Polishing composition, substrate manufacturing method and polishing method

Abstract

To provide a composition for polishing capable of achieving high processability while suppressing increase of fine undulation in polishing a magnetic disk substrate.SOLUTION: A composition for polishing a magnetic disk substrate is provided. The composition for polishing contains silica particles as an abrasive and water. The silica particles have an average projected area (SP50-100) of particles (particles of D50 or more) of which the volume-based diameter is in the range of cumulative 50% or more from the small-diameter side and 100% or less in SEM image analysis of 40% or more and 65% or less relative to an average area (SC50-100) of a peripheral length equivalent circle of each particle corresponding to the particles of D50 or more and an average projected area (SP0-50) of particles (particles of less than D50) of which the volume-based diameter is in the range of cumulative 0% or more from the small-diameter side and less than 50% in SEM image analysis of more than 65% and 90% or less relative to an average area (SC0-50) of a peripheral length equivalent circle of each particle corresponding to the particles of less than D50.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Conventionally, the manufacturing process of magnetic disk substrates, which require a high-precision surface, includes a step of polishing the substrate, which is the raw material of the substrate, using a polishing liquid. For example, in the manufacture of nickel-phosphorus-plated 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 magnetic disk substrates. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4255976 Summary of the Invention [Problem to be solved by the invention]

[0004] In the polishing of magnetic disk substrates, efforts to improve the quality of the substrate surface are continually underway to increase recording capacity. In recent years, silica abrasive grains have been used in place of alumina abrasive grains from the primary polishing stage in order to achieve higher quality substrate surfaces after finish polishing. Compared to polishing with alumina abrasive grains, polishing with silica abrasive grains does not involve the abrasive grains penetrating the substrate, is superior in reducing defects such as scratches, and is more likely to achieve high surface quality. On the other hand, polishing with silica abrasive grains is difficult to achieve the same processing power as slurries containing alumina abrasive grains, making it difficult to improve processing power. However, when silica abrasive grains are used to improve the processing power, as is the case when alumina abrasive grains are used, microwaviness generally worsens. High processability and low microwaviness are in a contradictory relationship, where improving one will worsen the other, so it is not easy to significantly improve processability while suppressing an increase in microwaviness.

[0005] The present invention has been made in view of the above circumstances, and aims to provide a polishing composition that can suppress an increase in microwaviness and exhibit high processability when polishing a magnetic disk substrate. Another related object is to provide a method for manufacturing a substrate and a method for polishing a substrate using the polishing composition. [Means for solving the problem]

[0006] The polishing composition for magnetic disk substrates provided herein contains silica particles as abrasive grains and water. The silica particles are particles whose volume-based particle diameters, as determined by SEM image analysis, are in the range of 50% to 100% cumulatively from the smallest diameter side (D 50 average projected area (SP) of particles 50-100 ) but the above D 50 The average area of ​​the circle equivalent to the perimeter of each particle (SC 50-100 The silica particles are particles (D) whose volume-based particle diameters determined by SEM image analysis are in the range of 0% to less than 50% cumulatively from the smallest diameter side. 50 Average projected area (SP) of particles 0-50 ) but the above D 50 The average area of ​​the circle equivalent to the circumference of each particle that falls under the particle size (SC 0-50 ) is greater than 65% and less than or equal to 90%.

[0007] The polishing composition contains silica particles containing D 50 The average area of ​​the particle equivalent to the circumference (SC 50-100 ) to the average projected area (SP 50-100 ) ratio ((SP / SC) 50-100 ) and D 50 The average area of ​​the circle equivalent to the circumference of particles less than 0-50 ) to the average projected area (SP0-50 ) ratio ((SP / SC) 0-50 ) are within the specified ranges. Here, the ratio of the average projected area to the average area of ​​the circle equivalent to the circumference (SP / SC ratio) represents the irregularity of the particles, and a smaller SP / SC ratio means a higher irregularity. 50 SP / SC ratio and D 50 The polishing composition contains silica particles as abrasive grains, each of which has an SP / SC ratio within an appropriate range, and can achieve high processability while suppressing the increase in microwaviness when polishing a magnetic disk substrate. "Exhibiting high processability while suppressing the increase in microwaviness" means that the ratio of the polishing rate (processability) to the microwaviness (hereinafter also referred to as "rate / waviness ratio") is improved, and means, for example, that the degree of increase in microwaviness is low relative to the degree of improvement in the polishing rate.

[0008] In some preferred embodiments, the silica particles are 50 The average aspect ratio of the particles (A 50-100 ) is between 1.25 and 1.70. 50-100 When is in the above range, a high rate / waviness ratio is likely to be obtained.

[0009] In some preferred embodiments, the silica particles are 50 SP / SC ratio of particles less than 10 ... 0-50 ) but D 50 SP / SC ratio of the particles (SP / SC) 50-100 The polishing composition, the method for manufacturing a substrate, and the method for polishing a substrate (hereinafter the same) disclosed herein can be suitably carried out using such silica particles.

[0010] In some preferred embodiments, the silica particles have a volume-based cumulative 50% particle diameter (D 50 The polishing composition disclosed herein has a large particle size (D 50The abrasive grains contain silica particles with an SP / SC ratio in an appropriate range. 50 Even if the D of silica particles is relatively small, high processability can be achieved. 50 A relatively small value is also preferable from the viewpoint of suppressing an increase in microwaviness that accompanies improved processability.

[0011] In some preferred embodiments, the polishing composition further comprises an acid and an oxidizing agent. By including the silica particles, the acid, and the oxidizing agent in combination, it becomes easier to achieve a practical polishing rate in polishing a magnetic disk substrate.

[0012] According to the present specification, a method for manufacturing a magnetic disk substrate is provided. The manufacturing method includes step (1) of polishing a substrate to be polished with any of the polishing compositions disclosed herein. This manufacturing method allows for the efficient production of magnetic disk substrates having high-quality surfaces. In some embodiments, the substrate manufacturing method further includes step (2) of polishing the substrate to be polished with a final polishing composition after step (1). The final polishing composition preferably contains colloidal silica. By performing step (2) after step (1), magnetic disk substrates having higher-quality surfaces can be efficiently manufactured.

[0013] The present specification also provides a method for polishing a substrate. The polishing method includes step (1) of supplying any of the polishing compositions disclosed herein to a substrate to be polished and polishing the substrate. Such a polishing method can efficiently improve the surface quality of the polished object. In some embodiments, the method for polishing a substrate further includes step (2) of supplying a finish polishing composition to the substrate to be polished after step (1) and polishing the substrate to be polished. The finish polishing composition preferably contains colloidal silica. By performing step (2) after step (1), a higher-quality substrate surface can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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.

[0015] <Polishing composition> (silica particles) The polishing composition disclosed herein contains silica particles as abrasive grains. The silica particles may be in the form of secondary particles formed by aggregation of a plurality of primary particles, or may be in the form of secondary particles formed by association of a plurality of primary particles. Furthermore, silica particles in the form of primary particles and silica particles in the form of secondary particles may be mixed.

[0016] The silica particles are D 50 The ratio of the average projected area to the average circular area equivalent to the perimeter of the particle ((SP / SC) 50-100 ) is between 40% and 65%. 50 The above particles refer to particles having a particle diameter that falls within the range of 50 to 100% cumulative from the small diameter side in the volume-based cumulative particle size distribution obtained by SEM image analysis. The cumulative volume distribution is represented, for example, by a curve in a graph with particle diameter on the horizontal axis and cumulative volume (%) on the vertical axis, extending from the end (lower left) at 0% cumulative and the small diameter side of the particle diameter to the upper right, and reaching the end (upper right) at 100% cumulative and the large diameter side of the particle diameter. 50 These particles are particles that belong to the larger diameter side and account for 50% or more of all silica particles by volume. (SP / SC) 50-100 By having a particle size of 40% or more, the particle breakage is suppressed against both the polishing load and shear stress, and (SP / SC) 50-100 By having a certain degree of irregularity of 65% or less, D 50 The particles can be efficiently acted upon. On the other hand, (SP / SC) 50-100If the ratio exceeds 65%, the particles are less likely to break down, but the low irregularity makes the particles more likely to roll, and the horizontal processing force relative to the polished surface is relatively insufficient compared to the vertical processing force, which makes it more likely to cause a decrease in the rate / waviness ratio. 50-100 If the ratio is less than 40%, for example, about 30 to 36%, the particles are less likely to break down due to the polishing load, but they are more likely to break down due to shear stress. As a result, the horizontal processing force relative to the polished surface is insufficient compared to the vertical processing force, which makes it more likely that the rate / waviness ratio will decrease. (SP / SC) 50-100 If the difference is even smaller, for example, about 15 to 20%, the particles tend to break down easily due to the polishing load, and the polishing rate tends to decrease.

[0017] The silica particles are D 50 The ratio of the average projected area to the average circular area equivalent to the perimeter of particles less than 1 / 2 (SP / SC) 0-50 ) is preferably greater than 65% and less than 90%. 50 "Particles under 10 ... 50 Particles smaller than 50% of all silica particles by volume are particles that belong to the small diameter side (SP / SC). 0-50 Since the ratio is less than 90%, the above D 50 It is believed that the small particles contribute effectively to suppress the deterioration of micro-waviness due to the accumulation of the above-mentioned processing marks. 0-50 is greater than 65%. 50 It is believed that this is useful for suppressing the occurrence and accumulation of processing marks caused by small particles. Note that the above mechanism is the inventor's speculation based on experimental results, and the technology disclosed herein should not be interpreted as being limited to the above mechanism.

[0018] In some embodiments, the (SP / SC) of silica particles 50-100is suitably 41% or more, and from the viewpoint of obtaining a higher rate / waviness ratio, is preferably 43% or more (for example, 45% or more), may be 48% or more, or may be 50% or more. 50-100 The ratio may be, for example, 63% or less, and is advantageously 62% or less or 60% or less from the viewpoint of improving the polishing rate, and is preferably 55% or less (for example, 53% or less) from the viewpoint of easily obtaining a higher rate / waviness ratio. 50-100 It can be preferably implemented in an embodiment where, for example, is 43% or more and 55% or less.

[0019] In some embodiments, the (SP / SC) of silica particles 0-50 is suitably 68% or more, and from the viewpoint of obtaining a higher rate / waviness ratio, it is preferably 70% or more. 0-50 is suitably 88% or less, preferably 85% or less, may be 80% or less, or may be 75% or less. 0-50 is preferably 68% or more and 90% or less, 68% or more and 85% or less, 70% or more and 90% or less, or 70% or more and 85% or less, for example.

[0020] In some embodiments, the (SP / SC) of silica particles 0-50 is the (SP / SC) of the silica particles 50-100 It is preferable that the ratio is 1.20 to 2.50 times (SP / SC). 0-50 / (SP / SC) 50-100 is 1.20 or more, D 50 Less than a particle D 50 These particles can be understood to have a degree of irregularity, calculated as the ratio of the average projected area to the average area of ​​a circle equivalent to the circumference (SP / SC ratio), of 1.20 times or more. (SP / SC) 50-100 is within the above range, and (SP / SC) 0-50 / (SP / SC) 50-100With silica abrasive grains with a D in the range of 1.20 to 2.50, 50 The above particle action and D 50 The effect of the fine particles and the fine particles is well balanced, and the effect of suppressing the increase in microwaviness while exhibiting high processability can be suitably realized. 0-50 / (SP / SC) 50-100 may be 1.25 or more, 1.30 or more, 1.35 or more, or 1.45 or more. In some embodiments, (SP / SC) 0-50 / (SP / SC) 50-100 may be 2.20 or less, 2.00 or less, or 1.90 or less. 0-50 (SP / SC) 50-100 It is preferably 10% or more (for example, 10 to 45%) larger than the above, and more preferably 15% or more (for example, 15 to 40%) larger than the above.

[0021] Silica particles D 50 The average aspect ratio of the particles (A 50-100 ) is not particularly limited and may be, for example, 1.20 or more and 2.00 or less. From the viewpoint of easily obtaining high processability while suppressing an increase in microwaviness, in some embodiments, A 50-100 is preferably 1.25 or more, more preferably 1.30 or more, may be 1.35 or more, or may be 1.36 or more. 50-100 is suitably 1.80 or less, preferably 1.70 or less, may be 1.60 or less, may be 1.50 or less, may be 1.45 or less, or may be 1.42 or less. 50-100 In the silica particles having the (SP / SC) 50-100 and (SP / SC) 0-50 The effect of setting the value of the temperature to a predetermined range can be preferably exhibited.

[0022] The average aspect ratio of the entire silica particle (A all) is not particularly limited, but is typically greater than 1.00, and may be, for example, 1.01 or greater. In some embodiments, the average aspect ratio (A all ) may be, for example, 1.05 or more, and from the viewpoint of maintaining or improving processability, it is preferably 1.10 or more, more preferably 1.11 or more, and may be more than 1.15 or may be more than 1.20. In some embodiments, the average aspect ratio (A all From the viewpoint of particle strength, the average aspect ratio (A) is suitably 2.00 or less or less than 2.00, preferably 1.70 or less, more preferably 1.50 or less, 1.40 or less, or 1.30 or less. all From the viewpoint of suppressing the development of microwaviness, A is preferably less than 1.30, more preferably less than 1.25, and may be less than 1.20 or less than 1.18 (for example, 1.15 or less). all and A 50-100 The relationship between A and A is not particularly limited. all A than 50-100が It is appropriate that it is 0.10 or more (for example, about 0.10 to 0.50) larger, and it is preferable that it is 0.15 or more (for example, about 0.15 to 0.30) larger.

[0023] Silica particle D 50 That is, the cumulative 50% particle size on a volume basis as determined by SEM image analysis may be, for example, 500 nm or less, preferably 400 nm or less, more preferably 350 nm or less, or may be 325 nm or less, 300 nm or less, 280 nm or less, 250 nm or less, 220 nm or less, 200 nm or less, or 180 nm or less. According to the technology disclosed herein, it is possible to obtain such a relatively D 50 Even when using silica particles with small D, high processability can be achieved and the increase in micro-waviness can be suppressed. 50For example, the thickness may be 30 nm or more, and from the viewpoint of improving processability, it is preferably 40 nm or more, may be 55 nm or more, may be 65 nm or more, may be 75 nm or more, may be 80 nm or more, may be 90 nm or more, or may be 100 nm or more.

[0024] Silica particle D 50 , average aspect ratio (A all ), D 50 The average aspect ratio of the particles (A 50-100 ), D 50 The average projected area (SP 50-100 ), D 50 The average area of ​​the particle equivalent to the circumference (SC 50-100 ), D 50 Less than the average projected area of ​​particles (SP 0-50 ) and D 50 The average area of ​​the circle equivalent to the circumference of particles less than 0-50 ) is determined by the following method. That is, using a scanning electron microscope (SEM), 1,000 or more particles contained in the silica particles to be measured (which may be one type of silica particles or a mixture of two or more types of silica particles) are observed in an SEM image containing 50 or more particles within one field of view. The observation magnification is 20,000 to 50,000 times. Then, for the smallest rectangle circumscribing each particle image, the length of its long side (long diameter value) is divided by the length of its short side (short diameter value) to calculate the long diameter / short diameter ratio (aspect ratio) of each particle. In addition, the radius r of an ideal circle (perfect circle) having an area equal to the projected area of ​​each particle image is subtracted by 4πr 3 The value obtained by / 3 is calculated as the volume of each particle. In addition, the outer perimeter (circumference) of each particle is measured from the projected image of the particle image, and the area of ​​a circle (circumference-equivalent circle) having the same circumference as the outer perimeter is calculated. Here, the above aspect ratio, projected area, volume, circumference, and area of ​​the circumference-equivalent circle are measured or calculated by counting each particle independently dispersed in the polishing composition as one particle, regardless of whether it is a primary particle or a secondary particle. D 50The particle diameter is determined by obtaining a volume-based particle size distribution from the volume of the predetermined number of particles, and by taking the particle diameter at the point where the cumulative distribution from the small diameter side reaches 50%. 50 The average aspect ratio (A) is calculated by obtaining a volume-based particle size distribution from the volume of the above-mentioned predetermined number of particles, and is calculated as the particle diameter at which the cumulative total from the small diameter side reaches 50%. all ) is the average aspect ratio based on the number of all silica particles (number-average aspect ratio), and can be determined by arithmetically averaging the aspect ratios of all the particles of the specified number. 50 The average aspect ratio of the particles (A 50-100 ) is D in the above volume-based particle size distribution 50 Particles with a particle size of 0.1 or more (D 50 The aspect ratio of these particles can be calculated by arithmetically averaging the particle size. 50 The average projected area (SP 50-100 ) and the average area of ​​the circle equivalent to the circumference (SC 50-100 ) is the number of particles D 50 The projected area of ​​the particles and the area of ​​the circle equivalent to the perimeter of the particles can be calculated by arithmetically averaging the SP 50-100 SC 50-100 By dividing by (SP / SC) 50-100 D 50 Less than the average projected area of ​​particles (SP 0-50 ), average area of ​​circle equivalent to circumference (SC 0-50 ) and (SP / SC) 0-50 is the number of particles D 50 Other than particles that fall under the category of particles under 10 ... 50-100 , SC 50-100 and (SP / SC) 50-100 can be found in the same way. Above D 50 , A all , A 50-100 , SP 50-100 , SC 50-100 , SP 0-50 and SC 0-50can be determined using a general SEM and image analysis software. For example, a scanning electron microscope "SU8000" manufactured by Hitachi High-Technologies Corporation or image analysis particle size distribution measurement software "Mac-View" manufactured by Mountec Co., Ltd. can be used. The same applies to the examples described below.

[0025] Above (SP / SC) 50-100 , (SP / SC) 0-50 , A 50-100 , A all , D 50 This can be adjusted by selecting the type of silica particles used, selecting and adjusting the silica production method, or mixing two or more types of silica particles with different particle shapes. For example, the silica particles disclosed herein can be obtained by selecting one type of particle group having a specific particle size and aspect ratio, or by selecting two or more types of particle groups and mixing them in an appropriate ratio, based on the description of this specification and taking into account common general knowledge. Furthermore, based on the description of this specification and taking into account common general knowledge, it is also possible to adopt a method of obtaining irregular-shaped particles by crushing porous silica gel under appropriate conditions, or a method of growing the obtained irregular-shaped particles by adding a predetermined amount of silicate under appropriate conditions (e.g., pH, temperature, etc.) to obtain irregular-shaped particles with a desired particle size. The silica particles disclosed herein can be obtained by using one type of particle obtained alone or by mixing it with other silica particles having different particle properties.

[0026] Also, D 50 The ratio of the average projected area to the average circular area equivalent to the particle's perimeter, i.e. (SP / SC) 50-100 is D 50 The above can be adjusted by the average number of primary particles contained in one particle (hereinafter also referred to as "average bond number"), the degree of overlap of primary particles in secondary particles containing two or more primary particles in an aggregated or associated form, etc. More specifically, when comparing particles of the same diameter, the surface roughness of secondary particles tends to increase as the average bond number increases (SP / SC). 50-100tends to become smaller, and when the degree of overlap between the primary particles in a secondary particle formed by combining two or more primary particles increases, (SP / SC) 50-100 tends to be large. (SP / SC) 0-50 The average bond number and the degree of overlap of primary particles can be adjusted by selecting the type of silica particles to be used, selecting or adjusting the silica production method, mixing two or more types of silica particles having different particle shapes, etc.

[0027] As silica particles, the specified (SP / SC) 50-100 and (SP / SC) 0-50 As long as the above conditions are satisfied, various silica particles containing silica as the main component can be used. Here, silica particles containing silica as the main component refer to particles in which 90% by weight or more, for example 95% by weight or more, typically 98% by weight or more, of the particles is silica. Examples of silica particles that can be used include, but are not limited to, colloidal silica, agglomerated silica, precipitated silica (also referred to as precipitated silica), sodium silicate silica, alkoxide silica, fumed silica, dried silica, and detonation silica. Furthermore, silica particles obtained using the above silica particles as raw materials can also be used. Examples of such silica particles include silica particles obtained by subjecting the above raw material silica particles (hereinafter also referred to as "raw silica") to one or more treatments selected from heat treatments such as heating, drying, and calcination, pressure treatments such as autoclaving, mechanical treatments such as crushing and grinding, and surface modification. Examples of surface modification include chemical modifications such as the introduction of functional groups and metal modification. The silica particles in the technology disclosed herein may contain one type of silica particles as described above, or two or more types in combination.

[0028] The content of silica particles in the polishing composition is not particularly limited, and may be, for example, 0.1 wt% or more, preferably 0.5 wt% or more, more preferably 1 wt% or more, even more preferably 3 wt% or more, and particularly preferably 5 wt% or more. When multiple types of silica particles are contained, the content is the total content of these. An increase in the content of silica particles tends to result in higher processability. From the viewpoint of the surface smoothness of the substrate after polishing and the stability of polishing, the content is suitably 30 wt% or less, preferably 25 wt% or less, more preferably 15 wt% or less, and even more preferably 10 wt% or less.

[0029] In the polishing composition disclosed herein, the content of silica particles in the solid content contained in the polishing composition is preferably 90% by weight or more of the total solid content, more preferably 95% by weight or more, and even more preferably 98% by weight or more, for example, 99% by weight or more, from the viewpoint of better demonstrating the effects of the technology disclosed herein. Note that, in this specification, the solid content contained in the polishing composition refers to the residue, i.e., non-volatile content, after evaporating water from the polishing composition at a temperature at which bound water is not removed, for example, 60°C.

[0030] 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, dents, residual alumina, and penetration defects. As used herein, "substantially free of alumina particles" means that the proportion of alumina particles in the total solid content of the polishing composition is 1% by weight or less, more preferably 0.5% by weight or less, and typically 0.1% by weight or less. A polishing composition with a 0% by weight proportion 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.

[0031] The polishing composition disclosed herein can be preferably implemented in an embodiment that does not substantially contain particles other than silica particles, i.e., non-silica particles. Here, "does not substantially contain non-silica particles" means that the proportion of non-silica particles in the total solid content of the polishing composition is 1 wt% or less, more preferably 0.5 wt% or less, typically 0.1 wt% or less. In such an embodiment, the application effect of the technology disclosed herein can be suitably exhibited.

[0032] (acid) The polishing composition disclosed herein preferably contains an acid as a polishing accelerator. The acid may be either an inorganic acid or an organic acid. Examples of organic acids include organic carboxylic acids, organic sulfonic acids, and amino acids each having about 1 to 18 carbon atoms, typically about 1 to 10 carbon atoms. The acids may be used alone or in combination of two or more.

[0033] 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.

[0034] Specific examples of organic acids include citric acid, maleic acid, malic acid, glycolic acid, succinic acid, itaconic acid, malonic acid, iminodiacetic acid, gluconic acid, lactic acid, mandelic acid, tartaric acid, formic acid, acetic acid, propionic acid, butyric acid, adipic acid, oxalic acid, valeric acid, enanthic acid, caproic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, cyclohexanecarboxylic acid, phenylacetic acid, benzoic acid, crotonic acid, oleic acid, linoleic acid, linolenic acid, ricinoleic acid, and methacrylic acid. , glutaric acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, tartronic acid, glyceric acid, hydroxybutyric acid, hydroxyacetic acid, hydroxybenzoic acid, salicylic acid, isocitric acid, methylenesuccinic acid, gallic acid, ascorbic acid, nitroacetic acid, oxaloacetic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, and other organic carboxylic acids; glycine, alanine, glutamic acid, aspartic acid, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, phenylalanine, tryptophan, tyrosine, proline, Amino acids such as lysine, cystine, glutamine, asparagine, lysine, and arginine; nicotinic acid; picric acid; picolinic acid; phytic acid; 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethanehydroxy-1,1,2-triphosphonic acid, ethane-1 , 2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, α-methylphosphonosuccinic acid, aminopoly(methylenephosphonic acid), etc.; organic sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, aminoethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, 2-naphthalenesulfonic acid, sulfosuccinic acid, 10-camphorsulfonic acid, isethionic acid, taurine, etc.

[0035] Examples of preferred acids from the viewpoint of polishing efficiency include phosphoric acid, phosphonic acid, maleic acid, hydrochloric acid, nitric acid, sulfuric acid, sulfamic acid, phytic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, methanesulfonic acid, etc. Among these, phosphoric acid, phosphonic acid, maleic acid, hydrochloric acid, nitric acid, and sulfuric acid are preferred.

[0036] The acid may be used in the form of a salt thereof. Examples of the salt include metal salts, ammonium salts, alkanolamine salts, etc. of the inorganic acids and organic acids described above. Examples of the metal salts include alkali metal salts such as lithium salts, sodium salts, and potassium salts. Examples of the ammonium salts include quaternary ammonium salts such as tetramethylammonium salts and tetraethylammonium salts. Examples of the alkanolamine salts include monoethanolamine salts, diethanolamine salts, and triethanolamine salts. Specific examples of salts include alkali metal phosphates and alkali metal hydrogen phosphates such as tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate; alkali metal salts of the organic acids exemplified above; and alkali metal salts of glutamic acid diacetic acid, alkali metal salts of diethylenetriaminepentaacetic acid, alkali metal salts of hydroxyethylethylenediaminetriacetic acid, and alkali metal salts of triethylenetetraminehexaacetic acid. The alkali metal in these alkali metal salts may be, for example, lithium, sodium, or potassium.

[0037] The polishing composition disclosed herein may preferably contain an inorganic acid salt, such as an alkali metal salt or an ammonium salt, such as potassium chloride, sodium chloride, ammonium chloride, potassium nitrate, sodium nitrate, ammonium nitrate, or potassium phosphate.

[0038] 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. The acid is preferably an inorganic acid. The acid salt is preferably an inorganic acid salt.

[0039] 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, for example, 0.001 mol / L or more, preferably 0.01 mol / L or more, more preferably 0.05 mol / L or more, even more preferably 0.07 mol / L or more, and particularly preferably 0.09 mol / L or more. By increasing the molar concentration of the acid, higher processability can be achieved. From the viewpoint of surface quality after polishing and polishing stability, the molar concentration of the acid is suitably 1.2 mol / L or less, preferably 1 mol / L or less, more preferably 0.8 mol / L or less, even more preferably 0.5 mol / L or less, and particularly preferably 0.3 mol / L or less (for example, 0.2 mol / L or less).

[0040] (oxidizing agent) The polishing composition disclosed herein preferably contains an oxidizing agent. 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. The oxidizing agent preferably contains at least hydrogen peroxide, and more preferably consists of hydrogen peroxide.

[0041] The content of the oxidizing agent in the polishing composition is preferably 0.05 mol / L or more, more preferably 0.1 mol / L or more, even more preferably 0.15 mol / L or more, particularly preferably 0.3 mol / L or more, in consideration of the speed of oxidizing the object to be polished and therefore the processability. Also, the content of the oxidizing agent in the polishing composition is preferably 1 mol / L or less, more preferably 0.8 mol / L or less, even more preferably 0.6 mol / L or less, in consideration of maintaining surface precision.

[0042] (water) The polishing composition disclosed herein typically contains, in addition to the abrasive grains described above, water in which the abrasive grains are dispersed. As the water, ion-exchanged water, pure water, ultrapure water, distilled water, etc. can be preferably used. The ion-exchanged water can typically be deionized water.

[0043] The polishing composition disclosed herein can be preferably implemented, for example, in a form in which the solid content is 0.5 wt % to 30.0 wt %. The solid content is more preferably 1.0 wt % to 20.0 wt %. The polishing composition can typically be a slurry composition.

[0044] (Other ingredients) The polishing composition disclosed herein may further contain, as needed, known additives that can be used in polishing compositions, such as surfactants, water-soluble polymers, dispersants, chelating agents, preservatives, antifungal agents, and basic compounds, to the extent that the effects of the present invention are not significantly impaired.

[0045] The surfactant is not particularly limited, and any of anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants can be used. The use of a surfactant can improve the dispersion stability of the polishing composition. The surfactant can be used alone or in combination of two or more. The surfactant typically has a molecular weight of 1×10 6 The water-soluble organic compound may be less than 1000 ppm. Specific examples of anionic surfactants include polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl sulfates, alkyl sulfates, polyoxyethylene alkyl sulfates, alkyl sulfates, alkyl benzene sulfonates, alkyl phosphates, polyoxyethylene alkyl phosphates, polyoxyethylene sulfosuccinates, alkyl sulfosuccinates, alkyl naphthalene sulfonates, alkyl diphenyl ether disulfonic acids, polyacrylic acids, sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzene sulfonate, polyoxyethylene alkyl ether sodium sulfate, polyoxyethylene alkyl phenyl ether ammonium sulfate, polyoxyethylene alkyl phenyl ether sodium sulfate, and salts thereof. Other specific examples of anionic surfactants include polyalkylarylsulfonic acid compounds such as naphthalenesulfonic acid-formaldehyde condensates, methylnaphthalenesulfonic acid-formaldehyde condensates, anthracenesulfonic acid-formaldehyde condensates, and benzenesulfonic acid-formaldehyde condensates; melamine-formaldehyde resin sulfonic acid compounds such as melamine sulfonic acid-formaldehyde condensates; ligninsulfonic acid compounds such as ligninsulfonic acid and modified ligninsulfonic acid; aromatic aminosulfonic acid compounds such as aminoarylsulfonic acid-phenol-formaldehyde condensates; polyisoprene sulfonic acid, polyvinylsulfonic acid, polyallylsulfonic acid, polyisoamylenesulfonic acid, polystyrenesulfonic acid; and salts thereof. Alkali metal salts such as sodium salts and potassium salts are preferred as salts. Specific examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, and alkylalkanolamides. Specific examples of cationic surfactants include alkyltrimethylammonium salts, alkyldimethylammonium salts, alkylbenzyldimethylammonium salts, and alkylamine salts. Specific examples of amphoteric surfactants include alkyl betaine type, fatty acid amidopropyl betaine type, alkyl imidazole type, amino acid type, and alkyl amine oxide type.

[0046] In a polishing composition containing a 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 0.002% by weight or more. From the viewpoint of processability, the content is suitably 3.0% by weight or less, preferably 0.5% by weight or less, for example, 0.1% by weight or less. From the viewpoint of processability, the technology disclosed herein can be preferably implemented in an embodiment in which the polishing composition does not substantially contain a surfactant.

[0047] The polishing composition disclosed herein may contain a water-soluble polymer. By including a water-soluble polymer, the surface quality after polishing can be improved. Examples of water-soluble polymers include polyalkylarylsulfonic acid compounds such as naphthalenesulfonic acid formaldehyde condensates, methylnaphthalenesulfonic acid formaldehyde condensates, and anthracenesulfonic acid formaldehyde; melamine formalin resin sulfonic acid compounds such as melamine sulfonic acid formaldehyde condensates; ligninsulfonic acid compounds such as ligninsulfonic acid and modified ligninsulfonic acid; aromatic aminosulfonic acid compounds such as aminoarylsulfonic acid-phenol-formaldehyde condensates; and others, such as polyisoprene sulfonic acid, polyvinyl sulfonic acid, and polyallyl sulfonic acid. Examples of water-soluble polymers include sulfonic acid, polyisoamylene sulfonic acid, polystyrene sulfonate, polyacrylate, polyvinyl acetate, polymaleic acid, polyitaconic acid, polyvinyl alcohol, polyglycerin, polyvinylpyrrolidone, copolymers of isoprene sulfonic acid and acrylic acid, polyvinylpyrrolidone-polyacrylic acid copolymers, polyvinylpyrrolidone-vinyl acetate copolymers, diallylamine hydrochloride-sulfur dioxide copolymers, carboxymethyl cellulose, salts of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, pullulan, chitosan, chitosan salts, etc. The water-soluble polymers can be used alone or in combination of two or more.

[0048] In an embodiment of the polishing composition containing a water-soluble polymer, the content of the water-soluble polymer in the polishing composition is suitably, for example, 0.001 wt% or more. In an embodiment containing a plurality of water-soluble polymers, the content is the total content thereof. From the viewpoint of the surface smoothness of the polished object after polishing, the content is preferably 0.003 wt% or more, more preferably 0.005 wt% or more, and even more preferably 0.007 wt% or more. Furthermore, from the viewpoint of processability, the content is suitably 1.0 wt% or less, preferably 0.5 wt% or less, for example, 0.1 wt% or less. Note that, from the viewpoint of processability, the technology disclosed herein can be preferably implemented in an embodiment in which the polishing composition does not substantially contain a water-soluble polymer.

[0049] Examples of dispersants include polycarboxylic acid-based dispersants such as sodium polycarboxylic acid salts and ammonium polycarboxylic acid salts; naphthalenesulfonic acid-based dispersants such as sodium naphthalenesulfonate and ammonium naphthalenesulfonate; alkylsulfonic acid-based dispersants; polyphosphate-based dispersants; polyalkylenepolyamine-based dispersants; quaternary ammonium-based dispersants; alkylpolyamine-based dispersants; alkylene oxide-based dispersants; polyhydric alcohol ester-based dispersants; etc. The dispersants can be used alone or in combination of two or more.

[0050] 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). The chelating agents can be used alone or in combination of two or more.

[0051] 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.

[0052] The polishing composition can contain a basic compound as needed. 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, carbonates, hydrogencarbonates, quaternary ammonium or salts thereof, ammonia, amines, phosphates, hydrogenphosphates, organic acid salts, etc. The basic compounds can be used alone or in combination of two or more.

[0053] (pH) The pH of the polishing composition disclosed herein is not particularly limited. The pH of the polishing composition can be, for example, 12.0 or less, typically 0.5 to 12.0, or 10.0 or less, typically 0.5 to 10.0. From the viewpoint of processability, surface quality, etc., the pH of the polishing composition can be 7.0 or less, for example 0.5 to 7.0, more preferably 5.0 or less, typically 1.0 to 5.0, and even more preferably 4.0 or less, for example 1.0 to 4.0. The pH of the polishing composition can be, for example, 3.0 or less, typically 1.0 to 3.0, preferably 1.0 to 2.0, and more preferably 1.0 to 1.8. To achieve the above pH in the polishing liquid, a pH adjuster such as an organic acid, an inorganic acid, or a basic compound can be added as needed. The above pH is preferably applicable to polishing compositions for magnetic disk substrates such as nickel-phosphorus substrates. It is particularly preferably applicable to polishing compositions for primary polishing.

[0054] (polishing liquid) The polishing composition disclosed herein is typically supplied to a polishing object in the form of a polishing liquid containing the polishing composition and used to polish the object. The polishing liquid can be prepared, for example, by diluting the polishing composition. Here, dilution typically refers to dilution with water. Alternatively, the polishing composition can be used as a polishing liquid as is. That is, the concept of a polishing composition in the technology disclosed herein encompasses both a polishing liquid (working slurry) that is supplied to a polishing object and used to polish the object, and a concentrated liquid that is diluted and used as a polishing liquid. Polishing compositions in the form of such concentrated liquids are advantageous from the standpoints of convenience and cost reduction during production, distribution, storage, etc. The concentration ratio can be, for example, about 1.5 to 50 times. From the standpoint of storage stability of the concentrated liquid, a concentration ratio of, for example, 2 to 20 times, typically about 2 to 10 times, is appropriate.

[0055] (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 of the polishing composition (typically, 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 are composed of Part A, which contains abrasive grains, and Part B, which contains components other than the abrasive grains. Part A, which contains abrasive grains, may further contain a dispersant. Examples of components other than the abrasive grains contained in Part B include acids. Part B may also contain water-soluble polymers and other additives. An oxidizing agent, such as hydrogen peroxide, may be further mixed during mixing. For example, when the oxidizing agent is supplied in the form of an aqueous solution, the aqueous solution can serve as Part C, which constitutes the multi-component polishing composition.

[0056] <Application> The polishing composition disclosed herein can be preferably used for polishing magnetic disk substrates such as nickel-phosphorus substrates, glass substrates, and carbon substrates. Furthermore, the plating material may be a disk substrate having a metal layer or metal compound layer other than a nickel-phosphorus plating layer on the surface of a substrate disk. In particular, the polishing composition is suitable as a polishing composition for nickel-phosphorus plated substrates having a nickel-phosphorus plating layer on an aluminum alloy substrate disk. For such applications, the application of the technology disclosed herein is particularly meaningful.

[0057] The polishing composition disclosed herein can be particularly useful in applications requiring high polishing efficiency, such as the preliminary polishing step in the manufacturing process of magnetic disk substrates, which requires a highly accurate surface after the final polishing step. When multiple preliminary polishing steps are performed before the final polishing step, the polishing composition can be used in any of the preliminary polishing steps, and the same or different polishing compositions can be used in these preliminary polishing steps. The polishing composition disclosed herein is suitable, for example, as a polishing composition used in the primary polishing step, i.e., the first polishing step, of magnetic disk substrates. In particular, it can be preferably used in the first polishing step, i.e., the first polishing step, after nickel phosphorus plating in the manufacturing process of nickel phosphorus substrates.

[0058] The polishing composition disclosed herein is suitable for polishing a magnetic disk substrate having a surface roughness of about 20 Å to 300 Å as measured by a laser scanning surface roughness meter "TMS-3000WRC" manufactured by Schmitt Measurement System Inc., for example, to adjust the surface roughness of the magnetic disk substrate to 10 Å or less. For such applications, it is particularly useful to apply the technology disclosed herein. Here, "surface roughness" refers to the arithmetic mean roughness (Ra).

[0059] <Polishing method> The polishing composition disclosed herein can be suitably used for polishing a magnetic disk substrate, for example, in an embodiment including the following steps. A preferred embodiment of a method for polishing an object to be polished using the polishing composition disclosed herein is described below. Hereinafter, the object to be polished is also referred to as a substrate to be polished. That is, a polishing liquid (working slurry) containing any of the polishing compositions disclosed herein is prepared. The preparation of the polishing liquid may include adjusting the concentration or pH of the polishing composition to prepare the polishing liquid. The concentration adjustment may be, for example, dilution. Alternatively, the polishing composition may be used as the polishing liquid as it is.

[0060] The polishing liquid is then supplied to the object to be polished, and polished in a conventional manner. For example, the object to be polished is placed in a conventional polishing device, and the polishing liquid is supplied to the surface of the object to be polished, i.e., the surface to be polished, through the polishing pad of the polishing device. Typically, while the polishing liquid is continuously supplied, the polishing pad is pressed against the surface of the object to be polished, and the two are moved relative to each other. The movement can be, for example, a rotational movement. Through this polishing process, polishing of the object to be polished is completed.

[0061] 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. The suede type may be a buff pad, and typically may be a polishing pad in a non-buffed state (so-called non-buff pad) whose surface has not been buffed. Such suede type polishing pads (typically polyurethane polishing pads) are easy to process and easily achieve high-quality substrate surfaces. Note that the polishing pad used in the technology disclosed herein does not contain abrasive grains.

[0062] After polishing (specifically, after the primary polishing of the magnetic disk substrate), it is preferable to wash the substrate (washing step). The washing step is typically carried out using a washer. In the washing step, a washing liquid may be used, or washing may be carried out using only running water without using a washing liquid. Ultrasonic treatment may be carried out by applying ultrasonic waves to the substrate immersed in the washing liquid or water. By carrying out such a washing step, abrasive grains remaining on the substrate after polishing can be efficiently removed.

[0063] The polishing machine used in the polishing step may be a double-sided polishing machine that polishes both sides of the object to be polished simultaneously, or a single-sided polishing machine that polishes only one side of the object to be polished. When the polishing step is a preliminary polishing step, in some embodiments, a double-sided polishing machine can be preferably used as the polishing machine that performs the polishing step. When a finish polishing step is performed after the primary polishing step, a single-sided polishing machine can be preferably used as the polishing machine that performs the finish polishing step.

[0064] The polishing step as described above can be part of a manufacturing process for a magnetic disk substrate, such as a nickel phosphorus substrate. Therefore, this specification provides a method for manufacturing and polishing a magnetic disk substrate, which includes the polishing step.

[0065] The polishing composition disclosed herein can be preferably used in a preliminary polishing step, such as a primary polishing step, of an object to be polished. This specification provides a method for manufacturing and polishing a magnetic disk substrate, which includes a preliminary polishing step using any of the polishing compositions described above. The method includes step (1) of supplying the object to be polished with the polishing composition disclosed herein to polish the object. The method may include a final polishing step after the preliminary polishing step. The polishing composition used in the final polishing step is not particularly limited. Therefore, the subject matter disclosed herein includes a method for manufacturing and polishing a magnetic disk substrate, which includes, in this order, step (1) of polishing the object to be polished with a polishing composition containing abrasive grains disclosed herein, and step (2) of polishing the object to be polished with a polishing composition (e.g., a final polishing composition) different from the polishing composition used in step (1). This manufacturing method allows for efficient production of magnetic disk substrates.

[0066] The abrasive grains used in step (2) are not particularly limited, and for example, colloidal silica is preferably used. By using colloidal silica, a polished product with high surface precision can be efficiently produced. The particle shape of the colloidal silica is not particularly limited, and may be, for example, spherical or non-spherical, but spherical colloidal silica is preferably used.

[0067] The final polishing composition that can be used in step (2) contains, for example, water in addition to abrasive grains. In addition, the final polishing composition can contain optional components (such as acids, oxidizing agents, basic compounds, and various additives) similar to those of the polishing composition described above, as needed. [Example]

[0068] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to those shown in these examples.

[0069] <Preparation of Polishing Composition> Polishing compositions according to Examples 1 to 7 and Comparative Examples 1 to 9 were prepared by mixing silica abrasive grains, phosphoric acid, 31% hydrogen peroxide solution, and deionized water. The pH of the polishing compositions was 1.5. As the silica abrasive grains, several types of silica particles with different particle diameters, particle shapes, particle size distributions, and aspect ratios were prepared, and the cumulative 50% particle diameters (D 50 ), D 50 The average area of ​​the particle equivalent to the circumference (SC 50-100 ) to the average projected area (SP 50-100 ) ratio ((SP / SC) 50-100 ), and D 50 The average area of ​​the circle equivalent to the circumference of particles less than 0-50 ) to the average projected area (SP 0-50 ) ratio ((SP / SC) 0-50 The abrasive grains used were those containing the above silica particles alone or in combination so that the values ​​of the silica particles in the polishing composition varied within a predetermined range. The silica particle concentration in the polishing composition was 7 wt %, the phosphoric acid concentration was 0.1 mol / L, and the hydrogen peroxide concentration was 0.4 mol / L.

[0070] <Polishing> The polishing composition according to each example was used as a polishing liquid to polish an object under the following conditions. The object to be polished was an aluminum substrate for a hard disk having an electroless nickel-phosphorus plating layer on its surface. The diameter of the object to be polished (substrate to be polished) was 3.5 inches (a doughnut shape with an outer diameter of approximately 95 mm and an inner diameter of approximately 25 mm) and a thickness of 1.75 mm, and the surface roughness Ra (the arithmetic mean roughness of the nickel-phosphorus plating layer measured with a laser scanning surface roughness meter "TMS-3000WRC" manufactured by Schmitt Measurement System Inc.) before polishing was 130 Å.

[0071] [Polishing conditions] Polishing equipment: System Seiko double-sided polishing machine, model "9.5B-5P" Polishing pad: FILWEL polyurethane pad, product name "CR200" Number of substrates to be polished: 15 (3 substrates / carrier x 5 carriers) Polishing fluid supply rate: 135 mL / min Polishing load: 120g / cm 2 Upper surface plate rotation speed: 27 rpm Lower surface plate rotation speed: 36rpm Sun gear rotation speed: 8 rpm Polishing amount: Total thickness of both sides of each substrate: approx. 2.2 μm The amount of polishing was calculated based on the following formula. Polishing amount [μm] = weight loss of substrate due to polishing [g] / (substrate area [cm 2 ] × density of nickel phosphorus plating [g / cm 3 ]) x 10 4

[0072] (processability) The polishing rate was calculated for both surfaces of a substrate to be polished using the polishing composition of each example under the above polishing conditions. The polishing rate was calculated based on the following formula. The results were converted into relative values, with the polishing rate of Comparative Example 1 taken as 100%, and are shown in the "Polishing Rate" column of Table 1. The higher the polishing rate, the higher the processability. Polishing rate [μm / min] = weight loss of substrate due to polishing [g] / (substrate area [cm 2 ] × density of nickel phosphorus plating [g / cm 3 ] × polishing time [min]) × 10 4

[0073] (micro waviness) After polishing with the polishing composition of each example, one Ni-P substrate was randomly selected from the Ni-P substrates (polished substrates) set in each carrier during polishing, for a total of three Ni-P substrates. Microwaviness was measured on the front and back surfaces of these three Ni-P substrates, a total of six surfaces, using a ZYGO non-contact surface profilometer "NEWVIEW5032" under conditions of an objective lens magnification of 2.5x, an intermediate lens magnification of 0.5x, and a bandpass filter of 80-500 μm. Measurements were performed on each of the six surfaces at four points spaced 90° apart, 37 mm radially outward from the center of the polished substrate, and the average value of these 24 points was recorded as the microwaviness (Å) value. The obtained values ​​were converted into relative values, with the value for Comparative Example 1 set to 100%, and are shown in the "Microwaviness" column in Table 1. The smaller the value, the more suppressed the microwaviness.

[0074] (rate / swell ratio) The ratio of the polishing rate to the microwaviness was calculated and shown in the "Rate / Waviness Ratio" column in Table 1. If the "Rate / Waviness Ratio" is 105% or higher, it is determined that high processability has been achieved while suppressing an increase in microwaviness.

[0075] [Table 1]

[0076] As shown in Table 1, the (SP / SC) of silica particles 50-100 is between 40% and 65% and (SP / SC) 0-50 In Examples 1 to 7, which used polishing compositions having a rate / waviness ratio of greater than 65% and less than 90%, the rate / waviness ratio was 105% or greater, and the effect of suppressing the increase in microwaviness while improving processability was obtained. (SP / SC) 50-100 meets 40% to 65% (SP / SC) 0-50 In Comparative Example 7, in which a polishing composition having a surface roughness of 65% or less was used, the processability improved, but the microwaviness increased even more, resulting in a low rate / waviness ratio (SP / SC). 50-100In Comparative Examples 2 to 6, 8, and 9, which used polishing compositions that did not satisfy the condition of 40% or more and 65% or less, none of them were able to achieve a rate / waviness ratio of 105% or more.

[0077] 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 for magnetic disk substrates, comprising: The abrasive includes silica particles and water. The silica particles are particles whose volume-based particle diameters determined by SEM image analysis are in the range of 50% to 100% cumulatively from the smallest diameter side (D ５０ Average projected area (SP) of particles ５０－１００ ) is the D ５０ The average area of ​​the circle equivalent to the perimeter of each particle (SC ５０－１００ ) is 40% or more and 57% or less of the total; and The silica particles are particles whose volume-based particle diameters determined by SEM image analysis are in the range of 0% or more and less than 50% cumulatively from the small diameter side (D ５０ Average projected area (SP) of particles ０－５０ ) is the D ５０ The average area of ​​the circle equivalent to the circumference of each particle that falls under the particle size (SC ０－５０ ) is more than 65% and not more than 90%.

2. A polishing composition for magnetic disk substrates, comprising: The abrasive includes silica particles and water. The silica particles have an average projected area (SP 50-100 ) of particles (D 50 or larger particles) whose volume-based particle diameters, as determined by SEM image analysis, are in a cumulative range of 50% to 100% from the smallest diameter side, and the average projected area (SP 50-100 ) of the average area (SC 50-100 ) of a circle corresponding to the perimeter of each particle corresponding to the D 50 or larger particles, The silica particles have an average projected area (SP 0-50 ) of particles whose volume-based particle diameters, determined by SEM image analysis, are in the cumulative range of 0% or more and less than 50% from the smallest diameter side (particles less than D 50 ), which is greater than 65% and less than 90% of the average area (SC 0-50 ) of a circle corresponding to the perimeter of each particle corresponding to the particles less than D 50 , and The silica particles have an average aspect ratio (A 50-100 ) of D 50 or larger particles of 1.50 or smaller.

3. The silica particles are ５０ The average aspect ratio (A ５０－１００ 3. The polishing composition according to claim 1, wherein the value of (a) is 1.25 or more and 1.50 or less.

4. The silica particles are ０－５０ The SP for ０－５０ The ratio ((SP / SC) ０－５０ ) is the SC ５０－１００ The SP for ５０－１００ The ratio ((SP / SC) ５０－１００ 4. The polishing composition according to claim 1, wherein the polishing ratio is 1.20 to 2.50 times the polishing ratio of the polishing composition according to claim 1.

5. The silica particles have a volume-based cumulative 50% particle diameter (D ５０ 5. The polishing composition according to claim 1, wherein the average particle size is 40 nm or more and 400 nm or less.

6. 6. The polishing composition according to claim 1, further comprising an acid and an oxidizing agent.

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

8. A method for polishing a substrate, comprising: (1) supplying the polishing composition according to any one of claims 1 to 6 to a substrate to be polished, and polishing the substrate.

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