JPWO2013146135A1 - Method for manufacturing glass substrate for information recording medium and information recording medium - Google Patents

Abstract

The center position (C2) of the first through-holding hole (520C) of the carrier (500) has a diameter of the glass substrate (1) of Dmm, and the first through-holding hole (520C) from the center position (C1) of the carrier (500). ) Is provided at a position satisfying the relational expression [(D / 4) ≦ r ≦ (D / 2)], where rmm is the distance to the center position (C2).

Description

  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 in 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 grinding / polishing step for ensuring high surface shape accuracy. In order to achieve high-precision shape quality of the glass substrate, two or more stages of grinding / polishing processes in which slurry and grinding / polishing pads having different processing capabilities are effectively combined are applied. A technique related to the manufacturing of a conventional glass substrate is disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-015105 (Patent Document 1).

JP 2007-015105 A

  A glass substrate used as an information recording medium is generally ground / polished by holding a plurality of glass substrates in through-holding holes provided in a carrier. In recent years, in order to reduce costs, there is a tendency to increase the number of glass substrates per carrier used in grinding / polishing.

  Also, in order to increase the recording density per sheet, it has come to be used as an information recording area up to the vicinity of the end face on the outer peripheral side of the glass substrate, so that the shape finish of the end face on the outer peripheral side of the glass substrate High accuracy is also demanded.

  When the through-holding hole is provided so as to be closest to the carrier, the glass substrate is also placed near the center position of the carrier. When the glass substrate is placed at the center of the carrier, the glass substrate placed at the center in the polishing process when the double-side polishing apparatus is driven is a region between the inner periphery of the polishing plate and the outer periphery of the surface plate (hereinafter referred to as the outer periphery of the surface plate). , Referred to as a middle zone region)) through the same position.

  When the glass substrate passes through the same position of the polishing pad intensively, in the polishing process, uneven wear of the polishing pad occurs in a portion where the glass substrate passes on the polishing pad, and polishing in the middle zone region of the polishing pad. The pad hardness will decrease.

  When the hardness of the polishing pad in the middle zone region of the surface plate decreases, the glass substrate tilts and settles when the glass substrate passes through the region where the hardness is decreased, and the end surface shape of the glass substrate becomes non-uniform.

  The present invention has been made in view of the above problems, and is capable of suppressing the occurrence of non-uniform hardness areas on a polishing pad of a surface plate in a polishing process using a double-side polishing apparatus. The object is to provide a method for manufacturing a glass substrate for a medium and an information recording medium.

  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. And a surface polishing step of polishing the main surface of the glass substrate while supplying an abrasive.

  The double-side polishing apparatus is located on the upper side of the glass substrate, has an upper surface plate having an upper polishing pad on the glass substrate side, and is located on the lower side of the glass substrate, and has a lower polishing pad on the glass substrate side. A disk-shaped carrier that is provided with a plurality of through-holding holes for holding the glass substrate and is sandwiched between the upper polishing pad and the lower polishing pad and that performs a predetermined rotational movement by the planetary gear mechanism. With.

  The through-holding hole has one first through-holding hole arranged in the vicinity of the center position of the carrier and a plurality of second through-holding holes arranged annularly around the first through-holding hole. .

  The center position of the first through-holding hole is [(D / 4) when the diameter of the glass substrate is Dmm and the distance from the center position of the carrier to the center position of the first through-holding hole is rmm. ) ≦ r ≦ (D / 2)].

  In another embodiment, the auxiliary is smaller in diameter than the through-holding hole at a position radially inward of the carrier than the second through-holding hole arranged annularly around the first through-holding hole. It further has a through hole.

  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 one of the above, and the magnetic thin film layer formed on the main surface of the glass substrate Prepare.

  According to the present invention, in a polishing process using a double-side polishing apparatus, a method for producing a glass substrate for an information recording medium capable of suppressing the occurrence of a non-uniform hardness region on a polishing pad of a surface plate and An information recording medium can be provided.

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. 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 a top view which shows the carrier in a reference technique. It is a top view of the lower side polishing pad in a reference technique. It is a top view which shows the carrier in other embodiment. It is a figure which shows the evaluation result in Example 1-2 and Comparative Example 1-2.

  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 spin coating, and about 0.04 μm to about 0.00 in the case of sputtering. In the case of the electroless plating method, 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.

  In addition, 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, you may provide a base layer and a protective layer as needed. 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.

  Further, 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 that prevents 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.

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.

[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 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. Aluminosilicate glass, and SiO ₂ of 58 wt% to 75 wt%, and _Al 2 _{O 3} of 5 wt% to 23 wt%, and Li ₂ O 3 wt% to 10 wt%, 4 wt% to 13 wt % 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.

  The glass blank material may be formed by cutting out a 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, by using alumina abrasive grains having a particle size of # 400 (particle size of about 40 to 60 μm), 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.

  Further, the outer peripheral end surface and the inner 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 polishing 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.

  By the second lapping step (step S31), 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 and the like 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, 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 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 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 cleaning of the surfaces of the upper polishing pad 310 and the lower polishing pad may be performed in any step in the polishing step (step S30), or may be performed in any step in the polishing step (step S30). Alternatively, it may be performed after the polishing process (step S30) ends.

  After polishing both main surfaces of the glass substrate 1 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.

  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 or more and 0.5 μm or less. 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.

  Note 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 both main surfaces of the glass substrate with detergent, pure water, ozone, IPA (isopropyl alcohol), UV (ultraviolet) ozone, or the like, the deposits attached to both 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, the detailed structure of the carrier 500 employed in the double-side polishing apparatus 2000 used in the second polishing step in the above-described grinding / polishing step will be described with reference to FIGS. FIG. 5 is a plan view showing a carrier 500 in the present embodiment, FIG. 6 is a plan view showing a dimensional relationship of the carrier in the present embodiment, and FIG. 7 is a plan view of the glass substrate 1.

  Referring to FIG. 5, 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 23 through holding holes 520 for holding the glass substrate 1. In the present embodiment, the through-holding hole 520 is annularly arranged around one first through-holding hole 520C disposed in the vicinity of the center position C1 of the carrier 500 and the first through-holding hole 520C. Each of the second through-holding holes 520P. In the present embodiment, the second through-holding holes 520P are arranged in a double ring shape, and eight through-holding holes 520P are arranged at equal intervals on the inner annular line r1, and on the outer annular line r2. In addition, 14 through-holding holes 520P are arranged at equal intervals. The diameter of the through-holding hole 520 is about 66.5 mm.

  Here, referring to FIG. 6, the center position C2 of the first through-holding hole 520C is the diameter of the glass substrate 1 being Dmm, and from the center position C1 of the carrier 500 to the center position C2 of the first through-holding hole 520C. When the distance is rmm, it is provided at a position (region indicated by S in the figure) that satisfies the relational expression [(D / 4) ≦ r ≦ (D / 2)].

  In the present embodiment, since the diameter D of the glass substrate 1 is 65 mm, the center position C2 of the first through-holding hole 520C is provided at a position of 16.25 mm ≦ r ≦ 32.5 mm.

  In the double-side polishing apparatus 2000 according to 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.

  8 and 9, when the center position C1 of the carrier 500 and the center position C2 of the first through-holding hole 520C overlap, that is, the first through-holding hole 520C is provided at the center of the carrier 500. The double-side polishing apparatus 2000 will be described. FIG. 8 shows the carrier 500 when the first through-holding hole 520 </ b> C is provided at the center of the carrier 500.

  When double-side polishing of the glass substrate 1 is performed by the double-side polishing apparatus 2000 using the carrier 500 shown in FIG. 8, the glass disposed at the center when the double-side polishing apparatus 2000 is driven as shown in FIG. The substrate 1 intensively passes through the middle belt region BL1 that is the same position of the lower polishing pad 410.

  The glass substrate 1 intensively passes through the middle band region BL1 which is the same position of the lower polishing pad 410 as the lower side of the glass substrate 1 on the lower polishing pad 410 passes the lower side in the polishing step. The uneven wear of the polishing pad 410 occurs, and the hardness of the lower polishing pad 410 in the middle band region of the lower surface plate 400 decreases.

  When the hardness of the lower polishing pad 410 in the middle band region BL1 of the lower surface plate 400 decreases, the glass substrate 1 tilts and sinks when the glass substrate 1 passes through the decreased hardness region, and the end face shape of the glass substrate Becomes uneven. This occurs not only in the lower polishing pad 410 but also in the upper polishing pad 310.

  On the other hand, the carrier 500 in the present embodiment shown in FIG. 5 is provided such that the center position C2 of the first through-holding hole 520C is shifted from the center position C1 of the carrier 500.

  Thus, the glass substrate 1 held by the first through-holding hole 520C passes through the same positions of the upper polishing pad 310 and the side polishing pad 410 even when the double-side polishing apparatus 2000 performs double-side polishing of the glass substrate 1. It is suppressed.

  As a result, it is possible to suppress the occurrence of uneven wear of the upper polishing pad 310 and the lower polishing pad 410 and to prevent the hardness of the upper polishing pad 310 and the lower polishing pad 410 from decreasing. As a result, even when double-side polishing is performed, the glass substrate 1 can be kept uniform in the end face shape without being inclined and settling.

(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 115 per condition.

  In Example 1 and Example 2, the distance from the center position C1 of the carrier 500 to the center position C2 of the first through-holding hole 520C was rmm = 20 mm. On the other hand, in Comparative Example 1, a carrier in which the center position C2 of the first through-holding hole 520C is provided at the center position C1 of the carrier 500 is used, and in Comparative Example 2, a carrier having a diameter of 15 mm that is 16.25 mm or less. Using.

  Further, in the second embodiment, as shown in FIG. 10, the second through-holding hole 520p arranged in a ring around the first through-holding hole 520C is penetrated at a position inside the carrier 500 in the radial direction. The glass substrate 1 having the auxiliary through hole 520M having a smaller diameter than the holding hole 520 was used. This glass substrate was provided with four auxiliary through holes 520M. The diameter of the auxiliary through hole 520M is 26 mm, and the distance from the center position C1 of the carrier 500 to the center position of the auxiliary through hole 520M is 50 mm.

  When only one first through-holding hole 520C is provided at a position shifted from the center position C1 of the carrier 500, the center of gravity of the carrier 500 is shifted and the auxiliary through-hole 520M is distorted in the carrier 500 during polishing. May occur, and the upper polishing pad 310 and the lower polishing pad 410 may be damaged. Therefore, it is preferable to provide the auxiliary through hole 520M at a position where the center of gravity of the carrier 500 is the center position of the carrier 500. Thereby, it is possible to suppress the occurrence of scratches on the upper polishing pad 310 and the lower polishing pad 410 due to the distortion of the carrier 500.

  In each example and each comparative example, the double-side polishing apparatus used in the second polishing step is preliminarily processed using a glass substrate different from the glass substrate used in this test, and the upper and lower polishing pads are used. The second polishing step was carried out after adjusting the conditions showing the inherent tendency. Specifically, before carrying out this test, the double-side polishing apparatus used in this test is used so that the carrier used in each example and each comparative example is used, and the total machining time is approximately 40 hours in total. The glass substrate was processed in advance using For the pre-processing, a glass substrate similar to the glass substrate created by the procedure up to the step S33 was used. By the pre-processing, the wear on the polishing pad, which is specific to the carrier of the example and the comparative example, can be seen.

(End measurement of glass substrate)
FIG. 11 shows the evaluation results in Examples 1 and 2 and Comparative Examples 1 and 2. For the glass substrates obtained in Examples 1 and 2 and Comparative Examples 1 and 2, using a stylus type surface measuring machine, the shape of the end surface portion of the glass substrate is R1 in the radial direction from the center of the glass substrate. Measure the height of the glass substrate at the point (22.25 mm), the point R2 (27.25 mm), and the point R3 (31.25 mm), and connect the line connecting the heights of R1 and R2. As a reference line, the relative displacement amount of the height of the R3 position was analyzed. If the analysis result is within ± 0.18 μm, it was determined as a good product.

  Further, in Examples 1 and 2 and Comparative Examples 1 and 2, end face measurement was performed on each of 50 glass substrates, and the ratio of non-defective products was examined. 86% or more of glass substrates were within ± 0.18 μm. Was evaluated as “A”, and when it was less than 86%, it was rejected as evaluation “C”.

  As a result of the end face measurement, evaluation “A” was obtained in Example 1 and Example 2 as shown in FIG. 11. In Comparative Examples 1 and 2, the evaluation was “C”.

  Thus, as a result of end face measurement, the end face shape was poor in Comparative Example 1 and Comparative Example 2, and the end face shape was good in Example 1 and Example 2. In Comparative Example 1 and Comparative Example 2, the glass substrate held at the center of the carrier repeatedly passes through the middle band region BL1 of the upper polishing pad 310 and the lower polishing pad 410, thereby causing uneven wear of the middle band region BL1. proceed. As a result, the hardness of the upper polishing pad 310 and the lower polishing pad 410 in the middle band region BL1 of the upper polishing pad 310 and the lower polishing pad 410 is reduced.

  When the glass substrate 1 passes through the region where the hardness has decreased due to the decrease in the hardness of the middle belt region BL1 of the upper polishing pad 310 and the lower polishing pad 410, the glass substrate 1 is inclined and settled, and the end face shape of the glass substrate Is considered to be non-uniform.

  On the other hand, in Example 1 and Example 2, the frequency of passing through the middle band region BL1 of the glass substrate is reduced, and uneven wear of the upper polishing pad 310 and the lower polishing pad 410 in the middle band region BL1 is suppressed. As a result, it is considered that the inclination and sedimentation of the glass substrate 1 were reduced, and the end face shape of the glass substrate was improved.

  For the polishing surface plate used in Example 1 and Example 2, the average thickness of the upper and lower polishing pads was measured after the main processing. Thickness measurement was performed for the upper polishing pad and the lower polishing pad at two locations near the inner periphery, the middle belt region, and the outer periphery, for a total of six locations, and the average value of the upper polishing pad and the lower polishing pad. Asked.

  As shown in FIG. 11, compared to Example 1, in Example 2, the wear of the upper polishing pad 310 and the lower polishing pad 410 was about 15 μm smaller on average. In the case of Example 2, by providing the auxiliary through hole 520M, the center of gravity position of the carrier 500 is corrected at the center position C1 of the carrier 500, so that the vertical distortion generated in the carrier 500 is This is because it is reduced as compared with the carrier 500 of the first embodiment, and the occurrence of scratches on the upper polishing pad 310 and the lower polishing pad 410 is suppressed.

  Furthermore, with respect to the glass substrate obtained by the said Example 1-2 and the comparative example 1-2, the chemical strengthening process (S40) shown in FIG. 3, the washing | cleaning process (S50), and a magnetic thin film formation process ( 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. In the information recording medium using the glass substrate obtained in Comparative Example 1-2, an unrecordable area was generated near the outer periphery of the information recording medium. On the other hand, the information recording medium using the glass substrate obtained in Example 1-2 was capable of good recording even near the outer periphery of the information recording medium.

  The above embodiment describes the case where the present invention is applied to the second polishing step (precise polishing) S34. However, even if the present invention is applied to the first polishing step (rough polishing) S33. Alternatively, even when the present invention is applied to both the first polishing step (rough polishing) S33 and the second polishing step (precision polishing) S34, the same effects can be obtained.

  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, 400 lower surface plate, 410 lower polishing pad, 500 carrier, 510 main body, 520 through-holding hole, 520C first through-holding hole, 520P second through-holding hole, 520M auxiliary through-hole, 2000 double-side polishing apparatus.

Claims (3)

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 through-holding hole is
One first through-holding hole disposed in the vicinity of the center position of the carrier;
A plurality of second through-holding holes arranged annularly around the first through-holding hole,
The center position of the first through-holding hole is
When the diameter of the glass substrate is Dmm and the distance from the center position of the carrier to the center position of the first through hole is rmm, [(D / 4) ≦ r ≦ (D / 2)] A method for producing a glass substrate for an information recording medium provided at a position satisfying the relational expression.   The auxiliary through-hole having a smaller diameter than the through-holding hole is further provided at a position on the inner side in the radial direction of the carrier than the second through-holding hole disposed annularly around the first through-holding hole. The manufacturing method of the glass substrate for information recording media of Claim 1. 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;
With
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 through-holding hole is
One first through-holding hole disposed in the vicinity of the center position of the carrier;
A plurality of second through-holding holes arranged annularly around the first through-holding hole,
The center position of the first through-holding hole is
When the diameter of the glass substrate is Dmm and the distance from the center position of the carrier to the center position of the first through hole is rmm, [(D / 4) ≦ r ≦ (D / 2)] An information recording medium provided at a position satisfying the relational expression.

Images