TW202104523A - Method for polishing magnetic disk substrate - Google Patents

Abstract

The present invention provides a polishing process of a magnetic disk substrate, which reduces undulations, shallow pits, and sags on the surface of the substrate after the rough polishing step in the multi-stage polishing method. A polishing method that uses the same polishing machine to perform the following steps (1) to (3): performing a previous stage polishing step with a polishing agent composition A, the polishing agent composition A containing colloidal silica A with an average primary particle diameter of 10 to 150 nm, pulverized wet silica particles with an average particle diameter of 200 to 500 nm, a water-soluble polymer compound and water, wherein the amount of the colloidal silica A in all silica particles is 20 to 80% by mass, the amount of the pulverized wet silica particles in all silica particles is 20 to 80% by mass, and a ratio of the particle diameter of the pulverized wet silica to that of the colloidal silica A is 2.0 to 15.0, and the concentration of all silica particles is 2 to 40% by mass; (2) performing a rinse step; and (3) performing a subsequent polishing step with a polishing agent composition B containing colloidal silica B and water.

Description

Grinding method of magnetic disk substrate

The present invention relates to a method for polishing electronic parts such as magnetic recording media such as semiconductors and hard disks. In particular, it relates to a polishing method for aluminum hard disk substrates, which are widely used as substrates for magnetic recording media. Among them, it relates to a method for polishing a substrate for a magnetic recording medium with a nickel-phosphorus plating film formed on the surface of an aluminum alloy substrate. In particular, it relates to a polishing method that is performed in a polishing step before the final polishing step when polishing a substrate for a magnetic recording medium with a nickel-phosphorus plating film formed on the surface of an aluminum alloy substrate by a multi-step polishing method.

In recent years, magnetic disk drives have been miniaturized and increased in capacity, and higher recording density has been sought. Therefore, it is necessary to improve the detection sensitivity of magnetic signals with high recording density, and technologies to further reduce the flying height of the magnetic head and reduce the unit recording area are being developed. For magnetic disk substrates, in order to cope with the low buoyancy of the magnetic head and ensure the recording area, it is strictly required to improve smoothness and flatness (reduce surface roughness, undulations, and sags) and reduce surface defects (reduce residual abrasive particles, scratches, Protrusions, depressions, etc.).

In response to this requirement, from the viewpoint of both improving surface quality and productivity such as small undulations and small sags, most of the polishing methods for magnetic disk substrates use a multi-stage polishing method with more than two stages of polishing steps (patented Literature 1). Generally speaking, in the final polishing step of the multi-stage polishing method, that is, the finishing polishing step, from the viewpoint of reducing surface roughness, reducing scratches, protrusions, dents and other defects, a combination of abrasives containing silicon dioxide particles is used Things. On the other hand, in the previous grinding step (also called rough grinding step), from the viewpoint of improving productivity It can be seen that abrasive compositions containing alumina particles are mostly used.

However, when polishing aluminum hard disk substrates, compared with aluminum alloy substrates, the hardness of aluminum oxide particles is quite high. Therefore, the undulations increase due to the fixation of the aluminum oxide abrasive grains on the substrate. This situation adversely affects the finish polishing. And become a problem.

As a countermeasure to such problems, some people have disclosed a polishing method that uses an abrasive composition containing colloidal silica in a rough polishing step (Patent Documents 2 to 6). In addition, it has also been proposed to increase the grinding speed by combining colloidal silica and pulverized wet silica particles (Patent Document 7).

In addition, a multi-stage polishing method in which two polishing slurries are sequentially supplied to the same polishing platen has also been proposed to improve the undulation (Patent Document 8).

With the increase in the magnetic recording density of hard disks, the requirements for surface smoothness have become stricter than before, and there is a strong demand for improvement of undulations or shallow pits. Shallow pits are shallower and smaller than conventional pits. In addition to removing the conventional pits, further reduction of shallow pits has become a problem.

[Prior Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 62-208869

[Patent Document 2] JP 2010-167553 A

[Patent Document 3] JP 2011-527643 A

[Patent Document 4] JP 2014-29754 A

[Patent Document 5] JP 2014-29755 A

[Patent Document 6] JP 2012-155785 A

[Patent Document 7] WO2015/146941 Publication

[Patent Document 8] JP 2018-174012 A

With the increase in the capacity of disk drives, the requirements for the surface quality of the substrate have become more stringent. In the polishing step of the disk substrate, it is sought to maintain productivity and further reduce the fluctuations, shallow pits, and pits on the substrate surface. Collapsed.

Therefore, the present invention provides a polishing step of a magnetic disk substrate, which can maintain productivity and reduce the undulations, shallow pits, and edges of the substrate surface after the rough polishing step in the multi-stage polishing method.

In order to solve the above-mentioned problems, according to the present invention, the following method for polishing a magnetic disk substrate can be provided.

[1] A method for polishing a magnetic disk substrate, which has the following steps (1) to (3), and each step (1) to (3) is performed by the same polishing machine:

(1) The abrasive composition A is supplied to the grinder to perform the previous polishing step of the magnetic disk substrate; the abrasive composition A contains colloidal silica A with an average primary particle size of 10 to 150 nm and an average particle size of 200 to 500nm crushed wet silica particles, water-soluble polymer compounds and water. Among all silica particles, the colloidal silica A accounts for 20~80% by mass. The crushed wet silica particles The proportion of silica particles is 20~80% by mass. The ratio of the average particle size of the pulverized wet silica particles to the average primary particle size of the colloidal silica A is 2.0~15.0. The concentration of silicon oxide particles is 2-40% by mass;

(2) A step of subjecting the magnetic disk substrate obtained in step (1) to a rinsing process; and

(3) The polishing composition B containing colloidal silica B and water is supplied to the polishing machine, and the subsequent polishing step of the magnetic disk substrate is performed.

[2] The polishing method of the magnetic disk substrate as described in [1] above, wherein the particle size is 30~70nm The proportion of particles in the colloidal silica A is 10 to 90% by mass.

[3] The method for polishing a magnetic disk substrate as described in [1] above, wherein the water-soluble polymer compound is a copolymer containing a monomer having a carboxylic acid group and a monomer having an amide group as essential monomers, and The weight average molecular weight is 1,000 to 1,000,000.

[4] The method for polishing a magnetic disk substrate as described in [1] above, wherein the water-soluble polymer compound is a copolymer containing a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers, and The weight average molecular weight is 1,000 to 1,000,000.

[5] The method for polishing a magnetic disk substrate as described in [1] above, wherein the water-soluble polymer compound requires a monomer having a carboxylic acid group, a monomer having an amide group, and a monomer having a sulfonic acid group A copolymer of monomers with a weight average molecular weight of 1,000 to 1,000,000.

[6] The method for polishing a magnetic disk substrate according to any one of [3] to [5] above, wherein the single system having a carboxylic acid group is selected from monomers of acrylic acid or its salt, methacrylic acid or its salt .

[7] The method for polishing a magnetic disk substrate as described in [3] or [5], wherein the single system having an amide group is selected from the group consisting of acrylamide, methacrylamide, N-alkylacrylamide, One or more monomers of N-alkylmethacrylamide.

[8] The method for polishing a magnetic disk substrate according to the above [4] or [5], wherein the single system having a sulfonic acid group is selected from isoprene sulfonic acid, 2-propenylamide-2-methylpropane Sulfonic acid, 2-methacrylamide-2-methyl propane sulfonic acid, styrene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, isoamylene sulfonic acid, vinyl naphthalene sulfonic acid and their salts monomer.

[9] The method for polishing a magnetic disk substrate according to any one of [1] to [8] above, wherein the abrasive composition A and the abrasive composition B further contain an acid and/or a salt thereof, and have a pH value (25°C) in the range of 0.1 to 4.0.

[10] The method for polishing a magnetic disk substrate according to any one of [1] to [9] above, wherein the abrasive composition A and the abrasive composition B further contain an oxidizing agent.

[11] The method for polishing a magnetic disk substrate according to any one of [1] to [10] above, wherein the substrate for a magnetic recording medium on which a nickel-phosphorus plating film is formed on the surface of the aluminum alloy substrate is polished in multiple stages When the method is used for polishing, it is performed in the polishing step before the final polishing step.

According to the present invention, the following effects can be obtained: a substrate with reduced undulations, shallow pits, and sags on the substrate surface after the rough polishing step in the multi-stage polishing method can be produced with high productivity.

A, B, C, D: point

j, k, m, t: line

Fig. 1 is a cross-sectional view of a substrate for explaining the measurement of sag when polishing the surface of the substrate.

Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments, and changes, corrections, and improvements can be made without departing from the scope of the invention.

The present invention is a method for polishing a magnetic disk substrate that includes a rough grinding step and a fine grinding step in a multi-stage grinding method. The rough grinding step is carried out in the same grinding machine: using a specific colloidal silica A that has been pulverized The first rough grinding of the abrasive composition A of wet silica particles, water-soluble polymer compounds and water; the rinsing treatment after the first rough grinding; and the abrasive combination containing colloidal silica B and water after the rinsing treatment Subsequent rough grinding of the object B; thereby, the grinding speed can be maintained and the undulations, shallow pits and sags on the substrate surface after the rough grinding step can be reduced. The present invention is based on this knowledge.

The following describes the substrate polishing method of the present invention. The substrate to be polished in the substrate polishing method of the present invention is a magnetic disk substrate, preferably a nickel-phosphorus plated aluminum magnetic disk substrate.

The polishing method of the magnetic disk substrate of the present invention has the following steps (1) to (3), and each step (1) to (3) is performed by the same polishing machine:

(1) The polishing composition A is supplied to the polishing machine, and the first step of polishing the disk substrate is performed Step; The abrasive composition A contains colloidal silica A with an average primary particle size of 10~150nm, pulverized wet silica particles with an average particle size of 200~500nm, water-soluble polymer compounds and water, all of the dioxide Among the silicon particles, the colloidal silica A accounts for 20 to 80% by mass, and the crushed wet silica particles account for 20 to 80% by mass. The crushed wet silica A accounts for 20 to 80% by mass. The ratio of the average particle size of the particles to the average primary particle size of the colloidal silica A is 2.0-15.0, and the concentration of all silica particles is 2-40% by mass;

(2) A step of subjecting the magnetic disk substrate obtained in step (1) to a rinsing process; and

(3) The polishing composition B containing colloidal silica B and water is supplied to the polishing machine, and the subsequent polishing step of the magnetic disk substrate is performed.

For each step, a detailed description is given below.

Step (1): Front grinding

The substrate polishing method of the magnetic disk substrate of the present invention has step (1), which is a rough polishing step in a multi-stage polishing method, which will contain colloidal silica A, pulverized wet silica particles, water-soluble polymer compounds, and The aqueous abrasive composition A is supplied to the polishing target surface of the substrate to be polished, the polishing pad is brought into contact with the polishing target surface, and the polishing pad and/or the substrate to be polished are moved to polish the polishing target surface. The grinder used in step (1) is not particularly limited, and a conventional grinder for polishing magnetic disk substrates can be used.

Step (2): Rinse treatment

From the viewpoint of reducing the undulations on the substrate surface after the rough polishing step in the multi-stage polishing method, the substrate polishing method of the magnetic disk substrate of the present invention has the step (1) after the step (1) is used in the same polishing machine. The obtained substrate is subjected to the intermediate washing step (step (2)) of the washing treatment. The rinsing liquid used for the rinsing treatment is not particularly limited, but from the viewpoint of manufacturing cost, water such as distilled water, ion exchange water, pure water, and ultrapure water can be used. In addition, from the viewpoint of productivity, step (2) does not take out the substrate to be polished from the polishing machine used in step (1), but is performed in the same polishing machine. Specifically, step (2) may include supplying a rinse liquid to the polishing target surface of the substrate to be polished, and moving the substrate to be polished to rinse the polishing target surface. In addition, in the present invention, the rinsing treatment refers to treatment for the purpose of discharging the abrasive grains and polishing debris remaining on the surface of the substrate. It is related to grinding (chemical mechanical polishing) with abrasive grains while dissolving the surface of the substrate. The flattening process is different from the polishing process.

Step (3): After grinding

From the viewpoint of reducing the undulations on the substrate surface after the rough polishing step in the multi-stage polishing method, the substrate polishing method of the present invention has the step (3) of supplying the abrasive composition B containing colloidal silica B and water to the rinse The polishing target surface of the substrate obtained in the processing step (2) is brought into contact with the polishing pad and the polishing target surface, and the polishing pad and/or the substrate to be polished are moved to polish the polishing target surface. From the viewpoint of productivity improvement and the reduction of undulations on the substrate surface after the rough polishing step, steps (1) to (3) are continuously performed in the same polishing machine and polishing pad.

The substrate polishing method of the present invention can be applied as the following method: For a substrate for a magnetic recording medium on which a nickel-phosphorus plating film is formed on the surface of an aluminum alloy substrate, when the substrate is polished in a multi-stage polishing method, it is before the final polishing step. During the grinding step. The substrate polishing method of the present invention is used in the first rough polishing step (1), washing treatment step (2), and subsequent rough polishing step (3) in the above-mentioned multi-stage polishing method. The agent composition contains specific colloidal silica A, pulverized wet silica particles, and water-soluble polymer compounds to efficiently produce shallow pits, undulations and sags on the substrate surface after the rough grinding step. Reduced substrate. Hereinafter, the abrasive composition used in the substrate polishing method of the present invention will be described.

(A) Abrasive composition A

The abrasive composition A used in the step (1) of the substrate polishing method of the present invention is an aqueous composition containing colloidal silica A and pulverized wet silica particles, which contains a water-soluble polymer compound as an essential component . Here, the water-soluble polymer compound is preferably (a) to have a carboxylic acid Copolymers in which monomers with carboxylic acid groups and monomers with amide groups are essential monomers, (b) copolymers in which monomers with carboxylic acid groups and monomers with sulfonic acid groups are essential monomers, (c) A copolymer containing monomers having carboxylic acid groups, monomers having amide groups, and monomers having sulfonic acid groups as essential monomers. In addition, the abrasive composition A may further contain an acid and/or its salt for pH adjustment or as an optional component. In addition, an oxidizing agent may be contained as a polishing accelerator.

(A-1) Colloidal silica A

The colloidal silica A contained in the abrasive composition A of the present invention generally has an average primary particle size of 10 to 150 nm, preferably 20 to 100 nm. By setting the average primary particle size to 10 nm or more, it is possible to suppress a decrease in the polishing rate. By setting the average primary particle size to 150 nm or less, it is possible to suppress deterioration of surface smoothness such as undulations and shallow pits. By making the ratio of 30-70 nm particles to colloidal silica A to be 10 to 90% by volume, and more preferably 12 to 80% by volume, the surface smoothness of undulations or shallow pits can be improved.

It is known that colloidal silica has a spherical shape, a chain shape, a candy type (a granular shape with protrusions on the surface), an irregular shape, and the like, and its primary particles are monodispersed in water to form a colloidal shape. The colloidal silica A used in the present invention is preferably spherical or nearly spherical colloidal silica. By using spherical or nearly spherical colloidal silica, the surface smoothness of shallow pits can be improved.

The colloidal silica A can be obtained by the water glass method, the alkoxysilane method, etc.; the water glass method uses sodium silicate or potassium silicate as the raw material, so that the raw material undergoes condensation reaction in an aqueous solution to grow the particles; the alkoxy In the silane method, alkoxysilanes such as tetraethoxysilane are hydrolyzed under acid or alkali to undergo condensation reaction to grow particles.

(A-2) Wet silica particles

The wet silica particles contained in the abrasive composition A of the present invention refer to the wet silica particles obtained by adding an aqueous alkali silicic acid solution and an inorganic acid or an aqueous inorganic acid solution to the reaction vessel as precipitated silicic acid. Particles made of silica, wet silica particles do not contain the above colloidal oxygen Silica.

The alkali silicate aqueous solution as the raw material of the wet silica includes a sodium silicate aqueous solution, a potassium silicate aqueous solution, a lithium silicate aqueous solution, and the like. In general, it is preferable to use a sodium silicate aqueous solution. Examples of the inorganic acid include sulfuric acid, hydrochloric acid, nitric acid, and the like. Generally, sulfuric acid is preferably used. After the completion of the reaction, the reaction liquid was filtered, washed with water, and then dried with a dryer to reduce the water content to 6% or less. The dryer can be any of a static dryer, a spray dryer, and a fluid dryer. After that, it is pulverized with a pulverizer such as a jet mill, and then classified to obtain wet silica particles. In this way, the wet silica particles pulverized by the pulverization step have corners in the particle shape, and the grinding ability is higher than that of the nearly spherical particles.

The average particle size of the wet silica particles is generally 200 to 500 nm, preferably 250 to 400 nm. By setting the average particle diameter to 200 nm or more, it is possible to suppress a decrease in the polishing rate. By setting the average particle diameter to 500 nm or less, it is possible to suppress deterioration of surface smoothness such as undulations and shallow pits.

The ratio (b/a) of the average particle size (b) of wet silica particles to the average primary particle size (a) of colloidal silica A is 2.0~15.0, preferably 2.5~12.0, more preferably 3.0~ 10.0. By making the ratio of the average particle diameters 2.0 or more, the polishing speed can be increased. By setting the ratio of average particle diameters to 15.0 or less, it is possible to suppress deterioration of surface smoothness such as undulations and shallow pits.

The total concentration of colloidal silica A and wet silica particles is 2-40% by mass of the abrasive composition A, preferably 3-30% by mass. By making the total concentration of silicon dioxide particles 2% by mass or more, it is possible to suppress a decrease in the polishing rate. By making the total concentration of silicon dioxide particles 40% by mass or less, it is not necessary to use excess silicon dioxide particles, and a sufficient polishing rate can be maintained.

The ratio of colloidal silica A to all silica particles is 20 to 80% by mass, preferably 30 to 70% by mass. By setting the ratio of colloidal silica A to 20% by mass or more, deterioration of surface smoothness such as undulations and shallow pits can be suppressed. By setting the ratio of colloidal silica A to 80% by mass or less, it is possible to suppress a decrease in the polishing rate.

The proportion of the wet silica particles to the total silica particles is 20 to 80% by mass, preferably 30 to 70% by mass. By setting the ratio of the wet silica particles to 80% by mass or less, deterioration of surface smoothness can be suppressed. By setting the ratio of the wet silica particles to 20% by mass or more, it is possible to suppress a decrease in the polishing rate.

The abrasive composition A may contain silica particles other than colloidal silica A and wet silica particles. For example, it may contain fumed silica. Smoked silicon dioxide is formed by hydrolyzing volatile silane compounds (usually silicon tetrachloride) in a mixed gas flame of oxygen and hydrogen (around 1000°C), so it is extremely fine and high-purity silicon dioxide particles. Compared with colloidal silica, colloidal silica is dispersed into individual particles and exists as primary particles. In contrast, a large number of primary particles of smoked silica are aggregated and linked into chains to form secondary particles. By forming the secondary particles, the holding force to the polishing pad can be improved, and the polishing speed can be increased.

(A-3) Water-soluble polymer compound

The water-soluble polymer compound contained in the abrasive composition A is preferably any one of the following copolymers: (a) Copolymerization with monomers having carboxylic acid groups and monomers having amide groups as essential monomers (B) Copolymers with monomers with carboxylic acid groups and monomers with sulfonic acid groups as essential monomers; (c) monomers with carboxylic acid groups, monomers with amide groups and The monomer of the sulfonic acid group is an essential monomer.

(A-3-1) Monomers with carboxylic acid groups

As the monomer having a carboxylic acid group, an unsaturated aliphatic carboxylic acid and its salt are preferably used. Specifically, acrylic acid, methacrylic acid, maleic acid, itaconic acid, and these salts can be cited. Examples of the salt include sodium salt, potassium salt, magnesium salt, ammonium salt, amine salt, and alkylammonium salt.

(A-3-2) Monomers with amide groups

As specific examples of the monomer having an amide group, acrylamide, methacrylamide, N-alkyl acrylamide, N-alkyl methacrylamide, and the like can be used. Specific examples of N-alkylacrylamide and N-alkylmethacrylamide include N-methacrylamide, N-ethacrylamide, N- N-Propyl acrylamide, N-isopropyl acrylamide, N-n-butyl acrylamide, N-isobutyl acrylamide, N-second butyl acrylamide, N-tertiary butyl Acrylic amide, N-methyl methacrylamide, N-ethyl methacrylamide, N-n-propyl methacrylamide, N-isopropyl methacrylamide, N-n-butyl methyl Methacrylamide, N-isobutyl methacrylamide, N-secondary butyl methacrylamide, N-tertiary butyl methacrylamide, etc.

(A-3-3) Monomer with sulfonic acid group

Specific examples of the monomer having a sulfonic acid group include: isoprene sulfonic acid, 2-propenamide-2-methylpropanesulfonic acid, 2-methacrylamide-2-methylpropanesulfonate Acid, styrene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, isoamylene sulfonic acid, naphthalene sulfonic acid and their salts, etc. Preferable examples include 2-acrylamide-2-methylpropanesulfonic acid, 2-methacrylamide-2-methylpropanesulfonic acid, and their salts.

(A-3-4) Copolymer

The water-soluble polymer compound contained in the abrasive composition A is preferably a copolymer. When the water-soluble polymer compound is (a) a copolymer containing a monomer having a carboxylic acid group and a monomer having an amide group as essential monomers, the ratio of the constituent units derived from the monomer having a carboxylic acid group is preferable It is 50~95mol%, more preferably 60~93mol%. The ratio of the constituent unit derived from the monomer having an amide group is preferably 5 to 50 mol%, and more preferably 7 to 40 mol%. When it is (b) a copolymer containing a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers, the ratio of the constituent unit derived from the monomer having a carboxylic acid group is preferably 30 to 95 mol %, more preferably 40~90mol%. The ratio of the monomer having a sulfonic acid group is preferably 5 to 70 mol%, more preferably 10 to 60 mol%. When (c) a copolymer containing a monomer having a carboxylic acid group, a monomer having an amide group, and a monomer having a sulfonic acid group as essential monomers, a structural unit derived from a monomer having a carboxylic acid group The ratio is preferably 50 to 95 mol%, more preferably 60 to 93 mol%, and even more preferably 70 to 90 mol%. The ratio of the constituent unit derived from the monomer having an amide group is preferably 1-40 mol%, more preferably 3-30 mol%, and still more preferably 5-20 mol%. The ratio of the constituent unit derived from the monomer having a sulfonic acid group is preferably 0.01-20 mol%, more preferably 0.1-10 mol%, and still more preferably 0.2-5 mol%.

(A-3-5) Manufacturing method of water-soluble polymer compound

The method for producing the water-soluble polymer compound is not particularly limited, but an aqueous solution polymerization method is preferred. According to the aqueous solution polymerization method, a water-soluble polymer compound that forms a uniform solution can be obtained. As the polymerization solvent for the above-mentioned aqueous solution polymerization, an aqueous solvent is preferred, and water is particularly preferred. In addition, in order to improve the solubility of the above-mentioned monomer components in the solvent, an organic solvent may be appropriately added during the polymerization of each monomer within a range that does not cause adverse effects. As said organic solvent, alcohols, such as isopropanol, and ketones, such as acetone, are mentioned. These can be used individually by 1 type or in combination of 2 or more types.

Hereinafter, the production method of the water-soluble polymer compound using the above-mentioned aqueous solvent will be explained. A conventional polymerization initiator can be used for the polymerization reaction, but it is particularly preferable to use a radical polymerization initiator. Examples of radical polymerization initiators include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate, hydroperoxides such as tertiary butyl hydroperoxide, and water-soluble solutions such as hydrogen peroxide. Peroxides, ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide, dialkyl peroxides such as di(tertiary butyl) peroxide and tertiary butyl cumyl peroxide Azo compounds such as oil-soluble peroxides such as azobisisobutyronitrile, and 2,2-azobis(2-methylpropionamidine) dihydroxide. These peroxide-based radical polymerization initiators can be used alone or in combination of two or more. Among the above-mentioned peroxide-based radical polymerization initiators, from the viewpoint of easy control of the molecular weight of the produced water-soluble polymer compound, a persulfate or an azo compound is preferred, and azobisisobutyl is particularly preferred. Nitrile.

The amount of the radical polymerization initiator used is not particularly limited, and it is preferably used in a ratio of 0.1 to 15% by mass, particularly 0.5 to 10% by mass, based on the total mass of all monomers of the water-soluble polymer compound. By setting the ratio to 0.1% by mass or more, the copolymerization rate can be increased, and by setting it to 15% by mass or less, the stability of the water-soluble polymer compound can be improved.

In addition, depending on the situation, the water-soluble polymer compound may also be produced using a water-soluble redox-based polymerization initiator. Examples of redox polymerization initiators include oxidizing agents (such as the above-mentioned peroxides) and sodium bisulfite, ammonium bisulfite, ammonium sulfite, and sodium hyposulfite (sodium sulfite). Hydrosulfite) and other reducing agents or combinations of iron alum and potassium alum.

In the production of a water-soluble polymer compound, a chain transfer agent may be appropriately added to the polymerization system to adjust the molecular weight. Examples of chain transfer agents include sodium phosphite, sodium hypophosphite, potassium hypophosphite, sodium sulfite, sodium bisulfite, thioacetic acid, mercaptopropionic acid, thioglycolic acid, 2-propanethiol, 2-mercaptoethanol, and Thiophenol and so on.

The polymerization temperature in the production of the water-soluble polymer compound is not particularly limited, but the polymerization temperature is preferably 60 to 100°C. By setting the polymerization temperature to 60°C or higher, the polymerization reaction progresses smoothly and the productivity is excellent, and by making it 100°C or lower, coloring can be suppressed.

In addition, the polymerization reaction may be carried out under pressure or reduced pressure, but the installation of equipment for the pressure or reduced pressure reaction requires cost, so it is preferably carried out under normal pressure. The polymerization time is preferably 2 to 20 hours, especially 3 to 10 hours.

After the polymerization reaction, it is neutralized with a basic compound as required. Examples of basic compounds used for neutralization include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide, ammonia water, monoethanolamine, and two Organic amines such as ethanolamine and triethanolamine.

(A-3-6) Weight average molecular weight

The weight average molecular weight of the water-soluble polymer compound is 1,000 to 1,000,000, preferably 2,000 to 800,000, and more preferably 3,000 to 600,000. In addition, the weight average molecular weight of the water-soluble polymer compound is measured by gel permeation chromatography (GPC) in terms of polyacrylic acid. When the weight average molecular weight of the water-soluble polymer compound is less than 1,000, the undulation after polishing becomes worse. Moreover, when it exceeds 1,000,000, the viscosity of the aqueous solution becomes high and it becomes difficult to handle.

(A-3-7) Concentration

The concentration of the water-soluble polymer compound in the abrasive composition A is 0.0001 to 3.0% by mass in terms of solid content, preferably 0.0005 to 2.0% by mass, and more preferably 0.001 to 1.0% by mass. When the concentration of the water-soluble polymer compound is less than 0.0001% by mass, the effect of adding the water-soluble polymer compound cannot be sufficiently obtained. When the concentration of the water-soluble polymer compound is more than 3.0% by mass, the effect of adding the water-soluble polymer compound tends to be flat. It is not economical to add excess water-soluble polymer compounds.

(A-4) Acid and/or its salt

In the abrasive composition A, an acid and/or its salt can be used for pH adjustment or as an optional component. Examples of the acid and/or its salt used include inorganic acid and/or its salt and organic acid and/or its salt.

Examples of inorganic acids and/or salts thereof include inorganic acids and/or salts thereof such as nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, phosphonic acid, pyrrolidinic acid, and tripolyphosphoric acid.

Examples of organic acids and/or their salts include amino carboxylic acids such as glutamic acid and aspartic acid and/or their salts, citric acid, tartaric acid, oxalic acid, nitroacetic acid, maleic acid, malic acid, and amber Carboxylic acid such as acid and/or its salt, organic phosphonic acid and/or its salt. One kind or two or more kinds of these acids and/or their salts can be used.

Examples of the organic phosphonic acid and/or its salt include those selected from 2-aminoethylphosphonic acid, 1-hydroxyethylene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethyl Diamine tetra (methylene phosphonic acid), diethylene triamine penta (methylene phosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethyl Alkyl-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methane hydroxyphosphonic acid, 2-phosphonobutane-1,2 -At least one compound of dicarboxylic acid, 1-phosphoranylbutane-2,3,4-tricarboxylic acid, α-methylphosphoranylsuccinic acid and its salts.

Combining two or more of the above-mentioned compounds is also a preferred embodiment. Specifically, examples include: a combination of sulfuric acid and/or its salt and organophosphonic acid and/or its salt, phosphoric acid and/or its salt and organophosphine Combinations of acids and/or their salts, etc.

(A-5) Oxidizing agent

The abrasive composition A may contain an oxidizing agent as a polishing accelerator. As an oxidant, it can be used Peroxide, permanganic acid or its salt, chromic acid or its salt, peroxy acid or its salt, halogen oxyacid or its salt, oxo acid or its salt, a mixture of two or more of these oxidants, etc. .

Specifically, examples include: hydrogen peroxide, sodium peroxide, barium peroxide, potassium peroxide, potassium permanganate, metal salts of chromic acid, metal salts of dichromic acid, persulfuric acid, sodium persulfate, persulfuric acid Potassium, ammonium persulfate, peroxyphosphoric acid, sodium peroxyborate, performic acid, peracetic acid, hypochlorous acid, sodium hypochlorite, calcium hypochlorite, etc. Among them, hydrogen peroxide, persulfuric acid and its salts, hypochlorous acid and its salts, etc. are preferred, and hydrogen peroxide is more preferred.

The content of the oxidizing agent in the abrasive composition A is preferably 0.01 to 10.0% by mass. More preferably, it is 0.1 to 5.0% by mass.

(A-6) Physical properties (pH) of abrasive composition A

The pH value (25°C) of the abrasive composition A is preferably in the range of 0.1 to 4.0. More preferably, it is 0.5 to 3.0. By making the pH value (25°C) of the polishing agent composition A 0.1 or more, surface roughness can be suppressed. By making the pH value (25°C) of the polishing agent composition A 4.0 or less, it is possible to suppress a decrease in the polishing rate.

(B) Abrasive composition B

The abrasive composition B used in the step (3) of the substrate polishing method of the present invention is an aqueous composition containing colloidal silica B, which contains a water-soluble polymer compound as an optional component. Furthermore, acid and/or its salt, oxidizing agent, etc. may also be contained.

(B-1) Colloidal silica B

The colloidal silica B contained in the abrasive composition B preferably has an average particle size (D50) of 10 to 150 nm. More preferably, it is 20 to 100 nm. Colloidal silica can be obtained by the water glass method: using alkali metal silicates such as sodium silicate and potassium silicate as raw materials, the raw materials undergo condensation reaction in an aqueous solution to grow particles. Or it can also be obtained by the alkoxysilane method: using alkoxysilane such as tetraethoxysilane as a raw material, the raw material is subjected to condensation reaction by hydrolysis of an acid or alkali in water containing a water-soluble organic solvent such as alcohol. Make the particles grow.

It is known that colloidal silica has a spherical shape, a chain shape, a candy shape, an irregular shape, etc., and its primary particles are monodispersed in water to form a colloidal shape. The colloidal silica B contained in the abrasive composition B is particularly preferably spherical or nearly spherical colloidal silica.

The concentration of colloidal silica B in the abrasive composition B is preferably 0.1 to 20% by mass. More preferably, it is 0.2 to 10% by mass.

(B-2) Water-soluble polymer compound

The abrasive composition B may contain a water-soluble polymer compound as an optional component. The water-soluble polymer compound contained in the abrasive composition B is preferably a mixture of a polymer containing a monomer having a carboxylic acid group as an essential monomer and a polymer containing a monomer having a sulfonic acid group as an essential monomer And/or a copolymer containing a monomer having a carboxylic acid group and a monomer having a sulfonic acid group as essential monomers. As a specific example of each monomer, the same compound as the case of the abrasive composition A can be mentioned.

(B-2-1) Monomers with carboxylic acid groups

As the monomer having a carboxylic acid group, an unsaturated aliphatic carboxylic acid and its salt are preferably used. Specifically, acrylic acid, methacrylic acid, maleic acid, itaconic acid, and these salts can be cited. Examples of the salt include sodium salt, potassium salt, magnesium salt, ammonium salt, amine salt, and alkylammonium salt.

(B-2-2) Monomers with sulfonic acid groups

Specific examples of the monomer having a sulfonic acid group include: isoprene sulfonic acid, 2-propenamide-2-methylpropanesulfonic acid, 2-methacrylamide-2-methylpropanesulfonate Acid, styrene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, isoamylene sulfonic acid, vinyl naphthalene sulfonic acid and their salts, etc.

(B-2-3) Monomers with amide groups

As other monomers, monomers having an amide group can also be used. Specifically, acrylamide, methacrylamide, N-alkyl acrylamide, N-alkyl methacrylamide, etc. are mentioned.

(B-2-4) Proportion of constituent units

Among the water-soluble polymer compounds, the ratio of constituent units derived from monomers with carboxylic acid groups is relatively It is preferably 5 to 95 mol%, more preferably 8 to 92 mol%, and still more preferably 10 to 90 mol%. The ratio of the constituent unit derived from the monomer having a sulfonic acid group is preferably 5 to 95 mol%, more preferably 8 to 92 mol%, and still more preferably 10 to 90 mol%. In the case of a polymer mixture, the above-mentioned ratio indicates a preferable range of the ratio of the constituent unit derived from the monomer having a carboxylic acid group and the ratio of the constituent unit derived from the monomer having a sulfonic acid group based on the entire mixture. .

(B-2-5) Manufacturing method of water-soluble polymer compound

As in the case of the abrasive composition A, the method for producing the water-soluble polymer compound is preferably an aqueous solution polymerization method. According to the aqueous solution polymerization method, a water-soluble polymer compound that forms a uniform solution can be obtained. Specifically, a method of producing a water-soluble polymer compound by radical polymerization using a radical polymerization initiator using an aqueous solvent can be cited. As a radical polymerization initiator, persulfate, water-soluble peroxide, oil-soluble peroxide, azo compound, etc. are mentioned. In addition, as the initiator, a water-soluble redox-based polymerization initiator may also be used. A chain transfer agent can also be appropriately added to the polymerization system to adjust the molecular weight of the water-soluble polymer compound. After the polymerization reaction is over, it can be neutralized with a basic compound if necessary.

(B-2-6) Weight average molecular weight

The weight average molecular weight of the water-soluble polymer compound is 1,000 to 1,000,000, preferably 2,000 to 800,000, and more preferably 3,000 to 600,000. In addition, the weight average molecular weight of the water-soluble polymer compound is measured by gel permeation chromatography (GPC) in terms of polyacrylic acid. When the water-soluble polymer compound is a mixture of polymers, the above-mentioned range of the weight average molecular weight is a preferable range of the weight average molecular weight of the entire mixture.

(B-2-7) Concentration

The concentration of the water-soluble polymer compound in the abrasive composition B is 0.0001 to 3.0% by mass in terms of solid content, preferably 0.0005 to 2.0% by mass, and more preferably 0.001 to 1.0% by mass.

(B-3) Acid and/or its salt

The abrasive composition B can use an acid and/or its salt for pH adjustment or as an optional component. Examples of the acid and/or its salt used include inorganic acid and/or its salt and organic acid and/or its salt.

Examples of inorganic acids and/or salts thereof include inorganic acids and/or salts thereof such as nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, phosphonic acid, pyrrolidinic acid, and tripolyphosphoric acid.

Examples of organic acids and/or their salts include amino carboxylic acids such as glutamic acid and aspartic acid and/or their salts, citric acid, tartaric acid, oxalic acid, nitroacetic acid, maleic acid, malic acid, and amber Carboxylic acid such as acid and/or its salt, organic phosphonic acid and/or its salt. One kind or two or more kinds of these acids and/or their salts can be used.

Examples of the organic phosphonic acid and/or its salt include those selected from 2-aminoethylphosphonic acid, 1-hydroxyethylene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethyl Diamine tetra (methylene phosphonic acid), diethylene triamine penta (methylene phosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethyl Alkyl-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methane hydroxyphosphonic acid, 2-phosphonobutane-1,2 -At least one compound of dicarboxylic acid, 1-phosphoranylbutane-2,3,4-tricarboxylic acid, α-methylphosphoranylsuccinic acid and its salts.

Combining two or more of the above-mentioned compounds is also a preferred embodiment. Specifically, examples include: a combination of sulfuric acid and/or its salt and organophosphonic acid and/or its salt, phosphoric acid and/or its salt and organophosphine Combinations of acids and/or their salts, etc.

(B-4) Oxidizing agent

The abrasive composition B may contain an oxidizing agent as an optional component. As the oxidizing agent that may be contained in the abrasive composition B, peroxide, permanganic acid or its salt, chromic acid or its salt, peroxy acid or its salt, halogen oxyacid or its salt, oxyacid or its salt can be used. Salt, a mixture of two or more of these oxidizing agents, etc.

Specifically, examples include: hydrogen peroxide, sodium peroxide, barium peroxide, potassium peroxide, potassium permanganate, metal salts of chromic acid, metal salts of dichromic acid, persulfuric acid, sodium persulfate, Potassium persulfate, ammonium persulfate, peroxyphosphoric acid, sodium peroxyborate, performic acid, peracetic acid, hypochlorous acid, sodium hypochlorite, calcium hypochlorite, etc. Among them, hydrogen peroxide, persulfuric acid and its salts, hypochlorous acid and its salts, etc. are preferred, and hydrogen peroxide is more preferred.

The content of the oxidizing agent in the abrasive composition B is preferably 0.01 to 10.0% by mass, and more preferably 0.05 to 5.0% by mass.

(B-5) Physical properties (pH) of abrasive composition B

The pH value (25°C) of the abrasive composition B is preferably in the range of 0.1 to 4.0. More preferably, it is 0.5 to 3.0. By making the pH value (25°C) of the polishing agent composition B 0.1 or more, surface roughness can be suppressed. By making the pH value (25°C) of the polishing agent composition B 4.0 or less, it is possible to suppress a decrease in the polishing rate.

[Examples]

Hereinafter, the present invention will be described in detail based on embodiments, but the present invention is not limited to these embodiments. As long as it falls within the technical scope of the present invention, it can be implemented in various ways, and it goes without saying.

[Preparation method of abrasive composition]

The abrasive compositions used in Examples 1 to 7 and Comparative Examples 1 to 9 were abrasive compositions containing the materials described in Table 1 at the contents described in Table 1 in the first stage polishing. In the post-polishing, the abrasive composition containing the material described in Table 2 at the content described in Table 2 was used. In addition, in Table 1, the abbreviation for acrylic acid is AA, the abbreviation for N-tertiary butylacrylamide is TBAA, and the abbreviation for 2-propenamide-2-methylpropanesulfonic acid is ATBS. In addition, the results of the polishing test of each example and each comparative example are shown in Table 3.

Table 1

Table 2

[Average particle size of wet silica particles]

The average particle size of the wet silica particles was measured using a dynamic light scattering particle size analyzer (manufactured by Nikkiso Co., Ltd., MicrotracUPA). The average particle size of the wet silica particles is based on the volume, and the cumulative particle size distribution from the small particle size side becomes the average particle size (D50) of 50%.

[Particle size of colloidal silica]

The particle size (Heywood diameter) of colloidal silica is using a transmission electron microscope (TEM) (manufactured by JEOL Co., Ltd., a transmission electron microscope JEM2000FX (200kV) with a magnification of 100,000 times the field of view, and use Analysis software (manufactured by Mountech Co., Ltd., Mac-View Ver.4.0) analyzes the image to measure the Haywood diameter (equivalent circle diameter of the projected area). The average particle size of colloidal silica is analyzed in the above method The particle size of about 2000 colloidal silica particles is calculated by using the above analysis software (manufactured by Mountech Co., Ltd., Mac-View Ver.4.0) to calculate the cumulative particle size distribution from the small particle size side (cumulative The volume basis) is the average particle diameter (D50) calculated from the 50% particle diameter.

[Weight average molecular weight]

The weight average molecular weight of the water-soluble polymer compound is measured by gel permeation chromatography (GPC) in terms of polyacrylic acid. The GPC measurement conditions are shown below.

[GPC conditions]

Column: G4000PWXL (manufactured by Tosoh Corporation) + G2500PWXL (Tosoh Corporation)

Eluent: 0.2M phosphate buffer/acetonitrile=9/1 (volume ratio)

Flow rate: 1.0ml/min

Temperature: 40℃

Detection: 210nm (UV)

Sample: concentration 5mg/ml (injection volume 100μl)

Polymer for calibration curve: polyacrylic acid molecular weight (peak top molecular weight: Mp) 115,000, 28,000, 4100, 1250 (Chuanghe Science Co., Ltd., American Polymer Standards Corp.)

[Grinding conditions]

An electroless nickel-phosphorus-plated aluminum disk with an outer diameter of 95 mm was used as the polishing object, and the polishing was performed under the following polishing conditions.

[Preliminary grinding conditions]

Grinding machine: manufactured by SpeedFam Company Limited, 9B double-sided grinding machine

Polishing pad: manufactured by FILWEL CO., LTD., P1 gasket

Number of rotations of the pressing plate: Upper pressing plate -7.7rpm

Lower plate 23.5rpm

Abrasive composition supply amount: 90ml/min

Grinding time: Grinding time until the grinding amount is 1.2~1.5μm/single side (240~720 seconds).

Processing pressure: 120g/cm ²

In addition, the abrasive composition A was used in the first-stage polishing.

[Flushing conditions]

Grinding machine: the same as the previous grinding

Grinding pad: the same as the previous grinding

The number of rotations of the platen: the same as the previous grinding

Rinsing fluid supply: 3 liters/min

Rinse time: 20 seconds

Processing pressure: 120g/cm ²

In addition, pure water is used for the rinsing liquid.

[Post grinding conditions]

Grinding machine: the same as the previous grinding

Grinding pad: the same as the previous grinding

The number of rotations of the platen: the same as the previous grinding

Abrasive composition supply amount: 90ml/min

Grinding time: 40 seconds

Processing pressure: 120g/cm ²

In addition, the abrasive composition B was used in the subsequent polishing. The results of the polishing test under the above-mentioned polishing conditions are shown in Table 3. However, in Comparative Examples 7-9, the post-polishing was not performed.

[Grinding speed ratio]

The grinding speed ratio is measured by measuring the weight of the aluminum dish after grinding, and then calculated according to the following formula.

Grinding speed (μm/min) = reduction in mass of aluminum disc (g) / grinding time (min) / area of one side of aluminum disc (cm ² ) / density of electroless nickel-phosphorus coating film (g/cm ³ ) /2×10 ⁴

(In the above formula, the area of one side of the aluminum dish is 65.9cm ² , and the density of the electroless nickel-phosphorus coating film is 8.0g/cm ³ )

The polishing rate ratio is a relative value when the polishing rate of Comparative Example 2 obtained using the above formula is set to 1 (reference).

[ups and downs]

The undulation of the aluminum dish was measured using a three-dimensional surface structure analysis microscope using scanning white light interferometry manufactured by AMETEK, Inc.. The measuring conditions are the measuring device made by AMETEK, Inc. (New View 8300 (lens: 1.4 times, zoom: 1.0 times)), wavelength 100~500μm and 500~1000μm, measurement area is 6mm×6mm, analysis software (Mx) made by AMETEK, Inc. is used for analysis.

[Shallow pit]

The shallow pits were measured using a three-dimensional surface structure analysis microscope (New View 8300) using scanning white light interferometry manufactured by AMETEK, Inc..

The measurement conditions are as follows.

Lens 1.4 times

ZOOM 0.5 times

1 Measuring area of field of view 12mm×12mm

Measurement Type Surface

Measurement Mode CSI

Scan Length 5μm

Set a square that covers the entire aluminum dish with a side length of 95mm, divide it into 100 sections, and scan the entire surface of the aluminum dish with a diameter of 95mm. At this time, each scan data is set to overlap by 20%. Splice the obtained scan data and observe the entire surface of the aluminum disc. When observing each partition, zoom in with the mouse to confirm whether there are shallow pits. As a result of observing the entire surface of the aluminum dish, the case where almost no shallow pits were found was evaluated as "○ (good)". The case where a few shallow pits were found was evaluated as "△ (possible)". The case where a large number of shallow pits were found was evaluated as "× (bad)".

[Sagside Ratio]

As an evaluation of the shape of the end face, the sag that quantified the degree of end face collapse was measured. The sag is measured using a measuring device made by AMETEK, Inc. (New View 8300 (lens: 1.4 times, zoom: 1.0 times)) and analysis software (Metro Pro) made by AMETEK, Inc..

The method of measuring the sag is explained using FIG. 1. Figure 1 shows the object to be polished, that is, an aluminum disc with an outer diameter of 95mm that is electroless nickel-phosphorus plated, passing through the center of the disc and facing A cross-sectional view perpendicular to the ground surface. When measuring the sag, firstly set a vertical line h along the outer peripheral end of the disc, and set a line j parallel to the vertical line h and a distance of 3.90 mm from the vertical line h from the vertical line h toward the center of the disc on the ground surface. The intersection of the line of the disc profile and the line j is regarded as the point A. In addition, a line k parallel to the vertical line h and a distance from the vertical line h of 0.30 mm is provided, and the intersection of the line of the disc cross section and the line k is set as a point B. A line m connecting point A and point B is set, and a line t perpendicular to line m is set. The intersection of the line of the disc profile and line t is regarded as point C, and the intersection of line m and line t is regarded as point D. Then, the distance when the distance between the measurement points C-D reaches the maximum is regarded as the sag.

The sag ratio is a relative value when the sag of Comparative Example 2 measured by the above method is set to 1 (reference).

table 3

[the study]

From the comparison of Examples 1, 2, and 3 with Comparative Example 1, the comparison between Example 4 and Comparative Example 2, and the comparison between Example 7 and Comparative Example 3, it can be seen that by containing the water-soluble polymer compound, the polishing speed is increased and the polishing rate is reduced. The edges have also improved. In addition, Example 2 and Example 3 were obtained by changing the composition of the water-soluble polymer compound of Example 1. Example 4 is obtained by changing the ratio of particles with a particle size of 30 to 70 nm in the colloidal silica A of Example 1. Example 7 is obtained by changing the average particle size of colloidal silica A of Example 1 and the average particle size of wet silica particles.

From the comparison between Example 1 and Comparative Example 5, it can be seen that by making the proportion of wet silica particles 20% by mass or more, the polishing speed is increased, and the sag is also improved. From the comparison between Example 1 and Comparative Example 6, it can be seen that by setting the ratio of colloidal silica A to 20% by mass or more, the shallow pits are significantly reduced and the undulations are also improved. From the comparison between Example 7 and Comparative Example 4, it can be seen that by making the average particle size of the wet silica particles 500 nm or less, the shallow pits are reduced and the undulation is significantly improved. From the comparison between Example 1 and Comparative Example 7, the comparison between Example 2 and Comparative Example 8, and the comparison between Example 3 and Comparative Example 9, it can be seen that the undulation is improved by performing the post-polishing. It can be clearly seen from the above that by using the abrasive composition of the present application and polishing by the polishing method of the present application, the balance of polishing speed, undulations, shallow pits, and sags is improved.

Compared with Example 4, Examples 1, 5, and 6 have a higher proportion of particles with a particle size of 30~70nm in colloidal silica A. This is different. As a result, the grinding speed is further improved, and there are also fluctuations and shallow pits. Improved. In addition, in Example 5 and Example 6, the ratio of particles with a particle size of 30 to 70 nm in the colloidal silica A of Example 1 becomes higher.

[Industrial availability]

The substrate polishing method of the present invention can be used for polishing electronic parts such as magnetic recording media such as semiconductors and hard disks. Especially suitable for magnetic recording media such as glass disk substrate or aluminum disk substrate The surface of the body substrate is polished. Furthermore, it can be used for surface polishing of an aluminum magnetic disk substrate for a magnetic recording medium on which an electroless nickel-phosphorus plating film is formed on the surface of an aluminum alloy substrate.

A, B, C, D: point

j, k, m, t: line

Claims (11)

A method for polishing a magnetic disk substrate, which has the following steps (1) to (3), and each step (1) to (3) is performed by the same polishing machine; (1) The abrasive composition A is supplied to the grinder to perform the previous polishing step of the magnetic disk substrate; the abrasive composition A contains colloidal silica A with an average primary particle size of 10 to 150 nm and an average particle size of 200 to 500nm crushed wet silica particles, water-soluble polymer compounds and water. Among all silica particles, the colloidal silica A accounts for 20~80% by mass. The crushed wet silica particles The proportion of silica particles is 20~80% by mass. The ratio of the average particle size of the pulverized wet silica particles to the average primary particle size of the colloidal silica A is 2.0~15.0. The concentration of silicon oxide particles is 2-40% by mass; (2) A step of subjecting the magnetic disk substrate obtained in step (1) to a rinsing process; and (3) The polishing composition B containing colloidal silica B and water is supplied to the polishing machine, and the subsequent polishing step of the magnetic disk substrate is performed. For example, in the grinding method of the magnetic disk substrate of claim 1, the proportion of particles with a diameter of 30 to 70 nm in the colloidal silica A is 10 to 90% by mass. The polishing method for a magnetic disk substrate of claim 1, wherein the water-soluble polymer compound is a copolymer in which a monomer having a carboxylic acid group and a monomer having an amide group are necessary monomers, and its weight average molecular weight is 1,000~1,000,000. The method for polishing a magnetic disk substrate of claim 1, wherein the water-soluble polymer compound is a copolymer in which a monomer having a carboxylic acid group and a monomer having a sulfonic acid group are the necessary monomers, and the weight average molecular weight is 1,000~1,000,000. The method for polishing a magnetic disk substrate of claim 1, wherein the water-soluble polymer compound is a copolymerization of a monomer having a carboxylic acid group, a monomer having an amide group, and a monomer having a sulfonic acid group as essential monomers And its weight average molecular weight is 1,000 to 1,000,000. The polishing method for a magnetic disk substrate according to any one of claims 3 to 5, wherein the single system having a carboxylic acid group is selected from monomers of acrylic acid or its salt, methacrylic acid or its salt. According to claim 3 or 5, the method for polishing a magnetic disk substrate, wherein the single system having an amide group is selected from the group consisting of acrylamide, methacrylamide, N-alkylacrylamide, and N-alkylmethyl One or more monomers of acrylamide. According to claim 4 or 5, the polishing method of a magnetic disk substrate, wherein the single system having a sulfonic acid group is selected from the group consisting of isoprene sulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid, and 2-methylpropanesulfonic acid. Monoacrylamide-2-methyl propane sulfonic acid, styrene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, isopentenyl sulfonic acid, vinyl naphthalene sulfonic acid and their salts. According to the method for polishing a magnetic disk substrate according to any one of claims 1 to 8, wherein the abrasive composition A and the abrasive composition B further contain an acid and/or its salt, and the pH value (25° C.) is 0.1 ~4.0 range. According to the method for polishing a magnetic disk substrate according to any one of claims 1 to 9, wherein the abrasive composition A and the abrasive composition B further contain an oxidizing agent. The method for polishing a magnetic disk substrate according to any one of claims 1 to 10, wherein the substrate for a magnetic recording medium on which a nickel-phosphorus plating film is formed on the surface of the aluminum alloy substrate is polished by a multi-stage polishing method. It is carried out in the grinding step before the final grinding step.

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