Polishing composition, method of manufacturing substrate, and polishing method

Abstract

To provide a polishing composition which contains silica abrasive grains and can maintain low-height fine waviness while improving processability when polishing a magnetic disk substrate.SOLUTION: A composition for polishing magnetic disk substrates is provided. The polishing composition contains silica particles as abrasive grains, an acid, and an oxidizing agent. The silica particles have a minimum peak diameter Dpmin of greater than 80 nm and equal to or smaller than 200 nm, inclusive, in a weight-based particle size distribution obtained by the light transmission centrifugal sedimentation method, and a ratio (D99 / Dpmin) of a cumulative 99% particle diameter D99 to a minimum peak diameter Dpmin that is greater than 1.40 and less than or equal to 5.50 in a weight-based particle size distribution obtained by the light transmission centrifugal sedimentation method.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 solution. For example, in the manufacture of nickel-phosphorus-plated disk substrates (hereinafter also referred to as Ni-P substrates), polishing (primary polishing) that emphasizes polishing efficiency and final polishing (finish polishing) that is performed to achieve the surface precision of the final product are generally performed. Patent Documents 1 and 2 are cited as technical documents related to polishing compositions used for polishing magnetic disk substrates. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-1513 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-15184 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 substrate surfaces 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 to achieve higher quality substrate surfaces after finish polishing. Compared to polishing with alumina abrasive grains, polishing with silica abrasive grains prevents the abrasive grains from penetrating the substrate, reduces defects such as scratches, and facilitates 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 the processing power. Furthermore, polishing with silica abrasive grains involves not only maintaining or improving the processing power, but also increasing the microwaviness of the polished substrate. In the above-mentioned polishing, processability and microwaviness are in a contradictory relationship, with improving one resulting in a deterioration of the other, making it difficult to achieve both. In the above Patent Documents 1 and 2, the polishing rate in rough polishing and long-period defects on the substrate surface after rough polishing are evaluated, but microwaviness is not evaluated, and there is no suggestion about improving microwaviness or achieving both a processing force and microwaviness.

[0005] As described in the Examples below, "microwaviness" refers to waviness (arithmetic mean roughness) in the wavelength range of 80 to 500 μm observed using a non-contact surface profilometer. For its definition, see, for example, JIS B 0601:2013. Meanwhile, the long-period defects include dents (e.g., grinding scratches and polish-enhanced defects (PED)) that appear as small spots observed using an optical interference surface profilometer with a cutoff value of 2500 μm, and are a type of surface defect (see paragraphs 0006, 0020, and 0120 of Patent Document 1 and paragraphs 0005, 0017, and 0117 of Patent Document 2). While "microwaviness" evaluates the average unevenness of the substrate surface, "long-period defects" are defects that occur only in a small portion of the surface. Therefore, the long-period defects are a different evaluation item and technical concept from microwaviness in the technical field of magnetic disk substrate polishing.

[0006] As a result of extensive research, the present inventors have succeeded in creating a polishing composition that can improve processability while suppressing an increase in microwaviness by using a combination of silica abrasive grains having a specific particle size distribution, an acid, and an oxidizing agent, and have thus completed the present invention. That is, an object of the present invention is to provide a polishing composition that contains silica abrasive grains and can maintain low microwaviness and improve processability when polishing magnetic disk substrates. Another related object is to provide a method for manufacturing and polishing a substrate using the polishing composition. Yet another related object is to provide a polishing composition that can achieve at least one of reduced silica residue and reduced polishing resistance while maintaining low microwaviness and improving processability, and to provide a method for manufacturing and polishing a substrate using the polishing composition. [Means for solving the problem]

[0007] The polishing composition for magnetic disk substrates provided herein contains silica particles as abrasive grains, an acid, and an oxidizing agent. The silica particles have a minimum peak diameter D in a weight-based particle size distribution obtained by a light transmission centrifugal sedimentation method. pmin The minimum peak diameter D pmin The cumulative 99% particle diameter D in the weight-based particle size distribution obtained by the light transmission centrifugal sedimentation method 99 The ratio (D 99 / D pmin ) is greater than 1.40 and less than 5.50. pmin is within the above range, and D 99 / D pmin A polishing composition using a combination of silica particles having a particle size distribution in the above range, an acid, and an oxidizing agent can maintain low microwaviness and improve processability when polishing a magnetic disk substrate.

[0008] In some preferred embodiments, the silica particles have a minimum peak diameter D pmin The average particle diameter D in the weight-based particle size distribution obtained by the light transmission centrifugal sedimentation method meanThe ratio (D mean / D pmin ) is greater than 0.70 and not greater than 1.75. With this configuration, the effect of improving processability while maintaining low microwaviness is more effectively exhibited.

[0009] In some embodiments, the polishing composition further contains a nitrogen-containing compound. In some embodiments, the nitrogen-containing compound is at least one selected from ammonia and a nitrogen-containing organic compound. By using the nitrogen-containing compound, microwaviness is more easily reduced. In particular, it is more preferable to use a nitrogen-containing compound having 1 to 4 nitrogen atoms per molecule. In some embodiments, the nitrogen-containing compound has a structure including a carbon skeleton having 2 to 4 carbon atoms and consisting of a single bond bonded to at least one nitrogen atom contained in a molecule, and a hydrophilic group bonded to the end of the carbon skeleton. A nitrogen-containing compound having the above structure exhibits a better effect of reducing microwaviness.

[0010] In some embodiments, the polishing composition further comprises at least one selected from the group consisting of a phosphate ester, a phosphite ester, and an organic phosphonic acid compound. This configuration can reduce the phenomenon of silica particles remaining on the substrate surface after polishing (hereinafter also referred to as "silica residue") without impairing processability. In some embodiments, the phosphate ester and / or the phosphite ester has an organic group bonded to it via a phosphate ester bond, and the organic group is selected from organic groups having 6 or fewer carbon atoms and optionally containing an ether bond.

[0011] In some embodiments, the polishing composition further contains a water-soluble polymer (A). This configuration facilitates reducing the polishing resistance (frictional force) between the polishing pad and the object to be polished. Reducing the polishing resistance between the object to be polished and the polishing pad during polishing reduces the load on the carrier, preventing or suppressing deformation of the carrier and preventing pad scratches.

[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 above silica particles have a minimum peak diameter D pmin is greater than 80 nm and less than 200 nm. pmin The minimum peak diameter D pmin Cumulative 99% particle diameter D 99 The ratio (D 99 / D pmin ) is greater than 1.40 and less than 5.50. Here, the cumulative 99% particle diameter D 99 is the cumulative 99% particle size in the weight-based particle size distribution based on the light transmission centrifugal sedimentation method. pmin and minimum peak diameter D pmin Cumulative 99% particle diameter D 99 When the ratio is within the above range, it is easy to maintain low microwaviness and improve the polishing rate. pmin , Cumulative 99% particle size D 99 , and the minimum peak diameter D pmin Cumulative 99% particle diameter D 99 The ratio (D 99 / D pmin ) are simply D pmin , D 99 and the ratio (D 99 / D pmin ) is sometimes said.

[0017] The reason why the above configuration achieves the effects of the technology disclosed herein is thought to be as follows, although this is not to be construed as being particularly limiting. When silica particles are used as abrasive grains in polishing magnetic disk substrates, if an attempt is made to improve the polishing rate by increasing the particle size, it tends to become more difficult to maintain low microwaviness as the polishing rate increases, and an improvement in the polishing rate and a reduction in microwaviness tend to be in a contradictory relationship. Therefore, the inventors of the present invention have conducted extensive research and found that silica particles having a particle diameter of more than 80 nm and not more than 200 nm can easily achieve a good balance between low microwaviness and a polishing rate, and that a polishing powder containing a large number of particles having a particle diameter in the above range concentratedly and having a minimum peak diameter D pmin It was found that when the difference in particle size between the small and large particles and the amount of large particles are controlled within a predetermined, relatively small range, it is easy to achieve a good balance between low microwaviness and a polishing rate. pmin is greater than 80 nm and less than 200 nm, and the minimum peak diameter D pmin The difference in particle size between the small and large particles and the ratio (D 99 / D pmin ) is greater than 1.40 and not greater than 5.50, it has been found that a good balance between low microwaviness and a good polishing rate can be easily achieved. It should be noted that the above explanation is the inventor's consideration based on experimental results, and the technology disclosed herein should not be interpreted as being limited to the above mechanism.

[0018] In terms of polishing rate, in some embodiments, the minimum peak diameter D pmin may be 90 nm or more, 100 nm or more, 115 nm or more, 130 nm or more, 135 nm or more, or 140 nm or more. In addition, from the viewpoint of maintaining low microwaviness, in some embodiments, the minimum peak diameter D pmin may be 190 nm or less, 185 nm or less, 180 nm or less, 170 nm or less, or 160 nm or less.

[0019] In some embodiments, the ratio (D 99 / D pmin) may be 1.50 or greater, 1.55 or greater, 1.58 or greater, or 1.60 or greater. In some embodiments, the ratio (D 99 / D pmin ) may be 5.0 or less, may be 4.5 or less, may be 4.0 or less, may be 3.5 or less, may be 3.0 or less, may be 2.0 or less, or may be 1.8 or less.

[0020] Ratio(D 99 / D pmin ) is within the specified range, the cumulative 99% particle diameter D 99 is not particularly limited. 99 For example, D can be set to approximately 100 nm or more. 99 is preferably about 150 nm or more, may be about 170 nm or more, may be about 190 nm or more, may be 200 nm or more, may be 220 nm or more, may be 240 nm or more. 99 There is no particular upper limit to the D of the abrasive grains from the viewpoint of suppressing the increase in microwaviness. 99 is, for example, approximately 500 nm or less, suitably approximately 400 nm or less, preferably approximately 300 nm or less, may be approximately 290 nm or less, may be approximately 285 nm or less, may be approximately 280 nm or less, or may be approximately 275 nm or less.

[0021] In some preferred embodiments, the minimum peak diameter D pmin average particle size D mean The ratio (D mean / D pmin ) is greater than 0.70 and less than 1.75. Here, the average particle diameter D mean is the weight-average average diameter in the weight-based particle size distribution based on the light transmission centrifugal sedimentation method. pmin average particle size D mean The ratio (D mean / D pmin When the average particle diameter D is within the above range, it is easy to achieve both low microwaviness and a high polishing rate. mean and minimum peak diameter D pminaverage particle size D mean The ratio (D mean / D pmin ) are simply D mean and the ratio (D mean / D pmin ) is sometimes said.

[0022] Ratio(D mean / D pmin The reason why the effects of the technology disclosed herein can be easily realized by setting the minimum peak diameter D pmin average particle size D mean The ratio (D mean / D pmin ) can be an index of the broadness of the particle size distribution on the side of the silica particle average diameter. mean / D pmin ) being controlled within a predetermined, relatively small range means that the particle size distribution has a narrow tail on the small diameter side, and such silica particles tend to be concentrated with silica particles having a particle size that is particularly effective for achieving both low microwaviness and improved processability.

[0023] In some embodiments, the ratio (D mean / D pmin ) may be 0.75 or greater, 0.80 or greater, 0.85 or greater, 0.90 or greater, or 0.93 or greater. In some embodiments, the ratio (D mean / D pmin ) may be 1.50 or less, 1.40 or less, 1.30 or less, 1.20 or less, 1.10 or less, or 0.98 or less.

[0024] Average particle diameter D mean is not particularly limited. In some embodiments, the average particle diameter D mean The average particle size D may be 50 nm or more, 80 nm or more, 100 nm or more, 110 nm or more, 120 nm or more, 130 nm or more, or 140 nm or more.mean may be 250 nm or less, 200 nm or less, 170 nm or less, 160 nm or less, 150 nm or less, or 148 nm or less.

[0025] Abrasive grain D pmin , D mean and D 99 can be adjusted by selecting the silica particles to be used, mixing two or more types of silica particles having different particle size distributions, or performing a process to remove coarse particles.

[0026] In this specification, the D pmin , D mean and D 99 can be determined from the weight-based particle size distribution obtained by the light transmission centrifugal sedimentation method. Specifically, the smallest peak diameter among the peaks (maximum values) in the weight-based particle size distribution is defined as D pmin The weight-average average diameter in the weight-based particle size distribution is D mean The particle diameter corresponding to the cumulative 99% point in the weight-based particle size distribution is defined as D 99 The optical transmission centrifugal sedimentation method utilizes the difference in sedimentation velocity that occurs due to differences in particle size, and measures the particle size while classifying each particle in the abrasive grain, making it possible to detect coarse particles that may cause scratches more accurately than other methods (such as laser scattering and dynamic light scattering). The particle size distribution measured by the light transmission centrifugal sedimentation method is determined according to JIS Z 8823-2:2016. The specific procedure for measuring the particle size distribution is as follows: First, a disk-shaped cell is filled with a particle-free, transparent test liquid (e.g., an 8-24 wt.% sucrose aqueous solution), and a light beam that transmits through the test liquid is irradiated onto the cell. Then, while rotating the cell at a predetermined rotation speed (e.g., 24,000 rpm), a dispersion of abrasive particles is injected into the cell through an inlet coaxial with the rotation axis. This causes the particles in the dispersion to settle outward in the centrifugal direction, attenuating the light beam. The particle size distribution of the abrasive particles is then calculated based on the change in the attenuation of the light beam over time. The particle size distribution of the abrasive particles can be calculated using software that converts the change in the attenuation of the light beam into a particle size distribution.

[0027] The specific measurement method is as follows: Abrasive grains are dispersed in ion-exchanged water to prepare an abrasive grain dispersion for measurement. A disk centrifugal particle size distribution analyzer "DC24000 UHR" manufactured by CPS Instruments, USA, is used to determine the particle size distribution on a weight basis in accordance with JIS Z 8823-2. The particle size distribution can be measured under the conditions shown below. [Measurement conditions] Test solution introduced into the cell: Sucrose aqueous solution with a minimum concentration of 8% by weight and a maximum concentration of 24% by weight Amount of test solution injected into the cell: 12 mL Abrasive concentration of the abrasive dispersion for measurement: 2% by weight Amount of abrasive dispersion liquid injected for measurement: 0.1 mL Disk rotation speed: 24000 rpm Measurement range: 0.025μm to 1.0μm

[0028] The above measurement results show multiple particle size peaks. The smallest of these values ​​is the minimum peak diameter D pminAs the analysis software, the software "CPSV95b" in the above measurement device can be used. Specifically, among the peak diameters output in the "Detected Peaks" item when using the above software, the smallest value is taken as the minimum peak diameter D pmin The average particle diameter D mean and cumulative 99% particle diameter D 99 Similarly, the results output when using the above software can be used for the D of silica particles in the examples described later. pmin , D mean and D 99 is measured.

[0029] From the viewpoint of maintaining or improving processability, the average aspect ratio of the silica particles is preferably 1.05 or more, more preferably 1.15 or more, and even more preferably 1.20 or more (for example, 1.25 or more). From the viewpoint of efficiently improving surface quality, in some embodiments, the average aspect ratio is suitably 2.50 or less, preferably 2.0 or less, more preferably 1.70 or less, even more preferably 1.50 or less, and may be 1.35 or less. In silica particles having an average aspect ratio in such a range, D pmin and the ratio (D 99 / D pmin The effect of setting the value of the thickness of the resin film in the predetermined range is preferably exhibited.

[0030] The average aspect ratio of silica particles as abrasive grains is measured, for example, by the following method. Specifically, a scanning electron microscope (SEM) is used to observe a predetermined number of particles contained in the abrasive grains to be measured (which may be one type of abrasive grain or a mixture of two or more types of abrasive grains) in an SEM image containing 50 or more particles within one field of view. The observation magnification is 10,000 to 50,000 times. For each abrasive grain in the observed image, the smallest rectangle circumscribing each particle image is drawn. The long side length (long diameter value) of the rectangle drawn for each particle image is then divided by the short side length (short diameter value) to calculate the long diameter / short diameter ratio (aspect ratio). The average aspect ratio can be determined by arithmetically averaging the aspect ratios of the predetermined number of particles. The average aspect ratio can be determined using common image analysis software. The predetermined number, i.e., the number of particles for which the aspect ratio of each particle is calculated, is usually set to 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. For the measurement, 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. is used.

[0031] As silica particles, the specified D pmin and the ratio (D 99 / D pmin) are satisfied, and 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] In some embodiments, the polishing composition disclosed herein contains a nitrogen-containing compound. The nitrogen-containing compound contained in the polishing composition adsorbs to the magnetic disk substrate during polishing and protects the substrate, thereby eliminating surface irregularities and improving microwaviness. The number of nitrogen atoms contained in one molecule of the nitrogen-containing compound is not particularly limited, and nitrogen-containing compounds having 1 to 4 nitrogen atoms per molecule are preferably used. From the viewpoint of reducing microwaviness, the number of nitrogen atoms contained in one molecule of the nitrogen-containing compound is preferably 2 to 4, more preferably 2 or 3, and particularly preferably 2. The nitrogen-containing compounds can be used alone or in combination of two or more.

[0037] In some embodiments, it is preferable to use a nitrogen-containing compound having a structure including a carbon skeleton formed by a single bond bonded to at least one nitrogen atom contained in a molecule and a hydrophilic group bonded to the carbon skeleton. The carbon skeleton is bonded to the nitrogen atom by a single bond and is composed of a carbon-carbon single bond. Nitrogen-containing compounds contribute to reducing microwaviness by adsorbing to the magnetic disk substrate, but adsorption to the substrate can also reduce processability. As described above, nitrogen-containing compounds having a single-bond carbon skeleton bonded to a nitrogen atom and a hydrophilic group bonded to the carbon skeleton have a structure in which the hydrophilic group is bonded to a freely rotating carbon skeleton, and therefore are likely to spread easily in the polishing solution during polishing and adsorb to the magnetic disk substrate surface in a three-dimensional structure. Thus, nitrogen-containing compounds that can be three-dimensionally adsorbed to a substrate are more easily removed from the substrate surface by physical actions during polishing or cleaning than compounds that adsorb to a substrate in a planar manner, and are particularly easily removed by silica particles having a predetermined particle size distribution. Therefore, it is believed that this can better suppress deterioration in processability due to the adsorption of nitrogen-containing compounds to the substrate, and furthermore, can improve microwaviness while better maintaining or improving processability. Note that the above mechanism is the inventor's consideration based on experimental results, and the technology disclosed herein should not be interpreted as being limited to the above mechanism.

[0038] In the nitrogen-containing compound having a structure including a carbon skeleton and hydrophilic groups, the number of carbon atoms contained in the carbon skeleton is not particularly limited, but is preferably 2 or more. From the viewpoint of maintaining or improving processability, the upper limit of the number of carbon atoms contained in the carbon skeleton is suitably 10 or less, for example, may be 6 or less, preferably 4 or less, more preferably 3 or less, and even more preferably 2. Furthermore, the carbon skeleton may be composed of carbon-carbon single bonds that are easily rotatable in liquid, and may have substituents other than hydrophilic groups. In some embodiments, nitrogen-containing compounds are preferably used that contain a carbon skeleton that does not have substituents other than hydrophilic groups. Examples of hydrophilic groups bonded to the carbon skeleton include hydroxyl groups, amino groups, (poly)oxyalkylene groups including (poly)oxyethylene groups, sulfonic acid groups, sulfate groups, and carboxyl groups. From the viewpoint of removability from a substrate, the hydrophilic groups bonded to the carbon skeleton are preferably bonded to at least the terminal of the carbon skeleton. The number of hydrophilic groups bonded to one carbon skeleton is not particularly limited, but may be, for example, 1 to 3, with 1 or 2 being preferred.

[0039] In the nitrogen-containing compound having a structure including a carbon skeleton and a hydrophilic group, the number of carbon skeletons bonded to one nitrogen atom is 1 to 3, preferably 2. Typical examples of the carbon skeleton and the hydrophilic group bonded to the carbon skeleton include, for example, a hydroxyalkyl group and an alkylamino group. Suitable examples of the nitrogen-containing compound include a compound having one or more (specifically, 1, 2, or 3) hydroxyalkyl groups bonded to a nitrogen atom, a compound having one or more (specifically, 1, 2, or 3) alkylamino groups bonded to a nitrogen atom, and a compound having at least one hydroxyalkyl group and at least one alkylamino group bonded to a nitrogen atom. Among these, a compound having a structure in which the hydroxyalkyl group and the alkylamino group are bonded to a nitrogen atom is particularly preferred.

[0040] The nitrogen-containing compound may be ammonia or a nitrogen-containing organic compound. Of these, organic amines and other nitrogen-containing organic compounds are preferred. The nitrogen-containing organic compound may be any of aliphatic amine compounds, alicyclic amine compounds, and nitrogen-containing heterocyclic aromatic compounds. Of these, nitrogen-containing organic compounds having 1 to 4 (preferably 2 or 3) nitrogen atoms are preferred. Furthermore, from the viewpoint of maintaining and improving processability, nitrogen-containing organic compounds that do not have a nitrogen-containing aromatic ring (e.g., a pyrazine skeleton) or a guanidine skeleton are preferred. Examples of nitrogen-containing organic compounds having such structures include aliphatic amine compounds and alicyclic amine compounds. While protecting the substrate by adsorption to the substrate, such nitrogen-containing organic compounds are considered to be more easily removed from the substrate by silica particles having a specific particle size distribution than nitrogen-containing heterocyclic aromatic compounds or compounds having a guanidine skeleton. The amine compound may be any of primary amines, secondary amines, and tertiary amines, with secondary amines being preferred.

[0041] Examples of the aliphatic amine compound include trialkylamines such as trimethylamine, triethylamine, and tripropylamine; dialkylmonoalkanolamines such as dimethylmethanolamine, dimethylethanolamine, diethylmethanolamine, and diethylethanolamine; monoalkyldialkanolamines such as methyldimethanolamine, methyldiethanolamine, ethyldimethanolamine, and ethyldiethanolamine; monoalkanolamines such as monomethanolamine and monoethanolamine; dialkanolamines such as dimethanolamine and diethanolamine; trialkanolamines such as trimethanolamine and triethanolamine; ethylenediamine, ... Examples of suitable diamines include ethylenediamine, N,N,N',N'-tetramethylethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,4-diaminobutane, hexamethylenediamine, 3-(diethylamino)propylamine, 3-(dibutylamino)propylamine, 3-(methylamino)propylamine, and 3-(dimethylamino)propylamine; hydroxyl group-containing diamines such as 2-(2-aminoethylamino)ethanol, N-(2-aminoethyl)diethanolamine, N-aminoethylisopropanolamine, and N-aminoethyl-N-methylethanolamine; triamines such as diethylenetriamine; and triethylenetetramine. Among these, alkanolamines and hydroxyl group-containing diamines are preferred, with 2-(2-aminoethylamino)ethanol being more preferred.

[0042] Examples of the alicyclic amine compound include piperazine, alkylpiperazines such as N-methylpiperazine, N-ethylpiperazine, and 2,5-dimethylpiperazine, aminoalkylpiperazines such as N-aminomethylpiperazine and N-aminoethylpiperazine, and hydroxyalkylpiperazines such as hydroxyethylpiperazine. Among these, aminoalkylpiperazines are preferred, and N-aminoethylpiperazine is more preferred.

[0043] Examples of nitrogen-containing heterocyclic aromatic compounds include pyridines such as pyridine, 3-aminopyridine, and 4-dimethylaminopyridine; nicotinic acid; pyrazines such as pyrazine and 2-aminopyrazine; triazoles such as 1,2,3-triazole and 1,2,4-triazole; benzotriazoles such as 1,2,3-benzotriazole and 2,2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol; imidazoles; etc. Among these, 2,2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol is preferred.

[0044] Other nitrogen-containing compounds include ammonia, quaternary ammonium compounds, guanidine, and the like.

[0045] The molecular weight of the nitrogen-containing compound is equal to or greater than the molecular weight of ammonia, 17.03. Although not particularly limited, from the viewpoint of reducing microwaviness, in some embodiments, the molecular weight of the nitrogen-containing compound is equal to or greater than 50, suitably equal to or greater than 60, preferably equal to or greater than 80, more preferably equal to or greater than 100, may be equal to or greater than 120, or may be equal to or greater than 140. Furthermore, from the viewpoint of processability, in some embodiments, the molecular weight of the nitrogen-containing compound is suitably equal to or less than 500, preferably equal to or less than 300, more preferably equal to or less than 200, even more preferably equal to or less than 150, and may be equal to or less than 130.

[0046] The content of nitrogen-containing compound in polishing composition is not particularly limited, from the viewpoint of effectively exerting the effect of adding nitrogen-containing compound, in some embodiments, for example, it is suitable to be 0.001g / L or more, preferably 0.01g / L or more, more preferably 0.05g / L or more, even more preferably 0.10g / L or more, particularly preferably 0.15g / L or more, most preferably 0.17g / L or more.In addition, in some embodiments, from the viewpoint of maintaining processability, the content of above-mentioned nitrogen-containing compound is suitable to be 3g / L or less, preferably 1g / L or less, more preferably 0.8g / L or less, even more preferably 0.5g / L or less, particularly preferably 0.3g / L or less, most preferably 0.25g / L or less.

[0047] (acid) The polishing composition disclosed herein contains an acid as a polishing accelerator. The acid may be either an inorganic acid or an organic acid. Examples of the organic acid include organic carboxylic acids and organic sulfonic acids each having about 1 to 18 carbon atoms, typically about 1 to 10 carbon atoms. The acid may be used alone or in combination of two or more.

[0048] 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.

[0049] Specific examples of organic acids include citric acid, maleic acid, malic acid, glycolic acid, succinic acid, itaconic acid, malonic 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, 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, oxaloacetic acid, chloro ... organic carboxylic acids such as dichloroacetic acid, dichloroacetic acid, and trichloroacetic acid; phytic acid; organic phosphonic acids such as 1-hydroxyethylidene-1,1-diphosphonic 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, and α-methylphosphonosuccinic acid; and organic sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, 2-naphthalenesulfonic acid, sulfosuccinic acid, 10-camphorsulfonic acid, and isethionic acid.

[0050] 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.

[0051] The acid may be used in the form of a salt thereof. Examples of the salt include metal salts of the inorganic acids and organic acids described above. Examples of the metal salt include alkali metal salts such as lithium salts, sodium salts, and potassium 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; etc. The alkali metal in these alkali metal salts may be, for example, lithium, sodium, potassium, etc.

[0052] The polishing composition disclosed herein preferably contains an inorganic acid salt, such as an alkali metal salt, such as potassium chloride, sodium chloride, potassium nitrate, sodium nitrate, or potassium phosphate.

[0053] 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.

[0054] 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).

[0055] (oxidizing agent) The polishing composition disclosed herein contains an oxidizing agent. Examples of oxidizing agents include, but are not limited to, peroxide, nitric acid or its salt, periodic acid or its salt, peroxoacid or its salt, permanganic acid or its salt, chromic acid or its salt, oxyacid or its salt, metal salts, and sulfuric acid. The oxidizing agents can be used alone or in combination of two or more. Specific examples of oxidizing agents include hydrogen peroxide, sodium peroxide, barium peroxide, nitric acid, iron nitrate, aluminum nitrate, peroxomonosulfuric acid, metal peroxomonosulfates, peroxodisulfuric acid, 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, and ammonium iron sulfate. 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.

[0056] 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.

[0057] (Silica residue reducing agent) In some preferred embodiments, the polishing composition disclosed herein contains a silica residue-reducing agent. The silica residue-reducing agent can be one or more compounds selected from phosphate esters, phosphites, and organic phosphonic acid compounds, and can be water-soluble, with 1 g of the agent completely dissolving in 100 mL of pure water at 30°C. The use of the silica residue-reducing agent can reduce silica residue during primary polishing of magnetic disk substrates without impairing processability. The reasons for this are believed to be as follows: The silica residue-reducing agent contained in the polishing composition is dissolved in the composition and deposited in the form of a thin film on the substrate surface, preventing direct contact and adhesion of the silica abrasive particles to the substrate. Therefore, the silica abrasive particles are subsequently removed from the substrate along with the water-soluble silica residue-reducing agent during washing, resulting in reduced silica residue on the substrate. The above mechanism is the inventors' theory based on experimental results, and the technology disclosed herein should not be construed as being limited to the above mechanism.

[0058] The silica residue reducing agent disclosed herein can typically have a water solubility such that 1 g completely dissolves in 100 mL of pure water at a temperature of 30°C. This allows the silica residue reducing agent to dissolve in the polishing composition, move smoothly within the composition, and be positioned between the substrate and the silica abrasive grains. Furthermore, because the silica residue reducing agent is water-soluble, it can be easily removed by washing after polishing.

[0059] Complete solubility in pure water at 30°C can be assessed by adding 1 g of sample to a flask, stirring, and visually observing whether complete dissolution has occurred within 1 hour. This can be determined by observing the presence or absence of cloudiness, precipitate, or phase separation (organic / aqueous phases). Measurements are performed at ambient pressure. If it is difficult to determine whether 1 g of sample has completely dissolved in 100 mL of pure water, the solution can be centrifuged and the supernatant analyzed for the presence or absence of sample. In this case, it is desirable to use a sample size of 3. Alternatively, if the solubility in water (30°C) listed in public literature or the Safety Data Sheet (SDS) indicates or suggests a value of 1 g / 100 mL or greater, the above water solubility can be considered to be satisfied. The above conditions are also used in the examples described below.

[0060] The phosphate esters and phosphites used as silica residual reducing agents have one or two organic groups bonded by a phosphate ester bond. This organic group can be described as a substituent group in which one or two OH groups (typically OH groups directly bonded to the phosphorus atom) contained in phosphoric acid are substituted with hydrogen atoms. In some embodiments, the silica residual reducing agent has one or two organic groups. In some preferred embodiments, the silica residual reducing agent is selected from organic groups having six or fewer carbon atoms and optionally containing an ether bond. Limiting the number of carbon atoms in the organic group limits the size of the organic group, and thus the silica residual reducing agent, which tends to result in excellent water solubility and mobility. From the viewpoints of water solubility and mobility, the number of carbon atoms in the organic group may be five or fewer, four or fewer, three or fewer, or two or fewer (e.g., one). Limiting the number of carbon atoms in the organic group also tends to suppress hydrophobic interactions between the silica residual reducing agent and silica particles. The organic group may or may not contain an ether bond. In some embodiments, the organic group of the silica residue reducing agent may be free of ester bonds and vinyl groups.

[0061] Suitable examples of the organic group contained in the silica residue reducing agent include alkyl groups having 4 or less carbon atoms. The alkyl group may be linear or branched. From the viewpoints of water solubility, mobility, suppression of adsorption to silica particles, etc., the number of carbon atoms in the alkyl group may be 3 or less, 2 or less, or even 1. Examples of the alkyl group include methyl groups, ethyl groups, propyl groups (n-propyl groups, isopropyl groups), and butyl groups (n-butyl groups, sec-butyl groups, isobutyl groups, tert-butyl groups). The silica residue reducing agent may have one or two of the above alkyl groups.

[0062] Other suitable examples of the organic group contained in the silica residual reducing agent include alkoxyalkyl groups having 6 or less carbon atoms. From the viewpoints of water solubility, mobility, and suppression of adsorption to silica particles, the number of carbon atoms in the alkoxyalkyl group may be 5 or less, 4 or less, 3 or less, or even 2. Examples of the alkoxyalkyl group include a methoxymethyl group, an ethoxymethyl group, a propoxymethyl group, a butoxymethyl group, a methoxyethyl group, an ethoxyethyl group, a propoxyethyl group, a butoxyethyl group, a methoxypropyl group, an ethoxypropyl group, a propoxypropyl group, a methoxybutyl group, and an ethoxybutyl group. The silica residual reducing agent may have one or two of the above alkoxyalkyl groups. Alternatively, the silica residual reducing agent may have the above alkyl group and the above alkoxyalkyl group.

[0063] The phosphate ester used as the silica residue reducing agent can be any of a monophosphate ester, a diphosphate ester, and a triester phosphate. The phosphate ester can be used alone or in combination of two or more.

[0064] Examples of the phosphoric acid ester include alkyl acid phosphates such as monoalkyl acid phosphate (monomethyl acid phosphate, monoethyl acid phosphate, monoisopropyl acid phosphate, monobutyl acid phosphate, etc.) and dialkyl acid phosphate (dimethyl acid phosphate, diethyl acid phosphate, diisopropyl acid phosphate, dibutyl acid phosphate, etc.); alkenyl acid phosphates such as monoalkenyl acid phosphate and dialkenyl acid phosphate; mono(alkoxyalkyl) acid phosphate, di(alkoxyalkyl) acid phosphate, Among these, those exhibiting the above-mentioned water solubility are used from among alkoxyalkyl acid phosphates such as methyl acid phosphate (methoxymethyl acid phosphate, ethoxymethyl acid phosphate, butoxymethyl acid phosphate, methoxyethyl acid phosphate, ethoxyethyl acid phosphate, propoxyethyl acid phosphate, butoxyethyl acid phosphate, methoxypropyl acid phosphate, ethoxypropyl acid phosphate, propoxypropyl acid phosphate, methoxybutyl acid phosphate, ethoxybutyl acid phosphate, etc.); monoalkyl phosphates; and the like. These can be used alone or in combination of two or more. Among these, alkyl acid phosphate and alkoxyalkyl acid phosphate are preferred, and methyl acid phosphate, ethyl acid phosphate, isopropyl acid phosphate, butyl acid phosphate, and butoxyethyl acid phosphate are more preferred. The alkyl acid phosphate may be a mixture of monoalkyl acid phosphate and dialkyl acid phosphate, and the same applies to the alkoxyalkyl acid phosphate.

[0065] As the phosphite ester, those exhibiting the above-mentioned water solubility are preferably used from alkyl hydrogen phosphites such as dimethyl hydrogen phosphite, diethyl hydrogen phosphite, diisopropyl hydrogen phosphite, dibutyl hydrogen phosphite, and diisobutyl hydrogen phosphite. These can be used alone or in combination of two or more. Among them, diethyl hydrogen phosphite and dibutyl hydrogen phosphite are more preferred.

[0066] As the organic phosphonic acid compound, one or more of the above-mentioned water-soluble organic phosphonic acid compounds can be used without any particular limitation. A suitable example is nitrilotris(methylene phosphonic acid).

[0067] The molecular weight of the silica residual reducing agent is selected from an appropriate range that allows it to exhibit its function, and is not limited to a specific range. From the viewpoints of water solubility, mobility, and suppression of adsorption to silica particles, the molecular weight of the silica residual reducing agent is suitably 500 or less, and may be, for example, 300 or less, 250 or less, 200 or less, or 150 or less (e.g., less than 150). The lower limit of the molecular weight is approximately 100 or more, and may be, for example, 120 or more. Furthermore, the molecular weight of the phosphate ester used as the silica residual reducing agent is suitably 250 or less, and may be 220 or less, 200 or less, 185 or less, 165 or less, 150 or less (e.g., less than 150), 140 or less, or 130 or less (e.g., 125 or less). The molecular weight of the phosphite ester as a silica residual reducing agent is suitably 250 or less, and may be 200 or less, 160 or less, 150 or less (e.g., less than 150), or 145 or less. The molecular weight of the organic phosphonic acid compound as a silica residual reducing agent is suitably 500 or less, and may be 400 or less, 350 or less, 320 or less, or about 300. The lower limit of the molecular weight is approximately 100 or more, and may be, for example, 200 or more, 250 or more, or 280 or more.

[0068] The content of the silica residue-reducing agent in the polishing composition disclosed herein can be an appropriate amount that can achieve the silica residue-reducing effect without impairing processability, and may vary depending on the type, so it is not limited to a specific range. The content can be approximately 0.001 mM (mmol / L) or more, and is preferably approximately 0.01 mM or more. From the perspective of better demonstrating the silica residue-reducing effect, the content may be approximately 0.1 mM or more, approximately 0.3 mM or more, approximately 0.5 mM or more, approximately 1 mM or more, or approximately 2 mM or more. In some embodiments, the content of the silica residue-reducing agent may be approximately 5 mM or more, approximately 8 mM or more, or approximately 10 mM or more. A polishing composition containing approximately 15 mM or more (e.g., 18 mM or more, or even 22 mM or more) of the silica residue-reducing agent tends to easily achieve the silica residue-reducing effect while improving processability. The upper limit of the content of the silica residual reducing agent can be, for example, about 300 mM or less, suitably about 100 mM or less, may be about 50 mM or less, may be about 30 mM or less, or may be less than 15 mM. According to the technology disclosed herein, the desired effect can be achieved by adding a small amount of silica residual reducing agent, so the upper limit of the content of the silica residual reducing agent may be less than 10 mM, less than 7 mM, less than 5 mM, or less than 3 mM.

[0069] (Water-soluble polymer (A)) In some preferred embodiments, the polishing composition disclosed herein contains a water-soluble polymer (A). Use of the water-soluble polymer (A) can simultaneously reduce polishing resistance and improve processability. The reason for this is believed to be as follows: It is presumed that the water-soluble polymer (A) is adsorbed to each interface of the polishing field, such as a polishing pad or Ni-P substrate, promotes the diffusion of abrasive components, and promotes surface modification in a direction that alleviates polishing stress. 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.

[0070] The water-soluble polymer (A) disclosed herein is typically a polymer produced by polymerization of a monomer and has a plurality of monomer units derived from the monomer. In the polymer, the monomer units are also referred to as repeating units. The monomer units of the water-soluble polymer (A) refer to structural units derived from the monomers used in the synthesis of the water-soluble polymer (A), and have a structure corresponding to the monomers after incorporation into the polymer.

[0071] Although not particularly limited, vinyl monomers are preferably used as monomers for synthesizing the water-soluble polymer (A). Here, the vinyl monomer is a compound having a vinyl group with radical polymerizability. The water-soluble polymer (A) is preferably obtained by copolymerizing two or more vinyl monomers.

[0072] The water-soluble polymer (A) may contain one type of monomer unit alone or two or more types in combination. The monomers forming the monomer units are not particularly limited, but examples thereof include carboxylic acid group-containing monomers, sulfonic acid group-containing monomers, and amide group-containing monomers (e.g., (meth)acrylamide). Note that (meth)acryl refers to acrylic and methacrylic in a comprehensive sense.

[0073] Examples of monomers that form the monomer units include amide group-containing monomers (for example, N,N-dialkyl(meth)acrylamides, N-monoalkyl(meth)acrylamides), aromatic vinyl monomers (styrene, vinylnaphthalene, etc.), and the like.

[0074] Suitable examples of the monomer include acrylic acid, methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, N-tert-butylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N,N-dipropylacrylamide, N,N-diisopropylacrylamide, N,N-dibutylacrylamide, and styrene.

[0075] Although not particularly limited, the weight-average molecular weight (Mw) of the water-soluble polymer (A) is typically, for example, approximately 2,000 or more, and may be 4,000 or more. In some preferred embodiments, the Mw is 5,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, and particularly preferably 12,000 or more. In some embodiments, the Mw of the water-soluble polymer (A) may be 100,000 or less (e.g., less than 100,000), or may be 70,000 or less. In some preferred embodiments, the Mw is 50,000 or less, 30,000 or less, 20,000 or less, or 15,000 or less. By using a water-soluble polymer (A) having an appropriate Mw within the above range, it is possible to preferably achieve both reduced polishing resistance and improved processability.

[0076] The Mw of the water-soluble polymer (A) can be determined by aqueous gel permeation chromatography (GPC). Measurement can be carried out, for example, under the following conditions. [GPC measurement conditions] Equipment: Tosoh HLC-8320GPC Column: Tosoh TSKgel GMPWxL Eluent: 0.1N sodium nitrate Flow rate: 0.5mL / min Temperature: 40℃ Detection: Differential refractive index detector Sample: 0.1 wt% (injection volume 100 μL) Standard samples: PEG and PEO with known molecular weights

[0077] The method for obtaining the water-soluble polymer (A) is not particularly limited, and various polymerization methods known as methods for synthesizing water-soluble polymers can be appropriately employed. For example, aqueous solution polymerization is preferably employed. The solvent (polymerization solvent) used in aqueous solution polymerization is an aqueous solvent (typically water), which may contain an appropriate amount of alcohols such as isopropyl alcohol or ketones such as acetone in addition to water. The initiator used in the polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method. For example, radical polymerization initiators such as azo-based polymerization initiators and peroxide-based polymerization initiators are preferably used. A water-soluble redox-based polymerization initiator may also be used as the polymerization initiator. The amount of the polymerization initiator used can be a normal amount depending on the polymerization method and polymerization mode, and is not particularly limited. For example, the amount of the polymerization initiator can be within the range of approximately 0.001 to 15 parts by weight (preferably approximately 0.01 to 10 parts by weight, e.g., approximately 0.1 to 10 parts by weight) per 100 parts by weight of all monomer components to be polymerized. An appropriate amount of chain transfer agent may be added during polymerization for the purpose of controlling molecular weight, etc. The polymerization temperature can be appropriately selected depending on the types of monomers and solvents used, the type of polymerization initiator, etc., and can be, for example, about 60°C to 100°C. The polymerization time is preferably within a range of about 2 to 20 hours (e.g., 3 to 10 hours). After the polymerization reaction, neutralization with a basic compound may be carried out as necessary.

[0078] The concentration of the water-soluble polymer (A) in the polishing composition is not particularly limited. In some embodiments, the concentration is, for example, 0.0001% by weight or more, and may be 0.0005% by weight or more. From the viewpoint of effectively exhibiting the effects of containing the water-soluble polymer (A), in some preferred embodiments, the concentration is 0.001% by weight or more, may be 0.005% by weight or more, may be 0.01% by weight or more, may be 0.02% by weight or more, or may be 0.03% by weight or more. In some embodiments, the concentration of the water-soluble polymer (A) is suitably 3% by weight or less, and may be 2% by weight or less. From the viewpoint of processability and post-polishing washability, in some preferred embodiments, the concentration of the water-soluble polymer (A) is 1% by weight or less (e.g., less than 1% by weight), more preferably 0.2% by weight or less, even more preferably 0.1% by weight or less (e.g., less than 0.1% by weight), may be 0.07% by weight or less, or may be 0.05% by weight or less.

[0079] The amount of water-soluble polymer (A) contained in the polishing composition can also be determined by its relative relationship to the abrasive grains contained in the polishing composition. In some embodiments, the content of water-soluble polymer (A) relative to 100 parts by weight of abrasive grains contained in the polishing composition is, for example, 0.001 parts by weight or more, preferably 0.01 parts by weight or more, more preferably 0.1 parts by weight or more, even more preferably 0.5 parts by weight or more, and may even be 1 part by weight or more. In some embodiments, the content of water-soluble polymer (A) relative to 100 parts by weight of abrasive grains is approximately 10 parts by weight or less, preferably 5 parts by weight or less, more preferably 3 parts by weight or less, even more preferably 2 parts by weight or less, and may even be 1.5 parts by weight or less. By using an appropriate amount of water-soluble polymer (A) relative to the amount of abrasive grains, it is possible to preferably achieve both reduced polishing resistance and improved processability.

[0080] (water) The polishing composition disclosed herein typically contains water. 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.

[0081] 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.

[0082] (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.

[0083] 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.

[0084] 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.

[0085] The polishing composition disclosed herein may contain a water-soluble polymer (hereinafter also referred to as "optional water-soluble polymer") as an optional component. The optional water-soluble polymer does not include those that fall under the category of water-soluble polymer (A). By including the optional water-soluble polymer, the surface quality after polishing can be improved. Examples of the optional water-soluble polymer include polyalkylarylsulfonic acid compounds such as naphthalenesulfonic acid formaldehyde condensates, methylnaphthalenesulfonic acid formaldehyde condensates, and anthracenesulfonic acid formaldehyde; ligninsulfonic acid compounds such as ligninsulfonic acid and modified ligninsulfonic acid; and others, such as polyisoprene sulfonic acid, polyvinylsulfonic acid, polyallylsulfonic acid, polyisoamylenesulfonic acid, polystyrene sulfonates, polyacrylates, polyvinyl acetate, polymaleic acid, polyitaconic acid, polyvinyl alcohol, polyglycerin, copolymers of isoprene sulfonic acid and acrylic acid, carboxymethylcellulose, salts of carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and pullulan. The water-soluble polymers can be used alone or in combination of two or more.

[0086] In embodiments using any water-soluble polymer, the content of the water-soluble polymer in the polishing composition can be appropriately set within a range that does not significantly impair the effects of the present invention. Furthermore, the polishing composition disclosed herein can be implemented in an embodiment that is substantially free of any water-soluble polymer. From this perspective, in embodiments in which the polishing composition contains any water-soluble polymer and embodiments in which the polishing composition is substantially free of any water-soluble polymer, the proportion of the water-soluble polymer in the total water-soluble polymer (including the water-soluble polymer (A)) contained in the polishing composition may be 80% by weight or less, 50% by weight or less (e.g., less than 50% by weight), 30% by weight or less, 20% by weight or less, 10% by weight or less, or 5% by weight or less (e.g., 0 to 5% by weight).

[0087] Examples of dispersants include polycarboxylic acid-based dispersants such as sodium polycarboxylic acid salts, naphthalenesulfonic acid-based dispersants such as sodium naphthalenesulfonic acid salts, alkylsulfonic acid-based dispersants, polyphosphoric acid-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.

[0088] 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, phosphates, hydrogenphosphates, organic acid salts, etc. The basic compounds can be used alone or in combination of two or more.

[0089] (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.

[0090] (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.

[0091] (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.

[0092] <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.

[0093] 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.

[0094] 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).

[0095] <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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] The matters disclosed by this specification include the following: [1] A polishing composition for magnetic disk substrates, comprising: The polishing agent contains silica particles as abrasive grains, an acid, and an oxidizing agent, The silica particles are: The minimum peak diameter D in the weight-based particle size distribution obtained by the light transmission centrifugal sedimentation method pminis greater than 80 nm and less than or equal to 200 nm; and The above minimum peak diameter D pmin The cumulative 99% particle diameter D in the weight-based particle size distribution obtained by the light transmission centrifugal sedimentation method 99 The ratio (D 99 / D pmin ) is greater than 1.40 and not greater than 5.50. [2] The silica particles have a minimum peak diameter D pmin The average particle diameter D in the weight-based particle size distribution obtained by the light transmission centrifugal sedimentation method mean The ratio (D mean / D pmin ) is greater than 0.70 and not greater than 1.75. [3] The polishing composition according to [1] or [2] above, further comprising a nitrogen-containing compound. [4] The polishing composition according to any one of [1] to [3] above, which contains at least one selected from the group consisting of phosphate esters, phosphite esters, and organic phosphonic acid compounds. [5] The polishing composition according to any one of [1] to [4] above, further comprising a water-soluble polymer (A). [6] 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 [1] to [5] above. [7] A method for polishing a substrate, comprising the step of supplying the polishing composition according to any one of [1] to [6] above to a substrate to be polished and polishing the substrate. [Example]

[0105] 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.

[0106] <Test Example 1> <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. Polishing compositions according to Examples 8 to 14 were prepared by mixing silica abrasive grains, a nitrogen-containing compound shown in Table 1, phosphoric acid, 31% hydrogen peroxide solution, and deionized water. The pH of each of the polishing compositions was 1.5. As the silica abrasive grains, several types of silica particles with different particle diameters, particle shapes, and particle size distributions were prepared, and D pmin , D mean , D 99 , ratio (D mean / D pmin ) and ratio (D 99 / D pmin Abrasive grains containing the above silica particles alone or in combination were used so that the solubility (%) of silica particles varied within a predetermined range. The concentration of silica particles in the polishing composition was 7 wt %, the concentration of the nitrogen-containing compound (if present) was 0.2 g / L, the phosphoric acid concentration was 0.1 mol / L, and the hydrogen peroxide concentration was 0.5 mol / L. In Table 1, "AEEA" stands for "2-(2-aminoethylamino)ethanol" and "BTA" stands for "1,2,3-benzotriazole."

[0107] Abrasive grain D pmin , D mean and D 99 was determined from the particle size distribution on a weight basis obtained by a light transmission centrifugal sedimentation method.

[0108] The specific measurement method was as follows. Abrasive grains were dispersed in ion-exchanged water to prepare an abrasive grain dispersion for measurement. A disk centrifugal particle size distribution analyzer "DC24000 UHR" manufactured by CPS Instruments, USA, was used to determine the particle size distribution on a weight basis in accordance with JIS Z 8823-2. The particle size distribution measurement was carried out under the conditions shown below. [Measurement conditions] Test solution introduced into the cell: Sucrose aqueous solution with a minimum concentration of 8% by weight and a maximum concentration of 24% by weight Amount of test solution injected into the cell: 12 mL Abrasive concentration of the abrasive dispersion for measurement: 2% by weight Amount of abrasive dispersion liquid injected for measurement: 0.1 mL Disk rotation speed: 24000 rpm Measurement range: 0.025μm to 1.0μm

[0109] <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.

[0110] [Polishing conditions] Polishing equipment: Taiyo Co., Ltd. double-sided polishing machine, model "9B-5P / 3WAY" 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

[0111] (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 value, the higher the processability. When the polishing rate (relative value) is 105% or higher, the processability is determined to be improved. 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

[0112] (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 "NEWVIEW9000" under conditions of an objective lens magnification of 2.75x, 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 being 100%, and are shown in the "Microwaviness" column in Table 1. The smaller the value, the more suppressed the microwaviness. When the microwaviness (relative value) is 125% or less, it is determined that a low microwaviness is maintained.

[0113] (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. The higher the "Rate / Waviness Ratio," the better the balance between high processability and low microwaviness.

[0114] [Table 1]

[0115] As shown in Table 1, the minimum peak diameter D pmin is greater than 80 nm and less than 200 nm, and the minimum peak diameter D pmin and cumulative 99% particle diameter D 99 The ratio (D 99 / D pmin According to the polishing compositions of Examples 1 to 14 using silica particles having a D pmin and the ratio (D 99 / D pmin ) was used in the polishing compositions of Comparative Examples 1 to 9, which used silica particles having at least one of the above ranges. It was also confirmed that the polishing compositions of Examples 8 to 14, which contained various nitrogen-containing compounds, tended to reduce microwaviness and improve the polishing rate / waviness ratio compared to the polishing composition of Example 4, which did not contain a nitrogen-containing compound.

[0116] <Test Example 2> <Preparation of Polishing Composition> Polishing compositions according to Examples 15 to 20 were prepared by mixing silica abrasive grains, a silica residue reducing agent shown in Table 2, phosphoric acid, 31% hydrogen peroxide solution, and deionized water. A polishing composition according to Example 4 of Test Example 1 was also prepared. The pH of each of the polishing compositions was 1.5. The same silica particles as used in Example 4 were used as the silica abrasive grains. The concentration of the silica particles in the polishing composition was 7 wt %, the concentration of the silica residue reducing agent was 10 mmol / L, the phosphoric acid concentration was 0.1 mol / L, and the hydrogen peroxide concentration was 0.5 mol / L. Note that "HEDP" in Table 2 stands for "1-hydroxyethylidene-1,1-diphosphonic acid."

[0117] <Polishing> The polishing composition according to each example was used as a polishing liquid as it was, and an object to be polished was polished under the same conditions as in Test Example 1.

[0118] (Number of residual silica particles) The substrate polished under the above conditions was washed using a cleaning machine manufactured by CRESEN, and the number of silica particles remaining on the substrate surface was then measured. Specifically, the substrate was washed in running water under the following conditions without using a brush or cleaning agent, and water droplets adhering to the substrate were removed using a spin dryer, followed by drying. (Washing conditions) Cleaning agent application time: 0 seconds First wash time (running water only): 15 seconds Second wash time (running water only): 20 seconds Ultrasonic cleaning time (running water only): 20 seconds Spin dry time: 20 seconds Next, using a scanning electron microscope "SU8000" manufactured by Hitachi High-Technologies Corporation, the surfaces (both sides) of the substrate after cleaning were observed at a magnification of 50,000 times, with 10 visual fields per side. Then, using image analysis software "WinROOF" manufactured by Mitani Shoji Co., Ltd., the number of residual silica particles in each visual field was measured, and the average number of residual silica particles per visual field was calculated. The obtained values ​​are shown in the "Silica Residue" column in Table 2 as relative values, with the number of residual silica particles in Example 4 taken as 100%.

[0119] [Table 2]

[0120] As shown in Table 2, it was confirmed that the polishing compositions of Examples 15 to 20, which used various silica residue-reducing agents, reduced silica residue compared to the polishing composition of Example 4, which did not use a silica residue-reducing agent. Although not shown in the table, the polishing compositions of Examples 15 to 20 exhibited removal rates, microwaviness, and rate / waviness ratios that were comparable to those of the polishing composition of Example 4 (for example, approximately ±5%).

[0121] <Test Example 3> <Preparation of Polishing Composition> Polishing compositions according to Examples 21 to 24 were prepared by mixing silica abrasive grains, a water-soluble polymer (A) shown in Table 3, phosphoric acid, 31% aqueous hydrogen peroxide, and deionized water. A polishing composition according to Example 4 of Test Example 1 was also prepared. The pH of each of the polishing compositions was 1.5. The same silica particles as used in Example 4 were used as the silica abrasive grains. The concentration of the silica particles in the polishing composition was 7 wt %, the concentration of the water-soluble polymer (A) was 0.02 wt %, the phosphoric acid concentration was 0.1 mol / L, and the hydrogen peroxide concentration was 0.5 mol / L. The weight-average molecular weight Mw of the water-soluble polymer (A) used in each example was 1×10 4 It was.

[0122] The water-soluble polymer (A) used in Example 21 was a polymer of monomer components containing acrylic acid and diethylacrylamide in a molar ratio of 85:15. The water-soluble polymer (A) used in Example 22 was a polymer of monomer components containing acrylic acid and diethylacrylamide in a molar ratio of 95:5. The water-soluble polymer (A) used in Example 23 was a polymer of monomer components containing acrylic acid and styrene in a molar ratio of 90:10. The water-soluble polymer (A) used in Example 24 was a polymer of monomer components containing acrylic acid and dimethylacrylamide in a molar ratio of 85:15.

[0123] <Polishing> The polishing composition according to each example was used as a polishing liquid as it was, and an object to be polished was polished under the same conditions as in Test Example 1.

[0124] (polishing 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 "maximum" value was determined by arithmetically averaging the maximum values ​​of the motor load (motor torque) applied to the upper and lower plates during polishing. Furthermore, the "average" value was determined by arithmetically averaging the average values ​​of the motor torques for the upper and lower plates over a 50-second period from 150 seconds to 200 seconds after the start of polishing. The "maximum" and "average" values ​​were measured as the polishing resistance. The obtained values ​​were then converted to relative values, with the value of Example 4 being 100, and are shown in the "maximum (relative value)" and "average (relative value)" columns of "polishing resistance" in Table 3.

[0125] [Table 3]

[0126] As shown in Table 3, the polishing compositions of Examples 21 to 24, which used various water-soluble polymers (A), were able to reduce polishing resistance and improve processability compared to the polishing composition of Example 4, which did not use a water-soluble polymer (A). Although not shown in the table, the polishing compositions of Examples 21 to 24 exhibited removal rates, microwaviness, and rate / waviness ratios that were comparable to those of the polishing composition of Example 4 (for example, approximately ±5%).

[0127] 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 polishing agent contains silica particles as abrasive grains, an acid, and an oxidizing agent, The silica particles include: The minimum peak diameter D in the weight-based particle size distribution obtained by the light transmission centrifugal sedimentation method ｐｍｉｎ is greater than 80 nm and less than or equal to 200 nm; and The minimum peak diameter D ｐｍｉｎ The cumulative 99% particle diameter D in the weight-based particle size distribution obtained by the light transmission centrifugal sedimentation method ９９ The ratio (D ９９ / D ｐｍｉｎ ) is greater than 1.40 and not greater than 5.

50.

2. The silica particles have a minimum peak diameter D ｐｍｉｎ Average particle diameter D in the weight-based particle size distribution obtained by the light transmission centrifugal sedimentation method ｍｅａｎ The ratio (D ｍｅａｎ / D ｐｍｉｎ 2. The polishing composition according to claim 1, wherein the value of (a) is greater than 0.70 and less than or equal to 1.

75.

3. The polishing composition according to claim 1 or 2, further comprising a nitrogen-containing compound.

4. 3. The polishing composition according to claim 1, wherein the polishing composition comprises at least one selected from the group consisting of phosphate esters, phosphites, and organic phosphonic acid compounds.

5. The polishing composition according to claim 1 or 2, further comprising a water-soluble polymer (A).

6. A method for producing a magnetic disk substrate, comprising a step of polishing a substrate to be polished with the polishing composition according to claim 1 or 2.

7. 3. A method for polishing a substrate, comprising the step of supplying the polishing composition according to claim 1 to a substrate to be polished and polishing the substrate.

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