Polishing composition and method for producing magnetic disk substrate

Abstract

To provide a polishing composition capable of reducing abrasion resistance applied between a substrate and a polishing pad during polishing while maintaining practical workability when used in polishing of a Ni-P substrate.SOLUTION: A magnetic disk substrate polishing composition having a nickel phosphorous plating layer is provided. This polishing composition contains colloidal silica as abrasive grains, an acid, and water. This polishing composition further contains an additive A. The additive A is a (poly)oxyethylene alkyl ether phosphoric acid having a hydrocarbon group having 4 to 12 carbon atoms and oxyethylene units of 1 or more to 4 or less units. The content of the additive A is less than 0.1 wt.%.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. 2001-89749 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 workpiece 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 workpiece, and the load on the carrier also tends to increase. In such polishing, if the polishing resistance acting between the workpiece and the polishing pad during polishing can be reduced, the load on the carrier will be alleviated, and deformation of the carrier can be prevented or suppressed, and pad scratches can be prevented.

[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 contains colloidal silica as abrasive grains, an acid, and water, and which can reduce the polishing resistance between the substrate and the polishing pad during polishing 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] According to the present specification, there is provided a polishing composition for use in polishing a magnetic disk substrate having a nickel-phosphorus plating layer. This polishing composition contains colloidal silica as abrasive grains, an acid, and water. This polishing composition further contains Additive A. Additive A is a (poly)oxyethylene alkyl ether phosphate having an alkyl group having 4 to 12 carbon atoms and 1 to 4 oxyethylene units. The content of Additive A is less than 0.1% by weight. By adding the above-mentioned additive A to a polishing composition containing colloidal silica as an abrasive, it is possible to reduce the polishing resistance (polishing resistance between the substrate and the polishing pad) exerted between the substrate and the polishing pad during polishing of Ni-P substrates while maintaining the practical processability achieved by containing 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] A 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 the polishing resistance between the substrate and the pad during finish polishing of a Ni-P substrate while maintaining practical processability.

[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 a high polishing rate 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 differing in 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 a high polishing rate.

[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 a higher polishing rate. From the viewpoint of processability, etc., 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 polishing rate, 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 50 is 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 polishing efficiency, it may be, for example, 1.03 or more, 1.06 or more, or 1.08 or more. Furthermore, from the viewpoint of efficiently improving 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 average aspect ratio of all particles can then be calculated by arithmetically averaging the number-average aspect ratios from the aspect ratios of the predetermined number of particles. 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 a higher polishing rate. 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.

[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] In terms of polishing efficiency, 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, inorganic acid salts such as alkali metal salts and ammonium salts of inorganic acids can be preferably used as the salt. For example, in addition to the above-mentioned alkali metal phosphates and alkali metal hydrogen phosphates, potassium chloride, sodium chloride, ammonium chloride, potassium nitrate, sodium nitrate, ammonium nitrate, etc. can be preferably used. Among these, alkali metal phosphates and alkali metal hydrogen phosphates are preferred. Alkali metal hydrogen phosphates are particularly preferred.

[0035] The acid and its salt can be used alone or in combination of two or more (for example, 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 an inorganic acid salt.

[0036] The molar concentration of the acid in the polishing composition (when multiple types of acids are contained, the total molar concentration thereof) is not particularly limited, and is suitably 0.01 mol / L or more, preferably 0.05 mol / L or more, more preferably 0.08 mol / L or more, for example, 0.12 mol / L or more. Increasing the molar concentration of the acid tends to make it easier to obtain a practical polishing rate. The molar concentration of the acid is suitably 2 mol / L or less, preferably 1 mol / L or less, more preferably 0.5 mol / L or less, for example, 0.3 mol / L or less. By limiting the molar concentration of the acid, the surface precision of the object to be polished is likely to be improved.

[0037] (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.

[0038] (Additive A) The polishing composition disclosed herein contains Additive A. Additive A is a (poly)oxyethylene alkyl ether phosphate containing an alkyl group having 4 to 12 carbon atoms and 1 to 4 oxyethylene units (hereinafter also referred to as "OE units"). The content of Additive A in the polishing composition is less than 0.1 wt %. Additive A can be used alone or in combination of two or more. When the polishing composition contains multiple types of Additive A, the total amount is the above-mentioned content. By using a polishing composition containing Additive A, it is possible to reduce the polishing resistance (friction) between the substrate and the polishing pad during polishing while maintaining practical processability in polishing Ni-P substrates. The reason for the above-mentioned effect is thought to be as follows: Additive A has an alkyl group with a specific range of carbon atoms in its molecule, which is thought to exhibit appropriate adsorptivity to the polishing pad, thereby reducing the polishing resistance between the substrate and the polishing pad. Furthermore, Additive A has moderate water solubility due to the inclusion of a specific number of OE units in its molecule, and exhibits moderate adsorption to colloidal silica, which is thought to also act to reduce the polishing resistance between the colloidal silica and the substrate being polished. In this way, Additive A is thought to contribute to reducing the polishing resistance between the substrate and pad during polishing while maintaining practical processability by acting (moderately adsorbing) mainly on the polishing pad and colloidal silica. 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.

[0039] In view of the above-mentioned function, additive A can be referred to as a friction reducer or a polishing resistance reducer. Here, the friction reducer and the polishing resistance reducer refer to additives that enable a polishing composition containing the additive to achieve a polishing resistance of less than 90 (relative value basis) as evaluated in the examples described below, compared to a polishing composition of the same composition except that the additive is not added.

[0040] The polyoxyethylene alkyl ether phosphate used as additive A is a compound in which the hydrogen atoms of one or two OH groups (OH groups directly bonded to the phosphorus atom) in phosphoric acid (orthophosphoric acid, H3PO4) are substituted with organic groups, and the compound has one or two OH groups derived from phosphoric acid. The organic group has an alkyl group and a (poly)oxyethylene chain containing an oxyethylene unit. Here, the OE unit is a structural moiety represented by the following chemical formula (1): -CH2-CH2-O-;. The alkyl group and the (poly)oxyethylene chain are ether-bonded. That is, the structure of the organic group can be represented by the following chemical formula (2): RO-(CH2-CH2-O)n-;. In the above formula (2), R is an alkyl group. n is a real number satisfying the range of 1 to 4 (e.g., 1, 2, 3, or 4). (CH2-CH2-O)n may be a structure consisting of one OE unit, or a repeating structure of two or more OE units. Additive A may be used in the form of a salt of Additive A. Examples of the salt include metal salts of Additive A. Examples of the metal salt include alkali metal salts such as lithium salt, sodium salt, and potassium salt.

[0041] The number of carbon atoms in the alkyl group in Additive A can be appropriately set within the range of 4 to 12, if necessary, taking into consideration the relationship with the number of OE units so as to balance maintaining processability and reducing polishing resistance. The number of carbon atoms may be 6 or more, 8 or more, or 10 or more. The number of carbon atoms may be 10 or less, 8 or less, or 6 or less. The alkyl group may be linear or branched. Specific examples of the alkyl group include n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, hexyl, heptyl, 2-ethylhexyl, octyl, isooctyl, nonyl, isononyl, decyl, isodecyl, undecyl, and dodecyl (lauryl) groups.

[0042] When additive A has a structure in which the hydrogen atoms of two OH groups derived from phosphoric acid are substituted with organic groups (typically in the case of a phosphoric acid diester), the number of carbon atoms and the number of OE units refer to the total number in one molecule.

[0043] The amount of additive A contained in the polishing composition is less than 0.1 wt %. By limiting the amount of additive A in this way, aggregation of colloidal silica in the polishing composition is prevented or suppressed, making it easier to prepare the polishing composition and allowing the desired polishing performance to be exhibited. From the viewpoint of effectively exhibiting the effect of adding additive A (typically, the effect of reducing polishing resistance), the content of additive A in the polishing composition is, for example, 0.0001 wt % or more, and can be 0.0003 wt % or more. In some preferred embodiments, the content of additive A is 0.0005 wt % or more, more preferably 0.001 wt % or more, even more preferably 0.003 wt % or more, and may be 0.005 wt % or more, 0.01 wt % or more, or 0.03 wt % or more. The content of additive A in the polishing composition can be, for example, 0.08 wt % or less, or may be 0.06 wt % or less, 0.04 wt % or less, or 0.02 wt % or less (for example, less than 0.01 wt %). By limiting the amount of additive A used, processability is easily maintained, and the polishing composition tends to have excellent dispersion stability.

[0044] The amount of additive A contained in the polishing composition disclosed herein can also be determined by its relative relationship to the colloidal silica contained in the polishing composition. The content of additive A 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, 0.3 parts by weight or more, or even 0.5 parts by weight or more. It is believed that the greater the amount of additive A relative to the amount of colloidal silica, the more effectively additive A exerts its effect on the colloidal silica, thereby reducing the polishing resistance between the substrate and the polishing pad. Furthermore, the content of additive A relative to 100 parts by weight of colloidal silica is approximately 10 parts by weight or less, preferably less than 8 parts by weight, more preferably less than 5 parts by weight, even more preferably less than 3 parts by weight, and may be 1 part by weight or less, 0.5 parts by weight or less, or less than 0.3 parts by weight. By limiting the amount of additive A used relative to the colloidal silica, the processability of the colloidal silica is more easily exhibited, and the colloidal silica is less likely to aggregate, making the polishing composition more likely to have good dispersion stability.

[0045] (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.

[0046] 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. Furthermore, 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.

[0047] (Water-soluble polymer) The polishing composition disclosed herein may 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. Examples of water-soluble polymers include, but are not limited to, sulfonic acid polymers, 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 copolymers, carboxymethylcellulose and its salts, hydroxyethyl cellulose, hydroxypropyl cellulose, pullulan, chitosan and its salts, and the like. The water-soluble polymers may be used alone or in combination.

[0048] From the viewpoint of dispersion stability of the polishing composition, anionic polymers may be preferably used in some embodiments. A preferred example of anionic polymers is a sulfonic acid polymer. The proportion of sulfonic acid polymers in the water-soluble polymers contained in the polishing composition disclosed herein may be, for example, 50% by weight or more and 100% by weight or less, preferably 70% by weight or more and 100% by weight or less, more preferably 90% by weight or more and 100% by weight or less, even 95% by weight or more and 99% by weight or more and 100% by weight or less. Only one or more sulfonic acid polymers may be used as the water-soluble polymer.

[0049] Here, the sulfonic acid polymer refers to a polymer containing at least one type of repeating unit X having a sulfonic acid group as a repeating unit constituting the sulfonic acid polymer. The repeating unit X may be a repeating unit derived from a monomer having at least one sulfonic acid group per molecule. Examples of monomers having a sulfonic acid group include styrene sulfonic acid, isoprene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, isoamylene sulfonic acid, 2-(meth)acrylamido-2-methylpropane sulfonic acid, and methallyl sulfonic acid. The sulfonic acid polymer may contain two or more types of the repeating unit X. The sulfonic acid polymer may further contain a repeating unit not having a sulfonic acid group. The repeating unit not having a sulfonic acid group may be a repeating unit having an anionic functional group other than sulfonic acid, or may be a repeating unit not having an anionic functional group.

[0050] An example of a repeating unit having an anionic functional group other than sulfonic acid 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 polishing composition disclosed herein may contain, as the sulfonic acid polymer, 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 group and is not derived from a (meth)acrylic acid monomer.

[0051] Other examples of sulfonic acid polymers include polyalkylarylsulfonic acid compounds such as naphthalenesulfonic acid formaldehyde condensates, methylnaphthalenesulfonic acid formaldehyde condensates, and anthracenesulfonic acid formaldehyde condensates; melamine formalin resin sulfonic acid compounds such as melamine sulfonic acid formaldehyde condensates; ligninsulfonic acid compounds such as ligninsulfonic acid and modified ligninsulfonic acid; and aromatic aminosulfonic acid compounds such as aminoarylsulfonic acid-phenol-formaldehyde condensates.

[0052] In some embodiments, a sulfonic acid polymer that does not contain a repeating unit Y having a carboxy group can be preferably used. A polishing composition containing a sulfonic acid polymer that does not contain a repeating unit Y in combination with additive A tends to suppress the occurrence of defects (typically scratches) due to polishing. The sulfonic acid polymer that does not contain a repeating unit Y may further contain a repeating unit that does not contain a sulfonic acid group or a carboxy group (for example, a repeating unit that does not have an anionic functional group).

[0053] A preferred example of a sulfonic acid polymer is a polymer in which the ratio (molar ratio) of the number of moles of sulfonic acid group-containing repeating units X to the number of moles of all repeating units contained in the molecular structure of the polymer is 95% or more. For example, a sulfonic acid polymer substantially consisting of repeating units X can be used as the water-soluble polymer. In such a sulfonic acid polymer, 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 of the polishing composition disclosed herein, a sulfonic acid polymer in which the molar ratio of repeating units X is 100%, i.e., a sulfonic acid polymer consisting only of repeating units X having sulfonic acid groups, can be preferably used as the water-soluble polymer. Examples of such sulfonic acid polymers include homopolymers consisting of any one of the sulfonic acid group-containing monomers disclosed herein and copolymers consisting of two or more sulfonic acid 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.

[0054] The sulfonic acid polymer may be used in the form of a neutralized salt. Examples of the neutralized salt include alkali metal salts such as Na and K, ammonium salts, and alkylammonium salts. From the viewpoint of reducing defects, the sulfonic acid polymer may preferably be in the form of a salt other than Na salt (e.g., potassium salt), a form in which Na salt is cation-exchanged, or an unneutralized form.

[0055] The Mw of the water-soluble polymer (e.g., sulfonic acid 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.

[0056] The concentration [wt%] of the water-soluble polymer (preferably, a sulfonic acid 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 may be 0.05 wt% or less.

[0057] (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.

[0058] (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.

[0059] 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. 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 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, and polyoxyethylene alkyl phenyl ether sodium sulfate. 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; ligninsulfonic acid compounds such as ligninsulfonic acid and modified ligninsulfonic acid; and aromatic aminosulfonic acid compounds such as aminoarylsulfonic acid-phenol-formaldehyde condensates. As the salt, alkali metal salts such as sodium salts and potassium salts are preferred. 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 betaines and alkyl amine oxides.

[0060] In the polishing composition containing a surfactant, the surfactant content is suitably, for example, 0.0005% by weight or more. From the viewpoint of the smoothness of the polished surface, the content is preferably 0.001% by weight or more, more preferably 0.01% by weight or more. From the viewpoint of the polishing rate, the content is suitably 1% by weight or less, preferably 0.5% by weight or less, for example, 0.1% by weight or less.

[0061] 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).

[0062] 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.

[0063] (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 polishing efficiency, 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.

[0064] 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).

[0065] <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.

[0066] <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., an acid, additive A, 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.

[0067] <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.

[0068] 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).

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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).

[0075] 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.

[0076] 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).

[0077] <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.

[0078] 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.

[0079] 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.

[0080] 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]

[0081] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "%" indicating the amount used or the content is based on weight unless otherwise specified.

[0082] <Preparation of Polishing Composition> Example 1 A polishing composition containing colloidal silica (5 wt%) as abrasive grains, acid (0.15 mol / L), oxyethylene alkyl ether phosphate (0.05 wt%) containing an alkyl group having four carbon atoms and one oxyalkylene unit, hydrogen peroxide (0.4 wt%), and deionized water was prepared, with the pH adjusted to 2.0 with potassium hydroxide. The average primary particle diameter of the colloidal silica was 18 nm, and the 50% cumulative diameter (D 50 ) was 24 nm, and the average aspect ratio of the colloidal silica was 1.11.

[0083] (Examples 2 to 8, Comparative Examples 2 to 6) Instead of the oxyethylene alkyl ether phosphoric acid used in Example 1, a (poly)oxyethylene alkyl ether phosphoric acid with the carbon number of the alkyl group, the number of OE units, and the content shown in Table 1 was used, and the polishing composition according to each example was prepared in the same manner as in Example 1. Note that the polyoxyethylene alkyl ether phosphoric acid used in Comparative Example 5 has a phosphoric acid diester structure, and for this example, the carbon number of the alkyl group and the number of OE units shown in Table 1 are the total numbers within one molecule. Also, the polyoxyethylene alkyl ether phosphoric acid used in Comparative Examples 3 and 5 was added in the form of a sodium salt. The additive content in Comparative Examples 3 and 5 is the content as the Na salt.

[0084] (Comparative Example 1) A polishing composition according to this example was prepared in the same manner as in Example 1, except that oxyethylene alkyl ether phosphoric acid was not used.

[0085] (Comparative Examples 7 - 14) Instead of the oxyethylene alkyl ether phosphoric acid used in Example 1, compounds with the types and contents shown in Table 1 were used as additives, and the polishing composition according to each example was prepared in the same manner as in Example 1. Note that in Table 1, the carbon number of the alkyl group and the number of OE units in the compounds used as additives are appropriately shown.

[0086] <Polishing of Ni - P Substrate> [[ID=X]]The polishing composition according to each example was used as a polishing liquid as it was, and the polishing of the substrate to be polished was carried out under the following conditions. As the substrate to be polished, an aluminum substrate for a hard disk (Ni - P substrate) having an electroless nickel - phosphorus plating layer on its surface was pre - polished so that the surface roughness (arithmetic mean roughness (Ra)) measured by a laser scan type surface roughness meter "TMS - 3000WRC" manufactured by Schmitt Measurement System was 6 Å. The diameter of the above - mentioned object to be polished was 3.5 inches (doughnut type with an outer diameter of about 95 mm and an inner diameter of about 25 mm), and the thickness was 1.75 mm.

[0087] (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.

[0088] <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 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.

[0089] <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.

[0090] 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. A (Acceptable): Relative value of 80 or more (has practical workability) P(Poor): Relative value less than 80

[0091] <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.

[0092] 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. E (Excellent): Relative value less than 90 P(Poor): Relative value 90 or more

[0093] [Table 1]

[0094] As shown in Table 1, in polishing Ni-P substrates, Examples 1 to 8, in which a polishing composition containing colloidal silica abrasive grains, acid, and water was added with less than 0.1% of an additive, a (poly)oxyethylene alkyl ether phosphate (Additive A) having an alkyl group with 4 to 12 carbon atoms and 1 to 4 oxyethylene units, significantly reduced the polishing resistance between the substrate and the polishing pad while maintaining practical processability, compared to the polishing composition of Comparative Example 1, which did not contain the additive. On the other hand, Comparative Examples 2 to 5 and 7 to 14, in which an additive other than Additive A was used, either did not reduce the polishing resistance or had a poor effect. Furthermore, the polishing composition of Comparative Example 6, in which the content of Additive A was 0.1% or more, was unable to perform polishing due to phase separation caused by aggregation. The "-" in the "Polishing Resistance" and "Polishing Rate" columns in Table 1 indicates that polishing was not performed because polishing was not possible.

[0095] The above results show that a polishing composition containing colloidal silica as an abrasive, an acid, and water, and further containing less than 0.1 weight % of a (poly)oxyethylene alkyl ether phosphate having an alkyl group having 4 to 12 carbon atoms and 1 to 4 oxyethylene units, can reduce the polishing resistance between the substrate and the polishing pad during polishing while maintaining practical processability when polishing Ni-P substrates.

[0096] 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 method includes: abrasive grains made of colloidal silica; an acid; and water. Further containing additive A, the additive A is a (poly)oxyethylene alkyl ether phosphate containing an alkyl group having 4 to 10 carbon atoms and 1 to 4 oxyethylene units, A polishing composition, wherein the content of additive A is less than 0.1 wt %.

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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