Polishing composition, method for manufacturing a substrate, and polishing method

Abstract

The objective is to provide a polishing composition for polishing magnetic disk substrates that contains silica abrasive particles and can achieve both the maintenance of low minute waviness and improved machinability. [Solution] A composition for polishing magnetic disk substrates is provided. This polishing composition comprises silica particles as abrasive grains, an acid, and an oxidizing agent. Here, the silica particles have a volume-based aspect ratio distribution in which the cumulative 25% aspect ratio is 1.30 or less, and the cumulative 75% aspect ratio is 1.20 or more and 3.00 or less.

Description

[Technical Field]

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

[0002] Conventionally, the manufacturing process for magnetic disk substrates requiring high-precision surfaces includes a step of polishing the raw material of the substrate using a polishing solution. For example, in the manufacturing of nickel-phosphorus plated disk substrates (hereinafter also referred to as Ni-P substrates), polishing is generally performed with an emphasis on polishing efficiency (primary polishing), and final polishing is performed to achieve the surface accuracy of the final product (finishing polishing). Patent documents 1 and 2 are technical documents relating to polishing compositions used for polishing magnetic disk substrates. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2017 / 094592 [Patent Document 2] Japanese Patent Publication No. 2023-174608 [Overview of the project] [Problems that the invention aims to solve]

[0004] In the polishing of magnetic disk substrates, efforts to improve the quality of the substrate surface are continuously being made to increase recording capacity. In recent years, in order to achieve a higher quality substrate surface after finish polishing, silica abrasive grains have been used instead of alumina abrasive grains from the initial polishing stage. Polishing with silica abrasive grains does not cause the abrasive grains to penetrate the substrate, resulting in superior reduction of defects such as scratches and making it easier to obtain high surface quality. On the other hand, polishing with silica abrasive grains does not yield the same processing power as alumina abrasive slurry, making it a challenge to improve processing power. Furthermore, in addition to maintaining and improving processing power, polishing with silica abrasive grains also presents the challenge of increasing minute waviness on the substrate after polishing. In the polishing described above, processing power and minute waviness are in a conflicting relationship, and improving one will worsen the other, making it difficult to achieve both.

[0005] The inventors, after diligent research, focused on polishing vibration as a factor hindering the improvement of processability. By using a combination of silica abrasive grains having a specific aspect ratio distribution, an acid, and an oxidizing agent, they succeeded in creating a polishing composition that can improve processability while suppressing the increase of minute undulations by suppressing excessive polishing vibrations and exhibiting appropriate polishing action, thereby completing the present invention. In other words, the present invention aims to provide a polishing composition containing silica abrasive grains that can achieve both the maintenance of low minute undulations and improved processability in the polishing of magnetic disk substrates. Another related object is to provide a method for manufacturing a substrate and a polishing method using the above polishing composition. Further related objects are to provide a polishing composition that can achieve at least one of the following: reduction of silica residue and reduction of polishing resistance, while simultaneously maintaining low minute undulations and improving processability, and to provide a method for manufacturing a substrate and a polishing method using the polishing composition. [Means for solving the problem]

[0006] The magnetic disk substrate polishing composition provided herein comprises silica particles as abrasive grains, an acid, and an oxidizing agent. The silica particles have a volume-based aspect ratio distribution in which the cumulative 25% aspect ratio (A25) is 1.30 or less, and the cumulative 75% aspect ratio (A75) is 1.20 or more and 3.00 or less. A polishing composition containing abrasive grains satisfying the above characteristics can achieve both the maintenance of low minute undulations and improved machinability by exhibiting appropriate polishing action while suppressing excessive polishing vibrations during the polishing of magnetic disk substrates.

[0007] In some embodiments, the average secondary particle diameter based on volume, as determined by scanning electron microscope (SEM) image analysis of the above-mentioned silica particles, is 350 nm or less. When silica particles having a specific aspect ratio distribution and the above-mentioned average secondary particle diameter of 350 nm or less, as determined by SEM image analysis, are used, it is easier to achieve both low micro-undulation and improved processability in the polishing of magnetic disk substrates by suppressing excessive polishing vibrations while exhibiting appropriate polishing action.

[0008] In some embodiments, the number-based abundance of silica particles in which the particle size ratio obtained by dividing the circumference equivalent diameter by the Heywood diameter is 1.40 or less is 65% or more of the total silica particles. Particles with a particle size ratio obtained by dividing the circumference equivalent diameter by the Heywood diameter is 1.40 or less tend to contribute to both maintaining low minute waviness and improving processability. Therefore, using silica particles in which the abundance of particles exhibiting the above-mentioned predetermined particle size ratio is 65% or more makes it easier to achieve both maintaining low minute waviness and improving processability in the polishing of magnetic disk substrates.

[0009] In some embodiments, the polishing composition further comprises a nitrogen-containing compound. By using the nitrogen-containing compound, micro-swelling is more easily improved. In some embodiments, the nitrogen-containing compound is at least one selected from ammonia and nitrogen-containing organic compounds. Among these, 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 comprising a carbon skeleton having 2 to 4 carbon atoms, consisting of a single bond bonded to at least one of the nitrogen atoms contained in the 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 in improving micro-swelling.

[0010] In some embodiments, the polishing composition further comprises at least one selected from the group consisting of phosphate esters, phosphite esters, and organic phosphonic acid compounds. With such a configuration, the phenomenon of silica particles adhering to and remaining on the substrate surface after polishing (hereinafter also referred to as "silica residue" or "silica buildup") can be reduced without impairing workability. In some embodiments, the phosphate ester and / or phosphite ester have an organic group linked by its phosphate ester bond, and the organic group is selected from organic groups having 6 or fewer carbon atoms, which may contain an ether bond.

[0011] In some embodiments, the polishing composition further comprises a water-soluble polymer. This configuration makes it easier to reduce the polishing resistance (frictional force) between the polishing pad and the workpiece. Reducing polishing resistance is effective in suppressing excessive polishing vibration. Furthermore, if the polishing resistance between the workpiece and the polishing pad can be reduced during polishing, the load on the carrier can be alleviated, preventing or suppressing carrier deformation and preventing pad scratches.

[0012] In some embodiments, the polishing composition further comprises a glycol ether compound. With such a configuration, the effect of improving minute undulations is easily achieved.

[0013] This specification provides a method for manufacturing a magnetic disk substrate. The manufacturing method comprises a step (1) of polishing a substrate to be polished using one of the polishing compositions disclosed herein. According to this manufacturing method, a magnetic disk substrate having a high-quality surface can be manufactured productively. In some embodiments, the manufacturing method of the substrate further comprises a step (2) of polishing the substrate to be polished using a finishing polishing composition after step (1). The finishing polishing composition preferably contains colloidal silica. By performing step (2) after step (1), a magnetic disk substrate having an even higher-quality surface can be manufactured productively.

[0014] Furthermore, this specification provides a method for polishing a substrate. The polishing method comprises step (1) of supplying one 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 substrate polishing method further comprises step (2) of supplying a finishing polishing composition to the substrate to be polished and polishing the substrate after step (1). The finishing polishing composition preferably contains colloidal silica. By performing step (2) after step (1), a higher quality substrate surface can be obtained. [Modes for carrying out the invention]

[0015] Preferred embodiments of the present invention will be described below. Matters other than those specifically mentioned herein that are necessary for carrying out the present invention can be understood as design matters for those skilled in the art based on the prior art. The present invention can be carried out based on the contents disclosed herein and common technical knowledge in the art.

[0016] <Polishing composition> (Silica particles) The polishing compositions disclosed herein contain silica particles as abrasive grains. The silica particles may be in the form of secondary particles formed by the aggregation of multiple primary particles, or in the form of secondary particles formed by the association of multiple primary particles. Furthermore, silica particles in the form of primary particles and silica particles in the form of secondary particles may be mixed together.

[0017] (Aspect ratio distribution) The above-mentioned silica particles have a cumulative 25% aspect ratio (A25) of 1.30 or less in the volume-based aspect ratio distribution. In this invention, we have found that by focusing particularly on the A25 of the silica particles, it is possible to achieve both suppression of polishing vibration and improvement of the polishing rate. Here, "cumulative 25% aspect ratio" refers to the aspect ratio at the point where the cumulative volume from the side with the smallest aspect ratio reaches 25% in the cumulative volume distribution curve, where the total volume of the aspect ratio distribution of silica particles, determined on a volume basis, is 100%. The above-mentioned cumulative volume distribution curve is typically represented by a graph with the aspect ratio on the horizontal axis and the cumulative volume (%) on the vertical axis. When silica particles with a cumulative 25% aspect ratio (A25) of 1.30 or less are used, minute undulations tend to be reduced.

[0018] The reason for obtaining the above effects is not particularly limitedly interpreted, but can be considered as follows, for example. That the cumulative 25% aspect ratio (A25) in the aspect ratio distribution based on volume exceeds a predetermined value and is high means that many of the entire silica particles tend to be composed of particles with a high aspect ratio, that is, particles with a high degree of irregularity (the degree of distortion from a spherical shape; hereinafter the same). Thus, if the entire particles are composed only of particles with a high degree of irregularity, the polishing resistance applied between the polishing pad and the object to be polished tends to be high. When the polishing resistance exceeds a predetermined range and becomes high, excessive polishing vibration is likely to occur. That is, when the polishing resistance is high, the deformation of the polishing pad in the horizontal direction with respect to the rotation of the polishing table becomes large, and when the deformation amount exceeds a certain range, the polishing pad tries to return to its original shape. At this time, it is considered that the strain energy of the polishing pad is released and polishing vibration occurs. When excessive polishing vibration occurs, the processed area and the non-processed area of the particles with respect to the surface to be polished intermittently occur according to the vibration, that is, processing unevenness occurs, so that an appropriate polishing action cannot be exerted. When the cumulative 25% aspect ratio (A25) of the silica particles is 1.30 or less, since particles with a relatively low degree of irregularity exist at a certain ratio, an appropriate polishing action can be maintained without generating excessive polishing vibration during polishing. Also generally, particles with a low aspect ratio tend to contribute to reducing undulation. For these reasons, when the cumulative 25% aspect ratio (A25) of the silica particles is 1.3 or less, it is considered that suppression of reduction in processability and reduction in minute undulation are likely to be achieved.

[0019] The above silica particles also have a cumulative 75% aspect ratio (A75) in the volume-based aspect ratio distribution of 1.20 or more and 3.00 or less. Here, the "cumulative 75% aspect ratio" refers to the aspect ratio at the point where the cumulative volume from the side with a smaller aspect ratio becomes 75% in the cumulative volume distribution curve with the total volume of the aspect ratio distribution of silica particles determined on a volume basis being 100%. The above cumulative volume distribution curve is typically represented by a graph with the aspect ratio on the horizontal axis and the cumulative volume (%) on the vertical axis. When using silica particles with a cumulative 75% aspect ratio (A75) of 1.20 or more and 3.00 or less, the processability tends to improve.

[0020] The reason for obtaining the above effects is not particularly limited to an interpretation, but for example, it can be considered as follows. That the cumulative 75% aspect ratio (A75) in the volume-based aspect ratio distribution is lower than a predetermined value means that many of the entire silica particles tend to be composed of particles with a low degree of irregularity, that is, particles with a high degree of sphericity. Generally, particles with a high sphericity are likely to roll and move, so part of the stress generated by the friction between the particles and the polished surface is released by rolling and moving, and the processability tends to be inferior. For this reason, if the entire particles are composed only of particles with a high sphericity, it becomes difficult to obtain high processability. When the cumulative 75% aspect ratio (A75) of the silica particles is 1.20 or more, since there are a certain proportion of distorted particles with excellent processability, the processability tends to improve easily. On the other hand, when the aspect ratio of the particles becomes larger than 3.00, the particles become particles with a shape close to a rod shape, so they are likely to roll in the short diameter direction, and it tends to be difficult to obtain high processability. According to silica particles with a cumulative 75% aspect ratio (A75) of 3.00 or less, since the inclusion of particles having a rod shape that tends to reduce the processability is restricted, the reduction in processability is suppressed, and the polishing tends to be stabilized.

[0021] Note that the above explanation is the consideration of the inventor based on experimental results, and the technology disclosed here is not interpreted as being limited to the above mechanism.

[0022] From the viewpoint of improving machinability and reducing minute waviness, in some embodiments, A25 is preferably 1.25 or less, more preferably less than 1.20, and may also be 1.15 or less, 1.11 or less, 1.08 or less, or 1.06 or less. The lower limit of A25 is not particularly limited. In principle, A25 is 1 or more, and from the viewpoint of abrasive grain availability, it may be 1.01 or more, 1.02 or more, or 1.03 or more.

[0023] From the viewpoint of improving machinability, in some embodiments, A75 is preferably 1.22 or higher, more preferably 1.24 or higher, even more preferably 1.26 or higher, may also be 1.28 or higher, may also be 1.30 or higher, may also be 1.32 or higher, may also be 1.34 or higher, and may also be 1.45 or higher. Furthermore, from the viewpoint of suppressing a decrease in machinability and ensuring polishing stability, in some embodiments, A75 is preferably 2.70 or lower, more preferably 2.40 or lower, even more preferably 2.10 or lower, may also be 2.00 or lower, may also be 1.75 or lower, may also be 1.60 or lower, may also be 1.50 or lower, and may also be 1.40 or lower.

[0024] For the silica particles disclosed herein, the difference (A75-A25) between the cumulative 25% aspect ratio (A25) and the cumulative 75% aspect ratio (A75) in their volume-based aspect ratio distribution is not particularly limited. A large difference (A75-A25) indicates that particles located on the lower aspect ratio side tend to have greater sphericity, while particles located on the higher aspect ratio side tend to have greater irregularity. By using silica particles with a high difference (A75-A25), particles located on the lower aspect ratio side suppress the generation of excessive polishing vibrations, thereby suppressing a decrease in workability and contributing to the reduction of waviness, while particles located on the higher aspect ratio side contribute to improved workability. As a result, it is considered possible to achieve both the maintenance of low minute waviness and improved workability. From this viewpoint, the difference (A75-A25) is preferably greater than 0.15, more preferably 0.20 or greater, and may also be 0.25 or greater, 0.27 or greater, or 0.29 or greater. Furthermore, from the viewpoint of suppressing a decrease in machinability and the availability of abrasive grains, the above difference (A75-A25) is appropriate to be 2.10 or less, preferably 1.00 or less, and may also be 0.95 or less, 0.90 or less, or 0.31 or less.

[0025] For the silica particles disclosed herein, the ratio (A75 / A25) of the cumulative 75% aspect ratio (A75) to the cumulative 25% aspect ratio (A25) in their volume-based aspect ratio distribution is not particularly limited. A larger value of the above ratio (A75 / A25) means that particles located on the lower aspect ratio side tend to have greater sphericity, and particles located on the higher aspect ratio side tend to have greater irregularity. By using silica particles with a high above ratio (A75 / A25), particles located on the lower aspect ratio side suppress the generation of excessive polishing vibrations, thereby suppressing a decrease in workability and contributing to the reduction of waviness, while particles located on the higher aspect ratio side contribute to improved workability. As a result, it is considered possible to achieve both the maintenance of low minute waviness and improved workability. From this viewpoint, the above ratio (A75 / A25) is preferably greater than 1.14, more preferably 1.15 or higher, and may also be 1.20 or higher, 1.25 or higher, or 1.28 or higher. Furthermore, from the viewpoint of suppressing a decrease in machinability and the availability of abrasive grains, the above ratio (A75 / A25) is appropriate to be 2.50 or less, preferably 2.00 or less, more preferably 1.90 or less, and may also be 1.50 or less, 1.40 or less, or 1.30 or less.

[0026] The volume-based aspect ratio distribution of the silica particles described above can be adjusted by selecting and combining the silica particles used. For example, by mixing particles with a small aspect ratio with particles with a relatively large aspect ratio in an appropriate weight ratio, A25 and A75 in the aspect ratio distribution described above can be adjusted to the appropriate range disclosed herein.

[0027] In this specification, the cumulative volume aspect ratios that serve as the basis for A25 and A75 refer to the cumulative volume aspect ratio as understood as the overall characteristic of the silica particles contained in the polishing composition. Therefore, if the silica particles contained in the polishing composition are, for example, a mixture of two types of particles X and Y, the cumulative volume aspect ratio can be determined by measuring the aspect ratio and volume of the particles contained in the silica particles, using the silica particles as a mixture of particles X and Y as a measurement sample.

[0028] The specific procedure involves using a scanning electron microscope (SEM) to observe a predetermined number of 1000 or more particles contained in the silica particles to be measured (which may be a single type of silica particle or a mixture of two or more types of silica particles) in an SEM image containing 50 or more particles in one field of view. The observation magnification is set to 20,000 to 50,000 times. Then, for the smallest rectangle circumscribing each particle image, the ratio of the major axis to the minor axis (aspect ratio) of each particle is calculated by dividing the length of its long side (major axis) by the length of its short side (minor axis). Additionally, 4πr is calculated from the radius r of an ideal circle (true circle) having an area equal to the projected area of ​​each particle image. 3 The value obtained by / 3 is calculated as the volume of each particle. Here, the aspect ratio and volume are calculated by counting each independently dispersed particle in the polishing composition as one particle, regardless of whether it is a primary or secondary particle. Then, by deriving the cumulative volume distribution curve of the aspect ratio distribution from the aspect ratio and volume of the predetermined number of particles, the above-mentioned cumulative volume aspect ratio can be determined. Such cumulative volume aspect ratios can be determined using general image analysis software. Furthermore, the predetermined number of particles used to calculate the aspect ratio for each particle is usually appropriate to be 1,000 or more, and 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 above measurement, for example, a scanning electron microscope "SU8000" manufactured by Hitachi High-Technologies Corporation or image analysis type particle size distribution measurement software "Mac-View" manufactured by Mountec Co., Ltd. is used. The same applies to the embodiments described later.

[0029] The average particle diameter of the silica particles disclosed herein is not particularly limited. In some embodiments, from the viewpoint of reducing minute waviness, the average secondary particle diameter (D2) based on volume determined by scanning electron microscope (SEM) image analysis of the silica particles is appropriately approximately 350 nm or less, preferably 330 nm or less, and more preferably 300 nm or less. From the viewpoint of further reducing minute waviness, the average secondary particle diameter (D2) based on volume determined by SEM image analysis of the silica particles is more preferably 250 nm or less, more preferably 230 nm or less, and particularly preferably 200 nm or less. In some embodiments, the average secondary particle diameter (D2) based on volume determined by SEM image analysis of the silica particles is approximately 40 nm or more, appropriately approximately 70 nm or more, preferably 90 nm or more, more preferably 95 nm or more, and may be, for example, 100 nm or more, or 110 nm or more. By using such silica particles, it is desirable to achieve both high processability and low minute waviness.

[0030] The average secondary particle diameter (D2) of silica particles, determined by volume-based SEM image analysis, is calculated as follows: Using a scanning electron microscope (SEM), a predetermined number of particles (1000 or more) contained in the silica particles to be measured (which may be a single type of silica particle or a mixture of two or more types of silica particles) are observed in an SEM image containing 50 or more particles in one field of view. The observation magnification is set to 20,000 to 50,000 times. Then, 4πr is calculated from the radius r of an ideal circle (true circle) having an area equal to the projected area of ​​each particle image. 3 The value obtained by / 3 is calculated as the volume of each particle. Here, the volume is calculated by counting each independently dispersed particle in the abrasive composition as one particle, regardless of whether it is a primary or secondary particle. The average secondary particle diameter (D2) is obtained from the volume of the predetermined number of particles to obtain a volume-based particle size distribution, and is determined as the average particle diameter calculated from that volume-based distribution. Furthermore, the predetermined number of particles used to calculate the aspect ratio for each particle is usually appropriate to be 1,000 or more, and 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 above measurement, for example, a scanning electron microscope "SU8000" manufactured by Hitachi High-Technologies Corporation or image analysis type particle size distribution measurement software "Mac-View" manufactured by Mountec Co., Ltd. is used. The same applies to the embodiments described later.

[0031] Incidentally, one indicator of the degree of unevenness of a particle is the particle diameter ratio, which is obtained by dividing the equivalent circle diameter (hereinafter also called the "circumferential circle equivalent diameter"), which is calculated from the circumference of the particle, by the equivalent circle diameter (hereinafter also called the "Heywood diameter"), which has an area equal to the projected area. The larger the value of the above particle diameter ratio, the greater the unevenness of the particle, and the closer the value is to 1, the closer the shape of the particle is to a perfect sphere. Hereafter in this specification, unless otherwise specified, when "particle diameter ratio" is used, it refers to this "particle diameter ratio obtained by dividing the circumferential circle equivalent diameter by the Heywood diameter".

[0032] In some embodiments, the silica particles disclosed herein contain particles P having a particle diameter ratio of 1.40 or less in proportion to 65% or more of the total silica particles, on a number basis. That is, in some embodiments, the number basis abundance of particles P in the silica particles, where the particle diameter ratio obtained by dividing the circumference equivalent diameter by the Heywood diameter is 1.40 or less, is 65% or more of the total silica particles. Using silica particles with a particle abundance of the above particle diameter ratio within the above range makes it easier to maintain low minute waviness and improve processability. Hereinafter, in this specification, the number basis abundance ratio of particles with a particle diameter ratio within a predetermined range (e.g., 1.40 or less) in the total particles may be referred to as the "abundance rate of the predetermined particle diameter ratio." The lower limit of the particle diameter ratio of the above particles P is not particularly limited, but is typically 1 or more.

[0033] The reason why using silica particles in which the abundance of particles P with a particle size ratio of 1.40 or less is within the above range allows for both the maintenance of low micro-undulation and improved processability is not particularly limited, but can be understood as follows. That is, particles P with a particle size ratio of approximately 1.40 or less can exhibit high processing force due to having appropriate irregularities. On the other hand, if the particle size ratio becomes too large compared to 1.40, the particles tend to be easily broken by external forces, making it difficult to exhibit appropriate processing force. Therefore, it is considered that by using silica particles containing particles P with appropriate irregularities such as a particle size ratio of 1.40 or less at a ratio of approximately 65% ​​or more on a number basis, suitable processability can be obtained, and low micro-undulation can be suitably maintained.

[0034] In some embodiments, the abundance of particles P having a particle size ratio of 1.40 or less (typically 1 to 1.40) is more preferably 70% or more, may be 75% or more, 80% or more, 85% or more, 90% or more, or 92% or more. The upper limit of the abundance of particles P having a particle size ratio of 1.40 or less (typically 1 to 1.40) is not particularly limited and may be 100% or less, but from the viewpoint of availability, it may be 99% or less, 98% or less, or 95% or less.

[0035] The particle size ratio of silica particles, that is, the particle size ratio obtained by dividing the circumference equivalent diameter by the Heywood diameter, and the prevalence of a predetermined particle size ratio are determined by the following method. Specifically, a scanning electron microscope (SEM) is used to observe a predetermined number of particles (1000 or more) contained in the silica particles to be measured (which may be one type of silica particle or a mixture of two or more types of silica particles) in an SEM image containing 50 or more particles in one field of view. The observation magnification is set to 20,000 to 50,000 times. Then, using image analysis software, the outer circumference length of each particle is measured from the projected image of each particle, and the diameter of an ideal circle (true circle) having the same circumference length as the outer circumference length (circumference equivalent diameter) and the diameter of an ideal circle (true circle) having the same area as the projected area of ​​the particle (Heywood diameter) are determined. The particle size ratio of each particle is calculated by dividing the circumference equivalent diameter of each particle by the Heywood diameter. Here, the outer circumference length and projected area are measured or calculated by counting each independently dispersed particle in the polishing composition as one particle, regardless of whether it is a primary or secondary particle. The prevalence of a predetermined particle size ratio can be calculated by dividing the number of particles exhibiting a predetermined particle size ratio in the SEM image by the total number of particles. For the above measurement, for example, a scanning electron microscope "SU8000" manufactured by Hitachi High-Technologies Corporation or image analysis type particle size distribution measurement software "Mac-View" manufactured by Mountec Corporation is used. The same applies to the examples described later.

[0036] The silica particles are not particularly limited as long as they satisfy the predetermined cumulative 25% aspect ratio A25 and cumulative 75% aspect ratio A75, and various silica particles with silica as the main component can be used. Here, silica particles with silica as the main component refer to particles in which 90% or more by weight, for example 95% or more by weight, typically 98% or more by weight, is silica. Examples of silica particles that can be used are not particularly limited and include colloidal silica, condensed silica particles, precipitated silica (also called precipitated silica), sodium silicate silica, alkoxide silica, fumed silica, dried silica, explosion silica, etc. Furthermore, silica particles obtained using the above silica particles as raw materials can also be used. Examples of such silica particles may include silica particles obtained by applying one or more treatments selected from heat treatment such as heating, drying, and calcination, pressurization treatment such as autoclaving, mechanical treatment such as crushing and pulverization, and surface modification to the above raw material silica particles (hereinafter also referred to as "raw material silica"). 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 consist of one type of silica particle as described above, or a combination of two or more types.

[0037] The silica particle content in the polishing composition is not particularly limited, and may be, for example, 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more, even more preferably 3% by weight or more, and particularly preferably 5% by weight or more. The above content is the total content of multiple types of silica particles if multiple types are included. Higher processability tends to be obtained by increasing the silica particle content. From the viewpoint of surface smoothness of the substrate after polishing and polishing stability, the above content is appropriate at 30% by weight or less, preferably 25% by weight or less, more preferably 15% by weight or less, and even more preferably 10% by weight or less.

[0038] In the polishing compositions disclosed herein, the content of silica particles in the solid content of the polishing composition is preferably 90% by weight or more, 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 exhibiting the effects of the technology disclosed herein. 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.

[0039] The polishing compositions disclosed herein may preferably be carried out in a manner that substantially does not contain alumina particles. Examples of alumina particles include α-alumina particles. Such polishing compositions prevent quality degradation caused by the use of alumina particles. Quality degradation, as used herein, includes, for example, the occurrence of scratches and dents, alumina residue, and piercing defects. In this specification, "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. Polishing compositions in which the proportion of alumina particles is 0% by weight, i.e., polishing compositions that do not contain alumina particles, are particularly preferred. Furthermore, the polishing compositions disclosed herein may preferably be carried out in a manner that substantially does not contain α-alumina particles.

[0040] The polishing compositions disclosed herein can preferably be implemented in a manner that substantially does not contain particles other than silica particles, i.e., non-silica particles. Here, "substantially free of non-silica particles" means that the proportion of non-silica particles in the total solid content of the polishing composition is 1% by weight or less, more preferably 0.5% by weight or less, and typically 0.1% by weight or less. In such a manner, the effects of the technology disclosed herein can be suitably demonstrated.

[0041] (nitrogen-containing compounds) In some embodiments, the polishing compositions disclosed herein contain a nitrogen-containing compound. The nitrogen-containing compound contained in the polishing composition adsorbs to the magnetic disk substrate during polishing, protecting the substrate and thus eliminating surface irregularities, thereby improving minute undulations. The number of nitrogen atoms contained in one molecule of the nitrogen-containing compound is not particularly limited, but nitrogen-containing compounds having 1 to 4 nitrogen atoms per molecule are preferably used. From the viewpoint of reducing minute undulations, the number of nitrogen atoms contained in one molecule of the nitrogen-containing compound is more preferably 2 to 4, even more preferably 2 or 3, and particularly preferably 2. The nitrogen-containing compound can be used alone or in combination of two or more.

[0042] In some embodiments, it is preferable to use a nitrogen-containing compound having a structure that includes a carbon skeleton consisting of a single bond bonded to at least one nitrogen atom in a single molecule, and a hydrophilic group to which the carbon skeleton is bonded. The carbon skeleton is bonded to the nitrogen atom by a single bond and is composed of carbon-carbon single bonds. Nitrogen-containing compounds contribute to reducing minute waviness by adsorption to the magnetic disk substrate, but on the other hand, adsorption to the substrate can be a factor that reduces processability. A nitrogen-containing compound having a structure in which a single-bonded carbon skeleton bonded to a nitrogen atom and a hydrophilic group bonded to the carbon skeleton has a structure in which a hydrophilic group is bonded to a freely rotating carbon skeleton, so it is thought that it can spread easily in the liquid during polishing and be adsorbed onto the surface of the magnetic disk substrate in a three-dimensional structure. Nitrogen-containing compounds that can be adsorbed three-dimensionally onto the substrate in this manner are more easily removed from the substrate surface by physical actions during polishing and cleaning compared to those that are adsorbed planarly. In particular, they are preferably removed by silica particles having a predetermined particle size distribution. Therefore, it is believed that the decrease in processability due to the adsorption of nitrogen-containing compounds onto the substrate can be better suppressed, and furthermore, while maintaining or improving processability, minute waviness can be improved. It should be noted that the above mechanism is the inventor's consideration based on experimental results, and the technology disclosed herein is not to be interpreted as being limited to the above mechanism.

[0043] In a nitrogen-containing compound having the above-described carbon skeleton and hydrophilic group structure, the number of carbon atoms 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 in the carbon skeleton is appropriately 10 or less, for example, it may be 6 or less, preferably 4 or less, more preferably 3 or less, and even more preferably 2. Furthermore, the carbon skeleton may consist of carbon-carbon single bonds that can rotate freely in liquid, and may have substituents other than hydrophilic groups. In some embodiments, a nitrogen-containing compound containing a carbon skeleton without substituents other than hydrophilic groups is preferably used. 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, carboxyl groups, etc. From the viewpoint of removal from the substrate, it is preferable that the hydrophilic groups bonded to the carbon skeleton are bonded to at least the ends of the carbon skeleton. The number of hydrophilic groups bonded to a single carbon skeleton is not particularly limited, for example, 1 to 3, and 1 or 2 is preferred.

[0044] In the nitrogen-containing compound having the above-described carbon skeleton and hydrophilic group structure, the number of carbon skeletons bonded to a single nitrogen atom is 1 to 3, preferably 2. Typical examples of carbon skeletons and hydrophilic groups bonded to the carbon skeleton include, for example, hydroxyalkyl groups and alkylamino groups. Preferred examples of the above-described nitrogen-containing compound include a compound having a structure in which one or more (specifically, 1, 2, or 3) hydroxyalkyl groups are bonded to a nitrogen atom, a compound having a structure in which one or more (specifically, 1, 2, or 3) alkylamino groups are bonded to a nitrogen atom, and a compound having a structure in which at least one hydroxyalkyl group and at least one alkylamino group are bonded to a nitrogen atom. Among these, compounds having a structure in which the above-described hydroxyalkyl group and alkylamino group are bonded to a nitrogen atom are particularly preferred.

[0045] As nitrogen-containing compounds, ammonia and nitrogen-containing organic compounds can be used. Among these, nitrogen-containing organic compounds such as organic amines are preferred. As nitrogen-containing organic compounds, aliphatic amine compounds, alicyclic amine compounds, and nitrogen-containing heterocyclic aromatic compounds can all be used. Among 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 an aromatic ring containing nitrogen atoms (e.g., a pyrazine skeleton) or nitrogen-containing organic compounds that do not have a guanidine skeleton are preferably used. Examples of nitrogen-containing organic compounds having such structures include aliphatic amine compounds and alicyclic amine compounds. Such nitrogen-containing organic compounds are thought to protect the substrate by adsorption to the substrate, and are considered to be more easily removed from the substrate by silica particles having a predetermined particle size distribution compared to nitrogen-containing heterocyclic aromatic compounds and compounds having a guanidine skeleton. The above amine compounds can be primary amines, secondary amines, or tertiary amines, and those having the form of a secondary amine are preferably used.

[0046] Examples of aliphatic amine compounds 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; and Examples include diamines such as 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-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-containing diamines are preferred, and 2-(2-aminoethylamino)ethanol is more preferred.

[0047] Examples of alicyclic amine compounds include piperazines; 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.

[0048] 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-benzotriazole-1-yl)methyl]imino]bisethanol; imidazoles; and others. Among these, 2,2′-[[(methyl-1H-benzotriazole-1-yl)methyl]imino]bisethanol is preferred.

[0049] Other nitrogen-containing compounds include ammonia, quaternary ammonium compounds, guanidine, and the like.

[0050] The molecular weight of the nitrogen-containing compound is 17.03 or higher than that of ammonia. Although not particularly limited, from the viewpoint of reducing minute waviness, in some embodiments, the molecular weight of the nitrogen-containing compound is 50 or higher, 60 or higher is appropriate, 80 or higher is preferred, 100 or higher is more preferred, it may be 120 or higher, or 140 or higher. Furthermore, from the viewpoint of processability, in some embodiments, the molecular weight of the nitrogen-containing compound is 500 or less, 300 or less is preferred, 200 or less is more preferred, 150 or less is even more preferred, and it may be 130 or less.

[0051] The content of the nitrogen-containing compound in the polishing composition is not particularly limited, but from the viewpoint of effectively exhibiting the effect of adding the nitrogen-containing compound, in some embodiments it is appropriate to set it to, for example, 0.001 g / L or more, preferably 0.01 g / L or more, more preferably 0.05 g / L or more, even more preferably 0.10 g / L or more, particularly preferably 0.15 g / L or more, and most preferably 0.17 g / L or more. Also, in some embodiments from the viewpoint of maintaining processability, the content of the nitrogen-containing compound is appropriate to set it to 3 g / L or less, preferably 1 g / L or less, more preferably 0.8 g / L or less, even more preferably 0.5 g / L or less, particularly preferably 0.3 g / L or less, and most preferably 0.25 g / L or less.

[0052] (acid) The polishing compositions disclosed herein contain an acid as a polishing accelerator. Both inorganic and organic acids can be used as the acid. Examples of organic acids include organic carboxylic acids and organic sulfonic acids, typically having 1 to 18, or usually 1 to 10, carbon atoms. The acids can be used individually or in combination of two or more.

[0053] 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, thiosulfate, chloric acid, perchloric acid, chlorous acid, hydroiodic acid, periodic acid, iodic acid, hydrobromic acid, perbromic acid, bromic acid, chromic acid, nitrite, and others.

[0054] 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, ricinolenic acid, methacrylic acid, glutaric acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, tartonic acid, glyceric acid, hydroxybutyric acid, hydroxyacetic acid, hydroxybenzoic acid, salicylic acid, isocitric acid, methylene succinic acid, gallic acid, ascorbic acid, oxaloacetic acid, chloroacetic acid, and chloroacetic acid. Examples include organic carboxylic acids such as chloroacetic 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.

[0055] 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, and methanesulfonic acid. Among these, phosphoric acid, phosphonic acid, maleic acid, hydrochloric acid, nitric acid, and sulfuric acid are preferred.

[0056] Acids may also be used in the form of salts. Examples of salts include metal salts of the inorganic and organic acids mentioned above. Examples of metal salts 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; and so on. The alkali metals in these alkali metal salts may be, for example, lithium, sodium, potassium, etc.

[0057] The salts that may be included in the polishing compositions disclosed herein are preferably salts of inorganic acids, such as alkali metal salts. For example, potassium chloride, sodium chloride, potassium nitrate, sodium nitrate, potassium phosphate, etc., can be preferably used.

[0058] Acids and their salts can be used individually or in combination of two or more (e.g., 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 salt of the acid is preferably a salt of an inorganic acid.

[0059] The molar concentration of the acid in the polishing composition (or the total molar concentration if multiple types of acids are included) is not particularly limited, but is suitable to be, for example, 0.001 mol / L or higher, preferably 0.01 mol / L or higher, more preferably 0.05 mol / L or higher, even more preferably 0.07 mol / L or higher, and particularly preferably 0.09 mol / L or higher. Higher processability can be achieved by increasing the molar concentration of the acid. From the viewpoint of surface quality after polishing and polishing stability, the molar concentration of the acid is suitable to be 1.2 mol / L or lower, preferably 1 mol / L or lower, more preferably 0.8 mol / L or lower, even more preferably 0.5 mol / L or lower, and particularly preferably 0.3 mol / L or lower (for example, 0.2 mol / L or lower).

[0060] (Oxidizing agent) The polishing compositions disclosed herein contain an oxidizing agent. Examples of oxidizing agents include, but are not limited to, peroxides, nitric acid or its salts, periodic acid or its salts, peroxoacid or its salts, permanganic acid or its salts, chromic acid or its salts, oxygen acids or their salts, metal salts, sulfuric acids, etc. The oxidizing agent 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, peroxomonosulfate, metal peroxomonosulfate, peroxodisulfate, metal peroxodisulfate, peroxolinic acid, peroxosulfate, sodium peroxoborate, performic acid, peracetic acid, perbenzoic acid, perphthalic acid, hypobromous acid, hypoiodic acid, chloric acid, bromic acid, iodic acid, periodic acid, perchloric acid, hypochlorous acid, sodium hypochlorite, calcium hypochlorite, potassium permanganate, metal chromate, metal dichromate, iron chloride, iron sulfate, iron citrate, iron ammonium sulfate, etc. Preferred oxidizing agents include hydrogen peroxide, iron nitrate, periodic acid, peroxomonosulfate, peroxodisulfate, and nitric acid. The oxidizing agent preferably contains at least hydrogen peroxide, and more preferably consists of hydrogen peroxide.

[0061] The content of the oxidizing agent in the polishing composition is preferably 0.05 mol / L or more, more preferably 0.1 mol / L or more, even more preferably 0.15 mol / L or more, and particularly preferably 0.3 mol / L or more, taking into consideration the rate of oxidation of the object to be polished and, consequently, the workability. Furthermore, from the viewpoint of maintaining surface accuracy, the content of the oxidizing agent in the polishing composition is preferably 1 mol / L or less, more preferably 0.8 mol / L or less, and even more preferably 0.6 mol / L or less.

[0062] (Silica residue reducing agent) In some preferred embodiments, the polishing compositions disclosed herein include a silica residue reducing agent. The silica residue reducing agent can be one or more compounds selected from phosphate esters, phosphite esters, and organophosphonic acid compounds, and can be a water-soluble compound such that 1 g completely dissolves in 100 mL of pure water at a temperature of 30°C. By using the above silica residue reducing agent, silica residue can be reduced in the primary polishing of magnetic disk substrates without impairing workability. The reason for this is thought to be, for example, as follows: The silica residue reducing agent contained in the polishing composition is dissolved in the composition and arranged as a thin film on the substrate surface, and is thought to suppress direct contact and adhesion of silica abrasive grains to the substrate between the silica abrasive grains and the substrate. Therefore, the silica abrasive grains are removed from the substrate along with the water-soluble silica residue reducing agent by subsequent washing, and as a result, silica residue on the substrate is reduced. It should be noted that the above mechanism is the inventors' consideration based on experimental results, and the technology disclosed herein is not to be interpreted as being limited to the above mechanism.

[0063] The silica residue reducing agent disclosed herein may typically be water-soluble, with 1 g completely dissolving 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 particles. Furthermore, since the silica residue reducing agent is water-soluble, it can be easily removed by washing after polishing.

[0064] The complete solubility of a sample in pure water at 30°C can be evaluated by placing 1g of the sample in 100mL of pure water in a flask, stirring and mixing, and visually observing whether it has completely dissolved within one hour. The result can be determined by the presence or absence of turbidity, precipitate, or phase separation (organic phase / aqueous phase, etc.). The measurement should be performed at atmospheric pressure. If it is difficult to determine whether 1g of the sample has completely dissolved in 100mL of pure water, the measurement solution can be centrifuged and the presence or absence of the sample in the supernatant can be analyzed. In this case, it is desirable to use N=3. Alternatively, if the solubility in water (30°C) indicated in publicly available information such as literature or in the SDS (Safety Data Sheet) is 1 (g / 100mL) or higher, or suggests that it is satisfied, the above water solubility may be considered to be satisfied for convenience. The above conditions will also be adopted in the embodiments described later.

[0065] Phosphate esters and phosphite esters used as silica residue reducing agents have one or two organic groups linked by phosphate ester bonds. These organic groups can be described as substituents that substitute for hydrogen atoms in one or two OH groups contained in phosphoric acid (typically OH groups directly bonded to the phosphorus atom). In some embodiments, the number of organic groups in the silica residue reducing agent is one or two. In some preferred embodiments, the silica residue reducing agent is selected from those having organic groups with six or fewer carbon atoms, which may include ether bonds. Limiting the number of carbon atoms in the organic group leads to limiting the size of the organic group and, consequently, the silica residue reducing agent, resulting in a tendency for excellent water solubility and mobility. The number of carbon atoms in the organic group may be five or less, four or less, three or less, or two or less (e.g., one) from the viewpoint of water solubility and mobility. Furthermore, limiting the number of carbon atoms in the organic group tends to suppress hydrophobic interactions between the silica residue reducing agent and silica particles. The organic group may or may not include ether bonds. In some embodiments, the organic groups of the silica residue reducing agent may not contain ester bonds or vinyl groups.

[0066] A preferred example of the organic group possessed by the silica residue reducing agent is an alkyl group having 4 or fewer carbon atoms. The alkyl group may be linear or branched. From the viewpoint of water solubility, mobility, and suppression of adsorption with silica particles, the number of carbon atoms in the alkyl group may be 3 or less, 2 or less, or 1. Examples of alkyl groups include methyl group, ethyl group, propyl group (n-propyl group, isopropyl group), and butyl group (n-butyl group, sec-butyl group, isobutyl group, tert-butyl group). The silica residue reducing agent may have one or two of the above alkyl groups.

[0067] Other preferred examples of the organic group possessed by the silica residue reducing agent include alkoxyalkyl groups having 6 or fewer carbon atoms. From the viewpoint of water solubility, mobility, and suppression of adsorption with silica particles, the number of carbon atoms of the alkoxyalkyl group may be 5 or less, 4 or less, 3 or less, or 2. Examples of alkoxyalkyl groups include methoxymethyl group, ethoxymethyl group, propoxymethyl group, butoxymethyl group, methoxyethyl group, ethoxyethyl group, propoxyethyl group, butoxyethyl group, methoxypropyl group, ethoxypropyl group, propoxypropyl group, methoxybutyl group, and ethoxybutyl group. The silica residue reducing agent may have one or two of the above alkoxyalkyl groups. Alternatively, the silica residue reducing agent may have the above alkyl group and the above alkoxyalkyl group.

[0068] Any of the following phosphate esters can be used as silica residue reducing agents: monophosphate esters, diphosphate esters, and triester phosphates. The phosphate esters can be used individually or in combination of two or more.

[0069] The above phosphate esters include alkyl acid phosphates such as monoalkyl acid phosphates (monomethyl acid phosphate, monoethyl acid phosphate (also called monoethyl phosphate), monoisopropyl acid phosphate, monobutyl acid phosphate, etc.), dialkyl acid phosphates (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) From among alkoxyalkyl acid phosphates such as (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, etc., those exhibiting the above-mentioned water solubility are used. These can be used individually or in combination of two or more. Among these, alkyl acid phosphates and alkoxyalkyl acid phosphates are preferred, and methyl acid phosphate, ethyl acid phosphate, isopropyl acid phosphate, butyl acid phosphate, and butoxyethyl acid phosphate are more preferred. Alkyl acid phosphates may also be mixtures of monoalkyl acid phosphates and dialkyl acid phosphates. The same applies to alkoxyalkyl acid phosphates.

[0070] As the phosphite ester, those exhibiting the above-mentioned water solubility are preferably used from among alkyl hydrogen phosphates such as dimethyl hydrogen phosphite, diethyl hydrogen phosphite, diisopropyl hydrogen phosphite, dibutyl hydrogen phosphite, and diisobutyl hydrogen phosphite. These can be used individually or in combination of two or more. Among these, diethyl hydrogen phosphite and dibutyl hydrogen phosphite are more preferred.

[0071] As the organic phosphonic acid compound, one or more of the above-mentioned water-soluble organic phosphonic acid compounds can be used without particular limitation. A preferred example is nitrilotris (methylenephosphonic acid).

[0072] The molecular weight of the silica residue reducing agent is selected within an appropriate range that allows it to exert its function, and is not limited to a specific range. From the viewpoint of water solubility, mobility, and suppression of adsorption with silica particles, a molecular weight of 500 or less is appropriate for the silica residue reducing agent, but it may also be 300 or less, 250 or less, 200 or less, or 150 or less (e.g., less than 150). The lower limit of the above molecular weight is approximately 100 or more, but it may also be 120 or more. Furthermore, a molecular weight of phosphate ester as a silica residue reducing agent is appropriate to be 250 or less, but it may also 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 phosphorous acid ester used as a silica residue reducing agent is suitable to be 250 or less, but may also 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 used as a silica residue reducing agent is suitable to be 500 or less, but may also be 400 or less, 350 or less, 320 or less, or around 300. The lower limit of the above molecular weight is approximately 100 or more, but may also be, for example, 200 or more, 250 or more, or 280 or more.

[0073] The amount of silica residue reducing agent in the polishing compositions disclosed herein can be an appropriate amount that can achieve a silica residue reduction effect without impairing workability, and may also vary depending on the type of agent, so it is not limited to a specific range. The above content can be approximately 0.001 mM (mmol / L) or more, and approximately 0.01 mM or more is appropriate. From the viewpoint of better exhibiting the silica residue reduction effect, the above 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 above silica residue reducing agent may be approximately 5 mM or more, approximately 8 mM or more, or approximately 10 mM or more. Polishing compositions containing approximately 15 mM or more (e.g., 18 mM or more, and even 22 mM or more) of silica residue reducing agent tend to easily obtain a workability improvement effect while obtaining a silica residue reduction effect. The upper limit of the silica residue reducing agent content can be, for example, approximately 300 mM or less, approximately 100 mM or less is appropriate, it may be approximately 50 mM or less, approximately 30 mM or less, or less than 15 mM. According to the technology disclosed herein, the desired effect can be achieved by adding a small amount of silica residue reducing agent, so the upper limit of the silica residue reducing agent content may be less than 10 mM, less than 7 mM, less than 5 mM, or less than 3 mM.

[0074] (Water-soluble polymer) In some preferred embodiments, the polishing compositions disclosed herein include a water-soluble polymer. By using a water-soluble polymer, it is possible to achieve both a reduction in polishing resistance and an improvement in processability. The reason for this is thought to be as follows: The water-soluble polymer is adsorbed onto each interface of the polishing field, such as the polishing pad or Ni-P substrate, promoting the diffusion of the abrasive components, and surface modification proceeds in a direction that relieves polishing stress. It should be noted that the above mechanism is the inventor's consideration based on experimental results, and the technology disclosed herein is not to be interpreted as being limited to the above mechanism. Reducing polishing resistance is also effective in suppressing excessive polishing vibration, and contributes to suppressing the decrease in processability caused by excessive polishing vibration.

[0075] The water-soluble polymers disclosed herein are typically polymers produced by the polymerization of monomers, and have multiple monomer units derived from said monomers. In the above polymers, monomer units are also called repeating units. Monomer units of water-soluble polymers refer to structural units derived from monomers used in the synthesis of water-soluble polymers, and have a structure corresponding to the monomer after it has been incorporated into the polymer. The water-soluble polymers disclosed herein may contain monomer units one type alone or two or more types in combination.

[0076] While not particularly limited, vinyl monomers are preferably used as monomers in the synthesis of water-soluble polymers. Here, vinyl monomers are compounds having a vinyl group that exhibits radical polymerization. In some embodiments, water-soluble polymers are preferably obtained by copolymerizing two or more vinyl monomers.

[0077] Examples of monomers that form monomer units in the water-soluble polymers disclosed herein include carboxylic acid group-containing monomers, sulfonic acid group-containing monomers, and amide group-containing monomers (e.g., (meth)acrylamide), from the viewpoint of the solubility of the water-soluble polymers in water. (Meth)acrylic refers comprehensively to acrylic and methacrylic.

[0078] Furthermore, from the viewpoint of giving hydrophobicity to water-soluble polymers, examples of monomers that form monomer units contained in the water-soluble polymers disclosed herein include amide group-containing monomers (e.g., N,N-dialkyl(meth)acrylamide, N-monoalkyl(meth)acrylamide), aromatic vinyl monomers (styrene, vinylnaphthalene, etc.), and the like.

[0079] Preferred examples of monomers disclosed herein include, for example, 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, styrene, styrene derivatives such as styrenesulfonic acid, and the like.

[0080] Non-limiting examples of water-soluble polymers disclosed herein include styrene / styrene sulfonic acid copolymer, methyl methacrylate / styrene sulfonic acid copolymer, bis(4-hydroxyphenyl)sulfone / 4-hydroxybenzenesulfonic acid copolymer, bis(4-hydroxyphenyl)methane / 4-hydroxybenzenesulfonic acid copolymer, (meth)acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer, (meth)acrylic acid / 2-hydroxy-3-(allyloxy)-propanesulfonic acid copolymer, p-vinylphenol / [N,N-dimethyl-1-(4-vinylphenoxy)methaneamine] copolymer, acrylic acid / N-tert-butylacrylamide copolymer, acrylic acid / N-tert-butylacrylamide / 2-acrylamido- Examples include 2-methylpropanesulfonic acid copolymer, acrylic acid / N-tert-butylacrylamide / acrylamide copolymer, acrylic acid / 2-acrylamide-2-methylpropanesulfonic acid / N-tert-butylacrylamide copolymer, acrylic acid / N-tert-butylacrylamide / acrylamide / 2-acrylamide-2-methylpropanesulfonic acid copolymer, acrylic acid / acrylamide / N-tert-butylacrylamide / 2-acrylamide-2-methylpropanesulfonic acid copolymer, acrylic acid / dimethylacrylamide copolymer, acrylic acid / diethylacrylamide copolymer, acrylic acid / styrene copolymer, naphthalenesulfonic acid formaldehyde condensate, diallylamine copolymer, vinylphosphonic acid copolymer, and the like.

[0081] While not particularly limited, the weight-average molecular weight (Mw) of the above-mentioned water-soluble polymer is usually, 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. Also, in some embodiments, the Mw of the water-soluble polymer may be 100,000 or less (for example, less than 100,000), or 70,000 or less. In some preferred embodiments, the Mw may be 50,000 or less, 30,000 or less, 20,000 or less, or 15,000 or less. By using a water-soluble polymer having an appropriate Mw within the above range, it is possible to preferably achieve both a reduction in polishing resistance and an improvement in processability.

[0082] For water-soluble polymers, values ​​based on aqueous gel permeation chromatography (GPC) can be used as the Mw (mold). Measurements can be performed, for example, under the following conditions. [GPC measurement conditions] Equipment: Tosoh Corporation, HLC-8320GPC Column: TSKgel GMPWxL, manufactured by Tosoh Corporation. Eluent: 0.1N sodium nitrate Flow rate: 0.5mL / min Temperature: 40℃ Detection: Differential refractive index detector Sample: 0.1% by weight (injection volume 100 μL) Standard samples: PEG and PEO with known molecular weights

[0083] The method for obtaining the above-mentioned water-soluble polymer is not particularly limited, and various polymerization methods known as synthesis methods for water-soluble polymers can be appropriately employed. For example, aqueous solution polymerization is preferably employed. As the solvent (polymerization solvent) used in aqueous solution polymerization, an aqueous solvent (typically water) is used, and in addition to water, an appropriate amount of alcohols such as isopropyl alcohol and ketones such as acetone may be included. The initiator used for 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 polymerization initiators and peroxide polymerization initiators can be preferably used. A water-soluble redox polymerization initiator may also be used as the polymerization initiator. The amount of the above-mentioned polymerization initiator used can be the usual amount depending on the polymerization method and polymerization mode, and is not particularly limited. For example, the amount of polymerization initiator can be in the range of approximately 0.001 to 15 parts by weight (preferably approximately 0.01 to 10 parts by weight, for example approximately 0.1 to 10 parts by weight) per 100 parts by weight of the total monomer components to be polymerized. During polymerization, an appropriate amount of chain transfer agent may be added for the purpose of adjusting the molecular weight, etc. The polymerization temperature can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and can be, for example, around 60°C to 100°C. The polymerization time is preferably in the range of approximately 2 to 20 hours (for example, 3 to 10 hours). After the polymerization reaction, neutralization with a basic compound may be carried out as needed.

[0084] The concentration of the water-soluble polymer in the polishing composition is not particularly limited. In some embodiments, the concentration may be, for example, 0.0001% by weight or more, or 0.0005% by weight or more. From the viewpoint of effectively exhibiting the effects of containing the water-soluble polymer, in some preferred embodiments, the concentration may be 0.001% by weight or more, 0.005% by weight or more, 0.01% by weight or more, 0.02% by weight or more, or 0.03% by weight or more. Also, in some embodiments, it is appropriate for the concentration of the water-soluble polymer to be 3% by weight or less, or 2% by weight or less. From the viewpoint of processability and ease of cleaning and removal after polishing, in some preferred embodiments, the concentration of the water-soluble polymer may be 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), or 0.07% by weight or less, or 0.05% by weight or less.

[0085] The amount of water-soluble polymer 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 per 100 parts by weight of abrasive grains in the polishing composition is appropriately set to, 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 be 1 part by weight or more. Also, in some embodiments, the content of water-soluble polymer per 100 parts by weight of abrasive grains is appropriately set to 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 be 1.5 parts by weight or less. By using an appropriate amount of water-soluble polymer relative to the amount of abrasive grains, it is possible to preferably achieve both a reduction in polishing resistance and an improvement in processability.

[0086] The polishing compositions disclosed herein may also contain other water-soluble polymers other than the water-soluble polymers described above (hereinafter also referred to as "other water-soluble polymers"). By including other water-soluble polymers, the surface quality after polishing can be improved. Examples of other water-soluble polymers include polyalkylaryl sulfonic acid compounds such as methylnaphthalene sulfonic acid formaldehyde condensate and anthracene sulfonic acid formaldehyde; lignin sulfonic acid compounds such as lignin sulfonic acid and modified lignin sulfonic acid; and others such as polyisoprene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyisoamylene sulfonic acid, polystyrene sulfonate, polyacrylate, polyvinyl acetate, polymaleic acid, polyitaconic acid, polyvinyl alcohol, polyglycerin, copolymer of isoprene sulfonic acid and acrylic acid, carboxymethylcellulose, salts of carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, pullulan, etc. Other water-soluble polymers can be used individually or in combination of two or more. In embodiments using other water-soluble polymers, the content of the other water-soluble polymers in the polishing composition can be appropriately set within a range that does not significantly impede the effects of the present invention. Furthermore, the polishing composition disclosed herein can be carried out in a manner that substantially does not contain other water-soluble polymers. From this viewpoint, in embodiments in which the polishing composition contains other water-soluble polymers and embodiments in which it substantially does not contain other water-soluble polymers, the proportion of other water-soluble polymers to the total amount of water-soluble polymers 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., 0-5% by weight).

[0087] (Glycol ether compound) In some preferred embodiments, the polishing compositions disclosed herein include a glycol ether compound. By using a glycol ether compound, minute undulations can be reduced while maintaining workability.

[0088] Examples of glycol ether compounds disclosed herein include compounds having a skeletal structure derived from glycols such as methylene glycol, ethylene glycol, propylene glycol, diethylene glycol, and triethylene glycol, and having one or more ether bonds. The number of ether bonds in the glycol ether compound is not particularly limited as long as it is one or more, but in some embodiments, the number of ether bonds is preferably two or more, and may be three or more, or four or more. Furthermore, the number of ether bonds in the glycol ether compound disclosed herein is appropriately 10 or less, and may be eight or less, seven or less, six or less, five or less, or four or less. Using such glycol ether compounds makes it easier to reduce minute undulations while maintaining processability.

[0089] Furthermore, the number of carbon atoms in the glycol ether compounds disclosed herein is not particularly limited, but is preferably 3 or more, may be 4 or more, 5 or more, 6 or more, or 7 or more. The number of carbon atoms in the glycol ether compounds is preferably 16 or less, may be 14 or less, 12 or less, 10 or less, or 8 or less. Using such glycol ether compounds makes it easier to reduce minute undulations while maintaining processability.

[0090] The molecular weight of the glycol ether compounds disclosed herein is not particularly limited, but is preferably 60 or higher, more preferably 75 or higher, and may also be 80 or higher, or 100 or higher. The molecular weight of the glycol ether compounds is preferably 250 or lower, more preferably 200 or lower, and may also be 180 or lower. Using such glycol ether compounds makes it easier to reduce minute waviness while maintaining processability.

[0091] The molecular weight per ether bond of the glycol ether compounds disclosed herein is preferably 35 or more, may be 38 or more, may be 40 or more, or may be 43 or more. Furthermore, the molecular weight per ether bond of the glycol ether compounds is appropriately 100 or less, preferably 65 or less, and may be 55 or less. In this specification, "molecular weight per ether bond" can be calculated by dividing the molecular weight of the glycol ether compound by the number of ether bonds contained in the glycol ether compound.

[0092] The glycol ether compounds disclosed herein may be compounds without hydroxyl groups, or compounds having one or more hydroxyl groups. In some preferred embodiments, the number of hydroxyl groups in the glycol ether compound is 3 or less, may be 2 or less, may be 1 or less, or may be 0. Using such glycol ether compounds makes it easier to reduce minute undulations while maintaining processability.

[0093] Preferred examples of glycol ether compounds disclosed herein include dimethoxyethane, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, and dipropylene glycol dimethyl ether. Among these, dimethoxyethane, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, and dipropylene glycol dimethyl ether are preferred from the viewpoint of achieving both improved processability and reduction of minute waviness.

[0094] The content of the glycol ether compound in the polishing composition is not particularly limited, but from the viewpoint of effectively exhibiting the effect of adding the glycol ether compound, in some embodiments it is appropriate to set it to, for example, 0.005 g / L or more, preferably 0.01 g / L or more, more preferably 0.10 g / L or more, even more preferably 0.20 g / L or more, particularly preferably 0.30 g / L or more, and most preferably 0.35 g / L or more. Also, in some embodiments from the viewpoint of maintaining processability, the content of the nitrogen-containing compound is appropriate to set it to 6 g / L or less, preferably 2 g / L or less, more preferably 1.5 g / L or less, even more preferably 1 g / L or less, particularly preferably 0.6 g / L or less, and most preferably 0.5 g / L or less.

[0095] (water) The polishing compositions disclosed herein typically contain water. Preferably, the water used can be deionized water, pure water, ultrapure water, distilled water, etc. Deionized water is typically deionized water.

[0096] The abrasive compositions disclosed herein may preferably be implemented, for example, in a form having a solid content of 0.5% to 30.0% by weight. A form having a solid content of 1.0% to 20.0% by weight is more preferred. The abrasive compositions may typically be in the form of a slurry.

[0097] (Other ingredients) The polishing compositions disclosed herein may further contain, as necessary, known additives that can be used in polishing compositions, such as surfactants, dispersants, chelating agents, preservatives, fungicides, and basic compounds, to the extent that the effects of the present invention are not significantly hindered.

[0098] The surfactant is not particularly limited, and any anionic surfactant, nonionic surfactant, cationic surfactant, or amphoteric surfactant can be used. The use of a surfactant may improve the dispersion stability of the abrasive composition. The surfactant can be used alone or in combination of two or more. Typically, the above surfactant has a molecular weight of 1 × 10⁻⁶.6 It may be a water-soluble organic compound of less than 100%.

[0099] In polishing compositions containing a surfactant, the surfactant content is preferably 0.0005% by weight or more. From the viewpoint of surface smoothness after polishing, the above content is preferably 0.001% by weight or more, more preferably 0.002% by weight or more. Furthermore, from the viewpoint of processability, the above content is preferably 3.0% by weight or less, preferably 0.5% by weight or less, for example 0.1% by weight or less. The technology disclosed herein can preferably be implemented in a manner in which the polishing composition substantially does not contain a surfactant, from the viewpoint of processability.

[0100] Examples of dispersants include polycarboxylic acid-based dispersants such as sodium polycarboxylate salts; naphthalene sulfonic acid-based dispersants such as sodium naphthalene sulfonate salts; alkyl sulfonic acid-based dispersants; polyphosphate-based dispersants; alkylene oxide-based dispersants; polyhydric alcohol ester-based dispersants; and the like. Dispersants can be used individually or in combination of two or more.

[0101] The polishing composition may contain basic compounds as needed. Here, a basic compound refers to a compound that, when added to the polishing composition, has the function of increasing the pH of the composition. Examples of basic compounds include alkali metal hydroxides, carbonates and bicarbonates, phosphates and hydrogen phosphates, and organic acid salts. Basic compounds can be used individually or in combination of two or more.

[0102] (pH) The pH of the polishing compositions disclosed herein is not particularly limited. The pH of the polishing composition may be, for example, 12.0 or less, typically 0.5 to 12.0, and 10.0 or less, typically 0.5 to 10.0. From the viewpoint of processability and surface quality, the pH of the polishing composition may 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 may 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. pH adjusting agents such as organic acids, inorganic acids, and basic compounds may be included as needed to achieve the above pH in the polishing solution. The above pH can be preferably applied to polishing compositions for magnetic disk substrates such as nickel-phosphorus substrates, for example. It can be preferably applied to polishing compositions for primary polishing in particular.

[0103] (polishing liquid) The polishing compositions disclosed herein are typically supplied to an object to be polished in the form of a polishing solution containing the polishing composition and used for polishing the object. The polishing solution may be prepared, for example, by diluting the polishing composition. Here, dilution is typically done with water. Alternatively, the polishing composition may be used as is as a polishing solution. In other words, the concept of a polishing composition in the art disclosed herein encompasses both a polishing solution (working slurry) supplied to an object to be polished and used for polishing the object, and a concentrated solution that is diluted and used as a polishing solution. Polishing compositions in the form of such a concentrated solution are advantageous in terms of convenience and cost reduction during manufacturing, distribution, and storage. The concentration ratio can be, for example, about 1.5 to 50 times. From the viewpoint of storage stability of the concentrated solution, for example, a concentration ratio of about 2 to 20 times, typically 2 to 10 times, is appropriate.

[0104] (Multi-component abrasive composition) The polishing compositions disclosed herein may be mono-component or multi-component, including two-component types. For example, the polishing composition may be configured such that a mixture of its components, typically a part A containing some of the components other than water, and a part B containing the remaining components, is used to polish an object to be polished. A multi-component polishing composition according to some preferred embodiments comprises a part A containing abrasive particles and a part B containing components other than abrasive particles. Part A containing abrasive particles may further contain a dispersant. Examples of components other than abrasive particles in part B include acids. Part B may also contain water-soluble polymers or other additives. During mixing, an oxidizing agent, such as hydrogen peroxide, may be further added. For example, if the oxidizing agent is supplied in the form of an aqueous solution, the aqueous solution may constitute part C of the multi-component polishing composition.

[0105] <Application> The polishing compositions disclosed herein can be preferably applied to polish magnetic disk substrates such as nickel-phosphorus substrates, glass substrates, and carbon substrates. Furthermore, the plated material may be a disk substrate having a metal layer or metal compound layer other than the nickel-phosphorus plating layer on the surface of the base disk. In particular, the polishing composition is suitable for nickel-phosphorus plated substrates having a nickel-phosphorus plating layer on an aluminum alloy base disk. Applying the techniques disclosed herein is especially beneficial in such applications.

[0106] The polishing compositions disclosed herein can be particularly useful in applications requiring high polishing efficiency, such as the pre-polishing step in the manufacturing process of magnetic disk substrates, where a high-precision surface is required after the finish polishing step. If there are multiple pre-polishing steps prior to the finish polishing step, the compositions can be used in any of the pre-polishing steps, and the same or different polishing compositions can be used in these pre-polishing steps. The polishing compositions disclosed herein are suitable, for example, as polishing compositions used in the primary polishing step, i.e., the first polishing step, of magnetic disk substrates. In particular, they can be preferably used in the first polishing step, i.e., the primary polishing step, after nickel-phosphorus plating, in the manufacturing process of nickel-phosphorus substrates.

[0107] The polishing compositions disclosed herein are suitable for polishing magnetic disk substrates with a surface roughness of approximately 20 Å to 300 Å, as measured by a Schmitt Measurement System Inc. laser scanning surface roughness meter "TMS-3000WRC", to adjust the surface roughness of the magnetic disk substrates to 10 Å or less. The application of the techniques disclosed herein is particularly significant in such applications. Here, surface roughness refers to the arithmetic mean roughness (Ra).

[0108] <Polishing method> The polishing compositions disclosed herein can be suitably used for polishing magnetic disk substrates, for example, in embodiments including the following operations. A preferred embodiment of a method for polishing an object using the polishing compositions disclosed herein will be described below. Hereinafter, the object to be polished will also be referred to as the polished substrate. In other words, a polishing solution (working slurry) containing any of the polishing compositions disclosed herein is prepared. Preparing the polishing solution may involve adjusting the concentration or pH of the polishing composition. For example, dilution can be used to adjust the concentration. Alternatively, the polishing composition may be used as is as the polishing solution.

[0109] Next, the polishing solution is supplied to the object to be polished, and polishing is performed by conventional methods. For example, the object to be polished is set in a general polishing device, and the polishing solution is supplied to the surface of the object, i.e., the surface to be polished, through the polishing pad of the device. Typically, the polishing solution is supplied continuously, and the polishing pad is pressed against the surface of the object to be polished, causing the two to move relative to each other. This movement may be, for example, rotational movement. Through this polishing process, the polishing of the object is completed.

[0110] The polishing pads that can be used are not particularly limited. For example, polishing pads of the rigid foamed polyurethane type, nonwoven fabric type, suede type, etc. can be used. The suede type may be a buffing pad, and typically it may be a polishing pad in a non-buffed state (a so-called non-buffing pad) whose surface has not been buffed. Such suede-type polishing pads (typically made of polyurethane) have excellent processability and make it easy to achieve high quality on the substrate surface. Note that the polishing pads used in the technology disclosed herein do not contain abrasive grains.

[0111] After polishing (specifically, after primary polishing of the magnetic disk substrate), it is preferable to clean the substrate (cleaning step). The cleaning step is typically carried out using a cleaning machine. In the cleaning step, a cleaning solution may be used, or the cleaning may be done with running water only without a cleaning solution. Ultrasonic treatment may be performed by applying ultrasonic waves to the substrate immersed in the cleaning solution or water. By performing such a cleaning step, abrasive particles remaining on the substrate after polishing can be efficiently removed.

[0112] The polishing apparatus used in the polishing process may be a double-sided polishing apparatus that polishes both sides of the object to be polished simultaneously, or a single-sided polishing apparatus that polishes only one side of the object to be polished. If the above polishing process is a preliminary polishing process, in some embodiments, a double-sided polishing apparatus may be preferably used as the polishing apparatus for the polishing process. If a finish polishing process is performed after the primary polishing process, a single-sided polishing apparatus may be preferably used as the polishing apparatus for the finish polishing process.

[0113] The polishing process described above may be part of the manufacturing process for a magnetic disk substrate, such as a nickel-phosphorus substrate. Therefore, this specification provides a method for manufacturing a magnetic disk substrate and a method for polishing it, including the polishing process described above.

[0114] The polishing compositions disclosed herein may be preferably used in a preliminary polishing step of an object to be polished, for example, a primary polishing step. This specification provides a method for manufacturing and polishing a magnetic disk substrate, which includes a step of performing preliminary polishing using any of the polishing compositions described herein. The method includes a step (1) of supplying the polishing composition disclosed herein to an object to be polished and polishing the object. The method may include a finish polishing step after the preliminary polishing step. The polishing composition used in the finish polishing step is not particularly limited. Accordingly, the disclosures in this specification include a method for manufacturing and polishing a magnetic disk substrate, which includes, in this order, a step (1) of polishing an object to be polished with a polishing composition containing abrasive grains disclosed herein, and a step (2) of polishing an object to be polished with a different polishing composition (e.g., a finish polishing composition) than the polishing composition used in step (1). According to such a manufacturing method, magnetic disk substrates can be manufactured efficiently.

[0115] The abrasive grains used in step (2) are not particularly limited, but colloidal silica is preferably used. By using colloidal silica, polished products with high surface accuracy can be efficiently manufactured. The particle shape of the colloidal silica is not particularly limited, and may be spherical or non-spherical, but spherical colloidal silica is preferably used.

[0116] Furthermore, the finishing polishing composition that may be used in step (2) may contain, for example, water in addition to abrasive grains. In addition, the finishing polishing composition may contain optional components (acids, oxidizing agents, basic compounds, various additives, etc.) similar to those in the polishing composition described above, as needed.

[0117] The matters disclosed in this specification include the following: [1] A composition for polishing magnetic disk substrates, It contains silica particles as abrasive grains, an acid, and an oxidizing agent. The above silica particles are an abrasive composition in which, in a volume-based aspect ratio distribution, the cumulative 25% aspect ratio is 1.30 or less, and the cumulative 75% aspect ratio is 1.20 or more and 3.00 or less. [2] The polishing composition according to [1] above, wherein the silica particles have a volume-based average secondary particle diameter (D2) of 350 nm or less determined by SEM image analysis. [3] The polishing composition according to [1] or [2] above, wherein the particle size ratio obtained by dividing the circumference equivalent diameter by the Heywood diameter is 1.40 or less in the silica particles, the number-based presence rate of particles P is 65% or more of the total silica particles. [4] The polishing composition described above further comprises a nitrogen-containing compound, as described in any of [1] to [3] above. [5] The polishing composition according to any one of [1] to [4] above, wherein the polishing composition comprises at least one selected from the group consisting of phosphate esters, phosphite esters, and organic phosphonic acid compounds. [6] The polishing composition described above is the polishing composition described in any one of [1] to [5], further comprising a water-soluble polymer. [7] The polishing composition according to any one of [1] to [6] above, further comprising a glycol ether compound. [8] A method for manufacturing a magnetic disk substrate, comprising the step of polishing a substrate to be polished using the polishing composition described in any of [1] to [7] above. [9] A method for polishing a substrate, comprising the step of supplying a polishing composition described in any of [1] to [7] above to a substrate to be polished and polishing the substrate. [Examples]

[0118] The following describes some embodiments of the present invention, but the present invention is not intended to be limited to those shown in these embodiments.

[0119] <Test Example 1> <Preparation of polishing composition> Polishing compositions according to Examples 1-12 and Comparative Examples 1-3 were prepared by mixing silica abrasive grains, phosphoric acid, 31% hydrogen peroxide solution, and deionized water. The pH of each of the above polishing compositions was 1.5. As silica abrasive grains, multiple types of silica particles with different particle sizes, particle size distributions, and particle shapes were prepared, and polishing grains containing these silica particles alone or in combination were used so that the number-based abundance of particles P, where the average secondary particle diameter D2, cumulative 25% aspect ratio A25, cumulative 75% aspect ratio A75, and particle size ratio obtained by dividing the circumference equivalent diameter by the Heywood diameter is 1.40 or less, differed within a predetermined range. The concentration of silica particles in the polishing composition was 7% by weight, the phosphoric acid concentration was 0.1 mol / L, and the hydrogen peroxide concentration was 0.4 mol / L.

[0120] The average secondary particle diameter D2, cumulative 25% aspect ratio A25, cumulative 75% aspect ratio A75, and the prevalence of a predetermined particle size ratio were calculated based on images observed by a scanning electron microscope (SEM). Specifically, these were calculated using the method described herein.

[0121] <Polishing> The polishing compositions for each example were used as polishing solutions, and the objects to be polished were polished under the following conditions. The objects to be polished were aluminum substrates for hard disks, which had an electroless nickel-phosphorus plating layer on their surface. The objects to be polished (substrates to be polished) were donut-shaped with an outer diameter of approximately 95 mm and an inner diameter of approximately 25 mm, and a thickness of 1.75 mm. The surface roughness Ra (arithmetic mean roughness of the nickel-phosphorus plating layer measured by a laser scanning surface roughness meter "TMS-3000WRC" manufactured by Schmitt Measurement System Inc.) before polishing was 130 Å.

[0122] [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 sheets (3 sheets / carrier × 5 carriers) Supply rate of polishing liquid: 135 mL / min Polishing load: 120 g / cm 2 Rotation speed of upper platen: 27 rpm Rotation speed of lower platen: 36 rpm Rotation speed of sun gear: 8 rpm Amount of polishing: Approximately 2.2 μm thickness in total for both sides of each substrate The above amount of polishing was obtained based on the following calculation formula. Amount of polishing [μm] = Weight reduction of substrate due to polishing [g] / (Area of substrate [cm 2 × Density of nickel-phosphorus plating [g / cm 3 ) × 10 4

[0123] (Workability) When the substrate to be polished was polished under the above polishing conditions using the polishing composition according to each example, the polishing rate (polishing removal rate) on both sides was calculated. The polishing rate was obtained based on the following calculation formula. The obtained results were converted to relative values with the polishing rate of Comparative Example 1 as 100% and shown in the column of "Polishing Rate" in Table 1. The larger the value of the polishing rate, the higher the workability. When the above polishing rate (relative value) is 105% or more, it is determined that the workability has been improved. Polishing rate [μm / min] = Weight reduction of substrate due to polishing [g] / (Area of substrate [cm 2 × Density of nickel-phosphorus plating [g / cm 3 × Polishing time [min]) × 10 4

[0124] (Micro waviness) After polishing with the polishing composition for each example, a total of three Ni-P substrates were extracted from the polished Ni-P substrates. The micro-undulation was measured on all six surfaces (front and back) of these three Ni-P substrates using a ZYGO non-contact surface shape measuring instrument, "NEWVIEW9000," under the conditions of objective lens magnification 2.75x, intermediate lens magnification 0.5x, and bandpass filter 80-500 μm. Measurements were taken at four points at 90° intervals, 37 mm radially outward from the center of the polished substrate, for each of the six surfaces. The average of these 24 points was taken as the micro-undulation (Å) value. The obtained values ​​were converted to relative values, with the value of Comparative Example 1 set to 100%, and are shown in the "Micro-undulation" column of Table 1. A smaller value indicates suppressed micro-undulation. A micro-undulation (relative value) of 125% or less indicates that low micro-undulation was maintained.

[0125] (Rate / Swell ratio) The ratio of the polishing rate to the aforementioned minute waviness was calculated and is shown in the "Rate / Waviness Ratio" column of Table 1. A higher "Rate / Waviness Ratio" indicates a better balance between high machinability and low minute waviness.

[0126] (polishing resistance) The polishing resistance between the substrate to be polished and the polishing pad during polishing using the polishing compositions of Example 2, Comparative Examples 1 and 3 was obtained from the polishing apparatus. Specifically, the "maximum value" was defined as the arithmetic mean of the maximum values ​​of the motor load (motor torque) applied to the upper and lower polishing plates during polishing. The "average value" was defined as the arithmetic mean of the average values ​​of the motor torque for the upper and lower polishing plates during the 50-second period from 150 seconds to 200 seconds after the start of polishing. The above "maximum value" and "average value" were measured as the polishing resistance. The obtained values ​​were then converted to relative values ​​with the value of Comparative Example 1 set to 100, and are shown in the "Maximum Value (Relative Value)" and "Average Value (Relative Value)" columns of "Polishing Resistance" in Table 1.

[0127] [Table 1]

[0128] As shown in Table 1, the polishing compositions of Examples 1 to 12, which used silica particles with a cumulative 25% aspect ratio A25 of 1.30 or less and a cumulative 75% aspect ratio A75 of 1.20 or more and 3.00 or less, tended to show an improvement in polishing rate while maintaining low minute waviness compared to Comparative Example 1, where the cumulative 75% aspect ratio A75 was less than 1.20, resulting in a higher rate / waviness ratio. Furthermore, the polishing compositions of Comparative Examples 2 and 3, which had a cumulative 75% aspect ratio A75 of 1.20 or more and 3.00 or less but a cumulative 25% aspect ratio A25 greater than 1.30, showed an extreme decrease in polishing rate. The polishing composition of Comparative Example 3 showed significantly greater polishing resistance compared to Comparative Example 1, and it was confirmed that the excessive polishing resistance prevented proper polishing action, resulting in an extreme decrease in polishing rate.

[0129] <Test Example 2> <Preparation of polishing composition> Polishing compositions according to each of Examples 13 to 20 were prepared by mixing silica abrasive grains, the nitrogen-containing compound shown in Table 2, phosphoric acid, 31% hydrogen peroxide solution, and deionized water. A polishing composition according to Example 1 of Test Example 1 was also prepared. The pH of each of the above polishing compositions was 1.5. The same silica particles used in Example 1 were used as the silica abrasive grains. The concentration of silica particles in the polishing composition was 7% by weight, 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 0.4 mol / L. Note that "AEEA" in Table 2 refers to "2-(2-aminoethylamino)ethanol" and "BTA" refers to "1,2,3-benzotriazole".

[0130] <Polishing> The polishing compositions for each example were used as polishing solutions, and the object to be polished was polished under the same conditions as in Test Example 1.

[0131] (Processability and minute waviness) The polishing rate on both sides of a substrate to be polished under the above polishing conditions using the polishing composition for each example was measured in the same manner as in Test Example 1. The obtained values ​​were converted to relative values ​​with the value of Example 1 set to 100%, and are shown in the "Polishing Rate" column of Table 2. In addition, the minute waviness of the substrate after polishing was measured in the same manner as in Test Example 1. The obtained values ​​were converted to relative values ​​with the value of Example 1 set to 100%, and are shown in the "Mint Waviness" column of Table 2. The ratio of the polishing rate to the above minute waviness was calculated and is shown in the "Rate / Waviness Ratio" column of Table 2.

[0132] [Table 2]

[0133] As shown in Table 2, the polishing compositions of Examples 13 to 20, which contain various nitrogen-containing compounds, were found to reduce minute undulations and improve the rate / undulation ratio compared to the polishing composition of Example 1, which does not contain nitrogen-containing compounds.

[0134] <Test Example 3> <Preparation of polishing composition> Polishing compositions according to each of Examples 21 to 28 were prepared by mixing silica abrasive grains, the silica residue reducing agent shown in Table 3, phosphoric acid, 31% hydrogen peroxide solution, and deionized water. A polishing composition according to Example 1 of Test Example 1 was also prepared. The pH of each of the above polishing compositions was 1.5. The same silica particles used in Example 1 were used as the silica abrasive grains. The concentration of silica particles in the polishing composition was 7% by weight, the concentration of the silica residue reducing agent (if present) was 10 mmol / L, the phosphoric acid concentration was 0.1 mol / L, and the hydrogen peroxide concentration was 0.4 mol / L. Note that "HEDP" in Table 3 refers to "1-hydroxyethylidene-1,1-diphosphonic acid".

[0135] <Polishing> The polishing compositions for each example were used as polishing solutions, and the object to be polished was polished under the same conditions as in Test Example 1.

[0136] (processability) The polishing rate on both sides of a substrate to be polished under the above polishing conditions using the polishing composition for each example was measured in the same manner as in Test Example 1. The obtained values ​​were converted to relative values ​​with the value of Example 1 set to 100%, and are shown in the "Polishing Rate" column of Table 3.

[0137] (Number of residual silica particles) After polishing the substrates under the above conditions, we cleaned them using a cleaning machine manufactured by Crescent, and then measured the number of silica particles remaining on the substrate surface. Specifically, without using a brush or cleaning agent, the substrates were cleaned in running water under the following conditions, and the water droplets adhering to the substrates were removed with a spin dryer and dried. (Washing conditions) Detergent 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 drying time: 20 seconds Next, using a scanning electron microscope "SU8000" manufactured by Hitachi High-Technologies Corporation, the cleaned substrate surface (both sides) was observed at a magnification of 50,000x, with 10 fields of view per surface. Then, using image analysis software "WinROOF" manufactured by Mitani Corporation, the number of residual silica particles in each field of view was measured, and the average number of residual silica particles per field of view was calculated. The obtained values ​​are shown in the "Silica Residue" column of Table 3 as relative values, with the number of residual silica particles in Example 1 set to 100%.

[0138] [Table 3]

[0139] As shown in Table 3, the polishing compositions of Examples 21 to 28, which used various silica residue reducing agents, showed reduced silica residue compared to the polishing composition of Example 1, which did not use a silica residue reducing agent. Although not shown in the table, the polishing compositions of Examples 21 to 28 showed a similar degree of minute waviness (for example, approximately ±5%) as the polishing composition of Example 1.

[0140] <Test Example 4> <Preparation of polishing composition> Polishing compositions according to each of Examples 29 to 36 were prepared by mixing silica abrasive grains, the water-soluble polymers shown in Table 4, phosphoric acid, 31% hydrogen peroxide solution, and deionized water. A polishing composition according to Example 1 of Test Example 1 was also prepared. The pH of each of the above polishing compositions was 1.5. The same silica particles used in Example 1 were used as the silica abrasive grains. The concentration of silica particles in the polishing composition was 7% by weight, the concentration of the water-soluble polymer (if present) was 0.2 g / L, the phosphoric acid concentration was 0.1 mol / L, and the hydrogen peroxide concentration was 0.4 mol / L. The weight-average molecular weight Mw of the water-soluble polymers used in each example was 1 × 10⁻⁶. 4 That was the case.

[0141] The water-soluble polymer used in Example 29 is a polymer of monomer components containing acrylic acid (AA) and N,N-diethylacrylamide (DEAM) in a molar ratio of 85:15. The water-soluble polymer used in Example 30 is a polymer of monomer components containing acrylic acid (AA) and N,N-diethylacrylamide (DEAM) in a molar ratio of 95:5. The water-soluble polymer used in Example 31 is a polymer of monomer components containing acrylic acid (AA) and styrene (St) in a molar ratio of 90:10. The water-soluble polymer used in Example 32 is a polymer of monomer components containing acrylic acid (AA) and N,N-dimethylacrylamide (DMAM) in a molar ratio of 85:15. The water-soluble polymer used in Example 33 is a polymer of monomer components containing acrylic acid (AA) and 2-acrylamido-2-methylpropanesulfonic acid (ATBS) in a molar ratio of 80:20. The water-soluble polymer used in Example 34 is a polymer of monomer components containing acrylic acid (AA) and N-tert-butylacrylamide (TBAA) in a molar ratio of 90:10. The water-soluble polymer used in Example 35 is a polymer of monomer components containing acrylic acid (AA) and styrene (St) in a molar ratio of 90:10. The water-soluble polymer used in Example 36 is a polymer of monomer components containing acrylic acid (AA), N-tert-butylacrylamide (TBAA), acrylamide (AM), and 2-acrylamido-2-methylpropanesulfonic acid (ATBS) in a molar ratio of 80:16:2:2.

[0142] <Polishing> The polishing compositions for each example were used as polishing solutions, and the object to be polished was polished under the same conditions as in Test Example 1.

[0143] (processability) The polishing rate on both sides of a substrate to be polished under the above polishing conditions using the polishing composition for each example was measured in the same manner as in Test Example 1. The obtained values ​​were converted to relative values ​​with the value of Example 1 set to 100%, and are shown in the "Polishing Rate" column of Table 4.

[0144] (polishing resistance) The polishing resistance between the substrate to be polished and the polishing pad during polishing using the polishing composition for each example was obtained from the polishing apparatus. Specifically, the "maximum value" was defined as the arithmetic mean of the maximum values ​​of the motor load (motor torque) applied to the upper and lower polishing plates during polishing. Furthermore, the "average value" was defined as the arithmetic mean of the average values ​​of the motor torque for the upper and lower polishing plates during the 50-second period from 150 seconds to 200 seconds after the start of polishing. The above "maximum value" and "average value" were measured as the polishing resistance. The obtained values ​​were then converted to relative values ​​with the value of Example 1 set to 100, and are shown in the "Maximum Value (Relative Value)" and "Average Value (Relative Value)" columns of "Polishing Resistance" in Table 4.

[0145] [Table 4]

[0146] As shown in Table 4, the polishing compositions of Examples 29 to 36, which used various water-soluble polymers, were found to reduce polishing resistance while maintaining high processability compared to the polishing composition of Example 1, which did not use water-soluble polymers. Although not shown in the table, the polishing compositions of Examples 29 to 36 showed a similar degree of minute waviness (for example, approximately ±5%) as the polishing composition of Example 1.

[0147] <Test Example 5> <Preparation of polishing composition> Polishing compositions according to each of Examples 37 to 42 were prepared by mixing silica abrasive grains, glycol ether compounds shown in Table 5, phosphoric acid, 31% hydrogen peroxide solution, and deionized water. A polishing composition according to Example 1 of Test Example 1 was also prepared. The pH of each of the above polishing compositions was 1.5. The same silica particles used in Example 1 were used as the silica abrasive grains. The concentration of silica particles in the polishing composition was 7% by weight, the concentration of the glycol ether compound (if present) was 0.4 g / L, the phosphoric acid concentration was 0.1 mol / L, and the hydrogen peroxide concentration was 0.4 mol / L.

[0148] <Polishing> The polishing compositions for each example were used as polishing solutions, and the object to be polished was polished under the same conditions as in Test Example 1.

[0149] (Processability and minute waviness) The polishing rate on both sides of a substrate was measured using the polishing composition for each example under the above polishing conditions, using the same method as in Test Example 1. The obtained values ​​were converted to relative values ​​with the value of Example 1 set to 100%, and are shown in the "Polishing Rate" column of Table 5. In addition, the minute waviness of the substrate after polishing was measured using the same method as in Test Example 1. The obtained values ​​were converted to relative values ​​with the value of Example 1 set to 100%, and are shown in the "Mint Waviness" column of Table 5. The ratio of the polishing rate to the above minute waviness was calculated and is shown in the "Rate / Waviness Ratio" column of Table 5.

[0150] [Table 5]

[0151] As shown in Table 5, it was confirmed that the polishing compositions of Examples 37 to 42, which contain various glycol ether compounds, reduced minute waviness and improved the rate / waviness ratio compared to the polishing composition of Example 1, which does not contain glycol ether compounds.

[0152] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above.

Claims

1. A composition for polishing magnetic disk substrates, It contains silica particles as abrasive grains, an acid, and an oxidizing agent. The silica particles in the polishing composition have a volume-based aspect ratio distribution in which the cumulative 25% aspect ratio is 1.30 or less, and the cumulative 75% aspect ratio is 1.20 or more and 3.00 or less.

2. The polishing composition according to claim 1, wherein the silica particles have an average secondary particle diameter based on volume determined by scanning electron microscope image analysis of 350 nm or less.

3. The polishing composition according to claim 1, wherein the silica particles have a particle size ratio obtained by dividing the circumference equivalent diameter by the Heywood diameter of 1.40 or less, and the number-based abundance of particles with this ratio is 65% or more of the total silica particles.

4. The polishing composition according to any one of claims 1 to 3, further comprising a nitrogen-containing compound.

5. The polishing composition according to any one of claims 1 to 3, wherein the polishing composition comprises at least one selected from the group consisting of phosphate esters, phosphite esters, and organic phosphonic acid compounds.

6. The polishing composition according to any one of claims 1 to 3, further comprising a water-soluble polymer.

7. The polishing composition according to any one of claims 1 to 3, further comprising a glycol ether compound.

8. A method for manufacturing a magnetic disk substrate, comprising the step of polishing a substrate to be polished using the polishing composition described in any one of claims 1 to 3.

9. A method for polishing a substrate, comprising the step of supplying a polishing composition according to any one of claims 1 to 3 to a substrate to be polished and polishing the substrate.

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