GB2566876A - Method for producing magnetic disk substrate - Google Patents
Method for producing magnetic disk substrate Download PDFInfo
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- GB2566876A GB2566876A GB1900767.3A GB201900767A GB2566876A GB 2566876 A GB2566876 A GB 2566876A GB 201900767 A GB201900767 A GB 201900767A GB 2566876 A GB2566876 A GB 2566876A
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
- G11B5/8404—Processes or apparatus specially adapted for manufacturing record carriers manufacturing base layers
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- Manufacturing & Machinery (AREA)
- Manufacturing Of Magnetic Record Carriers (AREA)
- Finish Polishing, Edge Sharpening, And Grinding By Specific Grinding Devices (AREA)
Abstract
Provided is a method for producing a magnetic disk substrate, which is capable of reducing scratches in the substrate surface after polishing, while maintaining a high polishing rate. The present disclosure relates to a method for producing a magnetic disk substrate, which comprises a polishing step for polishing a substrate to be polished with use of a polishing liquid composition containing abrasive grains and water, and wherein the abrasive grains are particles each having a cutting depth of from 5 nm to 25 nm (inclusive), said cutting depth being the depth of a recess that is formed when each abrasive grain cuts the substrate surface.
Description
METHOD FOR PRODUCING MAGNETIC DISK SUBSTRATE
Technical Field [0001] The present disclosure relates to a method for producing a magnetic disk substrate and a method for polishing a substrate.
Background Art [0002] In recent years, a magnetic disk drive has become increasingly smaller in size and larger in capacity, and needs to have higher recording density. Ib increase the recording density, the detection sensitivity of a magnetic signal should be improved. Therefore, technological development has advanced to further reduce the flying height of a magnetic head and to reduce the unit recording area. On the other hand, to ensure such a low flying height of the magnetic head and the recording area, a magnetic disk substrate is strictly required to improve smoothness and flatness (i.e., to reduce surface roughness, waviness, and edge rounding of the end side of the substrate) and to reduce surface defects (such as residual abrasive grains, scratches, protrusions, and pits).
[0003] Ib meet these requirements, in terms of improving both the productivity and the surface quality such as better smoothness and higher resistance to scratches, a method for producing a hard disk substrate usually employs a multistage polishing system that includes two or more stages of polishing. In a final polishing process (i.e., a finish polishing process) of the multistage polishing system, the substrate is generally polished with a finish polishing liquid composition containing colloidal silica particles to reduce the surface roughness and the defects such as scratches. In a polishing process (also referred to as a rough polishing process) prior to the finish polishing process, the substrate is generally polished with a polishing liquid composition containing alumina particles and silica particles to improve the productivity. For example, Patent Documents 1 to 2 propose a method for producing a magnetic disk substrate, in which a polishing liquid composition containing silica particles as abrasive grains is used in a rough polishing process. This method can reduce sticking of the particles into the substrate.
Prior Art Documents
Patent Documents [0004] Patent Document 1: JP 2016-069552 A Patent Document 2'· JP 2014-116057 A
Disclosure of Invention
Problem to be Solved by the Invention [0005] It is necessary to further reduce the defects such as scratches on the substrate surface after polishing while ensuring a high polishing rate in the rough polishing process in order to achieve higher density, including higher capacity and higher integration.
[0006] With the foregoing in mind, the present disclosure provides a method for producing a magnetic disk substrate that can reduce scratches on the substrate surface after polishing while ensuring a high polishing rate.
Means for Solving Problem [0007] The present disclosure relates to a method for producing a magnetic disk substrate. The method includes a polishing process for polishing a substrate to be pohshed with a polishing liquid composition containing abrasive grains and water.
The abrasive grains are particles with which a cutting depth falls in the range of 5 nm to 25 nm. The cutting depth is a depth of depression formed when a surface of the substrate is cut away by the abrasive grains.
[0008] The present disclosure relates to a method for producing a magnetic disk substrate. The method includes a polishing process for polishing a substrate to be pohshed with a polishing liquid composition containing abrasive grains and water. A cutting depth is in the range of 5 nm to 25 nm in the polishing process. The cutting depth is a depth of depression formed when a surface of the substrate is cut away by the abrasive grains.
[0009] The present disclosure relates to a method for polishing a substrate. The method includes polishing a substrate to be pohshed with a polishing liquid composition containing abrasive grains and water. A cutting depth is in the range of 5 nm to 25 nm during the polishing. The cutting depth is a depth of depression formed when a surface of the substrate is cut away by the abrasive grains. The substrate to be polished is a substrate that is used for production of a magnetic disk substrate.
Effects of the Invention [0010] The present disclosure can produce a magnetic disk substrate by reducing scratches on the substrate surface after polishing while ensuring a high polishing rate. Thus, the present disclosure can maintain the productivity of the substrate and also improve the substrate yield.
Brief Description of Drawings [0011] [FIG. 1] FIG. 1 is an example of a photograph of konpeito-Hke silica particles observed with a transmission electron microscope (also referred to as “TEM” in the following).
[FIG. 2] FIG. 2 is an example of a photograph of irregularly shaped silica particles observed with a TEM.
[FIG. 3] FIG. 3 is an example of a photograph of precipitated silica particles observed with a TEM.
[FIG. 4] FIG. 4 is a diagram for explaining an embodiment of a polishing system.
[FIG. 5] FIG. 5 is a diagram for explaining a method for measuring a cutting depth.
Description of the Invention [0012] The present disclosure is based on the findings that scratches on the substrate surface after polishing can be reduced while ensuring a high polishing rate when a cutting depth in the polishing process is set within a predetermined range, or when particles with which the cutting depth falls in the predetermined range are used as abrasive grains. In the production of a magnetic disk substrate, the substrate yield can generally be improved by suppressing the generation of scratches. Therefore, the present disclosure can maintain the productivity and also improve the substrate yield in the production of a magnetic disk substrate.
[0013] The present disclosure relates to a method for producing a magnetic disk substrate (also referred to as a “production method of the present disclosure” in the following). The production method of the present disclosure includes a polishing process for polishing a substrate to be pohshed with a polishing liquid composition containing abrasive grains and water. A cutting depth is in the range of 5 nm to 25 nm in the polishing process. The cutting depth is a depth of depression formed when a surface of the substrate is cut away by the abrasive grains. Further, the present disclosure relates to a method for producing a magnetic disk substrate. This method includes a polishing process for polishing a substrate to be pohshed with a polishing liquid composition containing abrasive grains and water. The abrasive grains are particles with which a cutting depth falls in the range of 5 nm to 25 nm. The cutting depth is a depth of depression formed when a surface of the substrate is cut away by the abrasive grains. The production methods of the present disclosure can produce a magnetic disk substrate with high substrate yield and better productivity by reducing scratches while ensuring a high polishing rate.
[0014] In the production of a magnetic disk, the substrate to be pohshed generally undergoes a grinding process, followed by a rough polishing process, a finish polishing process, and a magnetic layer formation process. From the viewpoint of further improving the final substrate quality the polishing process in the production method of the present disclosure is preferably applied to the rough polishing process.
[0015] In the present disclosure, scratches on the substrate surface can be detected by e.g., an optical microscope and quantitatively evaluated as the number of scratches. Specifically the number of scratches may be evaluated by a method as described in Examples.
[0016] In the present disclosure, the term “cutting depth” means a depth of depression formed when a surface of the substrate is cut away by the abrasive grains. The term “depression” may include cutting marks, recesses, and grooves. The “cutting depth” may be, e.g., a depth of depression formed when the substrate is pohshed under conditions such that the abrasive grains are arranged in a single layer on the surface of the substrate. Moreover, the “cutting depth” may be preferably a depth of depression formed when the substrate is pohshed with the polishing liquid composition having a concentration such that the abrasive grains are arranged in a single layer on the surface of the substrate. In this case, the “concentration such that the abrasive grains are arranged in a single layer on the surface of the substrate” can be calculated as a concentration of the particles (abrasive grains), assuming that a plurality of particles (abrasive grains) are arranged on a polishing pad so that they are in contact with each other, but do not overlap with each other in the thickness direction of the substrate, as shown in FIG. 5. Moreover, the cutting depth can be calculated by measuring a depth of depression formed when the substrate is polished with a polishing machine, a polishing pad, and a polishing load that are used, e.g., for polishing and preferably for rough polishing. In an embodiment, a value of the cutting depth may be the average maximum depth of depression on the substrate surface calculated per one abrasive particle after polishing the substrate under conditions such that the abrasive grains are arranged in a single layer on the surface of the substrate, and preferably after polishing the substrate for a predetermined time (e.g., 30 seconds) with the polishing liquid composition having a concentration such that the abrasive grains are arranged in a single layer on the surface of the substrate. Specifically, the cutting depth may be calculated by a measurement method as described in Examples.
[0017] The following is an example of the measurement method of the cutting depth.
The cutting depth may be measured by, e.g., the following steps G) to (iv).
G) A substrate is pohshed so that depression with a predetermined depth (e.g., 1.0 nm or less) is formed on the substrate surface, and this substrate is used as a substrate to be pohshed.
Gi) A polishing liquid for measuring a cutting depth is prepared to have a concentration such that the abrasive grains are arranged in a single layer on the surface of the substrate, e.g., to have a concentration of the abrasive grains calculated by the following formulas.
[Calculation method of concentration of abrasive grains]
Mass per one particle (g/partide) = volume per one particle (cm3/particle) x specific gravity of particles (g/cm3)
Cross-sectional area per one particle = π x [average secondary particle diameter (cm) /2]2
Concentration of abrasive grains (% by mass) = surface area of polishing pad (cm2) x [mass per one particle (g/particle) I cross-sectional area per one particle (cm2/p article)] I [flow rate of polishing liquid (g/min) x polishing time (min)] x 100 (iii) The polishing surface of the substrate to be polished is polished for a predetermined time (e.g., 30 seconds) with the polishing liquid for measuring a cutting depth. The polishing conditions may be, e.g., conditions as described in Examples.
(iv) The average maximum depth of depression on the substrate surface after polishing is calculated per one abrasive particle as a cutting depth. The average maximum depth of depression per one abrasive particle may be measured by a method as described in Examples.
[0018] In the polishing process in the production method of the present disclosure, from the viewpoint of improving the polishing rate, the cutting depth is 5 nm or more, preferably 6 nm or more, and more preferably 7 nm or more. From the viewpoint of reducing scratches, the cutting depth is 25 nm or less, preferably 15 nm or less, and more preferably 9 nm or less. In one embodiment, from the viewpoint of improving the polishing rate and reducing scratches, the cutting depth is 5 nm or more and 25 nm or less, preferably 6 nm or more and 15 nm or less, and more preferably 7 nm or more and 15 nm or less. Further, in another embodiment, from the viewpoint of improving the polishing rate and reducing scratches, the cutting depth is 5 nm or more and 25 nm or less, preferably 5 nm or more and 9 nm or less or 10 nm or more and 25 nm or less, and more preferably 6 nm or more and 9 nm or less or 10 nm or more and 20 nm or less, and further preferably 7 nm or more and 9 nm or less or 10 nm or more and 17 nm or less.
[0019] [Polishing liquid composition]
The polishing liquid composition used in the polishing process in the production method of the present disclosure (also referred to as “polishing liquid composition I” in the following) contains abrasive grains and water.
[0020] [Abrasive grains]
The abrasive grains in the polishing liquid composition I may be, e.g., abrasive grains with which the cutting depth falls in the above range. The abrasive grains may be used, e.g., in the form of a slurry or powder. From the viewpoint of ease of production of the polishing liquid composition I, the abrasive grains are preferably in the form of a slurry. Therefore, the present disclosure relates to abrasive grains for polishing a magnetic disk substrate, with which the cutting depth falls in the range of 5 nm to 25 nm. Moreover, the present disclosure relates to a slurry (dispersion) containing the abrasive grains for polishing a magnetic disk substrate, with which the cutting depth falls in the range of 5 nm to 25 nm.
[0021] Examples of the abrasive grains include alumina particles and silica particles. From the viewpoint of improving the polishing rate and reducing scratches, the silica particles are preferred. The silica particles may be, e.g., colloidal silica, precipitated silica, fumed silica, ground silica, or surface-modified silica. From the viewpoint of improving the polishing rate and reducing scratches, the silica particles are preferably colloidal silica.
[0022] The colloidal silica may be obtained by, e.g., a particle growth method (also referred to as a “water glass method” in the following) using an aqueous solution of alkali silicate as a material, or a condensation method (also referred to as a “sol· gel method” in the following) of a hydrolysate of alkoxysilane. From the viewpoint of ease of production and economic efficiency, the water glass method is preferred. The silica particles obtained by the water glass method and the sol·gel method can be produced by a conventionally known method. The precipitated silica particles are produced by a precipitation method, which will be described later.
[0023] The silica particles used as abrasive grains may be calcined silica or silica obtained by pulverizing the calcined silica (both may be collectively referred to as “calcined silica” in the following). The calcined silica may be produced by calcining, e.g., the above silica (except for the colloidal silica). In this context, the pulverization means the process of breaking lumps of fine particles into smaller pieces. From the viewpoint of improving the polishing rate and reducing scratches, the content ofthe calcined silica in the abrasive grains is preferably less than 50% by mass, more preferably 30% by mass or less, and further preferably 15% by mass or less.
[0024] <Non-spherical silica particles A>
The abrasive grains preferably contain non-spherical silica particles A (also referred to as “particles A” in the following) as silica particles. The particles A may be, e.g., particles with which the cutting depth falls in the above range.
[0025] From the viewpoint of improving the polishing rate and reducing scratches, the average sphericity of the particles Ais preferably 0.60 or more, and more preferably 0.63 or more. Furthermore, the average sphericity of the particles Ais preferably 0.85 or less, more preferably 0.80 or less, and further preferably 0.75 or less. In the present disclosure, the average sphericity of the particles Ais the average sphericity of at least 500 particles A contained in the polishing liquid composition I. The sphericity of a particle A can be obtained by using, e.g., TEM observation and image analysis software to determine a projected area S and a projected perimeter L of the particle A and substituting the values S and L into the following equation.
Sphericity = 4π x S/L2 [0026] From the viewpoint of improving the polishing rate and reducing scratches, the sphericity of the individual particles Ais preferably 0.60 or more, and more preferably 0.63 or more. Furthermore, the sphericity of the individual particles Ais preferably 0.85 or less, more preferably 0.80 or less, and further preferably 0.75 or less. [0027] From the viewpoint of improving the polishing rate, the average minor axis of the particles Ais preferably 100 nm or more, more preferably 110 nm or more, even more preferably 150 nm or more, and further preferably 180 nm or more.
Furthermore, from the viewpoint of reducing scratches, the average minor axis of the particles Ais preferably 500 nm or less, more preferably 450 nm or less, even more preferably 420 nm or less, still more preferably 400 nm or less, yet more preferably 350 nm or less, much more preferably 300 nm or less, and further preferably 250 nm or less. In the present disclosure, the average minor axis of the particles Ais the average minor axis of at least 500 particles A contained in the polishing liquid composition I. The minor axis of a particle A can be obtained by using, e.g., TEM observation and image analysis software to create a projected image of the particle A and drawing the smallest rectangle that circumscribes the projected image. In this case, the minor axis of the particle A corresponds to the length of a short side of the rectangle.
[0028] From the viewpoint of improving the polishing rate and reducing scratches, the BET specific surface area of the particles Ais preferably 50 m2/g or less, more preferably 40 m2/g or less, and further preferably 30 m2/g or less. Furthermore, the BET specific surface area of the particles Ais preferably 5 m2/g or more, more preferably 10 m2/g or more, even more preferably 20 m2/g or more, and further preferably 25 m2/g or more. In the present disclosure, the BET specific surface area can be calculated by a nitrogen adsorption method (also referred to as a “BET method” in the following). Specifically, the BET specific surface area may be calculated by a measurement method as described in Examples.
[0029] From the viewpoint of improving the polishing rate and reducing scratches, the average primary particle diameter D Ia of the particles A is preferably 60 nm or more, more preferably 70 nm or more, even more preferably 75 nm or more, and further preferably 80 nm or more. Furthermore, the average primary particle diameter D Ia of the particles Ais preferably 250 nm or less, more preferably 220 nm or less, even more preferably 200 nm or less, and further preferably 180 nm or less.
[0030] In the present disclosure, the average primary particle diameter D Ia of the particles A can be calculated by the following formula using the BET specific surface area S (m2/g). Specifically, the average primary particle diameter D Ia of the particles A may be calculated by a measurement method as described in Examples.
Average primary particle diameter (nm) = 2727/S [0031] From the viewpoint of improving the polishing rate and reducing scratches, the average secondary particle diameter D2a of the particles Ais preferably 150 nm or more, more preferably 160 nm or more, even more preferably 170 nm or more, and further preferably 180 nm or more. Furthermore, the average secondary particle diameter D2a of the particles Ais preferably 580 nm or less, more preferably 500 nm or less, even more preferably 400 nm or less, still more preferably 350 nm or less, yet more preferably 300 nm or less, much more preferably 250 nm or less, and further preferably 200 nm or less.
[0032] In the present disclosure, the average secondary particle diameter D2a of the particles Ais the volume average particle diameter based on a scattering intensity distribution that is measured by a dynamic light scattering method. In the present disclosure, the “scattering intensity distribution” is a particle size distribution on a volume basis of submicron particles obtained by dynamic light scattering (DLS) or quasielastic light scattering (QLS). Specifically, the average secondary particle diameter D2a of the particles A may be determined by a method as described in Examples.
[0033] From the viewpoint of improving the polishing rate and reducing scratches, the individual particles A preferably have a shape such that a plurality of precursor particles are aggregated or fused. The precursor particles are silica particles with a particle size smaller than the secondary particle diameter of the particles A. The particles A are preferably at least one type of silica particles selected from konpeito-like silica particles Aa, irregularly shaped silica particles Ab, irregularly shaped, konpeito-like silica particles Ac, and precipitated silica particles Ad. Among them, the irregularly shaped silica particles Ab and the precipitated silica particles Ad are more preferred. The particles A may be one type of non-spherical silica particles or a combination of two or more types of non-spherical silica particles.
[0034] In the present disclosure, the konpeito-like silica particles Aa (also referred to as “particles Aa” in the following) are silica particles, each of which has specific wart-like projections on the spherical surface (see FIG. l). The individual particles Aa preferably have a shape such that the largest precursor particle al and one or more small precursor particles a2 are aggregated or fused. Specifically, the particle size of the precursor particles a2 is not more than one-fifth of the precursor particle al. It is also preferable that some of a plurality of small-diameter precursor particles a2 are embedded in one large- diameter precursor p article a 1. The p articles Aa may be produced by the method disclosed in, e.g., JP 2008-137822 A. The particle size of a precursor particle can be obtained in the following manner. First, the precursor particle is observed with, e.g., a TEM, and then an equivalent circular diameter, i.e., the diameter of a circle having the same area as the projected area of that precursor particle in the TEM image is calculated to provide the particle size. The particle size of the individual precursor particles in the irregularly shaped silica particles Ab and the irregularly shaped, konpeito-like silica particles Ac can also be obtained in the same manner.
[0035] In the present disclosure, the irregularly shaped silica particles Ab (also referred to as “particles Ab” in the following) are silica particles, each of which includes two or more precursor particles, preferably two or more and ten or less precursor particles that are aggregated or fused (see FIG. 2). The individual particles Ab preferably have a shape such that two or more precursor particles with a particle size that is not more than 1.5 times the particle size of the smallest precursor particle are aggregated or fused. The particles Ab may be produced by the method as disclosed in, e.g., JP 2015-86102 A.
[0036] In the present disclosure, the irregularly shaped, konpeito-lihe silica particles Ac (also referred to as “particles Ac” in the following) include the particles Ab as precursor particles cl, and the individual particles Ac have a shape such that the largest precursor particle cl and one or more small precursor particles c2 are aggregated or fused. Specifically, the particle size of the precursor particles c2 is not more than one-fifth of the precursor particle cl.
[0037] Examples of the method for producing the particles Aa, the particles Ab, and the particles Ac include a water glass method, a sol·gel method, and a grinding method. From the viewpoint of improving the polishing rate and reducing scratches, the water glass method is preferred.
[0038] In the present disclosure, the precipitated silica particles Ad (also referred to as “particles Ad” in the following) are silica particles produced by a precipitation method. From the viewpoint of improving the polishing rate and reducing scratches, the individual particles Ad preferably have a shape such that a plurality of primary particles are aggregated, and more preferably have a shape such that a plurality of primary particles with a relatively large particle size are aggregated, as shown in FIG.
3.
[0039] The particles Ad may be produced by known methods such as a method described in TOSOH Research and Tbchnology Review, vol. 45 (2001), pages 65 to 69. Specific examples of the method for producing the particles Ad include a precipitation method in which silica particles are precipitated by a neutralization reaction between silicate such as sodium silicate and mineral add such as sulfuric add. The neutralization reaction is preferably performed under alkaline conditions at a relatively high temperature. This can accelerate the growth of silica primary partides, so that the primary partides are aggregated into a flocculent mass and then predpitated. Preferably, the resulting predpitates may further be ground, thus providing the partides Ad.
[0040] From the viewpoint of improving the polishing rate and reducing scratches, the partides A preferably indude at least one type selected from the partides Aa, Ab,
Ac, and Ad, and more preferably indude at least one type selected from the partides Ab and Ad. From the viewpoint of improving the polishing rate and reducing scratches, the total amount of the partides Aa, Ab, Ac, and Ad in the partides Ais preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, and further preferably substantially 100% by mass.
[0041] From the viewpoint of improving the polishing rate and reducing scratches, the content of the particles Ain the polishing liquid composition I is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and further preferably 2% by mass or more. Furthermore, from the viewpoint of economic efficiency, the content of the particles Ain the polishing liquid composition I is preferably 30% by mass or less, more preferably 25% by mass or less, and further preferably 20% by mass or less.
[0042] <Spherical silica particles B>
When the polishing liquid composition I contains the particles A as abrasive grains, it may further contain preferably spherical silica particles B (also referred to as “particles B” in the following) as abrasive grains. The particles B may be, e.g., particles with which the cutting depth falls in the above range.
[0043] From the viewpoint of improving the polishing rate and reducing scratches, the average sphericity of the particles B is preferably 0.85 or more, and more preferably 0.87 or more. Furthermore, from the same viewpoint, the average sphericity of the particles B is preferably 1.00 or less, and more preferably 0.95 or less. The sphericity of the individual particles B is preferably 0.85 or more, and more preferably 0.87 or more. Furthermore, the sphericity of the individual particles B is preferably 1.00 or less, and more preferably 0.95 or less. The average sphericity and the sphericity of the particles B can be calculated in the same manner as the particles A.
[0044] From the viewpoint of improving the polishing rate, the average minor axis of the particles B is preferably 20 nm or more, more preferably 30 nm or more, and further preferably 40 nm or more. Furthermore, from the viewpoint of reducing scratches, the average minor axis of the particles B is preferably 200 nm or less, more preferably 150 nm or less, and further preferably 110 nm or less. The average minor axis of the particles B can be calculated in the same manner as the particles A.
[0045] From the viewpoint of improving the polishing rate and reducing scratches, the average minor axis of the particles Ais preferably larger than that of the particles
B. From the viewpoint of improving the polishing rate and reducing scratches, the ratio of the average minor axis of the particles A to the average minor axis of the particles B in the polishing liquid composition I, (average minor axis of particles A) / (average minor axis of particles B), is preferably 1.4 or more, more preferably 2.0 or more, and further preferably 2.5 or more. Furthermore, from the same viewpoint, the ratio of the average minor axis of the particles A to the average minor axis of the particles B is preferably 5.6 or less, more preferably 5.0 or less, even more preferably 4.7 or less, and further preferably 4.5 or less.
[0046] From the viewpoint of improving the polishing rate and reducing scratches, the average primary particle diameter D 1b of the particles B is preferably 20 nm or more, more preferably 30 nm or more, and further preferably 40 nm or more. Furthermore, from the same viewpoint, the average primary particle diameter D1b of the particles B is preferably 150 nm or less, more preferably 120 nm or less, and further preferably 100 nm or less. The average primary particle diameter D 1b of the particles B can be calculated in the same manner as the particles A.
[0047] From the viewpoint of improving the polishing rate and reducing scratches, the average secondary particle diameter D2b of the particles B is preferably 20 nm or more, more preferably 30 nm or more, and further preferably 40 nm or more. Furthermore, from the same viewpoint, the average secondary particle diameter D2b of the particles B is preferably 200 nm or less, more preferably 150 nm or less, and further preferably 120 nm or less. The average secondary particle diameter D2b of the particles B can be calculated by the same measurement method as the particles A. [0048] The particles B may be, e.g., colloidal silica, fumed silica, or surface-modified silica. Moreover, the particles B may be, e.g., colloidal silica that is commonly on the market. From the viewpoint of improving the polishing rate and reducing scratches, the particles B are preferably colloidal silica. The particles B may be one type of spherical silica particles or a combination of two or more types of spherical silica particles.
[0049] Examples of the method for producing the particles B include a water glass method, a sol-gel method, and a grinding method. From the viewpoint of improving the polishing rate and reducing scratches, the water glass method is preferred. The particles B are preferably in the form of a slurry when they are used.
[0050] From the viewpoint of improving the polishing rate and reducing scratches, the content of the particles B in the polishing liquid composition I is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and further preferably 1.5% by mass or more. Furthermore, from the viewpoint of economic efficiency, the content of the particles B in the polishing liquid composition I is preferably 10% by mass or less, more preferably 8% by mass or less, and further preferably 6% by mass or less.
[0051] When the abrasive grains in the polishing liquid composition I include the particles A and the particles B, from the viewpoint of improving the polishing rate and reducing scratches, the ratio (mass ratio) A/B of the content of the particles A to the content of the particles B in the polishing liquid composition I is preferably 10/90 or more, more preferably 15/85 or more, and further preferably 25/75 or more. Furthermore, from the same viewpoint, the mass ratio A/B is preferably 99/1 or less, more preferably 90/10 or less, and further preferably 75/25 or less. When the particles A include a combination of two or more types of spherical silica particles, the content of the particles A indicates the total content of two or more types of spherical silica particles. The same is true for the content of the particles B.
[0052] If the abrasive grains in the polishing liquid composition I include abrasive particles other than the particles A and the particles B, the abrasive particles may be, e.g., particles with which the cutting depth falls in the above range. From the viewpoint of improving the polishing rate and reducing scratches, the total content of the particles A and the particles B with respect to all the abrasive grains in the polishing liquid composition I is preferably 98.0% by mass or more, more preferably 98.5% by mass or more, even more preferably 99.0% by mass or more, still more preferably 99.5% by mass or more, yet more preferably 99.8% by mass or more, and further preferably substantially 100% by mass.
[0053] [pH adjuster]
From the viewpoint of improving the polishing rate, reducing scratches, and adjusting the pH, the polishing liquid composition I may contain a pH adjuster. From the same viewpoint, the pH adjuster is preferably at least one selected from adds and salts.
[0054] Examples of the adds indude the following: inorganic adds such as nitric add, sulfuric add, sulfurous add, persulfuric add, hydrochloric add, perchloric add, amidosulfonic add, phosphoric add, polyphosphoric add, and phosphonic add; and organic adds such as organic phosphoric add and organic phosphonic add. In particular, from the viewpoint of improving the polishing rate and reducing scratches, the adds are preferably at least one selected from phosphoric add, sulfuric add, and l-hydroxyethylidene-l,l-diphosphonic add, more preferably at least one selected from sulfuric add and phosphoric add, and farther preferably phosphoric add.
[0055] Examples of the salts indude the following: salts of the above adds and at least one selected from metals, ammonia, and alkylamine. The specific examples of the metals indude metals of Groups 1 to 11 of the periodic table. In particular, from the viewpoint of improving the polishing rate and reducing scratches, salts of the above adds and metals of Group 1 or ammonia are preferred.
[0056] From the viewpoint of improving the polishing rate and reducing scratches, the content of the pH adjuster in the polishing liquid composition I is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.05% by mass or more, and further preferably 0.1% by mass or more. Furthermore, from the same viewpoint, the content of the pH adjuster in the polishing liquid composition I is preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less, and further preferably 2.5% by mass or less.
[0057] [Oxidizing agent]
From the viewpoint of improving the polishing rate and reducing scratches, the polishing liquid composition I may contain an oxidizing agent. From the same dewpoint, examples of the oxidizing agent indude peroxide, permanganic add or its salt, chromic add or its salt, peroxoadd or its salt, and oxyadd or its salt. Among them, the oxidizing agent is preferably at least one selected from hydrogen peroxide, iron (III) nitrate, peracetic add, ammonium peroxodisulfate, iron (III) sulfate, and ammonium iron (III) sulfate. From the dewpoint of improving the polishing rate, preventing the adhesion of metal ions to the surface of a substrate to be polished, and ease of availability, hydrogen peroxide is more preferred. These oxidizing agents may be used indiddually or in combinations of two or more.
[0058] From the dewpoint of improving the polishing rate and reducing scratches, the content of the oxidizing agent in the polishing liquid composition I is preferably
0.01% by mass or more, more preferably 0.05% by mass or more, and further preferably 0.1% by mass or more. Furthermore, from the same viewpoint, the content of the oxidizing agent in the polishing liquid composition I is preferably 4.0% by mass or less, more preferably 2.0% by mass or less, and further preferably 1.5% by mass or less.
[0059] [Water]
The polishing liquid composition I contains water as a medium. The water may be, e.g., distilled water, ion-exchanged water, pure water, or ultrapure water.
From the viewpoint of ease of handling of the polishing liquid composition, the content of water in the polishing liquid composition I is preferably 61% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and further preferably 85% by mass or more. Furthermore, from the same viewpoint, the content of water in the polishing liquid composition I is preferably 99% by mass or less, more preferably 98% by mass or less, and further preferably 97% by mass or less. [0060] [Other components]
The polishing liquid composition I may contain other components as needed. The other components may include, e.g., a thickening agent, a dispersing agent, an anticorrosive agent, basic substances, a polishing rate improver, a surface-active agent, and a polymer compound. In this case, the polishing liquid composition I preferably contains the other components to the extent that they do not inhibit the effects of the present disclosure. The content of the other components in the polishing liquid composition I is preferably 0% by mass or more, more preferably more than 0% by mass, and further preferably 0.01% by mass or more. Furthermore, the content of the other components in the polishing liquid composition I is preferably 10% by mass or less, and more preferably 5% by mass or less.
[0061] [Alumina abrasive grains]
Ta reduce sticking of alumina particles into the substrate, the content of alumina abrasive grains in the polishing liquid composition I is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and even more preferably 0.02% by mass or less. It is further preferable that the polishing liquid composition I does not substantially contain alumina abrasive grains. In the present disclosure, the phrase “not substantially contain alumina abrasive grains” may mean any of the following: G) the polishing liquid composition I does not contain alumina particles; (ii) the polishing liquid composition I does not contain alumina particles in an amount sufficient to function as abrasive grains; and (iii) the polishing liquid composition I does not contain alumina particles in an amount that would affect the polishing results.
The content of the alumina particles in the polishing liquid composition I is preferably 5% by mass or less, more preferably 2% by mass or less, even more preferably 1% by mass or less, and further preferably substantially 0% by mass with respect to the total amount of the abrasive grains in the polishing liquid composition I.
[0062] [pH]
From the viewpoint of improving the polishing rate and reducing scratches, the pH of the polishing liquid composition I is preferably 0.5 or more, more preferably 0.7 or more, even more preferably 0.9 or more, still more preferably 1.0 or more, yet more preferably 1.2 or more, and further preferably 1.4 or more. Furthermore, from the same viewpoint, the pH of the polishing liquid composition I is preferably 6.0 or less, more preferably 4.0 or less, even more preferably 3.0 or less, still more preferably 2.5 or less, and further preferably 2.0 or less. The pH is preferably adjusted by the above adds or any known pH adjuster. The pH of the polishing liquid composition I is a value that can be measured at a temperature of 25°C with a pH meter, and preferably a value that is obtained 30 seconds after an electrode of the pH meter is immersed in the polishing liquid composition.
[0063] [Preparation of polishing liquid composition]
The polishing liquid composition I can be prepared by blending, e.g., the partides A and water, and optionally at least one selected from the partides B, a pH adjuster, an oxidizing agent, and other components with a known method. For example, the polishing liquid composition I may be obtained by blending at least the partides A and water. In the present disdosure, the term ‘blend” may indicate that the partides A and water, and optionally the partides B, a pH adjuster, an oxidizing agent, and other components are mixed simultaneously or in any order. The blending can be performed, e.g., with a mixer such as a homomixer, a homogenizer, an ultrasonic disperser, or a wet ball mill. The blending amount of each component for the preparation of the polishing liquid composition I may be the same as the content of each component in the polishing liquid composition I, as described above.
[0064] In the present disclosure, “the content of each component in the polishing liquid composition” means the amount of each component that the polishing liquid composition contains when it is used for polishing. Therefore, if the polishing liquid composition I is produced as a concentrate, the content of each component in the polishing liquid composition may be increased by an amount corresponding to the concentration.
[0065] [Substrate to be polished]
The substrate to be pohshed of the present disclosure is a substrate that is used for the production of a magnetic disk substrate. For example, the substrate may be a Ni-P plated aluminum alloy substrate. In the present disclosure, the “Ni-P plated aluminum alloy substrate” is produced by grinding the surface of an aluminum alloy base material and then subjecting the aluminum alloy base material to an electroless Ni-P plating treatment. After polishing the surface of the substrate to be pohshed in the polishing process of the present disclosure, a magnetic layer is formed on the polished substrate surface by sputtering or the like, so that a magnetic disk can be produced. The substrate to be pohshed may have any shape, including a shape with a flat portion such as a disk, plate, slab, or prism and a shape with a curved portion such as a lens. Among them, a disk-shaped substrate is preferred. When the substrate to be pohshed has a disk shape, the outer diameter is, e.g., 10 to 120 mm and the thickness is, e.g., 0.5 to 2 mm.
[0066] [Polishing process]
In the polishing process in the production method of the present disclosure, e.g., the substrate to be pohshed is sandwiched between surface plates to which a polishing pad is attached, and the polishing liquid composition I is supphed to the polishing surface. Then, the polishing pad or the substrate to be polished is moved while applying pressure, thereby polishing the substrate. The polishing process of the present disclosure may include adjusting the polishing conditions so that the cutting depth falls in the above range. For example, the polishing process may include selecting the abrasive grains with which the cutting depth will fall in the above range under a polishing load of 3 kPa or more and 30 kPa or less.
[0067] From the viewpoint of improving the polishing rate and reducing scratches, the polishing load in the polishing process is preferably 30 kPa or less, more preferably kPa or less, even more preferably 20 kPa or less, still more preferably 18 kPa or less, yet more preferably 16 kPa or less, and further preferably 14 kPa or less.
Furthermore, the polishing load is preferably 3 kPa or more, more preferably 5 kPa or more, even more preferably 7 kPa or more, still more preferably 8 kPa or more, and further preferably 9 kPa or more. In the present disclosure, the “polishing load” indicates the pressure of a surface plate applied to the polishing surface of the substrate to be polished during polishing. The polishing load can be adjusted by applying air pressure or weight to, e.g., the surface plate and the substrate.
[0068] From the viewpoint of improving the polishing rate and reducing scratches, the amount of polishing per 1 cm2 of the substrate to be polished in the polishing process is preferably 0.20 mg or more, more preferably 0.30 mg or more, and further preferably 0.40 mg or more. Furthermore, from the same viewpoint, the amount of polishing per 1 cm2 of the substrate to be polished is preferably 2.50 mg or less, more preferably 2.00 mg or less, and further preferably 1.60 mg or less.
[0069] From the viewpoint of economic efficiency, the supply rate of the polishing liquid composition I per 1 cm2 of the substrate to be polished in the polishing process is preferably 0.25 mL/min or less, more preferably 0.20 mL/min or less, even more preferably 0.15 mL/min or less, and further preferably 0.10 mL/min or less. Furthermore, from the viewpoint of improving the polishing rate, the supply rate of the polishing liquid composition I per 1 cm2 of the substrate to be polished is preferably 0.01 mL/min or more, more preferably 0.03 mL/min or more, and further preferably 0.05 mL/min or more.
[0070] The polishing liquid composition I may be continuously supplied to a pofishing machine by using, e.g., a pump in the poEshing process. Moreover, the poEshing Equid composition I may be suppEed to a poEshing machine as a single solution containing all the components. Alternatively, in view of the storage stabiEty or the like of the poEshing Equid composition, it may be divided into a pluraEty of component solutions, and two or more component solutions may be suppEed. In the latter case, the pluraEty of component solutions are mixed, e.g., in a supply pipe or on the substrate to be poEshed to form the poEshing Equid composition I of the present disclosure.
[0071] [PoEshing method]
The present disclosure relates to a method for polishing a substrate (also referred to as a “polishing method of the present disclosure” in the following). The polishing method of the present disclosure includes polishing a substrate to be pohshed with a polishing liquid composition containing abrasive grains and water. A cutting depth is in the range of 5 nm to 25 nm during the polishing. The cutting depth is a depth of depression formed when a surface of the substrate is cut away by the abrasive grains. The substrate to be pohshed is a substrate that is used for the production of a magnetic disk substrate. The polishing method of the present disclosure can produce a magnetic disk substrate with high substrate yield and better productivity by reducing scratches while ensuring a high polishing rate. The specific polishing method and conditions may be performed in the same manner as the above production method of the present disclosure. From the viewpoint of further improving the final substrate quality, the polishing method of the present disclosure is preferably applied to the rough polishing process.
[0072] The production method and the polishing method of the present disclosure can be performed by a polishing system for a magnetic disk substrate, as shown in FIG. 4. The polishing system includes a first polishing machine 1 for a rough polishing process, a cleaning unit 2 for a cleaning process, and a second polishing machine 3 for a finish polishing process. Therefore, the present disclosure relates to a polishing system for a magnetic disk substrate. The polishing system includes a polishing machine 1 that pohshes (rough polishing) a substrate to be pohshed with the polishing liquid composition I of the present disclosure, a cleaning unit 2 that cleans the substrate that has been pohshed by the polishing machine 1, and a polishing machine 3 that pohshes (finish polishing) the cleaned substrate with a polishing liquid composition II. From the viewpoint of reducing defects such as protrusions after the finish polishing process, the polishing liquid composition II used in the finish polishing process preferably contains silica particles as abrasive grains. From the viewpoint of reducing long wavelength waviness after the finish polishing process, the silica particles are preferably colloidal silica. From the viewpoint of reducing defects such as protrusions after the finish polishing process, it is preferable that the polishing liquid composition II used in the finish polishing process does not substantially contain alumina abrasive grains. In the present disclosure, the term dong wavelength waviness” indicates waviness that is observed at a wavelength of 500 to 5000 μηι. By reducing long wavelength waviness of the substrate surface after polishing, the flying height of a magnetic head of a magnetic disk drive can be reduced, and the recording density of a magnetic disk can be improved.
Examples [0073] Hereinafter, the present disclosure will be described in more detail by way of examples. However, the following examples are merely illustrative and are not intended to limit the present disclosure.
[0074] The polishing liquid composition I was prepared in the following manner, and polishing of a substrate to be pohshed was performed under the following conditions. The method for preparing the polishing liquid composition I, the additives used, the measurement methods of parameters, the polishing conditions (polishing method), and the evaluation method will be described below.
[0075] 1. Preparation of polishing liquid composition I
Using abrasive grains (non-spherical silica particles A, spherical silica particles B, and alumina abrasive grains) in Table 1, an add (phosphoric add), an oxidizing agent (hydrogen peroxide), and water, polishing liquid compositions I of Examples 1 to 6 and Comparative Examples 1 to 14 were prepared, as shown in Table
3. The content of each component in the polishing liquid compositions I was 5% by mass for the abrasive grains, 1.5% by mass for the phosphoric add, and 0.8% by mass for the hydrogen peroxide. The pH of the polishing liquid compositions I was 1.6.
The types of the non-spherical silica partides Aused as abrasive grains were irregularly shaped silica partides and predpitated silica partides. In Table 1, the irregularly shaped silica partides Al, A2, and A8 to A10 were partides (colloidal silica) produced by the water glass method. The irregularly shaped silica partides A7 were partides (colloidal silica) produced by the sol·gel method. The predpitated silica partides A3 to A6 were partides produced by the predpitation method. The spherical silica partides B used as abrasive grains were partides (colloidal silica) produced by the water glass method. The pH was measured with a pH meter (manufactured by DKK-TOA CORPORATION), and the values obtained 30 seconds after the immersion of an electrode in each of the polishing liquid compositions were used (the same is true for the following). [0076] [TABLE 1]
| Particle | Type of particle | BET specific surface area (m2/g) | Average primary particle diameter (nm) | Average secondary particle diameter (nm) | Average minor axis (nm) |
| A1 | Irregularly shaped silica | 30.1 | 90.6 | 173 | 189 |
| A2 | Irregularly shaped silica | 28.0 | 97.4 | 186 | 249 |
| A3 | Precipitated silica | 15.0 | 181.8 | 346 | 418 |
| A4 | Precipitated silica | 19.0 | 143.5 | 495 | 507 |
| A5 | Precipitated silica | 16.0 | 170.4 | 426 | 491 |
| A6 | Precipitated silica | 48.0 | 56.8 | 301 | 280 |
| A7 | Irregularly shaped silica (sol-gel method) | 36.5 | 74.7 | 103 | 102 |
| A8 | Irregularly shaped silica | 51.0 | 53.5 | 75 | 68 |
| A9 | Irregularly shaped silica | 49.0 | 55.7 | 103 | 102 |
| A10 | Irregularly shaped silica | 12.1 | 225.4 | 587 | 804 |
| A11 | Alumina | 24.9 | 109.5 | 313 | - |
| A12 | Alumina | 11.2 | 243.5 | 645 | - |
| B1 | Spherical silica | 60.8 | 44.9 | 54 | 51 |
| B2 | Spherical silica | 51.0 | 53.5 | 91 | 91 |
| B3 | Spherical silica | 30.5 | 89.4 | 109 | 109 |
| B4 | Spherical silica | 18.6 | 146.6 | 168 | 165 |
| B5 | Spherical silica | 9.5 | 287.1 | 301 | 301 |
The silica particles other than the particles A7 were produced by the water glass method.
[0077] 2. Measurement method of each parameter 5 [0078] [Measurement method of BET specific surface area of abrasive grains]
The BET specific surface area S was measured in the following manner.
After the following “pretreatment’’ was performed, a measurement sample of about 0.1 g was accurately weighed in a measuring cell to four decimal places (i.e., the place of 0.1 mg). The measurement sample was dried in an atmosphere at 110°C for 30 minutes immediately before measuring the specific surface area. Then, the specific surface area was measured by the BET method using a specific surface area measuring device (Micromeritics Automatic Surface Area Analyzer, FlowSorb III 2305 manufactured by Shimadzu Corporation).
[Pretreatment]
The abrasive grains in the form of a slurry were put in a petti dish and dried in a hot air dryer at 150°C for 1 hour. The dried sample was finely pulveiized in an agate mortar, thus providing a measurement sample.
[0079] [Measurement method of average primary particle diameter of abrasive grains]
The average primary particle diameter of the abrasive grains was calculated by the following formula using the above BET specific surface area S (m2/g).
Average primary particle diameter (nm) = 2727/S.
[0080] [Measurement method of average secondary particle diameter of silica abrasive grains]
The silica particles were diluted with ion-exchanged water to prepare a dispersion containing 1% by mass of the silica particles. Then, the dispersion was placed in the following measuring device, and a volume particle size distribution of the silica particles was obtained. As a result, the particle diameter (Z-average value) at which the cumulative volume frequency of the volume particle size distribution reached 50% was defined as a secondary particle diameter.
Measuring device ' Zetasizer Nano “Nano S” manufactured by Malvern Panalytical Ltd.
(Measurement conditions)
Amount of sample ' 1.5 mL
Laser: He-Ne, 3.0 mW, 633 nm
Scattering light detection angle: 173° [0081] [Measurement method of average secondary particle diameter of alumina abrasive grains]
An aqueous solution containing 0.5% by mass of POIZ 530 (polycarboxylate polymer type surfactant manufactured by Kao Corporation) was used as a dispersion medium and placed in the following measuring device. Subsequently, a sample (alumina particles) was added so that the transmittance was 75 to 95%. Then, ultrasonic waves were applied to the sample for 5 minutes, and the particle size was measured.
Measuring device' laser beam difftaction/scatteiing particle size distribution analyzer LA920 manufactured by HORIBALtd.
Circulation strength: 4
Ultrasonic intensity: 4 [0082] [Measurement method of shape and average minor axis of abrasive grains]
The abrasive grains were observed with a TEM (JEM-2000FX, 80 kV, 10000-50000X manufactured by JEOL Ltd.), and TEM images were photographed and scanned into a personal computer as image data using a scanner. Then, the projected image data of 500 particles were analyzed by analysis software (WinROOF (Ver 3.6) available from Mitani Corporation). The minor axes of the individual particles were measured, and the average of these minor axes (average minor axis) was calculated. [0083] 3. Polishing test
Polishing of a substrate to be polished was performed in accordance with the following processes (l) and (2). The conditions of each process were as follows.
(1) Polishing process: polishing the polishing surface of the substrate to be polished with the polishing liquid composition I (2) Cleaning process: cleaning the substrate obtained by the process (l) [0084] [Substrate to be polished]
The substrate to be polished was a Ni-P plated aluminum alloy substrate.
The substrate to be polished had a thickness of 1.27 mm and a diameter of 95 mm. [0085] [Process (l): polishing]
Polishing machine: double-sided polishing machine (9B Double Side Polisher manufactured by Speedfam Co., Ltd.)
Number of substrates to be polished: 10
Polishing liquid: polishing liquid compositions I in Examples 1 to 9 and Comparative Examples 1 to 17
Polishing pad: suede type (foam layer: polyurethane elastomer), thickness: 1.0 mm, average pore diameter: 30 pm, compressibility of surface layer: 2.5% (“CR200” manufactured by FILWEL CO., LTD.)
Number of revolutions of surface plate: 35 rpm
Polishing load: set value shown in Tables 3 to 4
Supply of polishing liquid: 100 mL/min (corresponding to 0.076 mL/min per 1 cm2 of a surface of the substrate to be polished)
Polishing time: 6 minutes [0086] [Process (2): cleaning]
The substrates obtained by the process (l) were cleaned under the following conditions.
First, an alkaline cleaning composition of pH 12 containing 0.1% by mass of KOH aqueous solution was placed in a tank, and each of the substrates obtained by the process (l) was immersed in the alkaline cleaning composition for 5 minutes.
Next, the substrates were rinsed with ion exchanged water for 20 seconds after the immersion. Then, the rinsed substrates were transferred to a scrub cleaning unit in which cleaning brushes were mounted, so that the substrates were cleaned.
[0087] 4. Measurement of cutting depth
The cutting depth was measured by the following measurement method.
First, substrates were previously prepared for the measurement. Specifically, the substrates similar to those used in the polishing test were subjected to rough polishing and finish polishing by a known method, so that depression with a depth of 1.0 nm or less was formed on the substrate surface. The depth of the depression on the substrate surface was measured by an optical interferometric surface profile measuring device “OptiFLAT III” (manufactured by KLA-Tencor Corporation) under the measurement conditions of the cutting depth, as will be described later.
Next, the substrates thus prepared were polished under the same conditions as those of the process (l) in Examples 1 to 9 and Comparative Examples 1 to 17, as shown in Tables 3 to 4, except that the concentration of the abrasive grains was changed as shown in Table 2 and the polishing time was 30 seconds. The specific polishing conditions were as follows. The concentration of the abrasive grains means a concentration such that the abrasive grains were arranged in a single layer on the surface of the substrate. The concentration was calculated in the following manner.
Then, the average maximum depth of depression on the substrate surface after polishing was calculated per one abrasive particle as a cutting depth.
Specifically, the polished substrates were cleaned in the same manner as the process (2). Then, using the optical interferometric surface profile measuring device OptiFLAT III” (manufactured by KLA-Ifencor Corporation), any cross-sectional profile was taken for each substrate to measure the maximum depth of depression under the measurement conditions of the cutting depth, as will be described later. In this case, the maximum depth of depression was measured at 5 points per surface of 4 substrates. Accordingly, the average of the measured values at a total of 20 points was calculated as a cutting depth. Tables 3 to 4 show the results.
[0088] <Polishing conditions>
Polishing machine: double-sided polishing machine (9B Double Side Polisher manufactured by Speedfam Co., Ltd.)
Polishing pad: “CR200” manufactured by FILWEL CO., LTD.
Number of substrates: 4
Polishing load: set value shown in Tables 3 to 4 (3.6 to 19.3 kPa)
Number of revolutions of surface plate: 35 rpm
Flow rate of polishing liquid: 100 mL/min (corresponding to 0.190 mL/min per 1 cm2 of a surface of the substrate)
Polishing time: 30 seconds [0089] [Calculation method of concentration of abrasive grains]
The cutting depth means a depth of depression formed when the substrate is polished under conditions such that the abrasive grains (particles) are arranged in a single layer on the surface of the substrate. These conditions can be set by adjusting the concentration of the abrasive grains in the polishing liquid composition and the amount of the polishing liquid composition. In this case, assuming that the abrasive grains contained in the polishing liquid composition were arranged on the polishing pad so that a plurality of abrasive grains (particles) were in contact with each other, but did not overlap with each other in the thickness direction of the substrate, as shown in FIG. 5, the concentration of the abrasive grains in the polishing liquid composition was calculated based on the following formula. Table 2 shows the calculated values.
«Calculation formula for concentration of abrasive grains>
• Surface area (both sides) of polishing pad: 5526 cm2 • Specific gravity of silica: 2.2 g/cm3 • Specific gravity of alumina: 4.0 g/cm3 • Particle diameter of abrasive grains: average secondary particle diameter (cm) • Flow rate of pobshing bquid composition: 100 mL/min • Pobshing time: 30 seconds • Mass of pobshing liquid composition: 50 g (specific gravity of pobshing liquid:
1) • Mass per one particle (g/partide) = volume per one partide (cm3/partide) x specific gravity of partides (g/cm3) = (4/3) x π x (average secondary partide diameter/2)3 x specific gravity of partides (g/cm3) • Cross-sectional area per one partide (cm2/partide) = π x (average secondary partide diameter/2)2 • Concentration of abrasive grains (% by mass) = 5526 (cm2) x mass per one partide (g/partide) I cross-sectional area per one partide (cm2/partide) / 50 x 100 [0090] <Measurement conditions of cutting depth>
Measuring equipment: optical interferometric surface profile measuring device “OptiFLAT III” (manufactured by KLA-Tencor Corporation)
Radius Inside/Outi 14.87 mm 147.83 mm
Center X/Y 55.44 mm 153.38 mm
Low Cutoff: 2.5 mm
Inner Mask: 18.50 mm
Outer Mask: 45.5 mm
Long Period: 2.5 mm
Wa Correction: 0.9
Rn Correction: 1.0
No Zemike Terms: 8 [0091] [TABLE 2]
| Table 2 | Particle diameter (nm) | Concentration of abrasive grain (% by mass) |
| Ex. 1 | 173 | 0.28 |
| Ex. 2 | 186 | 0.30 |
| Ex. 3 | 346 | 0.56 |
| Ex. 4 | 195 | 0.32 |
| Ex. 5 | 294 | 0.48 |
| Ex. 6 | 260 | 0.42 |
| Ex. 7 | 186 | 0.30 |
| Ex. 8 | 186 | 0.30 |
| Ex. 9 | 186 | 0.30 |
| Comp. Ex. 1 | 54 | 0.09 |
| Comp. Ex. 2 | 91 | 0.15 |
| Comp. Ex. 3 | 109 | 0.18 |
| Comp. Ex. 4 | 168 | 0.27 |
| Comp. Ex. 5 | 301 | 0.49 |
| Comp. Ex. 6 | 301 | 0.49 |
| Comp. Ex. 7 | 157 | 0.25 |
| Comp. Ex. 8 | 103 | 0.17 |
| Comp. Ex. 9 | 88 | 0.14 |
| Comp. Ex. 10 | 75 | 0.12 |
| Comp. Ex. 11 | 103 | 0.17 |
| Comp. Ex. 12 | 587 | 0.95 |
| Comp. Ex. 13 | 313 | 0.92 |
| Comp. Ex. 14 | 645 | 1.90 |
| Comp. Ex. 15 | 186 | 0.30 |
| Comp. Ex. 16 | 186 | 0.30 |
| Comp. Ex. 17 | 186 | 0.30 |
[0092] 5. Evaluation method [Measurement method and evaluation of polishing rate in process (l)]
The weights of each substrate before and after polishing were measured with a scale (BP-2 IOS manufactured by Sartorius Ltd.), and a mass decrement was determined from the change in mass of each substrate. Then, the average mass decrement of the total of 10 substrates was obtained and divided by the polishing time to give a polishing rate. The polishing rate was calculated by the following formulas. Moreover, the relative value of the polishing rate was calculated when the value of
Example 1 was set to 100.0 as a reference. Tables 3 to 4 show the results.
Mass decrement (g) = {mass before polishing (g) - mass after polishing (g)} Polishing rate (mg/min) = mass decrement (mg) / polishing time (min) [0093] The following is the evaluation criteria for the polishing rate.
<E valuation criteria>
Polishing rate: evaluation mg/min or more: “A: The polishing rate is good and the substrate yield is expected to be higher.” mg/min or more and less than 20 mg/min: “B: The substrate yield needs to be improved for actual production.”
Less than 10 mg/min: “C: The substrate yield is greatly reduced.” [0094] [Evaluation method of scratch after process (2)]
Measuring equipment: optical microscope, main body BX60M, digital camera DP70 (manufactured by Olympus Corporation)
Evaluation: The number of scratches was measured by dark-field observation (field of view 550 x 420 pm) using an objective lens (200X) and an intermediate lens (2.5X). First, any two substrates were selected from the 10 substrates after the process (2). Then, 4 points on each side of the substrate that were located 30 mm from the center and spaced 90 degrees apart from one another were observed, so that the above observation was performed on a total of 16 points of the two substrates.
The observed images were captured into a personal computer (PC) to calculate the number of scratches (i.e., the relative value when the value of Example 1 was set to 100 as a reference) by analysis software (WinROOF (Ver 3.6) available from Mitani Corporation). Tables 3 to 4 show the results.
[0095] The following is the evaluation criteria for the number of scratches.
<E valuation criteria>
Number of scratches (relative value): evaluation
More than 0 and 150 or less: “A: The generation of scratches is significantly suppressed and the substrate yield is expected to be even higher.”
More than 150 and 175 or less: “B: The generation of scratches is suppressed and the substrate yield is expected to be higher.”
More than 175 and 200 or less: “C- Actual production can be performed.”
More then 200: “D: the substrate yield is greatly reduced.” [0096] [Evaluation method of alumina residue]
The surfaces of each substrate after the process (2) were observed by a scanning electron microscope (S’4800 manufactured by Hitachi, Ltd.) at a magnification of 10000X, and the presence or absence of alumina residue was confirmed.
[0097] 6. Results
Tables 3 to 4 show the results of the evaluations.
[0098] [TABLE 3]
Composition of polishing liquid composition (abrasive grain: 5% by mass, phosphoric acid: 1.5% by mass, hydrogen peroxide: 0.8% by mass, pH: 1.6) [0099] [TABLE 4]
| Table 4 | Polishing liquid composition | Polishing process | Polishing rate | Scratch | Alumina residue | |||
| Particle A | Load (kPa) | Cutting depth (nm) | mg/min | Evaluation | Relative value | Evaluation | ||
| Comp. Ex. 15 | A2 | 3.6 | 3.4 | 6.9 | C | 98 | A | absence |
| Comp. Ex. 16 | A2 | 6.2 | 4.4 | 14.1 | B | 105 | A | absence |
| Ex. 2 | A2 | 9.8 | 8.9 | 25.8 | A | 107 | A | absence |
| Ex. 7 | A2 | 11.6 | 10.0 | 27.3 | A | 128 | A | absence |
| Ex. 8 | A2 | 13.4 | 15.0 | 29.9 | A | 136 | A | absence |
| Ex. 9 | A2 | 16.3 | 23.1 | 36.3 | A | 148 | A | absence |
| Comp. Ex. 17 | A2 | 19.3 | 30.7 | 40.5 | A | 198 | C | absence |
Composition of polishing liquid composition (abrasive grain: 5% by mass, phosphoric acid: 1.5% by mass, hydrogen peroxide: 0.8% by mass, pH: 1.6) Polishing load: 9.8 kPa [0100] As shown in Tables 3 to 4, Examples 1 to 9, in which the cutting depth was 5 nm or more and 25 nm or less, reduced scratches while ensuring a high polishing rate, as compared to Comparative Examples 1 to 11 and 15 to 16, in which the cutting depth was less than 5 nm, and Comparative Examples 12 to 14 and 17, in which the cutting depth was more than 25 nm.
Industrial Applicability [0101] The present disclosure can reduce scratches while ensuring a high polishing rate, and thus can improve the substrate yield as well as the productivity in the production of a magnetic disk substrate. The present disclosure can be suitably apphed to the production of a magnetic disk substrate.
Description of Reference Numerals [0102] 1 First polishing machine
Cleaning unit
Second polishing machine
Claims (10)
- [ 1] A method for producing a magnetic disk substrate, comprising:a polishing process for polishing a substrate to be pohshed with a polishing liquid composition containing abrasive grains and water, wherein the abrasive grains are particles with which a cutting depth falls in a range of 5 nm to 25 nm, and the cutting depth is a depth of depression formed when a surface of the substrate is cut away by the abrasive grains.
- [2] The method for producing the magnetic disk substrate according to claim 1, wherein the cutting depth is a depth of depression formed when the substrate is pohshed under conditions such that the abrasive grains are arranged in a single layer on the surface of the substrate.
- [3] The method for producing the magnetic disk substrate according to claim 1 or 2, wherein the abrasive grains include non-spherical silica particles A.
- [4] The method for producing the magnetic disk substrate according to claim 3, wherein an average minor axis of the non-spherical silica particles Ais 100 nm or more.
- [5] The method for producing the magnetic disk substrate according to claim 3 or 4, wherein an average secondary particle diameter of the non-spherical silica particles Ais 170 nm or more.
- [6] The method for producing the magnetic disk substrate according to any one of claims 1 to 5, wherein a content of calcined silica in the abrasive grains is less than 50% by mass.
- [7] The method for producing the magnetic disk substrate according to any one of claims 1 to 6, wherein a content of alumina abrasive grains in the polishing liquid composition is 0.1% by mass or less.
- [8] The method for producing the magnetic disk substrate according to any one of claims 1 to 7, wherein the polishing process is a rough polishing process.
- [9] The method for producing the magnetic disk substrate according to any one of claims 1 to 8, wherein the substrate to be polished is a Ni-P plated aluminum alloy substrate.[ 10] A method for producing a magnetic disk substrate, comprising:a polishing process for polishing a substrate to be polished with a polishing liquid composition containing abrasive grains and water, wherein a cutting depth is in a range of 5 nm to 25 nm in the polishing process, and the cutting depth is a depth of depression formed when a surface of the substrate is cut away by the abrasive grains.[ 11] The method for producing the magnetic disk substrate according to claim 10, wherein the abrasive grains are silica particles with which the cutting depth falls in the range of 5 nm to 25 nm.[ 12] The method for producing the magnetic disk substrate according to any one of claims 1 to 10, wherein the polishing process includes adjusting polishing conditions so that the cutting depth is in the range of 5 nm to 25 nm.
- [13] A method for polishing a substrate, comprising:polishing a substrate to be polished with a polishing liquid composition containing abrasive grains and water, wherein a cutting depth is in a range of 5 nm to 25 nm during the polishing, the cutting depth is a depth of depression formed when a surface of the substrate is cut away by the abrasive grains, and the substrate to be pohshed is a substrate that is used for production of a magnetic disk substrate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2016129252 | 2016-06-29 | ||
| PCT/JP2017/023804 WO2018003878A1 (en) | 2016-06-29 | 2017-06-28 | Method for producing magnetic disk substrate |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB201900767D0 GB201900767D0 (en) | 2019-03-06 |
| GB2566876A true GB2566876A (en) | 2019-03-27 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB1900767.3A Withdrawn GB2566876A (en) | 2016-06-29 | 2017-06-28 | Method for producing magnetic disk substrate |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JP6997083B2 (en) |
| GB (1) | GB2566876A (en) |
| MY (1) | MY191975A (en) |
| TW (1) | TWI731113B (en) |
| WO (1) | WO2018003878A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115820128A (en) * | 2022-11-22 | 2023-03-21 | 深圳市永霖科技有限公司 | Chemical mechanical polishing solution for indium phosphide polishing and polishing process |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2002167240A (en) * | 2000-11-29 | 2002-06-11 | Hitachi Plant Eng & Constr Co Ltd | Method of washing crystallized glass substrate |
| JP2009245467A (en) * | 2005-09-30 | 2009-10-22 | Hoya Corp | Process for producing glass substrate for magnetic disk, and process for producing magnetic disk |
| JP2016027517A (en) * | 2014-06-30 | 2016-02-18 | 花王株式会社 | Abrasive liquid composition for magnetic disk substrate |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| MY124578A (en) * | 1997-06-17 | 2006-06-30 | Showa Denko Kk | Magnetic hard disc substrate and process for manufacturing the same |
-
2017
- 2017-06-28 GB GB1900767.3A patent/GB2566876A/en not_active Withdrawn
- 2017-06-28 MY MYPI2018002955A patent/MY191975A/en unknown
- 2017-06-28 JP JP2018525227A patent/JP6997083B2/en active Active
- 2017-06-28 WO PCT/JP2017/023804 patent/WO2018003878A1/en active Application Filing
- 2017-06-29 TW TW106121755A patent/TWI731113B/en active
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2002167240A (en) * | 2000-11-29 | 2002-06-11 | Hitachi Plant Eng & Constr Co Ltd | Method of washing crystallized glass substrate |
| JP2009245467A (en) * | 2005-09-30 | 2009-10-22 | Hoya Corp | Process for producing glass substrate for magnetic disk, and process for producing magnetic disk |
| JP2016027517A (en) * | 2014-06-30 | 2016-02-18 | 花王株式会社 | Abrasive liquid composition for magnetic disk substrate |
Also Published As
| Publication number | Publication date |
|---|---|
| JPWO2018003878A1 (en) | 2019-04-18 |
| TW201802203A (en) | 2018-01-16 |
| MY191975A (en) | 2022-07-21 |
| JP6997083B2 (en) | 2022-01-17 |
| GB201900767D0 (en) | 2019-03-06 |
| WO2018003878A1 (en) | 2018-01-04 |
| TWI731113B (en) | 2021-06-21 |
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