JP5769284B2 - 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 demands, a polishing liquid composition containing an azole such as benzotriazole (BTA) has been proposed as a polishing liquid composition capable of reducing scratches (see, for example, Patent Document 1).

  On the other hand, a copolymer having a functional group such as a carboxylic acid group or a sulfonic acid group is used as a polishing composition capable of reducing scratches in order to obtain surface characteristics expected for a magnetic disk substrate. The polishing liquid composition to contain is proposed (for example, refer patent documents 2-5).

JP 2007-92064 A JP 2001-155332 A 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 with a conventional polishing liquid composition. In addition to scratching on the surface of the substrate after polishing, the nano-surface on the surface of the substrate after polishing is not sufficient. There is a need to further reduce protrusion defects.

  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 liquid composition cannot sufficiently satisfy the small number of nanoprotrusion defects and scratches 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 realize reduction of scratches and nanoprotrusion defects on the surface of the substrate after polishing, and a method for producing a magnetic disk substrate using the same.

  The present invention contains silica particles, a heterocyclic aromatic compound, a polymer having at least one of a sulfonic acid group and a carboxylic acid group, and an acid, and the heterocyclic aromatic compound contains nitrogen in the heterocyclic ring. The present invention relates to a polishing liquid composition for a magnetic disk substrate containing two or more atoms.

  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 composition for a magnetic disk substrate of the present invention, in addition to scratches on the surface of the substrate after polishing, the magnetic disk substrate in which nano-protrusion defects on the surface of the substrate after polishing are reduced, particularly the magnetic field of the perpendicular magnetic recording system. The effect that a disk substrate can be manufactured is preferably achieved.

[Nanoprotrusion defect]
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.

[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 is a polishing composition for a magnetic disk substrate, comprising silica particles, a heterocyclic aromatic compound, a polymer having at least one of a sulfonic acid group and a carboxylic acid group, and an acid. The ring aromatic compound relates to a polishing liquid composition for a magnetic disk substrate (hereinafter, also referred to as “polishing liquid composition of the present invention”) containing two or more nitrogen atoms in a heterocyclic ring.

  According to the polishing composition of the present invention, not only the scratch can be reduced but also the effect of reducing the 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 nano-protrusion defects on the substrate surface after polishing are not clear, a heterocyclic aromatic compound forms a protective film on the substrate to be polished during polishing In addition, the polymer having at least one of a sulfonic acid group and a carboxylic acid group reduces the friction between the polishing pad and the substrate to be polished, thereby reducing the vibration between the two. It is presumed that scratches can be further reduced, and further, nanoprojection defects can be reduced. However, the present invention is not limited to this mechanism.

[Silica particles]
The polishing liquid composition of the present invention contains silica particles. Examples of the silica particles used in the polishing liquid composition of the present invention include colloidal silica, fumed silica, and surface-modified silica. From the viewpoint of reducing scratches on the substrate surface after polishing and reducing nanoprotrusion defects, colloidal silica is used. Silica is preferred. The silica particles may be commercially available, or may be obtained by a known production method that is generated from an aqueous silicic acid solution. The usage form of the silica particles is preferably a slurry from the viewpoint of operability. In addition, the silica particle used for this invention may consist of 1 type of silica particles, or may mix 2 or more types of silica particles.

The silica particles used in the present invention preferably satisfy the following conditions (a) and (b).
Condition (a): The average particle diameter (S2) measured by transmission electron microscope observation is 1 to 40 nm;
Condition (b): The standard deviation of the particle diameter measured at a detection angle of 30 degrees by the dynamic light scattering method is divided by the average particle diameter measured at the detection angle of 30 degrees by the dynamic light scattering method and multiplied by 100. The CV (coefficient of variation) value (CV30) and the standard deviation of the particle diameter measured at a detection angle of 90 degrees by the dynamic light scattering method are 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%.

[Average particle diameter of silica particles]
The average particle diameter of the silica particles is measured with two types of average particle diameters, that is, an average particle diameter (S2) measured by transmission electron microscope observation, and a detection angle of 90 degrees by dynamic light scattering. An average particle size based on the scattering intensity distribution is used. These average particle diameters are measured by the method described in the examples.

  The average particle diameter (S2) measured by transmission electron microscope observation of the silica particles used in the present invention is preferably 1 from the viewpoint of reducing scratches, surface roughness and nanoprojection defects without impairing productivity. It is -40nm, More preferably, it is 5-37nm, More preferably, it is 10-35nm.

The average particle size based on the scattering intensity distribution measured at a detection angle of 90 degrees in the dynamic light scattering method of silica particles used in the present invention reduces scratches, surface roughness and nanoprotrusion defects without sacrificing productivity. 1-40 nm is preferable, 5-37 nm is more preferable, and 10-35 nm is further more preferable.

[CV90 of silica particles]
In the present invention, the CV value of the silica particles is a coefficient of variation obtained by dividing the standard deviation based on the scattering intensity distribution by the average particle diameter and multiplying by 100 in the dynamic light scattering method. Particularly in the specification, a CV value measured at a detection angle of 90 degrees (side scatter) is referred to as CV90, and a CV value measured at a detection angle of 30 degrees (forward scatter) is referred to as CV30. Specifically, the CV value of the silica particles can be measured by the method described in Examples. The CV90 of the silica particles is preferably 1 to 35%, more preferably 5 to 34%, and further preferably 10 to 33% from the viewpoint of reducing scratches and nanoprotrusion defects on the substrate surface after polishing.

[ΔCV value of silica particles]
As described above, the ΔCV value of silica particles is obtained by dividing the standard deviation obtained by measurement based on the scattering intensity distribution at a detection angle of 30 degrees (forward scattering) by the dynamic light scattering method by the average particle diameter and multiplying by 100. The coefficient of variation (CV90) obtained by dividing the standard deviation by the average particle diameter and multiplying by 100, obtained by the measurement based on the value of the coefficient of variation (CV30) and the scattering intensity distribution at a detection angle of 90 degrees (side scatter). ) (ΔCV = CV30−CV90). Specifically, it can be measured by the method described in Examples. The ΔCV value of the silica particles is preferably 0 to 10%, more preferably 0.01 to 10%, and still more preferably 0.01 to 7% from the viewpoint of reducing scratches and nanoprotrusion defects on the substrate surface after polishing. Preferably, 0.01 to 5% is even more preferable.

  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, nanoprotrusion defects, and substrate surface waviness 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, nano-projection defects and substrate surface waviness after polishing are further reduced. However, the present invention is not limited to these estimation mechanisms.

  That is, by paying attention to the ΔCV value, it is possible to easily detect the presence of non-spherical particles in a particle dispersion sample that has been difficult to detect in the past. Therefore, a polishing liquid composition containing such non-spherical particles Can be avoided, and as a result, it is considered that the reduction of scratches and nanoprotrusions can be achieved.

Here, whether the particles in the particle dispersion sample are spherical or non-spherical is generally determined by a method using the angle dependency of the diffusion coefficient (D = Γ / q ² ) measured by the dynamic scattering method as an index (for example, Jpn. Pat. Appln. KOKAI Publication No. 10-195152). Specifically, the smaller the angle dependency shown in the graph plotting Γ / q ² with respect to the scattering vector q ^{2, the} more the average shape of the particles in the dispersion is judged to be spherical, and the angle dependency is The larger the particle size, the more the average shape of the particles in the dispersion is judged to be non-spherical. In other words, the conventional method using the angular dependence of the diffusion coefficient measured by the dynamic scattering method as an index assumes that the uniform shape of particles is dispersed throughout the system, and the particle shape, particle size, etc. It is a method of detecting and measuring. Therefore, it is difficult to detect non-spherical particles present in a part of the dispersion sample in which spherical particles are predominant.

 On the other hand, in the dynamic light scattering method, when measuring a spherical particle dispersion solution of 200 nm or less in principle, the measurement result does not depend on the detection angle because the scattering intensity distribution is almost constant regardless of the detection angle. . However, the scattering intensity distribution of dynamic light scattering of a spherical dispersion containing non-spherical particles varies greatly depending on the detection angle due to the presence of non-spherical particles, and the distribution of the scattering intensity distribution becomes broader at lower detection angles. . Therefore, the measurement result of the scattering intensity distribution of dynamic light scattering depends on the detection angle, and the ΔCV value, which is one of the indicators of “angle dependency of the scattering intensity distribution measured by the dynamic light scattering method”, is It is considered that a few non-spherical particles existing in the spherical particle dispersion solution can be measured by measuring. Note that the present invention is not limited to these mechanisms.

Scattering intensity distribution In this specification, “scattering intensity distribution” means three sub-micron particles obtained by dynamic light scattering (DLS) or quasielastic light scattering (QLS). It means the particle size distribution of the scattering intensity in the particle size distribution (scattering intensity, volume conversion, number conversion). Usually, the sub-micron particles have Brownian motion in a solvent, and the intensity of scattered light changes (fluctuates) with time when irradiated with laser light. For this fluctuation of scattered light intensity, for example, an autocorrelation function is obtained using a photon correlation method (JIS Z 8826), and a diffusion coefficient (D) indicating a Brownian motion velocity is calculated by cumulant method analysis. Furthermore, the average particle diameter (d: hydrodynamic diameter) can be obtained using the Einstein-Stokes equation. In addition to polydispersity index (PI) by cumulant method, particle size distribution analysis includes histogram method (Marquardt method), Laplace inverse transformation method (CONTIN method), non-negative least square method (NNLS method), etc. There is.

In the particle size distribution analysis of the dynamic light scattering method, the polydispersity index (PI) by the cumulant method is generally widely used. However, in the detection method that enables detection of non-spherical particles that are slightly present in the particle dispersion, the average particle size (from the particle size distribution analysis by the histogram method (Marquardt method) or the Laplace inverse transform method (CONTIN method)) It is preferable to obtain d50) and the standard deviation, calculate a CV value (Coefficient of variation: a value obtained by dividing the standard deviation by the average particle size and multiply by 100), and use the angular dependence (ΔCV value).
(Reference material)
Text of the 12th Scattering Study Group (held on November 22, 2000) Scattering Basic Course "Dynamic Light Scattering Method" (Mitsuhiro Shibayama, University of Tokyo)
Text of the 20th Scattering Study Group (held on December 4, 2008) Measurement of size distribution of nanoparticles by dynamic light scattering (Doshisha University Yasumori Mori)

Angular Dependence of Scattering Intensity Distribution In this specification, “angle dependence of scattering intensity distribution of particle dispersion” means that the scattering intensity distribution of the particle dispersion is measured at different detection angles by the dynamic light scattering method. The size of the fluctuation of the scattering intensity distribution according to the scattering angle. For example, if the difference in the scattering intensity distribution between the detection angle of 30 degrees and the detection angle of 90 degrees is large, it can be said that the angle dependence of the scattering intensity distribution of the particle dispersion is large. Therefore, in this specification, the measurement of the angle dependence of the scattered intensity distribution includes obtaining a difference (ΔCV value) between measured values based on the scattered intensity distribution measured at two different detection angles.

  As a combination of the two detection angles used in the measurement of the angle dependence of the scattering intensity distribution, a combination of forward scattering and side or back scattering is preferable from the viewpoint of improving the accuracy of detection of non-spherical particles. From the same viewpoint, the forward scattering detection angle is preferably 0 to 80 degrees, more preferably 0 to 60 degrees, further preferably 10 to 50 degrees, and still more preferably 20 to 40 degrees. From the same viewpoint, the side or backscattering detection angle is preferably 80 to 180 degrees, and more preferably 85 to 175 degrees. In the present invention, 30 degrees and 90 degrees are used as two detection angles for obtaining the ΔCV value.

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

  In the above A), the ΔCV value can be reduced by removing silica aggregates of 50 to 200 nm by, for example, centrifugation or precision filter filtration (Japanese Patent Application Laid-Open No. 2006-102829 and Japanese Patent Application Laid-Open No. 2006-136996). Specifically, a colloidal silica aqueous solution appropriately diluted so as to have a silica concentration of 20% by weight or less can be removed under conditions where 50 nm particles calculated from the Stokes equation can be removed (for example, 10,000 G or more, centrifuge tube height of about 10 cm). The ΔCV value can be reduced by a method of centrifuging for 2 hours or more, a method of pressure filtration using a membrane filter (for example, Advantech, Sumitomo 3M, Millipore) having a pore size of 0.05 μm or 0.1 μm.

The silica particles are usually 1) a mixed liquid (seed liquid) of less than 10% by weight of No. 3 sodium silicate and seed particles (small particle silica) is put in the reaction layer, heated to 60 ° C. or higher, and 2 ) 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), 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 in a known spherical silica production process.

In addition, the silica particles of the present invention preferably satisfy the following conditions (c) and (d) from the viewpoint of reducing scratches and surface roughness without impairing productivity (without causing a decrease in the polishing rate). .
Condition (c): The sphericity measured by observation with a transmission electron microscope is 0.75 to 1;
Condition (d): Surface roughness calculated from specific surface area (SA1) measured by sodium titration method and specific surface area (SA2) converted from average particle diameter (S2) measured by transmission electron microscope observation The value of (SA1 / SA2) is 1.3 or more.

[Sphericality of silica particles]
In this specification, the true sphere ratio measured by observation of a silica particle with a transmission electron microscope is a projected area (A1) of one silica particle obtained by a transmission electron microscope and a circle whose circumference is the circumference of the particle. The ratio to the area (A2), that is, the value of “A1 / A2”, preferably the value of “A1 / A2” for any 50 to 100 colloidal silicas in the polishing composition of the present invention. The average value of Specifically, the sphericity of the silica particles 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 silica particles used in the polishing composition of the present invention is preferably 0.75 to 1, and preferably 0.75 to 0. 95 is more preferable, and 0.75 to 0.85 is more preferable.

[Surface roughness of silica particles]
In this specification, the surface roughness of the silica particles is the specific surface area (SA2) converted 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 a ratio to the above, is specifically measured by the method described in the examples. Here, the specific surface area (SA1) measured by the sodium titration method is to determine the specific surface area of the silica from the consumption of the sodium hydroxide solution when the sodium hydroxide solution is titrated against the silica. It can be said that it reflects the surface area. Specifically, the specific surface area (SA1) increases as the surface of the silica 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 silica 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 larger as the silica is spherical and has more ridge-like projections on the silica surface. As shown in the figure, the smaller and smoother the ridge-like protrusions on the silica surface, the smaller the value and the value approaches 1. The surface roughness of the silica particles used in the polishing composition of the present invention is preferably 1.3 or more, from the viewpoint of reducing scratches and surface roughness without impairing productivity, and is preferably 1.3 to 2.5. Is more preferable, and 1.3 to 2.2 is more preferable.

  The sphericity, surface roughness (SA1 / SA2), and average particle size (S2) of the silica particles can be adjusted using a conventionally known method for producing silica particles. 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 silica particles is not particularly limited, but a method of giving a desired particle size distribution by adding particles that become new nuclei in the particle growth process in the production stage, Examples include a method of mixing two or more types of silica particles having different particle size distributions so as to have a desired particle size distribution.

  The content of the silica particles in the polishing 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. In addition, from the viewpoint of reducing scratches and nanoprotrusion defects on the substrate surface after polishing, 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 silica particles 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.

[Heterocyclic aromatic compounds]
The heterocyclic aromatic compound contained in the polishing liquid composition of the present invention is a heterocyclic aromatic compound containing two or more nitrogen atoms in the heterocyclic ring from the viewpoint of reducing scratches and nanoprotrusion defects of the substrate after polishing. It is preferable that it has 3 or more nitrogen atoms in the heterocyclic ring, more preferably 3 to 9, more preferably 3 to 5, and still more preferably 3 or 4.

  The heterocyclic aromatic compound contained in the polishing liquid composition of the present invention includes pyrimidine, pyrazine, pyridazine, 1,2,3-triazine, 1, from the viewpoint of reducing scratches on the substrate after polishing and reducing nanoprotrusion defects. 2,4-triazine, 1,2,5-triazine, 1,3,5-triazine, 1,2,4-oxadiazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole Azole, 1,2,5-thiadiazole, 1,3,4-thiadiazole, 3-aminopyrazole, 4-aminopyrazole, 3,5-dimethylpyrazole, pyrazole, 2-aminoimidazole, 4-aminoimidazole, 5-amino Imidazole, 2-methylimidazole, 2-ethylimidazole, imidazole, benzimidazole, 1,2,3-triazole, 4-amino-1, 2,3-triazole, 5-amino-1,2,3-triazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, 5-amino-1,2,4-triazole, 3-mercapto -1,2,4-triazole, 1H-tetrazole, 5-aminotetrazole, 1H-benzotriazole, 1H-tolyltriazole, 2-aminobenzotriazole, 3-aminobenzotriazole, or their alkyl or amine substituents 1H-benzotriazole, 1H-tolyltriazole is more preferable, and 1H-benzotriazole is more preferable. Examples of the alkyl group of the alkyl-substituted product include a lower alkyl group having 1 to 4 carbon atoms, and more specifically, a methyl group and an ethyl group. Examples of the amine-substituted product include 1- [N, N-bis (hydroxyethylene) aminomethyl] benzotriazole and 1- [N, N-bis (hydroxyethylene) aminomethyl] tolyltriazole.

  The content of the heterocyclic aromatic compound in the polishing liquid composition of the present invention is 0.01 to 10 wt% with respect to the total weight of the polishing liquid composition from the viewpoint of reducing scratches on the substrate after polishing and reducing nanoprotrusion defects. %, More preferably 0.05 to 5% by weight, still more preferably 0.1 to 1% by weight. In addition, the heterocyclic aromatic compound in the polishing composition may be one kind or two or more kinds.

  The concentration ratio of silica particles to heterocyclic aromatic compound [silica particle concentration (% by weight) / heterocyclic aromatic compound concentration (% by weight)] in the polishing liquid composition is the substrate surface after polishing. From the viewpoint of reducing scratches and nanoprotrusion defects, 2 to 100 is preferable, 5 to 50 is more preferable, and 10 to 25 is more preferable.

[Polymer having at least one of sulfonic acid group and carboxylic acid group]
The polishing liquid composition of the present invention contains a polymer having at least one of a sulfonic acid group and a carboxylic acid group. From the viewpoint of reducing scratches and nanoprotrusions, the polymer preferably has a sulfonic acid group. The polymer adsorbs to the polishing pad to reduce frictional vibration during polishing, prevents the silica aggregate from falling off from the opening of the polishing pad, and synergistic effects with the heterocyclic aromatic compound described above, It is estimated that the scratches and nanoprotrusion defects of the substrate after polishing are remarkably reduced. However, the present invention is not limited to these estimation mechanisms. Moreover, it is preferable that this polymer does not contain a double bond in the main chain, that is, the main chain is a saturated hydrocarbon chain. Compared with a (co) polymer having a double bond in the main chain, it has excellent hydrolysis resistance and has the advantage of improving the quality stability as a polishing composition.

  In the present invention, “sulfonic acid group” refers to a sulfonic acid group and / or a salt thereof, and “carboxylic acid group” refers to a carboxylic acid group and / or a salt thereof. When these groups form a salt, the counter ion is not particularly limited, and specific examples include salts with metals, ammonium, alkylammonium, and the like. Specific examples of the metal include ions of metals belonging to the periodic table (long-period type) 1A, 1B, 2A, 2B, 3A, 3B, 4A, 6A, 7A, or Group 8. Among these metals, from the viewpoint of reducing nanoscratches, ions of metals belonging to Group 1A, 3B or 8 are preferable, and ions of sodium and potassium belonging to Group 1A are more preferable. Specific examples of alkylammonium include ions such as tetramethylammonium, tetraethylammonium, and tetrabutylammonium. Among these, ammonium salts, sodium salts, and potassium salts are more preferable.

  The polymer having at least one of a sulfonic acid group and a carboxylic acid group of the present invention polymerizes a monomer having an ionic hydrophilic group such as a monomer having a sulfonic acid group or a monomer having a carboxylic acid group. It is preferable that it is obtained by this. Polymerization of these monomers may be random, block, or graft.

  Examples of the monomer having a sulfonic acid group include isoprene sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, styrene sulfonic acid, methallyl sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, isoamido Examples thereof include lensulfonic acid and naphthalenesulfonic acid. Examples of the monomer having a carboxylic acid group include itaconic acid, (meth) acrylic acid, maleic acid and the like.

  Moreover, monomers other than the above can also be used for the polymer having at least one of a sulfonic acid group and a carboxylic acid group. Examples of other monomers that can be used in the polymer of the present invention include aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, and p-methylstyrene, methyl (meth) acrylate, (meth ) Aliphatic conjugates such as (meth) acrylic acid alkyl esters such as ethyl acrylate, octyl (meth) acrylate, butadiene, isoprene, 2-chloro-1,3-butadiene, 1-chloro-1,3-butadiene Diene, vinyl cyanide compounds such as (meth) acrylonitrile, vinylphosphonic acid, methacryloyloxymethyl phosphoric acid, methacryloyloxyethyl phosphoric acid, methacryloyloxybutyl phosphoric acid, methacrylyloxyhexyl phosphoric acid, methacrylyloxyoctyllin Acid, methacryloyloxydecyl phosphate, methacryloyloxy Lauryl phosphate, metallo-yl oxy stearyl phosphoric acid, phosphonic acid compounds such as methacryloyl oxy 1,4-dimethylcyclohexyl phosphate. These monomers can be used alone or in combination of two or more.

  Preferable specific examples of the polymer having at least one of a sulfonic acid group and a carboxylic acid group include polyacrylic acid and (meth) acrylic acid / isoprenesulfone from the viewpoint of reducing scratches on the substrate surface after polishing and nanoprotrusion defects. Acid copolymer, (meth) acrylic acid / 2- (meth) acrylamide-2-methylpropanesulfonic acid copolymer, (meth) acrylic acid / isoprenesulfonic acid / 2- (meth) acrylamide-2-methylpropanesulfone Acid copolymer, (meth) acrylic acid / maleic acid copolymer, formalin condensate of styrene sulfonic acid, formalin condensate of naphthalene sulfonic acid, styrene / isoprene sulfonic acid copolymer, and the following general formula (1) And any one or more of the structural units represented by (2) and the structure represented by the following general formula (3) From the same point of view, polyacrylic acid, (meth) acrylic acid / 2- (meth) acrylamido-2-methylpropanesulfonic acid copolymer, formalin condensation of styrenesulfonic acid Product, styrene / isoprene sulfonic acid copolymer, and at least one of the structural units represented by the following general formulas (1) and (2) and the structural unit represented by the following general formula (3) A copolymer is more preferable, and a copolymer having a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (3) is even more preferable.

R ¹ in the above general formulas (1) and (2) is a hydrogen atom or a carbon number of 1 from the viewpoint of increasing the adsorption amount of the copolymer to the polishing pad and reducing scratches 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} general formula (1) is an aryl group or one or more carbon atoms from the viewpoint of increasing the adsorption amount of the copolymer to the polishing pad and reducing scratches and nanoprotrusion defects on the substrate surface after polishing. It is an aryl group which may be substituted with 1 to 4 alkyl groups, and a phenyl group or a phenyl group which may be substituted with one or more alkyl groups having 1 to 4 carbon atoms is preferable, and a phenyl group is more preferable. The alkyl group having 1 to 4 carbon atoms may have a straight chain structure or a branched chain structure. R ³ in the above general formula (2) represents a hydrogen atom, an alkali metal atom, an alkaline earth from the viewpoint of increasing the amount of adsorption of the copolymer to the polishing pad and reducing scratches and nanoprotrusion defects on the substrate surface after polishing. It is preferably a metal atom (1/2 atom), ammonium or organic ammonium, or a hydrocarbon chain having 1 to 22 carbon atoms, and the hydrocarbon chain preferably has 1 to 18 carbon atoms, more preferably 1 to 12 carbon atoms. 1-8 are more preferable, and 1-4 are still more preferable. The hydrocarbon chain may be a straight chain structure or a branched chain structure, preferably an alkyl group or an alkenyl group, and more preferably an alkyl group. The copolymer may contain two or more types of hydrophobic structural units.

  The content of the structural units represented by the above general formulas (1) and (2) in all the structural units constituting the copolymer is from the viewpoint of reducing scratches on the surface of the substrate after polishing and nanoprojection defects. 5-95 mol% is preferable, 5-70 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.

R ^{4 in the} general formula (3) is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms from the viewpoint of reducing scratches and nanoprotrusion defects on the substrate surface after polishing. 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 ^{5 in the} general formula (3) has one or more sulfonic acid groups from the viewpoint of improving the solubility of the polymer in the polishing liquid composition and reducing scratches and nanoprotrusion defects on the substrate surface after polishing. An aryl group, preferably a phenyl group having one or more sulfonic acid groups, more preferably a phenyl group having one sulfonic acid group in any of the ortho, meta, and para positions, and a sulfonic acid group in the para position More preferred is a phenyl group. The polymer having at least one of a sulfonic acid group and a carboxylic acid group may contain two or more kinds of structural units having a sulfonic acid group.

  The content of the structural unit represented by the general formula (3) in all the structural units constituting the copolymer is 5 to 95 mol from the viewpoint of reducing scratches on the surface of the substrate after polishing and reducing nanoprotrusion defects. % Is preferable, 40 to 90 mol% is more preferable, 50 to 85 mol% is more preferable, and 60 to 80 mol% is still more preferable.

  The structural unit represented by the above general formulas (1) and (2) in all the structural units constituting the polymer having at least one of a sulfonic acid group and a carboxylic acid group, and the above general formula (3) The total content of the structural units is preferably 70 to 100 mol%, more preferably 80 to 100 mol%, and even more preferably 90 to 100 mol%, from the viewpoint of reducing scratches on the substrate surface after polishing and reducing the nanoprotrusion defects. Preferably, 95-100 mol% is still more preferable.

  The molar ratio of the structural unit represented by the general formulas (1) and (2) and the structural unit represented by the general formula (3) in all the structural units constituting the copolymer of the present invention ( The mol% of the structural unit represented by the general formulas (1) and (2) / the mol% of the structural unit represented by the general formula (3)) From the viewpoint, 5/95 to 95/5 are preferable, 10/90 to 60/40 are more preferable, 15/85 to 50/50 are further preferable, and 20/80 to 40/60 are even more preferable.

[Method for producing copolymer]
A method for producing a copolymer having at least one of the structural units represented by the general formulas (1) and (2) and the structural unit represented by the general formula (3) includes: Examples thereof include a polymerization 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. One or more kinds of these polymerization initiators can be used. From the viewpoint of reducing scratches and nanoprotrusions, the initiator concentration is preferably 1 to 100 mol%, more preferably 3 to 50 mol%, and even more preferably 5 to 30 mol% with respect to the monomer. Moreover, a chain transfer agent can be used as needed. The monomer concentration during polymerization is preferably 0.5 to 90% by weight, more preferably 1.0% to 50% by weight, and further preferably 3.0 to 30% by weight from the viewpoint of reducing scratches and nanoprotrusions. preferable. The polymerization temperature is preferably 40 to 300 ° C, more preferably 50 to 250 ° C, and still more preferably 60 to 200 ° C, from the viewpoint of reducing scratches and nanoprotrusions.

From the viewpoint of reducing scratches and nanoprotrusions, when producing a copolymer, it is preferable to perform the monomer conversion ratio from the start to the end of the polymerization reaction in the range of 0.5 to 2.0, more preferably. Is in the range of 0.7 to 1.3, more preferably in the range of 0.8 to 1.2, and even more preferably in the range of 0.9 to 1.1. When the conversion ratios of the monomers are made equal, there is less bias in the composition ratio of the polymer, so that scratch and nanoprojection reduction can be further reduced. For this reason, it is preferable to perform drop polymerization. The dropping rate and dropping time are adjusted appropriately so that the conversion ratio is within the above range. Here, the conversion ratio of the monomer is a ratio of the monomer changed to a polymer, and is represented by the following formula.
Conversion rate of monomer (%) = ((amount of charged monomer) − (amount of unreacted monomer)) / (amount of charged monomer) × 100
Further, the conversion ratio is calculated using the following formula when a copolymer is produced using, for example, two types of monomers (monomers A and B).
Conversion ratio = conversion ratio of monomer A / conversion ratio of monomer B

[Weight average molecular weight of polymer]
The weight average molecular weight of the polymer having at least one of a sulfonic acid group and a carboxylic acid group is preferably 500 to 120,000 from the viewpoint of reducing scratches and nanoprotrusion defects on the substrate surface after polishing. Is more preferable, 1000 to 30,000 is more preferable, 1000 to 10,000 is still more preferable, 1500 to 8000 is still more preferable. The weight average molecular weight is a value measured by the method described in Examples using gel permeation chromatography (GPC).

  When the polymer having at least one of a sulfonic acid group and a carboxylic acid group forms a salt at least partially, the counter ion is not particularly limited, and as in the case of the hydrophilic structural unit described above, And salts with metals, ammonium, alkylammonium and the like.

  The content of the polymer having at least one of a sulfonic acid group and a carboxylic acid group in the polishing liquid composition is preferably 0.001 to 1% by weight from the viewpoint of reducing scratches and nanoprotrusion defects on the substrate surface after polishing. , More preferably 0.005 to 0.5% by weight, still more preferably 0.01 to 0.2% by weight, even more preferably 0.01 to 0.1% by weight, even more preferably 0.01 to 0%. 0.075% by weight.

  The concentration ratio of silica particles to the polymer in the polishing composition [silica particle concentration (% by weight) / polymer concentration (% by weight)] is determined by the scratches and nanoprotrusions on the substrate surface after polishing. From the viewpoint of reducing defects, 5-5000 is preferable, 10-1000 is more preferable, and 25-500 is more preferable.

  Furthermore, the concentration ratio [heterocyclic aromatic compound concentration (wt%) / polymer concentration (wt%)] of the heterocyclic aromatic compound and the polymer in the polishing liquid composition is the substrate after polishing. From the viewpoint of reducing surface scratches and nanoprotrusion defects, 1 to 100 is preferable, 2 to 50 is more preferable, and 2.5 to 25 is even more preferable.

[acid]
The polishing composition of the present invention contains an acid. In the present invention, the acid includes an acid and / or a salt thereof. The acid 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 has a pK1 of 1.5 or less from the viewpoint of reducing scratches. More preferably, it is a compound exhibiting strong acidity that cannot be expressed by pK1, more preferably 1 or less. Examples thereof include inorganic acids such as nitric acid, sulfuric acid, sulfurous acid, persulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, tripolyphosphoric acid, amidosulfuric acid, 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-phosphonobutane Organic phosphonic acids such as 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, oxalic acid, nitroacetic acid, maleic acid, Examples thereof include carboxylic acids such as oxaloacetic acid and salts thereof. Among these, from the viewpoint of reducing scratches, inorganic acids, organic phosphonic acids, and salts thereof are preferable. Among inorganic acids and salts thereof, nitric acid, sulfuric acid, hydrochloric acid, perchloric acid and salts thereof are more preferable, and sulfuric 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 admixture of two or more. 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).

  There are no particular limitations on the counter ion when these acid salts are used, 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, 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.

[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.

[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 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 3.5 or less, more preferably 3.0 or less, still more preferably 2.5 or less, and even more preferably 2.0 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 3 or less, more preferably 2.5 or less, still more preferably 2.2 or less, and even more preferably 2.0 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, silica particles, a heterocyclic aromatic compound, a (co) polymer, an acid, and, if desired, other components are mixed by a known method. Can be prepared. At this time, the silica particles 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 nanoprojection defects on the substrate surface after polishing are reduced can be preferably 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. 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. Therefore, in the polishing step using the polishing liquid composition of the present invention, the polishing load 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. It is particularly suitable for Ni-P plated aluminum alloy substrates and glass substrates such as crystallized glass and tempered glass, among which Ni-P plated aluminum alloy substrates are suitable.

  Further, according to the present invention, in addition to scratching of the substrate surface after polishing, a magnetic disk substrate with reduced nano-projection defects on the substrate surface after polishing can be provided, so that a high degree of surface smoothness is required. It can be suitably used for polishing a 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 scratches on the polished substrate surface, a magnetic disk substrate with reduced nanoprojection defects on the polished substrate surface, particularly a perpendicular magnetic recording type magnetic disk substrate is preferred. Is 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 1-31, Comparative Examples 1-6: Preparation and Polishing of Polishing Liquid Composition>
The polishing liquid composition was prepared as described below to polish the substrate to be polished, and scratches and nanoprotrusion defects of the substrate after polishing were evaluated. The evaluation results are shown in Table 3 below. The polymer used, the method for preparing the polishing composition, the method for measuring each parameter, the polishing conditions (polishing method) and the evaluation method are as follows.

[Polymer]
The polymer having at least one of a sulfonic acid group and a carboxylic acid group used in the polishing liquid composition is the following polymer A-polymer F6. The polymer and its weight average molecular weight are shown in Table 1 below. In addition, the weight average molecular weight of these polymers was measured on condition of the following.
Polymer A: acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer sodium salt (AA / AMPS, molar ratio 90/10, manufactured by Toagosei Co., Ltd.);
Polymer B: Acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer sodium salt (AA / AMPS, molar ratio 95/5, manufactured by Toagosei Co., Ltd.);
Polymer C: Styrene / styrene sulfonic acid copolymer sodium salt (St / NaSS, molar ratio 60/40, synthesized by the following method);
Polymer D1: Styrene / styrene sulfonic acid copolymer sodium salt (St / NaSS, molar ratio 50/50, synthesized by the following method);
Polymer D2: Styrene / styrene sulfonic acid copolymer sodium salt (St / NaSS, molar ratio 50/50, synthesized by the following method);
Polymer E: Styrene / styrene sulfonic acid copolymer sodium salt (St / NaSS, molar ratio 30/70, synthesized by the following method);
Polymer F1: polyacrylic acid (PAA, manufactured by Toagosei Co., Ltd.);
Polymer F2: polyacrylic acid (PAA, manufactured by Toagosei Co., Ltd.);
Polymer F3: polyacrylic acid (PAA, manufactured by Toagosei Co., Ltd.);
Polymer F4: polyacrylic acid (PAA, manufactured by Nippon Shokubai Co., Ltd.);
Polymer F5: polyacrylic acid (PAA, manufactured by Kao Corporation);
Polymer F6: polyacrylic acid (PAA, manufactured by Nippon Shokubai Co., Ltd.)

[Method for producing sodium salt of styrene / styrene sulfonic acid copolymer]
Into a 1 L four-necked flask, 180 g of isopropyl alcohol (manufactured by Kishida Chemical), 270 g of ion-exchanged water, 10 g of styrene (manufactured by Kishida Chemical), and 40 g of sodium styrenesulfonate (manufactured by Wako Pure Chemical Industries) were charged. Using 7.2 g of azobis (2-methylpropionamidine) dihydrochloride (V-50, manufactured by Wako Pure Chemical Industries, Ltd.) as a reaction initiator, the polymerization was carried out dropwise at 83 ± 2 ° C. over 2 hours, followed by aging for 2 hours. Thereafter, the solvent was removed under reduced pressure to obtain a white powder polymer E. Polymers C, D1, and D2 were polymerized by the above-described method while changing the monomer species and the monomer ratio.

[Method for measuring weight average molecular weight of polymer]
The weight average molecular weight of the polymer was measured by a gel permeation chromatography (GPC) method under the following measurement conditions. The weight average molecular weight of each polymer is as shown in Tables 1 and 3 below.

[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 (Molecular weight (Mw): 590, 3600, 30,000, 96,400, 929,000, 842,000 (Tosoh, Nishio Kogyo, chemco))

[GPC conditions for PAA and AA / AMPS]
Column: TSKgel G4000PWXL + TSKgel G2500PWXL (manufactured by Tosoh Corporation)
Guard column: TSK guard column PWXL (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 (Molecular weight (Mp): 115,000, 288,000, 4100, 1250 (manufactured by Soka Kagaku and American Polymer Standards Corp.))

[Method for preparing polishing liquid composition]
In the composition shown below, a heterocyclic aromatic compound, the above-mentioned polymer, colloidal silica (silica ac), all manufactured by JGC Catalysts & Chemicals, Inc., Table 2 below, sulfuric acid, HEDP (1-hydroxyethylidene-1,1 -Diphosphonic acid), hydrogen peroxide water (oxidant), etc. were added to ion-exchanged water, and these were mixed to prepare the polishing liquid compositions of Examples 1-31 and Comparative Examples 1-6. Specifically, the concentration of each component in the polishing composition was prepared as follows.

Examples 1-31: Heterocyclic aromatic compounds (concentrations listed in Table 3), polymer 0.05% by weight, silica particles 5% by weight, sulfuric acid 0.5% by weight, HEDP 0.1% by weight, hydrogen peroxide 0 .5 wt% (pH 1.4-1.5);
Comparative Example 1: Heterocyclic aromatic compound (concentration shown in Table 3), silica particles 5% by weight, orthophosphoric acid 2% by weight, K ₂ HPO ₄ 0.8% by weight, hydrogen peroxide 0.62% by weight (pH 2) ;
Comparative Example 2: 0.05% by weight of polymer, 10% by weight of silica particles, 2.5% by weight of EDTA-Fe (pH 8-9);
Comparative Example 3: 0.05% by weight of polymer, 5% by weight of silica particles, 2% by weight of orthophosphoric acid, 0.8% by weight of K ₂ HPO ₄ , 0.62% by weight of hydrogen peroxide (pH 2);
Comparative Example 4: 0.05 wt% polymer, 5 wt% silica particles, 0.5 wt% sulfuric acid, 0.1 wt% HEDP, 0.5 wt% hydrogen peroxide (pH 1.4-1.5);
Comparative Example 5: Heterocyclic aromatic compound (concentration shown in Table 3), silica particles 5% by weight, sulfuric acid 0.5% by weight, HEDP 0.1% by weight, hydrogen peroxide 0.5% by weight (pH 1.4-1) .5);
Comparative Example 6: 0.05 wt% polymer, 5 wt% silica particles, 0.5 wt% sulfuric acid, 0.1 wt% HEDP, 0.5 wt% hydrogen peroxide (pH 1.4-1.5)

  The physical properties (specific surface areas SA1 and SA2, average particle size S2, surface roughness, sphericity, and ΔCV value) of the silicas a to c used were measured by the following methods, and the results are shown in Table 2 below. .

[Method of obtaining specific surface area (SA1) of silica particles 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 vessel (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 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) of silica particles by transmission electron microscope observation]
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 (5) to obtain the specific surface area (SA2).
SA2 = 6000 / (S2 × ρ) (5) (ρ: density of sample)
ρ: 2.2 (Colloidal silica)

[Method for measuring surface roughness of silica particles]
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 measuring the sphericity of silica particles]
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 2 calculates these average values, after calculating | requiring the sphericity rate of 100 silica particles.

[Measuring method of average particle diameter, CV90, and ΔCV value of silica particles measured by dynamic light scattering method]
[Average particle size and CV90]
Colloidal silica, sulfuric acid, HEDP, and hydrogen peroxide water were added to ion exchange 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 5.0% by weight, 0.5% 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 the silica particles was determined. Further, the CV value (CV90) of colloidal silica at a detection angle of 90 degrees was calculated as a value 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.
[ΔCV value]
Similar to the CV90 measurement method, the CV value (CV30) of colloidal silica at a detection angle of 30 degrees was measured, and the value obtained by subtracting CV90 from CV30 was determined to be the ΔCV value of the silica particles.
(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.)

[Polishing]
Using the polishing liquid compositions of Examples 1 to 31 and Comparative Examples 1 to 6 prepared as described above, the following substrate to be polished was polished under the following polishing conditions. Next, the nanoprojection defects and scratches on the polished substrate were measured and evaluated based on the following conditions. The results are shown in Table 3 below. The data shown in the following Table 3 is obtained by polishing each of the substrates to be polished 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 50 to 400 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: 8 minutes

[Measurement method of polishing rate]
The weight of each substrate before and after polishing was measured using a weigh scale ("BP-210S" manufactured by Sartorius) to determine the weight change of each substrate, and the average value of 10 substrates was used as the weight reduction amount, which was used as the polishing time. The value obtained by dividing by was used as the weight reduction rate. This weight reduction rate was introduced into the following formula and converted into a polishing rate (μm / min).
Polishing rate (μm / min) = weight reduction rate (g / min) / substrate single-sided area (mm ² ) / Ni-P plating density (g / cm ³ ) × 10 ⁶
(Substrate single-sided area: 6597 mm ² , Ni—P plating density: calculated as 7.9 g / cm ³ )

[Evaluation method of nanoprotrusion defects and scratches]
Measuring instrument: OSA6100, manufactured by KLA Tencor
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 3 below as relative values with Comparative Example 1 taken as 100.

  As shown in Table 3 above, when the polishing liquid compositions of Examples 1 to 31 were used, in addition to scratches on the substrate after polishing, nanoprojections on the substrate surface could be reduced as compared with Comparative Examples 1 to 6.

<Examples 32-33, Comparative Example 7: Evaluation Method of Storage Test>
A polishing composition was prepared by mixing 3 g of sulfuric acid, 3 g of hydrogen peroxide, 0.5 g of copolymer, and 93.5 g of ion-exchanged water in a 300 cm ³ plastic container, and stored at 80 ° C. for 1 week. The weight average molecular weight before and after storage was measured, and the substrate to be polished was polished.

  As Example 32, a copolymer of styrene / styrene sulfonic acid copolymer sodium salt (St / NaSS, molar ratio 33/67) was used, and as Example 33, methyl methacrylate / styrene sulfonic acid copolymer sodium salt ( The copolymer of MMA / NaSS (molar ratio 43/57) was used, and CS1106 (styrene / isoprenesulfonic acid Na copolymer JSR) having a double bond in the main chain was used as Comparative Example 7. In addition, the polymers of Examples 32 and 33 were synthesized in the same manner as the preparation method of the polymer E by changing the monomer species and the monomer ratio. The substrate to be polished, the polishing conditions, the molecular weight measurement method, and the scratch and nanoprojection number measurement method were also performed in the same manner as described above. The molecular weight measurement results and the number of scratches and nanoprotrusions after polishing are shown in the following Table 4 as relative values with 100 before storage of each experimental example.

  As shown in Table 4 above, in Examples 32 and 33, there was almost no decrease in the molecular weight of the copolymer before and after storage, and the polishing results were good. On the other hand, in Comparative Example 7 using a copolymer having a double bond in the main chain, the molecular weight of the copolymer decreased after storage, and in the polishing experiment after storage, both the number of scratches and the number of nanoprotrusion defects increased. did.

<Production Examples 1 and 2: Evaluation of monomer conversion>
The amount of unreacted styrene or Na styrenesulfonate in each reaction time was measured under the following conditions. If the conversion rate of Na styrenesulfonate over time is Css, the conversion rate of styrene is Cst, and the ratio of the conversion rate of Na styrenesulfonate (Css / Cst) to the conversion rate of styrene (Cst) is 1.0 The conversion ratio is the same. When the conversion ratio is larger than 1.0, the conversion ratio of Na styrenesulfonate is higher than that of styrene. Moreover, when it is smaller than 1.0, it indicates that the conversion rate of styrene is higher than that of Na styrenesulfonate. Table 5 below shows the Css / Cst of the copolymers produced in Production Examples 1 and 2 below and the polishing evaluation results.

[Quantitative determination of unreacted styrene]
400 mg of the polymer was taken in a 10 ml volumetric flask, diluted with methyl acetate, filtered through a 0.45 μm PTFE filter, and unreacted styrene was calculated under the following GC conditions.
[GC condition]
Column: HP-FFAP size 30 m × 0.530 mm 1.00 μm (manufactured by Agilent Technologies)
Column flow rate: 1.0 mL / min
Detector: FID
Inlet temperature: 220 ° C
Sample size: 40 mg / mL
Oven temperature: 35 ° C. (10 min) → 10 ° C./min→220° C.

[Quantification method of unreacted sodium styrenesulfonate]
After taking 40 mg of polymer in a 10 ml volumetric flask and measuring up with 0.2 M phosphate buffer, unreacted sodium styrenesulfonate was calculated under the following HPLC conditions.
[HPLC conditions]
Column: Licro CART 250-4.0 RP-18 (5 μm) Merck column flow rate: 1.0 mL / min
Detection: UV210nm
Sample size: 4.0 mg / mL
Eluent: 0.2 M phosphate buffer / methanol = 60/40 vol%

Production Example 1
A 1 L four-necked flask was charged with 91 g of isopropyl alcohol (manufactured by Kishida Chemical), 137 g of ion exchange water, 10 g of styrene (manufactured by Kishida Chemical), and 40 g of sodium styrenesulfonate (manufactured by Wako Pure Chemical Industries), and the temperature was raised to 83 ° C. Then, 6.6 g of ammonium persulfate (manufactured by Wako Pure Chemical Industries, Ltd.) was added as a reaction initiator, polymerized for 2 hours, further aged for 2 hours, and then the solvent was removed under reduced pressure to obtain styrene / styrenesulfone. A sodium acid copolymer (33/67 mol%) was obtained. The weight average molecular weight of this copolymer was 16000. In Production Example 1, sampling was performed 5 minutes, 20 minutes, and 60 minutes after the ammonium persulfate was added, and the amount of unreacted monomer was measured by the method described above.

Production Example 2
A 1 L four-necked flask is charged with 230 g of isopropyl alcohol (manufactured by Kishida Chemical), 345 g of ion-exchanged water, 10 g of styrene (manufactured by Kishida Chemical), and 40 g of sodium styrenesulfonate (manufactured by Wako Pure Chemical Industries), and 6.6 g of ammonium persulfate. (Wako Pure Chemical Industries, Ltd.) was added as a reaction initiator, 70% by weight of the total reaction solution was dropped and polymerized at 65 ± 5 ° C. over 6 hours, and further aged for 2 hours, and then the solvent was removed under reduced pressure. By removing, a styrene / sodium styrenesulfonate copolymer (33/67 mol%) was obtained. The copolymer had a weight average molecular weight of 11,000. In Production Example 2, sampling was performed 5 minutes, 20 minutes, and 60 minutes after the start of dropping, and the amount of unreacted monomer was measured by the method described above.

  Polishing experiments were conducted using the copolymers of Production Examples 1 and 2. The polishing composition was the same as in Example 3 except that the copolymers of Production Examples 1 and 2 were used. The substrate to be polished, the polishing conditions, the molecular weight measurement method, and the scratch and nanoprojection number measurement method were also performed in the same manner as described above. The measurement results of the number of scratches and nanoprotrusions are shown as relative values with the above Comparative Example 1 as 100.

  As shown in Table 5 above, it was shown that the number of scratches and nanoprotrusions could be further reduced when the substrate was polished using a copolymer prepared by adjusting the monomer conversion ratio to 1.0.

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

Claims (6)

Containing silica particles, a heterocyclic aromatic compound, a polymer having at least one of a sulfonic acid group and a carboxylic acid group, and an acid,
The heterocyclic aromatic compound is pyrazine, pyridazine, 3,5-dimethylpyrazole, pyrazole, 2-methylimidazole, 2-ethylimidazole, imidazole, benzimidazole, 1,2,3-triazole, 1,2,4- Is selected from the group consisting of triazole, 1H-tetrazole, 1H-benzotriazole and 1H-tolyltriazole,
The polymer is one or more selected from the group consisting of polyacrylic acid, (meth) acrylic acid / 2- (meth) acrylamide-2-methylpropane sulfonic acid copolymer and styrene / styrene sulfonic acid copolymer. A polymer,
A polishing composition for a magnetic disk substrate , wherein the magnetic disk substrate is an Ni-P plated aluminum alloy substrate . The polymer is one or more polymers selected from the group consisting of (meth) acrylic acid / 2- (meth) acrylamide-2-methylpropanesulfonic acid copolymer and styrene / styrenesulfonic acid copolymer. The polishing composition for a magnetic disk substrate according to claim 1. The polymer, A acrylic acid / 2 - which is one or more polymers selected from the group consisting of acrylamide-2-methylpropane sulfonic acid copolymer and styrene / styrene sulfonic acid copolymer, according to claim 1 Or 3. 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 polymer has a weight average molecular weight of 1,000 to 100,000. The polishing composition for a magnetic disk substrate according to any one of claims 1 to 4, wherein the silica particles satisfy the following conditions (a) and (b).
(A) The average particle diameter (S2) measured by observation with a transmission electron microscope 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%.   A method for producing a magnetic disk substrate, comprising the step of polishing a substrate to be polished using the polishing composition for a magnetic disk substrate according to claim 1.