JP7492366B2 - Abrasive composition for magnetic disk substrates - Google Patents

Description

The present invention relates to an abrasive composition for magnetic disk substrates. In particular, the composition is used for polishing electronic components such as semiconductors and magnetic recording media such as hard disks, and in particular, the composition is used for polishing the surfaces of substrates for magnetic recording media such as glass magnetic disk substrates and aluminum magnetic disk substrates. More specifically, the present invention relates to an abrasive composition for magnetic disk substrates that is used in a rough polishing step prior to a final polishing step when polishing aluminum magnetic disk substrates for magnetic recording media, which have an electroless nickel-phosphorus plating film formed on the surface of an aluminum alloy substrate, by a multi-stage polishing method.

In recent years, magnetic disk drives have become smaller and have larger capacities, and there is a demand for higher recording density. Therefore, it is necessary to improve the detection sensitivity of high-density magnetic signals, and technological developments are being made to further reduce the flying height of the magnetic head and reduce the unit recording area. In order to accommodate the lower flying height of the magnetic head and ensure the recording area, magnetic disk substrates are strictly required to improve smoothness and flatness (reduced surface roughness, reduced waviness) and reduce surface defects (reduced adhesions such as abrasive grain residue and polishing debris, reduced scratches, reduced pits).

In response to such demands, from the viewpoint of achieving both improved surface quality and improved productivity, such as reduced abrasive residues, reduced adhesion such as polishing debris, and further reduced waviness, it has been proposed that a high polishing rate can be achieved and waviness can be reduced by using an abrasive composition containing α-alumina and intermediate alumina (Patent Document 1). However, the waviness reduction effect is insufficient, and improvements are required. In addition, in the polishing method for magnetic disk substrates, a multi-stage polishing method having two or more polishing steps is often adopted (Patent Document 2). In general, in the final polishing step of the multi-stage polishing method, that is, the finish polishing step, an abrasive composition containing silica particles is used from the viewpoint of reducing surface roughness, reducing scratches, reducing adhesion such as abrasive residues and polishing debris, and reducing pits. On the other hand, in the polishing step before that (also called the rough polishing step), an abrasive composition containing alumina particles is often used from the viewpoint of improving productivity.

However, when polishing aluminum hard disk substrates, alumina particles are much harder than aluminum alloy substrates, so abrasive residue and polishing debris adhere to the substrate surface, causing further waviness and other problems that adversely affect the finish polishing.

As a solution to this problem, a polishing method has been disclosed in which polishing using an alumina-containing polishing composition and polishing using a colloidal silica-containing polishing composition are performed using the same polishing machine in the rough polishing process (Patent Document 4).

JP 2005-23266 A Japanese Patent Application Laid-Open No. 62-208869 JP 2012-25873 A JP 2012-43493 A

In recent years, as the capacity of magnetic disk drives has increased, the requirements for the surface quality of substrates have become more stringent, and in the polishing process of magnetic disk substrates, there is a demand to reduce adhesions such as abrasive grain residue and polishing debris on the substrate surface while maintaining high productivity, and further to reduce waviness. However, the inventions proposed in the above Patent Documents 1 to 4 have difficulty in fully meeting such required performance.

In view of the above, the present invention aims to provide an abrasive composition for magnetic disk substrates that can reduce adhesion of abrasive grain residues and polishing debris on the substrate surface after the rough polishing process in a multi-stage polishing method while maintaining high productivity, and can also reduce waviness.

As a result of extensive research into the above-mentioned problems, the inventors discovered that the above-mentioned problems could be solved by using the following abrasive composition for magnetic disk substrates in the latter stage of the rough polishing process in a multi-stage polishing method, and arrived at the present invention. That is, the present invention is the following abrasive composition for magnetic disk substrates.

[1] A method for rough polishing a magnetic disk substrate, comprising the following steps (1) to (3), each of which is performed using the same polishing machine, comprising a polishing agent composition B used in step (3), the polishing agent composition B comprising colloidal silica, an organic sulfate ester salt compound, an aliphatic amine compound, and water, wherein the colloidal silica has a cumulative volume frequency of particles with a diameter of 50 nm of 35% or more and a cumulative volume frequency of particles with a diameter of 15 nm of 90% or less in a volume-based particle size distribution measured using a Heywood diameter, and the organic sulfate ester salt compound is represented by the following general formula (1) :

RO-(AO) _n -SO ₃ M General formula (1)

(In the above general formula (1), R represents a linear or branched alkyl group, alkenyl group, aryl group, or alkylaryl group having 5 to 21 carbon atoms, AO represents an oxyalkylene group having 2 or 3 carbon atoms, n represents a natural number of 1 to 30, and M represents an alkali metal, an alkaline earth metal, an ammonium ion, or an organic cation.)
The abrasive composition for magnetic disk substrates, wherein the aliphatic amine compound is at least one selected from the group consisting of ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, cyclohexylamine, piperazine, diethylamine, methylpropylamine, ethylpropylamine, triethylamine, ethylenediamine, 1,2-propanediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N-ethylethylenediamine, N,N,N',N'-tetramethylethylenediamine, N-methyl-1,3-propanediamine, 1,3-diaminopentane, diethylenetriamine, bis(hexamethylene)triamine, triethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and tetramethylhexamethylenediamine.
Step (1): Supplying an abrasive composition A containing α-alumina, intermediate alumina, and water to a polishing machine to perform a first stage of rough polishing of a magnetic disk substrate. Step (2): Rinsing the magnetic disk substrate obtained in the above step (1). Step (3): Supplying an abrasive composition B containing colloidal silica, an organic sulfate ester salt compound, and water to a polishing machine to perform a second stage of rough polishing of the magnetic disk substrate.

[ 2 ] The abrasive composition for magnetic disk substrates according to the above [1], further comprising an acid and/or a salt thereof.

[ 3 ] The abrasive composition for magnetic disk substrates according to the above [1] or [ 2], further comprising an oxidizing agent.

[ 4 ] The abrasive composition for magnetic disk substrates according to any one of [1] to [ 3 ] above, which is used for rough polishing of an electroless nickel-phosphorus plated aluminum magnetic disk substrate.

By using the abrasive composition for magnetic disk substrates of the present invention, the amount of abrasive residue, polishing debris, and other deposits on the substrate surface after the rough polishing step in the multi-stage polishing method is reduced, and substrates with reduced waviness can be produced with good productivity.

The following describes the embodiments of the present invention. The present invention is not limited to the following embodiments, and may be changed, modified, or improved without departing from the scope of the invention.

1. Abrasive Composition for Magnetic Disk Substrate An abrasive composition for magnetic disk substrates according to one embodiment of the present invention (hereinafter simply referred to as "abrasive composition") contains colloidal silica, an organic sulfate ester salt compound, and water. Here, the abrasive composition of this embodiment corresponds to "abrasive composition B" used in step (3).

Furthermore, the colloidal silica has a cumulative volume frequency of 50 nm particles in a volume-based particle size distribution measured by Heywood diameter of 35% or more , and a cumulative volume frequency of 15 nm particles in the particle size distribution of 90% or less.

On the other hand, the organic sulfate ester salt compound is a compound represented by the following general formula (1).
RO-(AO) _n -SO ₃ M General formula (1)

In the above general formula (1), R represents a linear or branched alkyl group, alkenyl group, aryl group, or alkylaryl group having 5 to 21 carbon atoms, AO represents an oxyalkylene group having 2 or 3 carbon atoms, n represents a natural number from 1 to 30, and M represents an alkali metal, an alkaline earth metal, an ammonium ion, or an organic cation.

Furthermore, the polishing composition of this embodiment may contain, as optional components, an aliphatic amine compound, an acid and/or its salt, an oxidizing agent, and other additives.

The polishing compound of the present embodiment has the following steps (1) to (3), and is used as abrasive composition B in step (3) in rough polishing of a magnetic disk substrate, in which each of the steps (1) to (3) is performed using the same polishing machine.
Step (1) A step of supplying an abrasive composition A containing α-alumina, intermediate alumina, and water to a polishing machine to perform preliminary rough polishing of a magnetic disk substrate.
Step (2): A step of rinsing the magnetic disk substrate obtained in the above step (1).
Step (3): A step of supplying a polishing agent composition B containing colloidal silica, an organic sulfate ester salt compound, and water to a polishing machine to perform a subsequent rough polishing of the magnetic disk substrate.
Each will be explained in detail below.

The colloidal silica used in the polishing compound composition of the present embodiment (=polishing compound composition B) can be obtained by a water glass method in which an alkali metal silicate such as sodium silicate or potassium silicate is used as a raw material and the raw material is subjected to a condensation reaction in an aqueous solution to grow particles.

Alternatively, it can be obtained by the alkoxysilane method, which uses alkoxysilane such as tetraethoxysilane as a raw material and grows particles by a condensation reaction caused by hydrolysis with an acid or alkali in water containing a water-soluble organic solvent such as alcohol, or by the reaction of metallic silicon with water.

Here, colloidal silica is known to have shapes such as spherical, chain-like, confetti-shaped, and irregular shapes, and the primary particles are monodispersed in water to form a colloid. In the polishing compound composition of this embodiment, the shape of such colloidal silica is preferably spherical or close to spherical.

The average particle size (D50) of the colloidal silica used is preferably 10 to 100 nm, more preferably 20 to 80 nm. Furthermore, the cumulative volume frequency of particles with a particle size of 50 nm in the volume-based particle size distribution measured using the Heywood diameter is 35% or more, and the cumulative volume frequency of particles with a particle size of 15 nm in the particle size distribution is 90% or less.

The term "cumulative volume frequency (%)" in this specification has the same meaning as it is normally used, and refers to the percentage (%) of the total volume of particles having a particle size equal to or smaller than a certain value relative to the total volume of all particles in a distribution obtained by accumulating the volumes of a group of target particles in order of particle size, starting from the particle with the smallest particle size.

For example, if the cumulative volume frequency of particles with a particle diameter of 15 nm is 50%, this means that the total volume of particles with a particle diameter of 15 nm or less accounts for 50% of the volume of all particles. Note that the Heywood diameter is a result obtained by analyzing images obtained by observation with an electron microscope and calculating the diameter equivalent to a circle with a projected area, and is a result that has been well known for a long time.

The colloidal silica contained in the polishing compound composition of this embodiment has a relatively low ratio of large particles with a particle diameter of 50 nm or more and small particles with a particle diameter of 15 nm or less to the total particles. Colloidal silica with such a particle size distribution is likely to be sufficiently retained by the polishing pad when it is supplied to the surface of an object being rubbed by the polishing pad.

In addition, due to the above particle size distribution, the gaps formed between the colloidal silica and the surface of the object tend to be smaller than the residual abrasive grains, polishing debris, etc. As a result, the residual abrasive grains and polishing debris are less likely to escape into the gaps between the colloidal silica and the surface of the object, increasing the frequency of collisions between the residual abrasive grains and polishing debris and the colloidal silica, allowing the residual abrasive grains and polishing debris to be efficiently removed from the surface of the object.

Furthermore, by ensuring a considerable number of colloidal silica particles with a particle size of 50 nm or less, it becomes easier for colloidal silica with a smaller particle size to get into the gap between one colloidal silica and the surface of the object. This makes it harder for residual abrasive grains and polishing debris to escape into the gap between the colloidal silica and the surface of the object, making them easier to remove from the surface of the object. In addition, because colloidal silica is spherical or close to spherical in shape, it tends not to adhere to or penetrate the surface of the object. Therefore, the colloidal silica itself is less likely to remain on the surface of the object.

The concentration of colloidal silica in the polishing composition is preferably 0.1 to 20 mass%, more preferably 0.2 to 10 mass%.

1-2. Organic Sulfate Compound The organic sulfate compound used in the polishing compound is, as already described above, the compound represented by the general formula (1).

Here, in the above general formula (1), n is preferably a natural number of 2 to 4. Furthermore, specific examples of M in the above general formula (1) include alkali metals such as sodium and potassium, alkaline earth metals such as calcium and magnesium, ammonium ions, quaternary ammonium ions, and organic amines such as triethanolamine.

Specific examples of organic sulfate compounds represented by the above general formula (1) include oxyethylene tridecyl ether sulfate (2 or 3 oxyethylene groups per molecule), oxyethylene lauryl ether sulfate (2 or 3 oxyethylene groups per molecule), oxyethylene nonyl ether sulfate (3 oxyethylene groups per molecule), oxyethylene octyl phenyl ether sulfate (3 oxyethylene groups per molecule), and oxyethylene nonyl phenyl ether sulfate (3 oxyethylene groups per molecule). In particular, it is preferable to use oxyethylene tridecyl ether sulfate (3 oxyethylene groups per molecule), oxyethylene lauryl ether sulfate (3 oxyethylene groups per molecule), oxyethylene octyl phenyl ether sulfate (3 oxyethylene groups per molecule), and oxyethylene nonyl phenyl ether sulfate (3 oxyethylene groups per molecule).

Furthermore, the organic sulfate ester salt compound may be contained in the polishing composition of this embodiment in one type or in combination of two or more types.

In addition, the content of the organic sulfate ester salt compound in the polishing composition is generally 0.0001 to 2.0 mass %, and preferably 0.0005 to 1.0 mass %.

1-3. Aliphatic Amine Compound To the polishing compound of this embodiment, an aliphatic amine compound can be added as an optional component. Specific examples of the aliphatic amine compound include ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, cyclohexylamine, piperazine, diethylamine, methylpropylamine, ethylpropylamine, triethylamine, ethylenediamine, 1,2-propanediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N-ethylethylenediamine, N,N,N',N'-tetramethylethylenediamine, N-methyl-1,3-propanediamine, 1,3-diaminopentane, diethylenetriamine, bis(hexamethylene)triamine, triethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and tetramethylhexamethylenediamine.

The aliphatic amine compound may be one or a combination of two or more selected from the group consisting of the above. The content of the aliphatic amine compound in the polishing composition is generally 0.00001 to 4.0 mass%, preferably 0.0001 to 2.0 mass%.

1-4. Acid and/or Salt Thereof Furthermore, the polishing compound composition of the present embodiment may contain an acid and/or a salt thereof for adjusting the pH value or as an optional component. Here, examples of the acid and/or a salt thereof include inorganic acids and/or salts thereof and organic acids and/or salts thereof.

Specific examples of inorganic acids and/or salts thereof include nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, phosphonic acid, pyrophosphoric acid, and tripolyphosphoric acid. These acids and/or salts thereof can be used alone or in combination of two or more.

On the other hand, specific examples of organic acids and/or salts thereof include aminocarboxylic acids and/or salts thereof, such as glutamic acid and aspartic acid, carboxylic acids and/or salts thereof, such as citric acid, tartaric acid, oxalic acid, nitroacetic acid, maleic acid, malic acid, and succinic acid, and organic phosphonic acids and/or salts thereof. These acids and/or salts thereof can be used alone or in combination of two or more.

Specific examples of organic phosphonic acids and/or salts thereof include at least one compound selected from 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-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, α-methylphosphonosuccinic acid, and salts thereof.

It is also a preferred embodiment to use two or more of the above compounds in combination. Specific examples include a combination of sulfuric acid and/or a salt thereof with an organic phosphonic acid and/or a salt thereof, and a combination of phosphoric acid and/or a salt thereof with an organic phosphonic acid and/or a salt thereof.

The polishing agent composition of the present embodiment may further contain an oxidizing agent as a polishing accelerator. Specific examples of the oxidizing agent include peroxides, permanganic acid or a salt thereof, chromic acid or a salt thereof, peroxoacid or a salt thereof, halogen oxoacid or a salt thereof, oxyacid or a salt thereof, and mixtures of two or more of these oxidizing agents.

More specifically, examples of such agents include hydrogen peroxide, sodium peroxide, barium peroxide, potassium peroxide, potassium permanganate, metal salts of chromate, metal salts of dichromate, persulfuric acid, sodium persulfate, potassium persulfate, ammonium persulfate, peroxolinic acid, sodium perborate, performic acid, peracetic acid, hypochlorous acid, sodium hypochlorite, and calcium hypochlorite. Among these, those using hydrogen peroxide, persulfuric acid and its salts, and hypochlorous acid and its salts are particularly preferred, and those using hydrogen peroxide are even more preferred.

The content of the oxidizing agent in the polishing composition is preferably 0.01 to 10.0 mass %, and more preferably 0.1 to 5.0 mass %.

2. Physical properties of the polishing composition (pH value)
The pH value (25°C) of the polishing compound is preferably in the range of 0.1 to 4.0, and more preferably 0.5 to 3.0. When the pH value (25°C) of the polishing compound is 0.1 or more, surface roughness can be suppressed. When the pH value (25°C) of the polishing compound is 4.0 or less, a decrease in the removal rate can be suppressed.

The polishing composition of this embodiment can be used for polishing various electronic components such as magnetic recording media such as hard disks. In particular, it is suitable for polishing aluminum magnetic disk substrates. It is even more suitable for polishing aluminum magnetic disk substrates that have been electrolessly nickel-phosphorus plated. Electroless nickel-phosphorus plating is generally performed under conditions of a pH value (25°C) of 4 to 6. Under conditions of a pH value (25°C) of 4 or less, nickel tends to dissolve, making plating difficult. On the other hand, with regard to polishing, for example, nickel tends to dissolve under conditions of a pH value (25°C) of 4 or less, so the use of the polishing composition of this embodiment is expected to have the effect of increasing the polishing rate.

3. Method for polishing magnetic disk substrate The polishing compound composition of the present embodiment is suitable for use in polishing magnetic disk substrates such as aluminum magnetic disk substrates and glass magnetic disk substrates, and is particularly suitable for use in polishing electrolessly nickel-phosphorus plated aluminum magnetic disk substrates.

The abrasive composition is an abrasive composition B used in step (3) when the rough polishing step is performed in the following three steps (1) to (3) in a method for polishing a magnetic disk substrate including a rough polishing step and a finishing step in a multi-stage polishing method. A specific polishing method is, for example, a method in which an abrasive pad is attached to the platen of a polishing machine, an abrasive composition is supplied to the surface to be polished of the object to be polished or to the polishing pad, and the surface to be polished is rubbed with the polishing pad. For example, when simultaneously polishing the front and back surfaces of a magnetic disk substrate, a method is used in which a double-sided polishing machine with a polishing pad attached to each of the upper and lower plates is used. In this method, the magnetic disk substrate is sandwiched between the polishing pads attached to the upper and lower plates, the abrasive composition is supplied between the polishing surface and the polishing pad, and the two polishing pads are rotated simultaneously to polish the front and back surfaces of the magnetic disk substrate. The polishing pads can be of any type, including urethane type, suede type, and nonwoven fabric type.

Step (1): Pre-stage rough polishing This is a step of supplying abrasive composition A containing α-alumina, intermediate alumina, and water to a polishing machine to perform pre-stage rough polishing, bringing a polishing pad into contact with a surface to be polished of a substrate to be polished, and moving the polishing pad and/or the substrate to be polished to polish the surface to be polished.

The polishing composition A used in this step is a polishing composition containing α-alumina, intermediate alumina, and water, and may further contain optional components such as an organic sulfate ester salt compound, an acid and/or its salt, and an oxidizing agent, as necessary, in the same manner as the polishing composition B (the polishing composition of this embodiment).

The abrasive composition A used in step (1) contains α-alumina and intermediate alumina, and examples of the intermediate alumina include γ-alumina, δ-alumina, and θ-alumina. The mixing ratio of α-alumina to intermediate alumina is preferably intermediate alumina/α-alumina (mass ratio) in the range of 0.05 to 2.0, more preferably in the range of 0.1 to 1.0, and even more preferably in the range of 0.15 to 0.5.

Here, the average particle size of the alumina is preferably in the range of 0.1 to 2.0 μm, and more preferably in the range of 0.2 to 1.0 μm. By making the average particle size of the alumina 0.1 μm or more, it is possible to suppress a decrease in the polishing rate. On the other hand, by making the average particle size of the alumina 2.0 μm or less, it is possible to suppress the deterioration of waviness after polishing.

Furthermore, the concentration of alumina in the polishing composition A is preferably in the range of 1 to 50 mass%, and more preferably in the range of 2 to 40 mass%. By making the concentration of alumina in the polishing composition A 1 mass% or more, it is possible to suppress a decrease in the polishing rate. On the other hand, by making the concentration of alumina 50 mass% or less, it is possible to suppress the use of more alumina than necessary, thereby reducing the cost of the polishing composition A and making it possible to perform polishing economically.

Furthermore, the oxidizing agent content in the polishing composition A is preferably in the range of 0.01 to 10.0 mass%, more preferably in the range of 0.1 to 5.0 mass%.

On the other hand, the pH value (25°C) of the polishing composition A is preferably in the range of 0.1 to 4.0, and more preferably in the range of 0.5 to 3.0.

Step (2): Rinse the substrate obtained in step (1) From the viewpoint of reducing the waviness of the substrate surface after the rough polishing step in the multi-stage polishing method, step (2) is performed in the same polishing machine after the above step (1), in which the substrate obtained in step (1) is rinsed. Here, the rinsing liquid used for rinsing the substrate is not particularly limited, but from the viewpoint of economy, water such as distilled water, ion-exchanged water, pure water, and ultrapure water is mainly used. At this time, from the viewpoint of productivity, step (2) is performed in the same polishing machine used in step (1) without removing the substrate to be polished from the polishing machine.

Step (3): Later-stage Rough Polishing From the viewpoint of reducing adhesions such as abrasive grain residues and polishing debris and reducing waviness after the rough polishing step in the multi-stage polishing method, a polishing agent composition B (corresponding to the polishing agent composition of this embodiment) containing colloidal silica, an organic sulfate ester salt compound, and water is supplied to the surface to be polished of the substrate that has been subjected to the rinsing step of the above step (2), and a polishing pad and/or the substrate to be polished is moved over the surface to be polished, thereby carrying out step (3). At this time, from the viewpoint of improving productivity and from the viewpoint of reducing adhesions such as abrasive grain residues and polishing debris and reducing waviness after the rough polishing step, the above steps (1) to (3) are all carried out using the same polishing machine.

The present invention will be described in detail below with reference to examples, but it goes without saying that the present invention is not limited to these examples and can be embodied in various forms as long as they fall within the technical scope of the present invention.

(Preparation of abrasive composition)
The polishing compound used in Examples 1 and 2, Reference Examples 1 to 5, and Comparative Examples 1 to 5 shown below is a polishing compound (=polishing compound composition B) containing the materials shown in Table 1 below in the amounts shown in Table 1. Here, the method for measuring the average particle size, the pre-polishing conditions in step (1), the rinsing conditions in step (2), and the post-coarse polishing conditions in step (3) are as shown below.

(Average particle size)
The average particle size of alumina was measured using a laser diffraction particle size distribution analyzer (SALD2200 manufactured by Shimadzu Corporation). The average particle size of alumina is the average particle size (D50) at which the cumulative particle size distribution from the small particle size side based on volume becomes 50%.

The particle diameter (Heywood diameter) of colloidal silica was measured as the Heywood diameter (diameter equivalent to a circle with a projected area) by photographing a field of view at a magnification of 100,000 times using a transmission electron microscope (TEM) (JEM2000FX (200 kV) manufactured by JEOL Ltd.) and analyzing the photograph using analysis software (Mac-View Ver. 4.0 manufactured by Mountec Co., Ltd.). The average particle diameter of colloidal silica was measured by analyzing approximately 2,000 colloidal silica particles using the method described above, and calculating the particle diameter at which the cumulative particle size distribution (accumulated volume basis) from the small particle size side is 50% using the above analysis software (Mac-View Ver. 4.0 manufactured by Mountec Co., Ltd.).

(Preliminary rough polishing conditions)
An electroless nickel-phosphorus plated aluminum magnetic disk substrate (hereinafter abbreviated as aluminum disk) having an outer diameter of 95 mm was used as the object to be polished, and polishing was carried out under the following polishing conditions.
Polishing machine: 9B double-sided polishing machine manufactured by SpeedFam Co., Ltd. Polishing pad: P1 pad manufactured by FILWEL Co., Ltd. Platen rotation speed: Upper platen -7.5 rpm
Lower surface plate 22.5 rpm
Amount of polishing compound supplied: 100 ml/min
Polishing time: 4.5 minutes Processing pressure: 100 g/ ^cm2
In the pre-stage polishing, abrasive composition A was used.

(Rinse conditions)
Polishing machine: same as previous rough polishing Polishing pad: same as previous rough polishing Platen rotation speed: same as previous rough polishing Rinse liquid supply amount: 3 L/min
Rinse time: 20 seconds Processing pressure: 15 g/ ^cm2
The rinse solution used was pure water.

(Conditions for later rough polishing)
Polishing machine: same as previous stage rough polishing Polishing pad: same as previous stage rough polishing Platen rotation speed: same as previous stage rough polishing Amount of polishing compound supplied: 100 ml/min
Polishing time: 80 seconds Processing pressure: 100 g/ ^cm2
In the latter polishing step, abrasive composition B was used.

The results of polishing tests using the polishing compositions of Examples 1 and 2, Reference Examples 1 to 5, and Comparative Examples 1 to 5 under the above conditions are shown in the following Table 2. Here, the evaluation items of the polishing rate ratio, the deposit count ratio, and the waviness ratio based on the results of the polishing tests were evaluated based on the following criteria.

(Evaluation of Polishing Rate (Polishing Rate Ratio))
The removal rate was calculated based on the following formula by measuring the mass of the aluminum disk lost after removal of the polishing agent.
Polishing rate (μm/min)=Amount of mass reduction of aluminum disk (g)/Polishing time (min)/Area of one side of aluminum disk (cm ² )/Density of electroless nickel-phosphorus plating film (g/cm ³ )/2×10 ⁴
(In the above formula, the area of one side of the aluminum disk was 65.9 cm ² , and the density of the electroless nickel-phosphorus plating film was 8.0 g/cm ³ .)

The polishing rate ratios of the polishing compositions of Examples 1 and 2, Reference Examples 1 to 5, and Comparative Examples 1 to 5 were evaluated according to the following criteria, based on the relative values when the measured polishing rate of Comparative Example 3 (0.184 μm/min) calculated based on the above formula was taken as 1 (reference).
◯: the polishing speed ratio is 0.95 or more compared to Comparative Example 3 (=1) Δ: the polishing speed ratio is in the range of 0.85 or more and less than 0.95 compared to Comparative Example 3 (=1) ×: the polishing speed ratio is less than 0.85 compared to Comparative Example 3 (=1) In the above, "◯" indicates an evaluation that the polishing speed is equal to or higher than that of Comparative Example 3, "Δ" indicates an evaluation that the polishing speed is ok for practical use, and "×" indicates an evaluation that the polishing speed is inferior.

(Evaluation of adhesion (adhesion count ratio))
In order to evaluate the presence or absence of adhesions such as abrasive grain residues and polishing debris on the surface of the aluminum disk substrate after polishing, a scanning electron microscope was used to count adhesions under the following conditions.
Measuring device: Field emission scanning electron microscope "JSM-7100" manufactured by JEOL Ltd.
Measurement conditions: Acceleration voltage 15 kV, observation magnification 20,000 times Measurement method: A secondary electron image of an aluminum magnetic disk substrate that has been polished up to the second stage is captured using the above-mentioned device and conditions with a contrast that makes the abrasive grain residue, polishing debris, and other attachments on the substrate appear white. After binarizing the captured image to black and white using photo retouching software, the number of pixels in the white area is calculated and counted as the number of attachments.

The deposit count ratios of the polishing compositions of Examples 1 and 2, Reference Examples 1 to 5, and Comparative Examples 1 to 5 were evaluated according to the following criteria, based on the relative values when the deposit count value (8755) of Comparative Example 3 obtained by the above method was taken as 1 (standard).
◎: The adhesion count ratio is less than 0.2 compared to Comparative Example 3 (=1). ○: The adhesion count ratio is in the range of 0.2 or more and less than 0.9 compared to Comparative Example 3 (=1). △: The adhesion count ratio is in the range of 0.9 or more and less than 1.0 compared to Comparative Example 3 (=1). ×: The adhesion count ratio is 1.0 or more compared to Comparative Example 3 (=1). In the above, ◎ indicates that the adhesion count is significantly lower than Comparative Example 3, "○" indicates that the adhesion count is lower than Comparative Example 3 or less, "△" indicates that the adhesion count is about the same as Comparative Example 3 and there are no practical problems, and "×" indicates that there are practical problems.

(Evaluation of waviness ratio)
The waviness of the aluminum disk was measured using a three-dimensional surface structure analysis microscope utilizing a scanning white light interferometry manufactured by Ametech Co., Ltd. The measurement conditions were a measurement device manufactured by Ametech Co., Ltd. (New View 8300 (lens: 1.4x, zoom: 1.0x)), a wavelength of 500 to 1000 μm, a measurement area of 6 mm x 6 mm, and analysis was performed using analysis software (Mx) manufactured by Ametech Co., Ltd.

The waviness ratios of the polishing compositions of Examples 1 and 2, Reference Examples 1 to 5, and Comparative Examples 1 to 5 were evaluated according to the following criteria, based on the relative values when the measured waviness value (0.92 Å) of Comparative Example 3 obtained by the above method was taken as 1 (standard).
◯: The waviness ratio is less than 1.01 compared to Comparative Example 3 (=1) Δ: The waviness ratio is in the range of 1.01 or more and less than 1.10 compared to Comparative Example 3 (=1) ×: The waviness ratio is 1.10 or more compared to Comparative Example 3 (=1) In the above, "◯" indicates an evaluation of having waviness equivalent to or better than Comparative Example 3, "Δ" indicates an evaluation of having waviness that does not cause any practical problems, and "×" indicates an evaluation of having poor waviness.

(Discussion)
In Comparative Example 3, although the particle size distribution of colloidal silica is within the range of the present invention, a polishing agent composition not containing a specific organic sulfate ester salt compound is used, and therefore the balance of polishing performance such as removal rate, deposit count, and waviness is inferior to Reference Examples 1 to 3 containing an organic sulfate ester salt compound having a specific structure. In other words, the effect of the present invention is exerted by using a polishing agent composition containing an organic sulfate ester salt compound having a specific structure as one embodiment, in addition to the particle size distribution of colloidal silica being within a specific range. Reference Examples 4 and 5 are the results of using a polishing agent composition having different colloidal silica particle size characteristics compared to the polishing agent composition of Reference Example 1.

However, in Comparative Examples 4 and 5, which use a polishing composition containing an organic sulfate ester salt compound that does not have a specific structure, unlike the polishing composition of the present invention, the deposit count ratio is not particularly improved compared to Comparative Example 3.

On the other hand, even though the polishing compound contains an organic sulfate ester salt compound having a specific structure, Comparative Examples 1 and 2, in which the particle size characteristics of the colloidal silica do not satisfy the conditions stipulated in the polishing compound of the present invention, show a poor balance between the polishing rate and waviness compared to Reference Example 1.

In the cases of Examples 1 and 2 , in which an aliphatic amine compound was further added as an optional component to the polishing compound of Reference Example 1, it was confirmed that the deposit count ratio was significantly reduced ( Reference Example 1 = 0.10, and Reference Example 2 = 0.08) compared to Reference Example 1 (0.89), and it was found that deposits such as abrasive grain residues and polishing debris on the substrate surface were significantly reduced. In other words, it was shown that the addition of an aliphatic amine compound contributed to a significant reduction in deposits.

From the above, it is clear that the use of the polishing agent composition of the present invention improves the polishing rate, reduces adhesions such as abrasive residues and polishing debris on the substrate surface, and improves waviness in a well-balanced manner. However, it is not easy to simultaneously achieve all of the following: improvement in polishing rate, reduction in adhesions such as abrasive residues and polishing debris on the substrate surface, and improvement in waviness. The polishing agent composition of the present invention has the excellent effect of being able to produce with good productivity substrates with reduced adhesions such as abrasive residues and polishing debris on the substrate surface and reduced waviness after the rough polishing process in a multi-stage polishing method.

The abrasive composition of the present invention can be used for polishing electronic components such as semiconductors and magnetic recording media such as hard disks. In particular, it can be used for surface polishing of substrates for magnetic recording media such as glass magnetic disk substrates and aluminum magnetic disk substrates. Furthermore, it can be used for surface polishing of aluminum magnetic disk substrates for magnetic recording media, which have an electroless nickel-phosphorus plating film formed on the surface of an aluminum alloy substrate.

Claims (4)

A method for rough polishing a magnetic disk substrate, comprising the steps (1) to (3) below, each of which is performed using the same polishing machine, comprising abrasive composition B used in step (3):
Colloidal silica,
An organic sulfate ester salt compound;
An aliphatic amine compound,
and water,
The colloidal silica is
a cumulative volume frequency of a particle diameter of 50 nm in a volume-based particle size distribution measured by Heywood diameter is 35% or more, and a cumulative volume frequency of a particle diameter of 15 nm in the particle size distribution is 90% or less,
The organic sulfate ester salt compound is
Represented by the following general formula (1) :

RO-(AO) _n -SO ₃ M General formula (1)

(In the above general formula (1), R represents a linear or branched alkyl group, alkenyl group, aryl group, or alkylaryl group having 5 to 21 carbon atoms, AO represents an oxyalkylene group having 2 or 3 carbon atoms, n represents a natural number of 1 to 30, and M represents an alkali metal, an alkaline earth metal, an ammonium ion, or an organic cation.)
The aliphatic amine compound is
The abrasive composition for magnetic disk substrates is at least one selected from the group consisting of ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, cyclohexylamine, piperazine, diethylamine, methylpropylamine, ethylpropylamine, triethylamine, ethylenediamine, 1,2-propanediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N-ethylethylenediamine, N,N,N',N'-tetramethylethylenediamine, N-methyl-1,3-propanediamine, 1,3-diaminopentane, diethylenetriamine, bis(hexamethylene)triamine, triethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and tetramethylhexamethylenediamine.
Step (1): Supplying an abrasive composition A containing α-alumina, intermediate alumina, and water to a polishing machine to perform a first stage of rough polishing of a magnetic disk substrate. Step (2): Rinsing the magnetic disk substrate obtained in the above step (1). Step (3): Supplying an abrasive composition B containing colloidal silica, an organic sulfate ester salt compound, and water to a polishing machine to perform a second stage of rough polishing of the magnetic disk substrate. 2. The abrasive composition for magnetic disk substrates according to claim 1, further comprising an acid and/or a salt thereof . 3. The abrasive composition for magnetic disk substrates according to claim 1, further comprising an oxidizing agent . 4. The abrasive composition for magnetic disk substrates according to claim 1 , which is used for rough polishing of an electroless nickel-phosphorus plated aluminum magnetic disk substrate .