving the polishing rate, reducing scratches, and suppressing silica aggregation, such as a phenyl group. The aralkyl group is preferably an aralkyl group having 7 to 12 carbon atoms, such as a benzyl group, from the viewpoints of improving the polishing rate, reducing scratches, and suppressing silica aggregation. The counter ion in the quaternary phosphonium salt is not particularly limited, but may be, for example, a chloride ion (Cl - ), hydroxide ion (OH - ) etc.

[0026] From the viewpoints of improving the polishing rate and reducing scratches, the total number of carbon atoms in Component D is preferably 10 or more, more preferably 13 or more, and even more preferably 15 or more, and from the viewpoint of suppressing silica aggregation, it is preferably 25 or less, more preferably 24 or less, and even more preferably 16 or less. More specifically, the total number of carbon atoms in Component D is preferably 10 or more and 25 or less, and more preferably 13 or more and 24 or less.

[0027] In one or more embodiments, Component D is preferably a compound represented by the following formula (I): [ka] In the above formula (I), R 1 , R 2 , R 3 and R 4 each independently represents an unsubstituted hydrocarbon group, and X - indicates an anion. In the above formula (I), R 1 , R 2 , R 3 and R 4 are each independently, from the viewpoints of improving the polishing rate, reducing scratches, and suppressing silica aggregation, preferably an alkyl group, an aryl group, or an aralkyl group, more preferably an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, or an aralkyl group having 7 to 12 carbon atoms, even more preferably an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 12 carbon atoms, and even more preferably an alkyl group having 4 to 6 carbon atoms or an aryl group having 6 carbon atoms (phenyl group). R 1 , R 2 , R 3 and R 4 From the viewpoints of improving the polishing rate, reducing scratches, and suppressing silica aggregation, it is preferable that at least three of the groups be the same. X - From the viewpoint of improving the polishing speed and reducing scratches, - (chloride ion) or OH - (hydroxide ion) is preferred.

[0028] From the viewpoint of improving the polishing rate and reducing scratches, the molecular weight of component D is preferably 250 or more, more preferably 280 or more, and even more preferably 300 or more. From the viewpoint of suppressing silica aggregation, there are no particular limitations, but a molecular weight of 450 or less is preferred.

[0029] In one or more embodiments, Component D may be at least one selected from tetrabutylphosphonium salts, tetraphenylphosphonium salts, and triphenylbenzylphosphonium salts, from the viewpoints of improving the polishing rate, reducing scratches, and suppressing silica aggregation.

[0030] The content of component D in the polishing liquid composition of the present disclosure is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.05% by mass or more, from the viewpoints of improving the removal rate and reducing scratches, and is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, from the viewpoint of suppressing silica aggregation. More specifically, the content of component D in the polishing liquid composition of the present disclosure is preferably 0.02% by mass or more and 0.1% by mass or less, and more preferably 0.05% by mass or more and 0.1% by mass or less. When component D is a combination of two or more types, the content of component D is the total content thereof.

[0031] The mass ratio A / D of the content of component A to the content of component D in the polishing liquid composition of the present disclosure is not particularly limited from the viewpoints of improving the removal rate and reducing scratches, and is preferably 10 or more, and from the same viewpoints, is preferably 150 or less, more preferably 50 or less, and even more preferably 30 or less. More specifically, the mass ratio A / D in the polishing liquid composition of the present disclosure is preferably 10 or more and 150 or less, more preferably 10 or more and 50 or less, and even more preferably 10 or more and 30 or less.

[0032] [Aqueous medium] Examples of the aqueous medium contained in the polishing liquid composition of the present disclosure include water such as distilled water, ion-exchanged water, pure water, and ultrapure water, or a mixed solvent of water and a solvent. Examples of the solvent include a water-miscible solvent (e.g., alcohol such as ethanol). When the aqueous medium is a mixed solvent of water and a solvent, the proportion of water relative to the total mixed medium is not particularly limited as long as the effects of the present disclosure are not impaired. From an economical viewpoint, for example, the proportion of water is preferably 95% by mass or more, more preferably 98% by mass or more, and even more preferably substantially 100% by mass. From the viewpoint of surface cleanliness of the substrate to be polished, ion-exchanged water and ultrapure water are preferred as the aqueous medium. The content of the aqueous medium in the polishing liquid composition of the present disclosure can be the remainder excluding Component A, Component B, Component C, Component D, and the optional components described below that are blended as necessary.

[0033] [Heterocyclic aromatic compounds (component E)] From the viewpoint of further reducing scratches, the polishing composition of the present disclosure may further contain a heterocyclic aromatic compound (including its salt) (hereinafter also referred to as "Component E"). Component E may be one type or a combination of two or more types.

[0034] From the viewpoint of further reducing scratches, component E is preferably a heterocyclic aromatic compound containing two or more nitrogen atoms in the heterocycle, more preferably three or more nitrogen atoms in the heterocycle, even more preferably three to nine nitrogen atoms, even more preferably three to five nitrogen atoms, and even more preferably three or four nitrogen atoms.

[0035] In one or more embodiments, Component E is preferably at least one selected from 1,2,4-triazole, 3-amino-1,2,4-triazole, 5-amino-1,2,4-triazole, 3-mercapto-1,2,4-triazole, 1H-tetrazole, 5-aminotetrazole, 1H-benzotriazole (BTA), 1H-tolyltriazole, 2-aminobenzotriazole, 3-aminobenzotriazole, and alkyl- or amine-substituted derivatives thereof. Examples of the alkyl group in the alkyl-substituted derivative include lower alkyl groups having 1 to 4 carbon atoms, and in one or more embodiments, examples include methyl and ethyl groups. In one or more embodiments, examples of the amine-substituted derivative include 1-[N,N-bis(hydroxyethylene)aminomethyl]benzotriazole and 1-[N,N-bis(hydroxyethylene)aminomethyl]tolyltriazole.

[0036] When the polishing liquid composition of the present disclosure contains component E, the content of component E in the polishing liquid composition of the present disclosure is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.02% by mass or more, from the viewpoint of further reducing scratches, and is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and even more preferably 0.2% by mass or less, from the viewpoint of further reducing scratches and suppressing a decrease in the polishing rate. More specifically, the content of component E in the polishing liquid composition of the present disclosure is preferably 0.005% by mass or more and 10% by mass or less, more preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.02% by mass or more and 1% by mass or less, even more preferably 0.02% by mass or more and 0.2% by mass or less, from the viewpoint of further reducing scratches and suppressing a decrease in the polishing rate. When component E is a combination of two or more types, the content of component E refers to the total content thereof.

[0037] [Aliphatic amine compound or alicyclic amine compound (component F)] From the viewpoint of further reducing scratches, the polishing liquid composition of the present disclosure may further contain at least one compound selected from an aliphatic amine compound and an alicyclic amine compound (hereinafter also referred to as "component F"). From the viewpoint of further reducing scratches, the number of nitrogen atoms or the total number of amino groups or imino groups in the molecule of component F is preferably 2 or more and 4 or less. Component F may be one type or a combination of two or more types.

[0038] In one or more embodiments, from the viewpoint of further reducing scratches, the aliphatic amine compound is preferably at least one selected from 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-aminoethylisopropanolamine, and N-aminoethyl-N-methylethanolamine, more preferably at least one selected from N-aminoethylethanolamine, N-aminoethylisopropanolamine, and N-aminoethyl-N-methylethanolamine, and even more preferably N-aminoethylethanolamine (AEA).

[0039] In one or more embodiments, from the viewpoint of further reducing scratches, the alicyclic amine compound is preferably at least one selected from piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, 1-amino-4-methylpiperazine, N-methylpiperazine, and hydroxyethylpiperazine (HEP), and more preferably hydroxyethylpiperazine (HEP).

[0040] When the polishing liquid composition of the present disclosure contains component F, the content of component F in the polishing liquid composition of the present disclosure is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.02% by mass or more, from the viewpoint of further reducing scratches, and is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and even more preferably 0.1% by mass or less, from the viewpoint of further reducing scratches and suppressing a decrease in the polishing rate. More specifically, the content of component F in the polishing liquid composition of the present disclosure is preferably 0.005% by mass or more and 10% by mass or less, more preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.02% by mass or more and 1% by mass or less, and even more preferably 0.02% by mass or more and 0.1% by mass or less, from the viewpoint of further reducing scratches and suppressing a decrease in the polishing rate. When component F is a combination of two or more types, the content of component F refers to the total content thereof.

[0041] [Other ingredients] In one or more embodiments, the polishing composition of the present disclosure may further contain other components as needed, such as a polymer compound, a thickener, a dispersant, a rust inhibitor, a basic substance, a surfactant, a solubilizer, etc.

[0042] [pH of polishing composition] From the viewpoints of improving the removal rate and reducing scratches, the pH of the polishing composition of the present disclosure is preferably 5 or less, more preferably 4 or less, even more preferably 3 or less, and even more preferably less than pH 2. From the same viewpoint, the pH is preferably 0.5 or more, more preferably 0.8 or more, and even more preferably 1 or more. From the same viewpoint, the pH of the polishing composition of the present disclosure is preferably 0.5 or more and 5 or less, more preferably 0.8 or more and 4 or less, even more preferably 1 or more and 3 or less, and even more preferably 1 or more and less than 2. The pH can be adjusted using the above-mentioned acid (component B) or a known pH adjuster. In the present disclosure, the pH is the pH of the polishing composition at 25°C, and can be measured using a pH meter. For example, the value can be measured 2 minutes after immersing the electrode of the pH meter in the polishing composition.

[0043] [Method of manufacturing the polishing composition] The polishing liquid composition of the present disclosure can be produced, for example, by blending components A, B, C, D, and an aqueous medium, and, if desired, optional components (components E, F, and other components) using a known method. That is, in another aspect, the present disclosure relates to a method for producing a polishing liquid composition, comprising blending at least components A, B, C, D, and an aqueous medium. In this disclosure, "blending" includes simultaneously or in any order mixing components A, B, C, D, and an aqueous medium, as well as optional components (components E, F, and other components) as needed. Component A may be mixed in the form of a concentrated slurry, or it may be diluted with water or the like before mixing. When component A comprises multiple types of silica particles, the multiple types of silica particles can be blended simultaneously or separately. When component B comprises multiple types of acids, the multiple types of acids can be blended simultaneously or separately. When component C comprises multiple types of oxidizing agents, the multiple types of oxidizing agents can be blended simultaneously or separately. When component D comprises multiple types of quaternary phosphonium salts, the multiple types of quaternary phosphonium salts can be blended together or separately. The blending can be carried out using a mixer such as a homomixer, homogenizer, ultrasonic disperser, or wet ball mill. The preferred blending amounts of each component in the method for producing the polishing composition can be the same as the preferred contents of each component in the polishing composition of the present disclosure described above.

[0044] In the present disclosure, the "content of each component in the polishing composition" refers to the content of each component at the time of use, that is, at the time when the polishing composition is first used for polishing. 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 because it further reduces production and transportation costs. The concentrate of the polishing composition of the present disclosure may be appropriately diluted with the above-mentioned aqueous medium when used, as needed. The dilution ratio is not particularly limited as long as the above-mentioned content (at the time of use) of each component can be ensured after dilution, and may be, for example, 10 to 100 times.

[0045] [Polishing liquid kit] In another aspect, the present disclosure relates to a kit for producing the polishing liquid composition of the present disclosure (hereinafter also referred to as the "polishing liquid kit of the present disclosure"). The polishing liquid kit of the present disclosure may be, for example, a polishing liquid kit (two-component polishing liquid composition) that contains a silica dispersion containing component A and an aqueous medium and an additive aqueous solution containing components B, C, and D in a mutually unmixed state, which are mixed at the time of use and diluted with an aqueous medium as needed. The aqueous medium contained in the silica dispersion may be the entire amount of water used to prepare the polishing liquid composition, or a portion thereof. The additive aqueous solution may contain a portion of the aqueous medium used to prepare the polishing liquid composition. The silica dispersion and the additive aqueous solution may each contain the above-mentioned optional components (component E, component F, and other components) as needed. The polishing liquid kit of the present disclosure can provide a polishing liquid composition that can reduce scratches on the substrate surface after polishing while maintaining a desired polishing rate.

[0046] [Substrate to be polished] In one or more embodiments, the substrate to be polished is a substrate used in the manufacture of a magnetic disk substrate. In one or more embodiments, a magnetic disk substrate can be manufactured by polishing the surface of the substrate to be polished with the polishing composition of the present disclosure, followed by forming a magnetic layer on the substrate surface by sputtering or the like.

[0047] Suitable substrate materials for polishing in the present disclosure include 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. Substrates containing metals such as aluminum, nickel, tungsten, and copper, and alloys containing these metals as their main components, are particularly suitable. Examples of suitable substrates include Ni-P-plated aluminum alloy substrates and glass substrates such as crystallized glass, tempered glass, aluminosilicate glass, and aluminoborosilicate glass, with Ni-P-plated aluminum alloy substrates being even more suitable. In the present 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.

[0048] 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. Of these, a disk-shaped substrate to be polished is suitable. In the case of a disk-shaped substrate to be polished, its outer diameter is, for example, about 2 to 100 mm, and its thickness is, for example, about 0.4 to 2 mm.

[0049] [Method of manufacturing magnetic disk substrate] Generally, magnetic disks are manufactured by polishing a substrate to be polished through a grinding step, a rough polishing step, and a finish polishing step, and then forming the substrate into a magnetic disk in a recording portion forming step. The polishing composition of the present disclosure can be used in a polishing step, preferably a finish polishing step, of polishing a substrate to be polished in a method for manufacturing a magnetic disk substrate. That is, 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") that includes a step of polishing a substrate to be polished using the polishing composition of the present disclosure (hereinafter also referred to as the "polishing step using the polishing composition of the present disclosure"). The substrate manufacturing method of the present disclosure is particularly suitable for manufacturing a magnetic disk substrate for perpendicular magnetic recording.

[0050] In one or more embodiments, the polishing step using the polishing liquid composition of the present disclosure is a step of supplying the polishing liquid composition of the present disclosure to a surface to be polished of a substrate to be polished, bringing a polishing pad into contact with the surface to be polished, and moving at least one of the polishing pad and the substrate to be polished. In another one or more embodiments, the polishing step using the polishing liquid composition of the present disclosure is a step of sandwiching the substrate to be polished between plates to which a polishing pad such as a nonwoven organic polymer-based polishing cloth is attached, and polishing the substrate to be polished by moving the platen and the substrate to be polished while supplying the polishing liquid composition of the present disclosure to a polishing machine.

[0051] When the polishing process of the substrate to be polished is performed in multiple stages, the polishing process using the polishing liquid composition of the present disclosure is preferably performed in the second stage or later, and more preferably in the final polishing process or finish polishing process. In this case, separate polishing machines may be used for each stage to avoid contamination with the abrasive or polishing liquid composition from the previous process, 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. The polishing machine is not particularly limited, and known polishing machines for substrate polishing can be used.

[0052] The polishing pad used in the present disclosure is not particularly limited, and for example, a suede type, a nonwoven fabric type, a polyurethane closed-cell type, or a two-layer type laminated with these can be used, and from the viewpoint of polishing speed, a suede type polishing pad is preferred.

[0053] The polishing load in the polishing step 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 the manufacturing method of the present disclosure, the 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.

[0054] In the polishing step using the polishing composition of the present disclosure, the supply rate of the polishing composition of the present disclosure is set to 1 / cm per 1 cm of the substrate to be polished from the viewpoint of reducing scratches. 2 The flow rate is 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.

[0055] The polishing composition of the present disclosure can be supplied to a polishing machine by, for example, continuous supply using a pump or the like. When supplying the polishing composition to a polishing machine, in addition to a method of supplying it as a single liquid containing all components, it can also be divided into a plurality of blending component liquids and supplied as two or more liquids, taking into consideration the stability of the polishing composition, etc. 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 produce the polishing composition of the present disclosure.

[0056] According to the substrate manufacturing method of the present disclosure, by using the polishing composition of the present disclosure, which can reduce scratches on the substrate surface after polishing while ensuring the polishing rate, it is possible to achieve the effect of manufacturing high-quality magnetic disk substrates with high yield and good productivity.

[0057] [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 includes polishing a substrate to be polished using the polishing composition of the present disclosure. According to the polishing method of the present disclosure, by using the polishing composition of the present disclosure, which can reduce scratches on the substrate surface after polishing while ensuring a polishing rate, high-quality magnetic disk substrates can be produced with high yield and good productivity. As described above, the substrate to be polished in the polishing method of the present disclosure includes those used in the production of magnetic disk substrates, and among these, substrates used in the production of magnetic disk substrates for perpendicular magnetic recording systems are preferred. The polishing method and conditions in the polishing method of the present disclosure can be the same as those in the substrate production method of the present disclosure described above.

[0058] In one or more embodiments, polishing a substrate to be polished with the polishing liquid composition of the present disclosure involves supplying the polishing liquid composition of the present disclosure to the surface to be polished of the substrate to be polished, bringing a polishing pad into contact with the surface to be polished, and moving at least one of the polishing pad and the substrate to be polished to perform polishing; alternatively, sandwiching the substrate to be polished between plates to which a polishing pad such as a nonwoven organic polymer-based polishing cloth is attached, and polishing the substrate to be polished by moving the platen and the substrate to be polished while supplying the polishing liquid composition of the present disclosure to a polishing machine. [Example]

[0059] Hereinafter, the present disclosure will be described in more detail with reference to examples, but these are merely illustrative examples and the present disclosure is not limited to these examples.

[0060] 1. Quaternary phosphonium salts or compounds (component D or non-component D) The quaternary phosphonium salts or compounds (D1 to D9) shown in Table 1 were as follows. D1: Tetrabutylphosphonium chloride [molecular weight: 294.88] D2: Tetraphenylphosphonium chloride [molecular weight: 374.84] D3: Triphenylbenzylphosphonium chloride [molecular weight: 388.87] D4: Tetrabutylphosphonium hydroxide [molecular weight 276.44] D5: Tetrakishydroxymethylphosphonium sulfate [molecular weight: 406.28] D6: Trimorpholinophosphine [molecular weight: 289.316] D7: Trisulfonylphenylphosphine-3,3',3''-trisulfonic acid trisodium salt [molecular weight: 568.41] D8: Triphenylphosphine [Molecular weight: 262.29] D9: Benzotriazole [molecular weight 119.12]

[0061] [Table 1]

[0062] 2. Preparation of Polishing Compositions (Examples 1 to 6, Comparative Examples 1 to 6) The polishing liquid compositions of Examples 1 to 6 and Comparative Examples 1 to 6 shown in Table 1 were prepared by blending and stirring component A (colloidal silica), component B (phosphoric acid), component C (hydrogen peroxide), component D or non-component D (D1 to D9 shown in Table 1), and water. The content (mass %, effective amount) of each component in each polishing liquid composition is as shown in Table 2. The content of water is the remainder excluding component A, component B, component C, and component D or non-component D.

[0063] In preparing each polishing composition, the following components B and C were used. (Component B) Phosphoric acid [Wako Pure Chemical Industries, Ltd., special grade] (Component C) Hydrogen peroxide solution [35% by mass, manufactured by ADEKA]

[0064] 2. Measurement of each parameter [Average secondary particle size of colloidal silica (component A)] A standard sample was prepared by adding component A (colloidal silica) and component B (phosphoric acid) used in preparing the polishing composition to ion-exchanged water and stirring. The contents of components A and B in the standard sample were 1% by mass and 2% by mass, respectively. This standard sample was analyzed using a dynamic light scattering device (DLS-6500, manufactured by Otsuka Electronics Co., Ltd.) according to the manufacturer's instructions. The particle size at which the area of ​​the scattering intensity distribution obtained by the cumulant method at a detection angle of 90° accounted for 50% of the total area after 200 integrations was determined, and this was taken as the average secondary particle size of the colloidal silica. The results are shown in Table 2.

[0065] [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 adopted. The results are shown in Table 2.

[0066] 3. Polishing method The polishing compositions of Examples 1 to 6 and Comparative Examples 1 to 6 prepared as described above were used to polish (finish polish) the following substrates under the polishing conditions shown below. The polishing rate and the number of scratches were then measured. The results are shown in Table 2. In addition, since silica aggregated in Comparative Example 5, polishing using the polishing composition of Comparative Example 5 was not performed.

[0067] [Substrate to be polished] The substrate to be polished was a Ni-P plated aluminum alloy substrate that had been roughly polished with a polishing composition containing an alumina abrasive. The substrate had a thickness of 0.6 mm, an outer diameter of 97 mm, and an inner diameter of 25 mm, and the center line average roughness Ra was 1 nm as measured by an AFM (Digital Instrument NanoScope IIIa Multimode AFM).

[0068] [Polishing conditions (finish polishing conditions)] Polishing tester: Speedfam "Double-sided 9B polishing machine" Polishing pad: Fujibo suede type (foam layer: polyurethane elastomer, thickness 0.9 mm, average pore size 10 μm) Polishing liquid composition supply amount: 100mL / min (substrate to be polished 1cm) 2 Feed rate per: 0.072 mL / min Lower surface plate rotation speed: 25rpm Polishing load: 13.0 kPa Polishing time: 5 minutes Number of boards: 10

[0069] 4. Evaluation [Evaluation of polishing speed] The weight of each substrate was measured before and after polishing using a Sartorius BP-210S, and the mass loss was calculated from the change in mass of each substrate. The average mass loss of all 10 substrates was divided by the polishing time to obtain the polishing rate, which was calculated using the following formula. The polishing rate measurement results are shown in Table 2 as relative values, with Comparative Example 1 set to 100. Mass loss (mg) = {mass before polishing (mg) - mass after polishing (mg)} Polishing speed (mg / min) = mass loss (mg) / polishing time (min)

[0070] [Scratch evaluation] Measuring equipment: KLA-Tencor "Candela OSA7100" Evaluation: Four substrates were randomly selected from the substrates 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 for the number of scratches are shown in Table 2 as relative values, with Comparative Example 1 set to 100.

[0071] [Evaluation of storage stability] The prepared polishing solution was left to stand at room temperature for 60 minutes, and then visually inspected for the presence or absence of precipitates. If sediment was observed at the bottom, it was determined that precipitates were present, and this was marked with "X" in Table 2. If no sediment was observed, it was determined that the storage stability was excellent, and this was marked with "O" in Table 2.

[0072] [Table 2]

[0073] As shown in Table 2 above, the polishing compositions of Examples 1 to 6 were superior in storage stability to the polishing compositions of Comparative Examples 1 to 4 and 6, and reduced scratches while maintaining the polishing rate. [Industrial Applicability]

[0074] According to the present disclosure, for example, a magnetic disk substrate suitable for high recording density can be provided.

Claims

1. A polishing composition for magnetic disk substrates, for polishing a Ni-P plated aluminum alloy substrate, comprising silica particles (component A), an acid (component B), an oxidizing agent (component C), a quaternary phosphonium salt having at least one unsubstituted hydrocarbon group (component D), and an aqueous medium.

2. The polishing composition according to claim 1 , having a pH of 1 or more and 3 or less.

3. 2. The polishing composition according to claim 1, wherein the hydrocarbon group of Component D is an alkyl group, an aryl group, or an aralkyl group.

4. 2. The polishing composition according to claim 1, wherein the total number of carbon atoms in component D is 10 or more.

5. 5. A method for producing a magnetic disk substrate, comprising a polishing step of polishing a Ni-P plated aluminum alloy substrate with the polishing composition according to claim 1.

6. 5. A method for polishing a substrate, comprising polishing a substrate to be polished with the polishing composition according to claim 1, wherein the substrate to be polished is a Ni-P plated aluminum alloy substrate used in the manufacture of magnetic disk substrates.

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