JP7778472B2 - Polishing composition, method for polishing substrate, and method for manufacturing substrate - Google Patents

Description

The present invention relates to a polishing composition used for polishing magnetic disk substrates, a method for polishing substrates, and a method for manufacturing substrates.

Traditionally, the manufacturing process for magnetic disk substrates, which require high-precision surfaces, includes a step of polishing the substrate's raw material, the workpiece, using a polishing solution. For example, the manufacture of nickel-phosphorus-plated disk substrates (hereinafter also referred to as Ni-P substrates) generally involves polishing (primary polishing) that emphasizes polishing efficiency, and final polishing (finish polishing) to achieve the surface precision of the final product. Patent Document 1 is an example of a technical document related to polishing compositions used to polish magnetic disk substrates.

JP 2015-125792 A

When polishing magnetic disk substrates, efforts are continually being made to improve the quality of the substrate surface in order to increase recording capacity. In recent years, silica abrasive grains have been used as abrasive grains from the primary polishing stage onwards to ensure higher quality substrate surfaces after finish polishing. Silica abrasive grains contained in polishing compositions may remain on the object being polished after polishing, but such residual particles are undesirable as they can cause a decrease in surface quality after finish polishing.

The present invention therefore aims to provide a polishing composition for use in polishing magnetic disk substrates, which reduces the amount of silica abrasive grains remaining on the object to be polished. Another related object is to provide a method for polishing a substrate using the polishing composition, and a method for manufacturing a substrate.

According to the present specification, a polishing composition for magnetic disk substrates is provided. The polishing composition contains silica particles as abrasive grains, an acid, an oxidizing agent, and water. This polishing composition has a logarithm to the base 10 (i.e., log ₁₀ X) of the amount of etching of a mild steel plate X [ng/h·mm ² ] measured in a mild steel etching test in which the mild steel plate is immersed in the polishing composition, of 2.0 to 4.0.

A polishing composition whose etching amount X for mild steel satisfies the above condition tends to exhibit a favorable etching effect on magnetic disk substrates when used to polish the magnetic disk substrate. Therefore, the polishing composition dissolves the surface of the magnetic disk substrate through its favorable etching effect, and silica abrasive grains that have adhered to or become embedded in the surface of the magnetic disk substrate during the polishing process tend to become detached from the surface. Therefore, the polishing composition can prevent silica abrasive grains from remaining on the surface of the magnetic disk substrate, which is the object to be polished. Furthermore, the polishing composition tends to prevent corrosion of polishing equipment, etc.

In a preferred embodiment of the technology disclosed herein (including polishing compositions, methods for polishing substrates, and methods for manufacturing substrates; the same applies hereinafter), the pH of the polishing composition is 1.0 or more and 3.0 or less. A polishing composition having a pH equal to or less than the upper limit mentioned above is more likely to satisfy the condition regarding the etching amount X for mild steel. Therefore, the polishing composition is more likely to suppress the residue of silica abrasive grains on the surface of the magnetic disk substrate, which is the object to be polished. Furthermore, a polishing composition having a pH equal to or greater than the lower limit mentioned above is more likely to suppress corrosion of polishing equipment, etc., and can also reduce the environmental impact.

According to a preferred embodiment of the technology disclosed herein, the acid comprises a first acid and a second acid that dissociates more easily than the first acid. By using a combination of two or more acids with different dissociation efficiencies, it is easy to control the pH of the polishing composition within an appropriate range while also satisfying the conditions for the etching amount X for mild steel. Therefore, the polishing composition makes it easy to suppress the residue of silica abrasive grains on the surface of the magnetic disk substrate, which is the object to be polished.

According to a preferred embodiment of the technology disclosed herein, the acid includes an organic acid. Use of an organic acid can effectively reduce residual silica abrasive grains on the magnetic disk substrate being polished, while preventing the pH of the polishing composition from decreasing excessively.

According to some preferred embodiments, the acid further contains an inorganic acid in addition to the organic acid. Here, the content C ₀ of the organic acid in the polishing composition is preferably 0.005 mol/L or more. Furthermore, the content C 1 _M of the inorganic acid in the polishing composition is preferably less than 0.14 mol/L. When the organic acid content C ₀ is not too low, the etching amount X for mild steel can be improved. Furthermore, when the content of the inorganic acid C 1 _M is not too high, an excessive decrease in the pH of the polishing composition can be prevented. Therefore, a polishing composition in which the organic acid content C ₀ and the inorganic acid content C 1 _M are each within the above ranges can suitably reduce the residual silica abrasive grains on the magnetic disk substrate to be polished while suppressing corrosion and environmental load of the polishing apparatus.

This specification also provides a method for polishing a substrate. The polishing method includes step (1) of supplying any of the polishing compositions disclosed herein to a substrate to be polished and polishing the substrate. This polishing method efficiently improves the surface quality of the polished product by reducing residual silica abrasive grains. In some embodiments, the substrate polishing method further includes step (2) of supplying a finish polishing composition to the substrate to be polished and polishing the substrate to be polished after step (1). The finish polishing composition preferably contains colloidal silica. By performing step (2) after step (1), a higher-quality substrate surface can be obtained.

The present specification also provides a method for manufacturing a magnetic disk substrate. The manufacturing method includes step (1) of polishing a substrate to be polished using any of the polishing compositions disclosed herein. This manufacturing method enables the efficient production of magnetic disk substrates with high-quality surfaces. In some embodiments, the substrate manufacturing method further includes step (2) of polishing the substrate to be polished using a finish polishing composition after step (1). The finish polishing composition preferably contains colloidal silica. By performing step (2) after step (1), magnetic disk substrates with higher-quality surfaces can be efficiently manufactured.

1 is an SEM image of the substrate surface after cleaning in Example 4. 10 is an SEM image of the substrate surface after cleaning in Example 9. 10 is an SEM image of the substrate surface after cleaning in Example 8. 10 is an SEM image of the substrate surface after cleaning in Example 14. 1 is a graph showing the relationship between the etching amount X and the number of residual silica particles [%] in a mild steel etching test.

Preferred embodiments of the present invention are described below. It should be noted that matters necessary for implementing the present invention other than those specifically mentioned in this specification can be understood as design matters for those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field.

(etching amount X for mild steel)
The polishing composition disclosed herein has an excellent etching amount X for mild steel. The etching amount X for mild steel refers to the weight loss per unit surface area and per unit time of a mild steel plate, as measured in the mild steel etching test described below, in which the mild steel plate is immersed in the polishing composition. A polishing composition with a high etching amount X for mild steel tends to exhibit a high etching effect on the surface of a magnetic disk substrate when used to polish the magnetic disk substrate. Therefore, the use of this polishing composition favorably improves the dissolution rate of the magnetic disk substrate surface by etching, thereby enabling at least a portion of particles (typically silica abrasive grains) adhered to or embedded in the surface of the magnetic disk substrate during the polishing process to be detached from the surface. The polishing composition, from which particles have been detached, can be favorably removed from the surface in a subsequent cleaning process or other process. Therefore, the polishing composition easily prevents silica abrasive grains from remaining on the magnetic disk substrate to be polished. The etching amount X of the polishing composition for mild steel can be specifically evaluated by the mild steel etching test described below.

[Mild steel etching test]
A polishing composition is prepared, and a mild steel plate is immersed in the polishing composition at a liquid temperature of 25° C. A steel material of SS400 (square) based on JIS G3101 is used as the mild steel plate. After the immersion time T [hours] has elapsed, the mild steel plate is removed from the polishing composition, which is the immersion liquid, washed with water, dried, and the weight W2 [ng] of the mild steel plate after drying is measured. From the weight W1 [ng] of the mild steel plate before immersion in the polishing composition, the weight W2 [ng] of the mild steel plate after drying, the immersion time T [hours], and the surface area SA [mm ² ] of the mild steel plate, the weight loss per unit surface area and per unit time of the mild steel plate, i.e., the etching amount X, is calculated from the following formula: Etching amount X [ng/h·mm ² ] = (weight W1 [ng] - weight W2 [ng]) / (immersion time T [hours] × surface area SA [mm ² ] of the mild steel plate). Specifically, the mild steel etching test can be carried out by the method shown in the examples described later.

The polishing composition disclosed herein has an etching amount X of 100 ng/h· ^mm2 or more when measured in the above-mentioned mild steel etching test in which the mild steel plate is immersed in the polishing composition. In other words, the polishing composition disclosed herein has a value when the etching amount X [ng/h· ^mm2 ] of the mild steel plate measured in the above-mentioned mild steel etching test in which the mild steel plate is immersed in the polishing composition is converted to a logarithm with base 10 (i.e., _log10X ) of 2.0 or more. A polishing composition showing an etching amount X equal to or greater than the above-mentioned lower limit tends to exhibit a suitable etching effect on the surface of a magnetic disk substrate, and is likely to suppress the residue of silica abrasive grains on the surface of the object to be polished. From the viewpoint of further reducing the residual silica abrasive grains, in a preferred embodiment, the _log10X is 2.3 or more, more preferably 2.7 or more, and even more preferably 3.0 or more (e.g., 3.3 or more).

On the other hand, if the etching amount X of the polishing composition on mild steel is too high, problems such as corrosion of polishing equipment components such as the polishing table may occur during polishing using the polishing composition. In a preferred embodiment, the polishing composition disclosed herein has a base 10 logarithm (log ₁₀ X) of the etching amount X [ng/h·mm ² ] of 4.0 or less. In the mild steel etching test, polishing compositions that exhibit an etching amount X of not more than the upper limit tend to suppress corrosion of the polishing equipment. In some embodiments, the log ₁₀ X may be 3.9 or less, 3.8 or less, 3.5 or less, or 3.0 or less.

<Polishing composition>
(Silica particles)
The polishing composition disclosed herein contains silica particles as abrasive grains. The silica particles have a volume-based average particle diameter in the range of 50 nm to 500 nm as determined by SEM image analysis. By using silica particles having such an average particle diameter as abrasive grains, both processability and surface quality can be achieved. The volume-based average particle diameter of the silica particles is preferably in the range of 50 nm to 300 nm, and more preferably in the range of 50 nm to 250 nm. This achieves further reduced microwaviness. The volume-based average particle diameter of the silica particles is preferably approximately 70 nm or more, more preferably approximately 90 nm or more, even more preferably approximately 110 nm or more, and particularly preferably approximately 130 nm or more (e.g., 150 nm or more). Silica particles with a large average particle diameter can easily achieve processability suitable for polishing (e.g., primary polishing) of magnetic disk substrates. Furthermore, from the viewpoint of improving microwaviness, the volume-based average particle size of the silica particles is suitably about 230 nm or less, preferably about 220 nm or less, more preferably about 210 nm or less, and even more preferably about 200 nm or less, and may be about 190 nm or less, about 185 nm or less, about 180 nm or less, about 175 nm or less, or about 170 nm or less. The effect of improving processability in polishing of magnetic disk substrates by the technology disclosed herein is preferably realized in an embodiment using silica particles having an average particle size limited as described above.

While not particularly limited, the average aspect ratio of the silica particles may be, for example, 1.0 or greater. In some embodiments, the average aspect ratio may be, for example, 1.02 or greater, or even 1.05 or greater. From the viewpoint of maintaining or improving processability, the average aspect ratio of the silica particles is preferably approximately 1.07 or greater, more preferably approximately 1.1 or greater (or 1.10 or greater), even more preferably approximately 1.11 or greater, and may even be approximately 1.12 or greater. Furthermore, from the viewpoint of efficiently improving surface quality, in some embodiments, the average aspect ratio is suitably 2.50 or less, and may be 2.0 or less, or 1.70 or less. The technology disclosed herein may also be suitably implemented in embodiments in which the average aspect ratio of the silica particles is 1.50 or less, or even 1.20 or less (e.g., 1.15 or less). In some embodiments, the average aspect ratio of the silica particles may be 1.1 or greater and 1.5 or less. Specific examples of the shape of particles with an aspect ratio of approximately 1.1 or more (non-spherical particles) include a peanut shape (i.e., the shape of a peanut shell), a cocoon shape, a shape with projections (e.g., a confetti candy shape), and a rugby ball shape.

The average particle size and average aspect ratio are determined by the following method. Specifically, using a scanning electron microscope (SEM), 1,000 or more particles contained in the silica particles to be measured (which may be one type of silica particle or a mixture of two or more types of silica particles) are observed in an SEM image containing 50 or more particles within one field of view. The observation magnification is 20,000 to 50,000 times. The long side length (long diameter value) of the smallest rectangle circumscribing each particle image is then divided by the short side length (short diameter value) to calculate the long diameter/short diameter ratio (aspect ratio) of each particle. Furthermore, the volume of each particle is calculated by 4πr ³ /3, where r is the radius of an ideal circle (perfect circle) having an area equal to the projected area of each particle image. Here, the aspect ratio and volume are calculated by counting each particle independently dispersed in the polishing composition as one particle, regardless of whether it is a primary particle or a secondary particle. The average particle size is determined by obtaining a volume-based particle size distribution from the volume of the predetermined number of particles, and calculating the average particle size from that standard. The average particle size can be determined using a general SEM and image analysis software. For example, a scanning electron microscope "SU8000" manufactured by Hitachi High-Technologies Corporation or image analysis particle size distribution measurement software "Mac-View" manufactured by Mountec Co., Ltd. can be used. The same applies to the examples described below.

Silica particles having the above average particle size or average aspect ratio can be adjusted by selecting the type of silica particles used, selecting or adjusting the silica production method, or mixing two or more types of silica particles with different particle shapes. For example, the silica particles disclosed herein can be obtained by selecting one type of particle group having a specific particle size and aspect ratio, or by selecting two or more types of particle groups and mixing them in an appropriate ratio, based on the description of this specification and taking into account common general technical knowledge as appropriate. Furthermore, based on the description of this specification and taking into account common general technical knowledge, it is also possible to employ a method of obtaining irregular-shaped particles by crushing porous silica gel under appropriate conditions, or a method of growing the obtained irregular-shaped particles by adding a predetermined amount of silicate under appropriate conditions (e.g., pH, temperature, etc.) to obtain irregular-shaped particles with the desired particle size. The silica particles disclosed herein can be obtained by mixing one type of particle obtained in this way alone or with other silica particles having different particle properties.

Various silica particles containing silica as the primary component can be used. Silica particles containing silica as the primary component refer to particles containing silica at least 90% by weight, e.g., at least 95% by weight, typically at least 98% by weight. Examples of silica particles that can be used include, but are not limited to, colloidal silica, agglomerated silica, precipitated silica (also referred to as precipitated silica), sodium silicate silica, alkoxide silica, fumed silica, dried silica, and detonation silica. Furthermore, silica particles obtained from the above-mentioned silica particles can also be used. Examples of such silica particles include silica particles obtained by subjecting the above-mentioned raw silica particles (hereinafter referred to as "raw silica") to one or more of the following treatments: heat treatment (e.g., heating, drying, or calcination); pressure treatment (e.g., autoclaving); mechanical treatment (e.g., crushing or grinding); and surface modification. Examples of surface modification include chemical modification (e.g., introduction of functional groups or metal modification). The silica particles disclosed herein can contain one or more of the above-mentioned silica particles, either singly or in combination.

In the technology disclosed herein, the silica particles may be in the form of secondary particles formed by agglomeration of multiple primary particles, or in the form of secondary particles formed by association of multiple primary particles. Furthermore, silica particles in the form of primary particles and silica particles in the form of secondary particles may be present together.

The content of silica particles in the polishing composition is not particularly limited, and is, for example, 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more, even more preferably 3% by weight or more, and particularly preferably 5% by weight or more. When multiple types of silica particles are contained, the above content refers to the total content of all of them. Increasing the content of silica particles tends to result in higher processability. From the viewpoint of surface smoothness of the substrate after polishing and polishing stability, the above content is appropriately 30% by weight or less, preferably 25% by weight or less, more preferably 15% by weight or less, and even more preferably 10% by weight or less.

In the polishing composition disclosed herein, the content of silica particles in the solid content of the polishing composition is preferably 90% by weight or more of the total solid content, more preferably 95% by weight or more, and even more preferably 98% by weight or more, for example, 99% by weight or more, in order to better demonstrate the effects of the technology disclosed herein. In this specification, the solid content of the polishing composition refers to the residue, i.e., non-volatile content, remaining after evaporating water from the polishing composition at a temperature at which bound water is not removed, for example, 60°C.

The polishing composition disclosed herein can be preferably implemented in an embodiment that is substantially free of alumina particles. Examples of alumina particles include α-alumina particles. Such polishing compositions prevent quality degradation due to the use of alumina particles. Examples of quality degradation include scratches and dents, residual alumina, and penetration defects. As used herein, "substantially free of alumina particles" means that the proportion of alumina particles in the total solid content of the polishing composition is 1% by weight or less, more preferably 0.5% by weight or less, and typically 0.1% by weight or less. A polishing composition with an alumina particle proportion of 0% by weight, i.e., a polishing composition that does not contain alumina particles, is particularly preferred. The polishing composition disclosed herein can also be preferably implemented in an embodiment that is substantially free of α-alumina particles.

The polishing composition disclosed herein can also be preferably implemented in an embodiment that is substantially free of particles other than silica particles, i.e., non-silica particles. Here, "substantially free of non-silica particles" means that the proportion of non-silica particles in the total solid content of the polishing composition is 1 wt % or less, more preferably 0.5 wt % or less, and typically 0.1 wt % or less. In such an embodiment, the effects of applying the technology disclosed herein can be optimally exhibited.

(acid)
The polishing composition disclosed herein contains an acid as a polishing accelerator. The acid may be either an inorganic acid or an organic acid. Examples of organic acids include organic carboxylic acids, organic sulfonic acids, and amino acids each having about 1 to 18 carbon atoms, typically about 1 to 10 carbon atoms. The acids may be used alone or in combination of two or more.

Specific examples of inorganic acids include phosphoric acid (orthophosphoric acid), nitric acid, sulfuric acid, hydrochloric acid, boric acid, sulfamic acid, phosphinic acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, hexametaphosphoric acid, carbonic acid, hydrofluoric acid, sulfurous acid, thiosulfuric acid, chloric acid, perchloric acid, chlorous acid, hydroiodic acid, periodic acid, iodic acid, hydrobromic acid, perbromic acid, bromic acid, chromic acid, and nitrous acid.

Specific examples of organic acids include citric acid, maleic acid, malic acid, glycolic acid, succinic acid, itaconic acid, malonic acid, iminodiacetic acid, gluconic acid, lactic acid, mandelic acid, tartaric acid, formic acid, acetic acid, propionic acid, butyric acid, adipic acid, oxalic acid, valeric acid, enanthic acid, caproic acid, caprylic 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, and methacrylic acid. , glutaric acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, tartronic acid, glyceric acid, hydroxybutyric acid, hydroxyacetic acid, hydroxybenzoic acid, salicylic acid, isocitric acid, methylenesuccinic acid, gallic acid, ascorbic acid, nitroacetic acid, oxaloacetic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, and other organic carboxylic acids; glycine, alanine, glutamic acid, aspartic acid, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, phenylalanine, tryptophan, tyrosine, proline, Amino acids such as lysine, cystine, glutamine, asparagine, lysine, and arginine; nicotinic acid; picric acid; picolinic acid; 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 , organic phosphonic acids such as 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 aminopoly(methylenephosphonic acid); organic sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, aminoethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, 2-naphthalenesulfonic acid, sulfosuccinic acid, 10-camphorsulfonic acid, isethionic acid, and taurine.

From the viewpoint of polishing efficiency, preferred acids include phosphoric acid, phosphonic acid, maleic acid, hydrochloric acid, nitric acid, sulfuric acid, sulfamic acid, phytic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, and methanesulfonic acid. Of these, phosphoric acid, phosphonic acid, maleic acid, hydrochloric acid, nitric acid, and sulfuric acid are preferred.

In a preferred embodiment of the polishing composition disclosed herein, the pKa1 (first-stage acid dissociation index, 25°C) of the acid contained in the polishing composition is -10.0 or greater and 2.5 or less. In some embodiments, the pKa1 of the acid may be, for example, 2.3 or less, 2.0 or less, less than 1.8, 1.5 or less, or 1.2 or less. Non-limiting examples of the acid include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, maleic acid, oxalic acid, pyrophosphoric acid, phosphinic acid, phosphonic acid, picric acid, picolinic acid, thiosulfuric acid, chloric acid, perchloric acid, hydroiodic acid, hydroperiodic acid, iodic acid, hydrobromic acid, perbromic acid, bromic acid, chromic acid, nitroacetic acid, trichloroacetic acid, dichloroacetic acid, benzenesulfonic acid, p-toluenesulfonic acid, etc. Among these, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and maleic acid are preferred, and phosphoric acid is more preferred. The acid contained in the polishing composition disclosed herein can be one selected from the above acids, or two or more selected from the above acids can be used in combination.

In a preferred embodiment of the polishing composition disclosed herein, the polishing composition contains two or more different acids. In particular, by using a combination of two or more acids that differ in the degree to which they contribute to the etching amount X of mild steel, it becomes easier to control the etching amount X of mild steel within a suitable range. Therefore, a polishing composition of this configuration reduces the amount of silica abrasive grains remaining on the surface of the object to be polished, making it easier to control the surface quality within a suitable range.

In some embodiments, the acid may be a combination of a first acid and a second acid that dissociates more easily than the first acid. Acids that dissociate more easily tend to have different etching amounts X for mild steel. Therefore, by using a first acid in combination with a second acid that dissociates more easily than the first acid, it tends to be possible to control the pH and other parameters of the polishing composition within suitable ranges while controlling the etching amount X for mild steel within a suitable range. Furthermore, using a first acid in combination with a second acid can be effective in suppressing pH fluctuations (typically pH increases) in the polishing composition as polishing progresses. This can be advantageous from the perspective of efficiently achieving a high-quality surface.

The pKa1 (first stage acid dissociation index, 25°C) of the first acid is not particularly limited and can 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 more, or even 2.0 or more. Non-limiting examples of acids that can be selected as the first acid include phosphoric acid, maleic acid, sulfurous acid, chlorous acid, nitrous acid, tripolyphosphoric acid, oxaloacetic acid, chloroacetic acid, phthalic acid, fumaric acid, malonic acid, citric acid, tartaric acid, polysulfonic acid, glutamic acid, salicylic acid, aspartic acid, glycine, arginine, tyrosine, valine, methionine, lysine, and leucine. Among these, phosphoric acid, malonic acid, citric acid, and maleic acid are preferred. These can be used alone or in combination of two or more. When the first acid is used in the form of a salt as described below, the pKa1 of the first acid is the pKa1 of the acid corresponding to the salt.

The pKa1 (first stage acid dissociation exponent, 25°C) of the second acid is not particularly limited as long as it is lower than the pKa1 of the first acid. The pKa1 of the second acid can be, for example, -10.0 or higher and 2.5 or lower. In some embodiments, the pKa1 of the second acid can be, for example, 2.3 or lower, 2.0 or lower, less than 1.8, 1.5 or lower, or 1.2 or lower. Non-limiting examples of acids that can be selected as the second acid include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, maleic acid, oxalic acid, pyrophosphoric acid, phosphinic acid, phosphonic acid, picric acid, picolinic acid, thiosulfuric acid, chloric acid, perchloric acid, hydroiodic acid, hydroperiodic acid, iodic acid, hydrobromic acid, perbromic acid, bromic acid, chromic acid, nitroacetic acid, trichloroacetic acid, dichloroacetic acid, benzenesulfonic acid, and p-toluenesulfonic acid. Of these, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and maleic acid are preferred. These can be used alone or in combination of two or more. When the second acid is used in the form of a salt as described below, the pKa1 of the second acid is the pKa1 of the acid corresponding to the salt.

In a preferred embodiment of the technology disclosed herein, the polishing composition contains an organic acid. The use of an organic acid improves the etching amount X for mild steel while suppressing an excessive decrease in the pH of the polishing composition, and particularly effectively reduces residual silica abrasive grains on the surface of the magnetic disk substrate being polished. There are no particular limitations on the reason why the use of an organic acid makes it easier to reduce residual silica abrasive grains. In some embodiments, this may be due to the organic acid interacting (e.g., forming a chelate complex) with metal ions contained in the object being polished (e.g., nickel ions contained in the plating layer when the object being polished is a nickel-phosphorus-plated magnetic disk substrate).

In some embodiments, the polishing composition contains an inorganic acid and an organic acid as acids. The use of an inorganic acid makes it easier to improve the etching amount X for mild steel. Improving the etching amount X for mild steel can particularly effectively reduce residual silica abrasive grains on the surface of a magnetic disk substrate, which is the object to be polished. Furthermore, the use of an organic acid tends to improve the etching amount X for mild steel while suppressing an excessive decrease in pH. Therefore, by using a combination of an inorganic acid and an organic acid, it is possible to improve the etching amount X for mild steel while suppressing an excessive decrease in pH compared to using an inorganic acid alone. Not having an excessively low pH contributes to reducing environmental impact, suppressing corrosion of the polishing equipment, and improving the safety of the polishing process or substrate manufacturing process. The acid contained in the polishing composition disclosed herein can be a combination of one or more inorganic acids selected from the above and one or more organic acids selected from the above.

The acid may be used in the form of a salt thereof. Examples of the salt include metal salts, ammonium salts, alkanolamine salts, etc. of the inorganic acids and organic acids described above. Examples of the metal salts include alkali metal salts such as lithium salts, sodium salts, and potassium salts. Examples of the ammonium salts include quaternary ammonium salts such as tetramethylammonium salts and tetraethylammonium salts. Examples of the alkanolamine salts include monoethanolamine salts, diethanolamine salts, and triethanolamine salts.
Specific examples of salts include alkali metal phosphates and alkali metal hydrogen phosphates such as tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate; alkali metal salts of the organic acids exemplified above; and alkali metal salts of glutamic acid diacetic acid, alkali metal salts of diethylenetriaminepentaacetic acid, alkali metal salts of hydroxyethylethylenediaminetriacetic acid, and alkali metal salts of triethylenetetraminehexaacetic acid. The alkali metal in these alkali metal salts may be, for example, lithium, sodium, or potassium.

Salts that can be contained in the polishing composition disclosed herein preferably include salts of inorganic acids, such as alkali metal salts and ammonium salts. For example, potassium chloride, sodium chloride, ammonium chloride, potassium nitrate, sodium nitrate, ammonium nitrate, potassium phosphate, potassium hydrogen sulfate, sodium hydrogen sulfate, and ammonium hydrogen sulfate can be preferably used.

The acids and their salts can be used singly or in combination of two or more (e.g., two or three). In some preferred embodiments, an acid can be used in combination with a salt of an acid different from the acid. The acid is preferably an inorganic acid. The acid salt is preferably a salt of an inorganic acid.

The acid content in the polishing composition (when multiple types of acids are contained, the total content thereof) is not particularly limited, and is suitably, for example, approximately 0.001 mol/L or more, preferably approximately 0.01 mol/L or more, more preferably approximately 0.05 mol/L or more, even more preferably 0.07 mol/L or more, and particularly preferably greater than 0.10 mol/L (e.g., 0.12 mol/L or more). By increasing the acid content, higher processability can be achieved. In some preferred embodiments, the acid content is 0.15 mol/L or more, and may be 0.2 mol/L or more, or even 0.25 mol/L or more. From the standpoint of surface quality after polishing and polishing stability, the acid content is suitably approximately 2 mol/L or less, preferably approximately 1.5 mol/L or less, more preferably approximately 1.0 mol/L or less, even more preferably approximately 0.8 mol/L or less, and particularly preferably approximately 0.7 mol/L or less (e.g., 0.6 mol/L or less).

When the first acid and the second acid are used in combination as acids (including acids and their salts), the content C1 of the first acid in the polishing composition is not particularly limited. When the first acid and the second acid are used in combination, the content C1 of the first acid in the polishing composition is, for example, approximately 0.0005 mol/L or more, preferably approximately 0.001 mol/L or more, more preferably approximately 0.005 mol/L or more, even more preferably 0.01 mol/L or more, and particularly preferably 0.03 mol/L or more. Increasing the content C1 of the first acid can improve the etching amount X for mild steel. From the viewpoint of improving surface quality, when the first acid and the second acid are used in combination, the content C1 of the first acid in the polishing composition is suitably approximately 1 mol/L or less, preferably approximately 0.7 mol/L or less, more preferably approximately 0.5 mol/L or less, and even more preferably approximately 0.3 mol/L or less (e.g., 0.25 mol/L or less).

When the first acid and the second acid are used in combination as acids (including acids and their salts), the content C2 of the second acid in the polishing composition is not particularly limited. When the first acid and the second acid are used in combination, the content C2 of the second acid in the polishing composition is, for example, suitably approximately 0.01 mol/L or more, preferably approximately 0.02 mol/L or more, more preferably approximately 0.05 mol/L or more, even more preferably 0.07 mol/L or more, and particularly preferably 0.10 mol/L or more. By increasing the content C2 of the second acid, higher processability can be achieved. From the viewpoint of optimally exerting the effect of the first acid without excessively lowering the pH, when the first acid and the second acid are used in combination, the content C2 of the second acid in the polishing composition is suitably approximately 1 mol/L or less, preferably approximately 0.5 mol/L or less, more preferably approximately 0.3 mol/L or less, even more preferably approximately 0.25 mol/L or less, and particularly preferably approximately 0.2 mol/L or less (e.g., less than 0.14 mol/L).

When a first acid and a second acid (including acids and their salts) are used in combination, the ratio (C2/C1) of the content C2 [mol/L] of the second acid to the content C1 [mol/L] of the first acid in the polishing composition is not particularly limited. In some embodiments, the ratio (C2/C1) may be, for example, 50 or less, 30 or less, 20 or less, 15 or less, 10 or less, or 5 or less. In addition, in some embodiments, the ratio (C2/C1) may be, for example, 0.05 or more, 0.1 or more, 0.2 or more, or 0.5 or more.

When an inorganic acid and an organic acid are used in combination as the acid (including the acid and its salt), the content C _M of the inorganic acid in the polishing composition is not particularly limited. When an inorganic acid and an organic acid are used in combination, the content C _M of the inorganic acid in the polishing composition is, for example, suitably about 0.01 mol/L or more, preferably about 0.02 mol/L or more, more preferably about 0.05 mol/L or more, even more preferably 0.07 mol/L or more, and particularly preferably 0.10 mol/L or more. By increasing the content C _M of the inorganic acid, higher processability can be achieved. From the viewpoint of optimally exerting the effect of the organic acid without excessively lowering the pH, when an inorganic acid and an organic acid are used in combination, the content C _M of the inorganic acid in the polishing composition is suitably about 1 mol/L or less, preferably about 0.5 mol/L or less, more preferably about 0.3 mol/L or less, even more preferably about 0.25 mol/L or less, and particularly preferably about 0.2 mol/L or less (e.g., less than 0.14 mol/L).

When an inorganic acid and an organic acid are used in combination as the acid (including the acid and its salt), the content C _O of the organic acid in the polishing composition is not particularly limited. When an inorganic acid and an organic acid are used in combination, the content C _O of the organic acid in the polishing composition is, for example, suitably about 0.0005 mol/L or more, preferably about 0.001 mol/L or more, more preferably about 0.005 mol/L or more, even more preferably 0.01 mol/L or more, and particularly preferably 0.03 mol/L or more. By increasing the organic acid content C _O , the etching amount X for mild steel can be improved. From the viewpoint of improving surface quality, when an inorganic acid and an organic acid are used in combination, the content C _O of the organic acid in the polishing composition is suitably about 1 mol/L or less, preferably about 0.7 mol/L or less, more preferably about 0.5 mol/L or less, and even more preferably about 0.3 mol/L or less (e.g., 0.25 mol/L or less).

When an inorganic acid and an organic acid are used in combination, the ratio ( _CM / _C0 ) of the inorganic acid content _CM [mol/L] to the organic acid content _CO [mol/L] in the polishing composition is not particularly limited. In some embodiments, the ratio ( _CM / _C0 ) may be, for example, 50 or less, 30 or less, 20 or less, 15 or less, 10 or less, or 5 or less. In addition, in some embodiments, the ratio ( _CM / _C0 ) may be 0.1 or more, 0.2 or more, 0.3 or more, or 0.5 or more.

(oxidizing agent)
The polishing composition disclosed herein contains an oxidizing agent. Examples of the oxidizing agent include, but are not limited to, peroxide, nitric acid or its salt, periodic acid or its salt, peroxoacid or its salt, permanganic acid or its salt, chromic acid or its salt, oxyacid or its salt, metal salts, and sulfuric acid. The oxidizing agent can be used alone or in combination of two or more. Specific examples of the oxidizing agent include hydrogen peroxide, sodium peroxide, barium peroxide, nitric acid, iron nitrate, aluminum nitrate, ammonium nitrate, peroxomonosulfuric acid, ammonium peroxomonosulfate, metal peroxomonosulfates, peroxodisulfate, ammonium peroxodisulfate, metal peroxodisulfates, peroxolinic acid, peroxosulfuric acid, sodium peroxoborate, performic acid, peracetic acid, perbenzoic acid, perphthalic acid, hypobromous acid, hypoiodous acid, chloric acid, bromic acid, iodic acid, periodic acid, perchloric acid, hypochlorous acid, sodium hypochlorite, calcium hypochlorite, potassium permanganate, metal chromates, metal dichromates, iron chloride, iron sulfate, iron citrate, ammonium iron sulfate, etc. 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 0.05 mol/L or more, more preferably 0.1 mol/L or more, even more preferably 0.15 mol/L or more, and particularly preferably 0.3 mol/L or more, taking into consideration the rate at which the object to be polished is oxidized and, therefore, processability. Furthermore, from the viewpoint of maintaining surface precision, the content of the oxidizing agent in the polishing composition is preferably 1 mol/L or less, more preferably 0.8 mol/L or less, and even more preferably 0.6 mol/L or less.

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

The polishing composition disclosed herein can be preferably implemented, for example, in a form in which the solids content is 0.5% by weight to 30.0% by weight. A form in which the solids content is 1.0% by weight to 20.0% by weight is more preferred. The polishing composition can typically be a slurry-like composition.

(Other ingredients)
The polishing composition disclosed herein may further contain, as needed, known additives that can be used in polishing compositions, such as surfactants, water-soluble polymers, dispersants, chelating agents, preservatives, antifungal agents, and basic compounds, to the extent that the effects of the present invention are not significantly impaired.

The surfactant is not particularly limited, and any of anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants can be used. The use of a surfactant can improve the dispersion stability of the polishing composition. The surfactant can be used alone or in combination of two or more. The surfactant can typically be a water-soluble organic compound with a molecular weight of less than 1 × 10 ⁶ .
Specific examples of anionic surfactants include polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl sulfates, alkyl sulfates, polyoxyethylene alkyl sulfates, alkyl sulfates, alkyl benzene sulfonates, alkyl phosphates, polyoxyethylene alkyl phosphates, polyoxyethylene sulfosuccinates, alkyl sulfosuccinates, alkyl naphthalene sulfonates, alkyl diphenyl ether disulfonic acids, polyacrylic acids, sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzene sulfonate, polyoxyethylene alkyl ether sodium sulfate, polyoxyethylene alkyl phenyl ether ammonium sulfate, polyoxyethylene alkyl phenyl ether sodium sulfate, and salts thereof.
Other specific examples of anionic surfactants include polyalkylarylsulfonic acid compounds such as naphthalenesulfonic acid-formaldehyde condensates, methylnaphthalenesulfonic acid-formaldehyde condensates, anthracenesulfonic acid-formaldehyde condensates, and benzenesulfonic acid-formaldehyde condensates; melamine formalin resin sulfonic acid compounds such as melamine sulfonic acid-formaldehyde condensates; lignin sulfonic acid compounds such as lignin sulfonic acid and modified lignin sulfonic acid; aromatic aminosulfonic acid compounds such as aminoarylsulfonic acid-phenol-formaldehyde condensates; polyisoprene sulfonic acid, polyvinyl sulfonic acid, polyallylsulfonic acid, polyisoamylenesulfonic acid, polystyrene sulfonic acid; and salts thereof. Alkali metal salts such as sodium salts and potassium salts are preferred as salts.
Specific examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, and alkylalkanolamides.
Specific examples of cationic surfactants include alkyltrimethylammonium salts, alkyldimethylammonium salts, alkylbenzyldimethylammonium salts, and alkylamine salts.
Specific examples of amphoteric surfactants include alkyl betaine type, fatty acid amidopropyl betaine type, alkyl imidazole type, amino acid type, and alkyl amine oxide type.

In polishing compositions containing a surfactant, the surfactant content is suitably, for example, 0.0005% by weight or more. From the viewpoint of surface smoothness after polishing, the content is preferably 0.001% by weight or more, and more preferably 0.002% by weight or more. From the viewpoint of processability, the content is suitably 3.0% by weight or less, preferably 0.5% by weight or less, for example, 0.1% by weight or less.

The polishing composition disclosed herein may contain a water-soluble polymer. By including a water-soluble polymer, the surface quality after polishing can be improved. Examples of water-soluble polymers include polyalkylarylsulfonic acid compounds such as naphthalenesulfonic acid formaldehyde condensates, methylnaphthalenesulfonic acid formaldehyde condensates, and anthracenesulfonic acid formaldehyde; melamine formalin resin sulfonic acid compounds such as melamine sulfonic acid formaldehyde condensates; ligninsulfonic acid compounds such as ligninsulfonic acid and modified ligninsulfonic acid; aromatic aminosulfonic acid compounds such as aminoarylsulfonic acid-phenol-formaldehyde condensates; and others, such as polyisoprene sulfonic acid, polyvinyl sulfonic acid, and polyallyl sulfonic acid. Examples of water-soluble polymers include sulfonic acid, polyisoamylenesulfonic acid, polystyrene sulfonate, polyacrylate, polyvinyl acetate, polymaleic acid, polyitaconic acid, polyvinyl alcohol, polyglycerin, polyvinylpyrrolidone, copolymers of isoprene sulfonic acid and acrylic acid, polyvinylpyrrolidone-polyacrylic acid copolymers, polyvinylpyrrolidone-vinyl acetate copolymers, diallylamine hydrochloride-sulfur dioxide copolymers, carboxymethylcellulose, salts of carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, pullulan, chitosan, and chitosan salts. The water-soluble polymers can be used alone or in combination of two or more.

In polishing compositions containing a water-soluble polymer, the content of the water-soluble polymer in the polishing composition is suitably, for example, 0.001 wt % or more. In polishing compositions containing multiple water-soluble polymers, the above content is the total content of these polymers. From the viewpoint of surface smoothness of the polished object after polishing, the above content is preferably 0.003 wt % or more, more preferably 0.005 wt % or more, and even more preferably 0.007 wt % or more. From the viewpoint of processability, the above content is suitably 1.0 wt % or less, preferably 0.5 wt % or less, for example, 0.1 wt % or less. Note that, from the viewpoint of processability, the technology disclosed herein can also be preferably practiced in polishing compositions in which the polishing composition is substantially free of a water-soluble polymer.

Examples of dispersants include polycarboxylic acid-based dispersants such as sodium polycarboxylic acid salts and ammonium polycarboxylic acid salts; naphthalenesulfonic acid-based dispersants such as sodium naphthalenesulfonate and ammonium naphthalenesulfonate; alkylsulfonic acid-based dispersants; polyphosphate-based dispersants; polyalkylenepolyamine-based dispersants; quaternary ammonium-based dispersants; alkylpolyamine-based dispersants; alkylene oxide-based dispersants; polyhydric alcohol ester-based dispersants; and the like. Dispersants can be used alone or in combination of two or more.

Examples of chelating agents include aminocarboxylic acid chelating agents and organic phosphonic acid chelating agents. Examples of aminocarboxylic acid chelating agents include ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetate, nitrilotriacetic acid, sodium nitrilotriacetate, ammonium nitrilotriacetate, hydroxyethylethylenediaminetriacetic acid, sodium hydroxyethylethylenediaminetriacetate, diethylenetriaminepentaacetic acid, sodium diethylenetriaminepentaacetate, triethylenetetraminehexaacetic acid, and sodium triethylenetetraminehexaacetate. Examples of organic phosphonic acid chelating agents include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetrakis(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, and α-methylphosphonosuccinic acid. Of these, organic phosphonic acid chelating agents are more preferred, and particularly preferred are ethylenediaminetetrakis(methylenephosphonic acid) and diethylenetriaminepenta(methylenephosphonic acid). A particularly preferred chelating agent is ethylenediaminetetrakis(methylenephosphonic acid). Chelating agents can be used alone or in combination of two or more.

Examples of preservatives and antifungal agents include isothiazolin-based preservatives such as 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one, parahydroxybenzoic acid esters, and phenoxyethanol.

The polishing composition can contain a basic compound if necessary. Here, a basic compound refers to a compound that has the function of increasing the pH of the polishing composition when added to the composition. Examples of basic compounds include alkali metal hydroxides, carbonates and hydrogen carbonates, quaternary ammonium or its salts, ammonia, amines, phosphates and hydrogen phosphates, and organic acid salts. The basic compounds can be used alone or in combination of two or more.

(pH)
The pH of the polishing composition disclosed herein is not particularly limited as long as it satisfies the above-described condition for the etching amount X for mild steel. The pH of the polishing composition can be, for example, 12.0 or less, typically 0.5 to 12.0, and may be 10.0 or less, typically 0.5 to 10.0. From the viewpoint of processability, surface quality, etc., the pH of the polishing composition can be 7.0 or less, for example 0.5 to 7.0, more preferably 5.0 or less, typically 1.0 to 5.0, and even more preferably 4.0 or less, for example 1.0 to 4.0. The pH of the polishing composition can be, for example, 3.0 or less, typically 1.0 to 3.0, preferably 1.0 to 2.0, and more preferably 1.0 to 1.8. From the viewpoint of easily satisfying the above-mentioned condition for the etching amount X for mild steel and easily reducing the residual silica abrasive grains, the pH of the polishing composition can be preferably 1.0 or more and less than 1.7, more preferably 1.0 or more and less than 1.6, and even more preferably 1.0 or more and 1.5 or less (for example, 1.3 or more and 1.5 or less). If necessary, a pH adjuster such as an organic acid, an inorganic acid, or a basic compound can be added so that the above pH is achieved in the polishing liquid. The above pH can be preferably applied to a polishing composition for a magnetic disk substrate such as a nickel-phosphorus substrate. In particular, it can be preferably applied to a polishing composition for primary polishing.

(Corrosion of polishing equipment, etc.)
If the etching amount X of the polishing composition for mild steel is too high, problems such as corrosion of polishing equipment components such as a polishing platen may occur during polishing using the polishing composition. In a preferred embodiment, the polishing composition disclosed herein does not discolor the surface of a stainless steel sheet in the stainless steel corrosion test described below. Such a polishing composition inhibits corrosion of stainless steel. Therefore, as a result, corrosion of polishing equipment containing stainless steel present in the surrounding environment during the polishing process is likely to be inhibited.

[Stainless steel corrosion test]
The polishing composition is used as a test liquid, and 0.10 mL of this test liquid is dropped onto a stainless steel plate, and after leaving it for 24 hours, the presence or absence of discoloration on the surface of the stainless steel plate is visually observed.The stainless steel plate is made of SUS304 steel material based on JIS G4303.In addition to the polishing composition, the test liquid may also be a composition that has the same composition as the polishing composition except that it does not contain abrasive grains.Specifically, the stainless steel corrosion test can be carried out by the method shown in the examples below.

(polishing liquid)
The polishing composition disclosed herein is typically supplied to a polishing object in the form of a polishing liquid containing the polishing composition and used to polish the object. The polishing liquid can be prepared, for example, by diluting the polishing composition. Here, dilution typically refers to dilution with water. Alternatively, the polishing composition can be used as a polishing liquid as is. That is, the concept of a polishing composition in the technology disclosed herein encompasses both a polishing liquid (working slurry) that is supplied to a polishing object and used to polish the object, and a concentrated liquid that is diluted and used as a polishing liquid. Polishing compositions in the form of such concentrated liquids are advantageous from the standpoints of convenience and cost reduction during production, distribution, storage, etc. The concentration ratio can be, for example, about 1.5 to 50 times. From the standpoint of storage stability of the concentrated liquid, a concentration ratio of, for example, 2 to 20 times, typically about 2 to 10 times, is appropriate.

(Multi-component polishing composition)
The polishing composition disclosed herein may be a single-component type or a multi-component type, such as a two-component type. For example, the polishing composition may be configured such that a part A containing some of the components, typically components other than water, and a part B containing the remaining components are mixed together and used to polish an object to be polished. Some preferred embodiments of the multi-component polishing composition are composed of a part A containing abrasive grains and a part B containing components other than the abrasive grains. The part A containing the abrasive grains may further contain a dispersant. Examples of components other than the abrasive grains contained in part B include acids. Part B may also contain water-soluble polymers and other additives. An oxidizing agent, such as hydrogen peroxide, may be further mixed during mixing. For example, when the oxidizing agent is supplied in the form of an aqueous solution, the aqueous solution can serve as part C constituting the multi-component polishing composition.

The polishing composition disclosed herein can be preferably used for polishing magnetic disk substrates such as nickel-phosphorus substrates, glass substrates, and carbon substrates. The plating material may also be a disk substrate having a metal layer or metal compound layer other than a nickel-phosphorus plating layer on the surface of a substrate disk. In particular, the polishing composition is suitable as a polishing composition for nickel-phosphorus plated substrates having a nickel-phosphorus plating layer on an aluminum alloy substrate disk. For such applications, the application of the technology disclosed herein is particularly meaningful.

The polishing composition disclosed herein can be used particularly effectively in applications requiring high polishing efficiency, such as the preliminary polishing step in the manufacturing process of magnetic disk substrates, which requires a highly accurate surface after the final polishing step. When multiple preliminary polishing steps are performed prior to the final polishing step, the polishing composition can be used in any of the preliminary polishing steps, and the same or different polishing compositions can be used in these preliminary polishing steps. The polishing composition disclosed herein is suitable, for example, as a polishing composition used in the primary polishing step, i.e., the first polishing step, of magnetic disk substrates. In particular, it can be preferably used in the first polishing step, i.e., the first polishing step, after nickel phosphorus plating in the manufacturing process of nickel phosphorus substrates.

The polishing composition disclosed herein is suitable for polishing magnetic disk substrates with a surface roughness of approximately 20 Å to 300 Å, as measured using a laser scanning surface roughness meter "TMS-3000WRC" manufactured by Schmitt Measurement Systems Inc., to adjust the surface roughness of the magnetic disk substrate to 10 Å or less. For such applications, it is particularly useful to apply the technology disclosed herein. Here, "surface roughness" refers to the arithmetic average roughness (Ra).

<Polishing method>
The polishing composition disclosed herein can be suitably used for polishing a magnetic disk substrate, for example, in an embodiment including the following steps. A preferred embodiment of a method for polishing an object to be polished using the polishing composition disclosed herein is described below. Hereinafter, the object to be polished is also referred to as a substrate to be polished.
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 adjusting the concentration or pH of the polishing composition to prepare the polishing liquid. The concentration adjustment may be, for example, dilution. Alternatively, the polishing composition may be used as the polishing liquid as it is.

The polishing liquid is then supplied to the object to be polished, and polishing is carried out in the usual manner. For example, the object to be polished is placed in a typical polishing device, and the polishing liquid is supplied to the surface of the object to be polished, i.e., the surface to be polished, through the polishing pad of the polishing device. Typically, while the polishing liquid is continuously supplied, the polishing pad is pressed against the surface of the object to be polished, and the two are moved relative to each other. This movement can be, for example, rotational movement. Through this polishing process, the polishing of the object to be polished is completed.

There are no particular limitations on the polishing pad that can be used. For example, polishing pads of hard foam polyurethane type, nonwoven fabric type, suede type, etc. can be used. The suede type may be a buff pad, or typically a polishing pad in a non-buffed state where the surface has not been buffed (so-called non-buff pad). Such suede type polishing pads (typically polyurethane polishing pads) are easy to process and can easily achieve high-quality substrate surfaces. Note that the polishing pads used in the technology disclosed herein do not contain abrasive grains.

After polishing (specifically, after the primary polishing of the magnetic disk substrate), it is preferable to wash the substrate (washing step). The washing step is typically carried out using a washer. In the washing step, a cleaning solution may be used, or washing may be carried out using running water only without a cleaning solution. Ultrasonic treatment may also be carried out, in which ultrasonic waves are applied to the substrate immersed in a cleaning solution or water. By carrying out such a washing step, silica remaining on the substrate after polishing can be efficiently removed.

The polishing machine used in the polishing process may be a double-sided polishing machine that polishes both sides of the object to be polished simultaneously, or a single-sided polishing machine that polishes only one side of the object to be polished. When the polishing process is a preliminary polishing process, in some embodiments, a double-sided polishing machine can be preferably used as the polishing machine that performs the polishing process. When a finish polishing process is performed after the primary polishing process, a single-sided polishing machine can be preferably used as the polishing machine that performs the finish polishing process.

The polishing process described above can be part of the manufacturing process for magnetic disk substrates, such as nickel phosphorus substrates. Therefore, this specification provides a method for manufacturing and polishing magnetic disk substrates that includes the polishing process described above.

The polishing composition disclosed herein can be preferably used in a preliminary polishing step, such as a primary polishing step, of an object to be polished. This specification provides a method for manufacturing and polishing a magnetic disk substrate, which includes a preliminary polishing step using any of the polishing compositions described above. The method includes step (1) of supplying the polishing composition disclosed herein to the object to be polished to polish the object. The method may include a final polishing step after the preliminary polishing step. The polishing composition used in the final polishing step is not particularly limited. Therefore, the subject matter disclosed in this specification includes a method for manufacturing and polishing a magnetic disk substrate, which includes, in this order, step (1) of polishing the object to be polished with a polishing composition containing abrasive grains disclosed herein, and step (2) of polishing the object to be polished with a polishing composition (e.g., a final polishing composition) different from the polishing composition used in step (1). This manufacturing method enables efficient production of magnetic disk substrates.

The abrasive grains used in step (2) are not particularly limited, but for example, colloidal silica is preferably used. By using colloidal silica, polished products with high surface precision can be efficiently produced. The particle shape of the colloidal silica is not particularly limited, and may be, for example, spherical or aspherical, but spherical colloidal silica is preferably used.

The final polishing composition that can be used in step (2) contains, for example, water in addition to abrasive grains. Furthermore, the final polishing composition can contain other components (acid, oxidizing agent, basic compound, various additives, etc.) similar to those of the polishing composition described above, as needed.

The following describes several examples of the present invention, but it is not intended that the present invention be limited to those examples.

[Preparation of Polishing Composition]
<Example 1>
Silica abrasive grains, acid, an oxidizing agent, and deionized water were mixed to prepare a composition with an abrasive grain concentration of 7 wt %, an acid concentration of 0.21 mol/L, and an oxidizing agent concentration of 0.4 mol/L, which was used as the polishing composition of this example. Phosphoric acid was used as the acid. 31% hydrogen peroxide solution was used as the oxidizing agent. Colloidal silica with a volume-based average particle size of 165 nm and an average aspect ratio of 1.13 as determined by SEM image analysis was used as the silica abrasive grains. The pH of the polishing composition was 1.4.

<Examples 2 to 16>
The polishing compositions of this example were prepared in the same manner as in Example 1, except that the types and concentrations of the acids were as shown in Table 1. The pH of the polishing compositions of each example was as shown in Table 1.

[Mild steel etching test]
A mild steel etching test was performed by immersing 50 mL of the polishing composition according to each example in a mild steel plate having a length of 20 mm, a width of 20 mm, and a thickness of 2 mm. The mild steel plate was immersed for 18 hours (T). The mild steel plate was made of SS400 (square) steel material according to JIS G3101. The temperature of the immersion liquid (polishing composition) was 25°C. Within 3 minutes after the immersion time T had elapsed, the mild steel plate was removed from the immersion liquid, washed with water, and then dried. The weight W2 [ng] of the dried mild steel plate was measured. From the weight W1 [ng] of the mild steel plate before immersion in the polishing composition, the weight W2 [ng] of the mild steel plate after drying, the immersion time T [hours], and the surface area SA [mm ^{2 ] of the mild steel plate, the etching amount X of the mild steel plate was calculated using the following formula: etching amount X [ng/h·mm 2 ]} = (weight W1 [ng] - weight W2 [ng]) / (immersion time T [hours] × surface area SA [mm ² ] of mild steel plate). The results of the etching amount X and the logarithm to base 10 (log ₁₀ X) of the etching amount X [ng/h·mm ² ] are shown in Table 1.

[Disc polishing]
The polishing composition according to each example was used as a polishing liquid to polish an object under the following conditions. The object to be polished was an aluminum substrate for a hard disk having an electroless nickel-phosphorus plating layer on its surface. The diameter of the object to be polished (substrate to be polished) was 3.5 inches (a doughnut shape with an outer diameter of approximately 95 mm and an inner diameter of approximately 25 mm), and the thickness was 1.75 mm. The surface roughness Ra (the arithmetic mean roughness of the nickel-phosphorus plating layer measured with a laser scanning surface roughness meter "TMS-3000WRC" manufactured by Schmitt Measurement System Inc.) before polishing was 130 Å.

(polishing conditions)
Polishing equipment: System Seiko double-sided polishing machine, model "9.5B-5P"
Polishing pad: Polyurethane pad manufactured by FILWEL, product name "CR200"
Number of substrates to be polished: 15 (3 substrates/carrier x 5 carriers)
Polishing liquid supply rate: 135 mL/min Polishing load: 120 g/cm ²
Upper surface plate rotation speed: 27 rpm
Lower surface plate rotation speed: 36 rpm
Sun gear rotation speed: 8 rpm
Amount removed: a total thickness of about 2.2 μm on both sides of each substrate. The amount removed was calculated based on the following formula.
Polishing amount [μm]=weight loss of substrate due to polishing [g]/(area of substrate [cm ² ]×density of nickel phosphorus plating [g/cm ³ ])×10 ⁴

[Polishing rate]
The polishing rate was calculated for both surfaces of a substrate to be polished using the polishing composition of each example under the above-mentioned polishing conditions. The polishing rate was calculated based on the following formula. The results were converted into relative values, with the polishing rate of Example 11 taken as 100%, and are shown in the "polishing rate" column of Table 1.
Polishing rate [μm/min]=weight loss of substrate due to polishing [g]/(area of substrate [cm ² ]×density of nickel phosphorus plating [g/cm ³ ]×polishing time [min])×10 ⁴

[Micro waviness]
After polishing using the polishing composition of each example, one Ni-P substrate was randomly selected from the Ni-P substrates (polished substrates) set in each carrier during the polishing process, for a total of three Ni-P substrates. Microwaviness was measured on the front and back surfaces of these three Ni-P substrates, a total of six surfaces, using a ZYGO non-contact surface profilometer "NEWVIEW5032" under conditions of an objective lens magnification of 2.5x, an intermediate lens magnification of 0.5x, and a bandpass filter of 80-500 μm. Measurements were performed on each of the six surfaces at four points spaced 90° apart from each other, 37 mm radially outward from the center of the polished substrate, and the average value of these 24 points was taken as the microwaviness (Å) value. The obtained values were converted into relative values [%], with the value of Example 11 taken as 100%, and are shown in the "Microwaviness" column of Table 1.

[Number of residual particles]
The substrates polished under the same conditions as those used to measure the polishing rate were washed using a cleaning machine manufactured by CRESEN, and the number of particles remaining on the substrate surface was then measured. Specifically, the substrates were washed in running water without using a brush or cleaning agent, and water droplets adhering to the substrates were removed using a spin dryer, followed by drying. The specific cleaning conditions were as follows:
(Washing conditions)
Disk substrate rotation speed during cleaning: 40 rpm
First cleaning time (running water only): 15 seconds First cleaning flow rate: 750 mL/min Second cleaning time (running water only): 20 seconds Second cleaning flow rate: 900 mL/min Ultrasonic cleaning time (running water only): 20 seconds Ultrasonic cleaning flow rate: 3000 mL/min Spin dry time: 20 seconds Spin dry rotation speed: 3000 rpm
Next, using a scanning electron microscope "SU8000" manufactured by Hitachi High-Technologies Corporation, the surfaces of the substrates after cleaning were observed at a magnification of 50,000x, with 10 visual fields per surface. Then, using image analysis software "WINROOF" manufactured by Mitani Shoji Co., Ltd., the number of residual particles in each visual field was measured, and the average number of residual particles per visual field was calculated. The results are shown in Table 1. The number of residual particles (%) in Table 1 is a relative value [%], with the number of residual particles in Example 11 taken as 100%. SEM images of the substrate surfaces after cleaning in Examples 4, 9, 8, and 14 are shown in Figures 1 to 4, respectively. Furthermore, Figure 5 shows a graph illustrating the relationship between the amount of etching X measured in the mild steel etching test for each example and the number of residual particles (%). In Figure 5, the horizontal axis represents the logarithm (log ₁₀ X) of the amount of etching X, with the base 10, and the vertical axis represents the number of residual particles [%].

[Stainless steel corrosion test]
A composition having the same composition as the polishing composition according to each example except that it does not contain abrasive grains was prepared, and used as the test solution for stainless steel corrosion.In addition, a circular stainless steel plate with a diameter of 25 mm and a thickness of 2 mm was prepared.As the stainless steel plate, SUS304 (circular) steel material based on JIS G4303 was used.0.10 mL of the test solution at a liquid temperature of 25 ° C was dropped onto the stainless steel plate, and it was left for 24 hours under the conditions of 25 ° C and 50 RH%, and then the surface of the stainless steel plate was visually observed.If the surface of the stainless steel plate was discolored, it was considered that corrosion had occurred and was evaluated as "x", and if it was not discolored, it was considered that no corrosion had occurred and was evaluated as "○".The results are shown in Table 1.

As shown in Table 1 and Figures 1 to 5, there was a tendency for the relationship between the etching amount X for mild steel and the number of residual particles to decrease as the etching amount X increased. The polishing compositions of Examples 1 to 10, in which the logarithm (log ₁₀ X) of the etching amount X for mild steel measured in the mild steel etching test was 2.0 or more and 4.0 or less, showed a significant reduction in the number of residual particles compared to the polishing compositions of Examples 11 to 15, in which the etching amount X was lower. Furthermore, the polishing compositions of Examples 1 to 10 did not cause corrosion of stainless steel plates in the stainless steel corrosion test. Furthermore, the polishing compositions of Examples 1 to 10 almost maintained or improved the removal rate and microwaviness level compared to the polishing compositions of Examples 11 to 15. Furthermore, in the polishing compositions (Examples 6 to 10) that used a combination of an organic acid and an inorganic acid, there was a tendency for the etching amount X for mild steel to change while maintaining the pH by changing the content of the organic acid. On the other hand, the polishing composition of Example 16, in which the log ₁₀ X measured in the mild steel etching test was greater than 4.0 and the pH was 1.0 or less, showed a reduction in the number of residual particles, but corrosion of the stainless steel plate occurred in the stainless steel corrosion test.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples given above.

Claims (7)

A composition for polishing magnetic disk substrates, comprising silica particles as abrasive grains, an acid, an oxidizing agent, and water,
A polishing composition, wherein the logarithm to the base 10 of the amount of etching X [ng/h·mm ² ] of a mild steel plate measured in a mild steel etching test in which the mild steel plate is immersed in the polishing composition is 2.3 or more and 4.0 or less. 2. The polishing composition according to claim 1, comprising , as the acid, a first acid and a second acid that dissociates more easily than the first acid. The polishing composition according to claim 1 or 2, wherein the pH of the polishing composition is 1.0 or more and 3.0 or less. The polishing composition according to any one of claims 1 to 3, wherein the acid comprises an organic acid. The acid further includes an inorganic acid,
The content _C of the organic acid is 0.005 mol/L or more,
The polishing composition according to claim 4, wherein the inorganic acid content C _M is less than 0.14 mol/L. A method for polishing a substrate, comprising step (1) of supplying the polishing composition according to any one of claims 1 to 5 to a substrate to be polished and polishing the substrate. A method for manufacturing a magnetic disk substrate, comprising step (1) polishing a substrate to be polished using the polishing composition according to any one of claims 1 to 5.