JP2004259421A - Polishing composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing composition capable of reducing a micro waviness on the surface of a substrate for memory hard disk to the practically sufficient degree without impairing the productivity, and also to provide a manufacturing method of the substrate. <P>SOLUTION: This polishing composition for a substrate for memory hard disk contains silica particles in a aqueous medium. In the silica particles, a standard deviation (δ) to the averaged particle size on the the number basis satisfies an inequality (1): δ≥0.3×r (wherein, r is the average particle size (nm) on the number basis, and δ is the standard deviation (nm) on the number basis), and also a cumulative volume frequency (V) in the range of the particle diameter 60 to 120 nm of the silica particle satisfies an inequality (2): V≥0.5×R and an inequality (3): V≤0.25×R+75 (wherein, R is the particle size (nm) of silica particle, and V is the cumulative volume frequency (%) from the side of small particle size of the silica particle) with respect to the particle diameter (R). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a polishing composition, a method for reducing micro-undulations on a substrate for a memory hard disk using the polishing composition, and a method for producing a substrate for a memory hard disk using the polishing composition.

  In recent years, memory hard disk drives are required to have a large capacity and a small diameter, and in order to increase a recording density, it is required to reduce a flying height of a magnetic head or to reduce a unit recording area. As a result, the surface quality required after polishing in the manufacturing process of memory hard disk substrates has become stricter year by year, and the surface roughness, average waviness, roll-off, reduction of protrusions, The size and depth of the scratches and pits allowed in response to the decrease in the unit recording area are becoming smaller.

  In response to such demands, an aluminum disk containing an abrasive mixed with a plurality of colloidal silica particles having different monomodal number particle size distributions capable of obtaining an aluminum disk substrate having a small average undulation and having few surface defects. A polishing composition for a substrate is known (Patent Document 1).

  However, such a polishing composition has a small undulation (short wavelength (50 to 50)) which is an intermediate wavelength between roughness and average undulation, which has recently been regarded as important for reducing the flying height of a magnetic head, even though the average undulation is reduced. 500 μm), which is insufficient for reducing long wavelengths (500 μm to 5 mm), and further improvement is required.

JP 2002-30274 A

  An object of the present invention is to provide a polishing composition capable of reducing micro-undulation on the surface of a memory hard disk substrate to a practically sufficient degree without impairing productivity, and a memory hard disk substrate using the polishing liquid composition. And a method for manufacturing a substrate for a memory hard disk.

That is, the gist of the present invention is:
[1] A polishing composition for a substrate for a memory hard disk comprising silica particles in an aqueous medium, wherein the silica particles are obtained by measurement by observation with a transmission electron microscope (TEM). The standard deviation (σ) based on the number with respect to the average particle diameter (r) based on the number is represented by the following formula (1):
σ ≧ 0.3 × r (1)
(In the formula, r represents the number-based average particle diameter (nm), and σ represents the number-based standard deviation (nm).)
And the cumulative volume frequency (V) of the silica particles in the range of 60 to 120 nm is based on the following formulas (2) and (3) with respect to the particle size (R):
V ≧ 0.5 × R (2)
V ≦ 0.25 × R + 75 (3)
(In the formula, R represents the particle diameter (nm) of the silica particles, and V represents the cumulative volume frequency (%) from the small particle diameter side of the silica particles.)
A polishing liquid composition that satisfies
[2] A method for reducing micro-undulations on a memory hard disk substrate, comprising a step of polishing a memory hard disk substrate using the polishing composition according to [1], and [3] the polishing according to [1]. The present invention relates to a method for manufacturing a memory hard disk substrate, which includes a step of polishing a Ni-P plated memory hard disk substrate using a liquid composition.

  ADVANTAGE OF THE INVENTION According to the polishing composition of the present invention, a disk substrate having practically sufficient smoothness with reduced surface undulations and surface defects such as micropits is efficiently obtained.

  The polishing composition of the present invention is a polishing composition for a memory hard disk substrate (hereinafter, referred to as a disk substrate), comprising an aqueous medium and specific silica particles as an abrasive.

  The silica particles used in the present invention have a number-based standard deviation (σ) with respect to the number-based average particle diameter (r) that satisfies the formula (1), and the silica particles have a particle size of 60 to 60. It has a specific particle size distribution such that the cumulative volume frequency (V) in the range of 120 nm satisfies the above formulas (2) and (3) with respect to the particle size (R). The polishing composition of the present invention has one of the major features that the silica particles are contained as an abrasive, and having such a configuration, a fine undulation on the surface of the disk substrate is practically sufficient. Can be reduced. Therefore, the surface of the disk substrate polished with the polishing composition of the present invention has excellent smoothness.

  In the present specification, “small undulations” are irregularities on the surface having a wavelength between roughness and undulation, and include short-wave undulations (50-500 μm undulation) and long-wave undulations (500 μm-5 mm undulation). are categorized.

  That is, the minute waviness becomes an index indicating the smoothness of the surface of the target object, and affects the flying height of the magnetic head. Therefore, the smaller the value of the minute waviness, the better the smoothness of the surface of the object, and the lower the flying height of the magnetic head becomes.

  In general, the minute undulation on the surface of the object is obtained as an average of each part randomly extracted from the surface of the object. On the surface of the object, the micro-undulations at individual positions are usually not uniform, but show a considerable variation. Therefore, in order to determine the minute waviness on the surface of the object, it is necessary to determine the measurement positions and the number of the measurement positions so that the population mean can be effectively estimated. Therefore, the reliability of the data largely depends on the selection of the measurement position and the number of the measurement positions. In the present invention, the minute undulation is obtained by the highly reliable measurement method.

  The details of the method for measuring minute undulations in the present invention will be described in Examples below.

  Examples of the silica particles used in the present invention include colloidal silica particles, fumed silica particles, and surface-modified silica particles. Colloidal silica particles are preferred from the viewpoint of obtaining higher smoothness of the surface of the disk substrate. The colloidal silica particles may be commercially available, or may be those obtained by, for example, a known production method of producing a silicic acid aqueous solution. The form of use of the silica particles is preferably a slurry.

  The particle size distribution of the silica particles can be determined by the following method. That is, a photograph obtained by observing the silica particles with a transmission electron microscope (TEM) manufactured by JEOL Ltd. (trade name: “JEM-2000FX”, 80 kV, 10,000 to 50,000 times) is taken into a personal computer as image data by a scanner, and analysis software “WinROOF” is used. (Distributor: Mitani Shoji Co., Ltd.), obtain the equivalent circle diameter of each individual silica particle for 1000 or more silica particle data, use that as the diameter, and use spreadsheet software “EXCEL” (manufactured by Microsoft). To obtain the number-based average particle diameter (r) and standard deviation value (σ).

In the present invention, the silica particles are such that the standard deviation value (σ) based on the number satisfies the formula (1) with respect to the average particle diameter (r) based on the number, but from the viewpoint of improving the polishing rate, Formula (4) is preferably satisfied, and formula (5) is more preferably satisfied.
σ ≧ 0.34 × r (4)
σ ≧ 0.375 × r (5)

From the viewpoint of reducing the surface roughness, it is preferable to satisfy Expression (6), and it is more preferable to satisfy Expression (7).
−0.2 × r + 25 ≧ σ (6)
−0.25 × r + 25 ≧ σ (7)

  Further, based on the particle size distribution data of the silica particles obtained by converting the particle diameter into the particle volume by the spreadsheet software “EXCEL”, the ratio of the particles having a certain particle diameter to the whole particles (% by volume) Is expressed as the cumulative frequency from the small particle diameter side, and the cumulative volume frequency (%) is obtained. By plotting the cumulative volume frequency against the particle size based on the particle size and cumulative volume frequency data of the silica particles obtained as described above, a particle size versus cumulative volume frequency graph can be obtained.

  In the present invention, in the silica particle, the cumulative volume frequency (V) in the particle diameter range of 60 to 120 nm is larger than the particle diameter (R) in the above-described formulas (2) and (3) in the graph of the particle diameter versus the cumulative volume frequency. However, from the viewpoint of improving the smoothness of the surface of the disk substrate by reducing minute waviness on the surface of the disk substrate, the cumulative volume frequency is 90% in the range of particle diameter of 105 nm or more. Those having the following particle size distribution are preferable.

Above all, from the viewpoint of being excellent in reducing scratches and reducing surface roughness, the particle size distribution of the silica particles in the particle size range of 60 to 120 nm is represented by the following formula (8):
V ≧ 0.60 × R-5 (8)
It is preferable to satisfy the following expression (9):
V ≧ 0.70 × R−10 (9)
More preferably, the formula (10):
V ≧ 0.80 × R−14 (10)
It is more preferable to satisfy the following.

In addition, from the viewpoint of being more excellent in reducing micropits, the particle size distribution of the silica particles in the particle size range of 60 to 120 nm is represented by the following formula (11)
V ≦ 0.35 × R + 65 (11)
It is preferable to satisfy the following expression (12):
V ≦ 0.45 × R + 55 (12)
It is more preferable to satisfy the following.

In the present invention, the formula (1) is an index indicating the spread of the particle size distribution of the silica particles, and the silica particles having the particle size distribution within such a range have a certain size or more of the particle size distribution. Means something.
Further, in the present invention, the formulas (2) and (3) are indices indicating the proportion of silica particles present, and the silica particles satisfying the formulas (2) and (3) in the range of particle diameter of 60 to 120 nm are: Means that the particles having a predetermined particle size are contained at a certain ratio or more.
By satisfying these equations, it is possible to reduce minute waviness to a practically sufficient level without impairing productivity.

Further, the silica particles have a particle size distribution in the range of 5 to 60 nm in terms of the expression (13) from the viewpoint of excellent reduction of carrier squeal.
V ≦ (2/3) × R + 50 (13)
Is preferably satisfied, and from the viewpoint of excellent reduction of micropits, the particle size distribution in the range of particle size of 30 to 60 nm is represented by the following formula (14):
V ≧ R-30 (14)
It is more preferable to satisfy the following.

  As the silica particles used in the present invention, as long as they have the above-mentioned particle size distribution, even if they are composed of one kind of silica particles having a specific particle size distribution, they have different particle size distributions. It may be a mixture of two or more types of silica particles. When two or more types of silica particles are used, the particle size distribution of the silica particles refers to the particle size distribution of the mixed silica particles.

  The method for adjusting the particle size distribution of the silica particles is not particularly limited.For example, when the silica particles are colloidal silica particles, the final product is added by adding particles serving as new nuclei in the growth process of the particles in the production stage. And a method of mixing two or more silica particles having different particle size distributions.

  As the abrasive, in addition to the silica particles, an abrasive generally used for polishing can also be used. Examples of the abrasive include: metals; metal or metalloid carbides, nitrides, oxides, borides; and diamond. The metal or metalloid element is derived from group 2A, 2B, 3A, 3B, 4A, 4B, 5A, 6A, 7A or 8 of the periodic table (long period type). Specific examples of the abrasive include aluminum oxide, silicon carbide, diamond, magnesium oxide, zinc oxide, titanium oxide, cerium oxide, zirconium oxide, and the like. Use of at least one of these abrasives improves the polishing rate. preferable. Among them, aluminum oxide, cerium oxide, zirconium oxide, titanium oxide and the like are suitable for polishing substrates for precision components such as substrates for magnetic recording media. Various crystal systems such as α, θ, and γ are known for aluminum oxide, but can be appropriately selected and used depending on the application.

  The average particle size of the primary particles of the abrasive other than the silica particles is 200 nm or less, and from the viewpoint of improving the polishing rate, is preferably 1 nm or more, more preferably 10 nm or more, and still more preferably 20 nm or more. From the viewpoint of reducing (Ra, Rmax) and undulation (Wa), the thickness is 200 nm or less, preferably 150 nm or less, more preferably 120 nm or less, and further preferably 100 nm or less. The average particle diameter of the primary particles is preferably 1 to 200 nm, more preferably 1 to 150 nm, further preferably 10 to 120 nm, and further preferably 20 to 100 nm. Furthermore, when the primary particles are aggregated to form secondary particles, similarly from the viewpoint of improving the polishing rate and reducing the surface roughness of the object to be polished, the average particle size of the secondary particles is , Preferably 50 to 3000 nm, more preferably 100 to 1500 nm, and still more preferably 200 to 1200 nm.

  The average particle size of the primary particles of the abrasive other than the silica particles is determined by analyzing an image observed with a scanning electron microscope (preferably 3000 to 100,000 times) and calculating the integrated particle size distribution from the small particle size side of the primary particles ( It can be determined by measuring the particle size (D50) at which the (by number) is 50%. Here, as the particle diameter of one primary particle, a biaxial average (average of a major axis and a minor axis) particle diameter is used. The average particle size of the secondary particles can be measured as a volume average particle size using a laser light diffraction method.

  The content of the silica particles in the polishing composition is preferably 0.5% by weight or more, more preferably 1% by weight or more, further preferably 3% by weight or more, and further preferably 5% by weight, from the viewpoint of improving the polishing rate. From the viewpoint of improving the surface quality and economical efficiency, preferably 20% by weight or less, more preferably 15% by weight or less, further preferably 13% by weight or less, further preferably 10% by weight or less. It is. That is, the content is preferably 0.5 to 20% by weight, more preferably 1 to 15% by weight, further preferably 3 to 13% by weight, and still more preferably 5 to 10% by weight in the polishing composition.

  In addition, the polishing liquid composition of the present invention can further improve the effect by further containing at least one selected from the group consisting of an acid, a salt thereof, and an oxidizing agent.

  The polishing composition of the present invention preferably contains an oxidizing agent from the viewpoint of further improving the polishing rate. Examples of the oxidizing agent include peroxide, permanganic acid or a salt thereof, chromic acid or a salt thereof, peroxoacid or a salt thereof, oxyacid or a salt thereof, metal salts, and sulfuric acid.

  Examples of the peroxide include hydrogen peroxide, sodium peroxide, barium peroxide, and the like; examples of permanganic acid or a salt thereof include potassium permanganate; and examples of the chromic acid or a salt thereof include a chromate metal salt and bichromium. Acid metal salts and the like; peroxoacids or salts thereof include peroxodisulfuric acid, ammonium peroxodisulfate, metal peroxodisulfate, peroxophosphoric acid, peroxosulfuric acid, sodium peroxoborate, performic acid, peracetic acid, perbenzoic acid, Phthalic acid and the like; oxygen acids or salts thereof, such as hypochlorous acid, hypobromous acid, hypoiodic acid, chloric acid, bromic acid, iodic acid, sodium hypochlorite, calcium hypochlorite; metals Examples of the salts include iron (III) chloride, iron (III) nitrate, iron (III) sulfate, iron (III) citrate, and iron (III) ammonium sulfate. Preferred oxidizing agents include hydrogen peroxide, iron (III) nitrate, peracetic acid, ammonium peroxodisulfate, iron (III) sulfate and iron (III) ammonium sulfate. In particular, hydrogen peroxide is preferable from the viewpoint that metal ions do not adhere to the substrate surface and are widely used and inexpensive. These oxidizing agents may be used alone or in combination of two or more.

  From the viewpoint of improving the polishing rate, 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, still more preferably 0.007% by weight or more, further preferably 0.01% by weight. From the viewpoint of improving surface quality by reducing surface roughness, fine undulations, reducing surface defects such as pits and scratches and improving surface quality and from the viewpoint of economy, preferably 20% by weight or less, more preferably 15% by weight. %, More preferably 10% by weight or less, more preferably 5% by weight or less. The content is preferably 0.002 to 20% by weight, more preferably 0.005 to 15% by weight, further preferably 0.007 to 10% by weight, and still more preferably 0.01 to 5% by weight in the polishing composition.

  Further, the polishing composition of the present invention preferably contains an acid and / or a salt thereof from the viewpoint of further increasing the polishing rate. As the acid and / or the salt thereof, a compound having a pK1 of 2 or less is preferable, and a compound having a pK1 of 1.5 or less is preferable, more preferably 1 or less, and still more preferably pK1 from the viewpoint of reducing minute scratches. A compound exhibiting such a strong acidity that it cannot be expressed by is desirable. Examples thereof include inorganic acids such as nitric acid, sulfuric acid, sulfurous acid, persulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, tripolyphosphoric acid, amidosulfuric acid, and salts thereof, and 2-aminoethylphosphonic acid. Acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1, 1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid , Methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane- , 3,4-tricarboxylic acid, organic phosphonic acids such as α-methylphosphonosuccinic acid and salts thereof, aminocarboxylic acids and salts thereof such as glutamic acid, picolinic acid and aspartic acid, oxalic acid, nitroacetic acid, maleic acid, oxalo Examples thereof include carboxylic acids such as acetic acid and salts thereof. Above all, from the viewpoint of reducing minute scratches, inorganic acids, organic phosphonic acids and salts thereof are preferable. Further, among inorganic acids and salts thereof, nitric acid, sulfuric acid, hydrochloric acid, perchloric acid and salts thereof are more preferable. Among organic phosphonic acids and salts thereof, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid) and salts thereof are more preferable. preferable. These acids and salts thereof may be used alone or in combination of two or more. Here, pK1 is usually the logarithm of the reciprocal of the acid dissociation constant (25 ° C.) of the organic compound or the inorganic compound, and pKa is the logarithm of the reciprocal of the first acid dissociation constant. The pK1 of each compound is described in, for example, Revised Fourth Edition Chemical Handbook (Basic Edition) II, pp 316-325 (Chemical Society of Japan), and the like. In the present invention, it is more preferable to use an acid having a pK1 of 2 or less and / or a salt thereof, from the viewpoint of reducing minute scratches and improving the polishing rate.

  The salts of these acids are not particularly limited, and specific examples include salts with metals, ammonium, alkylammonium, organic amines, and the like. Specific examples of metals include metals belonging to Group 1A, 1B, 2A, 2B, 3A, 3B, 4A, 6A, 7A, or 8 of the Periodic Table (Long Period Type). Among these, a salt with a metal or ammonium belonging to Group 1A is preferable from the viewpoint of reducing minute scratches.

  The content of the acid and its salt in the polishing composition is preferably 0.0001 to 5% by weight, more preferably 0.0003 to 4% by weight, from the viewpoint of exhibiting a sufficient polishing rate and improving the surface quality. And more preferably 0.001 to 3% by weight, more preferably 0.0025 to 2.5% by weight.

  As the aqueous medium in the polishing composition of the present invention, for example, distilled water, ion-exchanged water, ultrapure water and the like are used. The content thereof is preferably 55% by weight or more, more preferably 67% by weight or more, further preferably 75% by weight or more, further preferably 84% by weight, from the viewpoint of efficiently polishing the object to be polished. %, More preferably not more than 99.4979% by weight, more preferably not more than 98.9947% by weight, still more preferably not more than 96.992% by weight, further preferably not more than 94.9875% by weight. The content is preferably 55 to 99.4997% by weight, more preferably 67 to 98.9947% by weight, further preferably 75 to 96.992% by weight, further preferably 84 to 94.9875% by weight.

  The concentration of each component in the polishing composition may be either the concentration at the time of manufacturing the composition or the concentration at the time of use. Usually, a polishing liquid composition is produced as a concentrated liquid, which is often diluted at the time of use.

  Further, other components can be added to the polishing composition of the present invention as needed. Examples of the other components include a thickener, a dispersant, a rust inhibitor, a basic substance, and a surfactant.

  The polishing composition of the present invention can be prepared by mixing the above-mentioned abrasive and aqueous medium, and if desired, an oxidizing agent, an acid and / or a salt thereof, and other components, by a known method.

  It is preferable that the pH of the polishing composition of the present invention is appropriately determined according to the type of the workpiece and the required performance. The pH of the polishing composition is not necessarily limited depending on the material of the object to be polished, but generally, the pH of a metal material is acidic from the viewpoint of improving the polishing rate, and is preferably less than 7, more preferably 6 or less, furthermore It is preferably 5 or less, more preferably 4 or less. Further, from the viewpoint of the effect on the human body and the corrosiveness of the machine, the pH is preferably 1 or more, more preferably 1.1 or more, further preferably 1.2 or more, and further preferably 1.3 or more. In particular, in the case of a precision component substrate mainly made of a metal such as an aluminum alloy substrate plated with nickel-phosphorus (Ni-P), the pH is preferably acidic, and the pH is preferably 4.5 from the viewpoint of improving the polishing rate. The following is more preferred, and still more preferably 4 or less, still more preferably 3.5 or less, and still more preferably 3 or less. Therefore, the pH may be set in accordance with the purpose to be emphasized. However, in the case of a precision component substrate for a metal such as an Ni-P plated aluminum alloy substrate, the pH is set to 1 based on the above viewpoints. To 4.5, more preferably 1.1 to 4, further preferably 1.2 to 3.5, and still more preferably 1.3 to 3. The pH is adjusted by appropriately mixing inorganic acids such as nitric acid and sulfuric acid, organic acids such as oxalic acid, ammonium salts, aqueous ammonia, potassium hydroxide, sodium hydroxide, and basic substances such as amines in desired amounts. Can be.

  Examples of the method for reducing micro-undulations of the disk substrate of the present invention include a method of using the polishing composition of the present invention when polishing a substrate to be polished such as a memory hard disk substrate. As a method for polishing the substrate to be polished, a polishing composition is prepared by using the polishing composition of the present invention or by mixing the respective components so as to have the composition of the polishing composition of the present invention. The method includes a step of polishing a polished substrate. In particular, a substrate for precision parts such as a substrate for a memory hard disk can be suitably manufactured. In addition, the polishing composition of the present invention can exhibit a high polishing rate by remarkably reducing minute waviness of a disk substrate.

  The material of the object to be polished by the polishing composition of the present invention is, for example, a metal or semimetal such as silicon, aluminum, nickel, tungsten, copper, tantalum, titanium, and alloys thereof, and glass, glassy carbon. , A glassy substance such as amorphous carbon, a ceramic material such as alumina, silicon dioxide, silicon nitride, tantalum nitride, and titanium carbide; and a resin such as a polyimide resin. Among these, metals such as aluminum, nickel, tungsten, and copper and alloys containing these metals as main components are preferably polished objects, and for example, an Ni-P plated aluminum alloy substrate is more preferable.

  The step of polishing the disk substrate by the method for reducing minute waviness of the disk substrate of the present invention can be suitably performed using, for example, a known polishing machine. For example, a non-woven organic polymer polishing cloth or the like, preferably, a disk substrate is sandwiched between polishing disks to which a polyurethane polishing cloth is attached, and the polishing composition is flowed at a rate of 1 to 1 per disk substrate having a diameter of 95 mm. It is supplied to the surface to be polished at a rate of 30 mL / min, preferably 3 to 20 mL / min, and the load is applied while applying a constant pressure of usually 2.9 to 14.7 kPa, preferably 4.9 to 10.8 kPa. The polishing plate or the disk substrate is adjusted so that the relative speed between the platen or lower platen and the disk substrate is generally 0.1 to 2 m / sec, preferably 0.3 to 1 m / sec at the central portion of the platen. It is performed by polishing by moving.

  According to such a method for reducing micro-undulations on the disk substrate, the micro-undulations on the surface of the disk substrate are effectively reduced without impairing productivity, and furthermore, surface defects such as micropits are also reduced. Sufficient smoothness of the surface of the disk substrate can be obtained.

  Further, as one embodiment of the present invention, a method for producing a disk substrate, which includes a step of polishing a substrate to be polished with the polishing liquid composition of the present invention, in particular, using a polishing liquid composition of the present invention to form There is provided a method of manufacturing a disk substrate, comprising a step of polishing a plated disk substrate.

  The method for producing the Ni-P plated disk substrate of the present invention (hereinafter referred to as the disk substrate producing method) includes a step of polishing the substrate using the polishing composition of the present invention. Is preferably performed in the second and subsequent steps among a plurality of polishing steps, and is more preferably performed in the final polishing step. For example, by using a polishing slurry containing a known abrasive such as alumina abrasive grains, the first polishing step or the second polishing step causes short-wave undulations of 0.4 to 0.6 nm and long-wave undulations as minute undulations. The disk substrate (for example, an Ni-P plated aluminum alloy substrate) having a thickness of 0.35 to 0.5 nm is further polished by a polishing step using the polishing composition of the present invention. The polishing step using the polishing composition of the present invention may be performed, for example, in the same manner as the polishing step in the method for reducing minute waviness of the disk substrate.

  In the method for manufacturing a disk substrate of the present invention, a polishing process including only two steps is used to manufacture a disk substrate having a short wavelength undulation of 0.12 nm or less and a long wavelength undulation of 0.25 nm or less as minute undulations. If desired, the second step is preferably a step of polishing a disk substrate using the polishing composition of the present invention.

  ADVANTAGE OF THE INVENTION According to the manufacturing method of the disk substrate of this invention, the micro waviness is reduced and the Ni-P plating disk substrate which has excellent surface smoothness can be manufactured efficiently.

(Polished object)
Ni-P plated with a thickness of 1.27 mm and a diameter of 95 mm was rough-polished in advance with a polishing slurry containing alumina abrasive grains and finely undulated with 0.5 nm short-wave undulation and 0.45 nm long-wave undulation. Using an aluminum alloy substrate as an object to be polished, polishing evaluation was performed on the substrate using the polishing composition obtained in the following Examples and Comparative Examples.

Examples 1 to 6 and Comparative Examples 1 to 3
Add and mix colloidal silica (silica A to H), hydrogen peroxide (H ₂ O ₂ ), HEDP (1-hydroxyethylidene-1,1-diphosphonic acid) and the remaining water (ion-exchanged water) shown in Table 1. As a result, a polishing composition having the composition shown in Table 1 was prepared. The order of mixing is as follows. A 35 wt% aqueous solution of hydrogen peroxide is added to an aqueous solution obtained by diluting HEDP in water, then the remaining components are mixed, and finally, the colloidal silica slurry is mixed while stirring so as not to gel, and the polishing liquid is mixed. A composition was prepared.

In the table, silica A is "Cataloid SI-30" (manufactured by Catalyst Chemical Industry Co., Ltd.),
Silica B is "Cataloid SI-40" (manufactured by Catalyst Chemical Industry Co., Ltd.),
Silica C is "Cataloid SI-50" (manufactured by Catalyst Chemical Industry Co., Ltd.),
Silica D is "Cataloid SI-45P" (manufactured by Catalyst Kasei Kogyo),
Silica E is "Cataloid SI-80P" (manufactured by Catalyst Chemical Industry Co., Ltd.),
Silica F is "Syton520" (manufactured by DuPont),
Silica G is "Syton 524" (manufactured by DuPont),
Silica H is "Syton HS40" (manufactured by DuPont),
HEDP is 1-hydroxy-1,1-diphosphonic acid ( "Di Quest 2010", manufactured by Solutia Japan), and H ₂ O ₂ is 35 percent by weight aqueous hydrogen peroxide solution (manufactured by Asahi Denka Co., Ltd.)
Is shown.

  For the particle size distribution of the silica particles in the polishing composition, according to the method described in the following [measurement of the particle size distribution of the silica particles], measured the particle size, the number-based average particle size, standard deviation value and cumulative The volume frequency was determined and a graph of particle size versus cumulative volume frequency was created. FIG. 1 shows a graph of the particle size of the silica particles used in each example versus the cumulative volume frequency, and FIG. 2 shows a graph of the particle size of the silica particles used in each comparative example versus the cumulative volume frequency.

(Measurement of particle size distribution of silica particles)
Using the slurry-form silica particles as a sample, the sample was observed by a transmission electron microscope (TEM) manufactured by JEOL Ltd. (trade name "JEM-2000FX", 80 kV, 10,000 to 50,000 times), and a TEM image was photographed. . The photograph is taken into a personal computer as image data using a scanner, and the circle-equivalent diameter of each silica particle is determined using analysis software “WinROOF” (sold by Mitani Shoji). After analyzing the silica particle data, an average particle diameter and a standard deviation value based on the number of silica particles were obtained using spreadsheet software “EXCEL” (manufactured by Microsoft) based on the data. Table 2 shows the results.

  In addition, based on the particle size distribution data of the silica particles obtained by converting the particle diameter into the particle volume with spreadsheet software “EXCEL”, the ratio of the particles having a certain particle diameter to the total particles (% by volume) is calculated. Expressed as the cumulative frequency from the small particle diameter side, the cumulative volume frequency (%) was obtained.

  Based on the particle size and cumulative volume frequency data of the silica particles obtained as described above, the cumulative volume frequency was plotted against the particle size to obtain a graph of the particle size versus the cumulative volume frequency.

  In addition, using the polishing composition of Examples 1 to 6 and Comparative Examples 1 to 3, the object to be polished was polished under the following polishing conditions. Next, the micro undulations and micro pits on the surface of the object to be polished were measured and evaluated based on the following method. Each of the examples and comparative examples was evaluated using ten polished objects, and the fine waviness was an average of individual data obtained using each polished object. Table 3 shows the obtained results.

(Polishing conditions)
Polishing tester: Speed Fam Co., Ltd. "Double-sided 9B polishing machine"
Polishing pad: "Bellatrix N0058" manufactured by Kanebo
Polishing load: 7.8 kPa
Slurry supply amount: 100 mL / min Lower platen rotation speed: 30 r / min
Polishing time: 4 minutes Number of substrates loaded: 10

[Measurement of minute undulations]
Using a “New View 200” manufactured by Zygo, short-wave undulation and long-wave undulation were measured at two points (a total of four points) of the substrate to be measured every 180 ° under the following conditions, and the average of the measured values of the four points was measured. The value was calculated as the short-wave or long-wave undulation of one substrate.
Objective lens: 2.5x Michelson
Zoom ratio: 0.5x Filter: Band Pass
Filter type: FFT Fixed
Measurement wavelength:
・ Short wavelength swell: Filter High Wavelength 0.05mm
Filter Low Wavelength 0.50mm
・ Long wavelength swell: Filter High Wavelength 0.50mm
Filter Low Wavelength 5.00mm

[Method of measuring micro pits]
Observation with a differential interference microscope [Metal microscope “BX60M” (Olympus Corporation), magnification: 50 × (eyepiece: 10 ×, objective: 5 ×)) was performed using a line as shown in FIG. The number of micropits was counted while scanning for AB, CD, EF, and GH.
The results are shown in Table 3 based on the following evaluation criteria.

Evaluation criteria “◎”: less than 0.3 / face “O”: 0.3 / face or more, less than 1 piece / face “△”: 1 / face or more, less than 5 pieces / face “×”: 5 Pieces / side or more

  From the results in Table 3, it can be seen that, according to the polishing composition of Examples 1 to 6, fine undulations on the surface of the object to be polished and further micro pits are further reduced as compared with those of Comparative Examples 1 to 3. I understand.

  The polishing composition of the present invention is suitably used for the production of substrates for precision parts such as substrates for magnetic recording media, among others, Ni-P plated disk substrates.

FIG. 1 is a graph of the particle diameter of the silica particles used in each example versus the cumulative volume frequency. FIG. 2 is a graph of the particle diameter of the silica particles used in each comparative example versus the cumulative volume frequency. FIG. 3 is a schematic diagram showing a portion on the substrate scanned by a differential interference microscope when measuring the micropits.

Claims (6)

A polishing composition for a substrate for a memory hard disk comprising silica particles in an aqueous medium, wherein the silica particles are based on the number of silica particles obtained by measurement by observation with a transmission electron microscope (TEM). The standard deviation (σ) based on the number with respect to the average particle diameter (r) is represented by the following formula (1):
σ ≧ 0.3 × r (1)
(In the formula, r represents the number-based average particle diameter (nm), and σ represents the number-based standard deviation (nm).)
And the cumulative volume frequency (V) of the silica particles in the range of 60 to 120 nm is based on the following formulas (2) and (3) with respect to the particle size (R):
V ≧ 0.5 × R (2)
V ≦ 0.25 × R + 75 (3)
(In the formula, R represents the particle diameter (nm) of the silica particles, and V represents the cumulative volume frequency (%) from the small particle diameter side of the silica particles.)
A polishing liquid composition that satisfies the following.   The polishing composition according to claim 1, wherein the silica particles are colloidal silica particles.   3. The polishing composition according to claim 1, further comprising at least one member selected from the group consisting of an acid, a salt thereof, and an oxidizing agent.   The polishing composition according to any one of claims 1 to 3, wherein the pH is 1 to 4.5.   A method for reducing micro-undulations on a substrate for a memory hard disk, comprising a step of polishing a substrate for a memory hard disk using the polishing composition according to any one of claims 1 to 4.   A method for manufacturing a memory hard disk substrate, comprising the step of polishing a Ni-P plated memory hard disk substrate using the polishing composition according to claim 1.

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