JP2007168034A - Polishing liquid composite for hard disc substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing liquid composite for a hard disc substrate containing aluminum oxide particles as abrasive grains and capable of reducing piercing of the aluminum oxide particles on a substrate in manufacturing the hard disc substrate. <P>SOLUTION: This polishing liquid composite for the hard disc substrate contains the aluminum oxide particles and water, a volume medium grain diameter of secondary particles of the aluminum oxide particles is 0.1 to 0.7 μm and the content of the particles having the grain diameter of more than 1 μm in the aluminum oxide particles is less than 0.2 wt.%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  Recent memory hard disk drives are required to have a high capacity and a small diameter, and in order to increase the recording density, the flying height of the magnetic head is reduced to reduce the unit recording area. Along with this, the surface quality required after polishing in the manufacturing process of magnetic disk substrates has become stricter year by year, and it has been required to reduce surface roughness and micro-waviness in response to the low flying height of the head. Yes. In order to satisfy such a requirement, an abrasive slurry that can reduce scratches on the substrate after polishing is known (Patent Document 1 and Patent Document 2).

In recent years, a multi-stage polishing method having two or more stages of polishing processes has been adopted from the viewpoint of achieving both surface quality improvement and productivity improvement such as smoother and less scratches. In the final polishing step of the multi-stage polishing method, that is, the final polishing step, polishing can be performed with a polishing composition for finishing using colloidal silica particles in order to satisfy the requirements of reducing surface roughness and reducing scratches. On the other hand, in the polishing before the final polishing step, from the viewpoint of productivity, abrasive grains having a relatively large particle diameter that can realize a high polishing rate, for example, aluminum oxide particles tend to be used.
JP 2000-15560 A JP 2000-458 A

  However, it has been clarified that when aluminum oxide particles are used as abrasive grains, the abrasive grains easily pierce the substrate, and this piercing hinders the improvement of the substrate quality. Specifically, if the piercing of this abrasive grain remains without being removed even in the final polishing process, it can cause a defect in the media as a texture scratch, and if this piercing is strong, it is removed in the final polishing process. Even if this is the case, it has been found that the magnetic characteristics can be reduced, that is, the signal-to-noise ratio (SNR) can be reduced. In addition, it was found that even in a perpendicular recording substrate that is not subjected to a texture treatment, the piercing of the abrasive grains causes a recording error, a decrease in magnetic characteristics, a decrease in SNR, and the like.

  Accordingly, an object of the present invention is to provide a polishing liquid composition containing aluminum oxide particles as abrasive grains, which can reduce the sticking of aluminum oxide particles to the substrate in the production of a hard disk substrate. That is.

That is, the gist of the present invention is as follows.
[1] A polishing liquid composition for a hard disk substrate comprising aluminum oxide particles and water, wherein the secondary particles of the aluminum oxide particles have a volume-median particle diameter of 0.1 to 0.7 μm and are oxidized. A polishing liquid composition for a hard disk substrate, wherein the content of particles having a particle diameter of 1 μm or more in the aluminum particles is 0.2% by weight or less, and [2] a polishing liquid composition according to the above [1]. The present invention relates to a method of manufacturing a hard disk substrate having a step of polishing a polishing substrate.

  When the polishing composition of the present invention is used, for example, for polishing before a final polishing step of a hard disk substrate, it is possible to produce a substrate having excellent surface quality with low piercing of aluminum oxide while having an economical polishing rate. The effect that it can be produced.

  In the present invention, the “piercing” of the abrasive grains refers to a state in which the abrasive grains are pushed into the substrate and remain, unlike the abrasive grains attached to the substrate. This “piercing” is a polishing liquid composition containing colloidal particles as abrasive grains, as will be described later, and after polishing the substrate surface slightly to remove the abrasive grains adhering to the substrate, the substrate surface Can be examined by observation with a dark field microscope, or observation with an atomic force microscope or a scanning electron microscope (SEM).

If there is this piercing, defects such as deep scratches on the surface occur in texturing performed in the media forming process of the hard disk substrate, or the magnetic characteristics of the completed hard disk deteriorate, that is, the signal to noise ratio (SNR). This is thought to cause a decrease in Therefore, reducing the piercing of the abrasive grains is important for obtaining an excellent hard disk substrate.
The present invention makes it possible to reduce this piercing by controlling the particle diameter of aluminum oxide particles to a specific size and reducing coarse particles of a specific size present in the abrasive grains to a specific amount or less. It was made based on the knowledge that

That is, the hard disk substrate polishing liquid composition of the present invention is a hard disk substrate polishing liquid composition comprising aluminum oxide particles and water, wherein the volume-median particle diameter of secondary particles of aluminum oxide particles ( One feature is that D ₅₀ ) is 0.1 to 0.7 μm, and the content of particles having a particle diameter of 1 μm or more in the aluminum oxide particles is 0.2% by weight or less. By polishing with the polishing composition having such characteristics, the piercing of aluminum oxide particles to the substrate can be significantly reduced. Thereby, a hard disk substrate having excellent surface quality can be provided at an economical polishing rate.

<Aluminum oxide particles>
The polishing composition of the present invention contains aluminum oxide (hereinafter sometimes referred to as alumina) particles as an abrasive. The aluminum oxide particles used in the present invention are preferably alumina having a purity of 95% or more, more preferably from the viewpoint of reducing piercing, waviness reduction, surface roughness reduction, polishing rate improvement and surface defect prevention. Is 97% or more, more preferably 99% or more of alumina. Further, α-alumina is preferable from the viewpoint of improving the polishing rate, and intermediate alumina and amorphous alumina are preferable from the viewpoint of surface properties and undulation reduction. Intermediate alumina is a general term for crystalline alumina particles other than α-alumina particles, and specifically includes γ-alumina, δ-alumina, θ-alumina, η-alumina, κ-alumina, and mixtures thereof. Can be mentioned. Among the intermediate aluminas, γ-alumina, δ-alumina, θ-alumina and mixtures thereof are preferable from the viewpoint of improving the polishing rate and reducing waviness, and more preferably γ-alumina and θ-alumina. From the viewpoint of improving the polishing rate and reducing waviness, it is preferable to use a mixture of α-alumina, intermediate alumina and / or amorphous alumina, and a mixture of α-alumina and θ-alumina. More preferred. Further, the content of α-alumina particles in the aluminum oxide particles is preferably 20% by weight or more, more preferably 30% by weight or more, further preferably 40% by weight or more, from the viewpoint of improving the polishing rate and reducing waviness. Even more preferred is weight percent or more. In the present invention, the content of α-alumina particles in the alumina oxide particles is calculated by calculating the α-alumina peak area in X-ray diffraction with the 104-plane peak area of WA-1000 (manufactured by Showa Denko KK) being 100%. To find out.

  The volume median particle diameter of the secondary particles of the aluminum oxide particles is 0.7 μm or less, preferably 0.5 μm or less, and preferably 0.4 μm or less from the viewpoints of piercing reduction, waviness reduction, and surface roughness reduction. Is more preferably 0.35 μm or less, still more preferably 0.3 μm or less, and even more preferably 0.25 μm or less. Further, the particle diameter is 0.1 μm or more, preferably 0.15 μm or more, and more preferably 0.2 μm or more from the viewpoint of improving the polishing rate. That is, the particle diameter is 0.1 to 0.7 μm, preferably 0.1 to 0.5 μm, more preferably 0.1 to 0.4 μm, still more preferably 0.15 to 0.35 μm, More preferably, it is 0.15-0.3 micrometer, More preferably, it is 0.2-0.25 micrometer. Among them, the volume-median particle diameter of the secondary particles of the α-alumina particles is preferably 0.1 to 0.7 μm from the viewpoints of reducing piercing, reducing waviness and surface roughness, and improving the polishing rate. 0.1 to 0.5 μm is more preferable, 0.1 to 0.4 μm is more preferable, 0.1 to 0.35 μm is still more preferable, 0.15 to 0.3 μm is still more preferable, 0.15 Even more preferred is -0.25 [mu] m.

  The average particle diameter of the primary particles of the aluminum oxide particles is preferably 0.005 to 0.5 μm, more preferably 0.01 to 0.4 μm, and more preferably 0.03 to 0.3 μm, from the viewpoints of reducing sticking and waviness. More preferably, 0.05 to 0.2 μm is even more preferable. Among these, the average particle diameter of the primary particles of α-alumina particles is preferably 0.05 to 0.5 μm, more preferably 0.05 to 0.4 μm, from the viewpoints of improving the polishing rate, reducing waviness, and reducing sticking. 0.05 to 0.3 μm is more preferable, and 0.07 to 0.2 μm is even more preferable.

The average particle diameter (volume basis) of the primary particles of the abrasive and the volume-median particle diameter of secondary particles of 0.1 μm or less are observed with a manipulation electron microscope (preferably 3000 to 30000 times) or transmission electron microscope The image can be obtained by observing (preferably 10,000 to 300,000 times), analyzing the image, and measuring the particle diameter. Specifically, using an enlarged photograph or the like, the maximum length of each primary particle or secondary particle is measured for at least 200 particles, and the volume of a sphere having the length as a diameter is calculated. The particle size (D ₅₀ ) at which the cumulative particle size distribution (volume basis) is 50% is defined as the average particle size of primary particles or the volume median particle size of secondary particles, respectively. Further, the volume median particle diameter of the secondary particles exceeding 0.1 μm is measured by using a laser beam diffraction method.

The specific surface area of α-alumina measured by the BET method is preferably from 0.1 to 50 m ² / g, more preferably from 1 to 40 m ² / g, still more preferably ² from the viewpoint of improving the polishing rate and reducing waviness. ~ ²⁰ m2 / g. Furthermore, the specific surface area of the intermediate alumina or amorphous alumina measured by the BET method is preferably 30 to 300 m ² / g, more preferably 50 to ²⁰⁰ m ² / g.

  The content of aluminum oxide particles in the polishing composition is preferably 0.05% by weight or more, more preferably 0.1% by weight or more, and still more preferably 0.5% by weight, from the viewpoint of improving the polishing rate and reducing waviness. % Or more, even more preferably 1% by weight or more. The content is preferably 30% by weight or less, more preferably 20% by weight or less, still more preferably 15% by weight or less, and even more preferably 10% by weight or less, from the viewpoint of improving surface quality and economy. . That is, the content of aluminum oxide particles in the polishing composition is preferably 0.05 to 30% by weight, more preferably 0.1 to 20% by weight, still more preferably 0.5 to 15% by weight, and even more preferably. Is 1 to 10% by weight.

  The content of coarse particles having a particle diameter of 1 μm or more in the aluminum oxide particles is 0.2% by weight or less, preferably 0.15% by weight or less, more preferably 0.1% by weight, from the viewpoint of reducing sticking. Hereinafter, it is more preferably 0.05% by weight or less. In addition, the content of coarse particles having a particle diameter of 3 μm or more is preferably 0.05% by weight or less, more preferably 0.04% by weight or less, still more preferably 0.03% by weight or less, from the same viewpoint. Even more preferably, it is 0.02% by weight or less, and still more preferably 0.01% by weight or less. The “coarse particles having a particle diameter of 1 μm or more” or “coarse particles having a particle diameter of 3 μm or more” includes not only primary particles but also secondary particles in which primary particles are aggregated.

  For the measurement of the content of the coarse particles in the polishing liquid composition, a number counting system (Sizing Particle Optical Sensing method) can be used. For example, the content can be determined by measuring the abrasive particle diameter using “Accusizer 780” manufactured by Particle Sizing Systems, USA, and “Coulter Counter” manufactured by Coulter, etc. it can.

  The method for controlling the content of coarse particles having a particle diameter of 1 μm or more in the aluminum oxide particles is not particularly limited, and a general dispersion or particle removal method is used during or after the production of the polishing composition. be able to. For example, in order to obtain a specific average particle size, the aluminum oxide particle slurry uniformly crushed by a wet circulating bead mill is further subjected to a sedimentation method using a stationary sedimentation method or a centrifugal separator, or a microfiltration using a filtering material. Can be produced by subjecting to a method of removing coarse particles. About the removal method of a coarse particle, you may process by a single method each, or may combine and process 2 or more types, and there is no restriction | limiting also about the process order of a combination. Further, the processing conditions and the number of processing times can be appropriately selected and used.

<Water>
The water in the polishing composition of the present invention is used as a medium, and ion exchange water, pure water, ultrapure water, or the like can be used. The content of water in the polishing composition is preferably 55 to 99% by weight, more preferably 60 to 97% by weight, and still more preferably 70 to 95% by weight, from the viewpoint of efficiently polishing an object to be polished. .

<Acid> The polishing composition of the present invention preferably further contains an acid from the viewpoint of improving the polishing rate and reducing waviness.
The acid that can be used in the present invention is an acid having a pK1 of preferably 7 or less, more preferably 5 or less, still more preferably 3 or less, and even more preferably 2 or less, from the viewpoint of improving the polishing rate and reducing waviness. Here, pK1 is the logarithm of the reciprocal of the first acid dissociation constant, when the logarithm of the reciprocal of the acid dissociation constant (25 ° C.) is expressed as pKa. The pK1 of each compound is described, for example, in Chemical Handbook 4th edition (basic edition) II, pp316 to 325 (edited by the Chemical Society of Japan).

  Specific examples of acids that can be used in the present invention are shown below. Examples of inorganic acids include monovalent mineral acids such as nitric acid, hydrochloric acid, perchloric acid, and amidosulfuric acid, and polyvalent mineral acids such as sulfuric acid, sulfurous acid, phosphoric acid, pyrophosphoric acid, polyphosphoric acid, phosphonic acid, and phosphinic acid. . Organic acids include formic acid, acetic acid, glycolic acid, lactic acid, propanoic acid, hydroxypropanoic acid, butyric acid, benzoic acid, glycine and other monocarboxylic acids, oxalic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid Acids, itaconic acid, malic acid, tartaric acid, citric acid, isocitric acid, phthalic acid, polyvalent carboxylic acids such as nitrotriacetic acid, ethylenediaminetetraacetic acid, alkylsulfonic acids such as methanesulfonic acid and paratoluenesulfonic acid, ethylphosphoric acid, butylphosphorus Examples thereof include alkylphosphoric acids such as acids, phosphonohydroxyacetic acid, hydroxytylidenediphosphonic acid, phosphonobutanetricarboxylic acid, and phosphonic acids such as ethylenediaminetetramethylenephosphonic acid. Among these, from the viewpoint of improving the polishing rate and reducing waviness, polyvalent acids are preferred, more preferred are polyvalent mineral acids, polyvalent organic carboxylic acids and polyvalent organic phosphonic acids, and even more preferred are polyvalent mineral acids and polyvalent acids. Divalent organic carboxylic acid. Here, the polyvalent acid represents an acid having two or more hydrogen atoms capable of generating hydrogen ions in the molecule. Further, nitric acid, sulfuric acid, sulfonic acid and carboxylic acid are preferable from the viewpoint of preventing surface contamination of the object to be polished.

  Although the said acid may be used independently, it is preferable to mix and use 2 or more types. In particular, when polishing a metal surface such as a Ni-P plated substrate, the metal ions of the object to be polished are eluted during polishing, the pH of the polishing composition increases, and a high polishing rate cannot be obtained. In order to reduce the pH change, it is preferable to use a combination of an acid having a pK1 of less than 2.5 and an acid having a pK1 of 2.5 or more, and an acid having a pK1 of 1.5 or less and a pK1 of 2.5 or more. A combination with an acid is more preferred. In the case where such two or more acids are contained, considering the improvement in polishing rate, reduction in waviness, and availability, the acids having a pK1 of less than 2.5 include minerals such as nitric acid, sulfuric acid, phosphoric acid, and polyphosphoric acid. It is preferable to use an acid or an organic phosphonic acid. On the other hand, as the acid having a pK1 of 2.5 or more, from the same viewpoint, organic carboxylic acids such as acetic acid, succinic acid, malic acid, tartaric acid, citric acid, and itaconic acid are preferable. Among them, succinic acid, malic acid, tartaric acid Citric acid and itaconic acid are preferable, and citric acid is more preferable. From the viewpoint of improving the polishing rate and reducing waviness, when using an organic carboxylic acid having a pK1 of 2.5 or more, it is more preferable to use a combination of an oxycarboxylic acid and a divalent or higher polyvalent carboxylic acid. . For example, examples of the oxycarboxylic acid include citric acid, malic acid, and tartaric acid, and examples of the polyvalent carboxylic acid include succinic acid, maleic acid, and itaconic acid. Accordingly, it is preferable to use one or more of these in combination, and among them, it is preferable to combine citric acid and polyvalent carboxylic acid.

  The content of the acid in the polishing composition is preferably 0.002% by weight or more, more preferably 0.005% by weight or more, and still more preferably 0.007% by weight from the viewpoint of improving the polishing rate and reducing waviness. As mentioned above, it is still more preferably 0.01% by weight or more. The content is preferably 20% by weight or less, more preferably 15% by weight or less, still more preferably 10% by weight or less, and still more preferably 5% by weight or less, from the viewpoint of surface quality and economy. That is, the acid content in the polishing composition is preferably 0.002 to 20% by weight, more preferably 0.005 to 15% by weight, still more preferably 0.007 to 10% by weight, and still more preferably. 0.01 to 5% by weight. From the viewpoint of improving the polishing rate, the weight ratio of the acid having a pK1 of less than 2.5 and the acid having a pK1 of 2.5 or more [(acid having a pK1 of less than 2.5) / (pK1 of 2.5 or more). The acid)] is preferably 9/1 to 1/9, more preferably 7/1 to 1/7, and still more preferably 5/1 to 1/5.

<Oxidizing agent>
The polishing composition of the present invention preferably contains an oxidizing agent from the viewpoint of improving the polishing rate and reducing waviness. Although the polishing mechanism is unclear, it is presumed that the oxidizing agent has acted on the object to be polished so that the polishing effect of alumina has been sufficiently exerted. Examples of the oxidizing agent that can be used in the present invention include peroxides, metal peroxo acids or salts thereof, oxygen acids or salts thereof, nitrates, sulfates, metal salts of acids, and the like. Oxidizing agents are roughly classified into inorganic oxidizing agents and organic oxidizing agents according to their structures. Specific examples of these oxidizing agents are shown below. Examples of inorganic oxidizing agents include hydrogen peroxide, and also alkali metals such as sodium peroxide, potassium peroxide, calcium peroxide, barium peroxide, magnesium peroxide, or alkaline earth metal peroxides, peroxocarbonic acid. Peroxo carbonates such as sodium and potassium peroxocarbonate, peroxosulfuric acid such as ammonium peroxodisulfate, sodium peroxodisulfate, potassium peroxodisulfate, and peroxomonosulfuric acid, peroxonitric acid such as peroxonitric acid, sodium peroxonitrate, potassium peroxonitrate, or Peroxophosphates such as salts thereof, sodium peroxophosphate, potassium peroxophosphate, ammonium peroxophosphate or salts thereof, peroxoborates such as sodium peroxoborate, potassium peroxoborate, etc. Salts, peroxochromates such as potassium peroxochromate and sodium peroxochromate, permanganates such as potassium permanganate and sodium permanganate, sodium perchlorate, potassium perchlorate, chloric acid, hypochlorite Halogenic acid such as sodium acid, sodium periodate, potassium periodate, iodic acid, sodium iodate or derivatives thereof, and inorganic acid metal salts such as iron (III) chloride and iron (III) sulfate can be used. . As the organic oxidizing agent, percarboxylic acids such as peracetic acid, performic acid and perbenzoic acid, peroxides such as t-butyl peroxide and cumene peroxide, and iron (III) citrate can be used. Among these, inorganic oxidizers are preferred when the handling properties such as polishing rate improvement, availability, and water solubility are compared. Furthermore, in view of environmental problems, an inorganic peroxide containing no heavy metal is preferable. Further, from the viewpoint of preventing surface contamination of the substrate to be polished, hydrogen peroxide, peroxosulfates, halogen acids or derivatives thereof are more preferable, and hydrogen peroxide is more preferable. These peroxides may be used alone or in combination of two or more.

  The content of the oxidizing agent in the polishing composition is preferably 0.002% by weight or more, more preferably 0.005% by weight or more, and still more preferably 0.007% by weight, from the viewpoint of improving the polishing rate and reducing waviness. As mentioned above, it is still more preferably 0.01% by weight or more. The content is preferably 20% by weight or less, more preferably 15% by weight or less, still more preferably 10% by weight or less, and still more preferably 5% by weight or less, from the viewpoint of surface quality and economy. That is, the content of the oxidizing agent in the polishing composition is preferably 0.002 to 20% by weight, more preferably 0.005 to 15% by weight, still more preferably 0.007 to 10% by weight, and still more preferably. Is 0.01 to 5% by weight.

  Further, the polishing liquid composition of the present invention may further contain other components depending on the purpose of improving the polishing rate, reducing the waviness, and other purposes. Examples of other components include metal oxide abrasive grains such as colloidal silica, fumed silica, and colloidal titanium oxide, inorganic salts, thickeners, rust preventives, and basic substances. Examples of inorganic salts include ammonium nitrate, ammonium sulfate, potassium sulfate, nickel sulfate, aluminum nitrate, aluminum sulfate, and ammonium sulfamate. The inorganic salt can be used for the purpose of improving the polishing rate, improving the roll-off, and preventing caking of the polishing composition. The other components may be used alone or in combination of two or more. The content of the other components in the polishing composition is preferably from 0.05 to 20% by weight, more preferably from 0.05 to 10% by weight, still more preferably from 0.05 to 5%, from the viewpoint of economy. 5% by weight.

  Furthermore, a disinfectant, an antibacterial agent, etc. can be mix | blended as another component as needed. The content of these bactericides and antibacterial agents in the polishing liquid composition is preferably 0.0001 to 0.1% by weight from the viewpoint of exerting the function, and from the viewpoint of influence on polishing performance and economy. More preferably, it is 0.001-0.05 weight%, More preferably, it is 0.002-0.02 weight%.

In addition, although each said component density | concentration in the polishing liquid composition of this invention is a preferable density | concentration at the time of grinding | polishing, it may be a density | concentration at the time of manufacture of this composition. Usually, the polishing composition is produced as a concentrated solution, which is often diluted before use or during use.
The polishing composition can be produced by adding and mixing the target components by any method.

  The pH of the polishing composition is preferably determined as appropriate according to the type of the object to be polished and the required quality. For example, the pH of the polishing composition is preferably less than 7 from the viewpoint of improving the polishing rate and reducing waviness, and from the viewpoint of corrosion prevention of the processing machine and the safety of the worker, more preferably 0.1 to 6, More preferably, it is 0.5-5, Still more preferably, it is 1-5, More preferably, it is 1-4, More preferably, it is 1-3. If necessary, the pH may be adjusted with inorganic acids such as nitric acid and sulfuric acid, oxycarboxylic acids, polyvalent carboxylic acids, aminopolycarboxylic acids, organic acids such as amino acids, and metal salts and ammonium salts thereof, ammonia, sodium hydroxide, water It can adjust by mix | blending basic substances, such as a potassium oxide and an amine, with a desired quantity suitably.

  By using the polishing composition of the present invention, since the piercing of abrasive grains to the substrate is remarkably reduced, a hard disk substrate suitable for increasing the recording density can be provided.

<Substrate manufacturing method>
The method for producing a hard disk substrate of the present invention includes a step of polishing the substrate to be polished using the polishing composition (hereinafter sometimes referred to as “polishing step”).
The hard disk substrate that is the substrate to be polished according to the present invention is used as a substrate for a magnetic recording medium. As a specific example of the magnetic disk substrate, a substrate obtained by plating a Ni—P alloy on an aluminum alloy is typical. However, a glass or glassy carbon is used instead of the aluminum alloy, and a substrate obtained by applying Ni—P plating to the glass or glass. Alternatively, instead of Ni-P plating, a substrate in which various metal compounds are coated by plating or vapor deposition can be used.

  In the “polishing step”, the substrate to be polished is sandwiched by a polishing disk with a porous organic polymer polishing cloth or the like attached thereto, the polishing composition of the present invention is supplied to the polishing surface, and the pressure is applied. The substrate to be polished can be polished by moving the polishing disk and the substrate to be polished while adding. Therefore, the present invention relates to a method for polishing a substrate to be polished using the polishing composition. The polishing load for polishing is preferably 1 to 20 kPa, more preferably 2 to 15 kPa, and more preferably 3 to 10 kPa from the viewpoint of reducing the piercing of the aluminum oxide particles to the substrate and the productivity (polishing rate). More preferably, 4 to 8 kPa is even more preferable. Other polishing conditions (type of polishing machine, polishing temperature, polishing rate, supply amount of polishing liquid composition, etc.) are not particularly limited.

  Further, the substrate manufacturing method of the present invention is preferably a multistage polishing method having two or more stages of polishing processes, and the above-mentioned “polishing process” is performed in a process prior to the final polishing process which is the final process. Preferably it is done. In the polishing composition used in the final polishing step, the average primary particle size of the abrasive particles from the viewpoint of the surface quality of the hard disk substrate, for example, from the viewpoint of reducing waviness, reducing the surface roughness, and reducing surface defects such as scratches. The particle diameter is preferably 0.1 μm or less, more preferably 0.08 μm or less, further preferably 0.05 μm or less, and even more preferably 0.03 μm or less. Further, from the viewpoint of improving the polishing rate, the average particle diameter is preferably 0.005 μm or more, and more preferably 0.01 μm or more.

  As abrasive particles in the polishing liquid composition used in the final polishing step, fumed silica abrasive grains, colloidal silica abrasive grains and the like can be mentioned, from the viewpoint of reducing surface roughness and reducing surface defects such as scratches. Colloidal silica abrasive is preferred. The average particle diameter of primary particles of colloidal silica abrasive grains is preferably 0.005 to 0.08 μm, more preferably 0.005 to 0.05 μm, and still more preferably 0.01 to 0.03 μm.

  In the final polishing step, when using abrasive particles having an average primary particle size of 0.005 to 0.1 μm, the surface roughness is reduced, the aluminum oxide sticking is reduced, and the productivity (polishing time) is reduced. From the viewpoint, the polishing amount is preferably 0.05 to 0.5 μm, more preferably 0.1 to 0.4 μm, and further preferably 0.2 to 0.4 μm. There are no particular limitations on the other conditions (type of polishing machine, polishing temperature, polishing rate, supply amount of polishing liquid, etc.) when performing final polishing, and the polishing load is exemplified in the above-mentioned “polishing step”. It may be the same as the polishing load. The polishing amount can be determined as in the examples described later.

  The polishing composition of the present invention is particularly effective in the polishing process, but can be similarly applied to other polishing processes such as a lapping process.

  The hard disk substrate obtained by using the substrate manufacturing method of the present invention is suitable for increasing the recording density because the piercing of aluminum particles is remarkably reduced.

1. Preparation of Polishing Liquid Composition The polishing liquid compositions of Examples 1 to 7 and Comparative Examples 1 to 4 were prepared as follows.
(1) Nitric acid was added to 50 kg of an aluminum oxide slurry containing 10% by weight of aluminum oxide particles having a purity of 99.9% shown in Table 1, and the pH was adjusted to 3.
(2) The aluminum oxide slurry obtained in (1) was transferred to a cylindrical container having a diameter of 40 cm and a height of 50 cm.
(3) The aluminum oxide slurry in the container was stirred to be uniform.
(4) The aluminum oxide slurry after stirring was allowed to stand for 3 to 10 hours.
(5) The lower layer portion of the aluminum oxide slurry after standing was left about 5 cm, and the upper layer portion was transferred to another container having the same shape.
(6) The above operations (3) to (5) were further repeated 2 to 4 times to obtain an aluminum oxide slurry from which various coarse particles were removed.
(7) Various additives were added to the aluminum oxide slurry obtained in (6) so as to have the composition shown in Table 2, and the remainder was blended as ion-exchanged water and stirred.
(8) The slurry obtained in (7) was filtered with a back filter (manufactured by Hayward Japan Co., Ltd., model number: PE1-P03H-403) to obtain a polishing composition.

2. Polishing Method 1. Thickness 1.27 mm, diameter 3.5 inch Ni-P plated aluminum alloy substrate (short wavelength undulation 3.8 nm, long wavelength undulation 1.6 nm in measurement using “Zygo NewView 5032”) The surface was polished by a double-sided processing machine under the following setting conditions of the double-sided processing machine to obtain a polished article of a Ni—P plated aluminum alloy substrate used as a substrate for a magnetic recording medium.

The setting conditions for the double-sided machine are shown below.
<Setting conditions of double-sided machine>
Double-sided processing machine: 9B type double-sided processing machine manufactured by Speed Farm Co., Ltd. Polishing load: 9.8kPa
Polishing pad: 1P polishing pad manufactured by Fujibow Co., Ltd. Average pore diameter 45 μm
Surface plate rotation speed: 50r / min
Polishing liquid composition supply flow rate: 100ml / min
Polishing time: 4min
Number of substrates loaded: 10

3. Evaluation method (1) Polishing speed Each substrate before and after polishing is weighed (measured by “BP-210S” manufactured by Sartorius), and the weight change of each substrate is obtained. The value obtained by dividing the result by the polishing time was defined as the weight reduction rate. The weight reduction rate was introduced into the following formula and converted to a polishing rate (μm / min). Using the polishing rate of Comparative Example 1 as the reference value 100, the relative value (relative rate) of the polishing rate of each experimental example was determined. The results are shown in Table 3.
Weight reduction rate (g / min) = {weight before polishing (g) −weight after polishing (g)} / polishing time (min)
Polishing rate (μm / min) = Weight reduction rate (g / min) / Substrate single side area (mm ² )
/ Ni-P plating density (g / cm ³ ) × 10 ⁶

(2) Swelling Two were arbitrarily selected from the 10 substrates after polishing, and the two surfaces of each selected substrate were measured at 2 points (total 8 points) at 180 ° under the following conditions. The average value of the eight measured values was calculated as the short wavelength waviness or long wavelength waviness of the substrate. The relative value of the waviness of the substrate of each experimental example was determined with the waviness of the substrate of Comparative Example 1 as the reference value 100. The results are shown in Table 3.
Equipment: Zygo NewView5032
Lens: 2.5x Michelson
Zoom ratio: 0.5
Remove: Cylinder
Filter: FFT Fixed Band Pass
Short wavelength swell: 50-500μm
Long wavelength swell: 0.5-5mm
Area: 4.33mm x 5.77mm

(3) Measurement of coarse particle content The content of coarse particles was measured under the following measurement conditions. The results are shown in Table 3.

・ Measuring equipment: “Accuriser 780APS” manufactured by PSS
・ Injection Loop Volume: 1mL
・ Flow Rate: 60mL / min
・ Data Collection Time: 60sec
・ Number Channels: 128

(4) Measurement of volume median particle diameter of secondary particles The volume median particle diameter (D ₅₀ ), D ₁₀ and D ₉₀ of the secondary particles were measured under the following measurement conditions. The results are shown in Tables 1 and 3.
Measuring instrument: Laser diffraction / scattering type particle size distribution analyzer LA920 manufactured by Horiba, Ltd.
・ Circulation strength: 4
・ Ultrasonic intensity: 4

(5) Content of α-alumina particles After drying 20 g of the polishing composition prepared in step 5 at 105 ° C. for 5 hours to form a powder, an X-ray diffractometer (model number: RINT2500VPC, manufactured by Rigaku Corporation) was used, with a tube voltage of 40 kW and a tube current of 120 mA. The peak area was measured and the peak area of Showa Denko WA-1000 measured in the same way was determined by relative comparison. The results are shown in Table 3.
α-alumina content (% by weight) = (peak area of test sample) ÷ (peak area of WA-1000) × 100

(6) Evaluation of abrasive sticking 2. By observing the surface of the substrate after polishing the polishing substrate obtained by polishing so that the polishing amount becomes 0.05 μm ± 0.005 μm using the following polishing liquid composition, evaluated. The composition of the polishing composition, the polishing conditions, the method for measuring the polishing amount, and the method for observing the sticking are shown below.

<Polishing liquid composition>
Colloidal silica slurry (manufactured by DuPont, average particle diameter of primary particles 0.02 μm) is 7% by weight as silica particle concentration, and HEDP (1-hydroxyethylidene-1,1-diphosphonic acid, manufactured by Solusia Japan) is an effective component. A polishing liquid composition containing 2% by weight, hydrogen peroxide (manufactured by Asahi Denka) as an effective component, 0.6% by weight, and ion-exchanged water as a residue was used.

<Polishing conditions>
・ Polishing test machine: Speed Fam Co., Ltd., double-sided 9B polishing machine ・ Polishing pad: Fujibow Co., Ltd. urethane polishing pad
Polishing liquid composition supply amount: 100 mL / min
Polishing time: 0.5 to 2 min (adjusted so that the polishing amount becomes 0.05 μm ± 0.005 μm)
-Polishing load: 7.8 kPa-Number of substrates loaded: 10

<Polishing amount>
Each substrate before and after polishing was weighed (Sartorius, “BP-210S”) and measured to determine the amount of polishing.
Weight reduction (g) = {weight before polishing (g) −weight after polishing (g)}
Polishing amount (μm) = weight reduction amount (g) / substrate one side area (mm ² ) / 2
/ Ni-P plating density (g / cm ³ ) × 10 ⁶
(The area on one side of the substrate is calculated as 6597 mm ² and Ni-P plating density 8.4 g / cm ³ )

<Pricking observation>
Using an Olympus optical microscope (main body BX60M, digital camera DP70, objective lens 100 ×, intermediate lens 2.5 ×), dark field observation (field of view 100 × 75 μm) was performed, and the number of bright spots was measured.
In the above observation, two arbitrarily selected from the 10 substrates after polishing were observed, and a total of 16 points were observed at 4 points every 90 ° at a position of 30 mm from the center on both sides of the substrate, and the average number of observed bright spots The value was defined as the number of abrasive piercings.

Based on the number of abrasive piercings observed in the piercing observation and the following evaluation criteria, the piercing of abrasive grains was evaluated. The results are shown in Table 3.
<Evaluation criteria for piercing>
5: 100 or more 4: 30-99 3: 10-29 2: 5-9 1: 0-4

  From Table 3, it turns out that the board | substrate obtained in Examples 1-7 is what the piercing of the abrasive grain to a board | substrate was reduced significantly compared with the board | substrate obtained in Comparative Examples 1-4.

  By using the polishing composition of the present invention, a hard disk substrate suitable for increasing the recording density can be provided.

Claims (6)

  A polishing liquid composition for a hard disk substrate comprising aluminum oxide particles and water, wherein the volume median particle diameter of secondary particles of the aluminum oxide particles is 0.1 to 0.7 μm, and the aluminum oxide particles A polishing composition for a hard disk substrate, wherein the content of particles having a particle diameter of 1 μm or more is 0.2% by weight or less.   2. The polishing composition for a hard disk substrate according to claim 1, wherein the aluminum oxide particles contain 20% by weight or more of α-alumina particles.   The polishing composition for a hard disk substrate according to claim 2, wherein the average particle diameter of primary particles of the α-alumina particles is 0.05 to 0.5 µm.   The polishing composition for a hard disk substrate according to any one of claims 1 to 3, wherein the polishing composition has a pH of 0.1 to 6.   A method for manufacturing a hard disk substrate, comprising a step of polishing a substrate to be polished using the polishing composition according to claim 1. 6. The hard disk according to claim 5, further comprising a step of polishing the substrate obtained in the polishing step using a polishing liquid composition containing abrasive particles having an average primary particle diameter of 0.005 to 0.1 [mu] m. A method for manufacturing a substrate.