JP5360331B2 - Manufacturing method of glass substrate for HDD - Google Patents

Abstract

Provided is a process for producing a glass substrate for HDDs which inhibits head crushing even when used in a magnetic recording medium for HDDs that is to be mounted in an HDD equipped with a DFH head mechanism. Also provided are a glass substrate for HDDs and a magnetic recording medium for HDDs. The process for producing a glass substrate for HDDs includes a chemical strengthening step in which a glass substrate is chemically strengthened by immersing the glass substrate in a liquid for chemical strengthening. In the chemical strengthening step, the increase in the circumferential-direction TIR of the glass substrate through the chemical strengthening step is regulated to 0.5 µm or less by changing the attitude of the glass substrate within the chemical strengthening liquid in which the glass substrate is being immersed, and/or by flatting the temperature distribution of the chemical strengthening liquid, and/or by stirring the chemical strengthening liquid.

Description

  The present invention relates to a method for manufacturing a glass substrate for HDD, a glass substrate for HDD, and a magnetic recording medium for HDD.

  Generally, a magnetic recording medium for HDD (hard disk drive) is known as a typical information recording medium having a recording layer utilizing properties such as magnetism, light, and magnetomagnetism. Conventionally, an aluminum substrate has been widely used as an HDD substrate for manufacturing an HDD magnetic recording medium. However, in recent years, with the demand for reduction of the flying height of the magnetic head for improving the recording density, the surface smoothness is superior to that of the aluminum substrate and the surface defects are few, so that the flying height of the magnetic head can be reduced. The proportion of using glass substrates as HDD substrates is increasing.

  Magnetic recording media for HDDs mounted on mobile devices such as notebook personal computers require a substrate that is resistant to impacts. For example, as disclosed in Patent Document 1, it is subjected to chemical strengthening treatment to provide impact resistance. A glass substrate with improved resistance is often used.

  By the way, high-density recording has progressed recently, and for example, the appearance of a magnetic recording medium for HDD having a recording capacity of 500 GB and a surface recording density of 630 Gb / square inch or more with one 2.5-inch recording medium is expected. Has been. Accordingly, the head mechanism has been improved, and a head mechanism called DFH (dynamic flying height) is known. DFH is a technique in which a special metal is used for the mounting position of the head, and the head protrudes from the recording medium at a minute distance by thermal expansion of the metal. In such a DFH head mechanism, the gap between the head and the recording medium is reduced to about several nanometers, and a head crash due to poor tracking of the magnetic head with respect to the surface of the recording medium is likely to occur.

JP 2001-167427 A

  An object of the present invention is to provide a method for manufacturing a glass substrate for an HDD in which the occurrence of head crashes is suppressed even if the magnetic recording medium for the HDD has a high surface recording density as mounted on an HDD having a DFH head mechanism. It is providing the glass substrate for HDD manufactured by the manufacturing method, and the magnetic recording medium for HDD using the glass substrate for HDD.

  That is, one aspect of the present invention is a method for manufacturing a glass substrate for HDD, which includes a chemical strengthening step of subjecting a glass substrate to chemical strengthening treatment by immersing the glass substrate in a chemical strengthening treatment solution, before and after the chemical strengthening step. The increase in the TIR (total indicated runout) in the circumferential direction of the glass substrate is set to 0.5 μm or less.

  Another aspect of the present invention is a glass substrate for HDD manufactured by the method for manufacturing a glass substrate for HDD.

  Yet another aspect of the present invention is an HDD magnetic recording medium manufactured by providing a recording layer on a main surface of the HDD glass substrate.

  The above and other objects, features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

FIG. 1 is a manufacturing process diagram of a glass substrate for HDD according to an embodiment of the present invention. FIG. 2 is a partial side view showing the configuration of the main part of the double-side grinding machine used in the first and second lapping processes. FIG. 3 is an arrow view along the line III-III in FIG. 2, and is a plan view of the lower surface plate and the carrier. FIG. 4 is a longitudinal sectional view showing the configuration of the main part of the Oscar polisher used in the first polishing process. FIG. 5A is a plan view of a lower polishing dish of an Oscar polishing machine in which a ring-shaped jig having a loosely fitted glass substrate is arranged, and FIG. 5B is a view of the ring-shaped jig having a loosely fitted glass substrate. It is an expanded horizontal sectional view. FIG. 6A, FIG. 6B, and FIG. 6C are plan views showing the operation of the Oscar polisher. FIG. 7A is a perspective view of a carrier used to hold a glass substrate in the chemical strengthening process, and FIG. 7B is a side view of the carrier. FIG. 8A, FIG. 8B, FIG. 8C, and FIG. 8D are flowcharts of the chemical strengthening process performed in the conventional chemical strengthening process. FIG. 9A is a perspective view showing the surface shape of the glass substrate before chemical strengthening treatment, and FIG. 9B is a perspective view showing the surface shape of the glass substrate after performing conventional chemical strengthening treatment. . 10A is a height map of the main surface of the glass substrate before chemical strengthening treatment, FIG. 10B is a height map of the main surface of the glass substrate after conventional chemical strengthening treatment, and FIG. c) It is explanatory drawing which compares and shows the TIR of the circumferential direction of the glass substrate before and behind a chemical strengthening process. FIG. 11A, FIG. 11B, FIG. 11C, FIG. 11D, and FIG. 11E show chemical strengthening processes (specific examples) performed in the chemical strengthening process according to the embodiment of the present invention. It is a flowchart of method 1). FIG. 12A, FIG. 12B, and FIG. 12C are elevation maps of the main surface of the glass substrate for explaining the action obtained by the specific method 1. FIG. FIGS. 13 (a), 13 (b), 13 (c), and 13 (d) show a chemical strengthening process (specific methods 2 and 3) performed in the chemical strengthening process according to the embodiment of the present invention. It is a flowchart. FIG. 14A and FIG. 14B are elevation maps of the main surface of the glass substrate for explaining the action obtained by the specific method 2 or 3. FIG. 15 is a perspective view of a glass substrate for HDD according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to this embodiment.

  In order to suppress the occurrence of head crashes, the present inventors have a sufficiently high rotational speed in the circumferential direction of the recording medium as compared with the moving speed at which the magnetic head moves in the radial direction of the recording medium during operation of the HDD. Noted that it is important to suppress fluctuations in the surface condition in the circumferential direction of the recording medium. From this viewpoint, it has been found that it is effective that the TIR (total indicated runout), which is an index of the flatness of the surface of the recording medium, is small in the circumferential direction of the recording medium. In addition, the present inventors have obtained the knowledge that the chemical strengthening treatment performed for improving impact resistance and the like deteriorates the TIR in the circumferential direction of the glass substrate, thereby completing the present invention.

  Furthermore, the inventors of the present invention have the reason that the chemical strengthening treatment deteriorates the TIR in the circumferential direction of the glass substrate, such as temperature variation, concentration variation, or contamination of foreign substances in the chemical strengthening treatment solution in which the glass substrate is immersed. Since the environment is not uniform due to various factors, the present invention was completed with the knowledge that the surface shape of the glass substrate before and after the chemical strengthening treatment did not change uniformly.

<Method for producing glass substrate for HDD>
With reference to the process drawing shown in FIG. 1, the manufacturing method of the glass substrate for HDD is demonstrated.

[Glass melting process]
First, in the glass melting step, a glass material is melted. As a material of the glass substrate, for example, soda lime glass mainly composed of SiO ₂ , Na ₂ O, CaO; mainly composed of SiO ₂ , Al ₂ O ₃ , R ₂ O (R = K, Na, Li) Aluminosilicate glass; borosilicate glass; Li ₂ O—SiO ₂ glass; Li ₂ O—Al ₂ O ₃ —SiO ₂ glass; R′O—Al ₂ O ₃ —SiO ₂ glass (R ′ = Mg) , Ca, Sr, Ba) and the like can be used. Among these, aluminosilicate glass and borosilicate glass are particularly preferable because they are excellent in impact resistance and vibration resistance.

[Molding process]
Next, in the molding step, the molten glass material is poured into the lower mold and press-molded with the upper mold to obtain a disk-shaped glass substrate (referred to as a blank). Note that the blank may be produced by cutting a sheet glass formed by, for example, a downdraw method or a float method with a grinding stone, without using press molding.

  There is no limitation on the size of the glass substrate, that is, the blank. For example, glass substrates having various sizes such as 2.5 inches, 1.8 inches, 1 inch, and 0.8 inches in outer diameter can be manufactured. There is no limitation on the thickness of the glass substrate. For example, glass substrates having various thicknesses such as 2 mm, 1 mm, 0.8 mm, and 0.63 mm can be manufactured.

[Heat treatment process]
Next, in the heat treatment process, glass substrates produced by press molding or cutting are alternately stacked with heat-stable member setters and passed through a high-temperature electric furnace to reduce glass substrate warpage and glass crystallization. Promote.

[First wrapping step]
Next, in the first lapping step, both surfaces of the glass substrate are ground and the parallelism, flatness, and thickness of the glass substrate are preliminarily adjusted.

[Coring process]
Next, in the coring process, a circular hole is formed in the center of the glass substrate after the first lapping process. The drilling can be performed, for example, by grinding with a core drill or the like provided with a diamond grindstone or the like in the cutter portion.

[Inner / outer diameter machining process]
Next, in the inner / outer diameter processing step, the inner / outer diameter processing is performed by grinding the outer peripheral end surface and the inner peripheral end surface of the glass substrate with a drum-shaped grinding wheel using, for example, diamond.

[Second wrapping step]
Next, in the second lapping step, both surfaces of the glass substrate are ground again to finely adjust the parallelism, flatness and thickness of the glass substrate.

  In the first lapping step and the second lapping step, as shown in FIGS. 2 and 3, a known grinding machine 10 called a double-side grinding machine using a planetary gear mechanism can be used. The double-side grinding machine 10 includes a disk-shaped upper surface plate 11 and a lower surface plate 12 that are arranged vertically so as to be parallel to each other. The upper and lower surface plates 11 and 12 rotate in opposite directions. Diamond pellets 13 and 14 for grinding the main surface of the glass substrate are attached to the opposing surfaces of the upper and lower surface plates 11 and 12, respectively. A plurality of carriers 17 are disposed between the upper and lower surface plates 11 and 12. Each carrier 17 rotates in combination with a sun gear 15 provided around the rotation axis of the lower surface plate 12 and an internal gear 16 provided in an annular shape on the outer periphery of the lower surface plate 12. A plurality of holes 18 are formed in each carrier 17. A glass substrate is loosely fitted in each hole 18 and held. Although the glass substrate is not shown in FIGS. 2 and 3, for example, the glass substrate is shown with reference numeral 80 in FIG. The upper and lower surface plates 11, 12, the sun gear 15 and the internal gear 16 operate by separate driving.

  The grinding operation of the grinding machine 10 is performed as follows. That is, when the upper and lower surface plates 11 and 12 rotate in opposite directions, the carrier 17 sandwiched between the upper and lower surface plates 11 and 12 via the diamond pellets 13 and 14 holds a plurality of glass substrates. Thus, while rotating, it revolves in the same direction as the lower surface plate 12 with respect to the rotation center of the surface plates 11 and 12. Grinding liquid is supplied between the diamond pellet 13 of the upper surface plate 11 and the glass substrate and between the diamond pellet 14 of the lower surface plate 12 and the glass substrate to the grinding machine 10 operating in this way. Thus, the glass substrate is ground.

When this double-side grinding machine 10 is used, the weight of the surface plates 11 and 12 applied to the glass substrate and the rotational speed of the surface plates 11 and 12 are appropriately adjusted according to the desired grinding state. The weight in the first and second wrapping steps is preferably 60 g / cm ² (5.88 kPa) to 120 g / cm ² (11.77 kPa). The rotation speed of the surface plates 11 and 12 is preferably about 10 to 30 rpm, and the rotation speed of the upper surface plate 11 is preferably about 30 to 40% slower than the rotation speed of the lower surface plate 12. If the weight by the surface plates 11 and 12 is increased and the rotational speed of the surface plates 11 and 12 is increased, the grinding amount increases. However, if the load is too large, the surface roughness will not be good, and if the rotational speed is too fast, the flatness will not be good. Further, if the weights of the surface plates 11 and 12 are reduced and the rotational speed of the surface plates 11 and 12 is decreased, the amount of grinding is reduced and the production efficiency is lowered.

  At the end of the second lapping step, defects such as large undulations, chips and cracks in the glass substrate are almost removed. Moreover, as for the surface roughness of the main surface of a glass substrate, it is preferable that Ra is about 0.2 micrometer to 0.4 micrometer, and the flatness of a main surface has preferable 7-10 micrometers. By maintaining such a surface state, it is possible to efficiently perform polishing in the next first polishing step.

  In the first lapping step, large waviness, chips, cracks, etc. of the glass substrate are roughly removed so that the second lapping step can be performed efficiently. Therefore, diamond pellets 13 and 14 with a roughness of about # 1300 mesh to # 1700 mesh are used in the second lapping process, and diamond pellets with a roughness of about # 800 mesh to # 1200 mesh with a roughness higher than that are used in the first lapping process. 13 and 14 are preferably used. When the first lapping step is finished, the surface roughness of the main surface of the glass substrate is preferably Ra from about 0.4 μm to 0.8 μm, and the flatness of the main surface is preferably 10 to 15 μm.

  Moreover, it is preferable to perform the washing | cleaning process for removing the grinding fluid and glass powder which remained on the surface of the glass substrate after the 1st lapping process and / or after the 2nd lapping process.

  In addition, the surface roughness used by this embodiment is the value which measured the range of 1 micrometer x 1 micrometer using atomic force microscope (Digital Instruments company nanoscope). Further, the flatness used in the present embodiment is a value measured by a flatness measuring device, and a difference in height (Po-Vo value) between the highest position (Po) and the lowest position (Vo) on the surface of the glass substrate. It is.

[End face polishing process]
Next, in the end face polishing process, the outer peripheral end face and the inner peripheral end face of the glass substrate after the second lapping process are polished using an end face polishing machine.

[First polishing step]
Next, in the first polishing step, both surfaces of the glass substrate are polished. In the first polishing step, the glass substrate 80 is polished so that the shape of the HDD glass substrate according to the present embodiment can be finally obtained efficiently by using an Oscar polishing machine 20 as shown in FIGS. To do. The Oscar polishing machine 20 includes a rotating lower polishing dish 21 and an upper polishing dish 22 that swings the upper space of the lower polishing dish 21 in the horizontal direction (X ← → X). The glass substrate 80 accommodated in the ring-shaped jig 23 having an inner diameter larger than the outer diameter of the glass substrate 80 is disposed between the upper and lower polishing dishes 21 and 22, and the glass substrate 80 is rotated while rotating the glass substrate 80. Both surfaces of the substrate 80 are polished by upper and lower polishing dishes 21 and 22.

  In the Oscar polishing machine 20, the lower polishing dish 21 is rotated while supplying the polishing liquid with the glass substrate 80 as an object to be polished placed between the upper and lower polishing dishes 21 and 22. The glass substrate 80 is polished by the upper and lower polishing dishes 21 and 22 by swinging left and right with respect to FIGS. Depending on conditions, rotation of the glass substrate 80 can be promoted. As a result, the glass substrate 80 having a concentric point target shape can be manufactured. That is, fluctuations in the surface state in the circumferential direction of the glass substrate 80 can be suppressed. In the present embodiment, the glass substrate 80 having an outer diameter of 2.5 inches (63.5 mm) will be described as an example, but the size of the glass substrate 80 is not limited.

  In the present embodiment, the upper and lower polishing dishes 21 and 22 have a diameter of 1000 mm, and elastic suedes (only the suede 24 of the lower polishing dish 21 is shown in FIG. 5A) are attached to the opposing surfaces. ing. A glass substrate 80 is loosely fitted and held on a ring-shaped jig 23 (inner diameter 65 mm, outer diameter 67 mm, thickness 0.5 mm) manufactured from a resin material as shown in FIG. This is placed on the suede 24 of the lower polishing dish 21 for 100 sets. Then, the glass substrate 80 is sandwiched between the upper polishing dish 22 and the lower polishing dish 21 is rotated while supplying slurry containing cerium oxide or colloidal silica as abrasive grains (polishing material) as a polishing liquid. Is swung left and right with respect to FIGS. 4 to 6 within an arbitrary range. Thereby, the glass substrate 80 rotates within the ring-shaped jig 23 by the relative movement of the upper and lower polishing dishes 21 and 22, and both surfaces are polished in the circumferential direction.

[Chemical strengthening process]
(General)
Next, in the chemical strengthening step, the chemical strengthening layer (stress layer) is formed on the main surface, the outer peripheral end surface, and the inner peripheral end surface of the glass substrate by immersing the glass substrate in the chemical strengthening treatment liquid. That is, a chemical strengthening process is performed on the glass substrate. By forming the chemical strengthening layer on the main surface of the glass substrate, warpage of the glass substrate and roughening of the main surface can be prevented. By forming the chemically strengthened layer on the outer peripheral end surface and the inner peripheral end surface of the glass substrate, the impact resistance, vibration resistance, heat resistance, and the like of the glass substrate can be improved.

  In the chemical strengthening step, by immersing the glass substrate in a heated chemical strengthening solution, alkali metal ions such as lithium ions and sodium ions contained in the glass substrate are converted into alkali metal ions such as potassium ions having a larger ion radius. This is carried out by a replacement ion exchange method. Compressive stress is generated in the ion-exchanged region due to distortion caused by the difference in ion radius, and the main surface, outer peripheral end surface, and inner peripheral end surface of the glass substrate are strengthened by the stress layer, that is, the chemical strengthening layer. As a result of strengthening the surface of the glass substrate with the stress layer, the impact resistance of the glass substrate is further improved.

  There is no restriction | limiting in particular in a chemical strengthening process liquid, A well-known chemical strengthening process liquid can be used. Usually, it is common to use a molten salt containing potassium ions or a molten salt containing potassium ions and sodium ions. Examples of the molten salt containing potassium ions and sodium ions include potassium and sodium nitrates, carbonates, sulfates, and mixed molten salts thereof. Among these, it is preferable to use nitrate from the viewpoint that the melting point is low and deformation of the glass substrate can be prevented.

(Conventional chemical strengthening treatment)
The conventional chemical strengthening treatment is approximately as follows. First, as shown in FIG. 7A, a carrier 30 for holding a glass substrate 80 is used. The carrier 30 is a container whose top and bottom are open, and a plurality of holding rods 31 are installed in parallel to each other. As shown in FIG. 7B, the glass substrate 80 is held by the plurality of holding rods 31 at three points. Several tens of glass substrates 80 are arranged in parallel with each other with a slight gap and are simultaneously held by one carrier 30.

  As shown in FIG. 8A, the glass substrate 80 held on the carrier 30 is preheated to 300 ° C. in the electric furnace 40. As shown in FIG. 8 (b), a chemical strengthening treatment liquid prepared by mixing and dissolving potassium nitrate (60 mass%) and sodium nitrate (40 mass%) is prepared in a treatment liquid tank 50 and heated to 400 ° C. by a heater 51. To do. The preheated glass substrate 80 is immersed in the chemical strengthening treatment solution for about 20 minutes, and a reinforcing layer is formed over the entire surface of the glass substrate 80. As shown in FIG. 8C, after the glass substrate 80 that has been subjected to the chemical strengthening treatment is cooled by being immersed in a hot water tank 60 heated to 70 ° C. by a heater 61 for about 10 minutes, FIG. As shown in FIG.

  At this time, since the environment surrounding the glass substrate 80 is not uniform due to various factors such as temperature variation and concentration variation of the chemical strengthening treatment liquid or mixing of foreign matters, the surface shape of the glass substrate 80 before and after the chemical strengthening treatment is uniform. It does not change. For example, as shown in FIG. 9A, the glass substrate 80 having a substantially flat surface shape before the chemical strengthening treatment is deformed as shown in FIG. 9B. Become.

  As a result, as shown in FIGS. 10A, 10B, and 10C, the TIR in the circumferential direction of the glass substrate 80 deteriorates after the chemical strengthening treatment. FIG. 10A is a height map of the main surface 81 (see FIG. 15) of the glass substrate 80 before the chemical strengthening treatment. As shown in this figure, the flatness of the main surface 81 of the glass substrate 80 is relatively good before the chemical strengthening treatment. Therefore, as shown by a solid line (a) in FIG. 10C, the TIR in the circumferential direction of the main surface 81 of the glass substrate 80 is small. On the other hand, FIG.10 (b) is a height map of the main surface 81 of the glass substrate 80 after the conventional chemical strengthening process. As shown in this figure, after the chemical strengthening treatment, the surface shape of the main surface 81 of the glass substrate 80 is distorted. Therefore, as indicated by a broken line (b) in FIG. 10C, the TIR in the circumferential direction of the main surface 81 of the glass substrate 80 increases.

  In addition, the circumferential direction TIR in FIG. 10C is a value at a position indicated by a broken line in FIGS. 10A and 10B. Specifically, it is a value at a position of 0.75R from the center of the glass substrate 80, where R is the radius of the glass substrate 80.

  The “TIR in the circumferential direction of the glass substrate” means, for example, a plane that is optimally fitted to the main surface of the glass substrate by the least square method, and measures the height of the main surface of the glass substrate in a plurality of locations in the circumferential direction. The absolute value (P-V value) of the difference between the highest point (P) whose height is above the plane and the lowest point (V) below it.

  The TIR in the circumferential direction of the main surface 81 of the glass substrate 80 is, for example, a method for measuring the surface shape using interference of white light (for example, “Optiflat” manufactured by Phase Shift Technology) or a surface to be measured. By applying laser light obliquely, it is possible to obtain a higher reflectance than the vertical incidence method, and a method capable of measuring even a rough surface shape (for example, “Flat Master FM100XRA” manufactured by TROPEL). Can be measured.

  Thus, it has been found that the chemical strengthening treatment conventionally performed for improving the impact resistance of the glass substrate 80 deteriorates the TIR in the circumferential direction of the glass substrate 80. As a result, the surface state in the circumferential direction of the glass substrate 80 greatly fluctuated, and head crushing due to poor tracking of the magnetic head was likely to occur.

(Chemical strengthening treatment of this embodiment)
Therefore, in the present embodiment, the chemical strengthening process is intended to prevent the TIR in the circumferential direction of the glass substrate 80 from being deteriorated. Specifically, the amount of increase in TIR in the circumferential direction of the glass substrate 80 before and after the chemical strengthening step is set to 0.5 μm or less.

  According to this, since the amount of increase in the TIR in the circumferential direction of the glass substrate 80 before and after the chemical strengthening step is 0.5 μm or less, the deterioration in the circumferential direction TIR of the glass substrate 80 due to the chemical strengthening treatment is extremely limited. . Therefore, the TIR in the circumferential direction of the glass substrate 80 after the chemical strengthening process is suppressed to a small value, the fluctuation of the surface state in the circumferential direction of the glass substrate 80 is suppressed, and the occurrence of head crash due to the follow-up failure of the magnetic head is suppressed. Is done.

  In this embodiment, it is preferable that the increase amount of TIR in the circumferential direction of the glass substrate 80 before and after the chemical strengthening step is 0.3 μm or less. This is because the deterioration of the circumferential direction TIR of the glass substrate 80 due to the chemical strengthening process becomes more limited, and the occurrence of head crash due to the follow-up failure of the magnetic head is further suppressed.

  In the present embodiment, the TIR in the circumferential direction of the glass substrate 80 is the TIR in the circumferential direction at a position of 0.75R from the center of the glass substrate 80 when the radius of the glass substrate 80 is R.

  This has the following advantages. That is, the circumferential direction TIR in the same glass substrate has a correlation with the distance from the center of the glass substrate, and the circumferential direction TIR tends to increase as the distance from the center of the glass substrate increases. The position of 0.75R from the center of the glass substrate 80 is a relatively outer position in the main surface 81 of the glass substrate 80 or the recording area of the recording medium. Therefore, by limiting the amount of increase in TIR in the circumferential direction at a position of 0.75R from the center of the glass substrate 80 to 0.5 μm or less or 0.3 μm or less, the outer peripheral end and the inner surface of the main surface 81 of the glass substrate 80 Deterioration in the circumferential direction TIR is extremely limited in the entire main surface 81 including the peripheral edge, or in the entire recording area including the outer peripheral edge and the inner peripheral edge of the recording area of the recording medium. There is an advantage that the occurrence of is suppressed over a wide range.

(Specific method 1)
As a first specific method for setting the amount of increase in TIR in the circumferential direction of the glass substrate 80 before and after the chemical strengthening step to 0.5 μm or less, the glass substrate immersed in the chemical strengthening treatment liquid in the chemical strengthening step is as follows. It is possible to change the posture in the 80 chemical strengthening treatment liquid.

  According to this, the following operation is obtained. That is, when the posture of the glass substrate 80 in the chemical strengthening treatment liquid is not changed, the shape surrounding the glass substrate 80 is different for each part of the surface of the glass substrate 80 because the environment surrounding the glass substrate 80 is not uniform due to various factors. Changes can occur. On the other hand, by changing the posture of the glass substrate 80 in the chemical strengthening treatment liquid, it is possible to cancel the shape change that differs for each part. Therefore, the surface shape of the glass substrate 80 before and after the chemical strengthening process changes uniformly, and the TIR increase amount can be easily reduced to 0.5 μm or less.

  For example, as shown in FIG. 11A, the glass substrate 80 held on the carrier 30 is preheated to 300 ° C. in the electric furnace 40. As shown in FIG. 11 (b), a chemical strengthening treatment liquid prepared by mixing and dissolving potassium nitrate (60 mass%) and sodium nitrate (40 mass%) is prepared in a treatment liquid tank 50 and heated to 400 ° C. with a heater 51. To do. The preheated glass substrate 80 is immersed in the chemical strengthening treatment solution for about 10 minutes (first immersion). After immersion for 10 minutes, the glass substrate 80 is taken out of the treatment liquid tank 50 together with the carrier 30, and all the glass substrates 80 are rotated by 90 ° with respect to the center of the glass substrate 80 as indicated by arrows in the figure. After changing the attitude of the glass substrate 80 in this way, as shown in FIG. 11C, the glass substrate 80 is immersed again in the chemical strengthening treatment liquid for about 10 minutes (second immersion). As shown in FIG. 11 (d), the glass substrate 80 that has been subjected to the chemical strengthening treatment is cooled by being immersed in a hot water tank 60 heated to 70 ° C. by a heater 61 for about 10 minutes, and then FIG. 8 (e). As shown in FIG.

  In this way, as shown in FIG. 12A, the surface shape of the glass substrate 80 is changed into strain symmetrically through the center of the glass substrate 80 by the first immersion, as shown in FIG. As shown in FIG. 12C, since the orientation of the glass substrate 80 in the chemical strengthening treatment solution changed by 90 ° with respect to the center of the glass substrate 80 by the second immersion, these are combined, and as shown in FIG. Different shape changes will be canceled for each part of the surface. As a result, the amount of increase in TIR in the circumferential direction of the glass substrate 80 before and after the chemical strengthening step is 0.5 μm or less.

  In addition, this example is a case where the surface shape of the glass substrate changes in line symmetry passing through the center of the glass substrate, that is, the surface shape of the glass substrate changes at two predetermined positions facing the glass substrate at 180 °. For example, when the surface shape of the glass substrate changes only at a predetermined position, the glass substrate is rotated little by little at an angle smaller than 90 °, and each time the glass substrate is chemically strengthened. What is necessary is just to immerse in a liquid (for example, to immerse several times in total 3 times or more).

  One of the specific methods for setting the amount of increase in TIR in the circumferential direction to 0.5 μm or less is to grasp in advance the shape change of the glass substrate due to the chemical strengthening treatment, and to cancel the shape change according to the shape change. Furthermore, the purpose is to perform the chemical strengthening process in a plurality of times.

  If possible, the posture may be changed while the glass substrate 80 is immersed in the chemical strengthening treatment liquid without being taken out of the treatment liquid tank 50.

(Specific method 2)
As a second specific method of setting the amount of increase in TIR in the circumferential direction of the glass substrate 80 before and after the chemical strengthening step to 0.5 μm or less, the temperature distribution of the chemical strengthening treatment liquid is made uniform in the chemical strengthening step. Can be mentioned.

  According to this, the temperature variation of the chemical strengthening process liquid which immerses the glass substrate 80 is reduced. Therefore, the environment surrounding the glass substrate 80 becomes uniform, the surface shape of the glass substrate 80 before and after the chemical strengthening process changes uniformly, and the TIR increase amount can be easily reduced to 0.5 μm or less. .

  For example, as shown in FIG. 13A, the glass substrate 80 held on the carrier 30 is preheated to 300 ° C. in the electric furnace 40. As shown in FIG. 13 (b), a chemical strengthening treatment liquid prepared by mixing and dissolving potassium nitrate (60 mass%) and sodium nitrate (40 mass%) is prepared in a treatment liquid tank 50 and heated at 400 ° C. with heaters 51 to 55. Heat to. The preheated glass substrate 80 is immersed in the chemical strengthening treatment liquid for about 20 minutes. At this time, the temperature distribution of the chemical strengthening treatment liquid is made uniform by arranging the plurality of heaters 51 to 54 evenly around the treatment liquid tank 50. Further, by providing the heater 55 disposed in the circular hole at the center of the glass substrate 80, the temperature distribution of the chemical strengthening treatment liquid with respect to the glass substrate 80 can be made more uniform. As shown in FIG. 13C, the glass substrate 80 after the chemical strengthening treatment is cooled by being immersed in a hot water tank 60 heated to 70 ° C. by a heater 61 for about 10 minutes. As shown in FIG.

  By so doing, since the glass substrate 80 is immersed in the chemical strengthening treatment liquid having a uniform temperature distribution, as shown in FIGS. 14A and 14B, the periphery of the glass substrate 80 before and after the chemical strengthening treatment is obtained. Deterioration of the direction TIR is suppressed. FIG. 14A is a height map of the main surface 81 of the glass substrate 80 before chemical strengthening treatment, and FIG. 14B is the height map of the main surface 81 of the glass substrate 80 after chemical strengthening treatment according to 2 of this specific method. High and low map. As shown in this figure, the flatness of the main surface 81 of the glass substrate 80 is well maintained before and after the chemical strengthening treatment. As a result, the amount of increase in TIR in the circumferential direction of the glass substrate 80 before and after the chemical strengthening step is 0.5 μm or less.

  The specific method 2 for setting the increase in TIR in the circumferential direction to 0.5 μm or less is intended to stabilize the chemical reaction in the ion exchange method.

  Depending on the situation, the heater 55 arranged in the circular hole in the center of the glass substrate 80 may be omitted.

(Specific method 3)
A third specific method for setting the amount of increase in TIR in the circumferential direction of the glass substrate 80 before and after the chemical strengthening step to 0.5 μm or less includes stirring the chemical strengthening treatment liquid in the chemical strengthening step. .

  According to this, the concentration variation of the chemical strengthening process liquid which immerses the glass substrate 80 is reduced. Therefore, the environment surrounding the glass substrate 80 becomes uniform, the surface shape of the glass substrate 80 before and after the chemical strengthening process changes uniformly, and the TIR increase amount can be easily reduced to 0.5 μm or less. .

  For example, in FIG. 13B, the heater 55 arranged in the circular hole at the center of the glass substrate 80 is circularly moved or rotated like a stirring bar as indicated by an arrow in the figure.

  By so doing, since the glass substrate 80 is immersed in the chemical strengthening treatment liquid having a uniform concentration distribution, as shown in FIGS. 14A and 14B, the periphery of the glass substrate 80 before and after the chemical strengthening treatment is obtained. Deterioration of the direction TIR is suppressed. 14A is a height map of the main surface 81 of the glass substrate 80 before chemical strengthening treatment, and FIG. 14B is the height map of the main surface 81 of the glass substrate 80 after chemical strengthening treatment according to 3 of this specific method. High and low map. As shown in this figure, the flatness of the main surface 81 of the glass substrate 80 is well maintained before and after the chemical strengthening treatment. As a result, the amount of increase in TIR in the circumferential direction of the glass substrate 80 before and after the chemical strengthening step is 0.5 μm or less.

  The specific method 3 for setting the increase in TIR in the circumferential direction to 0.5 μm or less is intended to stabilize the chemical reaction in the ion exchange method.

  Depending on the situation, instead of the heater 55 disposed in the circular hole in the center of the glass substrate 80, a stirring rod having no heating function may be disposed in the circular hole in the center of the glass substrate 80. Good. Further, only the heater 51 may be left, and the plurality of heaters 52 to 54 disposed around the processing liquid tank 50 may be omitted. Further, the chemical strengthening treatment liquid is not limited to stirring in the circular hole in the central portion of the glass substrate 80, and the chemical strengthening treatment liquid is placed outside the circular hole in the central portion of the glass substrate 80, that is, around the glass substrate 80. You may stir. Further, the chemical strengthening treatment liquid may be stirred both inside and outside the circular hole at the center of the glass substrate 80.

[Second polishing step]
Next, in the second polishing step, both surfaces of the glass substrate after the chemical strengthening step are polished more precisely. In the second polishing process, a double-side polishing machine having a configuration similar to that of the double-side grinding machine 10 used in the first and second lapping processes shown in FIGS. 2 and 3 is used.

  In the second polishing step, instead of the diamond pellets 13 and 14, a soft polishing pad having a hardness of about 65 to 80 (Asker-C), which is softer than the suede used in the first polishing step, is used. For example, urethane foam or suede is preferably used as the polishing pad.

  As the polishing liquid, a slurry containing cerium oxide or the like similar to that in the first polishing step as abrasive grains (polishing material) can be used. However, in order to make the surface of the glass substrate smoother, it is preferable to use a polishing liquid having a finer grain size and less variation. For example, colloidal silica having an average particle size of 40 nm to 70 nm is preferably used as a polishing liquid in which slurry is dispersed in water as abrasive grains (abrasive). The mixing ratio of water and abrasive grains is preferably about 1: 9 to 3: 7.

The weight applied to the glass substrate by the upper and lower surface plates is preferably 90 g / cm ² (8.83 kPa) to 110 g / cm ² (10.8 kPa). Further, the rotational speed of the upper and lower surface plates is preferably 15 rpm to 35 rpm, and the rotational speed of the upper surface plate is preferably about 30% to 40% slower than the rotational speed of the lower surface plate.

  By appropriately adjusting the polishing conditions in the second polishing step, it is possible to reduce the flatness of the main surface of the glass substrate to 3 μm or less and the surface roughness Ra of the main surface of the glass substrate to 0.1 nm.

  The polishing amount in the second polishing step is preferably 2 μm to 5 μm. By setting the polishing amount within this range, it is possible to satisfactorily remove minute defects such as minute roughness and undulation generated on the surface of the glass substrate, or minute scratch marks generated in the previous steps.

  Thus, the TIR in the circumferential direction of the final glass substrate 80 is further reduced by including the polishing step of polishing the surface of the glass substrate 80 after the chemical strengthening step. Therefore, the occurrence of head crash is further suppressed.

[Washing process]
Next, in the cleaning process, the glass substrate after the second polishing process is scrubbed. However, the cleaning method is not limited to scrub cleaning, and any cleaning method may be used as long as it can clean the surface of the glass substrate after the polishing process.

  If necessary, the glass substrate subjected to scrub cleaning is subjected to ultrasonic cleaning and drying. The drying process is a process of drying the surface of the glass substrate after removing the cleaning liquid remaining on the surface of the glass substrate using IPA (isopropyl alcohol) or the like. For example, a water rinse cleaning process is performed on the glass substrate after scrub cleaning for 2 minutes to remove the cleaning liquid residue. Next, an IPA cleaning process is performed for 2 minutes, and water remaining on the surface of the glass substrate is removed by IPA. Finally, the IPA vapor drying step is performed for 2 minutes, and the liquid IPA adhering to the surface of the glass substrate is dried while being removed by the IPA vapor.

  The glass substrate drying process is not limited to this, and any drying method generally known as a glass substrate drying method such as spin drying or air knife drying may be used.

[Inspection process]
Next, in the inspection process, the glass substrate is visually inspected for the presence or absence of scratches, cracks, foreign matters, and the like. If it cannot be determined visually, an inspection is performed using an optical surface analyzer (for example, “OSA6100” manufactured by KLA-TENCOL).

  Glass substrates that are determined to be non-defective in the inspection process are stored in a dedicated storage cassette and vacuum packed in a clean environment so that no foreign matter adheres to the surface, and then shipped as HDD glass substrates. .

<Glass substrate for HDD>
Next, the glass substrate for HDD manufactured as described above will be described. As shown in FIG. 15, the glass substrate 80 for HDD according to the present embodiment has a high quality in which the TIR in the circumferential direction is suppressed to a small value on the main surface 81 and the fluctuation of the surface state in the circumferential direction is suppressed. This is a glass substrate for HDD.

<Magnetic recording medium for HDD>
Next, an HDD magnetic recording medium manufactured using the HDD glass substrate 80 will be described. The HDD magnetic recording medium according to the present embodiment is manufactured by providing a magnetic film as a recording layer on the main surface 81 of the HDD glass substrate 80. The magnetic film may be formed directly or indirectly on the main surface 81. The magnetic film may be formed on one side or both sides of the glass substrate 80.

  As a method for forming the magnetic film, a conventionally known method can be used. For example, a method in which a thermosetting resin in which magnetic particles are dispersed is spin-coated on the glass substrate 80, or a method in which sputtering or electroless plating is used. And the like. The film thickness by spin coating is about 0.3 μm to 1.2 μm, the film thickness by sputtering is about 0.01 μm to 0.08 μm, and the film thickness by electroless plating is 0.01 μm to 0.1 μm. From the viewpoint of thinning and high density, film formation by sputtering or electroless plating is preferable.

  The magnetic material used for the magnetic film is not particularly limited, and conventionally known materials can be used. Among them, a Co-based alloy or the like containing Ni and Cr as the basic material for adjusting the residual magnetic flux density is preferable in order to obtain high coercive force. Specifically, CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, CoCrPtSiO, and the like whose main component is Co are preferable.

  The magnetic film may be divided into a non-magnetic film (for example, Cr, CrMo, CrV, etc.) to have a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa, etc.) in which noise is reduced.

The other magnetic material, ferrite or iron - and that of the rare earth, in a non-magnetic film made of _SiO 2, BN, etc., Fe, Co, FeCo, in granular or the like of the structure obtained by dispersing magnetic particles such CoNiPt Good.

  The magnetic film may be either an inner surface type or a vertical type recording format.

  In order to improve the sliding of the magnetic head, a lubricant may be thinly coated on the surface of the magnetic film. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.

  In the present embodiment, if necessary, an underlayer or a protective layer may be provided in addition to the magnetic film as the recording layer. The underlayer in the HDD magnetic recording medium is selected according to the magnetic film. Examples of the material for the underlayer include at least one material selected from the group consisting of nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. In the case of a magnetic film containing Co as a main component, it is preferable to use Cr alone or a Cr alloy from the viewpoint of improving magnetic characteristics. 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 can be used.

  The protective layer is provided to prevent wear and corrosion of the magnetic film. Examples of the protective layer include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be continuously formed by an in-line sputtering apparatus together with the underlayer and the magnetic film. Further, these protective layers may be a single layer, or may have a multilayer structure composed of 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, colloidal silica fine particles are dispersed and applied in a tetraalkoxysilane diluted with an alcohol solvent on the Cr layer, and further baked to obtain silicon dioxide (SiO ₂ ). A layer may be formed.

  As described above, by using the HDD magnetic recording medium manufactured using the HDD glass substrate 80 according to the present embodiment as the substrate, the operation of the magnetic head at the time of high-speed rotation of the HDD can be stabilized. Can do.

  Further, according to the HDD magnetic recording medium manufactured using the HDD glass substrate 80 according to the present embodiment, the TIR in the circumferential direction is suppressed to a small value, and fluctuations in the surface state in the circumferential direction are suppressed. Since the glass substrate 80 is used, it is a high quality HDD magnetic recording medium in which the occurrence of head crashes is suppressed.

  In the present embodiment, the HDD magnetic recording medium manufactured using the HDD glass substrate 80 preferably has a rotational speed of 7000 rpm or more when loaded in a hard disk drive.

  According to this, a high-quality HDD magnetic recording medium is realized in which a head crash due to a poor tracking of the magnetic head hardly occurs even when rotated at a high speed of 7000 rpm or more.

  In the present embodiment, the lapping process and the polishing process are performed twice. However, the present invention is not limited to this, and the lapping process and the polishing process may be performed only once. Moreover, although the chemical strengthening process was performed before the second polishing process, it may be performed after the second polishing process depending on the situation.

  Furthermore, as measures against drop strength, the outer peripheral end face and the inner peripheral end face other than the main surface of the glass substrate may be strengthened, or the glass substrate is subjected to HF immersion treatment as an edge mitigation treatment for scratches generated on the glass substrate. Also good.

  The glass substrate for HDD according to the present embodiment is not limited to the use for manufacturing a magnetic recording medium for HDD, and can be used for the manufacture of, for example, a magneto-optical disk or an optical disk.

  The technical features of this embodiment are summarized as follows.

  The method for manufacturing a glass substrate for HDD according to the present embodiment is a method for manufacturing a glass substrate for HDD that includes a chemical strengthening step in which the glass substrate 80 is subjected to a chemical strengthening treatment by immersing the glass substrate 80 in a chemical strengthening treatment solution. The increase in TIR in the circumferential direction of the glass substrate 80 before and after the chemical strengthening step is 0.5 μm or less.

  According to this embodiment, since the amount of increase in the TIR in the circumferential direction of the glass substrate 80 before and after the chemical strengthening step is 0.5 μm or less, the deterioration of the TIR in the circumferential direction of the glass substrate 80 due to the chemical strengthening treatment is extremely limited. It becomes the target. Therefore, the TIR in the circumferential direction of the glass substrate 80 after the chemical strengthening step is suppressed to a small value, the variation in the surface state in the circumferential direction of the glass substrate 80 is suppressed, and the occurrence of head crashes is suppressed.

  In the present embodiment, the amount of increase in TIR in the circumferential direction of the glass substrate 80 before and after the chemical strengthening step is preferably set to 0.3 μm or less.

  According to this embodiment, the deterioration of the TIR in the circumferential direction of the glass substrate 80 due to the chemical strengthening process is further limited. Therefore, the occurrence of head crash is further suppressed.

  In the present embodiment, in the chemical strengthening step, the increase in TIR is set to 0.5 μm or less by changing the posture of the glass substrate 80 immersed in the chemical strengthening processing solution in the chemical strengthening processing solution.

  According to the present embodiment, the shape change that differs for each part of the surface of the glass substrate 80 that may occur when the posture of the glass substrate 80 is not changed is canceled by changing the posture of the glass substrate 80. Therefore, the surface shape of the glass substrate 80 before and after the chemical strengthening process changes uniformly, and the TIR increase amount can be easily reduced to 0.5 μm or less.

  In this embodiment, in the chemical strengthening step, the increase in TIR is set to 0.5 μm or less by uniformizing the temperature distribution of the chemical strengthening treatment liquid.

  According to this embodiment, the temperature variation of the chemical strengthening process liquid which immerses the glass substrate 80 is reduced. Therefore, the environment surrounding the glass substrate 80 becomes uniform, the surface shape of the glass substrate 80 before and after the chemical strengthening process changes uniformly, and the TIR increase amount can be easily reduced to 0.5 μm or less. .

  In the present embodiment, in the chemical strengthening step, the amount of increase in TIR is set to 0.5 μm or less by stirring the chemical strengthening treatment liquid.

  According to this embodiment, the concentration variation of the chemical strengthening process liquid which immerses the glass substrate 80 is reduced. Therefore, the environment surrounding the glass substrate 80 becomes uniform, the surface shape of the glass substrate 80 before and after the chemical strengthening process changes uniformly, and the TIR increase amount can be easily reduced to 0.5 μm or less. .

  In the present embodiment, after the chemical strengthening step, a polishing step (second polishing step) for polishing the surface of the glass substrate 80 is included.

  According to this embodiment, the TIR in the circumferential direction of the final glass substrate 80 is further reduced. Therefore, the occurrence of head crash is further suppressed.

  In the present embodiment, the TIR in the circumferential direction of the glass substrate 80 is the TIR in the circumferential direction at a position of 0.75R from the center of the glass substrate 80 when the radius of the glass substrate 80 is R.

  According to the present embodiment, the entire main surface 81 including the outer peripheral end and the inner peripheral end of the main surface 81 of the glass substrate 80, or the outer peripheral end and the inner peripheral end of the recording area of the recording medium are included. In the entire recording area, the deterioration of the TIR in the circumferential direction becomes extremely limited, and the occurrence of head crashes is suppressed over a wide range.

  The HDD glass substrate 80 according to this embodiment is manufactured by the method for manufacturing an HDD glass substrate.

  According to the present embodiment, a high-quality glass substrate for HDD 80 is obtained in which the TIR in the circumferential direction is suppressed to a small value and fluctuations in the surface state in the circumferential direction are suppressed.

  The HDD magnetic recording medium according to this embodiment is manufactured by providing a recording layer on the main surface 81 of the HDD glass substrate 80.

  According to the present embodiment, since the HDD glass substrate 80 in which the circumferential TIR is suppressed to a small value and the fluctuation of the surface state in the circumferential direction is suppressed, the occurrence of head crashes is suppressed. A quality HDD magnetic recording medium is obtained.

  The HDD magnetic recording medium according to the present embodiment is preferably used for a hard disk drive having a rotational speed of 7000 rpm or more.

  According to this embodiment, it is possible to obtain a high-quality HDD magnetic recording medium that is less likely to cause head crash due to poor tracking of the magnetic head even when rotated at a high speed of 7000 rpm or higher.

  According to the present embodiment, a method for manufacturing an HDD glass substrate 80 in which the occurrence of a head crash due to a poor tracking of a magnetic head with respect to the surface of a recording medium is suppressed, an HDD glass substrate 80 manufactured by the manufacturing method, and its Since an HDD magnetic recording medium using the HDD glass substrate 80 is provided, it can be applied to the DFH head mechanism and can contribute to the recent high-density recording.

  Hereinafter, the present invention will be described in more detail through examples and comparative examples. However, the present invention is not limited to this embodiment.

<Manufacture of glass substrates for HDD>
The glass substrate for HDD was manufactured according to the manufacturing process of FIG.

[1. Glass melting process, molding process]
An aluminosilicate glass having a Tg of 480 ° C. was used as the glass material, and the molten glass material was press-molded to produce a disk-shaped glass substrate (blank) having an outer diameter of 68 mm and a thickness of 0.93 mm.

[2. Heat treatment process]
By alternately laminating setters and glass substrates with an outer shape of 70 mm, a thickness of 2 mm, and a material of alumina, and passing them through a high-temperature electric furnace set at about 430 ° C. over 2 hours, Stress was reduced.

[3. First lapping process]
Both surfaces of the glass substrate were ground using a double-side grinding machine (manufactured by HAMAI). As grinding conditions, diamond pellets of # 1200 mesh were used, the load was 100 g / cm ² (9.81 kPa), the upper platen was rotated at 20 rpm, and the lower platen was rotated at 30 rpm.

[4. Coring process]
Using a cylindrical core drill equipped with a diamond grindstone, a circular hole having a diameter of 18 mm was formed in the center of the glass substrate.

[5. Inner / outer diameter machining process]
Using a drum-shaped diamond grindstone, the outer peripheral end surface and the inner peripheral end surface of the glass substrate were processed to have an inner diameter and an outer diameter of 65 mm and an inner diameter of 20 mm.

[6. Second wrapping step]
Both surfaces of the glass substrate were ground again using a double-side grinding machine (manufactured by HAMAI). As grinding conditions, diamond pellets of # 1700 mesh were used, the load was 100 g / cm ² (9.81 kPa), the upper platen was rotated at 20 rpm, and the lower platen was rotated at 30 rpm.

  The total grinding amount in the first and second lapping steps was 0.1 mm. As a result, the thickness of the glass substrate was 0.83 mm.

[7. End polishing process]
100 glass substrates were stacked, and in this state, the outer peripheral end surface and the inner peripheral end surface of the glass substrate were polished using an end surface polishing machine. Nylon fiber having a diameter of 0.2 mm was used as the brush hair of the polishing machine. As the polishing liquid, a slurry containing cerium oxide having an average particle diameter of 3 μm as abrasive grains (abrasive material) was used.

[8. First polishing step]
Both surfaces of the glass substrate were polished in the circumferential direction using an Oscar polishing machine as shown in FIGS. The TIR (circumferential direction TIR before the chemical strengthening step) in the circumferential direction of the obtained glass substrate was 0.7 μm (see Table 1). This TIR value is a TIR value in the circumferential direction at a position of 0.75R from the center of the glass substrate, where R is the radius of the glass substrate.

[9. Chemical strengthening process]
In Comparative Examples 1 and 2, the chemical strengthening process was performed as described with reference to FIGS. 8A, 8B, 8C, and 8D (conventional chemical strengthening process). The number of glass substrates held by the carrier was 50 (25 × 2 rows).

  In Examples 1 and 5, the chemical strengthening treatment was performed as described with reference to FIGS. 11 (a), (b), (c), (d), and (e) (the chemical strengthening treatment according to the present invention). Specific method 1). The number of glass substrates held by the carrier was 50 (25 × 2 rows).

  In Examples 2 and 6, the chemical strengthening process was performed as described with reference to FIGS. 13A, 13B, 13C, and 13D (a specific method of the chemical strengthening process according to the present invention). 2). The number of glass substrates held by the carrier was 50 (25 × 2 rows).

  In Examples 3 and 7, the chemical strengthening process was performed as described with reference to FIGS. 13A, 13B, 13C, and 13D (a specific method of the chemical strengthening process according to the present invention). 3). The number of glass substrates held by the carrier was 50 (25 × 2 rows). However, in FIG. 13B, only the heater 51 is left, and the plurality of heaters 52 to 54 disposed around the processing liquid tank 50 are omitted. In addition, in the circular hole at the center of the glass substrate 80, not the heater 55 but a stirring rod having no heating function was disposed. The rotation speed of the stirring rod was 60 rpm.

  In Examples 4 and 8, the chemical strengthening treatment was performed as described with reference to FIGS. 13A, 13B, 13C, and 13D (a specific method of the chemical strengthening treatment according to the present invention). Combination of 2 and 3). The number of glass substrates held by the carrier was 50 (25 × 2 rows). However, in FIG.13 (b), all the heaters 51-55 were used. The heater 55 was rotated like a stirring rod. The rotation speed was 60 rpm.

[10. Second polishing step]
Only the comparative example 2 and Examples 5-8 performed the 2nd polishing process. That is, both surfaces of the glass substrate were polished more precisely using a double-side polishing machine (manufactured by HAMAI). As polishing conditions, the polishing pad is made of urethane foam having a hardness of Asker-C and 70 degrees, and the polishing liquid is made by dispersing colloidal silica having an average particle diameter of 60 nm in water as abrasive grains (polishing material). A slurry was used, and the mixing ratio of water and abrasive grains was 2: 8. The weight was 90 g / cm ² (8.83 kPa), the rotation speed of the upper surface plate was 20 rpm, and the rotation speed of the lower surface plate was 30 rpm.

  The polishing amount in the first polishing step (Comparative Example 1, Examples 1 to 4) or the total polishing amount in the first and second polishing steps (Comparative Example 2 and Examples 5 to 8) are both 30 μm. did. As a result, the final glass substrate thickness was 0.8 mm.

[11. Cleaning process]
The glass substrate was scrubbed. A nonionic surfactant is used to increase the cleaning ability by diluting a mixture of potassium hydroxide (KOH) and sodium hydroxide (NaOH) at a mass ratio of 1: 1 as ultra-pure water (DI water). The liquid obtained by adding the agent was used. The cleaning liquid was supplied by spraying. After scrub cleaning, in order to remove the cleaning liquid remaining on the surface of the glass substrate, a water rinse cleaning process is performed in an ultrasonic bath for 2 minutes, an IPA cleaning process is performed in an ultrasonic bath for 2 minutes, and finally the glass substrate is cleaned with IPA vapor. The surface of was dried.

<Manufacture of HDD magnetic recording media>
A magnetic film (recording layer) was provided on the main surface of the obtained glass substrate to obtain a magnetic recording medium (vertical recording format). That is, from the glass substrate side, a base layer made of Ni—Al (thickness of about 100 nm), a recording layer made of Co—Cr—Pt (thickness 20 nm), and a protective layer made of DLC (Diamond Like Carbon) (thickness 5 nm) are sequentially formed. Laminated. 100 magnetic recording media were manufactured for each of Comparative Examples 1 and 2 and Examples 1 to 8.

<Evaluation of HDD magnetic recording media>
The head flying characteristics of the produced magnetic recording medium were evaluated. That is, the magnetic recording medium is rotated at 7000 rpm, and the magnetic head of the DFH head mechanism is used for this recording medium, and the number of follow-up failures of the magnetic head to the surface of the recording medium (total recording area per recording medium) Recorded and evaluated according to the following criteria. It is determined that head crashes and read / write errors are more likely to occur as the number of follow-up failures increases. The results are shown in Table 1.

(Evaluation criteria)
◎◎: The number of follow-up defects is 0 (perfect quality product)
◎: Number of follow-up failures is 1 (excellent product)
○: Number of follow-up failures is 2 to 4 (good product)
Δ: Number of follow-up failures is 5 to 9 (there is a variation in quality, but it cannot be used)
×: Number of follow-up defects is 10 or more (defective product)

  Table 1 shows the TIR in the circumferential direction of the glass substrate before the chemical strengthening step, the increase in the TIR in the circumferential direction of the glass substrate before and after the chemical strengthening step, the TIR in the circumferential direction of the glass substrate after the chemical strengthening step, and The TIR in the circumferential direction of the final glass substrate (the glass substrate after the chemical strengthening process in Comparative Example 1 and Examples 1 to 4 and the glass substrate after the second polishing process in Comparative Examples 2 and Examples 5 to 8) is also included. Indicated. These TIR values are the TIR values in the circumferential direction at a position of 0.75R from the center of the glass substrate, where R is the radius of the glass substrate.

<Consideration of results>
In Comparative Examples 1 and 2 where the conventional chemical strengthening treatment was performed, the increase in TIR in the circumferential direction of the glass substrate before and after the chemical strengthening process exceeded 0.5 μm (0.7 μm), and the head flying characteristics were inferior. It was.

  In Examples 1 and 5 in which the specific method 1 of the chemical strengthening treatment according to the present invention was performed, the increase in TIR in the circumferential direction of the glass substrate before and after the chemical strengthening step was 0.3 μm or less (0.3 μm). ), The head flying characteristics were more excellent.

  In Examples 2 and 6 in which the specific method 2 of the chemical strengthening treatment according to the present invention was performed, the increase in TIR in the circumferential direction of the glass substrate before and after the chemical strengthening step was 0.3 μm or less (0.3 μm). ), The head flying characteristics were more excellent.

  In Examples 3 and 7 in which the specific method 3 of the chemical strengthening treatment according to the present invention was performed, the amount of increase in TIR in the circumferential direction of the glass substrate before and after the chemical strengthening step was 0.5 μm or less (0.5 μm). ) Excellent head flying characteristics.

  In Examples 4 and 8 in which the specific methods 2 and 3 of the chemical strengthening treatment according to the present invention were performed simultaneously, the increase in TIR in the circumferential direction of the glass substrate before and after the chemical strengthening step was 0.3 μm or less. (0.2 μm), which is more excellent in the head flying characteristics.

  When Examples 5 to 8 in which the second polishing process was performed after the chemical strengthening process were compared with Examples 1 to 4 in which the second polishing process was not performed, Examples 5 to 8 had a TIR in the circumferential direction of the final glass substrate. It was even smaller and more excellent in head flying characteristics.

  This application is based on Japanese Patent Application No. 2011-146229 filed on June 30, 2011, the contents of which are included in the present application.

  In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized as gaining. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not limited to the scope of the claims. To be construed as inclusive.

  The present invention has wide industrial applicability in the technical fields of a method for manufacturing a glass substrate for HDD, a glass substrate for HDD, and a magnetic recording medium for HDD.

Claims (7)

A method for producing a glass substrate for HDD, comprising a chemical strengthening step of chemically strengthening a glass substrate by immersing the glass substrate in a chemical strengthening treatment liquid,
The manufacturing method of the glass substrate for HDD characterized by making the increase amount of TIR of the circumferential direction of the glass substrate before and behind a chemical strengthening process into 0.5 micrometer or less.   The method for producing a glass substrate for HDD according to claim 1, wherein an increase in TIR in the circumferential direction of the glass substrate before and after the chemical strengthening step is 0.3 μm or less.   2. The increase in TIR is set to 0.5 μm or less by changing the posture of the glass substrate immersed in the chemical strengthening treatment solution in the chemical strengthening treatment solution in the chemical strengthening step. Manufacturing method of glass substrate for HDD.   2. The method of manufacturing a glass substrate for HDD according to claim 1, wherein in the chemical strengthening step, the amount of increase in TIR is set to 0.5 μm or less by uniformizing the temperature distribution of the chemical strengthening treatment liquid.   The method for producing a glass substrate for HDD according to claim 1, wherein in the chemical strengthening step, the amount of increase in TIR is set to 0.5 μm or less by stirring the chemical strengthening treatment liquid.   The method for producing a glass substrate for HDD according to any one of claims 1 to 5, further comprising a polishing step for polishing the surface of the glass substrate after the chemical strengthening step. 7. The TIR in the circumferential direction of the glass substrate is a TIR in the circumferential direction at a position of 0.75R from the center of the glass substrate, where R is the radius of the glass substrate. The manufacturing method of the glass substrate for HDD of Claim 1.

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