WO2013146134A1

WO2013146134A1 - Manufacturing method for glass substrate for information recording medium, and information recording medium

Info

Publication number: WO2013146134A1
Application number: PCT/JP2013/056081
Authority: WO
Inventors: 小松　隆史
Original assignee: コニカミノルタ株式会社
Priority date: 2012-03-30
Filing date: 2013-03-06
Publication date: 2013-10-03

Abstract

　A carrier (500) has a plurality of auxiliary through holes (530). If the radius of the carrier (500) is Rmm, and the distance from the center position (C1) of the carrier (500) to the center position (C2) of the auxiliary through holes (530) is rmm, at least one of the through holes (530) is provided in a position that satisfies the following relational expression: [r≥(3/4)×R]. Furthermore, if the diameter of a glass substrate is Dmm, the diameter of the auxiliary through holes (530) is at least 1mm less than Dmm.

Description

Method for manufacturing glass substrate for information recording medium and information recording medium

The present invention relates to a method for manufacturing a glass substrate for information recording medium and an information recording medium, and in particular, includes a method for manufacturing a glass substrate for information recording medium used for manufacturing an information recording medium, and the glass substrate for information recording medium. The present invention relates to an information recording medium.

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. 2006-95636 (Patent Document 1) discloses a conventional technology relating to glass substrate manufacturing.

JP 2006-95636 A

In a conventional double-side polishing apparatus, a glass substrate is taken out after polishing, and then cleaned on a surface plate using pure water. For this reason, when restarting the polishing process, it is necessary to supply the slurry to the double-side polishing pad again.

The slurry is supplied from an area near the center between the inner surface of the surface plate and the outer surface of the surface plate of the double-side polishing apparatus, but until the slurry is supplied to the entire double-side polishing apparatus after the double-side polishing apparatus is driven, There was a difference in the arrival time of the slurry between the inner and outer glass substrates. For this reason, a difference has occurred in the processing amount of the glass substrate in the initial stage of processing within the surface plate. For this reason, the removal state varied in the processing marks generated in the previous step of the polishing step.

Particularly in recent years, as the quality level required for glass substrates has increased, the amount of processing traces on glass substrates has been increased to reduce scratches and deposits on the substrate surface and to increase the recording density of magnetic media. It is essential to reduce the variation in the processing marks on the glass substrate.

Also, scratches and deposits generated during the final polishing of the glass substrate adversely affect the characteristics of the information recording medium on which the subsequent magnetic thin film layer is formed.

The present invention has been made in view of the above problems, and by reducing the time difference from driving the double-side polishing apparatus until the slurry is supplied to the glass substrates located outside and inside, the glass substrate can be reduced. An object of the present invention is to provide a method of manufacturing a glass substrate for an information recording medium and an information recording medium using a double-side polishing apparatus capable of reducing the variation in processing traces.

The method for manufacturing a glass substrate for information recording medium according to the present invention is a method for manufacturing a glass substrate for information recording medium in which a magnetic thin film layer is formed on the main surface of a circular disk-shaped glass substrate, comprising a planetary gear mechanism. A surface polishing step of polishing the main surface of the glass substrate using a double-side polishing apparatus provided with an abrasive, and the double-side polishing apparatus is located on the upper side of the glass substrate. An upper surface plate having an upper polishing pad on the side, a lower surface plate having a lower polishing pad on the glass substrate side, and a plurality of through-holding holes for holding the glass substrate. And a disc-shaped carrier that is sandwiched between the upper polishing pad and the lower polishing pad and that performs a predetermined rotational movement by the planetary gear mechanism.

The carrier has a plurality of auxiliary through holes, and the auxiliary through holes are at least when the radius of the carrier is Rmm and the distance from the center position of the carrier to the center position of the auxiliary through hole is rmm. One auxiliary through hole is provided at a position satisfying the relational expression [r ≧ (3/4) × R], and when the diameter of the glass substrate is D mm, the diameter of the auxiliary through hole is 1 mm or more and less than Dmm.

In another embodiment, half or more of the plurality of auxiliary through holes 530 are provided at positions satisfying the relational expression [r ≧ (3/4) × R].

In another embodiment, all of the plurality of auxiliary through holes 530 are provided at positions satisfying the relational expression [r ≧ (3/4) × R].

In another embodiment, a plurality of grooves extending in parallel to each other are provided on the surfaces of the upper polishing pad and the lower polishing pad, and the interval between the adjacent grooves is not less than Dmm and less than [20 × D] mm. It is.

In another embodiment, the intervals between the plurality of grooves provided in the upper polishing pad are narrower than the intervals between the plurality of grooves provided in the lower polishing pad.

In another embodiment, the same number of auxiliary through holes as the through holding holes are provided at positions between the through holding holes at positions on the outer peripheral side of the through holding hole located on the outermost periphery.

In another embodiment, the auxiliary through hole has a diameter of 1 mm or more and less than 10 mm.
In the information recording medium based on this invention, the glass substrate obtained by the manufacturing method of the glass substrate for information recording media described in any of the above, and the magnetic thin film layer formed on the main surface of the glass substrate Prepare.

According to the present invention, by reducing the time difference between driving the double-side polishing apparatus and supplying the slurry to the glass substrates located on the outside and inside of the carrier, variation in processing marks on the glass substrate is reduced. It is possible to provide a method of manufacturing a glass substrate for an information recording medium and an information recording medium using a double-side polishing apparatus that can be reduced.

It is a perspective view which shows the glass substrate obtained by the manufacturing method of the glass substrate in embodiment. It is a perspective view which shows the magnetic disc provided with the glass substrate obtained by the manufacturing method of the glass substrate in embodiment. It is a flowchart figure 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. FIG. 5 is a cross-sectional view taken along line V in FIG. 4. It is a top view which shows the carrier in embodiment. It is a top view which shows the dimensional relationship of the carrier in embodiment. It is a top view of a glass substrate. It is sectional drawing of the upper side polishing pad and lower side polishing pad in embodiment. It is a top view which shows the groove shape of the upper side polishing pad and lower side polishing pad in embodiment. It is a top view which shows the other groove shape of the upper side polishing pad and lower side polishing pad in embodiment. It is a figure which shows the evaluation result in Example 1-3 and Comparative Example 1-4. It is a figure which shows the evaluation result in Example 4-6.

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 glass substrate 1 is not particularly limited, and is, for example, 0.8 inch, 1.0 inch, 1.8 inch, 2.5 inch, or 3.5 inch outer diameter. The thickness of the glass substrate 1 is, for example, 0.30 mm to 2.2 mm from the viewpoint of preventing breakage. As for the size of the glass substrate 1 in the present embodiment, the outer diameter is about 65 mm, the inner diameter is about 20 mm, and the thickness is about 0.8 mm. 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.

As shown in FIG. 2, in the magnetic disk 10, a magnetic film is formed on the front main surface 1A of the glass substrate 1 to form a magnetic thin film layer 2 including a magnetic recording layer. 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 formed continuously with an in-line type sputtering apparatus, such as an underlayer and a magnetic film. In addition, these protective layers may be a single layer, or may have a multilayer structure including the same or different layers.

Other protective layers may be formed on the protective layer or instead of the protective layer. For example, instead of the protective layer, colloidal silica fine particles are dispersed and coated on a Cr layer with tetraalkoxysilane diluted with an alcohol solvent, and then fired to form a silicon oxide (SiO2) layer. May be.

[Glass substrate manufacturing method]
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 step (step S20), a grinding / 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). For example, general aluminosilicate glass is used as the glass material. The aluminosilicate glass is composed of 58 mass% to 75 mass% SiO2, 5 mass% to 23 mass% Al2O3, 3 mass% to 10 mass% Li2O, and 4 mass% to 13 mass% Na2O. Contains 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.

The glass blank material may be formed by cutting out sheet glass (sheet 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 forming process)
Next, in the glass substrate forming step (step S20), the first lapping step 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.

Also, the inner peripheral end surface and the outer peripheral end surface of the glass substrate are polished into a mirror surface by a brush (step S22). As the abrasive grains, a slurry containing cerium oxide abrasive grains is used.

(Grinding / polishing process)
Next, in the grinding / polishing process (step S30), a second lapping process is performed on both main surfaces of the glass substrate (step S31). 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.

Next, as a first polishing process (rough polishing), warping of the glass substrate is corrected while removing scratches remaining on both main surfaces of the glass substrate in the second lapping process (step S31) (step S33). In the first polishing process, a double-side polishing apparatus using a planetary gear mechanism is used. For example, polishing is performed using a polishing pad such as hard velor, urethane foam, or pitch-impregnated suede. As the abrasive, a slurry mainly composed of general cerium oxide abrasive grains is used.

In the second polishing step (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 S34). 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. For example, polishing is performed using a polishing pad which is a soft polisher made of suede or velor. As the abrasive, a slurry mainly composed of general colloidal silica that is finer than the cerium oxide used in the first polishing step is used.

Here, the schematic configuration of the double-side polishing apparatus 2000 will be described with reference to FIGS. FIG. 4 is a partial perspective view of a double-side polishing apparatus 2000 used in the polishing process. 5 is a cross-sectional view taken along the line V in FIG.

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 attached to the lower surface, and the lower polishing pad 410 attached to the upper surface on the side (glass substrate side) facing the upper surface plate 300 of the lower surface plate 400 are provided.

The upper surface plate 300 is provided with a plurality of slurry supply holes 320. The opening diameter of the slurry supply hole 320 is about 8 mm to 15 mm. In the present embodiment, the slurry supply holes 320 are provided at 16 locations near the outer peripheral edge of the upper surface plate 300. The number and positions of the slurry supply holes 320 are not limited to the present embodiment. The position, quantity, and opening diameter of the slurry supply holes 320 are determined according to the amount of slurry supplied.

One end of a slurry supply tube 330 is connected to each of the slurry supply holes 320. The other end of the slurry supply tube 330 is connected to a tube-shaped powder ring 340 provided in an annular shape. A slurry supply port 350 is provided at a predetermined position of the powder ring 340. In the present embodiment, three slurry supply ports 350 are provided, but the quantity is arbitrary.

The powder ring 340 rotates together with the upper surface plate 300, and when the slurry supply port 350 is positioned below, the slurry supply nozzle 360 that supplies the slurry to the slurry supply port 350 is provided above the powder ring 340. Yes.

As shown in FIG. 5, the slurry supplied from the slurry supply nozzle 360 is supplied between the side polishing pad 310 and the lower polishing pad 410 through the slurry supply tube 330 and the slurry supply hole 320.

The upper polishing pad 310 and the lower polishing pad 410 are processing tools 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. 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.

In the second polishing step (step S34), the surfaces of the upper polishing pad 310 and the lower polishing pad 410 may be cleaned. The surface of the upper polishing pad 310 and the lower polishing pad may be cleaned in any process during the grinding / polishing process (step S30), and between any processes in the grinding / polishing process (step S30). It may be performed or may be performed after completion of the grinding / polishing process (step S30).

After both main surfaces of the glass substrate 1 are polished once or a plurality of times, the surfaces of the upper polishing pad 310 and the lower polishing pad 410 are cleaned in the double-side polishing apparatus 2000. The surfaces of the upper polishing pad 310 and the lower polishing pad 410 may be periodically cleaned each time one or more polishings are performed, or may be cleaned irregularly.

(Chemical strengthening process)
After the glass substrate is washed, the chemical strengthening layer is formed on both main surfaces of the glass substrate by immersing the glass substrate 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.

It should be noted that 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 the two main surfaces of the glass substrate with detergent, pure water, ozone, IPA (isopropyl alcohol), UV (ultraviolet) ozone, or the like, the deposits attached to the two main surfaces of the glass substrate are removed.

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 includes an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoFeZr alloy, an orientation control underlayer made of Ru, a perpendicular magnetic recording layer made of a CoCrPt alloy, a protective layer made of a C system, and a lubrication made of an F system. It is formed by sequentially depositing layers. By forming the magnetic thin film layer, 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)
Next, a detailed structure of the carrier 500 employed in the double-side polishing apparatus 2000 used in the first polishing process and the second polishing process in the above-described polishing process will be described with reference to FIGS. 6 is a plan view showing a carrier 500 in the present embodiment, FIG. 7 is a plan view showing a dimensional relationship of the carrier 500 in the present embodiment, FIG. 8 is a plan view of the glass substrate 1, and FIG. 4 is a cross-sectional view of an upper polishing pad 310 and a lower polishing pad 410 in the present embodiment. FIG.

Referring to FIG. 6, carrier 500 in the present embodiment has a disk-shaped main body 510, and has a thickness of about 0.30 mm to 2.2 mm, which is thinner than the thickness of glass substrate 1 to be held. The thickness is selected. The diameter of the carrier 500 is about 430 mm. For the main body 510, aramid fiber, FRP (glass epoxy), PC (polycarbonate), or the like is used.

The carrier 500 is provided with 22 through-holding holes 520 for holding the glass substrate 1. In the present embodiment, the through-holding holes 520 are arranged in a double ring shape, with eight through-holding holes 520 on the inner annular line r1 and through-holding holes 520 on the outer annular line r2. 14 are arranged. The diameter of the through-holding hole 520 is about 66.5 mm. The carrier 500 has a plurality of auxiliary through holes 530.

Referring to FIGS. 7 and 8, the auxiliary through-hole 530 has a radius of the carrier 500 as Rmm and a distance from the center position C1 of the carrier 500 to the center position C2 of the auxiliary through-hole 530 as rmm. It is provided at a position satisfying the relational expression r ≧ (3/4) × R].

In the present embodiment, all the auxiliary through-holes 530 satisfy the above relational expression, and are the same number (14) as the through-holding holes 520 at positions on the outer peripheral side with respect to the through-holding hole 520 located on the outermost periphery. An auxiliary through hole 530 is provided at a position between the through holding holes 520. Therefore, the outermost through-holes 520 and the auxiliary through-holes 530 are arranged in a staggered manner.

The position where the through-holding hole 520 is provided is sufficient if at least one auxiliary through-hole 530 is provided at a position satisfying the above relational expression. Therefore, if at least one auxiliary through hole 530 is provided at a position satisfying the above relational expression, even if the auxiliary through hole 530 is provided at a position [r <(3/4) × R]. Good.

Preferably, more than half of the auxiliary through holes 530 provided in the carrier 500 are provided at positions satisfying the relational expression [r ≧ (3/4) × R]. More preferably, all the auxiliary through holes 530 are provided at positions satisfying the relational expression [r ≧ (3/4) × R].

Furthermore, when the diameter of the glass substrate 1 is Dmm, the diameter of the auxiliary through hole 530 is 1 mm or more and less than Dmm. In the present embodiment, since the diameter of the glass substrate 1 is 65 mm, the maximum diameter of the auxiliary through hole 530 is set to less than 65 mm.

In the case of this embodiment, since the diameter of the carrier 500 is 430 mm, the radius R (mm) of the carrier 500 is 215 mm. Therefore, the distance r (mm) from the center position C1 of the carrier 500 to the center position C2 of the auxiliary through hole 530 is preferably 161.25 mm or more.

Referring to FIG. 9, in the present embodiment, the surface of upper polishing pad 310 is provided with a plurality of grooves 310g having a groove width G1, a groove depth D1, and an interval P1 between adjacent grooves. The lower polishing pad 410 is also provided with a similar groove 410g. The groove width G1 is about 1 mm to about 5 mm, the groove depth D1 is about 0.3 mm to about 2.0 mm, and the interval P1 between adjacent grooves is about 20 mm to about 500 mm. A groove 410 g similar to the surface of the upper polishing pad 310 is also provided on the surface of the lower polishing pad 410.

In this embodiment, the interval between the grooves 310g of the upper polishing pad 310 is preferably set narrower than the interval between the grooves 410g of the lower polishing pad 410. Thereby, the carrier 500 and the glass substrate 1 are easily attracted to the lower polishing pad 410. Thereby, adsorption | suction to the upper side polishing pad 310 of the carrier 500 and the glass substrate 1 at the time of raising the upper side polishing pad 310 can be avoided.

The pattern shape of the groove 310g of the upper polishing pad 310 and the pattern shape of the groove 410g of the lower polishing pad 410 may be the same or different. The pattern shape of the groove 310g of the upper polishing pad 310 and the pattern shape of the groove 410g of the lower polishing pad 410 are straight shapes in which grooves are provided in parallel at predetermined intervals, as shown in FIG. As described above, it is possible to adopt a lattice shape in which grooves intersect and other pattern shapes. 10 and 11, the pattern shape of the groove 310g of the upper polishing pad 310 is illustrated, but the pattern shape of the groove 410g of the lower polishing pad 410 is the same.

In the double-side polishing apparatus 2000 in the present embodiment, five carriers 500 are annularly arranged between the upper surface plate 300 and the lower surface plate 400. A gear is provided on the outer peripheral surface of the carrier 500, but the illustration of the gear is omitted. Further, the radius of the carrier 500 means a dimension when measured with a gear tip circle.

As described above, in the first polishing step and the second polishing step in the polishing step, a plurality of auxiliary through holes 530 are provided at positions satisfying the relational expression [r ≧ (3/4) × R], and the glass substrate 1 When the diameter of the carrier is Dmm, the carrier 500 having the auxiliary through-hole 530 having a diameter of 1 mm or more and less than Dmm is used to drive the double-side polishing apparatus and supply slurry to the double-side polishing apparatus. The slurry that moves to the outside in the radial direction due to the centrifugal force due to the above passes through the auxiliary through-hole 530, moves between the upper polishing pad 310 and the lower polishing pad 410, and by the upper polishing pad 310 and the lower polishing pad 410, The surface of the glass substrate 1 is polished.

As a result, compared with the case where the auxiliary through-hole 530 is not provided, the convergence time from the time when the double-side polishing apparatus is driven to the time when the slurry is supplied to the entire double-side polishing apparatus is reduced to the average time of slurry dispersion. be able to.

This reduces the difference in the machining allowance of the glass substrate at the initial stage of processing, and also suppresses variations in the processing marks of the previous process remaining on the glass substrate.

(Example)
Examples and comparative examples of the method for producing the glass substrate for information recording medium will be described below. In each of the following examples and comparative examples, the processes up to the “first polishing step (rough polishing)” in S33 shown in FIG. 3 were performed as described above. The total number of glass substrates is 110.

Before the “second polishing step (precision polishing)” of S34, the surface roughness of the glass substrate was measured. It was confirmed that there was no variation in the surface roughness of the glass substrate before performing S34. The surface roughness of 10 glass substrates was measured in each comparative example and each example, using Nanoscope Dimension V type manufactured by BECOL Instruments. It was confirmed that the surface roughness (Ra) measured for each glass substrate in a 10 μm square was within 6.0 mm to 7.2 mm.

As Example 1-6 and Comparative Example 1-4, the “second polishing step (precise polishing)” of S34 was performed using each of the glass substrates. Five carriers 500 were used in one “second polishing step (precision polishing)”. The number of glass substrates held by one carrier is 22. The diameter of the through-holding hole 520 is 66.5 mm. For the upper polishing pad 310 and the lower polishing pad 410, a soft polisher made of suede was used. As the abrasive, a slurry mainly composed of general colloidal silica, which is finer than the cerium oxide used in the first polishing step, was used.

(Comparative Example 1-4, Example 1-3)
The carrier 500 of Comparative Example 1 is not provided with the auxiliary through hole 530. The carrier 500 of Comparative Example 2 has an auxiliary through hole 530 having a diameter of 0.7 mm on the same circle on the circumference having a radius of 130 mm from the center position C1 of the carrier 500 (indicated as “inside” in FIG. 12). 14 were provided at regular intervals. An interval P1 between

adjacent grooves

310g and 410g provided in the upper polishing pad 310 and the lower polishing pad 410 is 40 mm.

The carrier 500 of Comparative Example 3 has an auxiliary through hole 530 having a diameter of 1.2 mm on the same circle on the circumference having a radius of 130 mm from the center position C1 of the carrier 500 (indicated as “inside” in FIG. 12). 14 were provided at regular intervals. An interval P1 between

adjacent grooves

The carrier 500 of Comparative Example 4 has an auxiliary through hole 530 having a diameter of 0.7 mm on the same circle on the circumference having a radius of 200 mm from the center position C1 of the carrier 500 (indicated as “outside” in FIG. 12). 14 were provided at regular intervals. An interval P1 between

adjacent grooves

In the carrier 500 of the first embodiment, an auxiliary through hole 530 having a diameter of 1.2 mm is provided on the same circle on the circumference having a radius of 200 mm from the center position C1 of the carrier 500 (indicated as “outside” in FIG. 12). 14 were provided at regular intervals. An interval P1 between

adjacent grooves

In the carrier 500 of the second embodiment, an auxiliary through hole 530 having a diameter of 4.0 mm is provided on the same circle on the circumference having a radius of 200 mm from the center position C1 of the carrier 500 (indicated as “outside” in FIG. 12). 14 were provided at regular intervals. An interval P1 between

adjacent grooves

In the carrier 500 of the third embodiment, an auxiliary through hole 530 having a diameter of 1.2 mm is provided on the same circle on the circumference having a radius of 200 mm from the center position C1 of the carrier 500 (indicated as “outside” in FIG. 12). Seven were provided at equal intervals. An interval P1 between

adjacent grooves

FIG. 12 shows the results of Comparative Example 1-4 and Example 1-3 according to the conditions and defect evaluation. Regarding the yield (yield by scratch evaluation), OSA7120 manufactured by KLA-Tencor was used, and a defect having a count of 20 or less that was regarded as a scratch was determined to be a non-defective product, Comparative Examples 1-4, and the implementation In Example 1-3, 50 sheets were measured, the ratio of non-defective products was investigated, and those with 88% or more were evaluated as “A” and passed. Moreover, the thing of less than 88% was set as evaluation "C", and was made disqualified.

As shown in FIG. 12, Comparative Examples 1-4 were all evaluated as “C” and failed. On the other hand, each of Examples 1-3 was evaluated as “A” and passed.

(Example 4-6)
In the carrier 500 of the fourth embodiment, an auxiliary through hole 530 having a diameter of 1.2 mm is provided on the same circle on the circumference having a radius of 200 mm from the center position C1 of the carrier 500 (indicated as “outside” in FIG. 13). Fourteen were provided at equal intervals. An interval P1 between

adjacent grooves

310g and 410g provided in the upper polishing pad 310 and the lower polishing pad 410 is 60 mm.

In the carrier 500 of the fifth embodiment, an auxiliary through hole 530 having a diameter of 1.2 mm is provided on the same circle on the circumference having a radius of 200 mm from the center position C1 of the carrier 500 (indicated as “outside” in FIG. 13). Fourteen were provided at equal intervals. An interval P1 between adjacent grooves of the

grooves

310g and 410g provided in the upper polishing pad 310 and the lower polishing pad 410 is 80 mm.

In the carrier 500 of the sixth embodiment, an auxiliary through hole 530 having a diameter of 1.2 mm is formed on the same circle on the circumference having a radius of 200 mm from the center position C1 of the carrier 500 (indicated as “outside” in FIG. 13). Fourteen were provided at equal intervals. The upper polishing pad 310 and the lower polishing pad 410 were not provided with the

grooves

310g and 410g.

FIG. 13 shows the results of the yield of each example and defect evaluation in Example 4-6. The yield (yield by scratch evaluation) is the same as described above. In Example 4-6, the evaluation of microwaviness was also performed.

The evaluation of micro waviness was measured using a non-contact surface profile measuring machine (New View 5,000) manufactured by Zygo. The measurement wavelength range of the swell component is 30 μm or more and 200 μm or less. In each of Examples 4-6, 20 glass substrates 1 were measured, and those with an average value of less than 0.8 mm were evaluated as “A” and passed. Moreover, the evaluation “B” having a lower pass rank than the evaluation “A” was set as a pass with a value of 0.8 to 1.0%.

As a result of the measurement, the waviness of the wide groove interval was smaller than that of the narrow groove interval. If the

grooves

310g and 410g are not provided, troubles due to friction may occur during the polishing operation, and it is better to provide the

grooves

310g and 410g.

As shown in FIG. 13, in Example 4, the evaluation of microwaviness was “B”, but the defect evaluation was “A” in all of Examples 4-6.

Furthermore, the chemical strengthening step (S40), the cleaning step (S50), and the magnetic thin film forming step (shown in FIG. 3) are performed on the glass substrates obtained in Examples 1-6 and Comparative Example 1-4. S60) was carried out to obtain an information recording medium.

This information recording medium was incorporated into a hard drive and a read / write test was conducted. Compared to the information recording medium using the glass substrate obtained by Comparative Example 1-4, the information recording medium using the glass substrate obtained by Example 1-6 has good recording characteristics, in particular, The information recording medium using the glass substrate obtained in Example 4-6 was excellent in recording characteristics.

Thus, in Example 1-6, in the second polishing step, the auxiliary through hole 530 is provided at a position satisfying the relational expression [r ≧ (3/4) × R] (outside; 200 mm position). A plurality of carriers 500 provided with a plurality of auxiliary through holes 530 having a diameter of 1.2 mm or 4 mm were used.

Accordingly, when the double-side polishing apparatus is driven and the slurry is supplied to the double-side polishing apparatus, the slurry that moves to the outside in the radial direction by the centrifugal force due to the rotation of the carrier 500 passes through the auxiliary through-hole 530, and the upper polishing pad 310 and The surface of the glass substrate 1 was polished by the upper polishing pad 310 and the lower polishing pad 410 while moving between the lower polishing pads 410.

As a result, when the auxiliary through hole 530 is not provided (Comparative Example 1), when the position of the auxiliary through hole 530 is inside (130 mm) (Comparative Examples 2 and 3), the hole diameter of the auxiliary through hole 530 is less than 1 mm. Compared to the case (Comparative Example 4), it is considered that the convergence time from the time when the double-side polishing apparatus was driven to the time when the slurry was supplied to the entire double-side polishing apparatus could be shortened to the average time of slurry dispersion. As a result, the difference in the machining allowance of the glass substrate at the initial stage of processing was reduced, and it was considered that the variation in the processing marks of the previous process remaining on the glass substrate was also suppressed. A ".

The surfaces of the upper polishing pad 310 and the lower polishing pad 410 are preferably provided with a plurality of

grooves

310g and 410g extending in parallel with each other, and the interval (P1) between the

adjacent grooves

310g and 410g is determined as an example. 1—40 mm is used in Example 3, 60 mm is used in Example 4, and 80 mm is used in Example 5.

In the case where the auxiliary through-hole 530 is not provided in the carrier 500, the convergence of the slurry diffusion was slow, and there was a problem that the processing rate of the glass substrate at the initial stage of processing varied. However, by providing the auxiliary through hole 530 in the carrier 500, it was possible to suppress variation in the processing rate of the glass substrate.

On the other hand, the surface of the upper polishing pad 310 and the lower polishing pad 410 is provided with a plurality of

grooves

310g and 410g extending in parallel with each other, so that minute waviness is generated with respect to the glass substrate. It was confirmed in.

From the evaluation results of the microwaviness in Example 4-6, the lower limit of the interval between the

grooves

310g and 410g is preferably equal to or larger than the diameter (D) of the glass substrate 1, and the upper limit of the interval is less than [20 × D] mm. Preferably there is. The reason why it is less than [20 × D] mm is that it is considered that the state is substantially the same as when no groove is provided.

The diameter of the auxiliary through hole 530 is preferably 1 mm or more and less than 10 mm. When the diameter of the auxiliary through hole 530 is 1 mm or less, as shown in Comparative Example 2 and Comparative Example 4, the defect evaluation is evaluated as “C”.

Further, if the diameter of the auxiliary through hole 530 is 10 mm or more, there is a possibility that the rigidity of the carrier 500 may be lowered, and the upper limit of the diameter of the auxiliary through hole 530 is preferably less than 10 mm.

Although the embodiments and examples of the present invention have been described above, the embodiments and examples disclosed this time are illustrative in all respects and should not be considered as restrictive. It is. 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.

1A front main surface, 1B back main surface, 1C inner peripheral end surface, 1D outer peripheral end surface, 1H hole, 2 magnetic thin film layer, 10 magnetic disk, 300 upper surface plate, 310 upper polishing pad, 310g, 410g groove, 320 slurry supply hole , 330 slurry supply tube, 340 powder ring, 350 slurry supply port, 360 slurry supply nozzle, 400 lower surface plate, 410 lower polishing pad, 500 carrier, 510 main body, 520 through holding hole, 530 auxiliary through hole, 2000 double-side polishing machine .

Claims

A method for producing a glass substrate for an information recording medium in which a magnetic thin film layer is formed on the main surface of a circular disk-shaped glass substrate,
A surface polishing step of polishing the main surface of the glass substrate using a double-side polishing apparatus equipped with a planetary gear mechanism while supplying an abrasive;
The double-side polishing apparatus includes:
Located on the upper side of the glass substrate, an upper surface plate having an upper polishing pad on the glass substrate side,
Located on the lower side of the glass substrate, a lower surface plate having a lower polishing pad on the glass substrate side,
A plurality of through-holding holes for holding the glass substrate, and a disc-shaped carrier that is sandwiched between the upper polishing pad and the lower polishing pad and performs a predetermined rotational movement by the planetary gear mechanism,
The carrier has a plurality of auxiliary through holes,
When the radius of the carrier is Rmm and the distance from the center position of the carrier to the center position of the auxiliary through hole is rmm, at least one of the auxiliary through holes is [r ≧ (3 / 4) × R] is provided at a position satisfying the relational expression, and the diameter of the auxiliary through hole is 1 mm or more and less than Dmm when the diameter of the glass substrate is Dmm. A method for manufacturing a substrate.
The production of the glass substrate for an information recording medium according to claim 1, wherein more than half of the plurality of auxiliary through holes 530 are provided at a position satisfying a relational expression [r ≧ (3/4) × R]. Method.
The method for producing a glass substrate for an information recording medium according to claim 2, wherein all of the plurality of auxiliary through holes 530 are provided at positions satisfying a relational expression of [r ≧ (3/4) × R]. .
A plurality of grooves extending in parallel with each other are provided on the surfaces of the upper polishing pad and the lower polishing pad,
4. The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein an interval between the adjacent grooves is not less than D mm and less than [20 × D] mm. 5.
5. The glass substrate for an information recording medium according to claim 4, wherein an interval between the plurality of grooves provided in the upper polishing pad is narrower than an interval between the plurality of grooves provided in the lower polishing pad. Production method.
6. The auxiliary through hole of the same number as the through holding hole is provided at a position between the through holding holes at a position on the outer peripheral side with respect to the through holding hole located on the outermost periphery. The manufacturing method of the glass substrate for information recording media in any one.
The method for producing a glass substrate for an information recording medium according to any one of claims 1 to 6, wherein the diameter of the auxiliary through hole is 1 mm or more and less than 10 mm.
A glass substrate obtained by a method for producing a glass substrate for an information recording medium;
A magnetic thin film layer formed on the main surface of the glass substrate;
An information recording medium comprising:
The manufacturing method of the glass substrate for information recording medium,
A surface polishing step of polishing the main surface of the glass substrate using a double-side polishing apparatus equipped with a planetary gear mechanism while supplying an abrasive;
The double-side polishing apparatus includes:
Located on the upper side of the glass substrate, an upper surface plate having an upper polishing pad on the glass substrate side,
Located on the lower side of the glass substrate, a lower surface plate having a lower polishing pad on the glass substrate side,
A plurality of through-holding holes for holding the glass substrate, and a disc-shaped carrier that is sandwiched between the upper polishing pad and the lower polishing pad and performs a predetermined rotational movement by the planetary gear mechanism,
The carrier has a plurality of auxiliary through holes,
When the radius of the carrier is Rmm and the distance from the center position of the carrier to the center position of the auxiliary through hole is rmm, at least one of the auxiliary through holes is [r ≧ (3 / 4) × R] is provided at a position satisfying the relational expression, and the diameter of the auxiliary through hole is 1 mm or more and less than Dmm when the diameter of the glass substrate is Dmm.