Polishing composition and method for producing magnetic disk substrate

Abstract

To provide a polishing composition which is used for polishing a Ni-P substrate and can reduce polishing resistance while maintaining practical processability.SOLUTION: There is provided a composition for polishing a magnetic disk substrate having a nickel-phosphorus plating layer. The polishing composition comprises a colloidal silica as an abrasive grain, an acid, an additive A, an additive B and water. The additive A is a polymer having a sulfonic acid (salt) group. In addition, the additive B is a nonionic surfactant having 10 or more oxyethylene units in one molecule.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polishing composition and a method for producing a magnetic disk substrate. [Background technology]

[0002] Conventionally, the manufacturing process of substrates requiring high-precision surfaces includes a step of polishing the substrate to be polished, which is the raw material of the substrate, using a polishing solution. For example, in the manufacture of nickel-phosphorus-plated magnetic disk substrates (hereinafter also referred to as Ni-P substrates), polishing that emphasizes polishing efficiency (primary polishing) and final polishing (finish polishing) that is performed to achieve the surface precision of the final product are generally performed. Patent Document 1 is an example of a technical document related to a polishing composition used for polishing Ni-P substrates. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-135052 Summary of the Invention [Problem to be solved by the invention]

[0004] Polishing of Ni-P substrates is typically performed by pressing a polishing pad against the object to be polished (Ni-P substrate) held by a carrier, supplying a polishing liquid between the object to be polished and the polishing pad, and relatively moving (e.g., rotating) the object to be polished and the polishing pad along the surface of the object to be polished. The carrier holds the side (edge) of the substrate to be polished during polishing. While not particularly limited, the carrier is typically a member that is thinner than the object to be polished and has holding holes called holes, and the object to be polished is placed within the holding holes. During polishing, the carrier receives a reaction force (a force that tries to move the object in the surface direction) against the action of the polishing pad on the object to be polished at the side of the holding holes.

[0005] Recently, as Ni-P substrates have become thinner, carriers have also become thinner. As carriers become thinner, their rigidity decreases, making them more susceptible to deformation under applied forces. When a carrier deforms, for example, a portion of the deformed carrier may penetrate the polishing pad, causing scratches on the pad. These scratches undesirably affect the surface quality of the polished object, necessitating the replacement of the polishing pad.

[0006] The reaction force acting on the carrier increases proportionally as the polishing resistance (frictional force) acting between the polishing pad and the object to be polished increases. In particular, in polishing using a polishing liquid containing colloidal silica as abrasive grains, the fineness of the abrasive grains facilitates adhesion between the polishing pad and the substrate, which tends to increase the frictional force between the polishing pad and the object to be polished, and the load on the carrier also tends to increase. In such polishing, if the polishing resistance acting between the object to be polished and the polishing pad during polishing can be reduced, the load on the carrier can be alleviated, and deformation of the carrier can be prevented or suppressed, thereby preventing pad scratches.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a polishing composition for use in polishing Ni-P substrates, which is composed of colloidal silica as abrasive grains, an acid, and water, and which can reduce polishing resistance while maintaining practical processability. Another related aim is to provide a method for producing a magnetic disk substrate using such a polishing composition. [Means for solving the problem]

[0008] This specification provides a polishing composition for use in polishing magnetic disk substrates having a nickel-phosphorus plating layer. This polishing composition contains colloidal silica as abrasive grains, an acid, additives A and B, and water. Additive A is a polymer having a sulfonic acid (salt) group. Additive B is a nonionic surfactant having 10 or more oxyethylene units per molecule. By adding the above additives A and B to a polishing composition containing colloidal silica as an abrasive, it is possible to reduce polishing resistance when polishing Ni-P substrates while maintaining practical processability due to the inclusion of colloidal silica abrasive and acid.

[0009] In some embodiments, an oxidizing agent is further included, which tends to provide good processability.

[0010] The polishing composition according to some embodiments has a pH within the range of 1 to 4. In such a pH environment, the effects of the technology disclosed herein are preferably realized.

[0011] In some embodiments, the average aspect ratio of the colloidal silica, as determined by transmission electron microscopy, is 1.0 or more and 1.2 or less. By setting the average aspect ratio of the colloidal silica to 1.0 or more and 1.2 or less, the colloidal silica rolls more easily during polishing, reducing polishing resistance, stabilizing processing and facilitating the realization of high surface quality after polishing. A polishing composition having such a configuration can be preferably used in a polishing step (e.g., a finish polishing step) that requires high surface quality after polishing.

[0012] The colloidal silica preferably has an average primary particle diameter of 1 nm or more and 50 nm or less. A polishing composition containing colloidal silica having an average primary particle diameter in the above range can easily achieve high surface quality after polishing. A polishing composition having such a configuration can be preferably used in a polishing process (e.g., a finish polishing process) that requires high surface quality after polishing.

[0013] The polishing composition according to some embodiments is used in a finish polishing step. The polishing composition disclosed herein contains colloidal silica abrasive grains, and is therefore particularly suitable for finish polishing, which requires high surface quality after polishing. The polishing composition disclosed herein can reduce polishing resistance while maintaining practical processability in the finish polishing of Ni-P substrates.

[0014] This specification also provides a method for producing a magnetic disk substrate. This method includes polishing a substrate to be polished with any of the polishing compositions disclosed herein. This method allows for efficient production of a magnetic disk substrate (Ni-P substrate). DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments of the present invention will be described below. It should be noted that matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field.

[0016] <Polishing composition> (abrasive grain) The polishing composition disclosed herein contains colloidal silica as abrasive grains. Colloidal silica functions to mechanically polish the surface of a Ni-P substrate. Colloidal silica synthesized through particle growth in an aqueous phase, such as sodium silicate silica or alkoxide silica, is preferably used as the colloidal silica. Silica abrasive grains containing this type of colloidal silica can suitably achieve high processability and good surface precision. When the silica abrasive grains disclosed herein contain colloidal silica, the colloidal silica contained in the silica abrasive grains may be one type or two or more types with different manufacturing conditions and / or physical properties. The colloidal silica may be surface-modified. Examples of surface modification include chemical modification such as the introduction of functional groups or metal modification. In some preferred embodiments, the abrasive grains contained in the polishing composition contain colloidal silica alone. By using colloidal silica alone, better surface precision (e.g., a surface with fewer scratches) can be achieved while maintaining high processability.

[0017] The average primary particle size of the colloidal silica is not particularly limited. In some embodiments, the average primary particle size of the colloidal silica measured by the BET method is 1 nm or more. Increasing the average primary particle size can achieve higher processability. From the viewpoint of processability, the average primary particle size is preferably 3 nm or more, more preferably 5 nm or more, even more preferably 7 nm or more, and particularly preferably 10 nm or more. Furthermore, from the viewpoint of obtaining a surface with higher surface precision, the average primary particle size is, for example, less than 100 nm, preferably 50 nm or less, more preferably 45 nm or less, even more preferably 40 nm or less, and particularly preferably 35 nm or less. In some preferred embodiments, the average primary particle size may be, for example, 30 nm or less, or may be, for example, 25 nm or less (e.g., 20 nm or less).

[0018] In the technology disclosed herein, the average primary particle diameter of colloidal silica refers to the average particle diameter determined based on the BET method. The average primary particle diameter of colloidal silica is calculated from the specific surface area (BET value) measured by the BET method by the following formula: D1 (nm) = (6000 / (true density (g / cm)) 3 )×BET value(m 2 The specific surface area can be measured using, for example, a surface area measuring device manufactured by Micromeritics, trade name "Flow Sorb II 2300." The same applies to the examples described later.

[0019] The 50% cumulative diameter (D) in the particle size distribution based on the number of particles observed by TEM (Transmission Electron Microscope) of colloidal silica 50 ) is not particularly limited, and is preferably 5 nm or more, more preferably 10 nm or more, from the viewpoint of processability, etc. From the viewpoint of obtaining higher processability, the 50% cumulative diameter (D 50 ) is more preferably 15 nm or more. From the viewpoint of obtaining a surface with higher surface precision, the D 50is suitably 200 nm or less, preferably 100 nm or less, more preferably 70 nm or less, even more preferably 50 nm or less, and particularly preferably 40 nm or less (for example, 30 nm or less).

[0020] The 50% cumulative diameter (D) in the particle size distribution based on the number of colloidal silica particles observed by TEM 50 ) can be determined by the following method. First, a colloidal silica dispersion is prepared by dispersing the colloidal silica to be measured in water. Then, a transmission electron microscope (TEM, Hitachi High-Technologies Corporation's STEM HD-2700) is used to photograph a predetermined number of particles (1,000 or more) observable by TEM contained in the colloidal silica to be measured at a magnification (e.g., 200,000 to 400,000 times) that allows approximately 100 particles to be observed in one field of view, thereby obtaining a TEM image. The area of ​​each particle is then calculated from the obtained TEM image, and the diameter of an ideal circle (perfect circle) having the same area as the calculated area is calculated as the particle size of each particle. The calculated particle diameters of the individual particles constituting the colloidal silica are plotted on the horizontal axis against the cumulative number (%) on the vertical axis, thereby obtaining a number-based particle size distribution based on TEM observation. The 50% cumulative diameter (D 50 ) is the particle size corresponding to the point where the cumulative number is 50% in the particle size distribution. The particle size distribution can be determined using image analysis software MacView manufactured by Mountech Co., Ltd. The same applies to the examples described later. The predetermined number, i.e., the number of particles for which the particle diameter of each particle is calculated, is suitably 1,000 or more, preferably 1,500 or more, from the viewpoint of improving measurement accuracy and reproducibility. There is no particular upper limit to the predetermined number. From the viewpoint of measurement efficiency, the predetermined number may be, for example, 5,000 or less, or 2,500 or less.

[0021] The particle shape of the colloidal silica is not particularly limited, and may be, for example, spherical or non-spherical. When the polishing composition disclosed herein is used in the finish polishing step of a Ni-P substrate, a shape close to spherical is preferred.

[0022] Although not particularly limited, the average aspect ratio of colloidal silica is, in principle, 1.0 or more, and from the viewpoint of processability, it may be, for example, 1.03 or more, 1.06 or more, or 1.08 or more. Furthermore, from the viewpoint of efficiently increasing surface precision, in some embodiments, the average aspect ratio is suitably 1.30 or less. By reducing the average aspect ratio of colloidal silica, the colloidal silica can be more easily rolled and moved, thereby reducing polishing resistance, stabilizing processing, and more effectively reducing scratches. From this viewpoint, the average aspect ratio of colloidal silica is preferably 1.20 or less, more preferably 1.18 or less (e.g., 1.15 or less). Herein, the average aspect ratio of colloidal silica refers to the average value of the major axis / minor axis ratio of the individual particles constituting the colloidal silica, i.e., the number-average aspect ratio. Hereinafter, unless otherwise specified, the average aspect ratio in this specification refers to the number-average aspect ratio.

[0023] The average aspect ratio of colloidal silica is measured based on TEM observation. Specifically, when obtaining the number-based particle size distribution based on the TEM observation, the long-side length (long diameter value) of the smallest rectangle circumscribing each particle image is divided by the short-side length (short diameter value) to calculate the long-side / short-side ratio (aspect ratio) of each particle. The aspect ratios of the predetermined number of particles are then arithmetically averaged to determine the average aspect ratio (number-average aspect ratio). The aspect ratios can be determined using image analysis software MacView manufactured by Mountech Co., Ltd. The same applies to the examples described below. The predetermined number, i.e., the number of particles for which the aspect ratio of each particle is calculated, is suitably 1,000 or more, preferably 1,500 or more, from the viewpoint of improving measurement accuracy and reproducibility. There is no particular upper limit to the predetermined number. From the viewpoint of measurement efficiency, the predetermined number may be, for example, 5,000 or less, or 2,500 or less.

[0024] The content of colloidal silica 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, and even more preferably 3% by weight or more. When multiple types of colloidal silica are contained, the content is the total content of these. Increasing the content of colloidal silica tends to achieve higher processability. From the viewpoint of the surface smoothness of the substrate after polishing and the dispersion stability of the abrasive grains, the content is suitably 25% by weight or less, preferably 20% by weight or less, more preferably 15% by weight or less, and even more preferably 10% by weight or less, for example, 8% by weight or less, and may be 6% by weight or less.

[0025] In some preferred embodiments, the polishing composition may contain substantially only colloidal silica as abrasive grains. Here, "substantially containing only colloidal silica" means that the proportion of colloidal silica in the total solid content of the polishing composition is 99% by weight or more, more preferably 99.5% by weight or more, and even more preferably 99.9% by weight or more. In such embodiments, the application effects of the technology disclosed herein can be suitably exhibited.

[0026] The polishing composition disclosed herein may contain silica particles other than the colloidal silica (e.g., fumed silica, precipitated silica, etc.) as long as the effects of the present invention are not significantly impaired. Non-silica particles may also be contained as long as the effects of the present invention are not significantly impaired. Non-silica particles may be inorganic particles, organic particles, or organic-inorganic composite particles. Specific examples of inorganic particles include oxide particles such as alumina particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese dioxide particles, zinc oxide particles, and 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. Examples of the alumina particles include α-alumina, intermediate aluminas other than α-alumina, and composites thereof. Intermediate alumina is a general term for alumina particles other than α-alumina, and specific examples include γ-alumina, δ-alumina, θ-alumina, η-alumina, κ-alumina, and composites thereof. Specific examples of organic particles include polymethyl methacrylate (PMMA) particles, poly(meth)acrylic acid particles, polyacrylonitrile particles, etc. Here, (meth)acrylic acid refers collectively to acrylic acid and methacrylic acid. The above particles other than colloidal silica can be used alone or in combination of two or more.

[0027] 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 a polishing composition prevents quality degradation due to the use of alumina particles. Examples of quality degradation include scratches and dents, residual alumina, and defects due to abrasive grain penetration. In this specification, "substantially free of specific abrasive grains, such as alumina particles," means that the proportion of the abrasive grains in the polishing composition is 1% by weight or less, more preferably 0.5% by weight or less, for example, 0.1% by weight or less, of the total solid content of the polishing composition. A polishing composition containing 0% by weight of alumina particles, i.e., a polishing composition containing no 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.

[0028] (acid) The polishing composition disclosed herein contains an acid. The acid functions to chemically polish the Ni-P substrate. The acid may be either an inorganic acid or an organic acid. The acid may be used alone or in combination of two or more.

[0029] 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.

[0030] Examples of organic acids include organic carboxylic acids, organic phosphonic acids, organic sulfones, amino acids, etc. The number of carbon atoms contained in these organic acids is, for example, about 1 to 18, and preferably, for example, about 1 to 10. Specific examples of organic acids include malonic acid, citric acid, isocitric acid, 1,2,4-butanetricarboxylic acid, maleic acid, malic acid, glycolic acid, succinic acid, itaconic 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, and benzoic acid. Organic carboxylic acids such as crotonic acid, oleic acid, linoleic acid, linolenic acid, ricinoleic acid, methacrylic acid, glutaric acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, tartronic acid, glyceric acid, hydroxybutyric acid, hydroxyacetic acid, hydroxybenzoic acid, salicylic acid, methylenesuccinic acid, gallic acid, ascorbic acid, nitroacetic acid, oxaloacetic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, nicotinic acid, picolinic acid, and other pyridine carboxylic acids; methyl acid phosphate, ethylenediamine ... Chill 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 Organic phosphonic acids such as ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, α-methylphosphonosuccinic acid, and aminopoly(methylenephosphonic acid); organic sulfonic acids such as ethanesulfonic acid, aminoethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, 2-naphthalenesulfonic acid, sulfosuccinic acid, 10-camphorsulfonic acid, and taurine;Amino acids such as glycine, alanine, glutamic acid, aspartic acid, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, phenylalanine, tryptophan, tyrosine, proline, cystine, glutamine, asparagine, lysine, and arginine;

[0031] From the viewpoint of processability, preferred acids include phosphoric acid, phosphonic acid, malonic acid, citric acid, maleic acid, hydrochloric acid, nitric acid, sulfuric acid, sulfamic acid, phytic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, etc. Among these, preferred acids include phosphoric acid, phosphonic acid, malonic acid, citric acid, and maleic acid.

[0032] 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.

[0033] Specific examples of salts that can be contained in the polishing composition disclosed herein 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 can be, for example, lithium, sodium, potassium, etc.

[0034] In some embodiments, the salt may be an inorganic acid salt such as an alkali metal salt or an ammonium salt of an inorganic acid. For example, in addition to the alkali metal phosphates and alkali metal hydrogen phosphates described above, potassium chloride, sodium chloride, ammonium chloride, potassium nitrate, sodium nitrate, ammonium nitrate, etc. may be used.

[0035] The acid and its salt can be used alone or in combination of two or more (for example, two or three). In some embodiments, an acid can be used in combination with a salt of an acid different from the acid. For example, an inorganic acid can be used as the acid, and an inorganic acid salt can be used as the acid salt.

[0036] The concentration of the acid in the polishing composition (when multiple types of acids are contained, the total concentration thereof) is not particularly limited. The concentration of the acid is usually 0.1 wt % or more, preferably 0.5 wt % or more, more preferably 0.8 wt % or more, even more preferably 1 wt % or more, and may be 1.2 wt % or more. Increasing the acid concentration tends to make it easier to obtain practical processability. The concentration of the acid in the polishing composition is usually 15 wt % or less, preferably 10 wt % or less, more preferably 5 wt % or less, and may be 3 wt % or less. By limiting the acid content, the surface precision of the object to be polished (Ni-P substrate) is likely to be improved.

[0037] (Additive A) The polishing composition disclosed herein contains Additive A. Additive A is a polymer having sulfonic acid (salt) groups (hereinafter also referred to as a "sulfonic acid (salt) group-containing polymer"). By using Additive A having sulfonic acid (salt) groups in combination with Additive B (a nonionic surfactant) described below, polishing resistance (friction) can be reduced while maintaining practical processability in polishing Ni-P substrates. The reason for this effect is thought to be, for example, as follows: Additive A and Additive B form a complex when they coexist. This complex exhibits appropriate adsorption to colloidal silica because Additive B contains a specific number of oxyethylene units in its molecule. As a result, this complex is interposed between the colloidal silica and the substrate to be polished, exhibiting a lubricating effect, which is thought to reduce the polishing resistance between the colloidal silica and the substrate to be polished. Furthermore, the Ni-P substrate may become negatively charged during polishing. On the other hand, it is believed that the colloidal silica to which such a complex is adsorbed is negatively charged, causing electrostatic repulsion against the Ni-P substrate, increasing the rolling frequency of the colloidal silica, and this action is also thought to reduce the polishing resistance. Note that the above mechanism is the inventors' speculation based on experimental results, and the technology disclosed herein should not be interpreted as being limited to the above mechanism.

[0038] The sulfonic acid (salt) group-containing polymer used as additive A refers to a polymer containing at least one type of repeating unit X having a sulfonic acid (salt) group as a repeating unit constituting the polymer. Here, "sulfonic acid (salt)" encompasses sulfonic acid and sulfonate salts, and refers to at least one of sulfonic acid and sulfonate salts. Furthermore, in this specification, "polymer" refers to a substance (compound, molecule) or mixture thereof having multiple repeating units (units derived from monomers), and may be a polymer produced by polymerization or a polymer derived from a natural product. Since sulfonic acid (salt) groups are anionic, additive A having a sulfonic acid (salt) group also has anionic properties. Additive A can be used alone or in combination of two or more types.

[0039] The repeating unit X contained in the additive A may be a repeating unit derived from a monomer having at least one sulfonic acid (salt) group per molecule. Examples of monomers having a sulfonic acid (salt) group include styrenesulfonic acid, isoprene sulfonic acid, vinylsulfonic acid, allylsulfonic acid, isoamylenesulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, and methallylsulfonic acid. The sulfonic acid (salt) group-containing polymer may contain two or more types of the repeating unit X. The sulfonic acid (salt) group-containing polymer may further contain a repeating unit not having a sulfonic acid (salt) group. The repeating unit not having a sulfonic acid (salt) group may be a repeating unit having an anionic functional group other than sulfonic acid (salt), or may be a repeating unit not having an anionic functional group.

[0040] An example of a repeating unit having an anionic functional group other than sulfonic acid (salt) is a repeating unit Y having a carboxy group. The repeating unit Y may be, for example, a repeating unit derived from (meth)acrylic acid. Here, "(meth)acrylic acid" is a concept that encompasses one or both of acrylic acid and methacrylic acid. The additive A may be a (meth)acrylic acid / sulfonic acid copolymer containing a carboxy group-containing repeating unit Y derived from (meth)acrylic acid and a repeating unit X. Examples of the (meth)acrylic acid / sulfonic acid copolymer include a (meth)acrylic acid / isoprene sulfonic acid copolymer, a (meth)acrylic acid / 2-acrylamido-2-methylpropane sulfonic acid copolymer, and a (meth)acrylic acid / isoprene sulfonic acid / 2-acrylamido-2-methylpropane sulfonic acid copolymer. The (meth)acrylic acid / sulfonic acid copolymer may further contain a repeating unit that does not have a sulfonic acid (salt) group and is not derived from a (meth)acrylic acid monomer.

[0041] In some embodiments, a sulfonic acid (salt) group-containing polymer that does not contain a repeating unit Y having a carboxy group can be used as additive A. The sulfonic acid (salt) group-containing polymer that does not contain a repeating unit Y may further contain a repeating unit that does not contain a sulfonic acid (salt) group or a carboxy group (e.g., a repeating unit that does not contain an anionic functional group).

[0042] Examples of sulfonic acid (salt) group-containing polymers include polymers in which the ratio (molar ratio) of sulfonic acid (salt) group-containing repeating units X to the total number of moles of repeating units contained in the molecular structure of the polymer is 95% or more. For example, a sulfonic acid (salt) group-containing polymer consisting essentially of repeating units X can be used as additive A. In such sulfonic acid (salt) group-containing polymers, the molar ratio of the repeating units X can be, for example, 98% or more, 99.5% or more, or even 99.9% or more. In some embodiments, additive A can be a sulfonic acid (salt) group-containing polymer in which the molar ratio of repeating units X is 100%, i.e., a sulfonic acid (salt) group-containing polymer consisting solely of repeating units X having sulfonic acid (salt) groups. Examples of such sulfonic acid (salt) group-containing polymers include homopolymers consisting of any one of the above sulfonic acid (salt) group-containing monomers and copolymers consisting of two or more sulfonic acid (salt) group-containing monomers. Examples of the homopolymer include polystyrene sulfonic acid, polyisoprene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyisoamylene sulfonic acid, etc. Among these, polystyrene sulfonic acid, that is, a homopolymer of styrene sulfonic acid, is preferred.

[0043] In some preferred embodiments, additive A is a polymer having a main chain and sulfonic acid (salt) groups, and a chemical structure having an aromatic ring in the main chain. The main chain of additive A is typically composed of multiple repeating units, and the main chain contains an aromatic ring. Examples of structures having an aromatic ring in the main chain include structures such as benzene, naphthalene, and anthracene, as well as melamine and lignin structures, which may exist in the main chain with an alkyl group such as a methyl group interposed therebetween. The sulfonic acid (salt) group is attached to the main chain as a side chain, and is usually attached directly to the main chain, but is not limited thereto, and may also be attached to the main chain via another group.

[0044] Suitable examples of the additive A having the above chemical structure include polyalkylarylsulfonic acid compounds such as naphthalenesulfonic acid formaldehyde condensates or salts thereof, methylnaphthalenesulfonic acid formaldehyde condensates or salts thereof, and anthracenesulfonic acid formaldehyde condensates or salts thereof; melamine formalin resin sulfonic acid compounds such as melamine sulfonic acid formaldehyde condensates or salts thereof; ligninsulfonic acid compounds such as ligninsulfonic acid or salts thereof, and modified ligninsulfonic acid or salts thereof; and aromatic aminosulfonic acid compounds such as aminoarylsulfonic acid-phenol-formaldehyde condensates or salts thereof.

[0045] When additive A is in the form of a neutralized salt, additive A may be in the form of an alkali metal salt such as Na or K, an alkaline earth metal salt such as Ca, an ammonium salt, an alkylammonium salt, or an alkanolamine salt such as monoethanolamine. Additive A may be preferably used in the form of an alkali metal salt such as a Na salt, for example.

[0046] The Mw of additive A is not particularly limited and may be, for example, approximately 400 or more, or 1,000 or more. In some preferred embodiments, the Mw of additive A is, for example, 1,500 or more, 2,000 or more, or 2,500 or more. The upper limit of the Mw of additive A is, for example, 300,000 or less, or 100,000 or less. In some preferred embodiments, the Mw of additive A is, for example, 50,000 or less, 10,000 or less (e.g., less than 10,000), 9,000 or less, or 5,000 or less. In other embodiments, the Mw of additive A may be 3,000 or more, 5,000 or more, 7,000 or more, or 9,000 or more. In other embodiments, the upper limit of the Mw of additive A may be, for example, 1,500,000 or less, 1,000,000 or less, or 500,000 or less. The Mw of additive A can be the weight average molecular weight (water-based, polyethylene glycol equivalent) determined by GPC.

[0047] The concentration of additive A in the polishing composition is not particularly limited, and may be, for example, 0.0001 wt % or more, or 0.0005 wt % or more. In some preferred embodiments, the concentration of additive A is, for example, 0.001 wt % or more, or 0.005 wt % or more, or 0.01 wt % or more, from the viewpoint of effectively exhibiting the effect of adding additive A. Furthermore, from the viewpoint of processability and post-polishing washability, the concentration of additive A is usually less than 1 wt %, preferably 0.2 wt % or less, more preferably 0.1 wt % or less, or may be 0.07 wt % or less, 0.05 wt % or less, or 0.03 wt % or less.

[0048] (Additive B) The polishing composition disclosed herein contains Additive B. Additive B is a nonionic surfactant having 10 or more oxyethylene units (hereinafter also referred to as "OE units") per molecule. By using Additive B having the above chemical structure and properties in combination with Additive A, polishing resistance (friction) can be reduced while maintaining practical processability in polishing Ni-P substrates. The mechanism behind this is as explained for Additive A, but to supplement, Additive B, having 10 or more OE units, is thought to be highly adsorbed to colloidal silica, thereby contributing to maintaining practical processability and reducing polishing resistance. Additive B can be used alone or in combination of two or more.

[0049] The nonionic surfactant used as additive B has a polyoxyethylene chain containing an OE unit (a chain structure consisting of two or more consecutive OE units). Here, the OE unit is a structural unit represented by the formula: —CH—CH—O—. In some preferred embodiments, the number of OE units in additive B may be 12 or more, 15 or more, 18 or more, 20 or more, 25 or more, 30 or more, 35 or more, 40 or more, or 45 or more. The greater the number of OE units, the more likely the adsorption to abrasive grains is to improve. The number of OE units in additive B may be, for example, 80 or less, or, from the viewpoint of dispersion stability, etc., 60 or less, 50 or less, 45 or less, 40 or less, 35 or less, 30 or less, 25 or less, 20 or less, or 16 or less. Note that the above number of OE units refers to the average OE number in a mixture containing different numbers of OE units.

[0050] The nonionic surfactant used as additive B may typically have a structure consisting of the polyoxyethylene chain as a hydrophilic region and a hydrophobic region. The hydrophobic region may be, for example, a hydrocarbon group or a group containing an atom other than carbon and hydrogen (such as phosphorus, nitrogen, oxygen, sulfur, fluorine, chlorine, bromine, or iodine). In additive B having two or more hydrophobic regions, the hydrophobic regions may be the same or different. In some preferred embodiments, the hydrophobic region contains a hydrocarbon group. The hydrocarbon group may be an aliphatic hydrocarbon group or a hydrocarbon group containing an aromatic ring, such as an aryl group or an alkylaryl group. The aliphatic hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group containing an unsaturated bond such as a carbon-carbon double bond, and may be linear or may contain a cyclic structure. The linear hydrocarbon group may be either linear or branched. Preferred examples of the hydrocarbon group constituting the hydrophobic region include alkyl groups and alkenyl groups.

[0051] In an embodiment in which a nonionic surfactant having an aliphatic hydrocarbon group is used as additive B, the carbon number of the aliphatic hydrocarbon group (e.g., alkyl group, alkenyl group) is suitably, for example, 4 or more, and may be 6 or more, 8 or more, 10 or more, 12 or more, 14 or more, 16 or more, 18 or more, or 20 or more. The larger the carbon number of the aliphatic hydrocarbon group, the more likely it is that a complex having a size that contributes to reducing polishing resistance will be formed. Furthermore, from the viewpoint of the dispersion stability of additive B, the carbon number of the aliphatic hydrocarbon group may be, for example, 80 or less, 60 or less, 40 or less, 30 or less, 24 or less, 22 or less, or 20 or less.

[0052] In some embodiments, Additive B may have a structure in which a polyoxyethylene chain and an aliphatic hydrocarbon group are linked via an ether bond or an ester bond. Examples of Additive B having such a structure include polyoxyethylene alkyl ethers, polyoxyethylene alkenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkenyl esters, etc.

[0053] A suitable example of additive B is a nonionic surfactant having a chemical structure consisting of the above-mentioned polyoxyethylene chain and an aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group as described above, and may contain a cyclic structure. A typical example of such additive B is a surfactant having the formula: RO-(CH2-CH2-O) n H; In the above formula, R is an aliphatic hydrocarbon group, such as an alkyl group or an alkenyl group. The number of carbon atoms in the aliphatic hydrocarbon group (e.g., an alkyl group or an alkenyl group) may be within the range of the number of carbon atoms for the aliphatic hydrocarbon group described above. Furthermore, n is a real number of 10 or more, and the number of OE units may be within the range described above.

[0054] Additive B may contain oxyalkylene units other than OE units (e.g., oxypropylene units, oxybutylene units) in addition to OE units, as long as the effects of the present invention are not impaired. In this case, the number of oxyalkylene units other than OE units contained in Additive B is preferably less than the number of OE units (e.g., 1 / 2 or less, 1 / 5 or less, or 1 / 10 or less of the number of OE units). Additive B may also contain hydroxyl groups, amide groups, alkanol groups having 1 to 2 carbon atoms, etc., as long as the effects of the present invention are not impaired.

[0055] Specific examples of additive B include POE (polyoxyethylene) butyl ether, POE ethylhexyl ether, POE octyl ether, POE decyl ether, POE isodecyl ether, POE lauryl ether, POE isotridecyl ether, POE cetyl ether, POE stearyl ether, POE oleyl ether, POE behenyl ether, POE monolaurate, POE monostearate, POE monooleate, and POE dioleate, each of which has 10 or more OE units.

[0056] The concentration of additive B contained in the polishing composition is not particularly limited, and can be, for example, 0.0001 wt% or more, or 0.0003 wt% or more. In some preferred embodiments, the concentration of additive B is, from the viewpoint of effectively exhibiting the effect of adding additive B, for example, 0.0005 wt% or more, or may be 0.001 wt% or more, or 0.003 wt% or more, or 0.005 wt% or more, or 0.008 wt% or more, or 0.01 wt% or more. In addition, the concentration of additive B in the polishing composition can be, for example, 0.1 wt% or less, or 0.06 wt% or less, or 0.04 wt% or less, or 0.02 wt% or less (for example, less than 0.01 wt%). By limiting the amount of additive B used, processability is easily maintained, and the polishing composition tends to have excellent dispersion stability.

[0057] The amount of additive B contained in the polishing composition can also be determined by its relative relationship to the colloidal silica contained in the polishing composition.The content of additive B relative to 100 parts by weight of colloidal silica contained in the polishing composition is, for example, 0.001 parts by weight or more, preferably 0.005 parts by weight or more, more preferably 0.01 parts by weight or more, even more preferably 0.05 parts by weight or more, and may be 0.1 parts by weight or more, or may be 0.2 parts by weight or more.Furthermore, the content of additive B relative to 100 parts by weight of colloidal silica is suitably approximately 10 parts by weight or less, preferably less than 5 parts by weight, more preferably less than 3 parts by weight, even more preferably less than 1 part by weight, and may be 0.5 parts by weight or less, or may be 0.3 parts by weight or less.By using an appropriate amount of additive B relative to the amount of colloidal silica, the polishing resistance can be effectively reduced.

[0058] The ratio of additive A to additive B is appropriately set so as to optimally exhibit the effects of the present invention, and is not limited to a specific range. B Concentration C of additive A A Weight ratio (C A / C B ) is, for example, 0.1 or more, may be 0.3 or more, may be 0.7 or more, may be 1.0 or more, or may be 1.2 or more. A / C B ) is, for example, 30 or less, and may be 15 or less, 10 or less, 8 or less, or 5 or less. By setting the ratio of additive A to additive B in an appropriate range, a composite that can contribute to reducing polishing resistance is easily formed.

[0059] (water) The polishing composition disclosed herein contains water. As the water, ion-exchanged water, pure water, ultrapure water, distilled water, etc. can be preferably used. The ion-exchanged water can be deionized water.

[0060] (oxidizing agent) The polishing composition disclosed herein can contain an oxidizing agent as needed. Examples of oxidizing agents include, but are not limited to, peroxides, nitric acid or its salts, periodic acid or its salts, peroxoacid or its salts, permanganic acid or its salts, chromic acid or its salts, oxyacids or their salts, metal salts, and sulfuric acids. The oxidizing agents 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.

[0061] When the polishing composition disclosed herein contains an oxidizing agent, the content of the oxidizing agent in the polishing composition is preferably 0.01 wt% or more, more preferably 0.05 wt% or more, even more preferably 0.1 wt% or more, or may be 0.2 wt% or more, or may be 0.3 wt% or more, based on the amount of the active ingredient, taking into consideration the rate at which the polishing composition oxidizes the object to be polished and, consequently, the processability. Also, from the viewpoint of improving the surface precision of the object to be polished, the content of the oxidizing agent in the polishing composition is preferably 5 wt% or less, more preferably 1 wt% or less, based on the amount of the active ingredient.

[0062] (Water-soluble polymer) The polishing composition disclosed herein can contain a water-soluble polymer as an optional component. The water-soluble polymer can protect the substrate during polishing and suppress the occurrence of defects (e.g., scratches) on the substrate surface. The water-soluble polymer referred to here is a compound having a weight-average molecular weight (Mw) of approximately 2000 or more, typically 4000 or more. The water-soluble polymer may be a homopolymer or a copolymer. Examples of water-soluble polymers that can be used include anionic polymers, nonionic polymers, cationic polymers, and amphoteric polymers, but do not include those corresponding to Additives A and B. Examples of such optional water-soluble polymers include, but are not limited to, polyacrylic acid and its salts, polyvinyl acetate, polymaleic acid, polyitaconic acid, polyvinyl alcohol, modified polyvinyl alcohol, polyglycerin, polyvinylpyrrolidone, copolymers of polyvinylpyrrolidone with polyacrylic acid and / or vinyl acetate, diallylamine hydrochloride sulfur dioxide copolymer, carboxymethylcellulose and its salts, hydroxyethyl cellulose, hydroxypropyl cellulose, pullulan, chitosan and its salts, etc. The optional water-soluble polymers can be used alone or in combination of two or more.

[0063] The Mw of the water-soluble polymer may be, for example, 2000 or more, or 2500 or more. From the viewpoint of improving the protection of the substrate surface and suppressing the occurrence of defects, in some embodiments, the Mw of the water-soluble polymer is preferably 3000 or more, more preferably 5000 or more, and may be 7000 or more, or 9000 or more. The upper limit of the Mw of the water-soluble polymer is not particularly limited, but may be, for example, 1.5 million or less, 1 million or less, 500,000 or less, 300,000 or less, 200,000 or less, 100,000 or less, 70,000 or less, 50,000 or less, or 30,000 or less. The Mw of the water-soluble polymer can be the weight-average molecular weight (water-based, polyethylene glycol equivalent) determined by GPC.

[0064] The concentration of the water-soluble polymer in the polishing composition is not particularly limited. The concentration can be, for example, 0.0001 wt % or more. From the viewpoint of enhancing the substrate protection effect during polishing, the concentration is preferably 0.0005 wt % or more, more preferably 0.001 wt % or more, and may be 0.002 wt % or more, 0.0025 wt % or more, or 0.003 wt % or more. Furthermore, from the viewpoint of favorably achieving both substrate protection during polishing and ease of cleaning and removal from the substrate after polishing, the concentration of the water-soluble polymer is usually 0.2 wt % or less, preferably 0.15 wt % or less, for example, 0.1 wt % or less, or may be 0.07 wt % or less, or 0.05 wt % or less. The polishing composition disclosed herein may be substantially free of the water-soluble polymer (any water-soluble polymer).

[0065] (basic compounds) The polishing composition may contain a basic compound as needed for purposes such as pH adjustment. Here, the 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 such as potassium hydroxide and sodium hydroxide, quaternary ammonium compounds such as quaternary ammonium hydroxide, ammonia, amines, etc. The basic compounds may be used alone or in combination of two or more.

[0066] (Other ingredients) The polishing composition disclosed herein may further contain, as needed, known additives that can be used in polishing compositions (e.g., polishing compositions for magnetic disk substrates such as Ni-P substrates), such as surfactants, chelating agents, preservatives, and anti-fungal agents, to the extent that the effects of the present invention are not significantly impaired.

[0067] The optional surfactant that can be used in addition to Additive A and Additive B may be any of anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Note that the optional surfactants referred to here do not include Additive A and Additive B. The optional surfactants may be used alone or in combination of two or more. Specific examples of the anionic surfactant include polyoxyethylene alkyl ether acetate, polyoxyethylene alkyl sulfate, alkyl sulfate, polyoxyethylene alkyl sulfate, alkyl sulfate, alkyl phosphate, polyoxyethylene alkyl phosphate, polyoxyethylene sulfosuccinate, alkyl sulfosuccinate, polyacrylic acid, sodium lauryl sulfate, ammonium lauryl sulfate, polyoxyethylene alkyl ether sodium sulfate, polyoxyethylene alkyl phenyl ether ammonium sulfate, and polyoxyethylene alkyl phenyl ether sodium sulfate. Specific examples of the nonionic surfactant include sorbitan fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, and alkylalkanolamides. Specific examples of the cationic surfactant include alkyltrimethylammonium salts, alkyldimethylammonium salts, alkylbenzyldimethylammonium salts, and alkylamine salts. Specific examples of the amphoteric surfactant include alkylbetaine and alkylamine oxide.

[0068] In the polishing composition of the embodiment containing the optional surfactant, the content of the surfactant 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, more preferably 0.01% by weight or more. From the viewpoint of processability, the content is suitably 1% 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 be substantially free of the optional surfactant.

[0069] Examples of the chelating agent include aminocarboxylic acid chelating agents and organic phosphonic acid chelating agents. Examples of the aminocarboxylic acid chelating agent 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. Among these, organic phosphonic acid chelating agents are more preferred, and among these, ethylenediaminetetrakis(methylenephosphonic acid) and diethylenetriaminepenta(methylenephosphonic acid) are preferred. A particularly preferred chelating agent is ethylenediaminetetrakis(methylenephosphonic acid).

[0070] 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, paraoxybenzoic acid esters, and phenoxyethanol.

[0071] (pH) The pH of the polishing composition disclosed herein is not particularly limited and can be selected, for example, from the range of 0.5 to 6.5. From the viewpoint of processability, etc., the pH of the polishing composition is, for example, 4.0 or less, preferably 3.7 or less, more preferably 3.5 or less, and may be 3.2 or less, 3.0 or less, 2.5 or less, or even 2.2 or less. The pH of the polishing composition can be, for example, 1.0 or more, and is suitably higher than 1.0. From the viewpoint of suppressing roughness of the substrate surface after polishing, it is preferably 1.2 or more, more preferably 1.5 or more (e.g., greater than 1.5), and may be 1.7 or more. The technology disclosed herein can be preferably implemented in an embodiment in which the pH of the polishing composition is 1.0 or more and 4.0 or less (e.g., 1.5 or more and 3.7 or less). The above-mentioned pH is particularly preferably applied to a polishing composition for finish polishing of Ni-P substrates.

[0072] In the technology disclosed herein, the pH of a polishing composition can be determined by performing three-point calibration using a pH meter and then inserting a glass electrode into the composition to be measured. The standard solutions are, 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), and carbonate pH standard solution: pH 10.01 (25°C).

[0073] <Concentrate> The polishing composition disclosed herein may be in a concentrated form (i.e., in the form of a concentrated polishing liquid) before being supplied to an object to be polished (e.g., a magnetic disk substrate). Such a concentrated polishing composition (concentrate) is advantageous from the viewpoints of convenience and cost reduction during production, distribution, storage, etc. The concentration ratio can be, for example, about 1.5 to 20 times in terms of volume. From the viewpoint of the storage stability of the concentrate, for example, a concentration ratio of about 2 to 10 times is appropriate. Such a concentrate can be diluted at a desired time to prepare a polishing composition (polishing liquid), and the polishing liquid can be supplied to an object to be polished. The dilution can be performed, for example, by adding water to the concentrate and mixing.

[0074] <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 Part A, which contains some of the components (e.g., components other than water), and Part B, which contains the remaining components, are mixed together and used to polish an object to be polished. Some preferred embodiments of the multi-component polishing composition include Part A, which contains abrasive grains (e.g., a dispersion liquid further containing a dispersing medium for the abrasive grains), and Part B, which contains at least some of the components other than the abrasive grains (e.g., acid, additives A and B, etc.). These are stored separately, for example, before use, and can be mixed at the time of use to prepare a single-component polishing composition. An oxidizing agent, such as hydrogen peroxide, or water for dilution, can be further added during mixing.

[0075] <Polishing process> The polishing composition disclosed herein can be suitably used for polishing an object to be polished (here, a Ni-P substrate) in an embodiment including, for example, the following steps: Hereinafter, a preferred embodiment of a method for polishing an object 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 adjusting the concentration (e.g., diluting) or adjusting the pH of the polishing composition to prepare the polishing liquid. Alternatively, the polishing composition may be used as the polishing liquid as it is.

[0076] Next, the polishing liquid is supplied to the object to be polished, and polishing is performed. For example, the object to be polished is set in a general polishing device, and the polishing liquid is supplied to the surface of the object to be polished (the surface to be polished) through the polishing pad of the polishing device. For example, 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 (for example, rotated).

[0077] The polishing pad that can be used is not particularly limited. For example, polishing pads such as hard foam polyurethane type, nonwoven fabric type, and suede type can be used. Suede type polishing pads (typically polyurethane polishing pads) are easy to process and can easily achieve high quality on the substrate surface. Note that the polishing pad used in the technology disclosed herein does not contain abrasive grains.

[0078] The suede-type polishing pad may be a buff pad or a polishing pad in a non-buffed state (so-called non-buff pad) where the surface is not buffed. Here, "buffing" refers to a process of roughly grinding the surface using a grindstone or the like, and typically refers to a process of removing the surface layer of the polishing pad to adjust the pore opening diameter and opening ratio.

[0079] Although not particularly limited, when a non-buff pad is used as a polishing pad, pad dressing and dummy polishing may be performed before polishing the target substrate (object to be polished) to adjust the polishing surface of the polishing pad to the desired condition. Here, pad dressing is a process in which the surface of the polishing pad is scraped off using a pad conditioner (pad dresser), and pores and fuzziness may be present on the surface of the polishing pad after the process. By polishing a polishing pad with such a surface using a dummy substrate (typically a substrate of the same type as the target substrate), the surface condition of the polishing pad after the pad dressing process is adjusted to a condition suitable for subsequent polishing of the target substrate. Meanwhile, a polishing pad with such a surface condition has a smoother pad surface than a buff pad and a smaller pore diameter (e.g., about 20 μm), making it easier for the polishing pad to adhere to the target substrate. Therefore, the polishing resistance between the substrate and the polishing pad tends to be high when using such a polishing pad. When polishing a substrate to be polished (Ni-P substrate) using such a polishing pad (typically a non-buff pad), the polishing resistance reduction effect achieved by using the polishing composition disclosed herein can be effectively exerted.

[0080] In the polishing method disclosed herein, the workpiece is set in a polishing apparatus while being held by a carrier, and polishing is performed. The carrier holds the side of the substrate to be polished during polishing, and is not particularly limited, but is usually a member having holding holes called holes, and the workpiece is placed in the holding holes to be polished.

[0081] The material of the carrier is not particularly limited, and examples thereof include resin materials such as aramid resin and polycarbonate resin, composite resin materials such as fiber-reinforced plastic (FRP), and composite materials combining these. Examples of such composite materials include carriers made of aramid laminates in which aramid nonwoven fabric is impregnated with epoxy resin. The technology disclosed herein is suitable for embodiments using a resin carrier such as aramid resin. In embodiments using a resin carrier, the polishing resistance reduction effect of the technology disclosed herein can prevent or suppress carrier deformation caused by the polishing resistance.

[0082] Furthermore, the carrier is usually thinner than the object to be polished. The thickness of the carrier is not limited to a specific range and is appropriately determined depending on the object to be polished, etc. The thickness of the carrier is, for example, 1.5 mm or less, usually 1 mm or less, and may be about 0.7 mm or less, or about 0.5 mm or less. Carriers having such thicknesses are prone to deformation when subjected to a large load during polishing. However, by applying the technology disclosed herein, the polishing resistance is reduced, the load on the carrier is alleviated, and deformation due to the load can be prevented or suppressed. The lower limit of the carrier thickness can be about 0.1 mm or more (e.g., 0.2 mm or more).

[0083] After polishing the object to be polished as described above, the object to be polished is washed. For example, an alkaline cleaning step is carried out in which the object to be polished is washed with an alkaline cleaning solution. The alkaline cleaning step includes, for example, contacting at least the surface of the object to be polished with the alkaline cleaning solution. For example, the object to be polished can be immersed in the alkaline cleaning solution to bring the alkaline cleaning solution into contact with the surface of the object to be polished. Ultrasonic treatment may be performed in which ultrasonic waves are applied to the object to be polished immersed in the alkaline cleaning solution. In addition to or instead of applying ultrasonic waves, scrubbing may be performed using a polyvinyl alcohol sponge, nonwoven fabric, nylon brush, or the like. The pH of the alkaline cleaning solution used in the alkaline cleaning step may be, for example, 7.5 or higher, and from the viewpoint of improving cleaning performance, it is preferably 8.0 or higher, more preferably 8.5 or higher, for example, 8.8 or higher. Furthermore, from the viewpoint of preventing roughening of the substrate surface due to cleaning, the pH of the alkaline cleaning solution is suitably 11 or lower, preferably 10 or lower, and more preferably 9.5 or lower. As the alkaline cleaning solution, an aqueous solution containing one or more of the basic compounds described above can be used. Among these, an aqueous solution of an alkali metal hydroxide is preferred, and for example, an aqueous potassium hydroxide solution can be preferably used. The alkaline cleaning step may be performed using a commercially available alkaline cleaning solution.

[0084] After polishing using the polishing liquid, the object to be polished may be rinsed with a non-alkaline rinse liquid before proceeding to the alkaline cleaning step. The rinse liquid may be water such as pure water or ion-exchanged water, or an acidic aqueous solution (e.g., an aqueous solution with a composition obtained by removing abrasive grains from the polishing liquid).

[0085] <Application> The polishing composition disclosed herein is used for polishing a nickel-phosphorus-plated magnetic disk substrate (Ni-P substrate). The Ni-P substrate is a magnetic disk substrate having a nickel-phosphorus-plated layer on the surface of the substrate. The material of the substrate can be, for example, an aluminum alloy, glass, glassy carbon, etc. The polishing composition disclosed herein can be preferably used for polishing a Ni-P substrate having a nickel-phosphorus-plated layer on an aluminum alloy substrate, for example. According to this specification, a method for manufacturing a Ni-P substrate, which includes a polishing step using the polishing composition disclosed herein and an alkaline cleaning step performed after the polishing step, and a Ni-P substrate manufactured by this method can be provided.

[0086] The polishing composition disclosed herein can be particularly preferably used in the final polishing step (finish polishing step) of Ni-P substrates. This specification provides a method for manufacturing a Ni-P substrate, which includes a final polishing step using the polishing composition disclosed herein and an alkaline cleaning step performed after the final polishing step, and a Ni-P substrate manufactured by this method. Note that final polishing refers to the final polishing step in the manufacturing process of the target object (i.e., a step in which no further polishing is performed after that step). The manufacturing method of the substrate may further include a rough polishing step or a pre-polishing step performed before the polishing step.

[0087] The polishing composition disclosed herein may be used in a polishing step upstream of the final polishing. Here, the polishing step upstream of the final polishing refers to a preliminary polishing step between the rough polishing step and the final polishing step. The preliminary polishing step includes at least a primary polishing step and may further include secondary, tertiary, etc. polishing steps. The above-mentioned 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 the final polishing.

[0088] The polishing composition disclosed herein can be preferably used, for example, for polishing Ni-P substrates whose surface roughness has been adjusted to 20 Å or less by an upstream process. Here, the surface roughness refers to the surface roughness (arithmetic mean roughness (Ra)) measured using a laser scanning surface roughness meter "TMS-3000WRC" manufactured by Schmitt Measurement Systems. It is particularly preferred to use the composition for polishing Ni-P substrates whose surface roughness has been adjusted to 10 Å or less. This allows for the efficient production of Ni-P substrates with high-quality surfaces. [Example]

[0089] Hereinafter, several embodiments of the present invention will be described, but the present invention is not intended to be limited to those shown in such embodiments.

[0090] <Preparation of Polishing Composition> (Example 1) A polishing composition containing colloidal silica (4% by weight) as abrasive grains, an acid (1.5% by weight), additive A (0.02% by weight), additive B (0.004% by weight), hydrogen peroxide (0.4% by weight) and deionized water, and adjusted to pH 2.0 with potassium hydroxide was prepared. The average primary particle size of the colloidal silica measured by the BET method was 18 nm, and the 50% cumulative diameter (D 50 ) of the colloidal silica in the number-based particle size distribution based on TEM observation was 24 nm. Also, the average aspect ratio of the colloidal silica based on TEM observation was 1.11. Phosphoric acid (orthophosphoric acid) was used as the acid. As additive A, sodium naphthalenesulfonate formaldehyde condensate with Mw of 3000 was used. As additive B, POE(13) cetyl ether with an OE unit number of 13 was used. In the column of "additive B" in Table 1, the number in parentheses attached to POE represents the OE unit number.

[0091] (Examples 2 to 5 and Comparative Examples 1 to 6) Polishing compositions according to each example were prepared in the same manner as in Example 1, except that the types and amounts of additive A and additive B were changed as shown in Table 1. The molar amounts of additive B in Examples 1 to 5 and Comparative Examples 3 to 6 are the same. In Table 1, additives with an OE unit number less than 10 are also described in the column of "additive B" for convenience. Also, in Table 1, "-" represents not used.

[0092] <Polishing of Ni-P Substrate> The polishing composition according to each example was used as a polishing solution to polish a substrate under the following conditions. The substrate to be polished was an aluminum substrate for hard disks (Ni-P substrate) with an electroless nickel-phosphorus plating layer on its surface, which had been pre-polished so that the surface roughness (arithmetic mean roughness (Ra)) measured with a laser scanning surface roughness meter "TMS-3000WRC" manufactured by Schmitt Measurement Systems, Inc. was 6 Å. The diameter of the substrate to be polished was 3.5 inches (donut-shaped with an outer diameter of approximately 95 mm and an inner diameter of approximately 25 mm) and the thickness was 1.75 mm.

[0093] (polishing conditions) Polishing equipment: CETR tabletop polishing machine, model "CP-4" Polishing pad: Suede non-buff type (manufactured by Fujibo) Polishing load: 131g / cm 2 Polishing platen rotation speed: 70 rpm Head rotation speed: 70 rpm Polishing fluid supply rate: 13 mL / min Polishing time: 300 seconds The substrate was fixed to a carrier (thickness 1.5 mm) attached to the head portion.

[0094] <Cleaning> The polished Ni-P substrate was immersed in pure water and subjected to ultrasonic treatment at a frequency of 170 kHz, then immersed in an alkaline cleaning solution (a cleaning solution "CSC-102B" available from Speedfam Clean Systems Co., Ltd. diluted 200 times by volume) and scrubbed with a polyvinyl alcohol sponge while applying ultrasonic waves at a frequency of 170 kHz. The substrate was then immersed in pure water and subjected to ultrasonic treatment at a frequency of 950 kHz, after which it was removed from an isopropyl alcohol atmosphere and dried.

[0095] <Polishing rate> The substrate is polished with the polishing composition of each example, and then washed, and the weight loss of the substrate is measured by polishing to calculate the polishing rate, and the average of these weight loss values ​​is used to obtain the polishing rate of each example. Specifically, the polishing rate is calculated according to the following formula: Polishing rate [μm / min] = weight loss of substrate due to polishing [g] / (single-sided area of ​​substrate [cm 2 ] × density of nickel phosphorus plating [g / cm 3 ] x polishing time [min]) x 10 4 Here, the surface area of ​​one side of the board is 66 cm 2 , the density of nickel phosphorus plating is 7.9g / cm 3 The obtained values ​​were converted into relative values, with the value of Comparative Example 1 being set at 100, and are shown in the "relative value" column of "polishing rate" in Table 1.

[0096] From the obtained relative values, the processability (removal rate) was judged according to the following two levels. The results are shown in the "Judgment" column of "Removal rate" in Table 1. ○: Relative value of 95 or more (has practical workability) ×: Relative value less than 95

[0097] <Measurement of abrasive resistance> The polishing resistance between the substrate to be polished and the polishing pad during polishing using the polishing composition of each example was obtained from the polishing apparatus. Specifically, the force Fx applied in the X-axis direction (horizontal direction) to the head holding the substrate to be polished was taken as the polishing resistance between the substrate to be polished and the polishing pad, and the average value of the force Fx over 120 seconds from 180 seconds after the start of polishing to the end of polishing (300 seconds) was measured as the polishing resistance. The obtained value was then converted into a relative value, with the value of Comparative Example 1 taken as 100, and is shown in the "Relative Value" column of "Polishing Resistance" in Table 1.

[0098] The degree of the polishing resistance reducing effect of the obtained relative values ​​of polishing resistance was judged according to the following two levels. The results are shown in the "Judgment" column of "Polishing resistance" in Table 1. 〇: Relative value 85 or less (pad scratches can be suppressed) ×: Relative value over 85

[0099] [Table 1]

[0100] As shown in Table 1, in polishing a Ni-P substrate, Examples 1 to 5, in which Additive A, a sulfonic acid (salt) group-containing polymer, and Additive B, a nonionic surfactant having 10 or more OE units per molecule, were added to a polishing composition containing colloidal silica abrasive grains, acid, and water, maintained practical processability while reducing the polishing resistance between the substrate and the polishing pad, compared to the polishing composition of Comparative Example 1, which did not contain Additives A and B. Furthermore, Comparative Example 2, in which Additive A was used without Additive B, achieved a polishing resistance reduction effect compared to Comparative Example 1, but this effect was not as great as that of Examples 1 to 5, in which Additive A and Additive B were used in combination. Comparative Examples 4 to 6, in which Additive B was used without Additive A, achieved an improved polishing rate compared to Comparative Example 1, but did not achieve a polishing resistance reduction effect. Furthermore, Comparative Example 3, in which Additive A and a nonionic surfactant with 9 OE units were used as Additive B, also achieved an improved polishing rate, but did not achieve a polishing resistance reduction effect.

[0101] The above results show that a polishing composition containing colloidal silica abrasive grains, acid, and water, and further containing additive A, which is a sulfonic acid (salt) group-containing polymer, and additive B, which is a nonionic surfactant having 10 or more OE units in one molecule, can reduce polishing resistance while maintaining practical processability when polishing Ni-P substrates.

[0102] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.

Claims

1. A polishing composition used for polishing a magnetic disk substrate having a nickel-phosphorus plating layer, comprising: The composition contains colloidal silica as an abrasive grain, an acid, an additive A, an additive B, and water, The additive A is a polymer having a sulfonic acid (salt) group, The polishing composition, wherein the additive B is a nonionic surfactant having 10 or more oxyethylene units in one molecule.

2. The polishing composition according to claim 1 , further comprising an oxidizing agent.

3. 3. The polishing composition according to claim 1, wherein the pH is within the range of 1 to 4.

4. 4. The polishing composition according to claim 1, wherein the colloidal silica has an average aspect ratio of 1.0 or more and 1.2 or less as determined by transmission electron microscope observation.

5. 5. The polishing composition according to claim 1, wherein the colloidal silica has an average primary particle size of 1 nm or more and 50 nm or less.

6. The polishing composition according to any one of claims 1 to 5, which is used in a finish polishing step.

7. A method for producing a magnetic disk substrate, comprising a step of polishing a substrate to be polished with the polishing composition according to any one of claims 1 to 6.

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