JP2011134388A - Polishing liquid composition for magnetic disk substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing liquid composition for a magnetic disk substrate capable of reducing a scratch on a substrate surface and a nano protrusion defect after polishing and to provide a method for manufacturing the magnetic disk substrate using the same. <P>SOLUTION: In the polishing liquid composition for the magnetic disk substrate containing colloidal silica, a heterocyclic aromatic compound including two or more nitrogen atoms in a heterocycle, an acid, an oxidizing agent and water, the colloidal silica has 0 to 10% ΔCV value, 1 to 35% CV90 and 1 to 40 nm average particle diameter. <P>COPYRIGHT: (C)2011,JPO&INPIT

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, technical 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, there have been proposed polishing liquid compositions that define the particle size distribution of colloidal silica as polishing particles and polishing liquid compositions containing azoles such as benzotriazole (BTA) (for example, patents). Reference 1 and 2).

  Patent Document 1 discloses a polishing liquid composition using colloidal silica having a specific particle size distribution. According to this polishing liquid composition, the particle size distribution of the colloidal silica is reduced. It is described that the surface roughness of a memory hard disk substrate can be reduced by sharpening the thickness.

  Patent Document 2 discloses a polishing liquid composition containing azoles, and it is described that according to this polishing liquid composition, scratches on the substrate surface of a memory hard disk substrate can be reduced.

JP 2004-204151 A JP 2007-92064 A

  In order to realize a further increase in capacity of the magnetic disk drive, it is not sufficient to reduce the surface roughness and scratches with the conventional polishing composition. In addition to the conventional problems, it is necessary to reduce nano-projection defects on the substrate surface after polishing.

  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 the magnetic disk of the perpendicular magnetic recording system, the texture process required for aligning the magnetization direction in the horizontal magnetic recording system is not required, and a magnetic layer is directly formed on the polished substrate surface. For this reason, it is necessary to remove defects on the substrate surface after polishing, which have been removed in the texture process, in the polishing process, and the required characteristics for the substrate surface quality after polishing have become more severe. The conventional polishing liquid composition cannot sufficiently satisfy the required level 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 relates to a polishing composition for a magnetic disk substrate containing colloidal silica, a heterocyclic aromatic compound containing two or more nitrogen atoms in the heterocyclic ring, an acid, an oxidizing agent, and water, wherein the colloidal silica is The ΔCV value is 0 to 10%, the CV90 is 1 to 35%, and the average particle size is 1 to 40 nm, where the ΔCV value is a detection angle of 30 ° by the dynamic light scattering method. (CV30) obtained by dividing the standard deviation based on the scattering intensity distribution at 100 by the average particle diameter based on the scattering intensity distribution and multiplying by 100 (CV30), and the standard deviation based on the scattering intensity distribution at a detection angle of 90 ° by the dynamic light scattering method Is a difference value (ΔCV = CV30−CV90) obtained by dividing by the average particle diameter based on the scattering intensity distribution and multiplying by 100 (ΔCV = CV30−CV90), and the CV90 is a detection angle 90 by the dynamic light scattering method. Scattering at ° The standard deviation based on the degree distribution is divided by the average particle diameter based on the scattering intensity distribution and multiplied by 100, and the average particle diameter is based on the scattering intensity distribution at a detection angle of 90 ° by the dynamic light scattering method. The present invention relates to a polishing liquid composition for a magnetic disk substrate having an average particle diameter.

  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 specification, the “nanoprotrusion defect” refers to a defect on the surface of a substrate after polishing in a manufacturing process of a magnetic disk substrate, and 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. If the nano-projections on the substrate surface after polishing can be reduced, the flying height of the magnetic head can be further reduced, so that a smaller magnetic signal can be detected. That is, by reducing the nanoprotrusions, the unit recording area can be made smaller and the recording density per substrate can be improved.

[scratch]
In this specification, “scratch” is a fine scratch on a 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. It can be detected by NS 1500 series manufactured by Hitachi High-Technologies Corporation 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).

  In the polishing composition for a magnetic disk substrate containing colloidal silica, an acid, and an oxidizing agent, the present invention uses a heterocyclic aromatic compound containing two or more nitrogen atoms in the heterocyclic ring and a specific colloidal silica. This is based on the knowledge that not only the scratch of the substrate after polishing can be reduced, but also the nano-projection defects of the substrate after polishing can be reduced, and a magnetic disk substrate that can meet the demand for higher recording capacity can be manufactured.

  Specifically, in the heterocyclic aromatic compound containing two or more nitrogen atoms in the heterocyclic ring, the average particle size, the value of the coefficient of variation (CV value) indicating the spread of the particle size distribution, and the dynamic light scattering method Control of colloidal silica using three parameters of angle dependence (ΔCV value) of scattering intensity distribution was added. Reduction of scratches, which has been conventionally known, is promoted by the combination of the heterocyclic aromatic compound containing two or more nitrogen atoms in the heterocyclic ring and the above control of colloidal silica, and nanoprotrusion defects are significantly reduced. Was found.

  That is, the present invention, in one aspect, is a polishing composition for a magnetic disk substrate, comprising colloidal silica, a heterocyclic aromatic compound containing two or more nitrogen atoms in the heterocyclic ring, an acid, an oxidizing agent, and water. The colloidal silica has a ΔCV value of 0 to 10%, a CV90 of 1 to 35%, and an average particle size of 1 to 40 nm, where the ΔCV value is a dynamic light scattering. The value obtained by dividing the standard deviation based on the scattering intensity distribution at the detection angle of 30 ° by the method by the average particle diameter based on the scattering intensity distribution and multiplying by 100 (CV30), and the scattering at the detection angle of 90 ° by the dynamic light scattering method It is a difference value (ΔCV = CV30−CV90) from a value obtained by dividing the standard deviation based on the intensity distribution by the average particle diameter based on the scattering intensity distribution and multiplying by 100 (ΔCV = CV30−CV90). By scattering method The standard deviation based on the scattering intensity distribution at a detection angle of 90 ° is divided by the average particle size based on the scattering intensity distribution and multiplied by 100. The average particle size is a detection angle of 90 ° by the dynamic light scattering method. The present invention relates to a magnetic disk substrate polishing liquid composition (hereinafter also referred to as the polishing liquid composition of the present invention) having an average particle diameter based on the scattering intensity distribution in FIG.

  According to the polishing liquid composition of the present invention, not only the scratch can be reduced but also the nanoprojection defect on the polished substrate surface can be reduced in the polished substrate.

  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 At the same time, by using colloidal silica with a small amount of 50-200 nm silica aggregates (non-spherical silica) formed by agglomeration of primary particles of colloidal silica, scratches can be further reduced, and nanoprotrusion defects can be further reduced. It is estimated that However, the present invention is not limited to this mechanism.

[ΔCV value]
In this specification, the ΔCV value of colloidal silica is the standard deviation of the particle diameter measured based on the scattering intensity distribution at a detection angle of 30 ° (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 diameter measured based on the scattering intensity distribution of ° C (CV30) and a detection angle of 90 ° (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 ° by the dynamic light scattering method and multiplying by 100. ) (ΔCV = CV30−CV90) and a value indicating the angular dependence of the scattering intensity distribution measured by the dynamic light scattering method. Specifically, the ΔCV value can be measured by the method described in Examples.

  The present inventors have found that there is a correlation between the ΔCV value of colloidal silica and the number of scratches, and that there is a correlation between the ΔCV value of colloidal silica and the content of non-spherical silica. . A 50-200 nm silica aggregate (non-spherical silica) produced by agglomeration of primary particles of colloidal silica is a causative substance for generation of scratches and nanoprotrusions, and since such aggregates are few, scratches and nanoprotrusions are reduced. Estimated.

  That is, by paying attention to the ΔCV value, it is possible to detect the presence of non-spherical particles in the colloidal silica particle dispersion liquid that has been difficult to detect in the past, and therefore, a polishing liquid composition containing such non-spherical particles can be obtained. It is believed that use can be avoided and, as a result, 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 particle size distributions of sub-micron or less particles obtained by dynamic light scattering (DLS) or quasielastic light scattering (QLS). It means the particle size distribution of scattering intensity among (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 document)
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)

[Angle dependence of scattering intensity distribution]
In this specification, “angle dependency of the scattering intensity distribution of the particle dispersion” means scattering according to the scattering angle when the scattering intensity distribution of the particle dispersion is measured at different detection angles by the dynamic light scattering method. The magnitude of fluctuation in intensity distribution. For example, if the difference in the scattering intensity distribution between the detection angle of 30 ° and the detection angle of 90 ° is large, it can be said that the angle dependency 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 °, more preferably 0 to 60 °, still more preferably 10 to 50 °, and still more preferably 20 to 40 °. From the same viewpoint, the side or backscattering detection angle is preferably 80 to 180 °, more preferably 85 to 175 °. In the present invention, 30 ° and 90 ° are used as two detection angles for obtaining the ΔCV value.

[Colloidal silica]
The colloidal silica used in the polishing composition of the present invention may be obtained by a known production method or the like produced from an aqueous silicic acid solution. The usage form of the silica particles is preferably a slurry from the viewpoint of operability.

[ΔCV value]
The ΔCV value of the colloidal silica used in the present invention is 0 to 10%, preferably 0 to 8%, more preferably 0 to 6 from the viewpoint of reducing scratches and nanoprotrusion defects on the substrate surface after polishing. %, Even more preferably 0 to 5%. Further, from the viewpoint of improving the productivity of the polishing composition, the ΔCV value is preferably 0.001% or more, and more preferably 0.01% or more.

[CV value]
The CV value (CV90) of the colloidal silica used in the present invention is 1 to 35%, preferably 5 to 34%, more preferably from the viewpoint of reducing scratches and nanoprotrusion defects on the substrate surface after polishing. 10 to 33%. Here, the CV value is a value of 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. The CV value measured at ° (side scatter) is called CV90, and the CV value measured at a detection angle of 30 ° (forward scatter) is called CV30. Specifically, the CV value of colloidal silica can be obtained by the method described in Examples.

[Average particle size]
The “average particle size of colloidal silica” in the present invention refers to the average particle size based on the scattering intensity distribution measured by the dynamic light scattering method, and unless otherwise specified, the “average particle size of colloidal silica” The average particle diameter based on the scattering intensity distribution measured at a detection angle of 90 ° in the dynamic light scattering method. The average particle diameter of the colloidal silica in the present invention can be specifically obtained by the method described in Examples.

  The average particle diameter of the colloidal silica used in the present invention is 1 to 40 nm, preferably 5 to 37 nm, more preferably 10 to 35 nm, from the viewpoint of reducing scratches and nanoprotrusion defects on the substrate surface after polishing. is there.

Examples of the method for adjusting the ΔCV value of colloidal silica include the following methods for preventing formation 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 at the time of colloidal silica production

  In the above A), ΔCV can be reduced by removing silica aggregates of 50 to 200 nm by, for example, centrifugation or fine filter filtration (Japanese Patent Laid-Open No. 2006-102829 and Japanese Patent 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). ΔCV can be reduced by a method of centrifuging for 2 hours or more, a method of pressure filtration using a membrane filter having a pore size of 0.05 μm or 0.1 μm (for example, Advantech, Sumitomo 3M, Millipore).

The colloidal silica particles are usually 1) a mixed solution (seed solution) of less than 10% by weight of No. 3 sodium silicate and seed particles (small particle silica) in a reaction layer, and heated to 60 ° C. or higher. 2) An acidic active silicic acid aqueous solution in which No. 3 sodium silicate is passed through a cation exchange resin and an alkali (alkali metal or quaternary ammonium) are dropped to grow a spherical particle with a constant pH. 3) It can be obtained by concentrating by evaporation or ultrafiltration after aging (Japanese Patent Application 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), ΔCV 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 colloidal silica production process.

  The method for adjusting the particle size distribution of the colloidal silica is not particularly limited, but a method of giving a desired particle size distribution by adding particles as a new nucleus in the particle growth process in the production stage, or a different particle size Examples thereof include a method of mixing two or more types of silica particles having a distribution to give a desired particle size distribution.

  The content of colloidal silica in the polishing composition of the present invention 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. More preferably, it is 4% by weight or more, and from the viewpoint of further improving the flatness of the substrate surface, it is preferably 20% by weight or less, more preferably 15% by weight or less, still more preferably 13% by weight or less, even more preferably. Is 10% by weight or less. That is, the content of the silica particles is preferably 0.5 to 20% by weight, more preferably 1 to 15% by weight, still more preferably 3 to 13% by weight, and even 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, 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 an alkyl or amine substituent thereof. 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. Note that the heterocyclic aromatic compound in the polishing composition may be one kind or two or more kinds.

  The concentration ratio of colloidal silica and heterocyclic aromatic compound [concentration of colloidal silica (% by weight) / concentration of heterocyclic aromatic compound (% 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.

[acid]
The polishing composition of the present invention contains an acid from the viewpoint of improving the polishing rate. In this specification, the use of an acid includes the use of 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. Preferred acids are 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, 2-aminoethylphosphonic 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, methanehydroxy Phosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4 Organic phosphonic acids such as tricarboxylic acid and α-methylphosphonosuccinic acid, aminocarboxylic acids such as glutamic acid, picolinic acid and aspartic acid, carboxylic acids such as citric acid, tartaric acid, oxalic acid, nitroacetic acid, maleic acid and oxaloacetic acid Is mentioned. Among these, inorganic acids, carboxylic acids, and organic phosphonic acids are preferable from the viewpoint of reducing scratches, and inorganic acids and organic phosphonic acids are more preferable from the viewpoint of improving the stability of the oxidizing agent and improving the waste liquid treatment properties. Among inorganic acids, nitric acid, sulfuric acid, hydrochloric acid, and perchloric acid are more preferable, and phosphoric acid and sulfuric acid are more preferable. Among the carboxylic acids, citric acid, tartaric acid, and maleic acid are more preferable, and citric acid is more preferable. Among organic phosphonic acids, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid), and salts thereof are more preferable. More preferred are -hydroxyethylidene-1,1-diphosphonic acid and aminotri (methylenephosphonic acid). 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).

  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 in the polishing composition is preferably 0.001 to 5% by weight, more preferably 0.01 to 4% by weight, from the viewpoint of improving the polishing rate and improving the safety of the working environment. More preferably, it is 0.05-3 weight%, More preferably, it is 0.1-2.0 weight%.

[Oxidant]
The polishing composition of the present invention contains an oxidizing agent from the viewpoint of improving the polishing rate. 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, hypobromous acid, 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 reducing the surface roughness of the substrate, it is preferably 4% by weight or less, more preferably 2% by weight or less, and still more 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.

[water]
The polishing composition of the present invention contains water as a medium. Examples of the water include distilled water, ion exchange water, and ultrapure 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.

[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.

[PH of polishing composition]
The pH of the polishing composition of the present invention is preferably 3.0 or less from the viewpoint of improving the polishing rate, more preferably 2.5 or less, still more preferably 2.0 or less, and even more preferably 1.8 or less. . Further, from the viewpoint of reducing the surface roughness of the substrate and improving the safety of the work environment, 0.5 or more is preferable, more preferably 0.8 or more, still more preferably 1.0 or more, and even more preferably 1.2 or more. It is. 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 of the substrate, improving the safety of the working environment and protecting the environment, the waste liquid pH of the polishing composition is preferably 0.8 or more, more preferably 1.0 or more, and still more preferably 1. .2 or more, even more preferably 1.5 or more. 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]
The polishing liquid composition of the present invention is prepared, for example, by mixing water, colloidal silica, a heterocyclic aromatic compound, an acid, an oxidizing agent, and, if desired, other components by a known method. it can. Under the present circumstances, colloidal silica may be mixed in the state of the concentrated slurry, and may be mixed after diluting with water etc. 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.

  In another aspect, the present invention provides a method for preparing a polishing liquid composition for a magnetic disk substrate containing colloidal silica, a heterocyclic aromatic compound, an acid, an oxidizing agent, and water, wherein the ΔCV value is 0 to 10%. And a method for preparing a polishing composition for a magnetic disk substrate, comprising selecting and / or using colloidal silica having a CV90 of 1 to 35% and an average particle diameter of 1 to 40 nm. obtain. If it is the polishing composition for magnetic disk substrates using the colloidal silica, scratches and nanoprotrusion defects on the substrate surface after polishing can be reduced. Of course, the polishing composition of the present invention can also be produced by this method of preparing a polishing composition for a magnetic disk substrate.

[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 a polishing process using the polishing liquid composition of the present invention). It is a manufacturing method. Thereby, it is possible to suppress a decrease in polishing rate, and preferably provide a magnetic disk substrate in which scratches and nanoprotrusion defects on the substrate surface after polishing are reduced without significantly impairing the productivity and surface roughness of the substrate after polishing. it can. 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 from the viewpoints of reduction of scratches and nanoprotrusion defects on the substrate surface after polishing and pad life. Preferably it is 35 micrometers or less. 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 and a nanoprotrusion defect 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]
In the polishing process using the polishing liquid composition of the present invention, the supply rate of the polishing liquid composition of the present invention is preferably 1 cm ^{2 of the} substrate to be polished from the viewpoint of reducing scratches on the surface of the substrate after polishing and reducing nanoprotrusion defects. Is 0.05 to 15 mL / min, 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, further More preferably, it is 0.12-0.5 mL / min.

  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.

  The polishing liquid compositions of Examples 1 to 5 and Comparative Examples 1 to 8 were prepared as described below to polish the substrate to be polished, and scratches and nanoprojection defects of the substrate after polishing and the polishing rate were evaluated. The evaluation results are shown in Table 1 below. A method for preparing the polishing liquid composition, a method for measuring each parameter, a polishing condition (polishing method), and an evaluation method are as follows.

[Method for preparing polishing liquid composition]
Colloidal silica (silica A to G: manufactured by JGC Catalysts & Chemicals, silica HI: manufactured by DA Nanomaterials), heterocyclic aromatic compound (1H-benzotriazole (BTA)), acid (sulfuric acid), and oxidizing agent The polishing composition of Examples 1-5 and Comparative Examples 1-8 was prepared using (hydrogen peroxide). The concentration of each component of Examples 1 to 5, Comparative Examples 1 to 3 and 6 to 8 was 5% by weight of colloidal silica, 0.4% by weight of sulfuric acid, 0.4% by weight of hydrogen peroxide, and 0.1% by weight of benzotriazole. %, The balance was ion exchange water. In Comparative Example 4, 5% by weight of colloidal silica, 2% by weight of phosphoric acid, 0.62% by weight of hydrogen peroxide, 0.1% by weight of benzotriazole, 0.8% by weight of K ₂ HPO ₄ , and the remaining ion-exchanged water did. In Comparative Example 5, 5% by weight of colloidal silica, 1% of maleic acid, 0.62% by weight of hydrogen peroxide, 0.1% by weight of benzotriazole, and 0.8% of K ₂ HPO ₄ were used.

[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, 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, and hydrogen peroxide in the standard sample were 5% by weight, 0.4% by weight, and 0.4% by weight, respectively. The total area of the scattering intensity distribution obtained by the Marquardt method at a detection angle of 90 ° when this standard sample is integrated 200 times with the dynamic light scattering device DLS-6500 manufactured by the same manufacturer 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 ° 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 ° 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]
[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: 5 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 1 below as relative values with Comparative Example 1 taken as 100.

  As shown in Table 1, when the polishing liquid compositions of Examples 1 to 5 were used, compared to Comparative Examples 1 to 8, in addition to scratches on the substrate after polishing, nanoprojections on the substrate surface could be reduced.

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

Claims (4)

A polishing liquid composition for a magnetic disk substrate comprising colloidal silica, a heterocyclic aromatic compound containing two or more nitrogen atoms in the heterocyclic ring, an acid, an oxidizing agent and water,
The colloidal silica has a ΔCV value of 0 to 10%, a CV90 of 1 to 35%, and an average particle size of 1 to 40 nm.
Here, the ΔCV value is obtained by dividing the standard deviation based on the scattering intensity distribution at a detection angle of 30 ° by the dynamic light scattering method by the average particle diameter based on the scattering intensity distribution and multiplying by 100 (CV30), A difference value (ΔCV = CV30−) obtained by dividing the standard deviation based on the scattering intensity distribution at a detection angle of 90 ° by the dynamic light scattering method by the average particle diameter based on the scattering intensity distribution and multiplying by 100 (CV90). CV90)
The CV90 is a value obtained by dividing a standard deviation based on a scattering intensity distribution at a detection angle of 90 ° by a dynamic light scattering method by an average particle diameter based on the scattering intensity distribution and multiplying by 100.
The magnetic particle substrate polishing liquid composition, wherein the average particle size is an average particle size based on a scattering intensity distribution at a detection angle of 90 ° by a dynamic light scattering method. The heterocyclic aromatic compound is pyrimidine, pyrazine, pyridazine, 1,2,3-triazine, 1,2,4-triazine, 1,2,5-triazine, 1,3,5-triazine, 1,2, 4-oxadiazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole, 1,2,5-thiadiazole, 1,3,4-thiadiazole, 3-aminopyrazole, 4-amino Pyrazole, 3,5-dimethylpyrazole, pyrazole, 2-aminoimidazole, 4-aminoimidazole, 5-aminoimidazole, 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. The polishing composition for a magnetic disk substrate according to claim 1, wherein the polishing liquid composition is selected from the group consisting of 2-aminobenzotriazole, 3-aminobenzotriazole and alkyl substitution products or amine substitution products thereof. The polishing composition for a magnetic disk substrate according to claim 1 or 2, wherein the acid has a pK1 of 2 or less. A method for producing a magnetic disk substrate, comprising a step of polishing a substrate to be polished using the polishing composition for a magnetic disk substrate according to claim 1.