JP5571915B2 - Polishing liquid composition for magnetic disk substrate - Google Patents

Description

  The present invention relates to a polishing composition for a magnetic disk substrate and a method for producing a magnetic disk substrate using the same.

  In recent years, magnetic disk drives have been reduced in size and capacity, and high recording density has been demanded. In order to increase the recording density, the unit recording area is reduced, and in order to improve the detection sensitivity of the weakened magnetic signal, technological development for lowering the flying height of the magnetic head has been advanced. Magnetic disk substrates have improved smoothness and flatness (reduced surface roughness, waviness, and edge sagging) and reduced defects (scratches, protrusions, pits) in order to reduce the flying height of the magnetic head and secure a recording area. Etc.) is becoming stricter. In response to such a demand, a polishing liquid composition containing a copolymer having a functional group such as a carboxyl group or a sulfonic acid group has been proposed (see, for example, Patent Documents 1 to 3).

  Patent Document 1 is a polishing liquid composition suitable for chemical mechanical polishing (CMP) of a semiconductor component, and includes a polymer having a sulfonic acid group to flatten the surface of an object to be polished and polishing rate. Disclosed is a polishing composition capable of increasing the thickness

  Patent Document 2 discloses a polishing composition for semiconductor parts suitable for chemical mechanical polishing (CMP), which is a polymer having a carboxylic acid group, a polymer having a sulfonic acid group, and a polymer having a phosphonic acid group. Disclosed is a polishing liquid composition that can contain at least two polymers among them to reduce the surface roughness of the object to be polished and increase the polishing rate.

  Patent Document 3 is a composition for polishing a Ni metal-containing substrate, which is a copolymer resin particle having a functional group capable of coordinating to a metal ion such as a sulfonic acid group in place of inorganic abrasive grains such as alumina and silica. Disclosed is a polishing composition capable of suppressing the occurrence of defects such as scratches and protrusions.

JP 2001-64631 A JP 2008-155368 A JP 2007-231209 A

  In order to realize a further increase in capacity of a magnetic disk drive, it is not sufficient to reduce scratches by using a conventional polishing composition, and in addition to scratches, waviness and nanoprotrusion defects on the substrate surface are further reduced. There is a need.

  As the capacity has increased, the recording method for magnetic disks has shifted from the horizontal magnetic recording method to the perpendicular magnetic recording method. In the manufacturing process of a perpendicular magnetic recording type magnetic disk, the texture process required for aligning the magnetization direction in the horizontal magnetic recording method is not required, and a magnetic layer is formed directly on the polished substrate surface. The required characteristics for quality are becoming stricter. The conventional polishing composition cannot satisfactorily satisfy the defects, scratches, and low surface waviness required for the surface of a perpendicular magnetic recording substrate.

  Accordingly, the present invention provides a polishing composition for a magnetic disk substrate that can reduce waviness and nanoprotrusion defects on the surface of the substrate after polishing, and a method for producing a magnetic disk substrate using the same.

［式（１）中、Ｒ¹は水素原子又は炭素数１〜４のアルキル基であり、Ｒ²は水素原子、ヒドロキシ基、炭素数１〜４のアルキル基、炭素数１〜４のアルコキシ基又はアリール基である。］ The present invention relates to a polishing liquid composition for a magnetic disk substrate comprising an abrasive and a copolymer having a structural unit represented by the following general formula (1) and a structural unit having a sulfonic acid group or a salt thereof. .

[In formula (1), R ¹ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ² is a hydrogen atom, a hydroxy group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms Or it is an aryl group. ]

  The method for producing a magnetic disk substrate of the present invention also relates to a method for producing a magnetic disk substrate including a step of polishing a substrate to be polished using the polishing composition for a magnetic disk substrate of the present invention.

  According to the polishing liquid composition of the present invention, for example, in addition to scratches on the polished substrate surface, waviness and nanoprotrusion defects on the polished substrate surface are reduced, and in particular, the magnetic field of the perpendicular magnetic recording system is reduced. The effect that a disk substrate can be manufactured is preferably achieved.

[Nanoprotrusion defects]
In the present invention, the “nanoprotrusion defect” is a defect on the surface of the substrate after polishing in the manufacturing process of the magnetic disk substrate, and means a convex defect having a size of less than 10 nm that can be detected optically. In order to increase the density and capacity of the magnetic disk, the distance between the magnetic head and the magnetic disk needs to be less than 10 nm. Therefore, the remaining nanoprotrusions are a cause of the consumption of the magnetic head and the recording density of the magnetic disk drive. May cause degradation or instability. If the nanoprojection defects are reduced in the polished substrate, the flying height of the magnetic head can be reduced, and the recording density of the magnetic disk substrate can be improved.

[undulation]
In the present invention, the “undulation” of the substrate means irregularities on the surface of the substrate having a wavelength longer than the roughness, and generally includes a long wavelength waviness (wavelength 0.4 to 2 mm) and a short wavelength waviness (wavelength 5 to 50 μm). In the present specification, unless otherwise stated, it refers to short wavelength waviness. By reducing the waviness of the substrate surface after polishing, the flying height of the magnetic head can be reduced, and the recording density of the magnetic disk substrate can be improved.

[scratch]
In the present invention, the “scratch” is a fine scratch on the substrate surface having a depth of 1 nm or more, a width of 100 nm or more, and a length of 1000 nm or more. The optical defect detection device Candala 6100 series manufactured by KLA Tencor, Hitachi It can be detected by NS 1500 series manufactured by High Technology, and can be quantitatively evaluated as the number of scratches. Further, the size and shape of the detected scratch can be analyzed with an atomic force microscope (AFM), a scanning electron microscope (SEM), and a transmission electron microscope (TEM).

  The present invention replaces the conventional polymer having a sulfonic acid group used for the purpose of reducing scratches (Cited Document 1, etc.) with hydrophobicity derived from a structural unit having a sulfonic acid group and a monomer such as styrene. In addition to reducing scratches on the substrate after polishing, it is possible to achieve reduction in nano-protrusion defects and waviness on the substrate surface after polishing, by using a polishing liquid composition containing a copolymer having the following structural units: Based on knowledge.

［式（１）中、Ｒ¹は水素原子又は炭素数１〜４のアルキル基であり、Ｒ²は水素原子、ヒドロキシ基、炭素数１〜４のアルキル基、炭素数１〜４のアルコキシ基又はアリール基である。］ That is, the present invention relates to a polishing liquid composition (hereinafter referred to as “a polishing agent”) containing an abrasive and a copolymer having a structural unit represented by the following general formula (1) and a structural unit having a sulfonic acid group or a salt thereof. Also referred to as “polishing liquid composition of the present invention”.

[In formula (1), R ¹ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ² is a hydrogen atom, a hydroxy group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms Or it is an aryl group. ]

  According to the polishing composition of the present invention, in the substrate after polishing, not only the scratch can be reduced, but also the effect of reducing waviness and nanoprojection defects on the surface of the substrate after polishing can be achieved.

  Although the details of the mechanism by which the polishing composition of the present invention can reduce not only scratches but also substrate surface waviness and nanoprotrusion defects after polishing are not clear, hydrophobic constituent units derived from monomers such as styrene in the copolymer As a result, the amount of the copolymer adsorbed on the polishing pad is increased, and the vibration of the polishing pad is suppressed. As a result, it is estimated that waviness and nanoprotrusion defects on the substrate surface after polishing are reduced. However, the present invention is not limited to this mechanism.

[Copolymer]
The polishing composition of the present invention is a copolymer having a structural unit represented by the above general formula (1) and a structural unit having a sulfonic acid group or a salt thereof (hereinafter also referred to as “copolymer of the present invention”). .). Hereinafter, the structural unit represented by the general formula (1) is also referred to as “hydrophobic structural unit”. The arrangement of the hydrophobic structural unit and the structural unit having a sulfonic acid group may be random, block, or graft. Moreover, as will be described later, structural units other than these structural units may be included within a range that satisfies all the predetermined content ranges.

[Hydrophobic building blocks]
The hydrophobic structural unit in the copolymer of the present invention is represented by the following general formula (1). R ^{1 in the following} general formula (1) is a hydrogen atom or an alkyl having 1 to 4 carbon atoms from the viewpoint of increasing the adsorption amount of the copolymer to the polishing pad and reducing the waviness and nanoprotrusion defects on the substrate surface after polishing. A hydrogen atom or an alkyl group having 1 to 3 carbon atoms, more preferably a hydrogen atom, a methyl group, or an ethyl group, and even more preferably a hydrogen atom or a methyl group. R ^{2 in the following} general formula (1) may be one substituent at any of the ortho, meta, and para positions, may be a substituent at two positions in the meta position, and other two or more positions. May be a substituent. R ² is a hydrogen atom, a hydroxy group, an alkyl group having 1 to 4 carbon atoms, a carbon number from the viewpoint of increasing the adsorption amount of the copolymer to the polishing pad and reducing waviness and nanoprotrusion defects on the substrate surface after polishing. It is a 1-4 alkoxy group or an aryl group, and a hydrogen atom or a 1 or more C1-C4 alkyl group is preferable, and a hydrogen atom is more preferable. When there are a plurality of R ² , they may be the same or different. The alkyl group having 1 to 4 carbon atoms and the alkoxy group having 1 to 4 carbon atoms may have a linear structure or a branched structure. Further, the copolymer of the present invention may contain two or more types of hydrophobic structural units.

  The content of the hydrophobic structural unit in all the structural units constituting the copolymer of the present invention is preferably from 5 to 95 mol% from the viewpoint of undulation of the substrate surface after polishing and reduction of nanoprojection defects. -70 mol% is more preferable, 10-60 mol% is still more preferable, 15-50 mol% is still more preferable, 20-40 mol% is still more preferable.

  Monomers that give hydrophobic structural units include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, α, 2-dimethylstyrene, 2,4-dimethylstyrene, 2, 5-dimethylstyrene, 2,4,6-trimethylstyrene, 2-ethylstyrene, 4-ethylstyrene, 4-isopropylstyrene, 2-methoxystyrene, 3-methoxystyrene, 4-methoxystyrene, 4-ethoxystyrene, 4 -Phenoxy styrene, 4-phenyl styrene, 2-hydroxy styrene, 4-hydroxy styrene and the like. Among these, from the viewpoint of reactivity and undulation of the substrate surface after polishing and reduction of nanoprotrusion defects, styrene is used. preferable.

［式（２）中、Ｒ³は水素原子又は炭素数１〜４のアルキル基であり、Ｒ⁴は１又は複数のスルホン酸基を有するアリール基である。］ [Structural unit having sulfonic acid group]
The structural unit having a sulfonic acid group in the copolymer of the present invention can be obtained, for example, by polymerizing a monomer having a sulfonic acid group. The structural unit having a sulfonic acid group is preferably represented by the following general formula (2) from the viewpoints of waviness of the substrate surface after polishing and reduction of nanoprotrusion defects. R ³ in the following general formula (2) is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms from the viewpoint of undulation of the substrate surface after polishing and reduction of nanoprotrusion defects. 3 is preferable, a hydrogen atom, a methyl group, or an ethyl group is more preferable, a hydrogen atom or a methyl group is more preferable, and a methyl group is still more preferable. R ^{4 in the following} general formula (2) is an aryl group substituted with one or a plurality of sulfonic acid groups from the viewpoint of solubility / dispersibility of the copolymer and reduction of waviness and nanoprotrusion defects on the substrate surface after polishing. A phenyl group substituted with one or more sulfonic acid groups, preferably a phenyl group having one sulfonic acid group at any of the ortho, meta, and para positions, or a phenyl group having a sulfonic acid group at two positions of the meta position Group is more preferable, and a phenyl group having a sulfonic acid group at the para position is more preferable. The copolymer of the present invention may contain a structural unit having two or more kinds of sulfonic acid groups. These sulfonic acid groups may take the form of neutralized salts.

[In Formula (2), R ³ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ⁴ is an aryl group having one or more sulfonic acid groups. ]

  The counter ion of the sulfonic acid group is not particularly limited, and specific examples include ions of metals, ammonium, alkylammonium and the like. Specific examples of the metal include metals belonging to the periodic table (long-period type) 1A, 1B, 2A, 2B, 3A, 3B, 4A, 6A, 7A, or Group 8. Among these metals, metals belonging to Group 1A, 3B, or Group 8 are preferable from the viewpoint of surface roughness and nanoscratch reduction, and sodium and potassium belonging to Group 1A are more preferable. Specific examples of alkylammonium include tetramethylammonium, tetraethylammonium, tetrabutylammonium and the like. Among these salts, ammonium salts, sodium salts, and potassium salts are more preferable.

  The content of the structural unit having a sulfonic acid group in all the structural units constituting the copolymer of the present invention is 5 to 95 mol% from the viewpoint of reducing the waviness of the substrate surface after polishing and the reduction of nanoprotrusion defects. Preferably, 40 to 90 mol% is more preferable, 50 to 85 mol% is more preferable, and 60 to 80 mol% is still more preferable.

  Examples of the monomer that provides a structural unit having a sulfonic acid group include isoprenesulfonic acid, 2- (meth) acrylamide-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylbenzylsulfonic acid, methallylsulfonic acid, Examples thereof include vinyl sulfonic acid, allyl sulfonic acid, isoamylene sulfonic acid, naphthalene sulfonic acid, and salts thereof. Among these, styrene sulfonic acid, methyl styrene sulfonic acid and salts thereof are preferable from the viewpoint of storage stability of the copolymer and reduction of waviness and nanoprotrusion defects on the substrate surface after polishing, and styrene sulfonic acid and The salt is more preferred. Alternatively, the structural unit having a sulfonic acid group may be obtained by sulfonating a (co) polymer (base polymer) containing the hydrophobic structural unit described above with a known sulfonating agent or the like.

  The total content of the hydrophobic structural unit and the structural unit having a sulfonic acid group in all the structural units constituting the copolymer of the present invention is the reduction of waviness and nanoprotrusion defects on the substrate surface after polishing. From the viewpoint, 70 to 100 mol% is preferable, 80 to 100 mol% is more preferable, 90 to 100 mol% is further preferable, and 95 to 100 mol% is even more preferable.

  The molar ratio of the hydrophobic structural unit and the structural unit having a sulfonic acid group in the total structural units constituting the copolymer of the present invention (mol% of hydrophobic structural unit / mol of the structural unit having a sulfonic acid group) %) Is preferably from 5/95 to 95/5, more preferably from 10/90 to 60/40, and more preferably from 15/85 to 50/50 mol, from the viewpoint of reduction of waviness on the substrate surface after polishing and reduction of nanoprotrusion defects. % Is more preferable, and 20/80 to 40/60 is even more preferable.

[Other structural units]
The copolymer of this invention may have other structural units other than said hydrophobic structural unit and the structural unit which has a sulfonic acid group. Other structural units include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and crotonic acid; hydroxyethyl acrylate, hydroxyethyl methacrylate, glycidyl acrylate, glycidyl methacrylate, ethylene glycol Hydroxy or glycidyl group-containing ethylenic monomers such as acrylate, ethylene glycol dimethacrylate, polyethylene glycol monoacrylate, polyethylene glycol monomethacrylate; acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N-diacetone Ethylenic amides such as acrylamide; aminoethyl acrylate, aminoethyl methacrylate, N, N-dimethyla Noethyl acrylate, N, N-dimethylaminoethyl methacrylate, N, N-diethylaminoethyl acrylate, N, N-diethylaminoethyl methacrylate, N, N, N-trimethylaminoethyl acrylate, N, N, N-trimethylaminoethyl methacrylate And ethylenic amines or salts thereof. The content of other structural units in all the structural units constituting the copolymer of the present invention is preferably 0 to 30 mol% from the viewpoint of undulation of the substrate surface after polishing and reduction of nanoprotrusion defects. -20 mol% is more preferable, 0-10 mol% is further more preferable, 0-5 mol% is further more preferable, Furthermore, substantially 0 mol% is preferable.

[Method for producing copolymer]
Examples of the method for producing the copolymer of the present invention include a monomer copolymerization method and a method obtained by using a sulfonating agent for the polymer, but are not limited to these methods. Preferred is a monomer copolymerization method. As the monomer copolymerization method, a known polymerization method such as bulk polymerization or solution polymerization can be used. The polymerization solvent for obtaining the copolymer of the present invention may be any as long as the solubility in water (20 ° C.) is 10% by weight or more. Examples include water, alcohols, ketones, and ethers. Examples of the alcohol solvent include methanol, ethanol, n-propanol, isopropanol, n-butanol, secondary butanol, tertiary butanol, isobutanol, diacetone alcohol and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, dipropyl ketone, methyl isobutyl ketone, methyl isopropyl ketone, and cyclohexanone. Examples of ether solvents include tetrahydrofuran, dioxane, glyme, cellosolves and the like. One or more of these can be mixed and used. As the polymerization initiator, a known radical initiator is used. For example, persulfates represented by ammonium persulfate, potassium persulfate, sodium persulfate, hydroperoxides represented by t-butyl hydroperoxide, dialkyl peroxides represented by di-t-butyl peroxide Acetyl peroxide, diacyl peroxides represented by benzoyl peroxide, ketone peroxides represented by methyl ethyl ketone peroxide, and azo polymerization initiators. If necessary, a chain transfer agent is used, and the solution is refluxed in a nitrogen gas stream at 40 to 300 ° C. to perform solution polymerization.

[Weight average molecular weight of copolymer]
The weight average molecular weight of the copolymer of the present invention is preferably 500 or more and 120,000 or less, more preferably 1000 or more and 100,000 or less, and more preferably 1000 or more and 30,000, from the viewpoints of waviness of the substrate surface after polishing and reduction of nanoprotrusion defects. The following is more preferable, 1000 or more and 10,000 or less are more preferable, and 1500 or more and 8000 or less are even more preferable. The weight average molecular weight is a value measured under the conditions described in Examples using gel permeation chromatography (GPC).

  When the copolymer of the present invention forms a salt at least partially, the counter ion is not particularly limited, and as in the case of the sulfonate group described above, ions of metal, ammonium, alkylammonium, etc. Is mentioned.

  The content of the copolymer of the present invention in the polishing composition is preferably from 0.001 to 1% by weight, more preferably from 0.005 to 5% from the viewpoint of reducing the waviness of the substrate surface after polishing and the reduction of nanoprotrusion defects. It is 0.5% by weight, more preferably 0.01 to 0.2% by weight, still more preferably 0.01 to 0.1% by weight, particularly preferably 0.01 to 0.075% by weight.

[Abrasive]
As the abrasive used in the present invention, abrasives generally used for polishing can be used, including metal, metal or metalloid carbide, nitride, oxide, boride, diamond. Etc. The metal or metalloid element is derived from Group 2A, 2B, 3A, 3B, 4A, 4B, 5A, 6A, 7A or Group 8 of the periodic table (long period type). Specific examples of the abrasive include aluminum oxide (alumina), silicon carbide, diamond, magnesium oxide, zinc oxide, titanium oxide, cerium oxide, zirconium oxide, silica, and the like, and one or more of these are used. This is preferable from the viewpoint of improving the polishing rate. Of these, alumina and colloidal silica are preferable from the viewpoint of waviness of the substrate surface after polishing and reduction of nanoprotrusion defects, and colloidal silica is more preferable.

  The colloidal silica may be obtained by a known production method or the like produced from a silicic acid aqueous solution. The usage form of the silica particles is preferably a slurry from the viewpoint of operability. The present invention is preferably based on the finding that waviness and nanoprotrusion defects on the substrate surface after polishing can be further reduced by combining predetermined silica particles described later with the above-mentioned copolymer.

  Specifically, in a preferred embodiment, the present invention focuses on the difference between the CV values (ΔCV values) at two different detection angles in addition to the average particle diameter that has been conventionally controlled, and these two parameters. In combination with the above-mentioned copolymer, the abrasive controlled using the above is based on the knowledge that in addition to the scratch after polishing, the waviness and nanoprotrusion defects on the substrate surface can be further reduced.

[Average particle size of abrasive]
[Average particle diameter based on scattering intensity distribution measured at a detection angle of 90 degrees in the dynamic light scattering method]
In the present specification, the average particle size of the abrasive includes two types of average particle size, that is, the average particle size (S2) measured by transmission electron microscope observation, and the detection angle of 90 degrees in the dynamic light scattering method. The average particle diameter based on the scattering intensity distribution measured in (1) is used, and specifically measured by the method described in the examples. The average particle diameter based on the scattering intensity distribution measured at a detection angle of 90 degrees in the dynamic light scattering method is preferably 1 to 40 nm, and preferably 5 to 37 nm from the viewpoint of reducing waviness and nanoprotrusion defects on the substrate surface after polishing. Is more preferable, and 10 to 35 nm is more preferable.

[ΔCV value of abrasive]
In this specification, the ΔCV value of the abrasive is the standard deviation of the particle diameter measured based on the scattering intensity distribution at a detection angle of 30 degrees (forward scattering) by the dynamic light scattering method, and the detection angle of 30 by the dynamic light scattering method. Scattering with a coefficient of variation (CV30) multiplied by 100 divided by the average particle size measured based on the scattering intensity distribution in degrees (CV30) and a detection angle of 90 degrees (side scattering) by the dynamic light scattering method A coefficient of variation (CV90) obtained by dividing the standard deviation of the particle diameter measured based on the intensity distribution by the average particle diameter measured based on the scattering intensity distribution at a detection angle of 90 degrees by the dynamic light scattering method and multiplying by 100. ) (ΔCV = CV30−CV90), specifically, it can be measured by the method described in the examples. The ΔCV value of the abrasive used in the polishing composition of the present invention is preferably 0 to 14%, more preferably 0 to 10% from the viewpoint of reducing scratches and surface roughness without impairing productivity. 0 to 7% is more preferable, and 0 to 5% is even more preferable.

[CV value of abrasive]
In this specification, the CV value of colloidal silica is a value of a coefficient of variation obtained by dividing the standard deviation based on the scattering intensity distribution in the dynamic light scattering method by the average particle diameter and multiplying by 100, and as described above, The CV value measured at a detection angle of 90 degrees (side scatter) is referred to as CV90, and the CV value measured at a detection angle of 30 degrees (forward scatter) is referred to as CV30. Specifically, it is obtained by the method described in the examples. Can do. The CV90 of colloidal silica used in the polishing composition of the present invention is preferably 1 to 35%, more preferably 5 to 34%, from the viewpoint of reducing scratches and surface roughness without impairing productivity. ~ 33% is more preferred.

  The inventors have found that there is a correlation between the ΔCV value of the abrasive and the content of the abrasive agglomerates (non-spherical particles), and by using an abrasive having a ΔCV value within a predetermined range, It was found that scratches on the substrate, waviness on the substrate surface after polishing, and nanoprotrusion defects can be reduced. The reason why such an effect is exerted is not clear, but by controlling the ΔCV value, 50 to 200 nm of abrasive aggregates (non-spherical particles) generated by agglomeration of the primary particles of the abrasive are reduced, and such agglomeration is performed. By combining a polishing material with less aggregate with the copolymer of the present invention, the formation of the agglomerates that occur during polishing is further suppressed, and friction vibration during polishing is reduced to polish from the opening of the polishing pad. It is presumed that the material aggregates are further prevented from falling off, and in addition to scratching of the substrate after polishing, waviness and nanoprotrusion defects on the substrate surface after polishing are further reduced. However, the present invention is not limited to these estimation mechanisms.

Examples of the method for adjusting the ΔCV value of the abrasive include the following methods for preventing formation of abrasive aggregates (non-spherical particles) of 50 to 200 nm in the preparation of the polishing liquid composition.
A) Method by filtration of polishing liquid composition B) Method by process control during production of abrasive

  When the abrasive is colloidal silica, in the above A), the ΔCV value can be obtained by removing silica aggregates of 50 to 200 nm by, for example, centrifugation or precision filter filtration (JP 2006-102829 and JP 2006-136996). Can be reduced.

Colloidal silica is usually 1) a mixed solution (seed solution) of less than 10% by weight of No. 3 sodium silicate and seed particles (small particle silica) is put in a reaction layer and heated to 60 ° C. or higher. ) Dropping an acidic active silicic acid aqueous solution obtained by passing No. 3 sodium silicate through a cation exchange resin and an alkali (alkali metal or quaternary ammonium) dropwise to grow a spherical particle with a constant pH, 3) Obtained by concentrating by evaporation or ultrafiltration after aging (Japanese Patent Laid-Open No. 47-1964, Japanese Patent Publication No. 1-223412, Japanese Patent Publication No. 4-55125, Japanese Patent Publication No. 4-55127). However, it is often reported that non-spherical particles can be produced by slightly changing the process in the same production process. For example, activated silicic acid is very unstable, and when a polyvalent metal ion such as Ca or Mg is intentionally added, an elongated silica sol can be produced. Further, the temperature of the reaction layer (evaporates when the boiling point of water is exceeded and the silica is dried at the gas-liquid interface), the pH of the reaction layer (silica particles are liable to be linked below 9), the SiO ₂ / M ₂ O of the reaction layer. (M is an alkali metal or quaternary ammonium), and non-spherical silica can be produced by changing the molar ratio (selectively producing non-spherical silica at 30 to 60) (Japanese Patent Publication No. 8-5657, Patent 2803134, JP, 2006-80406, JP, 2007-153671). Therefore, in the above-mentioned B), in the known spherical colloidal silica production process, the ΔCV value can be adjusted to be small by performing process control so as not to be a condition for generating non-spherical silica locally.

[Sphericality of abrasive]
In this specification, the true sphere ratio measured by observation of the abrasive with a transmission electron microscope is a circle with the projected area (A1) of one abrasive particle obtained by the transmission electron microscope and the circumference of the particle as the circumference. To the area (A2), that is, the value of “A1 / A2”, for example, the value of “A1 / A2” for any 50 to 100 abrasives in the polishing composition of the present invention It can be calculated as an average value. Specifically, the true sphericity of the abrasive can be measured by the method described in Examples. From the viewpoint of reducing scratches and surface roughness without impairing productivity, the sphericity of the abrasive used in the polishing composition of the present invention is 0.75 to 1, and 0.75 to 0.00. 95 is preferable, and 0.75 to 0.85 is more preferable.

[Surface roughness of abrasive]
In this specification, the surface roughness of the abrasive is the specific surface area (SA2) calculated from the specific surface area (SA1) measured by the sodium titration method and the average particle diameter (S2) measured by transmission electron microscope observation. The value of “SA1 / SA2”, which is the ratio of the above, is specifically measured by the method described in the examples. When applying the sodium titration method, the abrasive is preferably silica. Here, the specific surface area (SA1) measured by the sodium titration method is obtained from the consumption amount of the sodium hydroxide solution when the sodium hydroxide solution is titrated against the abrasive, and the actual surface area is calculated as follows. It can be said that it was reflected. Specifically, the specific surface area (SA1) increases as the surface of the abrasive material is richer in undulations or ridges. On the other hand, the specific surface area (SA2) calculated from the average particle diameter (S2) measured by a transmission electron microscope is calculated assuming that the abrasive is an ideal spherical particle. Specifically, the specific surface area (SA2) decreases as the average particle size (S2) increases. The specific surface area indicates the surface area per unit mass, and the value of the surface roughness (SA1 / SA2) is so large that the abrasive is spherical and has many hook-like protrusions on the abrasive surface. The value is smaller, the smaller the number of wrinkle-like protrusions on the surface of the abrasive and the smoother the surface, the smaller the value.

  From the viewpoint of reducing scratches and surface roughness without impairing productivity, the surface roughness (SA1 / SA2) of the abrasive used in the polishing composition of the present invention is 1.3 or more. 3-2.5 are preferable and 1.3-2.0 are more preferable.

  The sphericity, surface roughness (SA1 / SA2), and average particle size of the abrasive can be adjusted using a conventionally known method for producing an abrasive. For example, the production methods described in JP 2008-137822 A and JP 2008-169102 A can be exemplified, but the present invention is not limited thereto.

  The method of adjusting the particle size distribution of the abrasive is not particularly limited, and a method of giving a desired particle size distribution by adding particles as a new nucleus in the process of particle growth in the production stage, Examples include a method of mixing two or more kinds of abrasive particles having different particle size distributions so as to have a desired particle size distribution.

  The content of the abrasive in the polishing liquid composition is preferably 0.5% by weight or more, more preferably 1% by weight or more, further preferably 3% by weight or more, from the viewpoint of improving the polishing rate, and 4% by weight or more. Is even more preferred. Further, from the viewpoint of reducing the waviness of the substrate surface after polishing and the reduction of nanoprojection defects, it is preferably 20% by weight or less, more preferably 15% by weight or less, still more preferably 13% by weight or less, and even more preferably 10% by weight or less. preferable. That is, the content of the abrasive is preferably 0.5 to 20% by weight, more preferably 1 to 15% by weight, further preferably 3 to 13% by weight, and still more preferably 4 to 10% by weight.

  In addition, the concentration ratio of the abrasive to the copolymer [the concentration of the abrasive (wt%) / the concentration of the copolymer (wt%)] in the polishing composition is determined by the undulation of the substrate surface after polishing and nano From the viewpoint of reducing protrusion defects, 5-5000 is preferable, 10-1000 is more preferable, and 25-500 is more preferable.

[water]
The polishing composition of the present invention can contain water as a medium, and distilled water, ion exchange water, ultrapure water, or the like can be used as the water. From the viewpoint of the surface cleanliness of the substrate to be polished, ion exchange water and ultrapure water are preferable, and ultrapure water is more preferable. The content of water in the polishing composition is preferably 60 to 99.4% by weight, and more preferably 70 to 98.9% by weight. Moreover, you may mix | blend organic solvents, such as alcohol, in the range which does not inhibit the effect of this invention.

[acid]
The polishing liquid composition of the present invention preferably contains an acid and / or a salt thereof. The acid and / or salt thereof used in the polishing composition of the present invention is preferably a compound having a pK1 of 2 or less from the viewpoint of improving the polishing rate, and preferably pK1 from the viewpoint of reducing scratches. Is 1.5 or less, more preferably 1 or less, and still more preferably a compound exhibiting strong acidity that cannot be expressed by pK1. Preferred acids include nitric acid, sulfuric acid, sulfurous acid, persulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, tripolyphosphoric acid, amidosulfuric acid and the like, and salts thereof, 2-aminoethylphosphone Acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid), ethane-1,1, -diphosphonic acid, ethane-1 , 1,2-Triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic Acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobu Organic phosphonic acids such as N-2,3,4-tricarboxylic acid and α-methylphosphonosuccinic acid and salts thereof, aminocarboxylic acids such as glutamic acid, picolinic acid and aspartic acid and salts thereof, citric acid, tartaric acid and oxalic acid Carboxylic acids such as nitroacetic acid, maleic acid and oxaloacetic acid and salts thereof. Among these, inorganic acids, carboxylic acids, organic phosphonic acids, and salts thereof are preferable from the viewpoint of reducing scratches. Among inorganic acids and salts thereof, phosphoric acid, nitric acid, sulfuric acid, hydrochloric acid, perchloric acid and salts thereof are more preferred, and phosphoric acid and sulfuric acid are more preferred. Among the carboxylic acids and salts thereof, citric acid, tartaric acid, and maleic acid are more preferable, and citric acid is more preferable. Among organic phosphonic acids and salts thereof, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid) and their salts are more preferred. 1-hydroxyethylidene-1,1-diphosphonic acid and aminotri (methylenephosphonic acid) are more preferable. These acids and salts thereof may be used alone or in combination of two or more, but from the viewpoint of improving the polishing rate, reducing nanoprotrusions and improving the cleaning property of the substrate, use two or more in combination. It is more preferable to use a mixture of two or more acids selected from the group consisting of phosphoric acid, sulfuric acid, citric acid and 1-hydroxyethylidene-1,1-diphosphonic acid. Here, pK1 is a logarithmic value of the reciprocal of the first acid dissociation constant (25 ° C.) of the organic compound or inorganic compound. The pK1 of each compound is described in, for example, the revised 4th edition, Chemical Handbook (Basic Edition) II, pp316-325 (Edited by Chemical Society of Japan).

  The counter ion in the case of using these acid salts is not particularly limited, and specific examples thereof include salts with metals, ammonium, alkylammonium and the like. Specific examples of the metal include metals belonging to the periodic table (long-period type) 1A, 1B, 2A, 2B, 3A, 3B, 4A, 6A, 7A, or Group 8. Among these, a salt with a metal belonging to Group 1A or ammonium is preferable from the viewpoint of reducing scratches.

  The content of the acid and its salt in the polishing composition is preferably 0.001 to 5% by weight, more preferably 0.01 to 4% by weight, from the viewpoints of improving the polishing rate, surface roughness, and reducing scratches. More preferably, it is 0.05 to 3% by weight, and still more preferably 0.1 to 2.0% by weight.

[Oxidant]
The polishing composition of the present invention preferably contains an oxidant. As an oxidizing agent that can be used in the polishing liquid composition of the present invention, from the viewpoint of improving the polishing rate, peroxide, permanganic acid or a salt thereof, chromic acid or a salt thereof, peroxo acid or a salt thereof, oxygen acid or an acid thereof Examples thereof include salts, metal salts, nitric acids, sulfuric acids and the like.

  Examples of the peroxide include hydrogen peroxide, sodium peroxide, barium peroxide, etc., examples of the permanganic acid or salt thereof include potassium permanganate, and examples of the chromic acid or salt thereof include chromium. Acid metal salts, metal dichromates, and the like. Peroxo acids or salts thereof include peroxodisulfuric acid, ammonium peroxodisulfate, peroxodisulfate metal salts, peroxophosphoric acid, peroxosulfuric acid, sodium peroxoborate, and performic acid. Peroxyacetic acid, perbenzoic acid, perphthalic acid, etc., and oxygen acids or salts thereof include hypochlorous acid, hypobromite, hypoiodous acid, chloric acid, bromic acid, iodic acid, hypochlorous acid. Examples thereof include sodium chlorate and calcium hypochlorite. Examples of metal salts include iron (III) chloride, iron (III) sulfate, iron (III) nitrate, and iron citrate. III), ammonium iron (III), and the like.

  Preferable oxidizing agents include hydrogen peroxide, iron (III) nitrate, peracetic acid, ammonium peroxodisulfate, iron (III) sulfate, and iron (III) ammonium sulfate. As a more preferable oxidizing agent, hydrogen peroxide is mentioned from the viewpoint that metal ions do not adhere to the surface and are generally used and inexpensive. These oxidizing agents may be used alone or in admixture of two or more.

  The content of the oxidizing agent in the polishing liquid composition is preferably 0.01% by weight or more, more preferably 0.05% by weight or more, and further preferably 0.1% by weight or more from the viewpoint of improving the polishing rate. In view of surface roughness, waviness and scratch reduction, it is preferably 4% by weight or less, more preferably 2% by weight or less, and further preferably 1% by weight or less. Therefore, in order to improve the polishing rate while maintaining the surface quality, the content is preferably 0.01 to 4% by weight, more preferably 0.05 to 2% by weight, and still more preferably 0.1 to 1. % By weight.

[Other ingredients]
In the polishing composition of the present invention, other components can be blended as necessary. Examples of other components include a thickener, a dispersant, a rust inhibitor, a basic substance, and a surfactant. 0-10 weight% is preferable and, as for content of these other arbitrary components in polishing liquid composition, 0-5 weight% is more preferable. However, the polishing liquid composition of the present invention can exhibit the effect of reducing waviness and nanoprotrusion defects on the substrate surface after polishing without containing other components, particularly a surfactant. Furthermore, the polishing composition of the present invention can contain alumina abrasive grains and can be used in a rough polishing step prior to the final polishing step.

[PH of polishing composition]
The pH of the polishing composition of the present invention is preferably 4 or less, more preferably 3.5 or less, still more preferably 3 or less, and even more preferably 2.5 or less, from the viewpoint of improving the polishing rate. Moreover, 0.5 or more is preferable from a viewpoint of surface roughness reduction, More preferably, it is 0.8 or more, More preferably, it is 1.0 or more, More preferably, it is 1.2 or more. In addition, the waste liquid pH of the polishing composition is preferably 4 or less, more preferably 3.5 or less, still more preferably 3.5 or less, and even more preferably 3.0 or less, from the viewpoint of improving the polishing rate. Further, from the viewpoint of reducing the surface roughness, the waste liquid pH of the polishing composition is preferably 0.8 or more, more preferably 1.0 or more, still more preferably 1.2 or more, and even more preferably 1.5 or more. It is. The waste liquid pH refers to the polishing waste liquid in the polishing step using the polishing liquid composition, that is, the pH of the polishing liquid composition immediately after being discharged from the polishing machine.

[Method for preparing polishing liquid composition]
In the polishing composition of the present invention, for example, water, an abrasive, a copolymer, and, if desired, an acid and / or a salt thereof, an oxidizing agent, and other components are mixed by a known method. Can be prepared. At this time, the abrasive may be mixed in a concentrated slurry state or may be mixed after being diluted with water or the like. Although content and density | concentration of each component in the polishing liquid composition of this invention are the ranges mentioned above, you may prepare the polishing liquid composition of this invention as a concentrate as another aspect.

[Method of manufacturing magnetic disk substrate]
As another aspect, the present invention relates to a method of manufacturing a magnetic disk substrate (hereinafter also referred to as a manufacturing method of the present invention). The manufacturing method of the present invention includes a step of polishing a substrate to be polished using the above-described polishing liquid composition of the present invention (hereinafter, also referred to as “polishing process using the polishing liquid composition of the present invention”). It is a manufacturing method of a disk substrate. Thereby, in addition to scratches on the substrate surface after polishing, a magnetic disk substrate in which undulations and nanoprotrusion defects on the substrate surface after polishing are reduced can be provided. The manufacturing method of the present invention is particularly suitable for a method for manufacturing a magnetic disk substrate for perpendicular magnetic recording. Therefore, as another aspect, the manufacturing method of the present invention is a method of manufacturing a magnetic disk substrate for a perpendicular magnetic recording system including a polishing step using the polishing composition of the present invention.

  As a specific example of a method for polishing a substrate to be polished using the polishing liquid composition of the present invention, the substrate to be polished is sandwiched between a surface plate to which a polishing pad such as a non-woven organic polymer polishing cloth is attached. A method of polishing the substrate to be polished by moving the surface plate or the substrate to be polished while supplying the polishing composition of the invention to the polishing machine can be mentioned.

  In the case where the polishing process of the substrate to be polished is performed in multiple stages, the polishing process using the polishing composition of the present invention is preferably performed in the second stage and more preferably in the final polishing process. At that time, in order to avoid mixing of the polishing material and polishing liquid composition in the previous process, different polishing machines may be used, and in the case of using different polishing machines, polishing is performed for each polishing process. It is preferable to clean the substrate. Further, the polishing composition of the present invention can also be used in cyclic polishing in which the used polishing liquid is reused. The polishing machine is not particularly limited, and a known polishing machine for polishing a magnetic disk substrate can be used.

[Polishing pad]
The polishing pad used in the present invention is not particularly limited, and a polishing pad of a suede type, a nonwoven fabric type, a polyurethane closed-cell foam type, or a two-layer type in which these are laminated can be used. From the viewpoint, a suede type polishing pad is preferable.

  The average pore diameter of the surface member of the polishing pad is preferably 50 μm or less, more preferably 45 μm or less, still more preferably 40 μm or less, and even more preferably 35 μm or less, from the viewpoint of scratch reduction and pad life. From the viewpoint of holding the polishing liquid of the pad, the average pore diameter is preferably 0.01 μm or more, more preferably 0.1 μm or more, and still more preferably, in order to keep the polishing liquid in the pores and prevent the liquid from running out. It is 1 μm or more, more preferably 10 μm or more. Further, the maximum value of the pore size of the polishing pad is preferably 100 μm or less, more preferably 70 μm or less, still more preferably 60 μm or less, and particularly preferably 50 μm or less from the viewpoint of maintaining the polishing rate.

[Polishing load]
The polishing load in the polishing step using the polishing liquid composition of the present invention is preferably 5.9 kPa or more, more preferably 6.9 kPa or more, and further preferably 7.5 kPa or more. Thereby, since the fall of a grinding | polishing speed | rate can be suppressed, productivity can be improved. In the production method of the present invention, the polishing load refers to the pressure of the surface plate applied to the polishing surface of the substrate to be polished during polishing. In the polishing step using the polishing composition of the present invention, the polishing load is preferably 20 kPa or less, more preferably 18 kPa or less, and further preferably 16 kPa or less. Thereby, generation | occurrence | production of a scratch can be suppressed. Accordingly, in the polishing step using the polishing composition of the present invention, the polishing pressure is preferably 5.9 to 20 kPa, more preferably 6.9 to 18 kPa, and further preferably 7.5 to 16 kPa. The polishing load can be adjusted by applying air pressure or weight to at least one of the surface plate and the substrate to be polished.

[Supply of polishing liquid composition]
From the viewpoint of reducing scratches, the supply rate of the polishing composition of the present invention in the polishing step using the polishing composition of the present invention is preferably 1 to 15 mL / min per 1 cm ^{2 of the} substrate to be polished. More preferably 0.06 to 10 mL / min, still more preferably 0.07 to 1 mL / min, even more preferably 0.08 to 0.5 mL / min, even more preferably 0.12 to 0.5 mL / min. Minutes.

  As a method for supplying the polishing composition of the present invention to a polishing machine, for example, a method of continuously supplying using a pump or the like can be mentioned. When supplying the polishing composition to the polishing machine, in addition to the method of supplying one component containing all the components, considering the stability of the polishing composition, etc., it is divided into a plurality of compounding component liquids, Two or more liquids can be supplied. In the latter case, for example, the plurality of compounding component liquids are mixed in the supply pipe or on the substrate to be polished to obtain the polishing liquid composition of the present invention.

[Polished substrate]
Examples of the material of the substrate to be polished preferably used in the present invention include metals, metalloids such as silicon, aluminum, nickel, tungsten, copper, tantalum, and titanium, or alloys thereof, glass, glassy carbon, and amorphous. Examples thereof include glassy substances such as carbon, ceramic materials such as alumina, silicon dioxide, silicon nitride, tantalum nitride, and titanium carbide, and resins such as polyimide resin. Among these, a substrate to be polished containing a metal such as aluminum, nickel, tungsten, copper, or an alloy containing these metals as a main component is preferable. In particular, an Ni—P plated aluminum alloy substrate or an aluminosilicate glass is suitable. Aluminosilicate glass includes those having a crystal structure and those subjected to chemical strengthening treatment. You may perform a chemical strengthening process after grinding | polishing.

  Further, according to the present invention, in addition to scratching of the substrate surface after polishing, a magnetic disk substrate with reduced waviness and nanoprotrusion defects on the substrate surface after polishing can be provided, so that high surface smoothness is required. It can be suitably used for polishing a perpendicular magnetic recording type magnetic disk substrate.

  There is no restriction | limiting in particular in the shape of the said to-be-polished substrate, For example, what is necessary is just the shape which has planar parts, such as a disk shape, plate shape, slab shape, prism shape, and the shape which has curved surface parts, 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, the outer diameter is, for example, about 2 to 95 mm, and the thickness is, for example, about 0.5 to 2 mm.

[Polishing method]
As another aspect, the present invention relates to a method for polishing a substrate to be polished, which comprises polishing the substrate to be polished while bringing the above-mentioned polishing composition into contact with a polishing pad. By using the polishing method of the present invention, in addition to scratching of the substrate surface after polishing, waviness and nanoprotrusion defects on the substrate surface after polishing are reduced, particularly a perpendicular magnetic recording type magnetic disk substrate. Is preferably provided. Examples of the substrate to be polished in the polishing method of the present invention include those used in the manufacture of a magnetic disk substrate and a magnetic recording medium substrate as described above. A substrate used for production is preferred. The specific polishing method and conditions can be as described above.

[Examples 1 to 16, Comparative Examples 1 to 3]
Copolymer styrene / styrene sulfonic acid copolymer sodium salt (St / NaSS), polystyrene sulfonic acid sodium salt (NaSS), acrylic acid / styrene sulfonic acid copolymer sodium salt (AA / NaSS), or acrylic A polishing composition using acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer sodium salt (AA / AMPS) (see Table 2 below) and colloidal silica shown in Table 1 below as an abrasive. The substrate to be polished was prepared and the substrate was polished, and the waviness, scratches and nanoprojection defects of the substrate after polishing were evaluated. In addition, the average particle diameter in the following Table 1 is an average particle diameter based on a scattering intensity distribution measured at a detection angle of 90 degrees in the dynamic light scattering method. The evaluation results are shown in Table 2 below. The method for producing the copolymer, the method for preparing the polishing liquid composition, the method for measuring each parameter, the polishing conditions (polishing method), and the evaluation method are as follows.

[Method for producing copolymer]
As the (co) polymers in the following Table 2, (co) polymers produced by known solution polymerization were used. In addition, the manufacturing method of the copolymer used in Example 1 is shown as a representative example.

[Method for Producing Copolymer of Example 1]
Into a 1 L four-necked flask, 180 g of isopropyl alcohol (manufactured by Kishida Chemical), 370 g of ion-exchanged water, 5 g of styrene (manufactured by Kishida Chemical), and 45 g of sodium styrenesulfonate (manufactured by Wako Pure Chemical Industries) were charged. Azobis (2-methylpropionamidine) dihydrochloride 7.2 g (V-50, manufactured by Wako Pure Chemical Industries, Ltd.) was used as a reaction initiator, polymerized at 83 ± 2 ° C. for 2 hours, and further aged for 2 hours. By removing the solvent under reduced pressure, a white powdery styrene / sodium styrenesulfonate copolymer (10/90 mol%) was obtained. The copolymer had a weight average molecular weight of 7,100.

  The copolymers of Examples 2 to 16 and Comparative Example 2 were polymerized according to the above-described method while changing the monomer ratio. In Comparative Example 1, polystyrenesulfonic acid sodium salt (NaSS, manufactured by Tosoh Corporation) is used. In Comparative Example 3, acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer sodium salt (AA / AMPS, Toagosei Co., Ltd.) is used. Used). The polymerization ratio and weight average molecular weight of each (co) polymer are as shown in Table 2 below. The weight average molecular weight was measured by gel permeation chromatography (GPC) method under the following measurement conditions.

[GPC conditions for St / NaSS]
Column: TSKgel α-M + TSKgel α-M (manufactured by Tosoh Corporation)
Guard column: TSK guard column α (Tosoh)
Eluent: 60 mmol / L phosphoric acid, 50 mmol / L LiBr / DMF
Temperature: 40 ° C
Flow rate: 1.0 mL / min
Sample size: 3 mg / mL
Detector: RI
Conversion standard: Polystyrene

[GPC conditions for NaSS]
Column: TSKgel GMPWXL + TSKgel GMPWXL (manufactured by Tosoh Corporation)
Eluent: 0.2M phosphate buffer / CH ₃ CN = 7/3 (volume ratio)
Temperature: 40 ° C
Flow rate: 1.0 mL / min
Sample size: 2 mg / mL
Detector: RI
Conversion standard: Polyethylene glycol

[AA / NaSS and AA / AMPS GPC conditions]
Column: TSKgel G4000PWXL + TSKgel G2500PWXL (manufactured by Tosoh Corporation)
Eluent: 0.2 M phosphate buffer / CH ₃ CN = 9/1 (volume ratio)
Temperature: 40 ° C
Flow rate: 1.0 mL / min
Sample size: 5 mg / mL
Detector: RI
Conversion standard: Polyacrylic acid Na

[Method for preparing polishing liquid composition]
Colloidal silica shown in Table 1 below, (co) polymer shown in Table 2 below, sulfuric acid (special grade manufactured by Wako Pure Chemical Industries, Ltd.), HEDP (1-hydroxyethylidene-1,1-diphosphonic acid, Sorcia Japan Diquest 2010) and hydrogen peroxide water (concentration: 35% by weight manufactured by Asahi Denka Co., Ltd.) are added to ion-exchanged water and mixed to contain colloidal silica and copolymers shown in Table 2 below. The polishing liquid composition of Examples 1-16 and Comparative Examples 1-3 was prepared. The contents of colloidal silica, sulfuric acid, HEDP, and hydrogen peroxide in the polishing composition are 4.5% by weight, 0.4% by weight, 0.1% by weight, and 0.4% by weight, respectively. The coal content was as shown in Table 2 below.

[Measuring Method of Average Particle Size, CV Value, and ΔCV Value Measured by Dynamic Light Scattering Method of Abrasive Material (Colloidal Silica)]
[Average particle size and CV value]
Colloidal silica, sulfuric acid, HEDP, and hydrogen peroxide solution shown in Table 1 below were added to ion-exchanged water, and these were mixed to prepare a standard sample. The contents of colloidal silica, sulfuric acid, HEDP, and hydrogen peroxide in the standard sample were 5% by weight, 0.4% by weight, 0.1% by weight, and 0.4% by weight, respectively. The area of the scattering intensity distribution obtained by the Cumulant method at a detection angle of 90 degrees when this standard sample is integrated 200 times with the dynamic light scattering device DLS-6500 manufactured by Otsuka Electronics Co., Ltd. according to the instructions attached by the manufacturer. The average particle size of colloidal silica was determined. The CV value was obtained by dividing the standard deviation in the scattering intensity distribution measured according to the above measurement method by the average particle diameter and multiplying by 100 to obtain the CV value (CV90).
[ΔCV value]
The CV value (CV30) of the colloidal silica particles at a detection angle of 30 degrees was measured according to the above-described measurement method, and a value obtained by subtracting CV90 from CV30 was obtained to obtain a ΔCV value. The measurement conditions for CV90 and CV30 are as follows.
(Measurement conditions for DLS-6500)
Detection angle: 90 °
Sampling time: 4 (μm)
Correlation Channel: 256 (ch)
Correlation Method: TI
Sampling temperature: 26.0 (° C.)
Detection angle: 30 °
Sampling time: 10 (μm)
Correlation Channel: 1024 (ch)
Correlation Method: TI
Sampling temperature: 26.0 (° C.)

[Measurement method of sphericity of abrasive (colloidal silica)]
A sample containing colloidal silica is observed according to the instructions attached by the manufacturer using a transmission electron microscope (TEM) trade name “JEM-2000FX” (80 kV, 1 to 50,000 times, manufactured by JEOL Ltd.) A TEM image was taken. This photograph is taken into a personal computer as image data by a scanner, and the projected area (A1) of one particle and the circumference of the particle are defined as the circumference using analysis software “WinROOF ver. 3.6” (distributor: Mitani Corporation). The area (A2) of the circle to be measured was measured, and the ratio (A1 / A2) between the projected area (A1) of the particles and the area (A2) obtained from the circumference of the particles was calculated as the true sphere ratio. In addition, the numerical value of following Table 1 calculates these average values, after calculating | requiring the sphericity rate of 100 silica particles.

[Measurement method of surface roughness of abrasive (colloidal silica)]
As shown below, specific surface area (SA2) converted from specific surface area (SA1) measured by sodium titration method and average particle diameter (S2) measured by transmission electron microscope observation was obtained, and the ratio ( SA1 / SA2) was calculated as the surface roughness.

[Method for obtaining specific surface area (SA1) of colloidal silica by sodium titration method]
1) A sample containing colloidal silica corresponding to 1.5 g as SiO ₂ is collected in a beaker and transferred to a constant temperature reaction tank (25 ° C.), and pure water is added to make the liquid volume 90 ml. The following operation is performed in a constant temperature reaction tank maintained at 25 ° C.
2) A 0.1 mol / L hydrochloric acid solution is added so that the pH is 3.6 to 3.7.
3) Add 30 g of sodium chloride, dilute to 150 ml with pure water and stir for 10 minutes.
4) A pH electrode is set, and 0.1 mol / L sodium hydroxide solution is added dropwise with stirring to adjust the pH to 4.0.
5) The sample adjusted to pH 4.0 was titrated with 0.1 mol / L sodium hydroxide solution, and the titer and pH value in the range of pH 8.7 to 9.3 were recorded at 4 points or more. A calibration curve is prepared, where X is the titer of 1 mol / L sodium hydroxide solution and Y is the pH value at that time.
6) The consumption V (ml) of the 0.1 mol / L sodium hydroxide solution required for pH 4.0 to 9.0 per 1.5 g of SiO ₂ was determined from the following formula (1), and the following [a] Specific surface area SA1 [m ² / g] is determined according to ~ [b].
[A] The value of SA1 is calculated by the following formula (2), and when the value is in the range of 80 to 350 m ² / g, the value is SA1.
[B] When the value of SA1 according to the following formula (2) exceeds 350 m ² / g, SA1 is obtained again by the following formula (3), and the value is defined as SA1.
V = (A × f × 100 × 1.5) / (W × C) (1)
SA1 = 29.0V−28 (2)
SA1 = 31.8V−28 (3)
However, the meanings of the symbols in the above formula (1) are as follows.
A: Titration amount of 0.1 mol / L sodium hydroxide solution required for pH 4.0 to 9.0 per 1.5 g of SiO ₂ (ml)
f: titer of 0.1 mol / L sodium hydroxide solution C: SiO ₂ concentration of sample (%)
W: Amount of sample collected (g)

[Method for obtaining average particle diameter (S2) and specific surface area (SA2) by observation with a transmission electron microscope]
A sample containing colloidal silica is observed according to the instructions attached by the manufacturer using a transmission electron microscope (TEM) trade name “JEM-2000FX” (80 kV, 1 to 50,000 times, manufactured by JEOL Ltd.) Take a TEM image. This photograph is taken into a personal computer as image data by a scanner, and an equivalent circle diameter of each silica particle is obtained using analysis software “WinROOF ver. 3.6” (distributor: Mitani Corp.), which is used as the particle diameter. Thus, after calculating | requiring the particle diameter of 1000 or more silica particles, the average value is computed and it is set as the average particle diameter (S2) measured by transmission electron microscope observation. Next, the value of the average particle diameter (S2) obtained above is substituted into the following formula (4) to obtain the specific surface area (SA2).
SA2 = 6000 / (S2 × ρ) (4) (ρ: density of sample)
ρ: 2.2 (in the case of colloidal silica)

[Polishing]
Using the polishing liquid compositions of Examples 1 to 16 and Comparative Examples 1 to 3 prepared as described above, the following substrate to be polished was polished under the following polishing conditions. Next, the swell of the polished substrate, nanoprotrusion defects, and scratches were measured and evaluated based on the following conditions. The results are shown in Table 2 below. The data shown in the following Table 2 is obtained by polishing four substrates for each example and each comparative example, and measuring both surfaces of each substrate to be polished. Averaged.

[Polished substrate]
As the substrate to be polished, a substrate obtained by rough polishing an aluminum alloy substrate plated with Ni-P in advance with a polishing composition containing an alumina abrasive was used. The substrate to be polished has a thickness of 1.27 mm, an outer diameter of 95 mm, an inner diameter of 25 mm, a center line average roughness Ra measured by AFM (Digital Instrument Nanoscope IIIa Multi Mode AFM), 1 nm, and a long wavelength. The amplitude of the undulation (wavelength 0.4 to 2 mm) was 2 nm, and the amplitude of the short wavelength undulation (wavelength 5 to 50 μm) was 2 nm.

[Polishing conditions]
Polishing tester: "Fast double-sided 9B polishing machine" manufactured by Speedfam
Polishing pad: Fujibo's suede type (thickness 0.9mm, average hole diameter 30μm)
Polishing liquid composition supply amount: 100 mL / min (supply rate per 1 cm ^{2 of} polishing substrate: 0.072 mL / min)
Lower platen rotation speed: 32.5 rpm
Polishing load: 7.9 kPa
Polishing time: 4 minutes

[Evaluation method of nanoprotrusion defects and scratches]
Measuring instrument: OSA6100, manufactured by Candela Instruments
Evaluation: Four substrates were randomly selected from the substrates put in the polishing tester, and each substrate was irradiated with a laser at 10,000 rpm to measure nanoprotrusion defects and scratches. The total number of scratches (lines) on each of the four substrates was divided by 8 to calculate the number of nanoprotrusion defects and scratches per substrate surface. The results are shown in Table 2 below as relative values with Comparative Example 1 taken as 100.

[Evaluation method of swell]
Three substrates were arbitrarily selected from the eight substrates after polishing and measured under the following conditions. The average value of the three measured values was calculated as the short wavelength waviness of the substrate. The results are shown in Table 2 below as relative values with Comparative Example 1 taken as 100.
Measuring machine: Thor model M4224 (manufactured by Thor Technology)
Vibrometer: Laser Doppler vibrometer (iodine stabilized He-Ne laser: 633 nm)
Measurement wavelength: 5 to 50 μm (short wavelength swell)
Measurement position: Full board rotation speed of radius 20mm to 46mm from the substrate center: 6000rpm
Gain: 16
Filter: 10kHz
Laser range: 5mm / s / V
Track pitch: 0.01mm

  As shown in Table 2, when the polishing liquid compositions of Examples 1 to 16 were used, the substrate surface waviness and nanoprotrusions could be reduced in addition to the scratches on the substrate after polishing, as compared with Comparative Examples 1 to 3. . Further, the comparison between Example 6 and Example 13 shows that the use of an abrasive having a ΔCV value of 10 or less can further reduce scratches, undulations, and nanoprotrusions on the substrate after polishing.

[Examples 17 to 24, Comparative Examples 4 to 6: Polishing of glass substrate]
The glass substrate was grind | polished on the following grinding | polishing conditions using the polishing liquid composition of Examples 17-24 and Comparative Examples 4-6 prepared as follows. Evaluation of nanoprotrusion defects and waviness was performed by the following method. The results are shown in Table 3 below. The data shown in the following Table 3 shows that after polishing 10 substrates to be polished for each example and each comparative example, 4 samples were selected at random, measured on both sides of each substrate, and a total of 8 substrates were measured. The average of surface data was used.

[Method for preparing polishing liquid composition]
Colloidal silica a (Table 1), (co) polymer shown in Table 3 below, sulfuric acid (special grade manufactured by Wako Pure Chemical Industries, Ltd.), HEDP (1-hydroxyethylidene-1,1-diphosphonic acid, Sorcia Diquest 2010) manufactured by Japan Co., Ltd. was added to ion-exchanged water, and these were mixed to prepare polishing liquid compositions of Examples 17 to 24 and Comparative Examples 4 to 6. The contents of colloidal silica, sulfuric acid, and HEDP in the polishing liquid composition are 8.0% by weight, 0.4% by weight, and 0.13% by weight, respectively, and the copolymer content is shown in Table 3 below. It was as shown in.

  The copolymer of Example 17 was produced in the same manner as the copolymer of Example 1, and each copolymer of Examples 18 to 24 was polymerized by changing the monomer ratio according to the method described above. Went. In Comparative Example 4, polystyrene sulfonic acid sodium salt (NaSS, manufactured by Tosoh Corporation) is used. In Comparative Example 5, acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer sodium salt (AA / AMPS, Toagosei Co., Ltd.) is used. Used). The polymerization ratio and weight average molecular weight of each (co) polymer are shown in Table 3 below. In addition, the weight average molecular weight was measured by the gel permeation chromatography (GPC) method of the above-mentioned measurement conditions. In Comparative Example 6, Nalauryl sulfate (Emar 0, manufactured by Kao Corporation) was used instead of the copolymer.

[Glass substrate]
As the glass substrate, an aluminosilicate glass substrate coarsely polished in advance with a polishing liquid containing ceria abrasive grains was used. The glass substrate had a thickness of 0.635 mm, an outer diameter of 65 mm, and an inner diameter of 20 mm.

[Polishing conditions]
Polishing tester: "Fast double-sided 9B polishing machine" manufactured by Speedfam
Polishing pad: Suede type (thickness 0.9mm, average hole diameter 30μm)
Polishing liquid composition supply amount: 100 mL / min (supply rate per 1 cm 2 of substrate to be polished: about 0.3 mL / min)
Lower platen rotation speed: 32.5 rpm
Polishing load: 8.4 kPa

[Evaluation method of nano protrusion defects]
The nanoprotrusion defect was performed in the same manner as described above. The values in Table 3 are relative values when Comparative Example 4 is 100.

[Evaluation method of swell]
The polishing time was set so that the weight decreased by polishing was 17 mg or more and 17 mg or less, and the waviness of the polished substrate was measured under the following conditions to obtain the value of waviness per polishing amount. The value of the swell when 17 mg was reduced by interpolating from these values was calculated. Three wavinesses were measured for each polishing time, and the average value was calculated as the waviness of the substrate. The results are shown in Table 3 below as relative values with Comparative Example 4 taken as 100.
Measuring machine: New View 5032 (manufactured by Zygo)
Lens: 2.5 times zoom: 0.5 times Measurement wavelength: 159 to 500 μm (medium wavelength swell)
Measurement position: Radius 27mm from the center of the board
Analysis software: Zygo Metro Pro (manufactured by Zygo)

  As shown in Table 3, when the polishing liquid compositions of Examples 17 to 24 were used, the waviness and nanoprotrusions on the substrate surface of the substrate after polishing could be reduced as compared with Comparative Examples 4 to 6.

  According to the present invention, for example, a magnetic disk substrate suitable for increasing the recording density can be provided.

Claims (9)

It contains an abrasive and a copolymer having a structural unit represented by the following general formula (1) and a structural unit having a sulfonic acid group, or a salt thereof, and the copolymer has a weight average molecular weight of 1000 or more and 10,000. A polishing composition for a magnetic disk substrate, which is:

[In formula (1), R ¹ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ² is a hydrogen atom, a hydroxy group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms Or it is an aryl group. ] The polishing composition for a magnetic disk substrate according to claim 1, wherein the structural unit having a sulfonic acid group is represented by the following general formula (2).

[In Formula (2), R ³ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ⁴ is an aryl group having one or more sulfonic acid groups. ] The molar ratio of the structural unit represented by the general formula (1) to the structural unit having a sulfonic acid group in all the structural units constituting the copolymer is 5/95 to 95/5. Or a polishing composition for a magnetic disk substrate according to 2. The polishing composition for a magnetic disk substrate according to any one of claims 1 to 3 , wherein the abrasive satisfies the following conditions (a) and (b).
(A) The average particle diameter measured by a dynamic light scattering method at a detection angle of 90 degrees is 1 to 40 nm,
(B) CV (100) obtained by dividing the standard deviation of the particle diameter measured at a detection angle of 30 degrees by the dynamic light scattering method by the average particle diameter measured at the detection angle of 30 degrees by the dynamic light scattering method. The coefficient of variation) (CV30) and the standard deviation of the particle diameter measured at a detection angle of 90 degrees by the dynamic light scattering method are divided by the average particle diameter measured at a detection angle of 90 degrees by the dynamic light scattering method. The difference ΔCV (ΔCV = CV30−CV90) from the CV value (CV90) multiplied by 100 is 0 to 10%. The polishing composition for a magnetic disk substrate according to any one of claims 1 to 4 , wherein the abrasive satisfies the following condition (c).
(C) The sphericity measured by observation with a transmission electron microscope is 0.75 to 1. The polishing composition for a magnetic disk substrate according to any one of claims 1 to 5 , wherein the abrasive satisfies the following condition (d).
(D) Surface roughness (SA1 /) obtained by dividing the specific surface area (SA1) measured by the sodium titration method by the specific surface area (SA2) converted from the average particle diameter (S2) measured by observation with a transmission electron microscope. The value of SA2) is 1.3 or more. The polishing composition for a magnetic disk substrate according to any one of claims 1 to 6 , wherein the magnetic disk substrate is an Ni-P plated aluminum alloy substrate. The polishing composition for a magnetic disk substrate according to any one of claims 1 to 6 , wherein the magnetic disk substrate is a glass substrate. A method for manufacturing a magnetic disk substrate, comprising a step of polishing a substrate to be polished using the polishing liquid composition according to claim 1 .