JP7058097B2 - Method for manufacturing polishing composition and magnetic disk substrate - Google Patents

Description

The present invention relates to a polishing composition and a method for manufacturing a magnetic disk substrate using the polishing composition.

Conventionally, a substrate manufacturing process that requires a highly accurate surface includes a step of polishing an object to be polished, which is a raw material of the substrate, using a polishing liquid. For example, in the manufacture of a disc substrate (Ni-P substrate) plated with nickel phosphorus, in general, polishing that emphasizes polishing efficiency (primary polishing) and a final polishing process that is performed to finish the surface accuracy of the final product are performed. (Finish polishing process) is performed. Patent Documents 1 and 2 are mentioned as technical documents relating to a polishing composition used for polishing a magnetic disk substrate or the like.

Japanese Patent Application Laid-Open No. 2003-155471 Japanese Unexamined Patent Publication No. 2003-147337

In recent years, with respect to a polishing composition used for polishing a disk substrate such as a Ni-P substrate, it has been studied to use abrasive grains having a small average particle diameter from the viewpoint of realizing a higher quality surface. However, the polishing composition containing fine-grained abrasive grains tends to be inferior in processing power, and is used in polishing that requires a high polishing rate, such as polishing of a disk substrate such as a Ni-P substrate. In addition, there is a risk that such a request cannot be fully met. In addition, agglomeration of abrasive grains in the polishing composition can be a factor that increases scratches (polishing scratches) during substrate polishing. Therefore, in order to stably realize high quality (for example, a surface with a reduced number of scratches) on the surface after polishing, a polishing composition in which agglomeration of abrasive grains is less likely to occur is desirable.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polishing composition capable of effectively reducing the number of scratches present on the surface after polishing while maintaining a high polishing rate. And. Another related object is to provide a method for manufacturing a magnetic disk substrate using the above-mentioned polishing composition.

According to the present invention, a polishing composition is provided. This polishing composition contains abrasive grains, an acid, an oxidizing agent and water. The average primary particle diameter of the abrasive grains measured by the BET method is 1 nm or more and 50 nm or less. The pH of the polishing composition is 1.8 to 3.0. The amount of sodium hydroxide required to raise the pH by 1.0 is 0.03 mol / L or more and 0.2 mol / L or less. According to the polishing composition satisfying the above-mentioned characteristics, the number of scratches on the surface after polishing can be effectively reduced while maintaining a high polishing rate.

In a preferred embodiment of the polishing composition disclosed herein, silica particles are included as the abrasive grains. By using silica particles as the abrasive grains, the effect of the present invention can be more preferably exhibited.

The polishing composition disclosed herein is used for polishing a magnetic disk substrate. Among them, a nickel phosphorus substrate (Ni-P substrate) is mentioned as a preferable polishing object. When the polishing composition is applied to the magnetic disk substrate, the surface quality of the surface of the magnetic disk substrate after polishing can be improved and a high polishing rate can be achieved.

The polishing composition disclosed here is suitable as a polishing composition used in the finish polishing step. For example, the polishing composition is suitably used in the final polishing step of a magnetic disk substrate. Since the polishing composition disclosed herein effectively reduces the number of scratches after polishing, it is particularly useful to be used in a polishing process that requires high surface quality such as the finish polishing. ..

Further, according to the present invention, a method for manufacturing a magnetic disk substrate is provided. The manufacturing method includes a step of polishing a magnetic disk substrate using any of the polishing compositions disclosed herein. According to such a manufacturing method, a magnetic disk substrate having a high-quality surface can be manufactured with high productivity.

Hereinafter, preferred embodiments of the present invention will be described. Matters other than those specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in the art. The present invention can be carried out based on the contents disclosed in the present specification and the common general technical knowledge in the art.

The polishing composition disclosed herein is a polishing composition used for polishing (preferably finish polishing) a magnetic disk substrate, and includes abrasive grains, an acid, an oxidizing agent, and water. This polishing composition has a pH of 1.8 to 3.0, and the amount α of sodium hydroxide (NaOH) required to raise the pH by 1.0 is 0.03 mol / L or more. It is 0.2 mol / L or less.

<Amount of sodium hydroxide α>
In the technique disclosed herein, the amount of sodium hydroxide α required to raise the pH of the polishing composition by 1.0 shall be measured as follows. That is, a 0.1 mol / L sodium hydroxide aqueous solution (manufactured by Kanto Chemical Co., Ltd.) was dropped by immersing the electrode of the pH meter in the polishing composition (liquid temperature 25 ° C.) to be measured and stirring, and the pH was the initial value. Titration of 0.1 mol / L sodium hydroxide aqueous solution from to 1.0 increase is measured. Then, the sodium hydroxide amount α can be obtained by using the following formula (1).
α (mol / L) = 0.1 × A ÷ B (1)
A: Titration of 0.1 mol / L sodium hydroxide aqueous solution required to raise pH by 1.0 (L)
B: Volume (L) of the polishing composition

The polishing composition disclosed herein has a sodium hydroxide amount α of 0.03 mol / L or more, which is required to raise the pH by 1.0. As a result, a higher polishing rate can be realized as compared with the conventional polishing composition in which the sodium hydroxide amount α is less than 0.03 mol / L. The reason why such an effect can be obtained is considered as follows, for example. That is, from the viewpoint of processability, it is preferable to lower the pH of the polishing composition and increase the amount of hydrogen ions required for dissolving the surface of the substrate. However, even when a polishing composition having a low pH is used, when the polishing composition is applied to polishing a magnetic disk substrate, the metal on the substrate surface (for example, Ni in the case of a nickel phosphorus substrate) elutes as the polishing progresses. Then, the pH rises due to the consumption of hydrogen ions. As a result, the polishing speed tends to decrease. On the other hand, in polishing using the polishing composition having the sodium hydroxide amount α of 0.03 mol / L or more, the polishing composition has an appropriate buffering capacity, so that even if the polishing proceeds, the polishing has an appropriate buffering capacity. The decrease in hydrogen ions is suppressed, and pH fluctuations are unlikely to occur (typically, pH 1.8 to 3.0 is maintained). This is considered to contribute to the improvement of the polishing rate. However, it is not limited to this.

The amount of sodium hydroxide α required to raise the pH of the polishing composition by 1.0 is preferably 0.04 mol / L or more, more preferably 0.05 mol / L from the viewpoint of polishing rate and the like. Above, more preferably 0.06 mol / L or more. A polishing composition having a sodium hydroxide amount α of a predetermined value or more is less likely to cause pH fluctuation during polishing. Therefore, the effect of applying the techniques disclosed herein is appropriately exerted. On the other hand, if the sodium hydroxide amount α is too large, the abrasive grains may aggregate in the polishing composition and the number of scratches may tend to increase. From the viewpoint of achieving better surface accuracy (for example, a surface with a reduced number of scratches) while maintaining a high polishing rate, the sodium hydroxide amount α should be approximately 0.2 mol / L or less. Is suitable, preferably 0.18 mol / L or less, more preferably 0.16 mol / L or less, still more preferably 0.15 mol / L or less. The sodium hydroxide amount α may be, for example, 0.1 mol / L or less, typically 0.08 mol / L or less. In the technique disclosed herein, for example, the sodium hydroxide amount α is 0.03 mol / L or more and 0.2 mol / L or less (preferably 0.03 mol / L or more and 0.13 mol / L or less). It can be preferably carried out in an embodiment.

The amount α of sodium hydroxide required to raise the pH of the polishing composition by 1.0 is, for example, the type and concentration of the acid contained in the polishing composition (when a plurality of types of acids are contained, those types and the like). It can be adjusted by changing the compounding ratio). That is, by appropriately selecting the type, concentration and compounding ratio of the acid, the amount of sodium hydroxide α required to raise the pH of the polishing composition by 1.0 is adjusted to an appropriate range disclosed herein. can do.

<pH>
The pH (initial value) of the polishing composition is approximately 3.0 or less. From the viewpoint of polishing efficiency and the like, the pH of the polishing composition is preferably 2.8 or less, more preferably 2.6 or less. In some embodiments, the pH may be, for example, 2.2 or less, or 2.0 or less (eg, less than 2.0). The pH of the polishing composition is usually 1.8 or higher. From the viewpoint of suppressing pit defects and roughness of the surface of the substrate after polishing, the pH of the polishing composition is preferably 1.85 or higher, more preferably 1.9 or higher, still more preferably 1.95 or higher. .. In some embodiments, the pH may be, for example, 2.0 or higher, or 2.3 or higher (eg, 2.4 or higher). The technique disclosed herein can be preferably carried out, for example, in an embodiment in which the pH of the polishing composition is 1.8 or more and 2.6 or less. The above pH can be preferably applied to a polishing composition for polishing a magnetic disk substrate such as a nickel phosphorus substrate. In particular, it can be preferably applied to a polishing composition for finish polishing.
In the technique disclosed herein, the pH of the polishing composition can be grasped by calibrating the pH of the polishing composition at three points using a pH meter and then placing the glass electrode in the composition to be measured for measurement. .. The standard solution is, for example, oxalate pH standard solution: pH 1.68 (25 ° C.), phthalate pH standard solution: pH 4.01 (25 ° C.), neutral phosphate pH standard solution: pH 6.86 (25 ° C.). ° C.), carbonate pH standard solution: pH 10.01 (25 ° C.).

<Polishing composition>
(Abrasion grain)
The polishing composition disclosed herein contains abrasive grains. The abrasive grains have a specific average primary particle size. That is, the average primary particle diameter of the abrasive grains measured by the BET method is 1 nm or more. Higher polishing rates can be achieved by increasing the average primary particle size. From the viewpoint of polishing efficiency and the like, the average primary particle diameter is preferably 3 nm or more, more preferably 5 nm or more, still more preferably 10 nm or more, and particularly preferably 15 nm or more. Further, from the viewpoint of obtaining a surface with higher surface accuracy, the average primary particle diameter is preferably 50 nm or less, more preferably 45 nm or less, still more preferably 40 nm or less, and particularly preferably 35 nm or less. In some embodiments, the average primary particle size may be, for example, 30 nm or less, typically 25 nm or less (eg, 20 nm or less).

In the technique disclosed herein, the average primary particle size of the abrasive grains means the average particle size obtained based on the BET method. For example, when the abrasive grains are silica abrasive grains (that is, abrasive grains made of silica particles), the average primary particle diameter of the silica abrasive grains is D1 (nm) from the specific surface area S (m ² / g) measured by the BET method. ) = (6000 / 2.2) / S can be calculated. 2.2 in this formula is the value of the specific gravity of silica, which is the particle size of silica. The specific surface area can be measured, for example, by using a surface area measuring device manufactured by Micromeritex, trade name "Flow Sorb II 2300".

Although not particularly limited, the number average aspect ratio of the abrasive grains is 1 or more in principle, and the lower limit thereof is not particularly limited, but is, for example, 1.03 or more, typically 1.08 or more. May be good. Further, from the viewpoint of efficiently increasing the surface accuracy, it is usually appropriate that the average aspect ratio is 1.30 or less in some embodiments. By reducing the average aspect ratio of the entire particles, the abrasive grains can easily roll and move, so that the processing is stable and scratches can be reduced more preferably. The average aspect ratio of the entire particle is preferably 1.28 or less, more preferably 1.25 or less (for example, 1.2 or less). Here, the average aspect ratio of the abrasive grains means the average value of the major axis / minor axis ratios of the individual particles constituting the abrasive grains, that is, the number average aspect ratio. Hereinafter, unless otherwise specified, the average aspect ratio in the present specification means the above-mentioned number average aspect ratio.

The number average aspect ratio of the abrasive grains is measured by, for example, the following method. That is, using a transmission electron microscope (TEM, STEM HD-2700 manufactured by Hitachi High-Technologies Co., Ltd.), the abrasive grains to be measured (one type of abrasive grain particles may be used, or two or more types of abrasive particles). A mixture of grain particles may be used), and 1000 or more particles that can be observed by TEM are photographed at a magnification (for example, 200,000 to 400,000 times) that can be observed in about 100 particles in one field. Acquire a TEM image. Then, for the smallest rectangle circumscribing each particle image, the value obtained by dividing the length of the long side (value of the major axis) by the length of the short side (value of the minor axis) is the major axis / minor axis ratio of each particle (the value of the minor axis). Calculated as aspect ratio). Further, the area of each particle is calculated from the image of each particle, and the diameter of an ideal circle (perfect circle) having the same area as the calculated area is calculated as the particle diameter of each particle. That is, the cumulative particle size distribution of the abrasive grains to be measured is obtained by plotting the calculated particle diameters of the individual particles constituting the abrasive grains on the horizontal axis and the cumulative number (%) on the vertical axis. .. Then, the average aspect ratio of all the particles can be obtained by arithmetically averaging the number average aspect ratios of the particles in the predetermined cumulative range in the cumulative particle size distribution from the small diameter side from the aspect ratios of the predetermined number of particles. .. Each of the above aspect ratios can be obtained by using the image analysis software MacView manufactured by Mountech.

The material and properties of the abrasive grains are not particularly limited as long as they have the average primary particle diameter. For example, the abrasive grains can be any of inorganic particles, organic particles and organic-inorganic composite particles. Specific examples of the inorganic particles include silica particles, alumina particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese dioxide particles, zinc oxide particles, and oxide particles such as red iron oxide particles; Nitride particles such as silicon nitride particles and boron nitride particles; carbide particles such as silicon carbide particles and boron carbide particles; diamond particles; carbonates such as calcium carbonate and barium carbonate; and the like can be mentioned. Examples of the alumina particles include α-alumina, intermediate alumina other than α-alumina, and composites thereof. Intermediate alumina is a general term for alumina particles other than α-alumina, and specific examples thereof include γ-alumina, δ-alumina, θ-alumina, η-alumina, κ-alumina, and composites thereof. Specific examples of the organic particles include polymethylmethacrylate (PMMA) particles, poly (meth) acrylic acid particles, polyacrylonitrile particles, and the like. Here, (meth) acrylic acid has the meaning of comprehensively referring to acrylic acid and methacrylic acid. The abrasive grains may be used alone or in combination of two or more.

Silica particles are a preferred example of the abrasive grains that can be used in the techniques disclosed herein. The silica particles contained in the abrasive grains may be various silica particles containing silica as a main component. Here, the silica particles containing silica as a main component refer to particles in which 90% by weight or more, usually 95% by weight or more, typically 98% by weight or more of the particles are silica. Examples of the silica particles that can be used include, but are not limited to, colloidal silica (for example, sodium silicate silica, alkoxide silica, etc.), fumed silica, precipitated silica, and the like. Examples of the surface modification include introduction of a functional group and chemical modification such as metal modification. The abrasive grains in the technique disclosed herein may include one of such silica particles alone or in combination of two or more.

Colloidal silica is mentioned as a preferable example of silica particles that can be used as a constituent component of silica abrasive grains in the technique disclosed herein. Among them, it is preferable to use colloidal silica synthesized through particle growth in the aqueous phase, such as sodium silicate silica and alkoxide silica. With silica abrasive grains containing this type of colloidal silica, high polishing rates and good surface accuracy can be suitably achieved. When the silica abrasive grains disclosed herein contain colloidal silica, the colloidal silica contained in the silica abrasive grains may be one kind or two or more kinds having different production conditions and / or physical properties. .. Further, the silica abrasive grains may be composed of one kind or two or more kinds of colloidal silica, and may be composed of a combination of colloidal silica and other silica particles, that is, silica particles other than colloidal silica. May be good. In a preferred embodiment, the abrasive grains contained in the polishing composition contain colloidal silica alone. By using colloidal silica alone, better surface accuracy (eg, a surface with a reduced number of scratches) can be achieved while maintaining a high polishing rate.

The particle shape of colloidal silica is not particularly limited and may be spherical or non-spherical, for example, but when the polishing composition is used in the finish polishing step, a shape close to spherical is preferable.

In the polishing composition disclosed herein, the content of silica particles in the solid content contained in the polishing composition is not particularly limited. The content of the silica particles is preferably 40% by weight or more, more preferably 50% by weight or more, still more preferably 60% by weight or more, from the viewpoint of facilitating the effect of the present invention. , Even more preferably 80% by weight or more, particularly preferably 90% by weight or more, for example 99% by weight or more. In the present specification, the solid content contained in the polishing composition means a residual content after evaporating water from the polishing composition at a temperature at which the bound water is not removed, for example, 60 ° C., that is, a non-volatile content. ..

The content of the abrasive grains in the polishing composition is not particularly limited, but is typically 0.1% by weight or more, preferably 0.5% by weight or more, and more preferably 1% by weight or more. It is preferably 31% by weight or more, and more preferably 31% by weight or more. The above content is the total content of a plurality of types of abrasive grains when they are contained. Higher polishing rates tend to be achieved by increasing the content of abrasive grains. From the viewpoint of the surface smoothness of the substrate after polishing and the stability of polishing, the content is usually 25% by weight or less, preferably 20% by weight or less, more preferably 15% by weight or less, still more preferable. Is 10% by weight or less, for example, 8% by weight or less.

(water)
The polishing composition disclosed herein typically contains, in addition to the abrasive grains as described above, water in which the abrasive grains are dispersed. As the water, ion-exchanged water, pure water, ultrapure water, distilled water and the like can be preferably used. The ion-exchanged water can typically be deionized water.

The polishing composition disclosed herein can be preferably carried out, for example, in a form having a solid content of 0.5% by weight to 30.0% by weight. The form in which the solid content is 1.0% by weight to 20.0% by weight is more preferable. The polishing composition can typically be a slurry composition.

(acid)
The polishing composition disclosed herein is carried out in an embodiment containing an acid as a polishing accelerator. The acid that can be used is not particularly limited as long as the sodium hydroxide amount α required to raise the pH of the polishing composition by 1.0 satisfies the above range, and either an inorganic acid or an organic acid can be used. Is. Examples of the organic acid include organic carboxylic acids having 1 to 18 carbon atoms, typically 1 to 10 carbon atoms, organic phosphonic acids, organic sulfonic acids, amino acids and the like. The acid may be used alone or in combination of two or more.

Specific examples of the inorganic acid include phosphoric acid (ortrinic acid), nitrate, sulfuric acid, hydrochloric acid, boric acid, sulfamic acid, phosphinic acid, phosphonic acid, pyrophosphate, tripolyphosphate, tetrapolyphosphate, hexametaphosphate, carbonic acid, and fluoride. Hydrogenic acid, sulfite, thiosulfate, chloric acid, perchloric acid, chloric acid, hydroiodic acid, periodic acid, iodic acid, hydrobromic acid, perbromic acid, bromic acid, chromium acid, nitrite, etc. Can be mentioned.

Specific examples of organic acids include maleic acid, malic acid, glycolic acid, succinic acid, itaconic acid, malonic acid, imminodiacetic acid, gluconic acid, lactic acid, mandelic acid, tartrate acid, formic acid, acetic acid, propionic acid, butyric acid and adipine. Acid, oxalic acid, valeric acid, enanthic acid, caproic acid, capric acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, cyclohexanecarboxylic acid, phenylacetic acid, benzoic acid, crotonic acid , Oleic acid, linoleic acid, linolenic acid, ricinolenic acid, methacrylic acid, glutaric acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, tarthronic acid, glyceric acid, hydroxybutyric acid, hydroxyacetic acid, hydroxybenzoic acid, salicylic acid, isoquen Organic carboxylic acids such as acids, methylene succinic acid, gallic acid, ascorbic acid, nitroacetic acid, oxaloacetic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid; , Cysteine, methionine, phenylalanine, tryptophan, tyrosine, proline, cystine, glutamine, asparagine, lysine, arginine and other amino acids; nicotinic acid; picric acid; picolinic acid; methyl acid phosphate, ethyl acid phosphate, ethyl glycol acid phosphate, isopropyl acid Phosphate, phytic 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, ethanehydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid , Methanhydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, α-methylphosphonosuccinic acid, organic phosphonic acid such as aminopoly (methylenephosphonic acid); Examples thereof include ethanesulfonic acid, aminoethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, 2-naphthalenesulfonic acid, sulfosuccinic acid, 10-campersulfonic acid, organic sulfonic acid such as taurine and the like.

Examples of preferable acids from the viewpoint of polishing rate include phosphoric acid, malonic acid, maleic acid, hydrochloric acid, nitric acid, sulfuric acid, sulfamic acid, phytic acid, 1-hydroxyethylidene-1,1-diphosphonic acid and the like. Of these, phosphoric acid, malonic acid, maleic acid, nitric acid, and sulfuric acid are preferable.

In a preferred embodiment, the acid is a combination of phosphoric acid and a carboxylic acid having one or more hydroxyl groups in the molecular structure. The carboxylic acid may be either a monocarboxylic acid or a polycarboxylic acid (dicarboxylic acid, tricarboxylic acid, tetracarboxylic acid, etc.), but the dicarboxylic acid is preferable. Dicarboxylic acids include malonic acid, maleic acid, succinic acid, malic acid, oxalic acid, glutaric acid, adipic acid, pimelli acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, tartaric acid, and fumal. Examples thereof include acids, methylmalonic acid, dimethylmalonic acid, methylenesuccinic acid, gluconic acid, tartronic acid, glutamic acid, aspartic acid, oxaloacetate and cystine. Of these, malonic acid and maleic acid are preferable. By using these dicarboxylic acids and phosphoric acid in combination, the above-mentioned effects can be more exerted.

In a preferred embodiment of the polishing composition disclosed herein, the acid is a first acid (typically a weak acid) and a second acid that dissociates more easily (typically a strong acid). Are used in combination. By using the first acid in combination with the second acid, which is more likely to dissociate, the dissociation of the acid is better suppressed, and the application effect of the technique disclosed herein is more effectively exhibited. Can be done. The pKa1 of the first acid (acid dissociation constant of the first stage, 25 ° C.) is not particularly limited, but may be, for example, 1.8 or more and 5.0 or less. In some embodiments, the pKa1 of the first acid may be, for example, 1.9 or higher, typically 2.0 or higher. Examples of the first acid include phosphoric acid, maleic acid, sulfite, chloric acid, nitrite, tripolyphosphate, nicotinic acid, oxaloacetic acid, chloroacetic acid, phthalic acid, fumaric acid, malonic acid, tartaric acid, polysulfonic acid, Examples thereof include glutamic acid, salicylic acid, aspartic acid, glycine, arginine, tyrosine, valine, methionine, lysine, leucine and the like. Of these, phosphoric acid, malonic acid, and maleic acid are preferable. The pKa1 of the second acid (acid dissociation constant of the first stage, 25 ° C.) is not particularly limited as long as it is smaller than the pKa1 of the first acid, but may be, for example, -10.0 or more and 2.5 or less. In some embodiments, the pKa1 of the second acid may be, for example, 2.3 or less, typically 2.0 or less. The pKa1 of the second acid may be less than 1.8, 1.5 or less, and typically 1.2 or less. Examples of the second acid are hydrochloric acid, nitrate, sulfuric acid, phosphoric acid, maleic acid, oxalic acid, pyrophosphate, phosphinic acid, phosphonic acid, picric acid, picolinic acid, thiosulfate, chloric acid, perchloric acid, iodine. Examples thereof include hydride, periodated hydride, iodic acid, hydrobromic acid, perbromic acid, bromine acid, chromium acid, nitroacetic acid, trichloroacetic acid, dichloroacetic acid, benzenesulfonic acid, p-toluenesulfonic acid and the like. Of these, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and maleic acid are preferable.

When the first acid and the second acid are used in combination, the ratio of the molar concentration X (mol / L) of the first acid to the molar concentration Y (mol / L) of the second acid in the polishing composition. The value (X / Y) of is not particularly limited, but is usually 3 or less, preferably 2.6 or less. By using the first acid and the second acid in combination so as to have a specific molar ratio, the above-mentioned effects can be more preferably exhibited. In some embodiments, the value of the ratio (X / Y) may be, for example, 2 or less, typically 1.8 or less (eg, 1.7 or less). The lower limit of the value (X / Y) of the above ratio is not particularly limited, but is usually 0.01 or more, preferably 0.05 or more, and more preferably 0.1 or more. In the technique disclosed herein, for example, the ratio value (X / Y) of the molar concentration X of the first acid to the molar concentration Y of the second acid in the polishing composition is 0.12 or more and 2.6 or less. (Preferably 1 or more and 1.7 or less) can be preferably carried out.

The acid may be used in the form of a salt of the acid. Examples of the salt include metal salts, ammonium salts, alkanolamine salts and the like of the above-mentioned inorganic acids and organic acids. Examples of the metal salt include alkali metal salts such as lithium salt, sodium salt and potassium salt. Examples of the ammonium salt include quaternary ammonium salts such as tetramethylammonium salt and tetraethylammonium salt. Examples of the alkanolamine salt include monoethanolamine salt, diethanolamine salt, and triethanolamine salt.
Specific examples of the salt include alkali metal phosphates and alkali metals such as tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate. Hydrogen phosphate: Alkaline metal salt of organic acid exemplified above; Alkaline metal salt of diacetate diacetate, Alkaline metal salt of diethylenetriamine pentaacetic acid, Alkaline metal salt of hydroxyethylethylenediamine triacetic acid, Triethylenetetraminehexacetic acid Alkaline metal salts; etc. The alkali metal in these alkali metal salts can be, for example, lithium, sodium, potassium and the like.

As the salt that can be contained in the polishing composition disclosed herein, a salt of an inorganic acid, for example, an alkali metal salt or an ammonium salt can be preferably adopted. For example, potassium chloride, sodium chloride, ammonium chloride, potassium nitrate, sodium nitrate, ammonium nitrate, potassium phosphate and the like can be preferably used.

The acid and its salt can be used alone or in combination of two or more (eg, two or three). In a preferred embodiment, an acid and a salt of an acid different from the acid can be used in combination. In another preferred embodiment, the acid is preferably an inorganic acid. The acid salt is preferably an inorganic acid salt.

The molar concentration of the acid in the polishing composition (or the total molar concentration of the two acids if they are included) is the amount of sodium hydroxide required to raise the pH of the polishing composition by 1.0. There is no particular limitation as long as the above range is satisfied, but it is typically 0.01 mol / L or more, preferably 0.05 mol / L or more, more preferably 0.1 mol / L or more, and 0.15. More preferably, mol / L or more. In some embodiments, the molar concentration of acid may be, for example, 0.18 mol / L or higher, typically 0.25 mol / L or higher. Higher polishing rates can be achieved by increasing the molar concentration of acid. From the viewpoint of surface accuracy after polishing, polishing stability, etc., the molar concentration of the acid is usually 2 mol / L or less, and in some embodiments, the molar concentration of the acid is, for example, 1 mol / L. It may be L or less, and typically 0.5 mol / L or less.

(Oxidant)
The polishing composition disclosed herein contains an oxidizing agent. Examples of oxidizing agents are peroxides, nitrates or salts thereof, perioic acids or salts thereof, peroxo acid or salts thereof, permanganic acid or salts thereof, chromium acid or salts thereof, oxygen acids or salts thereof, metal salts and the like. , Sulfates and the like, but are not limited thereto. The oxidizing agent may be used alone or in combination of two or more. Specific examples of the oxidizing agent include hydrogen peroxide, sodium peroxide, barium peroxide, nitrate, iron nitrate, aluminum nitrate, ammonium nitrate, peroxomonosulfate, ammonium peroxomonosulfate, metal salt peroxo monosulfate, peroxodisulfate, and peroxodisulfuric acid. Ammonium sulfate, peroxodisulfuric acid metal salt, peroxophosphate, peroxosulfate, sodium peroxoborate, pergic acid, peracetic acid, perbenzoic acid, perphthalic acid, hypobromic acid, hypoiodic acid, chloric acid, bromine acid, Iodine acid, perioic acid, perchloric acid, hypochloric acid, sodium hypochlorite, calcium hypochlorite, potassium permanganate, metal chromate salt, metal heavy chromate salt, iron chloride, iron sulfate, Examples thereof include iron citrate and iron ammonium sulfate. Preferred oxidizing agents include hydrogen peroxide, iron nitrate, periodic acid, peroxomonosulfuric acid, peroxodisulfuric acid and nitric acid. It preferably contains at least hydrogen peroxide, and more preferably consists of hydrogen peroxide.

The content of the oxidizing agent in the polishing composition is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, still more preferably 0.3% by weight or more based on the amount of the active ingredient. .. If the content of the oxidant is too small, the rate of oxidizing the object to be polished slows down and the polishing rate decreases, which may be unfavorable for practical use. The content of the oxidizing agent in the polishing composition is preferably 5% by weight or less, more preferably 1% by weight or less, based on the amount of the active ingredient. If the content of the oxidizing agent is too large, the surface accuracy of the object to be polished tends to be lowered, which may be unfavorable for practical use.

(Basic compound)
The polishing composition may contain a basic compound, if necessary. Here, the basic compound refers to a compound having a function of raising the pH of the composition by being added to the polishing composition. Examples of basic compounds include alkali metal hydroxides, carbonates and bicarbonates, quaternary ammonium or salts thereof, ammonia, amines, phosphates and hydrogen phosphates, organic acid salts and the like. The basic compound may be used alone or in combination of two or more.

Specific examples of the alkali metal hydroxide include potassium hydroxide, sodium hydroxide and the like.
Specific examples of the carbonate and the hydrogen carbonate include ammonium hydrogen carbonate, ammonium carbonate, potassium hydrogen carbonate, potassium carbonate, sodium hydrogen carbonate, sodium carbonate and the like.
Specific examples of the quaternary ammonium or a salt thereof include quaternary ammonium hydroxides such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide; alkali metals of such quaternary ammonium hydroxides. Salt; etc. Examples of the alkali metal salt include sodium salts and potassium salts.
Specific examples of amines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, monoethanolamine, N- (β-aminoethyl) ethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, and anhydrous piperazine. , Piperazine hexahydrate, 1- (2-aminoethyl) piperazine, N-methylpiperazine, guanidine, azoles such as imidazole and triazole, and the like.
Specific examples of phosphates and hydrogen phosphate salts include alkalis such as tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate. Metal salts can be mentioned.
Specific examples of the organic acid salt include potassium oxalate, potassium tartrate, sodium potassium tartrate, ammonium tartrate and the like.

(Other ingredients)
The polishing composition disclosed herein is a polishing composition (for example, Ni-P substrate) containing a surfactant, a chelating agent, a preservative, an antifungal agent, etc., to the extent that the effect of the present invention is not significantly impaired. Etc., a known additive that can be used in a polishing composition for a magnetic disk substrate) may be further contained, if necessary.

The polishing composition may contain a surfactant, if necessary. The term "surfactant" as used herein refers to a compound having at least one hydrophilic moiety (typically a hydrophilic group) and one or more hydrophobic moieties (typically a hydrophobic group) in one molecule. The surfactant is not particularly limited, and any of anionic surfactant, nonionic surfactant, cationic surfactant, and amphoteric surfactant can be used. The use of a surfactant can improve the dispersion stability of the polishing composition. The surfactant may be used alone or in combination of two or more.
Specific examples of the anionic surfactant include polyoxyethylene alkyl ether acetic acid, polyoxyethylene alkyl sulfate ester, alkyl sulfate ester, polyoxyethylene alkyl sulfate, alkyl sulfuric acid, alkylbenzene sulfonic acid, alkyl phosphate ester, and polyoxyethylene. Alkyl phosphate ester, polyoxyethylene sulfosuccinic acid, alkyl sulfosuccinic acid, alkylnaphthalene sulfonic acid, alkyldiphenyl ether disulfonic acid, polyacrylic acid, sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzene sulfonate, sodium polyoxyethylene alkyl ether sulfate, Examples thereof include ammonium polyoxyethylene alkylphenyl ether sulfate and sodium polyoxyethylene alkylphenyl ether sulfate.
Other specific examples of anionic surfactants include polyalkylaryl sulfonic acid-based compounds such as naphthalene sulfonic acid formaldehyde condensate, methylnaphthalene sulfonic acid formaldehyde condensate, anthracene sulfonic acid formaldehyde condensate, and benzene sulfonic acid formaldehyde condensate. Melamine formalin resin sulfonic acid compound such as melamine sulfonic acid formaldehyde condensate; Lignin sulfonic acid compound such as lignin sulfonic acid and modified lignin sulfonic acid; Aromatic amino sulfonic acid such as aminoaryl sulfonic acid-phenol-formaldehyde condensate Examples include system compounds. As the salt, alkali metal salts such as sodium salt and potassium salt are preferable.
Specific examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, sorbitan fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, alkyl alkanolamide and the like. ..
Specific examples of the cationic surfactant include an alkyltrimethylammonium salt, an alkyldimethylammonium salt, an alkylbenzyldimethylammonium salt, an alkylamine salt and the like.
Specific examples of the amphoteric tenside include alkyl betaine, alkyl amine oxide and the like.

In the polishing composition of the embodiment containing a surfactant, it is appropriate that the content of the surfactant is, for example, 0.0005% by weight or more. The content is preferably 0.001% by weight or more, more preferably 0.01% by weight or more, from the viewpoint of surface smoothness after polishing. Further, from the viewpoint of the polishing rate and the like, the content is preferably 1% by weight or less, preferably 0.5% by weight or less, for example, 0.1% by weight or less.

Examples of chelating agents include aminocarboxylic acid-based chelating agents and organic phosphonic acid-based chelating agents. Examples of aminocarboxylic acid-based chelating agents include ethylenediamine tetraacetic acid, sodium ethylenediamine tetraacetate, nitrilotriacetic acid, sodium nitrilotriacetate, ammonium nitrilotriacetic acid, hydroxyethylethylenediamine triacetic acid, sodium hydroxyethylethylenediamine triacetate, and diethylenetriaminepentaacetic acid. , Diethylenetriamine pentaacetate sodium, triethylenetetramine hexaacetic acid and triethylenetetramine hexaacetate sodium. Examples of organic phosphonic acid-based chelating agents include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetrakis (methylenephosphonic acid), and diethylenetriaminepenta (methylenephosphonic acid). Acid), Etan-1,1-diphosphonic acid, Etan-1,1,2-triphosphonic acid, Etan-1-hydroxy-1,1-diphosphonic acid, Etan-1-hydroxy-1,1,2-triphosphonic acid , Etan-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid and α-methylphospho Contains nosuccinic acid. Of these, organic phosphonic acid-based chelating agents are more preferable, and among them, ethylenediaminetetrakis (methylenephosphonic acid) and diethylenetriaminepenta (methylenephosphonic acid) are mentioned. Particularly preferred chelating agents include ethylenediamine tetrakis (methylenephosphonic acid).

Examples of preservatives and fungicides include isothiazolin-based preservatives such as 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one, and paraoxybenzoic acid esters. , Phenoxyethanol and the like.

(Abrasive liquid)
The polishing composition disclosed herein is typically supplied to a polishing object (for example, a magnetic disk substrate) in the form of a polishing liquid containing the polishing composition, and is used for polishing the polishing object. .. The polishing liquid may be prepared, for example, by diluting (typically diluting with water) the polishing composition. Alternatively, the polishing composition may be used as it is as a polishing liquid. That is, the concept of the polishing composition in the technique disclosed herein includes a polishing liquid (working slurry) supplied to the polishing object and used for polishing the polishing object, and diluted and used as the polishing liquid. Both with concentrates are included. The polishing composition in the form of such a concentrated liquid is advantageous from the viewpoint of convenience and cost reduction in manufacturing, distribution, storage and the like. The concentration ratio can be, for example, about 1.5 to 50 times. From the viewpoint of storage stability of the concentrate, a concentration ratio of about 2 to 20 times (typically 2 to 10 times) is appropriate.

(Composition for multi-dosage form polishing)
The polishing composition disclosed herein may be a one-dosage form or a multi-dosage form including a two-dosage form. For example, a liquid A containing a part of the constituent components (typically a component other than water) of the polishing composition and a liquid B containing the remaining components are mixed to polish the object to be polished. It may be configured to be used in. The composition for multi-dosage form polishing according to a preferred embodiment includes a liquid A containing abrasive grains (typically, an abrasive grain dispersion liquid which may contain a dispersant) and components other than the abrasive grains (eg, acid, water-soluble). It is composed of a liquid B containing a sex polymer and other additives). Normally, these are stored separately before use and can be mixed at the time of use (during polishing of the substrate to be polished). At the time of mixing, an oxidizing agent such as hydrogen peroxide may be further mixed. For example, when the oxidizing agent (for example, hydrogen peroxide) is supplied in the form of an aqueous solution (for example, hydrogen peroxide solution), the aqueous solution can be the C liquid constituting the multi-agent polishing composition.

(Use)
The application of the techniques disclosed herein is not particularly limited. According to the technique disclosed herein, it is possible to provide a polishing composition capable of highly reducing scratches after polishing while maintaining a high polishing rate. The polishing composition disclosed herein includes, for example, a magnetic disk substrate, a semiconductor substrate such as a silicon wafer (for example, a silicon single crystal wafer obtained by slicing a silicon single crystal ingot), and optics such as a lens and a reflection mirror. It can be preferably used for polishing various polishing objects that require a highly accurate surface, such as materials. Above all, it is suitable for polishing magnetic disk substrates. Examples of the magnetic disk substrate referred to here include a Ni-P substrate (meaning a magnetic disk substrate having a nickel phosphorus plating layer on the surface of a substrate disk made of aluminum alloy or the like) and a glass magnetic disk substrate. It is particularly meaningful to apply the techniques disclosed herein in such applications of polishing magnetic disk substrates. Application to a Ni-P substrate is particularly preferable.

Since the polishing composition disclosed herein can highly reduce scratches on the surface after polishing, it can be particularly preferably used in the final polishing step (finish polishing step) of the object to be polished. According to this specification, a method for manufacturing a polished product (for example, a method for manufacturing a magnetic disk substrate) including a final polishing step using the polishing composition disclosed herein and a magnetic disk substrate manufactured by the method are provided. obtain. The final policing refers to the final policing step in the manufacturing process of the target product (that is, a step in which further policing is not performed after the step).

The polishing composition disclosed herein may also be used in a polishing step upstream of final policing. Here, the polishing step upstream of the final polishing refers to the pre-polishing step between the rough polishing step and the final polishing step. The pre-polishing step typically comprises at least a primary polishing step and may further include a secondary, tertiary ... Etc. polishing step. The polishing composition can be used in any of the polishing steps, and the same or different polishing compositions can be used in these polishing steps. The polishing composition disclosed herein may be used, for example, in a polishing step performed immediately before final polishing.

<Polishing process>
The polishing composition disclosed herein can be suitably used for polishing an object to be polished (for example, a magnetic disk substrate), for example, in an embodiment including the following operations. Hereinafter, a preferred embodiment of a method of polishing an object to be polished (typically a substrate to be polished) using the polishing composition disclosed herein will be described.
That is, a polishing liquid (working slurry) containing any of the polishing compositions disclosed herein is prepared. The preparation of the polishing liquid may include preparing the polishing liquid by subjecting the polishing composition to operations such as concentration adjustment (for example, dilution) and pH adjustment. Alternatively, the polishing composition may be used as it is as a polishing liquid.

Next, the polishing liquid is supplied to the object to be polished, and polishing is performed by a conventional method. For example, an object to be polished is set in a general polishing device, and a polishing liquid is supplied to the surface (surface to be polished) of the object to be polished through the polishing pad of the polishing device. Typically, while continuously supplying the polishing liquid, the polishing pad is pressed against the surface of the object to be polished to move them relatively (for example, rotational movement). The polishing of the object to be polished is completed through such a polishing step.

The polishing process as described above can be part of the manufacturing process of a substrate (eg, a magnetic disk substrate, typically a Ni-P substrate). Therefore, according to this specification, a method for manufacturing a substrate and a method for polishing a substrate including the above-mentioned polishing step are provided.

The method for manufacturing a magnetic disk substrate disclosed herein may further include an upstream polishing step (hereinafter, also referred to as “step (P)”) performed prior to the polishing step using the polishing composition described above. According to the aspect including the step (P), the effect of shortening the required time of the entire policing step and increasing the productivity can be realized. The step (P) may be one policing step using one kind of polishing composition, or may include two or more policing steps performed by sequentially using two or more kinds of polishing compositions. good.

The polishing composition used in the step (P) (hereinafter, also referred to as “polishing composition (P)”) is not particularly limited. For example, as the abrasive grains, the abrasive grains exemplified as the material that can be used in the above-mentioned polishing composition can be used. When the polishing composition contains silica particles, the silica particles may be the same as or different from the silica particles contained in the above-mentioned polishing composition. The difference between the silica particles contained in the polishing composition (P) and the silica particles contained in the above-mentioned polishing composition is, for example, one or two or more differences in particle size, particle shape, density and other characteristics. possible.

The polishing composition (P) typically contains water in addition to the abrasive grains. In addition, the polishing composition (P) can contain the same components as the above-mentioned polishing composition (acid, oxidizing agent, basic compound, polymer, surfactant, various additives, etc.). Although not particularly limited, the pH of the polishing composition (P) can be, for example, 12.0 or less (typically 0.5 to 12.0), preferably 7.0 or less (typically, 0.5 to 12.0). For example, 0.5 to 7.0), more preferably 5.0 or less (typically 1.0 to 5.0), still more preferably 4.0 or less (for example, 1.0 to 4.0). .. In a preferred embodiment, the pH of the polishing composition (P) can be 3.0 or less (typically 1.0 to 3.0).

Hereinafter, some examples of the present invention will be described, but the present invention is not intended to be limited to those shown in such examples.

<Examples 1 to 20>
[Preparation of polishing composition]
Multiple types of acids were prepared. The polishing compositions of Examples 1 to 20 containing abrasive grains in a proportion of 5% by weight by mixing one or more of these acids with abrasive grains, 31% hydrogen peroxide solution, and deionized water. Prepared. As the abrasive grains, colloidal silica having an average primary particle diameter of 18 nm was used. The pH of the polishing composition according to each example was adjusted with potassium hydroxide (KOH). Table 1 shows the type and concentration of the acid used in each example, the concentration of hydrogen peroxide, and the pH of the polishing composition. Further, for the polishing composition of each example, the amount of sodium hydroxide α required to raise the pH by 1.0 was calculated by the above-mentioned method. The results are shown in the "NaOH amount α" column of Table 1.

[Abrasion of disc]
The polishing composition according to each example was used as it was in the polishing liquid, and the object to be polished was polished under the following conditions. As the object to be polished, an aluminum substrate for a hard disk having an electroless nickel phosphorus plating layer on the surface was used. Here, the one pre-polished so that the value of the surface roughness (arithmetic mean roughness (Ra)) measured by the laser scan type surface roughness meter "TMS-3000WRC" manufactured by Schmitt Measurement System is 6 Å is used. bottom. The object to be polished (hereinafter, also referred to as “Ni-P substrate”) had a diameter of 3.5 inches (a donut shape having an outer diameter of about 95 mm and an inner diameter of about 25 mm) and a thickness of 1.27 mm.

(Polishing conditions)
Polishing device: Double-sided polishing machine manufactured by System Seiko Co., Ltd., model "9B-5P"
Polishing pad: Suede non-buff type Number of substrates to be polished: 20 (2 sheets / carrier x 5 carriers x 2 batches)
Polishing liquid supply rate: 130 mL / min Polishing load: 120 g / cm ²
Lower platen rotation speed: 25 rpm
Polishing time: 5 minutes

[Abrasion rate]
The polishing rate when the substrate to be polished was polished under the above polishing conditions using the polishing composition according to each example was calculated. The polishing rate was determined based on the following formula.
Polishing rate [μm / min] = Weight loss of substrate due to polishing [g] / (Substrate area [cm ² ] x Nickel phosphorus plating density [g / cm ³ ] x Polishing time [min]) x 10 ⁴
(Calculated as substrate single-sided area: 66 cm ² , Ni-P plating density: 7.9 g / cm ² )
The obtained values are shown in the "polishing rate" column of Table 1. Here, the polishing rate of 0.12 μm / min or more is referred to as “◎”, the polishing rate of 0.06 μm / min or more and less than 0.12 μm / min is referred to as “◎”, and the polishing rate of less than 0.06 μm / min is referred to as “×”. evaluated.

[scratch]
A total of 6 sheets (3 sheets / batch) were randomly selected from the above-polished substrates, and the number of scratches on both sides of each substrate was measured under the following measurement conditions, and the number of scratches on 6 sheets (12 surfaces in total) was measured. The total number of scratches per surface of the substrate was divided by 12 to calculate the number of scratches (lines / surface). Then, the relative value of the number of scratches in each example was evaluated when the number of scratches in Example 9 was 100. Here, those having a relative value of the number of scratches less than 50 were evaluated as "⊚", those having a relative value of 50 or more and less than 100 were evaluated as "◯", and those having a relative value of 100 or more were evaluated as "x". The results are shown in the "Scratch" column of Table 1.

[Scratch measurement conditions]
Measuring device: Candela OSA7100G manufactured by KLA Tencor Co., Ltd.
Spindle speed: 10000 rpm
Measuring range: 17,000-47,000 μm
Step size: 4 μm
Encoder multiplier: × 16
Detection channel: P-Sc channel

As shown in Table 1, the pH of the polishing composition is 1.8-3.0, from which the amount of NaOH required to raise the pH by 1.0 α is less than 0.03 mol / L. The polishing compositions of Examples 8, 11-14, 16-20 had an unsuitable polishing rate. Further, the polishing composition of Example 9 having a NaOH amount α of more than 0.2 mol / L and the polishing compositions of Examples 10 and 15 having a pH of 1.5 had a high polishing rate, but were polished. The number of scratches after that showed an increasing tendency. On the other hand, the pH of the polishing composition is 1.8 to 3.0, and the amount of NaOH α required to raise the pH by 1.0 is 0.03 mol / L or more and 0.2 mol. The polishing compositions of Examples 1 to 7 having a pH of / L or less had a good polishing rate, and the number of scratches after polishing was reduced as compared with Examples 10 and 15. From this result, the pH is 1.8 to 3.0, and the amount of NaOH α required to raise the pH by 1.0 is 0.03 mol / L or more and 0.2 mol / L or less. According to the composition for use, it was confirmed that a high-quality polished surface with a reduced number of scratches could be efficiently realized.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above.

Claims (4)

A polishing composition used for polishing magnetic disk substrates.
Contains abrasive grains, acid, oxidizer and water,
The average primary particle diameter of the abrasive grains measured by the BET method is 1 nm or more and 50 nm or less.
The pH is 1.8-3.0 and
A polishing composition in which the amount of sodium hydroxide required to raise the pH by 1.0 is 0.03 mol / L or more and 0.2 mol / L or less. The polishing composition according to claim 1, wherein the abrasive grains include silica particles. The polishing composition according to claim 1 or 2, which is used in the finish polishing step. A method for manufacturing a magnetic disk substrate, which comprises a step of polishing the magnetic disk substrate using the polishing composition according to any one of claims 1 to 3.