JP2024143467A - Polishing composition, substrate manufacturing method and polishing method - Google Patents

Abstract

To provide a composition for polishing with which, in polishing magnetic disk substrates, with silica abrasive grain included, it is possible to improve minute waviness and silica residue without impairing the ease of work and end shape.SOLUTION: Provided is a composition for polishing magnetic disk substrates. This polishing composition includes a silica particle as abrasive grain, an aromatic ring-containing compound, and water. The aromatic ring-containing compound is a compound having an aromatic ring and a functional group A or a salt thereof. The functional group A is selected from a group consisting of a sulfonic group, a phosphate group, a phosphonic acid group, an amino group, a carboxyl group, an aldehyde group, and a hydroxyl group. The silica particle is such that the average projection area (SP50-100) of a particle (D50 or greater) whose volume-based particle diameter by SEM image analysis is in the range from cumulative 50% from the small diameter side to 100% is 40% to 65% inclusive of the average area (SC50-100) of circumferential length equivalent circle of each particle that corresponds to the D50 or greater particle.SELECTED DRAWING: None

Description

The present invention relates to a polishing composition used for polishing magnetic disk substrates, a method for manufacturing the substrates, and a method for polishing the substrates.

Conventionally, the manufacturing process for magnetic disk substrates, which require a highly accurate surface, includes a step of polishing the substrate, which is the raw material of the substrate, using a polishing liquid. For example, in the manufacture of nickel-phosphorus plated disk substrates (hereinafter also referred to as Ni-P substrates), polishing that places emphasis on polishing efficiency (primary polishing) and final polishing (finish polishing) to achieve the surface accuracy of the final product are generally performed. Patent documents 1 to 3 are cited as technical documents related to polishing compositions used for polishing magnetic disk substrates. Patent document 3 relates to a method for manufacturing an abrasive slurry that contains alumina abrasive grains as an essential component.

JP 2007-63372 A JP 2017-182849 A JP 2010-260121 A

In polishing magnetic disk substrates, efforts are being made continuously to improve the quality of the substrate surface in order to increase the recording capacity. Magnetic disk substrates are usually polished by pressing a polishing pad against the substrate to be polished and moving them relative to each other. In polishing using a polishing pad, the edge of the substrate is subjected to a larger load not only due to the pressure on the polishing surface (polishing load) but also to a force from the side due to the sinking of the polishing pad, so the thickness of the substrate edge tends to decrease compared to the inner circumference. This type of edge shape is called roll-off (also called end surface sagging), and since it is not suitable for recording, it can be a limiting factor in increasing the recording capacity of magnetic disks. In recent years, silica abrasive grains have been used instead of alumina abrasive grains from the primary polishing stage in order to improve the quality of the substrate surface after finish polishing. Compared to polishing using alumina abrasive grains, polishing using silica abrasive grains does not penetrate the substrate, has excellent reduction in defects such as scratches, and is easy to obtain high surface quality. On the other hand, when polishing with silica abrasive grains, it is difficult to obtain the same processing power as with slurries containing alumina abrasive grains, and improving the processing power is a challenge.

In polishing using the above silica abrasive grains, in addition to maintaining and improving the processing force, an increase in microwaviness on the substrate after polishing is also an issue. In the above-mentioned polishing, processability and microwaviness are in a contradictory relationship in which improving one will worsen the other, and it is not easy to achieve both, and an increase in processing force may promote roll-off. In addition, the present inventors have focused on the phenomenon in which some of the silica particles used in polishing are not removed by cleaning after polishing and remain attached to the substrate surface after polishing (hereinafter referred to as "silica residue" or "silica residue"). If the silica residue on the substrate that has been polished and cleaned is reduced, a higher surface quality can be achieved, and it is considered desirable in terms of improving the yield of high-quality substrates. However, it is particularly difficult to reduce silica residue while taking into account the above-mentioned processability, roll-off, and microwaviness. For example, Patent Document 1 aims to provide a polishing liquid composition that is effective in reducing roll-off, and in the examples, the polishing rate is evaluated in addition to roll-off, but microwaviness is not evaluated, and there is no reference to silica residue. Patent Document 2 aims to provide a polishing composition that can reduce end sagging and achieve a high polishing rate, and proposes a polishing composition that contains an end shape improver having a specific structure, but does not consider suppressing microwaviness or reducing silica residue. None of Patent Documents 1 to 3 suggests reducing silica residue while taking into account processability, roll-off, and microwaviness in polishing using silica abrasive grains.

The present inventors have been developing a polishing composition that can improve microwaviness and silica residue without impairing processability or edge shape when polishing with silica abrasive grains. As a result of intensive research, they have succeeded in creating a polishing composition that solves the above problem by using a combination of silica abrasive grains with specific particle characteristics and an aromatic ring-containing compound with a specific structure, and have completed the present invention. In other words, the present invention aims to provide a polishing composition that contains silica abrasive grains and can improve microwaviness and silica residue without impairing processability or edge shape when polishing magnetic disk substrates. Another related object is to provide a method for manufacturing and polishing a substrate using the above polishing composition.

The magnetic disk substrate polishing composition provided by the present specification contains silica particles as abrasive grains, an aromatic ring-containing compound, and water. The aromatic ring-containing compound is a compound having an aromatic ring and a functional group A or a salt thereof, and the functional group A is selected from the group consisting of a sulfo group, a phosphoric acid group, a phosphonic acid group, an amino group, a carboxy group, an aldehyde group, and a hydroxy group. The silica particles have an average projected area (SP 50-100 ) of particles (D ₅₀ or more particles) whose volume-based particle diameters measured by SEM image _{analysis are in the cumulative range of 50% to 100% from the small diameter side, which is 40% to 65% of the average area (SC 50-100 ) of} the circumference-equivalent circle of each particle corresponding to the D 50 or more particles. Here, the ratio of the average projected area to the circumference-equivalent circle average area (SP/SC ratio) represents the irregularity of the particles, and a small SP/SC ratio means a high irregularity. A polishing composition using silica particles having an irregular structure in which the area ratio ((SP/SC) _50-100 ) of the average projected area (SP _50-100 ) to the average circular area equivalent to the circumference (SC _50-100 ) of D ₅₀ or more particles is within the above range in combination with the aromatic ring-containing compound can improve microwaviness and silica residue in polishing of magnetic disk substrates without impairing processability or edge shape.

In some preferred embodiments, the average projected area (SP _0-50 ) of the silica particles, whose volume-based particle diameters measured by SEM image analysis are in the cumulative range of 0% or more and less than 50% from the small diameter side (particles less than D ₅₀ ), is greater than 65% and less than 90% of the average area (SC _0-50 ) of the circle equivalent to the perimeter of each particle corresponding to the particles less than D ₅₀ . According to this configuration, in addition to the effect based on the _combination of silica particles having an area ratio (SP/SC) _50-100 of the average projected area (SP _50-100 ) to the average circular area equivalent to the circumference (SC _50-100 ) of the particles having a D of ₅₀ or more falling within a specific range and the aromatic ring-containing compound, the effect of improving microwaviness and silica residue without impairing processability or end shape is better exerted due to the effect of silica particles having the area ratio (SP/SC) _50-100 and the area ratio (SP/SC) _0-50 of the average projected area (SP _0-50 ) to the average circular area equivalent to the circumference (SC _0-50 ) of particles having a D of less than 50 falling within respective prescribed ranges.

In some preferred embodiments, the molecular weight (Mw) of the aromatic ring-containing compound is 2000 or less. When the Mw of the aromatic ring-containing compound is 2000 or less, the effect of improving silica residue is more pronounced.

In some preferred embodiments, the aromatic ring-containing compound is a compound having an oxyalkylene chain between the aromatic ring and the functional group A, or a salt thereof. By using an aromatic ring-containing compound having such a structure, the effects of the technology disclosed herein can be preferably obtained.

According to the present specification, a method for manufacturing a magnetic disk substrate is provided. The manufacturing method includes a step (1) of polishing a substrate to be polished using any of the polishing compositions disclosed herein. According to this manufacturing method, a magnetic disk substrate having a high-quality surface can be manufactured with good productivity. In some embodiments, the manufacturing method for the substrate further includes a step (2) of polishing the substrate to be polished using a finish polishing composition after the step (1). The finish polishing composition preferably contains colloidal silica. By carrying out the step (2) after the step (1), a magnetic disk substrate having a higher quality surface can be manufactured with good productivity.

The present specification also provides a method for polishing a substrate. The polishing method includes step (1) of supplying any one of the polishing compositions disclosed herein to a substrate to be polished and polishing the substrate to be polished. Such a polishing method can efficiently improve the surface quality of the polished object. In some embodiments, the method for polishing a substrate further includes step (2) of supplying a finish polishing composition to the substrate to be polished after step (1) and polishing the substrate to be polished. The finish polishing composition preferably contains colloidal silica. By carrying out step (2) after step (1), a substrate surface of higher quality can be obtained.

The following describes preferred embodiments of the present invention. Note that matters other than those specifically mentioned in this specification that are necessary for implementing the present invention can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common technical knowledge in the relevant field.

<Polishing Composition>
(Silica Particles)
The polishing composition disclosed herein contains silica particles as abrasive grains. The silica particles may be in the form of secondary particles formed by agglomeration of a plurality of primary particles, or in the form of secondary particles formed by association of a plurality of primary particles. In addition, the silica particles in the form of primary particles and the silica particles in the form of secondary particles may be mixed.

The silica particles have an area ratio (SP/SC) _50-100 of the average projected area ( _SC50-100 ) to the average circle area ( _SP50-100 ) corresponding to the circumference of _D50 or more particles of the silica particles of the silica particles of 40% or more and 65% or less. Here, _D50 or more particles refer to particles having a particle diameter in which the accumulation from the small diameter side falls within the range of 50 to 100% in the volume-based cumulative particle size distribution obtained by SEM image analysis. The cumulative volume distribution is represented, for example, by a curve extending from the end (lower left) of the accumulation 0% and the small diameter side of the particle diameter to the upper right and reaching the end (upper right) of the accumulation 100% and the large diameter side of the particle diameter in a graph with the horizontal axis being the particle diameter and the vertical axis being the cumulative volume (%). _D50 or more particles are particles belonging to the large diameter side of 50% or more on a volume basis among all silica particles. Silica particles having a suitable irregular structure with the (SP/SC) _50-100 in the above range can easily physically remove the aromatic ring-containing compound adsorbed on the magnetic disk substrate during polishing, and therefore can maintain or improve processability while obtaining the effect of improving microwaviness due to the aromatic ring-containing compound and maintaining or improving the end shape. In addition, silica particles having the irregular structure can easily obtain high processability. Specifically, when the (SP/SC) _50-100 of the silica particles is 40% or more, the collapse of the particles is suppressed against both the polishing load and the shear stress. Since the collapsed particles tend to be difficult to remove from the substrate, suppressing the collapse of the particles is advantageous in reducing silica residue on the substrate. Furthermore, when the (SP/SC) _50-100 has a certain degree of irregularity of 65% or less, the rolling of the particles is suppressed, and the particles with D ₅₀ or more can be efficiently acted on both the depth direction and the surface direction of the object to be polished, and it is considered that high processability is easily obtained. It should be noted that the above mechanism is the inventor's speculation based on experimental results, and the technology disclosed herein should not be interpreted as being limited to the above mechanism.

In some embodiments, the (SP/SC) _50-100 of the silica particles is suitably 41% or more, and from the viewpoint of further reducing the silica residue, it is advantageously 43% or more (e.g., 45% or more), preferably 47% or more (e.g., 50% or more), more preferably 53% or more, may be 55% or more, may be 57% or more, or may be 60% or more, and in some embodiments, from the viewpoint of improving the end shape, (SP/SC) _50-100 may be, for example, less than 65%, may be 64% or less, or may be 63% or less. The technology disclosed herein can be preferably implemented in an embodiment in which (SP/SC) _50-100 is, for example, 53% or more and 65% or less.

The silica particles preferably have an area ratio (SP/SC) _0-50 of the average projected area to the average area of a circle equivalent to the circumference of particles having a diameter of less than _D50 of more than 65% and not more than 90%. Particles having a diameter of less than _D50 refer to particles having a particle diameter in which the cumulative amount from the small diameter side falls within a range of 0% or more and less than 50% in a cumulative particle size distribution on a volume basis obtained by SEM image analysis. Particles having a diameter of less than _D50 are particles that belong to the small diameter side of less than 50% on a volume basis among all silica particles. According to silica particles in which the area ratio (SP/SC) _0-50 of the average projected area (SP _0-50 ) to the average circular area (SC _0-50 ) corresponding to the circumference of particles less than D ₅₀ and the area ratio (SP/SC) _50-100 are each within a predetermined range, in addition to the action based on the combination of the silica particle irregularity of (SP/SC) _50-100 and the aromatic ring-containing compound, the effect of improving microwaviness and silica residue without impairing processability or end shape is better exhibited due to the action of the particle characteristics based on (SP/SC) _0-50 and (SP/SC) _50-100 of the silica particles. Specifically, it is considered that by (SP/SC) _0-50 being 90% or less, the particles less than D ₅₀ effectively contribute to repairing the processing marks caused by processing by the particles on the large diameter side, and the deterioration of microwaviness due to the accumulation of the processing marks can be suppressed. In addition, it is believed that (SP/SC) _0-50 being greater than 65% is useful for suppressing the generation and accumulation of processing marks caused by particles with a diameter of less than D _50. Note that the above mechanism is the inventor's consideration based on experimental results, and the technology disclosed herein should not be interpreted as being limited to the above mechanism.

In some embodiments, the (SP/SC) _0-50 of the silica particles is suitably 68% or more (e.g., more than 68%), and from the viewpoint of the end shape, it is preferably 70% or more, and may be 75% or more, 78% or more, 80% or more, 83% or more, or 85% or more. In some embodiments, the (SP/SC) _0-50 may be less than 90% or may be 88% or less. In some embodiments, from the viewpoint of improving processability, the (SP/SC) _0-50 is preferably 85% or less, more preferably 80% or less, and even more preferably 75% or less. The technology disclosed herein can be preferably implemented in an embodiment in which the (SP/SC) _0-50 is, for example, 70% or more and 90% or less, 75% or more and 90% or less, 80% or more and 90% or less, or 83% or more and 90% or less.

In some embodiments, the (SP/SC) _0-50 of the silica particles is preferably 1.20 to 2.50 times the (SP/SC) _50-100 of the silica particles. (SP/SC) _0-50 /(SP/SC) _50-100 being 1.20 or more can be understood as indicating that the irregularity, understood as the ratio of the average projected area to the average area of a circle equivalent to the circumference (SP/SC ratio), of particles having _D50 or more is _1.20 times or more larger than that of particles having less than D50. With silica abrasive grains in which (SP/SC) _50-100 is within the above range and (SP/SC) _0-50 /(SP/SC) _50-100 is within the range of 1.20 or more and 2.50 or less, the action of the particles of D ₅₀ or more and the action of the particles of less than D ₅₀ are well balanced, and the effect of suppressing the increase in microwaviness while exhibiting high processability can be suitably realized. In some embodiments, (SP/SC) _0-50 /(SP/SC) _50-100 is preferably 1.25 or more, more preferably 1.30 or more, even more preferably 1.35 or more, and may be 1.45 or more. In some embodiments, (SP/SC) _0-50 /(SP/SC) _50-100 is preferably 2.20 or less, more preferably 2.00 or less, and even more preferably 1.90 or less (e.g., 1.60 or less). Also, (SP/SC) _0-50 is preferably 10% or more (eg, 10 to 45%) larger than (SP/SC) _50-100 , and more preferably 15% or more (eg, 15 to 40%) larger.

The average aspect ratio (A _50-100 ) of the silica particles having a D ₅₀ or more is not particularly limited, and may be, for example, 1.20 or more and 2.00 or less. From the viewpoint of easily obtaining high processability while suppressing an increase in microwaviness, in some embodiments, A _50-100 is preferably 1.25 or more, more preferably 1.30 or more, even more preferably 1.35 or more, and particularly preferably 1.36 or more. From the same viewpoint, in some embodiments, A _50-100 is suitably 1.80 or less, preferably 1.70 or less, more preferably 1.60 or less, even more preferably 1.50 or less, particularly preferably 1.45 or less, and may be 1.42 or less. In silica particles having such A _50-100 , the effect of setting the (SP/SC) _50-100 of the silica particles within a predetermined range, and further, in a preferred embodiment, the effect of setting the (SP/SC) _50-100 and (SP/SC) _0-50 within predetermined ranges, can be preferably exhibited.

The average aspect ratio (A _all ) of the entire silica particles is not particularly limited, but is typically more than 1.00, and may be, for example, 1.01 or more. In some embodiments, the average aspect ratio (A _all ) may be, for example, 1.05 or more, and is preferably 1.10 or more from the viewpoint of maintaining or improving processability, more preferably 1.11 or more, even more preferably more than 1.15, and particularly preferably more than 1.20. In addition, in some embodiments, the average aspect ratio (A _all ) is suitably 2.00 or less or less than 2.00 from the viewpoint of particle strength, preferably 1.70 or less, more preferably 1.50 or less, 1.40 or less, or 1.30 or less. In addition, the average aspect ratio (A _all ) is preferably less than 1.30, more preferably less than 1.25, and may be less than 1.20 or less (for example, 1.15 or less) from the viewpoint of suppressing the development of micro-waviness. The relationship between A _all and A _50-100 is not particularly limited. In some embodiments, A _{50-100 is} suitably 0.10 or more (e.g., about 0.10 to 0.50) larger than A _all , preferably 0.15 or more (e.g., about 0.15 to 0.40) larger, and more preferably 0.20 or more (e.g., about 0.20 to 0.40) larger.

The D ₅₀ of the silica particles, i.e., the cumulative 50% particle size on a volume basis by SEM image analysis, may be, for example, 500 nm or less, preferably 400 nm or less, more preferably 350 nm or less, 325 nm or less, 300 nm or less, 280 nm or less, 250 nm or less, 220 nm or less, 200 nm or less, or 180 nm or less. According to the technology disclosed herein, even if silica particles having a relatively small D ₅₀ are used, high processability can be exhibited and an increase in microwaviness can be suppressed. The ability to achieve the purpose using silica particles having a relatively small D ₅₀ can be advantageous from the viewpoint of improving the surface quality after polishing. From this viewpoint, in some embodiments, the D ₅₀ of the silica particles may be 160 nm or less, 140 nm or less, 120 nm or less, 100 nm or less, or 90 nm or less. The _D50 of the silica particles may be, for example, 30 nm or more. From the viewpoint of improving processability, in some embodiments, it is preferably 40 nm or more, more preferably 55 nm or more, even more preferably 65 nm or more, and particularly preferably 75 nm or more, and may be 80 nm or more, 90 nm or more, or 100 nm or more.

The D ₅₀ of silica particles, the average aspect ratio (A _all ), the average aspect ratio of particles with D ₅₀ or more (A _50-100 ), the average projected area of particles with D ₅₀ or more (SP _50-100 ), the average circular area equivalent to the circumference of particles with D ₅₀ or more (SC _50-100 ), the average projected area of particles with less than D ₅₀ (SP _0-50 ), and the average circular area equivalent to the circumference of particles with less than D ₅₀ (SC _0-50 ) are determined by the following method. That is, using a scanning electron microscope (SEM), 500 or more particles contained in the silica particles to be measured (which may be one type of silica particles or a mixture of two or more types of silica particles) are observed in an SEM image containing 50 or more particles in one visual field. The observation magnification is 20,000 to 50,000 times. Then, for the smallest rectangle circumscribing each particle image, the value obtained by dividing the length of its long side (long axis value) by the length of its short side (short axis value) is calculated as the long axis/short axis ratio (aspect ratio) of each particle. In addition, the value obtained by 4πr ³ /3 from the radius r of an ideal circle (true circle) having an area equal to the projected area of each particle image is calculated as the volume of each particle. In addition, the outer perimeter (circumference) of the particle is measured from the projected image of each particle image, and the area of a circle (circumference equivalent circle) having the same circumference as the outer perimeter is calculated. Here, the aspect ratio, projected area, volume, circumference and circumference equivalent circle area are measured or calculated by counting the particles independently dispersed in the polishing composition as one particle, regardless of whether they are primary particles or secondary particles. The D ₅₀ of silica particles is obtained by obtaining a volume-based particle size distribution from the volume of the above-mentioned predetermined number of particles, and is calculated as the particle diameter at the point where the cumulative value from the small diameter side is 50%. The average aspect ratio (A _all ) is the number-based average aspect ratio of the entire silica particles (number-average aspect ratio), and can be determined by arithmetically averaging the aspect ratios of all the above-mentioned predetermined number of particles. The average aspect ratio (A _50-100 ) of D ₅₀ or more particles can be determined by extracting particles having a particle diameter of D ₅₀ or more (D ₅₀ or more particles) in the above-mentioned volume-based particle size distribution, and arithmetically averaging the aspect ratios of these particles. The average projected area (SP _50-100 ) and average circumference-equivalent circle area (SC _50-100 ) of D ₅₀ or more particles can be determined by arithmetically averaging the projected areas and circumference-equivalent circle areas of the particles corresponding to D ₅₀ or more particles among the above-mentioned predetermined number of particles, and the area ratio (SP/SC) _50-100 can be determined by dividing the obtained SP _50-100 by SC _50-100 . The average projected area (SP _0-50 ), average circumference-equivalent circle area (SC _0-50 ) and area ratio (SP/SC) _0-50 of particles having D less than ₅₀ can be determined in the same manner as SP _50-100 , SC _50-100 and area ratio (SP/SC) _50-100 , except that the target particles are particles having D less than ₅₀ among the above-mentioned specified number of particles.
The above D ₅₀ , A _all , A _50-100 , SP _50-100 , SC _50-100 , SP _0-50 and SC _0-50 can be determined using a general SEM and image analysis software. For example, a scanning electron microscope "SU8000" manufactured by Hitachi High-Technologies Corporation and image analysis type particle size distribution measurement software "Mac-View" manufactured by Mountec Co., Ltd. can be used. The same applies to the examples described later.

The above (SP/SC) _50-100 , (SP/SC) _0-50 , A _50-100 , A _all , and D ₅₀ can be adjusted by selecting the type of silica particles to be used, selecting or adjusting the silica manufacturing method, mixing two or more types of silica particles having different particle shapes, etc. For example, based on the description of this specification and taking into consideration common general knowledge, one type of particle group having a specific particle size and aspect ratio is selected, or two or more types of particle groups are selected and mixed in an appropriate ratio, to obtain the silica particles disclosed herein. Also, based on the description of this specification and taking into consideration common general knowledge, it is possible to adopt, for example, a method of crushing porous silica gel under appropriate conditions to obtain irregular-shaped particles, or a method of growing the obtained irregular-shaped particles by adding a predetermined amount of silicate under appropriate conditions (pH, temperature conditions, etc.) to obtain irregular-shaped particles having a desired particle size. The silica particles disclosed herein can be obtained by mixing one type of particle obtained in this way alone or with other silica particles having different particle properties.

In addition, the ratio of the average projected area to the average area of the circle equivalent to the circumference of a _D50 or more particle, i.e., the area ratio (SP/SC) _50-100 , can be adjusted by the average number of primary particles contained in one _D50 or more particle (hereinafter also referred to as the "average bond number"), the degree of overlap of the primary particles in a secondary particle containing two or more primary particles in an aggregated or associated form, etc. More specifically, in comparison with the same particle size, as the average bond number increases, the surface unevenness of the secondary particle tends to increase, so the area ratio (SP/SC) _50-100 tends to decrease, and as the degree of overlap between the primary particles in a secondary particle in which two or more primary particles are bonded increases, the area ratio (SP/SC) _50-100 tends to increase. The area ratio (SP/SC) _0-50 can be adjusted in the same manner. The average bond number and the degree of overlap of primary particles can be adjusted by selecting the type of silica particles used, selecting or adjusting the silica production method, mixing two or more types of silica particles having different particle shapes, or the like.

The silica particles are not particularly limited as long as they satisfy a predetermined area ratio (SP/SC) of _50-100 , and various silica particles having silica as the main component can be used. Here, the silica particles having silica as the main component refer to particles in which 90% by weight or more, for example 95% by weight or more, typically 98% by weight or more of the particles are silica. Examples of silica particles that can be used are not particularly limited, and include colloidal silica, agglomerated silica, precipitated silica (also called precipitated silica), sodium silicate silica, alkoxide silica, fumed silica, dried silica, and detonation silica. Furthermore, silica particles obtained by using the above silica particles as a raw material can also be used. Examples of such silica particles include silica particles obtained by applying one or more treatments selected from heat treatments such as heating, drying, and baking, pressure treatments such as autoclaving, mechanical treatments such as crushing and pulverization, and surface modification to the above raw silica particles. Examples of surface modification include chemical modification such as introduction of functional groups and metal modification. The silica particles in the technology disclosed herein may contain one type of silica particles as described above alone or two or more types in combination.

The content of silica particles 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. When multiple types of silica particles are contained, the above content is the total content of them. By increasing the content of silica particles, higher processability tends to be obtained. From the viewpoint of the surface smoothness of the substrate after polishing and the stability of polishing, the above content is appropriately 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.

In the polishing composition disclosed herein, the content of silica particles in the solid content contained in the polishing composition is preferably 90% by weight or more of the total solid content, more preferably 95% by weight or more, and even more preferably 98% by weight or more, for example 99% by weight or more, from the viewpoint of better exerting the effects of the technology disclosed herein. In this specification, the solid content contained in the polishing composition refers to the residual content, 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.

The polishing composition disclosed herein can be preferably implemented in an embodiment that is substantially free of alumina particles. Examples of alumina particles include α-alumina particles. Such a polishing composition prevents quality degradation caused by the use of alumina particles. Examples of quality degradation include the occurrence of scratches and dents, residual alumina, and puncture defects. In this specification, "substantially free of alumina particles" means that the proportion of alumina particles in the total amount of solids contained in the polishing composition is 1% by weight or less, more preferably 0.5% by weight or less, and typically 0.1% by weight or less. A polishing composition with a proportion of alumina particles of 0% by weight, that is, a polishing composition that does not contain alumina particles, is particularly preferred. The polishing composition disclosed herein can also be preferably implemented in an embodiment that is substantially free of α-alumina particles.

The polishing composition disclosed herein can be preferably implemented in an embodiment that is substantially free of 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 contained in the polishing composition is 1% by weight or less, more preferably 0.5% by weight or less, typically 0.1% by weight or less. In such an embodiment, the application effect of the technology disclosed herein can be preferably exerted.

(Aromatic ring-containing compound)
The polishing composition disclosed herein contains an aromatic ring-containing compound, which is a compound having an aromatic ring and a functional group A or a salt thereof. The aromatic ring-containing compound is typically water-soluble, and The functional group A is contained in the polishing composition in a dissolved form. The functional group A is selected from the group consisting of a sulfo group, a phosphoric acid group, a phosphonic acid group, an amino group, a carboxy group, an aldehyde group, and a hydroxy group. Suitable examples of the aromatic ring include aromatic hydrocarbon rings such as a benzene ring, a naphthalene ring, and an anthracene ring. When the aromatic ring-containing compound is in the form of a salt, examples of the salt include metal salts. Examples of the metal salt include alkali metal salts. The alkali metal in the alkali metal salt may be, for example, lithium, sodium, potassium, etc. Among these, sodium salts are preferred. Polishing composition The aromatic ring-containing compound contained in the product is adsorbed to the magnetic disk substrate during polishing, and acts to eliminate surface irregularities by protecting the substrate, thereby improving microwaviness. The compounds contained therein may be used alone or in combination of two or more.

It is believed that the aromatic ring-containing compound is mainly adsorbed to the substrate at the aromatic ring (preferably aromatic hydrocarbon ring) portion, which is relatively hydrophobic. Since aromatic rings have high shape stability, the aromatic ring-containing compound is likely to be uniformly adsorbed to the substrate. Since the adsorption posture to the substrate is related to the adsorption strength to the substrate, the aromatic ring-containing compound can protect the substrate with good uniformity and suppress the development of micro-waviness. In addition, the aromatic ring-containing compound is arranged in a thin film on the substrate surface after polishing and before cleaning, and is thought to suppress direct contact and adhesion of silica particles to the substrate between the silica particles and the substrate. Therefore, the silica particles are removed from the substrate together with the aromatic ring-containing compound by the subsequent cleaning, which is thought to reduce the amount of silica remaining on the substrate. In addition, the high uniformity of substrate protection by the aromatic ring-containing compound can suppress uneven removal of silica particles during the cleaning, thereby reducing residual silica.

From the viewpoint of increasing the uniformity of substrate protection and suppressing a decrease in the polishing rate, in some embodiments, an aromatic ring-containing compound having a benzene ring or a naphthalene ring as the aromatic ring may be preferably used. An aromatic ring-containing compound having a naphthalene ring is more preferable. In addition, from the viewpoint of the shape stability of the hydrophobic portion, it is preferable that the aromatic ring of the aromatic ring-containing compound does not have a hydrophobic chain-like substituent. For example, it is preferable that the aromatic ring does not have a linear or branched alkyl group having 3 or more carbon atoms as a substituent, more preferably does not have an alkyl group having 2 or more carbon atoms, and even more preferably does not have an alkyl substituent.

During polishing, the aromatic ring-containing compound is mainly adsorbed to the substrate by the aromatic ring portion, while the functional group A with relatively high hydrophilicity tends to spread in the liquid, so it is considered that it is adsorbed to the magnetic disk substrate surface in a partially three-dimensional posture.Compared to the aromatic ring-containing compound that is adsorbed to the substrate in a three-dimensional posture as a whole in a planar posture, the aromatic ring-containing compound that is adsorbed to the substrate in this manner is easily removed from the substrate surface by the physical action during polishing or cleaning, and is particularly easily removed by the silica particles with a predetermined irregularity, so it is considered that it can better suppress the deterioration of processability due to the adsorption of the aromatic ring-containing compound to the substrate, and furthermore, can improve microwaviness while maintaining or improving processability.
It should be noted that the above mechanism is the inventor's speculation based on experimental results, and the technology disclosed herein should not be interpreted as being limited to the above mechanism.

In some embodiments, the aromatic ring-containing compound has a molecular weight (Mw) of 2000 or less, advantageously 1500 or more, preferably 1000 or less, and more preferably 800 or less (e.g., 700 or less). By limiting the Mw of the aromatic ring-containing compound to a predetermined value or less, the structural unit of the thin film becomes smaller, and the cleaning removability of silica particles remaining on the substrate through the thin film tends to improve. This makes it easier to reduce silica residue. From this perspective, in some embodiments, the Mw of the aromatic ring-containing compound may be 600 or less, 550 or less, 500 or less, or 450 or less. In addition, the Mw of the aromatic ring-containing compound may be, for example, 150 or more, and from the viewpoint of the protection of the substrate during polishing, it is appropriate to be 170 or more, advantageously 200 or more, preferably 300 or more, more preferably 350 or more, may be 370 or more, may be 390 or more, or may be 410 or more.
The Mw of the aromatic ring-containing compound is determined based on the chemical formula of the compound. When a nominal value is provided by a manufacturer or the like, that value can be used.

In some embodiments, the aromatic ring-containing compound is preferably a compound having an oxyalkylene chain between the aromatic ring and the functional group A or a salt thereof. Here, the oxyalkylene chain means an oxyalkylene structure or a chain structure portion due to repetition of the oxyalkylene structure. By having an oxyalkylene chain between the aromatic ring and the functional group A, the aromatic ring-containing compound is mainly adsorbed to the substrate at the aromatic ring portion, while the functional group A connected to the aromatic ring via the oxyalkylene chain tends to spread in the liquid, so that it is considered to be partially adsorbed to the magnetic disk substrate surface in a more three-dimensional posture. The aromatic ring-containing compound adsorbed to the substrate in such a posture is easily removed from the substrate surface by abrasive grains (particularly abrasive grains having the above-mentioned specific irregularity), so that the effect of suppressing the decrease in processability and improving microwaviness while maintaining or improving processability can be preferably exerted. In addition, due to the hydrophilicity of the oxyalkylene unit and the functional group A beyond it, the silica particles are easily removed together with the aromatic ring-containing compound during the above-mentioned cleaning, and the residual silica can be reduced.

The number of repetitions of the oxyalkylene structure (oxyalkylene unit) contained in the oxyalkylene chain may be 1 or 2 or more. From the viewpoint of enhancing removability from the substrate surface by interaction with the abrasive grains, in some embodiments, the number of repetitions of the oxyalkylene unit is preferably 3 or more, more preferably 4 or more. In addition, the number of repetitions of the oxyalkylene unit may be, for example, 30 or less, and in some embodiments, from the viewpoint of cleaning and removing silica particles remaining after polishing, it is appropriate to be 20 or less, preferably 16 or less, more preferably 12 or less, even more preferably 10 or less, and may be 8 or less, 6 or less, 5 or less, or 4 or less.

The oxyalkylene units contained in the oxyalkylene chain are preferably selected from oxyalkylene units having 2 to 4 carbon atoms, and more preferably from oxyalkylene units having 2 to 3 carbon atoms from the viewpoint of hydrophilicity. In some preferred embodiments, 50% or more (more preferably 75% or more) of the oxyalkylene units contained in the oxyalkylene chain are oxyethylene units. The oxyalkylene chain may be an oxyalkylene chain consisting of one or more oxyethylene units, that is, an oxyethylene chain represented by -(CH ₂ CH ₂ O) _n -. Here, n is the number of repetitions of the oxyethylene group, and is, for example, 1 to 30, preferably 2 to 20, more preferably 3 to 16.

In some embodiments, the aromatic ring-containing compound may be a compound represented by the following formula (I) or a salt thereof (e.g., an alkali metal salt, an ammonium salt, etc.):
RX-(C ₂ H ₄ O) _a (C ₃ H ₆ O) _b -B (I)
Here, in the above formula (I), R is an aryl group, X is an oxygen atom or a chemical bond, a is 0 to 30, b is 0 to 10, a+b is 30 or less, and B is a group selected from the group consisting of a sulfo group, a phosphate group, a phosphonic acid group, a carboxy group, and a hydroxy group. By combining an aromatic ring-containing compound that is the compound represented by the above formula (I) or a salt thereof with the silica particles having the above-mentioned moderately irregular structure, it is possible to suitably exhibit the effect of improving microwaviness and silica residue without impairing processability and end shape. In some embodiments, the above a is preferably 1 to 20, more preferably 2 to 16, and even more preferably 3 to 12. In some embodiments, the above b is preferably 0 to 4, more preferably 0 or 1, and even more preferably 0. In some embodiments, the above a+b is preferably 1 to 20, more preferably 2 to 16, even more preferably 2 to 14, and particularly preferably 3 to 12. In some embodiments, the above B is preferably a group selected from the group consisting of a sulfo group, a phosphate group, a phosphonic acid group, and a carboxy group. Examples of R include a phenyl group which may have a substituent, a naphthyl group which may have a substituent, etc. When R is a group having a substituent, the number of the substituents is preferably 2 or less, more preferably 1. The substituent is preferably a methyl group or an ethyl group, more preferably a methyl group. In some embodiments, R is preferably a phenyl group having no substituent, or a naphthyl group having no substituent, more preferably a naphthyl group having no substituent.

The content of the aromatic ring-containing compound in the polishing composition is not particularly limited, and in some embodiments, from the viewpoint of effectively exerting the effect of adding the aromatic ring-containing compound, 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. In some embodiments, from the viewpoint of maintaining processability, the content of the aromatic ring-containing compound is appropriate to be 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.

(acid)
The polishing composition disclosed herein preferably contains an acid as a polishing accelerator. The acid may be either an inorganic acid or an organic acid. The organic acid may be, for example, an organic carboxylic acid, an organic sulfonic acid, or an amino acid having about 1 to 18 carbon atoms, typically about 1 to 10 carbon atoms. The acid may be used alone or in combination of two or more kinds.

Specific examples of inorganic acids include phosphoric acid (orthophosphoric acid), nitric acid, sulfuric acid, hydrochloric acid, boric acid, sulfamic acid, phosphinic acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, hexametaphosphoric acid, carbonic acid, hydrofluoric acid, sulfurous acid, thiosulfuric acid, chloric acid, perchloric acid, chlorous acid, hydroiodic acid, periodic acid, iodic acid, hydrobromic acid, perbromic acid, bromic acid, chromic acid, and nitrous acid.

Specific examples of organic acids include citric acid, maleic acid, malic acid, glycolic acid, succinic acid, itaconic acid, malonic acid, iminodiacetic acid, gluconic acid, lactic acid, 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, crotonic acid, oleic acid, linoleic acid, and linolenic acid. Organic carboxylic acids such as carboxylic acid, ricinoleic acid, methacrylic acid, glutaric acid, fumaric acid, tartronic acid, glyceric acid, hydroxybutyric acid, hydroxyacetic acid, isocitric acid, methylenesuccinic acid, ascorbic acid, nitroacetic acid, oxaloacetic acid, chloroacetic acid, dichloroacetic acid, and trichloroacetic acid; glycine, alanine, glutamic acid, aspartic acid, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, proline, cystine, and glutamine , asparagine, lysine, arginine and other amino acids; phytic acid; 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethanehydroxy-1,1,2-triphosphonic acid, ethane- Examples of organic phosphonic acids include 1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, α-methylphosphonosuccinic acid, and aminopoly(methylenephosphonic acid); and organic sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, aminoethanesulfonic acid, sulfosuccinic acid, 10-camphorsulfonic acid, isethionic acid, and taurine.

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

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

As salts that may be contained in the polishing composition disclosed herein, salts of inorganic acids, such as alkali metal salts and ammonium salts, may be preferably used. For example, potassium chloride, sodium chloride, ammonium chloride, potassium nitrate, sodium nitrate, ammonium nitrate, potassium phosphate, etc. may be preferably used.

The acids and their salts may be used alone or in combination of two or more (e.g., two or three). In some embodiments, an acid may 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 an inorganic acid.

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

(Oxidizing Agent)
The polishing composition disclosed herein preferably contains an oxidizing agent.Examples of the oxidizing agent include, but are not limited to, peroxide, nitric acid or its salt, periodic acid or its salt, peroxo acid or its salt, permanganic acid or its salt, chromic acid or its salt, oxygen acid or its salt, metal salts, sulfuric acid, etc.The oxidizing agent can be used alone or in combination of two or more. Specific examples of the oxidizing agent include hydrogen peroxide, sodium peroxide, barium peroxide, nitric acid, iron nitrate, aluminum nitrate, ammonium nitrate, peroxomonosulfuric acid, ammonium peroxomonosulfate, metal peroxomonosulfate, peroxodisulfate, ammonium peroxodisulfate, metal peroxodisulfate, peroxolinic acid, peroxosulfuric acid, sodium peroxoborate, performic acid, peracetic acid, hypobromous acid, hypoiodous 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, ammonium iron sulfate, etc. Preferred examples of the oxidizing agent include hydrogen peroxide, iron nitrate, periodic acid, peroxomonosulfuric acid, peroxodisulfuric acid, and nitric acid. The oxidizing agent preferably contains at least hydrogen peroxide, and more preferably consists of hydrogen peroxide.

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, in consideration of the rate at which the polishing object is oxidized and therefore the processability. In addition, 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, in consideration of maintaining surface precision.

(water)
The polishing composition disclosed herein typically contains water to disperse the abrasive grains, in addition to the above-mentioned abrasive grains. As the water, ion-exchanged water, pure water, ultrapure water, distilled water, etc. can be preferably used. The ion-exchanged water can typically be deionized water.

The polishing composition disclosed herein can be preferably implemented, for example, in a form in which the solid content is 0.5% by weight to 30.0% by weight. More preferably, the solid content is 1.0% by weight to 20.0% by weight. The polishing composition can typically be a slurry-like composition.

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

The surfactant is not particularly limited, and any of anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants can be used. The use of surfactants can improve the dispersion stability of the polishing composition. The surfactants can be used alone or in combination of two or more. The surfactants can typically be water-soluble organic compounds with a molecular weight of less than 1×10 ⁶ .
Specific examples of anionic surfactants include polyoxyethylene alkyl ether acetate, polyoxyethylene alkyl sulfate, alkyl sulfate, polyoxyethylene alkyl sulfate, alkyl sulfate, alkyl phosphate, polyoxyethylene alkyl phosphate, polyoxyethylene sulfosuccinic acid, alkyl sulfosuccinic acid, polyacrylic acid, sodium lauryl sulfate, ammonium lauryl sulfate, sodium polyoxyethylene alkyl ether sulfate, melamine formalin resin sulfonic acid compounds such as melamine sulfonic acid formaldehyde condensates, polyisoprene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyisoamylene sulfonic acid, and salts thereof. As the salt, alkali metal salts such as sodium salts and potassium salts are preferred.
Specific examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkyl amines, and alkyl alkanolamides.
Specific examples of the cationic surfactant include alkyltrimethylammonium salts, alkyldimethylammonium salts, and alkylamine salts.
Specific examples of amphoteric surfactants include alkyl betaine type, fatty acid amidopropyl betaine type, amino acid type, and alkyl amine oxide type.

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

The polishing composition disclosed herein may contain a water-soluble polymer. By containing a water-soluble polymer, the surface quality after polishing can be improved. Examples of water-soluble polymers include melamine formalin resin sulfonic acid compounds such as melamine sulfonic acid formaldehyde condensates; and others include polyisoprene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyisoamylene sulfonic acid, polyacrylates, polyvinyl acetate, polymaleic acid, polyitaconic acid, polyvinyl alcohol, polyglycerin, polyvinylpyrrolidone, copolymers of isoprene sulfonic acid and acrylic acid, polyvinylpyrrolidone-polyacrylic acid copolymers, polyvinylpyrrolidone-vinyl acetate copolymers, diallylamine hydrochloride sulfur dioxide copolymers, carboxymethylcellulose, salts of carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, pullulan, chitosan, chitosan salts, etc. The water-soluble polymers can be used alone or in combination of two or more.

In an embodiment of the polishing composition that contains a water-soluble polymer, the content of the water-soluble polymer in the polishing composition is, for example, 0.001% by weight or more. In an embodiment that contains multiple water-soluble polymers, the above content is the total content of them. From the viewpoint of surface smoothness of the polished object after polishing, the above content is preferably 0.003% by weight or more, more preferably 0.005% by weight or more, and even more preferably 0.007% by weight or more. From the viewpoint of processability, the above content is preferably 1.0% by weight or less, and is preferably 0.5% by weight or less, for example 0.1% by weight or less. Note that the technology disclosed herein can be preferably implemented in an embodiment in which the polishing composition does not substantially contain a water-soluble polymer from the viewpoint of processability.

Examples of dispersants include polycarboxylic acid-based dispersants such as sodium polycarboxylate and ammonium polycarboxylate; alkylsulfonic acid-based dispersants; polyphosphoric acid-based dispersants; polyalkylene polyamine-based dispersants; quaternary ammonium-based dispersants; alkyl polyamine-based dispersants; alkylene oxide-based dispersants; polyhydric alcohol ester-based dispersants; etc. Dispersants can be used alone or in combination of two or more.

Examples of chelating agents include aminocarboxylic acid chelating agents and organic phosphonic acid chelating agents. Examples of aminocarboxylic acid chelating agents include ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetate, nitrilotriacetic acid, sodium nitrilotriacetate, ammonium nitrilotriacetate, hydroxyethylethylenediaminetriacetic acid, sodium hydroxyethylethylenediaminetriacetate, diethylenetriaminepentaacetic acid, sodium diethylenetriaminepentaacetate, triethylenetetraminehexaacetic acid, and sodium triethylenetetraminehexaacetate. Examples of organic phosphonic acid chelating agents include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetrakis(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, and α-methylphosphonosuccinic acid. Of these, organic phosphonic acid chelating agents are more preferred, and among these, ethylenediaminetetrakis(methylenephosphonic acid) and diethylenetriaminepenta(methylenephosphonic acid) are particularly preferred. A particularly preferred chelating agent is ethylenediaminetetrakis(methylenephosphonic acid). The chelating agents can be used alone or in combination of two or more.

Examples of preservatives and antifungal agents include isothiazolin-based preservatives such as 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one.

The polishing composition may contain a basic compound as necessary. Here, a basic compound refers to a compound that has the function of increasing the pH of the polishing composition when added to the composition. Examples of basic compounds include alkali metal hydroxides, carbonates and hydrogen carbonates, quaternary ammonium or salts thereof, ammonia, amines, phosphates and hydrogen phosphates, organic acid salts, etc. The basic compounds may be used alone or in combination of two or more.

(pH)
The pH of the polishing composition 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, or 10.0 or less, typically 0.5 to 10.0. From the viewpoint of processability, surface quality, and the like, 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. In order to realize the above pH in the polishing liquid, a pH adjuster such as an organic acid, an inorganic acid, or a basic compound may be contained as necessary. The above pH may be preferably applied to a polishing composition for a magnetic disk substrate such as a nickel phosphorus substrate. In particular, it may be preferably applied to a polishing composition for primary polishing.

(Polishing fluid)
The polishing composition disclosed herein is typically supplied to an object to be polished in the form of a polishing liquid containing the polishing composition, and used to polish the object to be polished. The polishing liquid may be prepared, for example, by diluting the polishing composition. Here, dilution typically refers to dilution with water. Alternatively, the polishing composition may be used as a polishing liquid as it is. That is, the concept of the polishing composition in the technology disclosed herein includes both a polishing liquid (working slurry) that is supplied to an object to be polished and used to polish the object to be polished, and a concentrated liquid that is diluted and used as a polishing liquid. Such a polishing composition in the form of a concentrated liquid is advantageous from the viewpoint of convenience and cost reduction during production, distribution, storage, etc. The concentration ratio can be, for example, about 1.5 to 50 times. From the viewpoint of storage stability of the concentrated liquid, a concentration ratio of, for example, 2 to 20 times, typically about 2 to 10 times, is appropriate.

(Multi-component polishing composition)
The polishing composition disclosed herein may be a single-component type or a multi-component type including a two-component type. For example, the polishing composition may be configured so that a part A containing some of the components, typically components other than water, and a part B containing the remaining components are mixed and used to polish an object to be polished. Some preferred embodiments of the multi-component polishing composition are composed of a part A containing abrasive grains and a part B containing components other than abrasive grains. The part A containing abrasive grains may further contain a dispersant. Examples of components other than abrasive grains contained in part B include acids. Part B may also contain water-soluble polymers and other additives. During mixing, an oxidizing agent such as hydrogen peroxide may be further mixed. For example, when the oxidizing agent is supplied in the form of an aqueous solution, the aqueous solution may be part C constituting the multi-component polishing composition.

<Applications>
The polishing composition disclosed herein can be preferably applied to polishing magnetic disk substrates such as nickel phosphorus substrates, glass substrates, and carbon substrates. The plating material may be a disk substrate having a metal layer or a metal compound layer other than a nickel phosphorus plating layer on the surface of a substrate disk. In particular, it is suitable as a polishing composition for a nickel phosphorus plated substrate having a nickel phosphorus plating layer on an aluminum alloy substrate disk. In such applications, it is particularly meaningful to apply the technology disclosed herein.

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

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

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

The polishing liquid is then supplied to the object to be polished, and polished in a conventional manner. For example, the object to be polished is set in a general polishing device, and the polishing liquid is supplied to the surface of the object to be polished, i.e., the surface to be polished, through the polishing pad of the polishing device. Typically, the polishing liquid is continuously supplied while the polishing pad is pressed against the surface of the object to be polished, causing the two to move relative to one another. The movement can be, for example, a rotational movement. Through this polishing process, the polishing of the object to be polished is completed.

The polishing pad that can be used is not particularly limited. For example, polishing pads of hard foam polyurethane type, nonwoven fabric type, suede type, etc. can be used. The suede type may be a buff pad, and typically may be a polishing pad in a non-buffed state in which the surface has not been buffed (so-called non-buff pad). Such suede type polishing pads (typically polyurethane polishing pads) are easy to process and can easily achieve high quality of the substrate surface. Note that the polishing pads used in the technology disclosed herein do not contain abrasive grains.

After polishing (specifically, after the primary polishing of the magnetic disk substrate), it is preferable to wash the substrate (cleaning step). The cleaning step is typically performed using a cleaning machine. In the cleaning step, a cleaning liquid may be used, or only running water may be used for cleaning without using a cleaning liquid. Ultrasonic treatment may be performed by applying ultrasonic waves to the substrate immersed in the cleaning liquid or water. By performing such a cleaning step, the abrasive grains remaining on the substrate after polishing can be efficiently removed.

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

The polishing step as described above can be part of a manufacturing process for a magnetic disk substrate, for example a nickel phosphorus substrate. Therefore, this specification provides a manufacturing method and a polishing method for a magnetic disk substrate that include the above polishing step.

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

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

The final polishing composition that can be used in step (2) contains, for example, water in addition to abrasive grains. In addition, the final polishing composition can contain optional components (acid, oxidizing agent, basic compound, various additives, etc.) similar to those of the polishing composition described above, as necessary.

Several examples of the present invention are described below, but it is not intended that the present invention be limited to those examples.

<Preparation of Polishing Composition>
Silica abrasive grains, the additives shown in Table 1, phosphoric acid, 31% hydrogen peroxide solution, and deionized water were mixed to prepare polishing compositions according to Examples 1 to 6 and Comparative Examples 2 to 7. Moreover, a polishing composition according to Comparative Example 1 was prepared in the same manner as in Example 1, except that the additives were not used. The pH of each of the polishing compositions was 1.5. As the silica abrasive grains, a plurality of kinds of silica particles with different particle diameters, particle shapes, particle size distributions, and aspect ratios were prepared, and the abrasive grains containing the above silica particles alone or in combination were used so that the cumulative ₅₀ % particle diameter (D ₅₀ ) on a volume basis by SEM image analysis, _{the area ratio (SP/SC) 50-100 of} the average projected area (SP _50-100 ) to the average circle area (SC 50-100 ) corresponding to the circumference of particles with D ₅₀ or more, and the area ratio (SP/SC) _0-50 of the average projected area (SP _0-50 ) to the average circle area (SC _0-50 ) corresponding to the circumference of particles with less than D 50 were different within a predetermined range. The concentration of the silica particles in the polishing composition was 7% by weight, the concentration of the additive was 0.2 g/L, the concentration of phosphoric acid was 0.1 mol/L, and the concentration of hydrogen peroxide was 0.5 mol/L. The silica particles used in Examples 1 to 6 had an average aspect ratio (A _50-100 ) of D ₅₀ or larger particles of 1.39 to 1.43, and an average aspect ratio (A _all ) of 1.12 to 1.23.

Here, in Table 1, "POE" represents an oxyethylene chain. For example, the additive used in Example 1 is represented by the chemical formula _{C10H7 -} O-( _C2H4O ) _n - _SO3Na , _and is an aromatic ring-containing compound in which the repeating number n of oxyethylene units in this chemical formula is 4. The naphthyl ether shown in Table 1 is β-naphthyl ether.

<Polishing>
The polishing composition according to each example was used as it was as a polishing liquid to polish an object under the following conditions. An aluminum substrate for a hard disk having an electroless nickel phosphorus plating layer on its surface was used as the object to be polished. The diameter of the object to be polished (substrate to be polished) was 3.5 inches (a doughnut shape with an outer diameter of about 95 mm and an inner diameter of about 25 mm), the thickness was 1.75 mm, and 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.

[Polishing conditions]
Polishing equipment: Taiyosha double-sided polishing machine, model "9B-5P/3WAY"
Polishing pad: Polyurethane pad manufactured by FILWEL, product name "CR200"
Number of substrates to be polished: 15 (3 substrates/carrier x 5 carriers)
Polishing liquid supply rate: 135 mL/min Polishing load: 120 g/ ^cm2
Upper platen rotation speed: 27 rpm
Lower surface plate rotation speed: 36 rpm
Sun gear rotation speed: 8 rpm
Amount polished: total thickness of about 2.2 μm on both sides of each substrate. The amount polished was calculated based on the following formula.
Polishing amount [μm]=weight loss of substrate due to polishing [g]/(substrate area [cm ² ]×density of nickel phosphorus plating [g/cm ³ ])×10 ⁴

(Processability)
The polishing rate on both sides of the substrate to be polished was calculated using the polishing composition according to each example under the above polishing conditions. The polishing rate was calculated based on the following formula. The results were converted into relative values with the polishing rate of Comparative Example 1 taken as 100%, and shown in the "polishing rate" column of Table 1. The higher the polishing rate, the higher the processability. When the polishing rate (relative value) is 95% or more, it is determined that the processability is not impaired.
Polishing rate [μm/min]=weight loss of substrate due to polishing [g]/(area of substrate [cm ² ]×density of nickel phosphorus plating [g/cm ³ ]×polishing time [min])×10 ⁴

(Micro waviness)
After polishing using the polishing composition according to each example, one Ni-P substrate was randomly selected from the Ni-P substrates (substrates after polishing) set in each carrier during the polishing, for a total of three Ni-P substrates. Microwaviness was measured for the front and back surfaces of these three Ni-P substrates, a total of six surfaces, using a non-contact surface profiler "NEWVIEW9000" manufactured by ZYGO Corporation, under the conditions of an objective lens magnification of 2.75 times, an intermediate lens magnification of 0.5 times, and a bandpass filter of 80 to 500 μm. Measurements were performed for each of the six surfaces at four points spaced at 90° intervals from the center of the polished substrate to a position 37 mm radially outward, and the average value of these 24 points was taken as the value of microwaviness (Å). The obtained values were converted into relative values with the value of Comparative Example 1 taken as 100%, and are shown in the "microwaviness" column of Table 1. The smaller the value, the more the microwaviness is suppressed. When the microwaviness (relative value) is 97% or less, it is determined that the microwaviness has been improved.

(End Shape)
For the front and back surfaces of the three Ni-P substrates extracted in the above microwaviness measurement, a total of six surfaces, were measured using a non-contact surface profiler "NEWVIEW9000" manufactured by ZYGO Corporation, with an objective lens magnification of 2.75 times and an intermediate lens magnification of 1.0 times, and the PV difference (Peak-Valley difference, maximum height difference) of the measurement position coordinates at the edge of the substrate (region 45.5 mm to 47.5 mm radially outward from the center of the substrate after polishing) was measured, and the average value of the PV difference of the six surfaces was calculated. The obtained value was converted into a relative value with the value of Comparative Example 1 set to 100%, and is shown in the "Edge Shape" column of Table 1. The smaller the value, the more improved the edge shape is compared to Comparative Example 1. If the value (relative value) of the edge shape is 100% or less, it is determined that the edge shape was not impaired.

(Number of residual silica particles)
The substrate to be polished was polished under the above-mentioned polishing conditions using the polishing composition according to each example, and then washed using a washing machine manufactured by CRESEN Co., Ltd., and the number of silica particles remaining on the surface of the substrate to be polished was measured. Specifically, the substrate to be polished was washed in running water under the following conditions without using a brush or a detergent, and the water droplets adhering to the substrate to be polished were removed by a spin dryer, and the substrate to be polished was then dried.
[Washing conditions]
Cleaning agent application time: 0 seconds First cleaning time (only running water): 15 seconds Second cleaning time (only running water): 20 seconds Ultrasonic cleaning time (only running water): 20 seconds Spin dry drying time: 20 seconds Next, using a scanning electron microscope "SU8000" manufactured by Hitachi High-Technologies Corporation, the substrate surface (both sides) after cleaning was observed at a magnification of 50,000 times in 10 fields per side. Then, using image analysis software "WinROOF" manufactured by Mitani Shoji Co., Ltd., the number of residual silica particles in each field was measured, and the average value of the number of residual silica particles per field was calculated. The obtained value was converted into a relative value with the number of residual silica particles in Comparative Example 1 taken as 100%, and shown in the "silica residue" column in Table 1. When the silica residue (relative value) is 95% or less, it is determined that the silica residue reduction effect has been obtained.

As shown in Table 1, in Examples 1 to 6, which used polishing compositions containing silica particles having an area ratio (SP/SC) _50-100 of 40% or more and 65% or less, and containing an aromatic ring-containing compound which is a compound having an aromatic ring and a functional group A or a salt thereof as an additive, the polishing rate was maintained at 95% or more and the end shape was maintained at 100% or less, while the microwaviness was reduced to 97% or less and the silica residue was reduced to 95% or less, and the microwaviness and silica residue were improved without impairing the processability and end shape. It was also confirmed that the polishing composition in which the additive used in Example 1 was changed to an aromatic ring-containing compound in which the number of repetitions n of the oxyethylene unit in the above chemical formula was 13, was able to similarly obtain the effect of reducing the microwaviness and silica residue without impairing the processability and end shape. Moreover, a comparison between Example 1 and Example 6 shows that Example 1, which used an aromatic ring-containing compound having an oxyethylene chain structure, obtained a more excellent silica residue reduction effect. On the other hand, Comparative Examples 2 to 5, in which the same aromatic ring-containing compound as in Example 1 was used in combination with silica particles having an area ratio (SP/SC) _50-100 of less than 40% or more than 65%, could not achieve either a polishing rate of 95% or more or a microwaviness of 97% or less, and no effect of reducing silica residue was observed. In addition, Comparative Examples 6 and 7, in which an additive having no aromatic ring was used instead of the aromatic ring-containing compound used in Example 1, could not achieve either a polishing rate of 95% or more or a microwaviness of 97% or less, and no effect of reducing silica residue was observed. From these results, it can be seen that the use of silica particles having an area ratio (SP/SC) _50-100 in the range of 40% to 65% inclusive in combination with an aromatic ring-containing compound which is a compound having an aromatic ring and a functional group A or a salt thereof plays an important role in improving microwaviness and silica residue without impairing high processability, or while maintaining or improving said processability, and without impairing the end shape.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples given above.

Claims (6)

A polishing composition for magnetic disk substrates, comprising:
The abrasive includes silica particles as abrasive grains, an aromatic ring-containing compound, and water,
The aromatic ring-containing compound is a compound having an aromatic ring and a functional group A or a salt thereof,
said functional group A is selected from the group consisting of a sulfo group, a phosphoric acid group, a phosphonic acid group, an amino group, a carboxy group, an aldehyde group and a hydroxy group;
The silica particles have an average projected area (SP _50-100 ) of particles (D ₅₀ or more particles) whose volume-based particle diameters, as determined by SEM image analysis, are in the cumulative range of 50% or more and 100% or less from the small diameter side, and the average projected area (SP 50-100 ) of the average area (SC _50-100 ) of circles equivalent to the perimeters of the particles corresponding to the D ₅₀ or more particles. The polishing composition according to claim 1, wherein the average projected area (SP _0-50 ) of the silica particles, whose volume-based particle diameters determined by SEM image analysis are in the range of 0% or more and less than 50% cumulatively from the small diameter side (particles less than D ₅₀ ), is more than 65% and not more than 90% of the average area (SC _0-50 ) of the circles equivalent to the perimeters of the particles less than D ₅₀ . The polishing composition according to claim 1 or 2, wherein the molecular weight of the aromatic ring-containing compound is 2000 or less. The polishing composition according to claim 1 or 2, wherein the aromatic ring-containing compound is a compound having an oxyalkylene chain between the aromatic ring and the functional group A, or a salt thereof. A method for manufacturing a magnetic disk substrate, comprising a step of polishing a substrate to be polished using the polishing composition according to claim 1 or 2. A method for polishing a substrate, comprising the step of supplying the polishing composition according to claim 1 or 2 to a substrate to be polished and polishing the substrate.