WO2014156798A1

WO2014156798A1 - Method of manufacturing glass substrate for information recording medium

Info

Publication number: WO2014156798A1
Application number: PCT/JP2014/057234
Authority: WO
Inventors: 小松　隆史
Original assignee: Hoya株式会社
Priority date: 2013-03-29
Filing date: 2014-03-18
Publication date: 2014-10-02

Abstract

Provided is a method of manufacturing a glass substrate for an information recording medium, the method enabling fluctuations in the thickness of the glass substrate to be reduced. The method of manufacturing a glass substrate for an information recording medium uses a polishing device that polishes a glass substrate held by a carrier (500) by using a polishing pad comprising a member having a plurality of foam holes. The carrier (500) is disposed so as to be rotatable. A plurality of holding holes (520) for accommodating glass substrates are formed in the carrier (500). The distance between the rotation center (C) of the carrier (500) and the centers of the holding holes (520) is substantially equal, and the holding holes (520) form a group in which the hole diameters are the same. A distance (d) that is between two holding holes (520, 520) and is on a line segment that connects the centers of the two holding holes that belong to the group in which the hole diameters are the same and that are adjacent in the circumferential direction around the rotation center (C), is 0.5mm-3.0mm.

Description

Manufacturing method of glass substrate for information recording medium

The present invention relates to a method for manufacturing a glass substrate for information recording medium, and more particularly to a method for manufacturing a glass substrate for information recording medium in which the glass substrate is polished using a polishing apparatus.

An information recording medium such as a magnetic disk is mounted as a hard disk on a computer or the like. An information recording medium is manufactured by forming a magnetic thin film layer including a recording layer using properties such as magnetism, light, or magnetomagnetism on the surface of a substrate. As the recording layer is magnetized by the magnetic head, predetermined information is recorded on the information recording medium.

The recording density of information recording media is improving year by year. Accordingly, high quality is required for the quality of substrates used for information recording media. Conventionally, an aluminum substrate has been used as a substrate for an information recording medium. However, as the recording density is improved, it is gradually being replaced by a glass substrate that is superior in smoothness and strength of the substrate surface as compared with an aluminum substrate.

The method for producing a glass substrate for an information recording medium has a polishing step for ensuring high surface shape accuracy. In order to achieve highly accurate shape quality of the glass substrate, two or more stages of polishing processes in which slurry and polishing pads having different processing capabilities are effectively combined are applied. For example, Japanese Unexamined Patent Application Publication No. 2007-015105 (Patent Document 1) discloses a conventional technology relating to glass substrate manufacturing.

Japanese Patent Laid-Open No. 2007-015105

In recent years, it has been required to use a glass substrate as a substrate for a larger diameter information recording medium in order to achieve both compatibility with the heat assist method and securing a recording area.

When an information recording medium having a large diameter is used for a hard disk, an existing information recording medium manufacturing method is applied. The so-called fluttering characteristic in which the information recording medium swings in a direction perpendicular to the rotation direction is simultaneously processed. It was found that there was variation between the substrates. Examining this problem, it was found that the variation in fluttering characteristics was strongly influenced mainly by the variation in the thickness of the glass substrate.

The present invention has been made in view of the above-described problems, and an object thereof is to provide a method for manufacturing a glass substrate for an information recording medium, which can reduce variations in the thickness of the glass substrate.

When polishing the main surface of a glass substrate with a conventional double-side polishing machine that uses a suede pad and a polishing carrier, the disk-shaped carrier rotates and revolves around the rotation axis of the upper and lower polishing surface plates. The surface is polished. At this time, since the glass substrate held by the holding hole at the same radial position from the center of the carrier moves relative to the polishing surface of the surface plate along the same locus, generally the processing characteristics are equal. There is expected.

In the process of manufacturing a large-diameter glass substrate, the present inventor has found that a variation in plate thickness occurs in the glass substrate held by the holding holes at the same radial position from the center of the carrier. Based on this, the present inventor has intensively studied a manufacturing method for reducing the variation in the thickness of the glass substrate held by the holding holes at the same radial position from the center of the carrier, and has completed the present invention. It was.

That is, the method for manufacturing a glass substrate for an information recording medium according to the present invention includes a polishing pad made of a member including a plurality of foam holes and a carrier that holds the glass substrate, and is held by the carrier using the polishing pad. The manufacturing method of the glass substrate for information recording media using the polishing apparatus which grinds the obtained glass substrate. The manufacturing method includes a step of preparing a glass substrate having a main surface and an outer diameter of 80 mm or more, and a step of polishing the main surface of the glass substrate using a polishing apparatus. The carrier of the polishing apparatus is provided to be able to rotate. The carrier is formed with a plurality of holding holes for accommodating the glass substrate. At least a part of the plurality of holding holes constitutes the same diameter hole group in which the distance between the rotation center of the carrier and the center of the holding hole is substantially equal. The distance between the two holding holes on a line segment connecting the centers of two holding holes that belong to the same diameter hole group and are adjacent to each other in the circumferential direction around the rotation center is 0.5 mm or more and 3.0 mm or less.

In the above manufacturing method, the polishing pad preferably has a hardness of 75 to 85 in terms of a type AO durometer hardness defined by ISO7619.

Preferably, in the above manufacturing method, at least a part of the plurality of holding holes constitutes a different diameter hole group in which the distance between the rotation center of the carrier and the center of the holding hole is different from the holding holes belonging to the same diameter hole group. ing. The distance between the two holding holes on the line segment connecting the centers of the holding holes belonging to the same diameter hole group and the holding holes belonging to the different diameter hole group is 0.5 mm or more and 3.0 mm or less.

Preferably, in the above manufacturing method, the polishing step includes a step of roughly polishing the glass substrate and a step of precisely polishing the glass substrate after the step of rough polishing. The carrier is included in a polishing apparatus used in the rough polishing step.

In the above manufacturing method, the information recording medium is preferably used for a heat-assisted magnetic recording apparatus.

In the above manufacturing method, the carrier is preferably formed using glass fiber reinforced epoxy as a material.

According to the manufacturing method of the present invention, variations in the thickness of the glass substrate for information recording media can be reduced.

It is a perspective view which shows the glass substrate used for a magnetic disc. It is a perspective view which shows the magnetic disc provided with the glass substrate. It is a flowchart which shows the manufacturing method of the glass substrate in embodiment. It is a fragmentary perspective view of the double-side polish apparatus used for a grinding | polishing process. It is a top view which shows typically the carrier of a 1st example. It is an enlarged vertical sectional view of a lower polishing pad. It is sectional drawing which shows typically the glass substrate hold | maintained at the conventional carrier. It is sectional drawing which shows typically the glass substrate hold | maintained at the carrier of this Embodiment. It is a top view which shows typically the carrier of a 2nd example. It is a top view which shows typically the carrier of a 3rd example. It is a figure which shows the arrangement | positioning and evaluation result of a holding hole of an Example and a comparative example.

Embodiments and examples based on the present invention will be described below with reference to the drawings. In the description of the embodiments and examples, when referring to the number, amount, and the like, the scope of the present invention is not necessarily limited to the number, amount, and the like, unless otherwise specified. In the description of the embodiments and examples, the same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated.

[Glass substrate 1 and magnetic disk 10]
With reference to FIG. 1 and FIG. 2, the glass substrate 1 obtained by the manufacturing method of the glass substrate for information recording media based on this Embodiment and the magnetic disc 10 provided with the glass substrate 1 are demonstrated first. FIG. 1 is a perspective view showing a glass substrate 1 used for a magnetic disk 10 (see FIG. 2). FIG. 2 is a perspective view showing a magnetic disk 10 provided with a glass substrate 1 as an information recording medium.

As shown in FIG. 1, a glass substrate 1 (glass substrate for information recording medium) used for a magnetic disk 10 has an annular disk shape with a hole 1H formed in the center. The circular disk-shaped glass substrate 1 has a front main surface 1A, a back main surface 1B, an inner peripheral end surface 1C, and an outer peripheral end surface 1D.

The size of the disk-shaped glass substrate 1 is defined as an outer diameter of 80 mm or more. By increasing the outer diameter of the glass substrate 1, the storage capacity of the magnetic disk 10 produced using the glass substrate 1 can be increased, and an information recording medium suitable for server use can be realized. For example, you may prescribe | regulate the outer diameter of the glass substrate 1 to 91 mm or more.

The thickness of the glass substrate 1 is, for example, 0.30 mm to 2.2 mm from the viewpoint of preventing breakage. The thickness of the glass substrate 1 is a value calculated by averaging the values measured at a plurality of arbitrary points that are point-symmetric on the glass substrate 1. For example, the glass substrate 1 may be thin with a thickness of 0.630 mm or less. In this case, the glass substrate 1 can be reduced in weight, and power consumption during rotation of the magnetic disk 10 can be reduced.

As shown in FIG. 2, the magnetic disk 10 includes a magnetic thin film layer 2. The magnetic thin film layer 2 includes a magnetic recording layer formed by forming a magnetic film on the front main surface 1A of the glass substrate 1 described above. In FIG. 2, the magnetic thin film layer 2 is formed only on the front main surface 1A, but the magnetic thin film layer 2 may also be formed on the back main surface 1B.

The magnetic thin film layer 2 is formed by spin-coating a thermosetting resin in which magnetic particles are dispersed on the front main surface 1A of the glass substrate 1 (spin coating method). The magnetic thin film layer 2 may be formed on the front main surface 1A of the glass substrate 1 by a sputtering method, an electroless plating method, or the like.

The film thickness of the magnetic thin film layer 2 formed on the front main surface 1A of the glass substrate 1 is about 0.3 μm to about 1.2 μm in the case of the spin coating method, and about 0.04 μm to about 0.00 in the case of the sputtering method. In the case of electroless plating, the thickness is about 0.05 μm to about 0.1 μm. From the viewpoint of thinning and high density, the magnetic thin film layer 2 is preferably formed by sputtering or electroless plating.

The magnetic material used for the magnetic thin film layer 2 is not particularly limited, and a conventionally known material can be used. However, in order to obtain a high coercive force, Co having high crystal anisotropy is basically used for the purpose of adjusting the residual magnetic flux density. A Co-based alloy to which Ni or Cr is added is suitable. Further, as a magnetic layer material suitable for heat-assisted recording, an FePt-based material may be used.

Further, a lubricant may be thinly coated on the surface of the magnetic thin film layer 2 in order to improve the sliding of the magnetic recording head. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon.

Furthermore, if necessary, an underlayer or a protective layer may be provided. The underlayer in the magnetic disk 10 is selected according to the magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni.

Also, the underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

Examples of the protective layer for preventing wear and corrosion of the magnetic thin film layer 2 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be continuously formed together with an underlayer, a magnetic film and the like by an in-line type sputtering apparatus. In addition, these protective layers may be a single layer, or may have a multilayer structure including the same or different layers.

Another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, tetraalkoxysilane is diluted with an alcohol-based solvent on a Cr layer, and then colloidal silica fine particles are dispersed and applied, followed by baking to form a silicon oxide (SiO ₂ ) layer. It may be formed.

[Method for Manufacturing Glass Substrate 1]
Next, a method for manufacturing a glass substrate for information recording medium (hereinafter simply referred to as a glass substrate) in the present embodiment will be described with reference to the flowchart shown in FIG. FIG. 3 is a flowchart showing a method for manufacturing the glass substrate 1 in the embodiment.

The glass substrate manufacturing method in the present embodiment includes a glass blank material preparation step (step S10), a glass substrate formation / grinding step (step S20), a polishing step (step S30), a chemical strengthening step (step S40), and a cleaning. The process (step S50) is provided. The magnetic thin film forming step (step S60) may be performed on the glass substrate (corresponding to the glass substrate 1 in FIG. 1) obtained through the chemical strengthening treatment step (step S40). The magnetic disk 10 as an information recording medium is obtained by the magnetic thin film forming step (step S60).

Hereinafter, details of each of these steps S10 to S60 will be described in order. In the following, simple cleaning appropriately performed between each of steps S10 to S60 is not described.

(Glass blank material preparation process)
In the glass blank material preparation step (step S10), the glass material constituting the glass substrate is melted (step S11). As the glass material, for example, a general aluminosilicate glass is used. The aluminosilicate glass is composed of 58 mass% to 75 mass% SiO ₂ , 5 mass% to 23 mass% Al ₂ O ₃ , 3 mass% to 10 mass% Li ₂ O, and 4 mass% to 13 mass. % Na ₂ O as a main component. The molten glass material is poured onto the lower mold and then press-molded with the upper mold and the lower mold (step S12). A disk-shaped glass blank (glass base material) is formed by press molding.

In addition to press molding, a glass blank material may be formed by cutting sheet glass (plate glass) formed by a downdraw method or a float method with a grinding wheel. Further, the glass material is not limited to aluminosilicate glass, and may be any material.

(Glass substrate formation / grinding process)
Next, in the glass substrate formation / grinding process (step S20), the first lapping process is performed on both main surfaces of the press-molded glass blank material for the purpose of improving dimensional accuracy and shape accuracy. (Step S21). Both main surfaces of a glass blank material are the main surfaces used as the front main surface 1A and the main surface used as the back main surface 1B in FIG. 1 through each process mentioned later (henceforth, both main surfaces) Also called). For example, alumina abrasive grains having a particle size of # 400 (particle size of about 40 to 60 μm) are used, and the surface roughness Rmax is finished to about 6 μm.

After the first lapping step, a coring (inner peripheral cut) process is performed on the center portion of the glass blank using a cylindrical diamond drill or the like (step S22). By the coring process, an annular glass substrate having a hole in the center is obtained. A predetermined chamfering process may be performed on the hole in the center. The inner peripheral end surface and the outer peripheral end surface of the glass substrate are polished into a mirror surface by a brush. As the abrasive grains, a slurry containing cerium oxide abrasive grains is used.

Next, a second lapping process is performed on both main surfaces of the glass substrate (step S23). The second lapping step is performed using a double-side grinding apparatus that uses a planetary gear mechanism. Specifically, press the surface plate from above and below both main surfaces of the glass blank material, supply water, grinding liquid or lubricating liquid onto both main surfaces, and move the glass blank material and the lapping surface plate relatively. Then, the second lapping step is performed.

In the second lapping step, the approximate parallelism, flatness, thickness, etc. of the glass substrate are preliminarily adjusted, and a glass base material having an approximately flat main surface is obtained. In the second lapping step, fine abrasive grains are used as compared with the first lapping step in order to reduce the generated grinding marks. For example, by attaching fixed abrasive grains such as a diamond tile pad on a surface plate, both surfaces of the glass substrate are finished to a surface roughness Rmax of about 2 μm. In the present embodiment, steps S10 and S20 are steps for preparing a glass substrate.

(Polishing process)
Next, in the polishing process (step S30), as a first polishing process (rough polishing), while removing scratches remaining on both main surfaces of the glass substrate in the second lapping process (step S23), The warp is corrected (step S31). In the first polishing step, a double-side polishing apparatus using a planetary gear mechanism is used, and polishing is performed using a suede pad made of foamed polyurethane or the like as a polishing pad. As the abrasive, a slurry as a liquid abrasive mainly composed of general cerium oxide abrasive grains is used.

In the second polishing process (precise polishing), the glass substrate is subjected to polishing again, and minute defects remaining on both main surfaces of the glass substrate are eliminated (step S33). Both main surfaces of the glass substrate are finished to have a mirror-like surface, thereby forming a desired flatness and eliminating the warpage of the glass substrate. In the second polishing step, a double-side polishing apparatus using a planetary gear mechanism is used. Polishing is performed using, for example, a suede pad, which is a soft polisher made of foamed polyurethane. As the polishing agent, a slurry as a liquid polishing agent mainly composed of general colloidal silica, which is finer than the cerium oxide used in the first polishing step, is used.

Here, a schematic configuration of the double-side polishing apparatus 2000 will be described with reference to FIG. FIG. 4 is a partial perspective view of a double-side polishing apparatus 2000 used in the polishing process.

The double-side polishing apparatus 2000 includes an upper surface plate (upper whetstone holding surface plate) 300, a lower surface plate (lower whetstone holding surface plate) 400, and a side (glass substrate side) facing the lower surface plate 400 of the upper surface plate 300. The upper polishing pad 310 mounted on the lower surface and the lower polishing pad 410 mounted on the upper surface on the side facing the upper surface plate 300 (glass substrate side) of the lower surface plate 400 are provided.

The upper polishing pad 310 and the lower polishing pad 410 are processing members for polishing both main surfaces of the glass substrate 1. The upper surface plate 300 and the lower surface plate 400 rotate in directions opposite to each other with respect to the revolution direction of the carrier 500. A surface of the upper polishing pad 310 facing the lower surface plate 400 forms an upper polishing surface 311. The surface of the lower polishing pad 410 facing the upper surface plate 300 forms a lower polishing surface 411. Carrier 500 is arranged in a gap formed between upper surface plate 300 and lower surface plate 400. A plurality of disk-shaped glass substrates 1 are held by the carrier 500. The detailed structure of the carrier 500 will be described later.

The glass substrate 1 is sandwiched between the upper surface plate 300 and the lower surface plate 400, and stress is applied in the thickness direction of the glass substrate by the upper surface plate 300 and the lower surface plate 400. As a result, both main surfaces of the glass substrate are pressed against the polishing surface 311 of the upper polishing pad 310 and the polishing surface 411 of the lower polishing pad 410. In this state, the carrier 500 rotates and revolves around the rotation axes of the upper surface plate 300 and the lower surface plate 400, whereby the main surface of the glass substrate 1 slides relative to the polishing surfaces 311 and 411. As the polishing surface 311 of the upper polishing pad 310 moves relative to one main surface of the glass substrate, the one main surface is polished. At the same time, the polishing surface 411 of the lower polishing pad 410 moves relative to the other main surface of the glass substrate, whereby the other main surface is polished.

In this way, both main surfaces of the glass substrate are polished simultaneously using the double-side polishing apparatus 2000. After the polishing process using the double-side polishing apparatus, the glass substrate 1 attached to the polishing surface 311 of the upper polishing pad 310 and the polishing surface 411 of the lower polishing pad 410 is taken out from the polishing pad.

(Chemical strengthening process)
After the glass substrate 1 is washed, the chemical strengthening layer is formed on both main surfaces of the glass substrate 1 by immersing the glass substrate 1 in the chemical strengthening treatment liquid (step S40). After the glass substrate 1 is cleaned, the glass substrate 1 is immersed for about 30 minutes in a chemical strengthening treatment solution such as a mixture solution of potassium nitrate (70%) and sodium nitrate (30%) heated to 300 ° C. By doing so, chemical strengthening is performed.

The alkali metal ions such as lithium ions and sodium ions contained in the glass substrate 1 are replaced by alkali metal ions such as potassium ions having a larger ion radius than these ions (ion exchange method).

Compressive stress is generated in the ion-exchanged region due to strain caused by the difference in ion radius, and both main surfaces of the glass substrate 1 are strengthened. For example, on both the main surfaces of the glass substrate 1, a chemical strengthening layer may be formed in a range from the surface of the glass substrate 1 to about 5 μm to improve the rigidity of the glass substrate 1. As described above, a glass substrate corresponding to the glass substrate 1 shown in FIG. 1 is obtained.

The glass substrate 1 may be further subjected to a polishing treatment with a machining allowance on both main surfaces of 0.1 μm to 0.5 μm. By removing the deposits remaining on the main surface of the glass substrate 1 after the chemical strengthening step, occurrence of head crashes in a magnetic disk manufactured using the glass substrate 1 is reduced. Further, by setting the machining allowance on both main surfaces in the polishing process to be 0.1 μm or more and 0.5 μm or less, the unevenness of stress generated by the chemical strengthening process does not appear on the surface. The manufacturing method of the glass substrate in the present embodiment is configured as described above.

A chemical strengthening step may be performed between the first polishing step (rough polishing) and the second polishing step (precision polishing).

(Washing process)
Next, the glass substrate is cleaned (step S50). By cleaning both main surfaces of the glass substrate 1 with detergent, pure water, ozone, IPA (isopropyl alcohol), UV (ultraviolet) ozone, etc., the deposits adhering to both main surfaces of the glass substrate 1 are removed. The

Thereafter, the number of deposits on the surface of the glass substrate 1 is inspected using an optical defect inspection apparatus or the like.

(Magnetic thin film formation process)
The magnetic thin film layer 2 is formed by forming a magnetic film on both main surfaces (or one of the main surfaces) of the glass substrate (corresponding to the glass substrate 1 shown in FIG. 1) that has been subjected to the chemical strengthening treatment. Is done. The magnetic thin film layer 2 is composed of an adhesion layer composed of a Cr alloy, a soft magnetic layer composed of a CoFeZr alloy, an orientation control underlayer composed of Ru, a perpendicular magnetic recording layer composed of a CoCrPt alloy, a protective layer composed of a C system, and an F system. The lubricating layer is formed by sequentially forming a film. By forming the magnetic thin film layer 2, a perpendicular magnetic recording disk corresponding to the magnetic disk 10 shown in FIG. 2 can be obtained.

The magnetic disk in the present embodiment is an example of a perpendicular magnetic disk composed of a magnetic thin film layer. The magnetic disk may be composed of a magnetic layer or the like as a so-called in-plane magnetic disk.

[Carrier 500]
Hereinafter, the detailed structure of the carrier 500 employed in the double-side polishing apparatus 2000 used in the first polishing step (step S31) in the above-described polishing step (step S30) will be described. FIG. 5 is a plan view schematically showing the carrier 500 of the first example. The carrier 500 in the present embodiment has a disc-shaped main body 510.

The thickness of the carrier 500 is about 0.30 mm to 2.2 mm, and a thickness smaller than the thickness of the glass substrate 1 to be held is selected. The diameter of the carrier 500 is about 430 mm. As the material of the main body 510, aramid fiber, glass epoxy, PC (polycarbonate) or the like is used, and glass fiber reinforced epoxy having excellent strength is preferably used. Main body 510 of carrier 500 of the present embodiment is made of glass fiber reinforced epoxy.

Referring also to FIG. 4, the double-side polishing apparatus 2000 includes a plurality of carriers 500. The double-side polishing apparatus 2000 according to the present embodiment includes five carriers 500 arranged in an annular shape between the upper surface plate 300 and the lower surface plate 400. A tooth portion (not shown) is formed on the outer peripheral surface of the carrier 500. The tooth portion provided on the outer peripheral surface of the carrier 500 meshes with a sun gear (not shown) provided at the center of the double-side polishing apparatus 2000 and an internal gear (not shown) provided on the outer periphery, and the carrier 500 revolves while rotating. To do. The center of rotation of the carrier 500 is shown as the rotation center C in FIG. In addition, the diameter of the carrier 500 means the dimension at the time of measuring with the tip circle of a tooth part.

The carrier 500 has a plurality of holding holes 520 for holding the glass substrate 1. The holding hole 520 is formed through the disc-shaped main body 510 of the carrier 500 in the thickness direction. When the glass substrate 1 is polished using the double-side polishing apparatus 2000, the glass substrate 1 is accommodated in the holding hole 520 and held by the carrier 500. The holding hole 520 has a shape that can accommodate the glass substrate 1 therein. The holding hole 520 has a circular shape in plan view so as to accommodate the disk-shaped glass substrate 1, and the circle has a diameter slightly larger than the diameter of the glass substrate 1. . For example, the holding hole 520 may be formed so that the glass substrate 1 having an outer diameter of 80 mm or more has a diameter that is approximately 1.5 mm larger than the diameter of the glass substrate 1.

In the present embodiment, the carrier 500 is provided with ten holding holes 520. The holding holes 520 are arranged in an annular shape in the circumferential direction around the rotation center C of the carrier 500. The holding holes 520 are arranged at equal intervals on the annular line r1 centered on the rotation center C. The center of the holding hole 520 having a circular shape in plan view exists on the annular line r1. Each holding hole 520 is arranged so that the distance between the center and the rotation center C of the carrier 500 is the same. The ten holding holes 520 shown in FIG. 5 constitute the same diameter hole group in which the distance between the rotation center of the carrier 500 and the center of the holding hole 520 is equal.

5 indicates a distance between the two holding holes 520 on a line segment connecting the centers of the two holding holes 520 adjacent to each other in the circumferential direction around the rotation center C. The holding hole 520 is provided so that the distance d between two adjacent holding holes 520 is in the range of 0.5 mm to 3.0 mm.

The reason why the distance d is 0.5 mm or more is that if the distance between the adjacent holding holes 520 is too small, the strength of the carrier 500 is lowered and the durability of the carrier 500 is disadvantageous. The lower limit value of the distance d to have is defined as 0.5 mm. Considering the durability of the carrier 500, it is advantageous that the distance d is larger, but in the present embodiment, the upper limit value of the distance d is defined as 3.0 mm.

Hereinafter, the concept of defining the upper limit value of the distance d will be described. FIG. 6 is an enlarged vertical sectional view of the lower polishing pad 410. In the following description, the lower polishing pad 410 will be mainly described, but the upper polishing pad 310 of the present embodiment also has the same configuration as the lower polishing pad 410.

As shown in FIG. 6, the lower polishing pad 410 is formed of a member including a plurality of foam holes 410h. In the position close to the polishing surface 411 of the lower polishing pad 410, a large number of foam holes 410h having relatively small sizes of the individual foam holes 410h are formed. The foam holes 410h having relatively large individual foam holes 410h are formed so as to extend in the thickness direction (vertical direction in FIG. 6) of the lower polishing pad 410 to a position away from the polishing surface 411 to some extent. Yes.

Thereby, in the thickness direction of the lower polishing pad 410, the number of the foam holes 410h is relatively large at a position close to the polishing surface 411, and the number of the foam holes 410h is relatively small at a position away from the polishing surface 411. Yes. A dense region where a large number of foam holes 410h are densely formed is formed at a position close to the polishing surface 411, and a relatively small number of foam holes 410h are provided sparsely at a position away from the polishing surface 411. A sparse region is formed. A dense foam hole 410h having a small diameter is formed in the dense region of the surface layer portion, and a large foam hole 410h is formed in the sparse region of the deep layer portion.

The glass substrate 1 held by the carrier 500 during the first polishing step (step S31) is pressed while being sandwiched between the upper polishing pad 310 and the lower polishing pad 410. During the first polishing process (step S31), the pressure from the glass substrate 1 acts on the lower polishing pad 410. When the lower polishing pad 410 receives pressure from the glass substrate 1, the deformation amount in the dense region of the surface layer portion is small, and the sparse region in the deep layer portion is greatly deformed. Therefore, in the lower polishing pad 410 that has received pressure from the glass substrate 1, the area in contact with the main surface of the glass substrate 1 is deformed, and the area around the area in contact with the glass substrate 1 is deformed. The annular region that is not in contact with the glass substrate 1 is similarly deformed.

FIG. 7 is a cross-sectional view schematically showing a glass substrate 1 held on a conventional carrier. FIG. 7 shows two glass substrates 1 held by adjacent holding holes among a plurality of holding holes provided in a conventional carrier. The glass substrate 1 applies pressure to the lower polishing pad 410, and the lower polishing pad 410 immediately below and around the glass substrate 1 is deformed so as to sink from the polishing surface 411.

In conventional carriers, the distance D between adjacent holding holes is set to a relatively large value exceeding 3.0 mm. Therefore, deformation of the lower polishing pad 410 due to pressure from the glass substrate 1 held in one holding hole, and lowering due to pressure from the glass substrate 1 held in another holding hole adjacent to the one holding hole. The deformation of the side polishing pad 410 is independent of each other. In other words, the sinking of the lower polishing pad 410 generated by the pressure from each of the two glass substrates 1 held in the adjacent holding holes does not affect each other, and each glass substrate 1 is separately lower The polishing pad 410 is deformed.

Thereby, the polishing rate of each glass substrate 1 is made uniform, and the polishing amount of the glass substrate 1 before and after the first polishing step becomes substantially the same. In this case, if there is a variation in the thickness of the glass substrate 1 in the step prior to the first polishing step, each glass substrate 1 is similarly polished. Therefore, the variation in the plate thickness also in the polished glass substrate 1. Remains, and the thickness of the polished glass substrate 1 does not converge to a constant value.

FIG. 8 is a cross-sectional view schematically showing the glass substrate 1 held by the carrier 500 of the present embodiment. FIG. 8 shows two glass substrates 1 held by adjacent holding holes 520 among the plurality of holding holes 520 provided in the carrier 500 of the present embodiment shown in FIG.

In the carrier 500 of the present embodiment, the distance d between the adjacent holding holes 520 is specified to be a value of 3.0 mm or less. When the interval between the holding holes 520 is reduced, the deformation of the lower polishing pad 410 that sinks under the pressure from the glass substrate 1 extends to the region that receives the pressure from the adjacent glass substrate 1. The sinking of the lower polishing pad 410 due to the pressure from the glass substrate 1 extends to a position directly below the other glass substrate 1 adjacent to the glass substrate 1, and the two glass substrates held in the adjacent holding holes 520. 1 causes the deformation of the lower polishing pad 410 to influence each other. Thereby, the plate | board thickness of the glass substrate 1 comes to influence the processing rate of the other glass substrate 1 adjacent to the said glass substrate 1. FIG.

For example, among the three glass substrates 1 arranged in order in the circumferential direction of the carrier 500, the thickness of the second glass substrate 1 at the center is relatively larger than that of the first and third glass substrates 1. When it is large, the deformation amount of the lower polishing pad 410 is relatively large immediately below and around the central glass substrate 1. At this time, the deformation of the lower polishing pad 410 by the central glass substrate 1 extends to the lower polishing pad 410 at a position immediately below the first and third glass substrates 1, and the first and third glass substrates 1 are The force received from the lower polishing pad 410 is weakened. As a result of the lower pressure acting on the first and third glass substrates 1 by the lower polishing pad 410, the first and third glass substrates 1 are compared with the processing rate of the second glass substrate 1 at the center. The processing rate of becomes relatively small.

By making the polishing rate of the adjacent glass substrates 1 non-uniform and making the polishing rate of the first and third glass substrates 1 relatively small, after the first polishing step is completed, The polishing amount becomes relatively large, and the polishing amount of the first and third glass substrates 1 becomes relatively smaller than that of the second glass substrate 1. That is, by increasing the polishing amount of the second glass substrate 1 having a relatively large plate thickness before polishing and decreasing the polishing amount of the first and third glass substrates having a relatively small plate thickness. The difference in plate thickness between the processed glass substrates 1 is reduced. In this way, the thickness of the glass substrate 1 can be converged to a constant value, and variations in the thickness of the glass substrate 1 can be reduced, so that the uniformity of the thickness of the plurality of glass substrates 1 after the polishing process can be improved. Can do.

Further, for example, among the three glass substrates 1 arranged in order in the circumferential direction of the carrier 500, the thickness of the second glass substrate 1 at the center is relative to that of the first and third glass substrates 1. If it is small, the amount of deformation of the lower polishing pad 410 is relatively large immediately below and around the first and third glass substrates 1. At this time, the deformation of the lower polishing pad 410 by the first and third glass substrates 1 also reaches the lower polishing pad 410 at a position directly below the second glass substrate 1 in the center, and the second glass substrate. The force that 1 receives from the lower polishing pad 410 is weakened. As a result of the lower pressure acting on the second glass substrate 1 at the center of the lower polishing pad 410, the second glass substrate 1 at the center is compared with the processing rate of the first and third glass substrates 1. The processing rate of becomes relatively small.

By making the polishing rate of the adjacent glass substrates 1 non-uniform and relatively reducing the polishing rate of the second glass substrate 1, the first and third glass substrates 1 of the first and third glass substrates 1 are completed after the first polishing process is completed. The polishing amount becomes relatively large, and the polishing amount of the second glass substrate 1 becomes relatively small as compared with the first and third glass substrates 1. That is, by polishing the first and third glass substrates 1 having a relatively large plate thickness before polishing, and reducing the polishing amount of the second glass substrate having a relatively small plate thickness. The difference in plate thickness between the processed glass substrates 1 is reduced. In this way, the thickness of the glass substrate 1 can be converged to a constant value, and variations in the thickness of the glass substrate 1 can be reduced, so that the uniformity of the thickness of the plurality of glass substrates 1 after the polishing process can be improved. Can do.

When the glass substrate 1 held in each holding hole 520 of the carrier 500 is rotated, it is possible to suppress the glass substrate 1 from affecting the polishing of only a specific position of the adjacent glass substrate 1, and one glass substrate It is possible to avoid a difference in the polishing amount in the circumferential direction of 1. Thereby, since it can prevent that the board | substrate thickness of the glass substrate 1 after grinding | polishing generate | occur | produces, the processing rate of the glass substrate 1 whole can be equalized.

The upper polishing pad 310 and the lower polishing pad 410 used in the present embodiment have a value of type AO durometer hardness defined by ISO7619 and have a hardness of 75 to 85. Alternatively, it has a hardness of 75 or more and 85 or less as a value of Type E durometer or Asker C hardness defined by JIS K 6253. By using a polishing pad having such hardness, the surface quality of the main surface of the glass substrate 1 after polishing can be ensured, so that both reduction in plate thickness variation and surface quality of the polished glass substrate 1 can be achieved. .

The carrier 500 of the present embodiment is used in the first first polishing process among the plurality of polishing processes in the manufacturing process of the glass substrate 1. In the first polishing process, the polishing amount of the glass substrate 1 is relatively large as compared with the subsequent second polishing process. Therefore, the polishing process in the first polishing step has a great influence on the variation in the thickness of the glass substrate 1 after polishing. That is, if the carrier 500 according to the present embodiment is used in the first polishing process that has a relatively large processing amount and a large influence on the variation in the plate thickness, the effect of reducing the variation in the plate thickness is more remarkable. Can get to.

In the heat-assisted recording type magnetic recording apparatus, it is possible to improve the recording density of the magnetic disk 10 by reducing the unit recording area of the medium as compared with the conventional one. In this case, if fluttering occurs in the magnetic disk 10, the reading position of the magnetic head is shifted, causing a reading error. If the heat-assisted magnetic disk 10 is manufactured using the glass substrate 1 of the present embodiment, variations in the thickness of the glass substrate 1 can be reduced, and variations in fluttering characteristics can be reduced. Therefore, the glass substrate 1 of the present embodiment can be particularly advantageously applied to a heat-assisted recording type magnetic recording apparatus.

FIG. 9 is a plan view schematically showing the carrier 500 of the second example. The carrier 500 of the second example is provided with 13 holding holes 520 for holding the glass substrate 1. In the second example, the holding holes 520 are arranged so as to form a double ring around the rotation center C of the carrier 500. Ten holding holes 521 are arranged at equal intervals in the outer annular line r1 in the radial direction of the carrier 500, and three holding holes 522 are arranged at equal intervals in the inner inner ring line r2. The carrier 500 is formed with three holding holes 522 arranged near the rotation center C and ten holding holes 521 arranged on the outer peripheral side of the carrier 500 with respect to the holding holes 522.

The ten holding holes 521 present on the annular line r1 constitute a group of identical diameter holes in which the distance between the rotation center C of the carrier 500 and the center of the holding hole 521 is equal. The distance between the centers of the three holding holes 522 existing on the inner annular line r2 and the rotation center C of the carrier 500 is relative to the distance between the holding hole 521 belonging to the same diameter hole group and the rotation center C of the carrier 500. Is getting smaller. The three holding holes 522 have the same distance between the rotation center C of the carrier 500 and the center of the holding hole 522, and the distance between the rotation center C and the center of the holding hole 522 is the same as that of the rotation center C and the holding hole 521. It is formed so as to be different from the distance from the center. The three holding holes 522 provided on the inner peripheral side of the carrier 500 constitute a different diameter hole group different from the same diameter hole group constituted by the holding holes 521 on the outer peripheral side of the carrier 500.

Similarly to the first example shown in FIG. 5, in the carrier 500 of the second example, among the plurality of holding holes 521 belonging to the same hole diameter group, the distance d between two holding holes 521 adjacent in the circumferential direction is In the range of 0.5 mm to 3.0 mm. Furthermore, the distance d between the two holding

holes

521 and 522 on the line segment connecting the centers of the holding hole 521 belonging to the same diameter hole group and the holding hole 522 belonging to the different diameter hole group is also 0. It exists in the range of 5 mm or more and 3.0 mm or less.

The durability of the carrier 500 can be ensured by defining the distance d between the holding

holes

521 and 522 to be 0.5 mm or more. By defining the distance d between the holding

holes

521 and 522 to be 3.0 mm or less, the deformation of the polishing pad by the two glass substrates 1 held in the adjacent holding

holes

521 and 522 affects each other. As a result, the amount of polishing of the glass substrate 1 adjacent in the radial direction of the carrier 500 can be changed in accordance with the thickness of the glass substrate 1 before polishing, thereby reducing variations in the thickness of the glass substrate 1 after polishing. Therefore, the uniformity of the thickness of the glass substrate 1 held by the holding hole 521 and the holding hole 522 having different distances from the rotation center C after the polishing process can be improved.

FIG. 10 is a plan view schematically showing the carrier 500 of the third example. Similarly to the first example shown in FIG. 5, the carrier 500 of the third example is provided with ten holding holes 520 for holding the glass substrate 1. In the carrier 500 of the third example, the two holding

holes

523 and 524 adjacent around the rotation center C are arranged so that the distance between each center and the rotation center C is slightly different. That is, the holding holes 523 are arranged so that the centers thereof are on the annular line r3, while the holding holes 524 are arranged so that the centers thereof are on the annular line r4. The annular line r3 and the annular line r4 have slightly different distances from the rotation center C, and the annular line r4 has a slightly smaller diameter than the annular line r3.

In the carrier 500 of the third example, the center of the holding hole 520 exists in a band-like region B between the annular line r3 and the annular line r4. The distance between the rotation center C and the holding hole 523 and the distance between the rotation center C and the holding hole 524 are not the same, but are approximately equal. The holding holes 523 and 524 of the third example constitute the same diameter hole group in which the distance between the rotation center C of the carrier 500 and the center of the holding hole 520 is substantially equal. The carrier 500 of the third example is provided with holding holes 523 and holding holes 524 at five locations. The holding holes 523 and the holding holes 524 are alternately arranged in the circumferential direction around the rotation center C.

A distance d shown in FIG. 10 indicates a distance between the two holding

holes

523 and 524 on a line segment connecting the centers of the two holding

holes

523 and 524 adjacent in the circumferential direction around the rotation center C. . The holding hole 520 is provided so that the distance d between two adjacent holding

holes

523 and 524 is in the range of 0.5 mm or more and 3.0 mm or less.

By defining the distance d between the holding

holes

523 and 524 to be 0.5 mm or more, the durability of the carrier 500 can be ensured. By defining the distance d between the holding

holes

523 and 524 to be 3.0 mm or less, the deformation of the polishing pad by the two glass substrates 1 held in the adjacent holding

holes

523 and 524 influences each other. As a result, the amount of polishing of the glass substrate 1 adjacent in the circumferential direction of the carrier 500 can be changed according to the thickness of the glass substrate 1 before polishing, thereby reducing the variation in the thickness of the glass substrate 1 after polishing. Therefore, the effect of improving the uniformity of the thickness of the glass substrate 1 held by the holding hole 523 and the holding hole 524 that are not the same distance from the rotation center C but are almost equal can be obtained similarly. be able to.

Hereinafter, examples and comparative examples of glass substrates for information recording media will be described. A glass substrate was produced according to the steps described with reference to FIG. Glass substrates 1 of Examples 1 and 2 and Comparative Example 1 in which only the carrier 500 used in the first polishing step (Step S31) was varied were produced. In Examples 1 and 2 and Comparative Example 1, a total of 13 holding

holes

520, 10 on the outer peripheral side and 3 on the inner peripheral side, are arranged so as to form a double ring around the rotation center C. The glass substrate 1 was polished using the carrier 500. The glass substrate 1 had an outer diameter of 91 mm and a thickness of 0.8 mm. The thickness of each carrier 500 was 0.65 mm. The material of the carrier 500 was a general glass epoxy.

In Example 1, the interval between the holding holes 520 adjacent in the circumferential direction of the carrier 500 was set to 2.5 mm. In the radial direction of the carrier 500, the centers of the holding holes 520 arranged on the outer peripheral side (corresponding to the holding holes 521 shown in FIG. 9) are arranged on the same circumference and the holding holes arranged on the inner peripheral side. The holding hole 520 is provided so that the center of the hole 520 (corresponding to the holding hole 522 shown in FIG. 9) is arranged on the same circumference. The interval between the holding holes 520 adjacent in the radial direction, that is, the interval between the holding hole 520 on the inner peripheral side and the holding hole 520 on the outer peripheral side was set to a large value exceeding 3.0 mm.

In Example 2, the interval between the holding holes 520 adjacent in the circumferential direction of the carrier 500 was set to 2.5 mm. In the radial direction of the carrier 500, the center of the holding hole 520 arranged on the outer peripheral side (corresponding to the holding hole 521 shown in FIG. 9) is slightly shifted in the radial direction and is disposed in the band-shaped region. The holding holes 520 are provided so that the centers of the holding holes 520 arranged on the side (corresponding to the holding holes 522 shown in FIG. 9) are slightly shifted in the radial direction and arranged in the band-shaped region. The interval between the holding holes 520 adjacent in the radial direction, that is, the interval between the holding hole 520 on the inner peripheral side and the holding hole 520 on the outer peripheral side was set to a small value of 0.5 mm or more and 3.0 mm or less.

In Comparative Example 1, the interval between the holding holes 520 adjacent to each other in the circumferential direction of the carrier 500 was set to 4 mm and a value exceeding 3.0 mm. In the radial direction of the carrier 500, the centers of the holding holes 520 arranged on the outer peripheral side (corresponding to the holding holes 521 shown in FIG. 9) are arranged on the same circumference and the holding holes arranged on the inner peripheral side. The holding hole 520 is provided so that the center of the hole 520 (corresponding to the holding hole 522 shown in FIG. 9) is arranged on the same circumference. The interval between the holding holes 520 adjacent in the radial direction, that is, the interval between the holding hole 520 on the inner peripheral side and the holding hole 520 on the outer peripheral side was set to a large value exceeding 3.0 mm.

The set value of the processing amount of the glass substrate 1 in the first polishing process using the carrier 500 of Examples 1 and 2 and Comparative Example 1 is set to 30 μm, and the glass substrate 1 held by five carriers 500 and processed at one time It was evaluated how much the thickness of the glass substrate 1 after polishing had variation among all the numbers. The thickness of the glass substrate 1 was measured using SI-F80 manufactured by Keyence Corporation after the cleaning process (step S50). “Excellent” when the standard deviation σ of the thickness value of the glass substrate 1 held by the same carrier 500 and polished simultaneously is less than 0.1 μm, “good” when less than 0.1 μm and less than 0.2 μm, The case of 0.2 μm or more and less than 0.5 μm was evaluated as “bad”.

FIG. 11 is a diagram showing the arrangement and evaluation results of the holding holes in the examples and comparative examples. As shown in FIG. 11, in the glass substrates 1 of Examples 1 and 2, the standard deviation σ of the plate thickness value was less than 0.2 μm, and good results were obtained in which the variation in the plate thickness was sufficiently small. In particular, the variation was small between the glass substrates 1 held in the holding holes 520 on the outer peripheral side or between the glass substrates 1 held in the holding holes 520 on the inner peripheral side. In Example 2 in which the interval between the holding holes 520 adjacent in the radial direction of the carrier 500 was defined, the standard deviation σ was less than 0.1 μm, which was particularly favorable. On the other hand, in the glass substrate 1 of Comparative Example 1, the standard deviation σ of the plate thickness value was large, and the variation in the plate thickness could not be reduced sufficiently.

From the evaluation results described above, the centers of the two holding holes 520 that belong to the same diameter hole group in which the distance between the rotation center C of the carrier 500 and the center of the holding hole 520 are substantially equal and that are adjacent to each other around the rotation center C in the circumferential direction. It is shown that the variation in the thickness of the glass substrate 1 after the polishing treatment can be reduced by setting the distance between the two holding holes on the line connecting the two to 0.5 mm or more and 3.0 mm or less. It was done. Accordingly, it has been clarified that, even in the magnetic disk 10 manufactured from the glass substrate 1 having an outer diameter of 80 mm or more, the variation in fluttering characteristics can be reduced by sufficiently reducing the variation in the thickness of the glass substrate 1.

As described above, the embodiment of the present invention has been described. However, it should be considered that the embodiment and example disclosed this time are examples in all respects and are not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 glass substrate, 2 magnetic thin film layer, 10 magnetic disk, 300 upper surface plate, 310 upper polishing pad, 311 and 411 polishing surface, 400 lower surface plate, 410 lower polishing pad, 410h foaming hole, 500 carrier, 510 body, 520 , 521 to 524 holding hole, 2000 double-side polishing machine, C rotation center, d distance, r1 to r4 annular line.

Claims

An information recording medium having a polishing pad made of a member including a plurality of foam holes and a carrier for holding a glass substrate, and using a polishing apparatus for polishing the glass substrate held by the carrier using the polishing pad A method for producing a glass substrate,
Preparing a glass substrate having a main surface and an outer diameter of 80 mm or more;
Polishing the main surface of the glass substrate using the polishing apparatus,
The carrier is provided to be able to rotate, and a plurality of holding holes for accommodating the glass substrate are formed,
At least some of the plurality of holding holes constitute a group of identical diameter holes in which the distance between the rotation center of the carrier and the center of the holding hole is substantially equal.
The distance between the two holding holes on the line connecting the centers of the two holding holes that belong to the same diameter hole group and are adjacent to each other in the circumferential direction around the rotation center is 0.5 mm or more and 3.0 mm or less. The manufacturing method of the glass substrate for information recording media.
The method for producing a glass substrate for an information recording medium according to claim 1, wherein the polishing pad has a hardness of 75 to 85 in terms of a type AO durometer hardness defined by ISO7619.
At least a part of the plurality of holding holes constitutes a different diameter hole group in which the distance between the center of rotation of the carrier and the center of the holding hole is different from the holding holes belonging to the same diameter hole group,
The distance between the two holding holes on the line connecting the centers of the holding hole belonging to the same diameter hole group and the holding hole belonging to the different diameter hole group is 0.5 mm or more and 3.0 mm or less. The manufacturing method of the glass substrate for information recording media of Claim 1 or 2.
The step of polishing includes a step of rough polishing the glass substrate, and a step of precisely polishing the glass substrate after the step of rough polishing,
The method for producing a glass substrate for an information recording medium according to any one of claims 1 to 3, wherein the carrier is included in the polishing apparatus used in the rough polishing step.
The method for producing a glass substrate for an information recording medium according to any one of claims 1 to 4, wherein the information recording medium is used in a heat-assisted magnetic recording apparatus.
The method for producing a glass substrate for an information recording medium according to any one of claims 1 to 5, wherein the carrier is formed from glass fiber reinforced epoxy.