JP2017102990A - Polishing liquid composition for magnetic disk substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing liquid composition for a magnetic disk substrate capable of reducing the long-wavelength waviness on the surface of the roughly-polished substrate without largely damaging a polishing speed in a rough polishing and further without largely deteriorating the roll-off after polishing.SOLUTION: A polishing liquid composition for magnetic disk substrate contains an aspherical silica particle A and water, in which a pH is not less than 0.5 and not more than 6.0, a ratio D2/D1 of an average secondary particle size D2 of an aspherical silica particle A to an average primary particle size D1 is not less than 2.1 and not more than 4.0, and the average secondary particle size D2 of the aspherical silica particle A is 180 nm or more.SELECTED DRAWING: None

Description

  The present disclosure relates to a polishing liquid composition for a magnetic disk substrate, a method for manufacturing a magnetic disk substrate, and a method for polishing a substrate.

  In recent years, magnetic disk drives have been reduced in size and capacity, and high recording density has been demanded. In order to increase the recording density, it is necessary to reduce the unit recording area and improve the detection sensitivity of the weakened magnetic signal. For this reason, technical development for lowering the flying height of the magnetic head has been underway. For magnetic disk substrates, the smoothness and flatness are improved (reduction of surface roughness, waviness, and edge sagging) and surface defects are reduced (residual abrasive, Reduction of scratches, protrusions, pits, etc.) is strictly demanded.

  In response to such demands, from the viewpoint of achieving both improvement in surface quality and productivity that are smoother and less scratched, a multi-stage polishing method having two or more stages of polishing processes in the method of manufacturing a magnetic disk substrate Is often adopted. In general, in the final polishing step of the multi-stage polishing method, that is, the final polishing step, a polishing composition for finishing that contains colloidal silica particles in order to satisfy the requirements of reducing surface roughness and scratches such as scratches, protrusions, and pits. In a polishing step (also referred to as a rough polishing step) prior to the final polishing step, a polishing liquid composition containing alumina particles as abrasive grains is used from the viewpoint of improving productivity. However, when alumina particles are used as abrasive grains, the piercing of alumina particles into the substrate may cause defects in the magnetic disk substrate or a magnetic disk having a magnetic layer applied to the magnetic disk substrate.

  Then, the polishing liquid composition which does not contain alumina particles but contains silica particles as abrasive grains has been proposed (Patent Documents 1 to 3).

JP 2014-1116057 A JP 2012-111869 A JP 2014-29754 A

  In a conventional polishing composition in which silica particles are used in place of alumina particles, alumina residue due to alumina adhesion or sticking can be suppressed, and protrusion defects on the substrate surface after polishing can be reduced. However, when rough polishing is performed with a polishing composition comprising silica particles instead of alumina particles, long-wave waviness on the substrate surface after polishing becomes a problem. And in order to reduce the long wavelength wave | undulation in rough | crude grinding | polishing, longer polishing time is required than the polishing liquid composition containing an alumina particle. Therefore, there is a problem that the flatness of the substrate surface is deteriorated due to a decrease in productivity and an increase in roll-off (end face sag).

  Therefore, even when silica particles are used as the abrasive grains, the present disclosure does not significantly impair the polishing rate in the rough polishing, and further does not significantly deteriorate the roll-off after the rough polishing. Provided is a polishing composition for a magnetic disk substrate capable of reducing long wavelength waviness.

  The present disclosure includes non-spherical silica particles A and water, and has a pH of 0.5 or more and 6.0 or less, and a ratio between an average secondary particle diameter D2 and an average primary particle diameter D1 of the non-spherical silica particles A. The present invention relates to a polishing composition for a magnetic disk substrate, wherein D2 / D1 is 2.1 or more and 4.0 or less, and the average secondary particle diameter D2 of the non-spherical silica particles A is 180 nm or more.

  The present disclosure relates to a method for manufacturing a magnetic disk substrate, which includes a step of polishing a substrate to be polished using the polishing composition according to the present disclosure.

  The present disclosure relates to a method for polishing a substrate, including a step of polishing a substrate to be polished using the polishing composition according to the present disclosure, wherein the substrate to be polished is a substrate used for manufacturing a magnetic disk substrate.

  According to the present disclosure, even when silica particles are used as the abrasive grains, the polishing rate in the rough polishing is not significantly impaired, and further, the roll-off after the rough polishing is not greatly deteriorated. The effect that long wave waviness can be reduced can be produced. As a result, the productivity of the magnetic disk substrate with improved substrate quality can be improved.

FIG. 1 is an example of a transmission electron microscope (hereinafter also referred to as “TEM”) observation photograph of a confetti type colloidal silica abrasive grain. FIG. 2 is an example of a TEM observation photograph of deformed colloidal silica abrasive grains. FIG. 3 is a cross-sectional view showing the measurement position of the substrate during the roll-off measurement.

  The present disclosure uses a polishing composition containing specific non-spherical silica particles as abrasive grains for rough polishing, without greatly reducing the polishing rate, and greatly aggravating roll-off after rough polishing. And based on the knowledge that long wavelength waviness can be reduced. In general, in the manufacture of a magnetic disk substrate, productivity can be improved if long-wave waviness can be reduced.

  The details of the mechanism that can reduce long-wave waviness without significantly reducing the polishing rate and greatly reducing roll-off after rough polishing by using specific non-spherical silica particles as the abrasive grains are not clear There is not, but it is guessed as follows. The substrate to be polished is usually a method of polishing the substrate to be polished by moving the surface plate or the substrate to be polished while sandwiching the substrate to be polished with a surface plate to which a polishing pad is attached and supplying the polishing composition to the polishing machine. It is polished by. Since the polishing pad sandwiching the substrate to be polished is easily deformed at the end of the substrate to be polished, it is considered that roll-off occurs when a higher load is applied at the end of the substrate surface than at the center of the substrate surface. On the other hand, in the polishing composition according to the present disclosure, by using specific non-spherical silica particles, the polishing rate of the inner peripheral portion of the substrate is improved compared to the outer peripheral portion of the substrate, and as a result, roll-off is suppressed. It is thought. Furthermore, it is considered that the magnitude of vibration that occurs between the polishing pad and the substrate during polishing can be reduced, and long-wave waviness can be reduced. However, the present disclosure need not be interpreted as being limited to these mechanisms.

  That is, the polishing composition according to the present disclosure contains non-spherical silica particles A and water, has a pH of 0.5 or more and 6.0 or less, and an average secondary particle diameter D2 of the non-spherical silica particles A and A polishing liquid for a magnetic disk substrate, wherein the ratio D2 / D1 to the average primary particle diameter D1 is 2.1 or more and 4.0 or less, and the average secondary particle diameter D2 of the non-spherical silica particles A is 180 nm or more. Relates to the composition.

  In the present disclosure, “undulation” of a substrate refers to irregularities on the surface of the substrate having a wavelength longer than the roughness. In the present disclosure, “long wavelength undulation” refers to undulation observed with a wavelength of 500 to 5000 μm. By reducing long-wave waviness on the substrate surface after polishing, the flying height of the magnetic head in the magnetic disk drive can be reduced, and the recording density of the magnetic disk can be improved. The long wavelength waviness of the substrate surface can be measured by the method described in the examples.

[Non-spherical silica particles A]
As described above, the polishing liquid composition according to the present disclosure contains non-spherical silica particles A (hereinafter also referred to as “particles A”).

The average sphericity of the particles A is preferably 0.60 or more, more preferably 0.70 or more, and preferably 0.85 or less, more preferably 0.80 or less, and even more preferably 0.75 or less. In the present disclosure, the average sphericity of the particles A is an average value of the sphericity of at least 200 particles A. The sphericity of the particle A can be calculated from the following equation by obtaining the projected area S and the projected perimeter L of the particle A using, for example, TEM observation and image analysis software.
Sphericality = 4π × S / L ²
The sphericity of the individual particles A is preferably 0.60 or more, more preferably 0.70 or more, and preferably 0.85 or less, more preferably 0.80 or less, like the average sphericity. 75 or less is more preferable.

  The average minor axis of the particles A is preferably 100 nm or more, more preferably 150 nm or more, further preferably 180 nm or more, and further 500 nm or less from the viewpoints of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness. Is preferable, 450 nm or less is more preferable, and 400 nm or less is still more preferable.

  In the present disclosure, the average minor axis of the particles A is an average value of the minor axes of at least 200 particles A. The minor axis of the particle A is the length of the short side of the rectangle when a minimum rectangle circumscribing the projected image of the particle A is drawn using, for example, TEM observation and image analysis software. Similarly, the major axis of the particle A is the length of the long side of the rectangle.

  The average aspect ratio of the particles A is preferably 1.10 or more, more preferably 1.15 or more, and further preferably 1.20 or more from the viewpoints of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness. From the same viewpoint, it is preferably 2.00 or less, more preferably 1.70 or less, and even more preferably 1.50 or less.

  In the present disclosure, the average aspect ratio of the particles A is an average value of the aspect ratios of at least 200 particles A. The aspect ratio of the particle A is the ratio of the major axis to the minor axis of the particle A (major axis / minor axis).

BET specific surface area of the particles A is increased polishing rate, roll-off reduction after rough grinding, and in view of the long wavelength waviness reduction is preferably 50 m ² / g or less, more preferably ^{40m 2 / g, 30m 2 /} g The following is more preferable, and 10 m ² / g or more is preferable, 15 m ² / g or more is more preferable, and 20 m ² / g or more is more preferable. In the present disclosure, the BET specific surface area can be calculated by a nitrogen adsorption method (hereinafter also referred to as “BET method”). Specifically, it can be calculated by the measurement method described in the examples.

  The average primary particle diameter D1 of the particles A is preferably 60 nm or more, more preferably 70 nm or more, still more preferably 80 nm or more, from the viewpoints of polishing rate improvement, roll-off reduction after rough polishing, and long-wave waviness reduction, and From the same viewpoint, 200 nm or less is preferable, 150 nm or less is more preferable, and 120 nm or less is still more preferable.

In the present disclosure, the average primary particle diameter of the particles A can be calculated from the following formula using the BET specific surface area S (m ² / g). Specifically, it can be calculated by the measurement method described in the examples.
Average primary particle diameter (nm) = 2727 / S

  The average secondary particle diameter D2 of the particles A is 180 nm or more, preferably 200 nm or more, more preferably 220 nm or more, from the viewpoints of polishing rate improvement, roll-off reduction after rough polishing, and long-wave waviness reduction, and 500 nm or less is preferable, 400 nm or less is more preferable, and 300 nm or less is still more preferable.

  In the present disclosure, the average secondary particle diameter of the particles A refers to an average particle diameter based on a scattering intensity distribution measured by a dynamic light scattering method. In the present disclosure, the “scattering intensity distribution” means a particle size distribution in terms of weight of sub-micron particles or less obtained by dynamic light scattering (DLS) or quasielastic light scattering (QLS). I mean. Specifically, the average secondary particle diameter of the particles A in the present disclosure can be obtained by the method described in Examples.

  The particle diameter ratio (D2 / D1) between the average secondary particle diameter D2 and the average primary particle diameter D1 of the particles A is from the viewpoint of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness. 1 or more, preferably 2.2 or more, more preferably 2.4 or more, and 4.0 or less, preferably 3.0 or less, and more preferably 2.8 or less.

  In the present disclosure, the particle size ratio (D2 / D1) may mean the degree of deformation of the particles A. In general, the average secondary particle diameter D2 measured by the dynamic light scattering method is such that when the silica particles are irregularly shaped particles, light scattering in the long direction is detected and the processing is performed. In view of this, the larger the degree of deformity, the larger the value. Since the average primary particle diameter D1 converted from the specific surface area value measured by the BET method is expressed in terms of a sphere based on the obtained particle volume, it is a smaller numerical value than the average secondary particle diameter D2. From the viewpoint of the polishing rate, the particle size ratio (D2 / D1) is preferably large in the above range.

  The coefficient of variation (hereinafter also referred to as “CV value”) of the secondary particle diameter of the particles A is preferably 10% or more from the viewpoint of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness. % Or more is more preferable, 20% or more is more preferable, 30% or less is preferable, and 28% or less is more preferable.

  In the present disclosure, the CV value of the secondary particle diameter of the particle A is based on the scattering intensity distribution at a detection angle of 90 ° by the dynamic light scattering method, and the standard deviation of the secondary particle diameter measured is the average secondary particle diameter. The value (unit:%) obtained by dividing and multiplying by 100. Specifically, the CV value can be measured by the method described in Examples.

  Examples of the particles A include colloidal silica, fumed silica, and surface-modified silica. From the viewpoint of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness, the particles A are preferably colloidal silica, and more preferably colloidal silica having the following specific shape.

  From the viewpoints of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness, the shape of the particles A is preferably silica particles having a particle size smaller than the secondary particle size of the particles A as precursor particles. The plurality of precursor particles are aggregated or fused. From the same point of view, the particle A is preferably at least one silica particle selected from a confetti-type silica particle Aa, a deformed-type silica particle Ab, and a deformed and confetti-type silica particle Ac. Silica particles Ab are more preferable.

  In the present disclosure, confetti-type silica particles Aa (hereinafter, also referred to as “particles Aa”) refer to silica particles having unique hook-shaped protrusions on the surface of spherical particles (see FIG. 1). The particle Aa preferably has a shape in which the largest precursor particle a1 and one or more precursor particles a2 having a particle size of 1/5 or less of the precursor particle a1 are aggregated or fused. The particles Aa are preferably in a state in which a plurality of precursor particles a2 having a small particle size are partially embedded in one precursor particle a1 having a large particle size. The particles Aa can be obtained, for example, by the method described in JP 2008-137822 A. The particle diameter of the precursor particles can be obtained as the equivalent circle diameter measured in one precursor particle in an observation image by TEM or the like, that is, the major axis of a circle having the same area as the projected area of the precursor particles. The particle diameters of the precursor particles in the silica particles Ab and the silica particles Ac can be obtained in the same manner.

  In the present disclosure, irregular-shaped silica particles Ab (hereinafter also referred to as “particles Ab”) have a shape in which two or more precursor particles, preferably two or more and ten or less precursor particles are aggregated or fused. This refers to silica particles (see FIG. 2). The particle Ab preferably has a shape in which two or more precursor particles having a particle size of 1.5 times or less are aggregated or fused on the basis of the particle size of the smallest precursor particle. The particles Ab can be obtained, for example, by the method described in JP-A-2015-86102.

  In the present disclosure, irregular and confetti-type silica particles Ac (hereinafter also referred to as “particles Ac”) have the particle Ab as the precursor particle c1, the largest precursor particle c1, and the particle size of the precursor particle c1. It is a shape in which one or more precursor particles c2 which are 1/5 or less are aggregated or fused.

  The particle A preferably contains one or more selected from the particles Aa, Ab and Ac. The total amount of the particles Aa, Ab and Ac in the particle A is preferably 50% by mass or more, more preferably 70% by mass or more from the viewpoint of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness. 80 mass% or more is still more preferable, 90 mass% or more is still more preferable, and substantially 100 mass% is still more preferable.

  From the viewpoints of suppressing a decrease in polishing rate in rough polishing, reducing roll-off and long-wave waviness after rough polishing, and reducing protrusion defects after rough polishing and final polishing, the particles A are flame-melting, sol-gel processing, and pulverization. Although it may be produced by a method, silica particles produced by a particle growth method using an alkali silicate aqueous solution as a starting material (hereinafter also referred to as “water glass method”) are preferable. The usage form of the particles A is preferably a slurry.

  The method for adjusting the particle size distribution of the particles A includes, for example, a method of giving a desired particle size distribution by adding particles serving as a new nucleus in the process of particle growth in the production stage, and a different particle size distribution. Examples thereof include a method of mixing two or more types of silica particles to give a desired particle size distribution.

  The content of the particles A in the polishing composition is preferably 0.1% by mass or more, more preferably 0.5% by mass or more from the viewpoints of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness. More preferably, 1% by mass or more is further preferable, 2% by mass or more is further more preferable, and from the viewpoint of economy, 30% by mass or less is preferable, 25% by mass or less is more preferable, and 20% by mass or less is more preferable. 15% by mass or less is even more preferable.

  When the polishing liquid composition according to the present disclosure contains silica particles other than the particles A, the content of the particles A with respect to the entire silica particles in the polishing liquid composition is improved in polishing rate, reduced roll-off after rough polishing, and From the viewpoint of reducing long wavelength waviness, it is preferably more than 98.0% by mass, more preferably 98.5% by mass or more, still more preferably 99.0% by mass or more, still more preferably 99.5% by mass or more, and 99.99% by mass. 8% by mass or more is even more preferable, and substantially 100% by mass is even more preferable.

[PH adjuster]
The pH of the polishing composition according to the present disclosure is 0.5 or more and 6.0 or less from the viewpoint of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness. The polishing composition according to the present disclosure preferably contains a pH adjuster from the viewpoint of improving the polishing rate, reducing roll-off after rough polishing, reducing long wavelength waviness, and adjusting pH. As a pH adjuster, 1 or more types chosen from an acid and a salt are preferable from the same viewpoint.

  Examples of the acid include inorganic acids such as nitric acid, sulfuric acid, sulfurous acid, persulfuric acid, hydrochloric acid, perchloric acid, phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, polyphosphoric acid, and amidosulfuric acid; organic phosphoric acid and organic phosphonic acid Organic acids such as, and the like. Among these, at least one selected from phosphoric acid, sulfuric acid, and 1-hydroxyethylidene-1,1-diphosphonic acid is preferable from the viewpoint of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness, and sulfuric acid and At least one selected from phosphoric acid is more preferable, and sulfuric acid is more preferable.

  As a salt, the salt of said acid and at least 1 sort (s) chosen from a metal, ammonia, and an alkylamine is mentioned, for example. Specific examples of the metal include metals belonging to Groups 1 to 11 of the periodic table. Among these, from the viewpoint of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness, a salt of the above acid with a metal belonging to Group 1 or ammonia is preferable.

  The content of the pH adjuster in the polishing composition is preferably 0.001% by mass or more, and 0.01% by mass or more from the viewpoints of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness. Is more preferably 0.05% by mass or more, still more preferably 0.1% by mass or more, and from the same viewpoint, 5.0% by mass or less is preferable, and 4.0% by mass or less is more preferable. 3.0 mass% or less is still more preferable, and 2.5 mass% or less is still more preferable.

[Oxidant]
The polishing composition according to the present disclosure may contain an oxidizing agent from the viewpoints of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness. Examples of the oxidizing agent include peroxide, permanganic acid or a salt thereof, chromic acid or a salt thereof, peroxo acid or a salt thereof, oxygen acid or a salt thereof, nitric acid, sulfuric acid, and the like from the same viewpoint. . Among these, at least one selected from hydrogen peroxide, iron nitrate (III), peracetic acid, ammonium peroxodisulfate, iron sulfate (III) and ammonium iron sulfate (III) is preferable. Hydrogen peroxide is more preferable from the viewpoint that metal ions do not adhere to the surface and are used for general purposes and are inexpensive. These oxidizing agents may be used alone or in admixture of two or more.

  The content of the oxidizing agent in the polishing liquid composition is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, further preferably 0.1% by mass or more, from the viewpoint of improving the polishing rate. And from the viewpoints of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness, 4.0% by mass or less is preferable, 2.0% by mass or less is more preferable, and 1.5% by mass or less is more preferable. preferable.

[water]
The polishing liquid composition according to the present disclosure contains water as a medium. Examples of water include distilled water, ion exchange water, pure water, and ultrapure water. The water content in the polishing composition is preferably 61% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, and 85% by mass because the handling of the polishing composition becomes easy. The above is more preferable, and from the same viewpoint, 99% by mass or less is preferable, 98% by mass or less is more preferable, and 97% by mass or less is more preferable.

[Other ingredients]
The polishing liquid composition according to the present disclosure may contain other components as necessary. Examples of other components include thickeners, dispersants, rust inhibitors, basic substances, polishing rate improvers, surfactants, and polymer compounds. The other components are preferably contained in the polishing liquid composition within a range not impairing the effects of the present disclosure, and the content of the other components in the polishing liquid composition is preferably 0% by mass or more, More than 0 mass% is more preferable, 0.1 mass% or more is still more preferable, 10 mass% or less is preferable, and 5 mass% or less is more preferable.

[Alumina abrasive]
In the polishing composition according to the present disclosure, the content of alumina abrasive grains is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, from the viewpoint of reducing protrusion defects, and 0.02% by mass. % Or less is further preferable, and it is more preferable that the alumina abrasive grains are not substantially contained. In the present disclosure, “substantially free of alumina abrasive grains” means that no alumina particles are contained, no alumina particles functioning as abrasive grains, or an amount of alumina particles that affect the polishing result. May not be included. The content of the alumina particles in the polishing liquid composition is preferably 2% by mass or less, more preferably 1% by mass or less, still more preferably 0.5% by mass or less, based on the total amount of abrasive grains in the polishing liquid composition. Even more preferably, it is substantially 0% by weight.

[PH]
The pH of the polishing composition according to the present disclosure is 0.5 or higher, preferably 0.7 or higher, more preferably 0.9 or higher, from the viewpoint of improving the polishing rate and reducing long wavelength waviness, and more preferably 1.0 or higher. The above is more preferable, 1.2 or more is still more preferable, 1.4 or more is still more preferable, and from the same viewpoint, it is 6.0 or less, 4.0 or less is preferable, and 3.0 or less is more Preferably, 2.5 or less is further preferable, and 2.0 or less is even more preferable. The pH is preferably adjusted using the aforementioned acid or a known pH adjuster. The above pH is the pH of the polishing composition at 25 ° C. and can be measured using a pH meter, and is preferably a value two minutes after the electrode of the pH meter is immersed in the polishing composition.

[Method for producing polishing composition]
The polishing composition according to the present disclosure is prepared by, for example, blending a silica slurry containing the particles A and, if desired, a pH adjusting agent, an oxidizing agent and other components by a known method, and adjusting the pH to 0.5 or more and 6 It can be manufactured by setting it to 0.0 or less. Therefore, this indication is related with the manufacturing method of the silica slurry used for manufacture of polishing liquid composition including the process of blending at least particles A and water. Furthermore, this indication is related with the manufacturing method of polishing liquid composition including the process of mix | blending at least particle | grains A and water, and including the process of adjusting pH to 0.5 or more and 6.0 or less as needed. In the present disclosure, “mixing” includes mixing the particles A and water, and, if necessary, a pH adjuster, an oxidizing agent and other components simultaneously or in any order. The blending can be performed using, for example, a mixer such as a homomixer, a homogenizer, an ultrasonic disperser, and a wet ball mill. The preferable compounding quantity of each component in the manufacturing method of polishing liquid composition is the same as the preferable content of each component in polishing liquid composition.

The manufacturing method of the polishing composition of the present disclosure preferably includes the following steps from the viewpoint of dispersibility of silica particles.
Step 1: Step of mixing water, a pH adjuster, and optionally an oxidizing agent to prepare a dispersion medium having a pH of 6.0 or less Step 2: Step of mixing the dispersion medium and silica slurry containing particles A In step 1, the pH of the resulting dispersion medium is preferably adjusted so that the pH of the polishing composition becomes a desired value.

  In the present disclosure, the “content of each component in the polishing liquid composition” refers to the content of each component at the time when the polishing liquid composition is used for polishing. Therefore, when the polishing liquid composition according to the present disclosure is prepared as a concentrate, the content of each component can be increased by the concentration.

[Polishing liquid kit]
The present disclosure relates to a polishing liquid kit for manufacturing a polishing liquid composition, which includes a container-containing slurry in which a silica slurry containing the particles A is stored in a container. The polishing liquid kit according to the present disclosure may further include a dispersion medium having a pH of 6.0 or less housed in a container different from the container-containing slurry. According to the present disclosure, even when silica particles are used as the abrasive grains, the polishing rate in the rough polishing is not significantly impaired, and further, the roll-off after the rough polishing is not greatly deteriorated. A polishing liquid kit from which a polishing liquid composition capable of reducing long wavelength waviness can be obtained can be provided.

  As the polishing liquid kit according to the present disclosure, for example, a solution (first liquid) containing silica slurry (first liquid) containing the particles A and other components that can be blended in a polishing liquid composition used for polishing an object to be polished. 2 liquid) is stored in a state where they are not mixed with each other, and a polishing liquid kit (2 liquid type polishing liquid composition) in which these are mixed at the time of use is mentioned. Examples of other components that can be blended in the polishing liquid composition include a pH adjuster and an oxidizing agent. The first liquid and the second liquid may each contain an optional component as necessary. Examples of the optional component include a thickener, a dispersant, a rust inhibitor, a basic substance, a polishing rate improver, a surfactant, and a polymer compound.

[Polished substrate]
The polishing composition according to the present disclosure is a substrate to be polished and a substrate used for manufacturing a magnetic disk substrate. For example, a Ni-P plated aluminum alloy substrate, silicate glass, aluminosilicate glass, Examples thereof include glass substrates such as crystallized glass and tempered glass, and an aluminum alloy substrate plated with Ni—P is preferable from the viewpoint of strength and ease of handling. In the present disclosure, the “Ni—P plated aluminum alloy substrate” refers to a surface of an aluminum alloy base material that has been subjected to electroless Ni—P plating after being ground. A magnetic disk can be manufactured by performing the process of forming a magnetic layer on the substrate surface by sputtering or the like after the process of polishing the surface of the substrate to be polished using the polishing composition according to the present disclosure. Examples of the shape of the substrate to be polished include a shape having a flat portion such as a disk shape, a plate shape, a slab shape, and a prism shape, and a shape having a curved surface portion such as a lens, and preferably a disk-shaped substrate to be polished. It is. In the case of a disk-shaped substrate to be polished, the outer diameter is, for example, 10 to 120 mm, and the thickness is, for example, 0.5 to 2 mm.

  In general, a magnetic disk is manufactured through a magnetic layer forming process in which a substrate to be polished that has undergone a grinding process is polished through a rough polishing process and a final polishing process. The polishing composition according to the present disclosure is preferably used for polishing in the rough polishing step.

[Method of manufacturing magnetic disk substrate]
The present disclosure includes a step of polishing a substrate to be polished using the polishing liquid composition of the present disclosure (hereinafter also referred to as “polishing step using the polishing liquid composition according to the present disclosure”). The present invention relates to a method (hereinafter also referred to as “substrate manufacturing method according to the present disclosure”).

  In the polishing process using the polishing liquid composition according to the present disclosure, for example, the substrate to be polished is sandwiched by a surface plate with a polishing pad attached thereto, the polishing liquid composition according to the present disclosure is supplied to the polishing surface, and pressure is applied. The substrate to be polished is polished by moving the polishing pad and the substrate to be polished.

  The polishing load in the polishing step using the polishing liquid composition according to the present disclosure is preferably 30 kPa or less, more preferably 25 kPa or less, from the viewpoints of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness. 20 kPa or less is more preferable, 3 kPa or more is preferable, 5 kPa or more is more preferable, and 7 kPa or more is more preferable. In the present disclosure, “polishing load” refers to the pressure of the surface plate applied to the surface to be polished of the substrate to be polished during polishing. The polishing load can be adjusted by applying air pressure or weight to the surface plate or the substrate.

In the polishing process using the polishing liquid composition according to the present disclosure, the polishing amount per 1 cm ^{2 of the} substrate to be polished is 0.20 mg from the viewpoint of improving the polishing rate, reducing roll-off after rough polishing, and reducing long wavelength waviness. The above is preferable, 0.30 mg or more is more preferable, 0.40 mg or more is more preferable, and from the same viewpoint, 2.50 mg or less is preferable, 2.00 mg or less is more preferable, and 1.60 mg or less is further preferable.

The supply rate of the polishing liquid composition per 1 cm ^{2 of the} substrate to be polished in the polishing step using the polishing liquid composition according to the present disclosure is preferably 2.5 mL / min or less from the viewpoint of economy, and is 2.0 mL / min. The following is more preferable, 1.5 mL / min or less is further preferable, and from the viewpoint of improving the polishing rate, 0.01 mL / min or more per 1 cm ^{2 of the} substrate to be polished is preferable, 0.03 mL / min or more is more preferable, 0.05 mL / min or more is more preferable.

  Examples of a method for supplying the polishing liquid composition according to the present disclosure to a polishing machine include a method of continuously supplying using a pump or the like. When supplying the polishing liquid composition to the polishing machine, in addition to the method of supplying it with one liquid containing all the components, considering the storage stability of the polishing liquid composition, etc., it is divided into a plurality of component liquids for blending. Two or more liquids can be supplied. In the latter case, for example, the plurality of compounding component liquids are mixed in the supply pipe or on the substrate to be polished to obtain the polishing liquid composition according to the present disclosure.

  According to the substrate manufacturing method according to the present disclosure, the long-wavelength undulation and roll-off of the substrate surface after rough polishing can be reduced without significantly impairing the polishing rate in rough polishing. The effect that it can manufacture efficiently can be show | played.

[Polishing method]
The present disclosure relates to a magnetic disk substrate polishing method (hereinafter, also referred to as a polishing method according to the present disclosure) including a polishing step using the polishing liquid composition according to the present disclosure.

  By using the polishing method according to the present disclosure, the long-wavelength undulation and roll-off of the substrate surface after the rough polishing can be reduced without significantly impairing the polishing speed in the rough polishing. The effect that productivity of can be improved can be show | played. The specific polishing method and conditions can be the same as those of the substrate manufacturing method according to the present disclosure described above.

  Hereinafter, the present disclosure will be described in more detail by way of examples. However, these examples are illustrative, and the present disclosure is not limited to these examples.

1. Preparation of polishing liquid composition Examples 1-4 and comparison using the abrasive grains (non-spherical silica particles A, alumina abrasive grains), pH adjuster (sulfuric acid), oxidizing agent (hydrogen peroxide), and water in Table 1 The polishing liquid compositions of Examples 1 to 4 were prepared. The content of each component in the polishing composition was 7.5% by mass of abrasive grains, 0.5% by mass of sulfuric acid, and 0.5% by mass of hydrogen peroxide. The pH of the polishing composition was 1.4. The particles A are colloidal silica particles produced by a water glass method. The pH was measured using a pH meter (manufactured by Toa DKK Co., Ltd.), and the value after 2 minutes after the electrode was immersed in the polishing composition was adopted (hereinafter the same).

2. Measuring method of each parameter [Measuring method of average minor diameter, average aspect ratio and average sphericity of silica particles]
A photograph obtained by observing silica particles with a TEM (“JEM-2000FX” manufactured by JEOL Ltd., 80 kV, 1 to 50,000 times) is captured as image data with a scanner on a personal computer, and analysis software (Mitani Corporation “WinROOF (Ver. 3. 6) ”) was used to analyze the projected images of 500 silica particles as follows.
The minor axis and major axis of each silica particle were determined, and the average value of the minor axis (average minor axis) was obtained. Further, an average aspect ratio (average aspect ratio) was obtained from a value obtained by dividing the major axis by the minor axis. Furthermore, from the area S and the perimeter length L of each silica particle, the sphericity of each silica particle was calculated by the following formula, and the average value of sphericity (average sphericity) was obtained.
Sphericality = 4π × S / L ²

[Measurement method of average primary particle diameter of silica abrasive grains]
The average primary particle diameter of the silica abrasive grains was calculated from the following formula using the BET specific surface area S (m ² / g) calculated by the BET method.
Average primary particle diameter (nm) = 2727 / S

The BET specific surface area S was subjected to the following [pre-treatment], then weighed about 0.1 g of the measurement sample into the measurement cell to 4 digits after the decimal point (0.1 mg digit), and 110 ° C. immediately before the measurement of the specific surface area. After being dried for 30 minutes under the above atmosphere, measurement was performed by the BET method using a specific surface area measuring device (Micromeritic automatic specific surface area measuring device, Flowsorb III2305, manufactured by Shimadzu Corporation).
[Preprocessing]
Slurry particles were placed in a petri dish and dried in a hot air dryer at 150 ° C. for 1 hour. The dried sample was finely pulverized in an agate mortar to obtain a measurement sample.

[Measuring method of average secondary particle diameter and CV value of silica particles]
Silica particles are diluted with ion-exchanged water, a dispersion containing 0.02% by mass of silica particles is prepared and used as a sample, and a dynamic light scattering device (“DLS-7000” manufactured by Otsuka Electronics Co., Ltd.) is used. It measured on condition of this. The particle diameter (D50) at which the area of the obtained particle size distribution in terms of weight was 50% of the whole was taken as the average secondary particle diameter. At the same time, the standard deviation in the obtained weight conversion distribution was divided by the average secondary particle diameter, and a value multiplied by 100 was taken as the CV value (unit:%).
Measurement conditions: Sample volume 30 mL
: Laser He-Ne, 3.0 mW, 633 nm
: Scattered light detection angle 90 °
: Accumulation count 200 times

[Measurement method of average secondary particle diameter of alumina abrasive grains]
An aqueous solution containing 0.5% by mass of Poise 530 (manufactured by Kao Corporation, polycarboxylic acid type polymer surfactant) is used as a dispersion medium, and is introduced into the following measuring apparatus, and subsequently the transmittance is 75 to 95%. In this manner, a sample (alumina particles) was put in, and after applying ultrasonic waves for 5 minutes, the particle size was measured.
Measuring instrument: Laser diffraction / scattering particle size distribution measuring device LA920 manufactured by Horiba, Ltd.
Circulation strength: 4
Ultrasonic intensity: 4

3. Polishing Substrate The substrate to be polished was polished under the following polishing conditions using the prepared polishing liquid compositions of Examples 1 to 4 and Comparative Examples 1 to 4.

[Polishing conditions]
Polishing machine: Double-side polishing machine (9B-type double-side polishing machine, manufactured by Speed Fam Co., Ltd.)
Substrate to be polished: Ni-P plated aluminum alloy substrate, thickness: 1.27 mm, diameter 95 mm, number of sheets: 10 polishing liquid: polishing composition polishing pad: suede type (foam layer: polyurethane elastomer), thickness: 1 0.0 mm, average pore diameter: 30 μm, compression ratio of surface layer: 2.5% (manufactured by Filwel)
Plate rotation speed: 40 rpm
Polishing load: 9.8 kPa (set value)
Polishing liquid supply amount: 60 mL / min
Polishing time: silica abrasive 5 minutes 30 seconds, alumina abrasive 3 minutes 30 seconds

4). Evaluation method [Evaluation of polishing rate]
The polishing rates of the polishing composition of Examples 1 to 4 and Comparative Examples 1 to 4 were evaluated as follows. First, the weight per substrate before and after polishing was measured (measured by Sartorius, “BP-210S”), and the amount of mass reduction was determined from the change in mass of each substrate. A value obtained by dividing the average mass reduction amount of all 10 sheets by the polishing time was defined as a polishing rate, and was calculated by the following formula. Furthermore, a relative value was calculated with Comparative Example 1 as 100.
Weight loss (g) = {mass before polishing (g) −mass after polishing (g)}
Polishing speed (mg / min) = mass reduction amount (mg) / polishing time (min)

[Evaluation of long wavelength swell]
Measurements were made on the following conditions for 10 surfaces after polishing, a total of 20 surfaces. The average value of the measured values on the 20 surfaces was calculated as the long wavelength waviness of the substrate. Furthermore, the relative value which set the comparative example 1 as 100.0 was computed.
Measuring equipment: “OptiFLAT III” manufactured by KLA Tencor
Radius Inside / Out: 14.87mm / 47.83mm
Center X / Y: 55.44mm / 53.38mm
Low Cutoff: 2.5mm
Inner Mask: 18.50mm
Outer Mask: 45.5mm
Long Period: 2.5mm
Wa Correction: 0.9
Rn Correction: 1.0
No Zernike Terms: 8

[Roll-off evaluation]
Select one of the 10 substrates after polishing, and use “New View 5032 (lens: 2.5 ×, zoom: 0.5 ×)” manufactured by Zygo for the roll-off value of the selected substrate. And measured as follows.
(Measurement condition)
As shown in FIG. 3, the positions of 43.0 mm and 44.0 mm from the center of the substrate surface toward the outer peripheral direction are point A and point B, respectively, and the center of the substrate surface on the extension line connecting points A and B A position where the distance is 46.6 mm from the first point is defined as point C. And the position of C point of 1 board | substrate after grinding | polishing calculates front and back 3 places (total 6 places), measures the distance of the thickness direction of the board | substrate from each C point to the substrate surface, and those average values are calculated. The roll-off value (nm) was used. For calculating the position of each measurement point, analysis software (Metro Pro) manufactured by Zygo was used. The closer the roll-off value is to a positive (plus) value, the higher the end of the substrate is, and it can be said that roll-off is suppressed.

[Alumina residue evaluation method]
The surface of each substrate after polishing was observed at a magnification of 10,000 with a scanning electron microscope (manufactured by Hitachi, Ltd .: S-4000), and the following three-stage evaluation was performed.
○: No alumina residue observed on the surface Δ: A slight alumina residue observed on the surface ×: Alumina residue observed on the surface

5). Results The results of each evaluation are shown in Table 1.

  As Table 1 shows, Examples 1-4 which contain a specific non-spherical silica particle as an abrasive grain have polishing rate compared with Comparative Examples 1-4 which do not contain a specific non-spherical silica as an abrasive grain. Long-wave waviness after polishing was reduced without significantly detracting from the roll-off and without significantly deteriorating roll-off.

  According to the present disclosure, roll-off and long-wave waviness after polishing can be reduced while maintaining the polishing rate, so that the productivity of manufacturing a magnetic disk substrate can be improved. The present disclosure can be suitably used for manufacturing a magnetic disk substrate.

Claims (10)

Comprising non-spherical silica particles A and water,
pH is 0.5 or more and 6.0 or less,
The ratio D2 / D1 of the average secondary particle diameter D2 and the average primary particle diameter D1 of the non-spherical silica particles A is 2.1 or more and 4.0 or less,
A polishing composition for a magnetic disk substrate, wherein the non-spherical silica particles A have an average secondary particle diameter D2 of 180 nm or more.   The polishing composition for a magnetic disk substrate according to claim 1, wherein the nonspherical silica particles A have an average sphericity of 0.85 or less.   The polishing composition for a magnetic disk substrate according to claim 1 or 2, wherein the non-spherical silica particles A have an average primary particle diameter D1 of 80 nm or more.   4. The polishing composition for a magnetic disk substrate according to claim 1, wherein the content of the alumina abrasive grains is 0.1% by mass or less.   The polishing composition for a magnetic disk substrate according to any one of claims 1 to 4, wherein a coefficient of variation CV of a secondary particle diameter of the non-spherical silica particles A is 30% or less.   The polishing composition for a magnetic disk substrate according to any one of claims 1 to 5, which is used for polishing an Ni-P plated aluminum alloy substrate.   The polishing composition for a magnetic disk substrate according to claim 1, further comprising a pH adjuster.   The polishing composition for a magnetic disk substrate according to any one of claims 1 to 7, further comprising an oxidizing agent.   A method for producing a magnetic disk substrate, comprising a step of polishing a substrate to be polished using the polishing composition for a magnetic disk substrate according to claim 1.   A step of polishing a substrate to be polished using the polishing composition for a magnetic disk substrate according to any one of claims 1 to 8, wherein the substrate to be polished is a substrate used for production of a magnetic disk substrate. A method for polishing a substrate.