JP2015076115A - Disk-shaped glass substrate for magnetic recording medium, and manufacturing method of disk-shaped glass substrate for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a disk-shaped glass substrate which can improve productivity, and cut out a disk-shaped glass substrate without contacting a wall surface of a cut groove when the disk-shaped glass substrate is cut out from a glass blank.SOLUTION: A manufacturing method of a disk-shaped glass substrate for magnetic recording medium includes: a cutting out step of cutting out a disk-shaped glass substrate from a glass blank; a polishing step of polishing a principal surface of the disk-shaped glass substrate; and a cleaning step of cleaning a surface of the disk-shaped glass substrate. The cutting out step irradiates the surface of the glass blank along a circular outline including a region for forming the disk-shaped glass substrate with a pulse laser beam having a pulse width of one femtosecond or more and less than one nanosecond to thereby process the glass blank, forms a cut groove having a groove width of 10 μm or more along the outline, and cuts out from the glass blank the disk-shaped glass substrate that is cut at the cut groove.

Description

  The present invention relates to a disk-shaped glass substrate for a magnetic recording medium and a method for producing a disk-shaped glass substrate for a magnetic recording medium.

  For example, in the method of manufacturing a disk-shaped glass substrate for magnetic recording media, (1) extraction step, (2) shape processing step (chamfering step), (3) lapping step, (4) end surface polishing step, (5) There is a manufacturing method in which the main surface polishing step, (6) chemical strengthening step, and (7) magnetic layer forming step are sequentially performed (see, for example, Patent Document 1).

Here, each said process is demonstrated.
(1) In the extraction step, a square glass base plate corresponding to the size of the disk-shaped glass substrate is prepared (cut) in advance, and the contour of the disk-shaped glass substrate is obtained using a glass cutter on the plane of each glass base plate. A circular cut line (scribe) is formed. Furthermore, the disc-shaped glass substrate can be extracted by the cut line progressing in the thickness direction due to the temperature difference between heating and cooling. And when processing a cut line, the draft is formed by inclining a cut line outside with respect to a plate | board thickness direction. One glass substrate is extracted from one glass base plate.
(2) In the shape processing step, the outer peripheral end surface and the inner peripheral end surface of the cut disc-shaped glass substrate are ground with a rotating grindstone, and the outer peripheral end surface and the inner peripheral end surface are chamfered.
(3) In the lapping step, the main surface of the disk-shaped glass substrate is lapped by a double-sided lapping device, and then immersed in a cleaning layer of water and a cleaning layer, and ultrasonic cleaning is performed.
(4) In the end surface polishing step, the end surface (inner periphery, outer periphery) is polished while rotating the disk-shaped glass substrate, and the disk-shaped glass substrate is washed after polishing.
(5) In the main surface polishing step, the main surface of the disk-shaped glass substrate is rotated by a polishing pad that is rotated while supplying a polishing liquid to the main surface of the rotating disk-shaped glass substrate in order to remove scratches and distortion remaining in the lapping step. To polish. Thereafter, the disk-shaped glass substrate is dipped in each of the cleaning baths of neutral detergent, pure water and steam drying, and then ultrasonically cleaned and dried.
(6) In the chemical strengthening step, the disc-shaped glass substrate is immersed in a chemical strengthening solution (mixed solution of potassium nitrate and sodium nitrate) to perform chemical strengthening treatment. Thereafter, the disk-shaped glass substrate is dipped in each of the cleaning baths of neutral detergent, pure water and steam drying, and then ultrasonically cleaned and dried.
(7) In the magnetic layer forming step, a magnetic film is formed on the main plane of the disk-shaped glass substrate.

JP 2006-99857 A

  However, in the extraction process of the above manufacturing method, when the disk-shaped glass substrate is extracted from the glass base plate even when the cutting groove is provided with a draft, the groove width of the cutting groove is almost zero and too small. It was difficult to prevent chipping and chipping due to contact between the cut surfaces.

  In the shape processing step, when the end face of the disk-shaped glass is processed, a draft is formed on the end face, so that the load is not uniform on the rotating grindstone, and the chamfered surface and the side wall surface are ground. The burden increases.

  In addition, when the end face and chamfering of a disk-shaped glass substrate are performed using a rotating grindstone, processing cracks due to grinding occur on the end surface and the chamfered surface of the disk-shaped glass substrate. May not be removed, and processing cracks may remain. In this case, there is a risk of chipping or cracking due to a processing crack (processing alteration layer) remaining during handling or processing of the disk-shaped glass substrate.

  Further, in the process of manufacturing a magnetic recording medium by forming a thin film such as a magnetic layer on the main plane of the disk-shaped glass substrate, when the disk-shaped glass substrate for the magnetic recording medium is heated and cooled, the end surface or the chamfered surface is formed. The remaining cracks (work-affected layer) may extend to cause problems such as chipping and cracking of the disk-shaped glass substrate for magnetic recording media.

  In view of the above circumstances, an object of the present invention is to provide a disk-shaped glass substrate for a magnetic recording medium and a method for manufacturing the disk-shaped glass substrate for a magnetic recording medium, which have solved the above problems.

In one proposal, a magnetic process having an extraction process for extracting a disk-shaped glass substrate from a glass base plate, a polishing process for polishing a main plane of the disk-shaped glass substrate, and a cleaning process for cleaning the surface of the disk-shaped glass substrate. A method for producing a disk-shaped glass substrate for a recording medium,
In the extracting step, the surface of the glass base plate is irradiated with a pulsed laser beam having a pulse width of 1 femtosecond or more and less than 1 nanosecond along a circular outline including a region where the disk-shaped glass substrate is formed. Manufacturing a disk-shaped glass substrate for a magnetic recording medium by processing, forming a cutting groove having a groove width of 10 μm or more along the contour, and extracting the disk-shaped glass substrate cut by the cutting groove from the glass base plate A method is provided.

  According to one aspect, a pulse width of 1 femtosecond or more and less than 1 nanosecond is irradiated and processed along a circular contour including a region for forming a disk-shaped glass substrate, and a groove width of 10 μm or more is formed. Since the cutting groove having the contour is formed along the contour, it becomes possible to extract the disk-shaped glass substrate without providing a draft in the cutting groove, and the contact between the cut surfaces is avoided in the extraction process, chipping, chipping Occurrence is suppressed. In addition, since it can be processed without grinding with a grindstone, large chipping does not occur due to grindstone processing, chipping does not remain on the end face or chamfered surface after grinding, and the disk-like glass substrate for magnetic recording media is chipped or cracked It is possible to suppress problems that occur. Furthermore, by shifting the irradiation position of the pulse laser beam for each disk-shaped glass substrate, it is possible to increase the number of disk-shaped glass substrates extracted per glass base plate and increase the production efficiency.

It is a perspective view which shows schematic structure of the laser processing machine which processes the disk shaped glass substrate for magnetic recording media by this invention. It is a side view which shows typically the structure of a laser generation part. It is a figure which shows the laser filament-ized scribing arrangement | positioning for cut | disconnecting a transparent material. It is a figure which illustrates the shape of the disk shaped glass substrate extracted by the pulse laser beam. It is a block diagram which shows the control system of a laser beam machine. It is a figure which shows each process of the manufacturing method of the disk shaped glass substrate for magnetic recording media. It is a figure which shows the procedure of the laser processing in an extraction process.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

[Configuration of laser processing machine]
FIG. 1 is a perspective view showing a schematic configuration of a laser beam machine for processing a disk-shaped glass substrate for a magnetic recording medium according to the present invention. As shown in FIG. 1, the laser processing machine 10 includes an XY table 30 on which a glass base plate 20 is loaded, a laser generator 40 that irradiates the surface (upper surface) of the glass base plate 20 with laser light, And a control unit 50.

  The glass base plate 20 is a glass material formed into a plate shape by, for example, a float method, a fusion method, a downdraw method, a redraw method, a press molding method, and the like, and is placed on the placement surface of the XY table 30 in advance. It is cut into possible sizes (X and Y dimensions). Moreover, since the glass base plate 20 has an area sufficiently larger than the diameter of the disk-shaped glass substrate 100 to be extracted, several tens of disk-shaped glass substrates 100 can be obtained.

  The XY table 30 includes a stage device that moves in a horizontal direction (X direction, Y direction), and a placement surface 32 on which the glass base plate 20 is placed is formed on the upper surface. A plurality of suction holes 34 (see FIG. 2) for vacuum-sucking the glass base plate 20 are arranged in the X and Y directions at predetermined intervals on the placement surface 32 of the XY table 30. Therefore, the glass base plate 20 is held in close contact with the placement surface of the XY table 30, and misalignment during laser processing is prevented.

The laser generator 40 is a laser that generates pulsed laser light PL made of, for example, a gas laser (eg, excimer laser) or a solid laser (eg, YAG laser, YVO ₄ laser, YLF laser, fiber laser, etc.). An oscillator 42 and an optical unit 44 are included. The optical unit 44 reflects the pulse laser light PL generated by the laser oscillator 42 to change the laser irradiation direction, and the pulse laser light PL from the reflection mirror 46 is the surface (upper surface) of the glass base plate 20. And a condensing lens 47 for condensing the light.

  The laser generator 40 is provided so as to be movable in the horizontal direction (X direction, Y direction), and has a circular shape corresponding to the inner and outer contours of the disk-shaped glass substrate 100 extracted from the glass base plate 20. It moves so as to form a cutting groove.

  The control unit 50 includes a computer that executes a control program inputted in advance, and relatively displaces the XY table 30 and the laser generation unit 40 to form a plurality of disk-shaped glass substrates 100 from a single glass base plate 20. Performs cutting control. Further, the control unit 50 adjusts the duty (%) with respect to one pulse time so that the pulse width of the pulsed laser light PL emitted from the laser generation unit 40 is an extremely short pulse (1 femtosecond (fs) or more, 1 nanometer). Second (ns)). The wavelength of the pulse laser beam PL is a wavelength including ultraviolet rays, visible light, and near infrared rays, and is set, for example, in the range of 1400 nm to 380 nm, preferably 1000 nm or less, preferably 450 nm or more. Is set.

  As a result, the laser generator 40 irradiates the glass base plate 20 with the pulsed laser light PL having an extremely short pulse width corresponding to a preset duty (%), and the light at the location where the pulsed laser light PL is irradiated. Processing can be performed with an increased energy absorption rate. In the present embodiment, the type of the pulse laser beam generated from the laser generator 40 is not limited to a specific laser beam, but a pulse laser beam having a pulse width that can be processed may be obtained.

Here, processing according to the type of pulsed laser light will be described. For example, in the case of an infrared laser, a near-infrared laser, a visible light laser (CO ₂ laser, excimer laser, YAG (Yttrium Aluminum Garnet) laser, YVO ₄ (Yttrium Ortho Vanadate single crystal) laser, YLF laser, fiber laser), pulse laser light If PL is a pulse with a short pulse width (for example, less than 1 nanosecond (ns)), processing involving melting, evaporation, and scattering can be performed on the glass base plate 20 that has absorbed laser light energy.

  In the case of an ultraviolet laser (harmonic laser, excimer laser), the absorption rate of light energy per pulse increases in the glass base plate 20 that absorbs laser light as the wavelength of the laser light becomes shorter. Less processing is done efficiently.

  In addition, when the pulse laser beam PL is an extremely short pulse laser beam having a pulse width of 1 femtosecond (fs) to 1 picosecond (ps), the glass base plate 20 is a material having a low light energy absorption rate per pulse. However, non-linear absorption due to the multiphoton process is caused, and processing with less thermal damage than the ultraviolet laser can be performed.

  Since the glass base plate 20 has a sufficiently large dimension with respect to the outer diameter (area) of the disk-shaped glass substrate 100, for example, 250 to 300 disk-shaped glass substrates 100 per sheet are obtained.

  Further, when the plurality of disc-shaped glass substrates 100 are cut by irradiating the glass base plate 20 with the pulsed laser light PL, the cutting positions of the disc-shaped glass substrates 100 in each row are ½ pitch in the X direction ( The circular cutting grooves are sequentially processed by shifting by 1 pitch = the distance between the centers of the adjacent disk-shaped glass substrates 100). Thereby, each disk-shaped glass substrate 100 can make the distance between the outer circumferences as small as possible. That is, it can arrange | position in the state (for example, staggered lattice state) where the cutting position of each disk-shaped glass substrate 100 was made to approach for every adjacent row | line | column, and the disk-shaped glass substrate 100 obtained from the glass base plate 20 can be arrange | positioned. It becomes possible to increase the number of production.

  FIG. 2 is a side view schematically showing the configuration of the laser generator. As shown in FIG. 2, in addition to the laser oscillator 42 and the optical unit 44 described above, the laser generator 40 rotates the optical unit 44 and the optical system moving table 60 that moves the optical unit 44 in the X and Y directions. And a support mechanism 70 for supporting the movement. The optical system moving table 60 includes the laser oscillator 42 and the optical unit 44 so that the processing position (pulse laser light irradiation coordinate position) irradiated with the pulse laser light PL from the optical unit 44 traces the outline of the disk-shaped glass substrate 100. Turn. The support mechanism 70 is connected to the optical system moving table 60 at a connecting portion 45 provided on the upper portion of the optical unit 44. The optical unit 44 includes an optical unit driving unit (see FIG. 3) that changes the irradiation angle of the pulsed laser light PL, and the angle with respect to the surface (upper surface) of the glass base plate 20 is set to the processing position (for example, the inclination of the chamfered surface). Change according to the angle.

  Further, each suction hole 34 provided in the XY table 30 has an upper end opened to the placement surface 32 and a lower end connected to a suction pipe 82 from the vacuum pump 80. Therefore, in the laser processing step, a negative pressure by the vacuum pump 80 is introduced into each suction hole 34, and the glass base plate 20 placed on the placement surface 32 is held in a horizontal state. In addition, an electromagnetic valve may be provided in each suction pipe 82 communicated with each suction hole 34 so that a region where laser processing is performed is partially sucked.

  Here, processing by irradiation with the pulse laser beam PL will be described. In the present embodiment, the processing by irradiation with the pulsed laser beam PL means laser processing including ablation processing and filament processing.

  That is, as a method of processing by irradiating the glass base plate 20 with the pulsed laser light PL, the portion that absorbed the laser light is removed by instantaneously melting, evaporating, and scattering while suppressing the influence of heat around the processing portion as much as possible. There is a method using ablation processing to process. As another processing method, there is a method using filament processing in which a pulsed laser beam PL is irradiated onto the glass base plate 20 to form a filament in the thickness direction (processing region) of the glass base plate 20. .

  FIGS. 3A and 3B are diagrams schematically showing a laser filament scribing arrangement for scribing a transparent material, where FIG. 3A is a front view and FIG. 3B is a side view. As shown in FIGS. 3A and 3B, the pulse laser beam PL having a short duration is converged inside the glass base plate 20 by the condenser lens 47. With an appropriate laser pulse energy, laser pulse, or sequence of pulses, or burst train of pulses, a laser filament 21 is generated in the glass blank 20 and has an internal microstructure having a shape defined by the volume of the laser filament 21. The denaturation of is created. By moving the glass base plate 20 relative to the laser beam during pulsed laser exposure, the filament track 23 is defined by a curved or linear path followed by the pulsed laser light PL in the glass base plate 20. A continuous trace of is permanently engraved in the processing area of the glass.

  The laser filament 21 can self-converge due to the nonlinear Kerr effect, and it is considered that the laser filament 21 is produced by a laser beam with low convergence and high intensity and short duration.

  The formation process of the laser filament 21 is considered to depend mainly on two processes. First, the spatial intensity profile of the pulsed laser light PL acts like a converging lens due to the nonlinear optical Kerr effect. This causes beam self-convergence, resulting in an increase in peak intensity.

  Also, in the high peak intensity region, multi-photon ionization, field ionization, and electron impact ionization of the medium begin to create a low density plasma in the high intensity portion of the laser beam. This plasma temporarily lowers the refractive index at the center of the beam path, causing the beam to diverge and break the filament. Then, due to the dynamic balance between the Kerr effect self-focusing and plasma divergence described above, a stable filament, sometimes called a plasma channel, is formed, and a filament is formed by the interaction of multiple refocused lasers. it is conceivable that.

Thus, it is considered that a filament is formed by balancing the two effects of self-convergence due to the Kerr effect and divergence due to plasma generation, and the strength of the filament is 10 ¹³ to 10 ¹⁴ W / cm ² . As the laser intensity increases, the number of filaments increases.

  The length and position of the laser filament 21 are the lens convergence position, the numerical aperture of the condenser lens 47, the laser pulse energy, the wavelength, the duration and the number of repetitions, the number of laser pulses applied to form each filament track 23, In addition, it is easily controlled by the optical properties and thermal / physical properties of the transparent medium. Since the exposure conditions of these pulsed laser beams PL extend over almost the entire thickness (Z direction) of the glass base plate 20 and finish without entering the upper surface or the lower surface, a sufficiently long and strong filament can be created. Accordingly, the laser beam is emitted from the lower surface of the glass base plate 20 at a divergence angle 24 so that the laser filament 21 is terminated by the beam convergence inside the glass base plate 20 and damage on the lower surface of the glass base plate 20 is avoided. Is done.

[Shape of disk-shaped glass substrate]
FIG. 4 is a diagram illustrating the shape of a disk-shaped glass substrate extracted by pulsed laser light. As shown in FIG. 4, the disk-shaped glass substrate 100 has an inner peripheral end surface 103 and an outer peripheral end surface 105 cut into a circular shape by irradiation with pulsed laser light PL, and is extracted from the glass base plate 20. In addition, after the inner peripheral end surface 103 and the outer peripheral end surface 105 are cut, the inner peripheral chamfered surfaces 102a and 102b and the outer peripheral chamfered surfaces 104a and 104b are chamfered by inclining the irradiation angle of the pulse laser beam PL.

  Then, the disk-shaped glass substrate 100 extracted from the glass base plate 20 is lapped on the main plane 101 by a double-sided lapping machine, and further, the main plane 101 is polished by a polishing pad that rotates with the supply of the polishing liquid. The glass substrate for magnetic recording medium is cleaned.

  The disk-shaped glass substrate 100 is a disk-shaped glass substrate for a magnetic recording medium used as a base material of a magnetic recording medium. For example, (1) for a magnetic recording medium having an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.635 mm. Disc-shaped glass substrate, (2) Disc-shaped glass substrate for magnetic recording medium having outer diameter of 65 mm, inner diameter of 20 mm and plate thickness of 0.8 mm, (3) For magnetic recording medium of outer diameter of 95 mm, inner diameter of 25 mm, plate thickness of 1.27 mm Disc-shaped glass substrate, (4) Disc-shaped glass substrate for magnetic recording medium having an outer diameter of 95 mm, inner diameter of 25 mm, and plate thickness of 1 mm, (5) Disc-shaped for magnetic recording medium having an outer diameter of 95 mm, inner diameter of 25 mm, and plate thickness of 0.8 mm Processing is performed to obtain any glass substrate.

  The inner peripheral chamfered surfaces 102a and 102b and the outer peripheral chamfered surfaces 104a and 104b are chamfered so as to obtain a disk-shaped glass substrate for a magnetic recording medium having a chamfer width of 0.15 mm and a chamfer angle of 45 °, for example.

  The disk-shaped glass substrate for a magnetic recording medium may be amorphous glass, crystallized glass, or tempered glass (for example, chemically tempered glass) having a tempered layer on the surface layer of the glass substrate.

  FIG. 5 is a block diagram showing a control system of the laser beam machine. As shown in FIG. 5, the control unit 50 includes a laser oscillator control unit 120, a mirror control unit 130, a lens control unit 140, a laser irradiation angle control unit 150, an XY table control unit 160, and an optical unit. And a system movement table control unit 170.

  The laser oscillator control unit 120 outputs a control signal for controlling the laser oscillator 42 provided in the laser generation unit 40, for example, a pulse having a pulse width of 1 femtosecond (fs) or more and less than 1 nanosecond (ns). Laser light PL is generated from a laser oscillator 42. The pulsed laser light PL emitted from the laser oscillator 42 is reflected by the reflection mirror 46 of the optical unit 44 and is collected by the condenser lens 47 at a predetermined cutting position on the surface (upper surface) of the glass base plate 20.

  The mirror control unit 130 outputs a control signal for controlling the mirror driving unit 210 that drives the reflection mirror 46 of the optical unit 44, and for example, has a predetermined amplitude set in advance around the optical axis in the reflection direction of the pulse laser beam. The reflection mirror 46 is vibrated so as to reciprocate. Depending on the amplitude of the pulse laser beam PL, the processing width with respect to the surface of the glass base plate 20 is set to an arbitrary dimension (for example, 10 μm or more), and the groove width M of the cutting groove is set to a predetermined value (M = 10 μm or more). Is done.

  The lens control unit 140 outputs a control signal for driving the condensing lens driving unit 220 that moves the condensing lens 47 in the optical axis direction, and determines the focal position of the pulsed laser light PL on the surface (upper surface) of the glass base plate 20. Further, the condenser lens 47 is displaced in the thickness direction (Z direction) with the extension of processing. Therefore, the pulsed laser light Pl condensed from the condenser lens 47 onto the glass base plate 20 makes the focal point of the condenser lens 47 coincide with the surface (upper surface) of the glass base plate 20 and then focuses on the glass base plate 20. Is displaced below the surface of the steel plate, and the processing region is expanded downward (thickness direction).

  The laser irradiation angle control unit 150 outputs a control signal for controlling the optical unit driving unit 230 that rotates the optical unit 44, and controls the irradiation direction of the laser pulse light PL emitted from the optical unit 44. Therefore, when the optical unit 44 cuts the glass base plate 20 along the outline of the disk-shaped glass substrate 100, the optical unit 44 irradiates the laser pulse light PL in the drooping direction, and when chamfering, the glass base plate 20 It is inclined so as to have a predetermined chamfering angle with respect to the surface.

  The XY table control unit 160 outputs a control signal for controlling the XY table driving unit 240 that drives the XY table 30 in the horizontal direction (X direction, Y direction), and has a large area. The XY table 30 is moved in the horizontal direction (X direction, Y direction) in accordance with the extraction position of the disk-shaped glass substrate 100 with respect to 20.

  The optical system moving table control unit 170 outputs a control signal for controlling the optical system moving table driving unit 250 that drives the optical system moving table 60, and cuts the glass base plate 20 along the contour of the disk-shaped glass substrate 100. In this manner, the optical unit 44 is turned about the axis of the disk-shaped glass substrate 100 as the center of rotation.

[Method of manufacturing disk-shaped glass substrate for magnetic recording medium]
FIG. 6 is a diagram showing each step of the manufacturing method of the disk-shaped glass substrate.
[Glass base plate loading process]
A glass base plate 20 is prepared by cutting a glass plate formed into a plate shape by a float method, a press molding method, a redraw method, a fusion method or the like into a square shape (rectangular shape or square shape) having a predetermined length. The glass base plate 20 is loaded on the mounting surface 32 of the XY table 30 of the laser processing machine 10 (S11). The glass base plate 20 is sucked into the suction holes 34 by the negative pressure of the vacuum pump 80 connected to the XY table 30, is brought into close contact with the placement surface 32, and is held.

[Extraction process]
Next, the control unit 50 of the laser processing machine 10 irradiates the glass base plate 20 with the pulsed laser light PL to extract the disk-shaped glass substrate 100 (S12). In this extraction step, the XY table 30 is moved in the horizontal direction (X) so that the region (the region to be cut) where the glass base plate 20 is extracted by the optical system moving table control unit 170 faces the movable region of the optical unit 44. Direction, Y direction). Then, the laser oscillator controller 120 causes the laser oscillator 42 of the laser generator 40 to emit pulsed laser light PL.

  At the same time, the mirror control unit 130 drives the mirror driving unit 210 to repeatedly displace the angle of the reflection mirror 46 of the optical unit 44. Thereby, the irradiation position of the pulse laser beam PL vibrates (reciprocates) in the groove width direction of the cutting groove, and the surface (upper surface) of the glass base plate 20 has a groove width of 10 μm or more (the ablation process described above and the filament). Processing). Instead of displacing the reflection mirror 46, the angle of the condensing lens 47 is repeatedly displaced to vibrate the irradiation position of the pulse laser beam PL on the surface of the glass base plate 20 in the groove width direction of the cutting groove (reciprocating motion). )

  Further, the lens control unit 140 drives the condensing lens driving unit 220 to move the condensing lens 47 in the optical axis direction, and the focal point of the pulsed laser light PL is displaced in the thickness direction (downward) of the glass base plate 20. Let the process extend downward. In this way, the optical system moving table driving unit 250 is controlled by the optical system moving table control unit 170 while displacing the pulse laser beam PL in the groove width direction and the thickness direction. Thereby, the optical system moving table 60 is driven, and the optical unit 44 is turned about the axis of the disk-shaped glass substrate 100 as a rotation center. As a result, the surface (upper surface) of the glass base plate 20 is irradiated with the pulsed laser light PL along the contour of the disk-shaped glass substrate 100 to process a circular cutting groove. Then, the disk-shaped glass substrate 100 having concentric large-diameter and small-diameter circular cut surfaces is cut out.

  Further, a chamfering process for tilting the irradiation direction of the pulsed laser light PL is performed according to the procedure described later. In this extraction process, the disk-shaped glass substrate 100 is extracted from the glass base plate 20 by irradiation with the pulsed laser beam PL, and the chamfering process is also performed. Is possible. Therefore, the production efficiency of the disk-shaped glass substrate 100 can be improved by reducing the number of steps of the manufacturing method, and the variation in the quality of the ground disk-shaped glass substrate 100 due to variations in the grinding ability of the rotating grindstone (such as chipping and chipping). Generation of scratches). And since it can suppress that the chip | tip and damage | wound with a grindstone generate | occur | produce on the end surface and chamfering surface of the disk shaped glass substrate 100, the processing time of an end surface grinding | polishing process can be shortened.

[Lapping process]
The main plane 101 of the disk-shaped glass substrate 100 is lapped by a double-sided lapping device (S13).

[End face polishing process]
A large number of disk-shaped glass substrates 100 are laminated, and the end surfaces (outer peripheral end surface, inner peripheral end surface) of each disk-shaped glass substrate 100 are polished using a polishing brush and abrasive grains. After polishing, the disc-shaped glass substrate 100 is washed to remove the abrasive grains (S14).

[Main surface polishing process]
Next, the main surface 101 of the disk-shaped glass substrate 100 is polished by a polishing pad that rotates while supplying a polishing liquid to the main surface 101 of the disk-shaped glass substrate 100 by a double-side polishing apparatus, and scratches and distortions remaining in the lapping process are removed. Remove. Thereafter, the disk-shaped glass substrate 100 is washed to remove the polishing liquid and dried (S15). In the main surface polishing step, only primary polishing using the above-described method for polishing a glass substrate for a magnetic recording medium may be performed. However, further secondary polishing and further tertiary to fifth polishing may be performed.

[Washing process]
The cleaning step is a step of cleaning and drying the polished glass substrate (S16). A specific cleaning method is not particularly limited. For example, cleaning can be performed by scrub cleaning using a detergent, ultrasonic cleaning in a state immersed in a detergent solution, ultrasonic cleaning in a state immersed in pure water, or the like. Also, the drying method is not particularly limited, and for example, drying is performed with isopropyl alcohol vapor.

  Further, glass substrate cleaning (inter-process cleaning) and glass substrate surface etching (inter-process etching) may be performed between the above steps. For example, the inter-process etching is performed by immersing the disc-shaped glass substrate 100 in an acidic solution (hydrofluoric acid, a mixed solution of hydrofluoric acid and sulfuric acid, or the like). When high mechanical strength is required for the glass substrate, a strengthening step (for example, a chemical strengthening step) for forming a reinforcing layer on the surface layer of the glass substrate is performed before the polishing step, after the polishing step, or between the polishing steps. May be.

  The glass substrate obtained by the manufacturing method including the above steps is further subjected to a magnetic layer forming step for forming a thin film such as a magnetic layer on the glass substrate to obtain a magnetic recording medium.

[About the procedure of extraction process]
FIG. 7 is a diagram showing a laser processing procedure in the extraction process.

  [Procedure 1] As shown in FIG. 7A, the pulse laser beam PL emitted from the laser oscillator 42 of the laser generator 40 is reflected on the surface (upper surface) of the glass base plate 20 through the condenser lens 47. The light is condensed at a predetermined position on the peripheral side (a position corresponding to the contour along the inner peripheral end surface 103 of the disk-shaped glass substrate 100 to be extracted). At this time, the pulse laser beam PL is focused on the cut portion of the surface of the glass base plate 20 and is processed (including the ablation processing and filament processing described above). Further, the pulse laser beam PL is vibrated (reciprocated) in the width direction of the cutting portion (cutting groove) to make the groove width 10 μm or more. Further, the pulse width of the pulsed laser light PL is an ultrashort pulsed laser light of 1 femtosecond (fs) or more and less than 1 nanosecond (ns). The pulse width is preferably 100 ps or less, more preferably 10 ps or less, and particularly preferably 1 ps or less. The pulse width is preferably 10 fs or more, more preferably 100 fs or more, and particularly preferably 200 fs or more.

  Further, the wavelength of the pulse laser beam PL is a wavelength including ultraviolet light, visible light, and near infrared light. For example, a wavelength in the range of 1400 nm to 380 nm is used. The wavelength of the pulse laser beam PL is preferably 1000 nm or less. Further, the wavelength of the pulse laser beam PL is preferably 450 nm or more. Further, the frequency of the pulse laser beam PL is preferably 0.1 MHz to 100 MHz.

  [Procedure 2] As shown in FIG. 7B, the optical system moving table 60 is driven by the optical system moving table driving unit 250, so that the optical unit 44 (reflection mirror 46, condensing lens 47) is a disc-shaped glass substrate. The center axis of the 100 inner periphery is turned. The turning speed at this time is calculated from the relationship between the thickness of the glass base plate 20 and the extension speed of the processing region AK.

  When the irradiation position of the pulse laser beam PL makes one round, the machining area AK at the machining start point and the ablation area AK at the machining end point are connected to form a circular cutting groove corresponding to the inner peripheral end face 103. Further, the processing region AK penetrates linearly in the thickness direction (Z direction) of the glass base plate 20, and an inclined surface like a draft is not generated. Then, by setting the groove width M of the cut groove by processing to M = 10 μm or more, the inner peripheral end surface 103 of the disk-shaped glass substrate 100 cut from the glass base plate 20 is extracted without contacting the wall surface of the cut groove. Is possible. Thereby, at the time of extraction, it is possible to suppress the occurrence of scratches and chipping on the inner peripheral end surface 103 of the disc-shaped glass substrate 100, and at the time of handling and processing the disc-shaped glass substrate, and the magnetic layer on the main plane of the disc-shaped glass substrate In the process of manufacturing a magnetic recording medium by forming a thin film such as the above, it is possible to prevent the disk-shaped glass substrate for magnetic recording medium from being chipped or cracked. Therefore, crack extension does not occur during handling by the robot hand during thin film formation, and productivity is improved.

  In order to sufficiently suppress the occurrence of scratches and chipping on the end face of the disk-shaped glass substrate 100 when the disk-shaped glass substrate 100 is extracted, the groove width M is preferably 10 μm or more, preferably 50 μm or more, and more preferably 75 μm or more. The thickness is preferably 100 μm or more.

  [Procedure 3] As shown in FIG. 7C, the circular portion 22 on the inner peripheral side is extracted after the irradiation position of the pulse laser beam PL has made one round. The circular portion 22 may be taken out by suction by vacuuming, for example, or a robot hand having an elongated claw at the tip may be used.

  [Procedure 4] As shown in FIG. 7D, the irradiation direction of the pulse laser beam PL is adjusted to the chamfering direction of the upper peripheral corner of the inner peripheral side of the disc-shaped glass substrate 100. That is, the optical unit 44 is tilted by a predetermined angle with respect to the central axis of the disc-shaped glass substrate 100 by the optical unit driving unit 230 and is processed by irradiating the inner peripheral side upper end corner of the disc-shaped glass substrate 100 with the pulsed laser light PL. . In this state, the optical system moving table 60 is driven to rotate the optical unit 44 (the reflection mirror 46 and the condensing lens 47) about the axis of the inner periphery of the disk-shaped glass substrate as the central axis. Thereby, the chamfering process can be performed on the inner peripheral side upper end corner of the disc-shaped glass substrate 100. Therefore, the inner peripheral chamfered surface 102a shown in FIG. 4 is chamfered.

  [Procedure 5] As shown in FIG. 7E, the irradiation direction of the pulsed laser light PL is adjusted to the chamfering direction of the inner peripheral lower end corner of the disc-shaped glass substrate 100. That is, the pulse laser beam PL is irradiated on the inner peripheral lower end corner of the disk-shaped glass substrate 100. In this state, the optical system moving table 60 is driven to rotate the optical unit 44 (the reflection mirror 46 and the condensing lens 47) about the center of the inner periphery of the disc-shaped glass substrate 100 as a central axis. Thereby, the chamfering process for the inner peripheral side lower end corner of the disc-shaped glass substrate 100 can be performed. Therefore, the inner peripheral chamfered surface 102b shown in FIG. 4 is chamfered.

  [Procedure 6] As shown in FIG. 7F, the pulse laser beam PL corresponds to a predetermined position on the outer peripheral side of the surface of the glass base plate 20 (corresponding to the contour along the outer peripheral end surface 105 of the disk-shaped glass substrate 100 to be extracted. Condensing at position). At this time, the pulse laser beam PL is focused on the cut portion of the surface (upper surface) of the glass base plate 20, and the cut portion is processed. Further, the pulse laser beam PL is vibrated (reciprocated) in the width direction of the cutting portion (cutting groove) to set the groove width M to M = 10 μm or more. Further, the pulse width of the pulse laser beam PL is an ultrashort pulse laser beam of 1 femtosecond (fs) or more and less than 1 nanosecond (ns), as in the above-described inner peripheral end face machining. The pulse width is preferably 100 ps or less, more preferably 10 ps or less, and particularly preferably 1 ps or less. The pulse width is preferably 10 fs or more, more preferably 100 fs or more, and particularly preferably 200 fs or more.

  Further, the wavelength of the pulse laser beam PL is a wavelength including ultraviolet light, visible light, and near infrared light. For example, a wavelength in the range of 1400 nm to 380 nm is used. The wavelength of the pulse laser beam PL is preferably 1000 nm or less. Further, the wavelength of the pulse laser beam PL is preferably 450 nm or more. Further, the frequency of the pulse laser beam PL is preferably 0.1 MHz to 100 MHz.

  Then, the optical system moving table 60 is driven to rotate the optical unit 44 (the reflection mirror 46 and the condensing lens 47) about the center of the inner periphery of the disk-shaped glass substrate 100 as a central axis. The turning speed at this time is calculated from the relationship between the thickness of the glass base plate 20 and the extension speed of the processing region AK.

  When the irradiation position of the pulse laser beam PL goes around, the machining area AK at the machining start point and the ablation area AK at the machining end point are connected to form a circular cutting groove corresponding to the outer peripheral end face 105. In addition, the processing area AK corresponding to the outer peripheral end face 105 penetrates linearly in the thickness direction of the glass base plate 20, and an inclined surface like a draft is not generated. Then, by setting the groove width M of the cut groove by processing to M = 10 μm or more, the outer peripheral end surface 105 of the disc-shaped glass substrate 100 cut from the glass base plate 20 can be extracted without contacting the wall surface of the cut groove. It becomes possible. Thereby, at the time of extraction, it is possible to suppress the occurrence of scratches and chipping on the inner peripheral end surface 103 of the disc-shaped glass substrate 100, and at the time of handling and processing the disc-shaped glass substrate, and the magnetic layer on the main plane of the disc-shaped glass substrate In the process of manufacturing a magnetic recording medium by forming a thin film such as the above, it is possible to prevent the disk-shaped glass substrate for magnetic recording medium from being chipped or cracked. Therefore, crack extension does not occur during handling by the robot hand during thin film formation, and productivity is improved.

  [Procedure 7] As shown in FIG. 7G, the irradiation direction of the pulsed laser light PL is adjusted to the chamfering direction of the upper corner of the outer peripheral side of the disc-shaped glass substrate 100. That is, the optical unit drive unit 230 tilts the optical unit 44 by a predetermined angle with respect to the central axis of the disc-shaped glass substrate 100 and irradiates the upper end corner portion on the outer periphery side of the disc-shaped glass substrate with the pulsed laser light PL. In this state, the optical system moving table 60 is driven to rotate the optical unit 44 (the reflection mirror 46 and the condensing lens 47) about the axis of the inner periphery of the disc-shaped glass substrate 100 as a central axis. Thereby, the chamfering process with respect to the outer peripheral side upper end corner | angular part of a disk shaped glass substrate can be performed. Therefore, the outer peripheral chamfered surface 104a shown in FIG. 4 is chamfered.

  [Procedure 8] As shown in FIG. 7H, the irradiation direction of the pulsed laser light PL is adjusted to the chamfering direction of the lower peripheral corner of the outer peripheral side of the disc-shaped glass substrate 100. That is, processing is performed by irradiating the lower end corner of the outer peripheral side of the disc-shaped glass substrate 100 with the pulsed laser light PL. In this state, the optical system moving table 60 is driven to rotate the optical unit 44 (the reflection mirror 46 and the condensing lens 47) about the center of the inner periphery of the disc-shaped glass substrate 100 as a central axis. Thereby, the chamfering process to the outer peripheral side lower end corner of the disc-shaped glass substrate 100 can be performed. Therefore, the outer peripheral chamfered surface 104b shown in FIG. 4 is chamfered.

  Thus, by controlling the irradiation direction of the pulse laser beam PL, the disk-shaped glass substrate 100 shown in FIG. 4 is extracted from the glass base plate 20, and the inner peripheral chamfered surfaces 102a and 102b and the outer peripheral chamfered surfaces 104a and 104b are extracted. Chamfering can be performed. Therefore, the inner and outer peripheries of the disk-shaped glass substrate and the chamfering of the inner and outer peripheries can be performed in one step, so that it is not necessary to perform chucking according to the processing position, and the burden on the glass substrate can be reduced. At the same time, it is possible to save the time and effort of chucking, and further, it becomes possible to process with high accuracy, so that a disk-shaped glass substrate for a magnetic recording medium excellent in concentricity and roundness can be obtained.

  Further, according to the present embodiment, the laser beam PL is irradiated along the contour of the disk-shaped glass substrate 100 to perform processing, and the cutting groove having a groove width of 10 μm or more is cut. The disc-shaped glass substrate 100 can be extracted without being provided, and contact between the cut surfaces is avoided during the extraction process, and chipping and chipping are suppressed.

  In addition, since the conventional chamfering process (shape processing process) using a rotating grindstone can be omitted, the number of processes can be reduced as compared with the conventional manufacturing method, and the production efficiency can be further increased. Further, it is possible to prevent the occurrence of chipping and cracking due to the process-affected layer (latent scratches, cracks).

  Further, since the irradiation position (cutting position) of the pulsed laser light PL on the glass base plate 20 can be set to an arbitrary position, the cutting positions of each disk-shaped glass substrate 100 are packed as much as possible as shown in FIG. It is possible to increase the production efficiency by increasing the number of disc-shaped glass substrates 100 obtained from the glass base plate 20.

DESCRIPTION OF SYMBOLS 10 Laser processing machine 20 Glass base plate 30 XY table 32 Mounting surface 34 Suction hole 40 Laser generating part 42 Laser oscillator 44 Optical unit 46 Reflecting mirror 47 Condensing lens 50 Control part 60 Optical system moving table 70 Support mechanism 80 Vacuum Pump 82 Suction piping 100 Disc-shaped glass substrate 101 Main plane 102a, 102b Inner peripheral chamfered surface 103 Inner peripheral end surface 104a, 104b Outer peripheral chamfered surface 105 Outer peripheral end surface 120 Laser oscillator control unit 130 Mirror control unit 140 Lens control unit 150 Laser irradiation angle control Unit 160 XY table control unit 170 optical system moving table control unit 210 mirror driving unit 220 condensing lens driving unit 230 optical unit driving unit 240 XY table driving unit 250 optical system moving table driving unit AK processing area PL pulse laser light

Claims (7)

A disk shape for a magnetic recording medium, comprising: an extraction step of extracting a disk-shaped glass substrate from a glass base plate; a polishing step of polishing a main plane of the disk-shaped glass substrate; and a cleaning step of cleaning the surface of the disk-shaped glass substrate. A method of manufacturing a glass substrate,
In the extracting step, the surface of the glass base plate is irradiated with a pulsed laser beam having a pulse width of 1 femtosecond or more and less than 1 nanosecond along a circular outline including a region where the disk-shaped glass substrate is formed. A disk for magnetic recording medium, characterized in that a cut groove having a groove width of 10 μm or more is formed along the contour, and the disk-shaped glass substrate cut by the cut groove is extracted from the glass base plate. For manufacturing a glass substrate.   2. The disk for magnetic recording medium according to claim 1, wherein the extracting step includes a chamfering step of chamfering the end surface by processing the end surface of the disk-shaped glass substrate by irradiating the pulse laser beam along the corner portion. For manufacturing a glass substrate.   The said extraction process processes the said cutting | disconnection groove | channel sequentially in the cutting position for extracting the said several disk shaped glass substrate to the said glass base plate by shifting the irradiation position of the said pulsed laser beam with respect to the said glass base plate. Or the manufacturing method of the disk shaped glass substrate for magnetic recording media of 2.   The manufacturing method of the disk shaped glass substrate for magnetic recording media in any one of Claims 1-3 which has an end surface grinding | polishing process which grind | polishes the end surface of the said disk shaped glass substrate after the said extraction process.   The method for producing a disk-shaped glass substrate for a magnetic recording medium according to any one of claims 1 to 4, wherein the pulsed laser beam has a wavelength of 1400 nm to 380 nm.   The method for producing a disk-shaped glass substrate for a magnetic recording medium according to claim 5, wherein the wavelength of the pulse laser beam is preferably 1000 nm to 450 nm.   A disk-shaped glass substrate for a magnetic recording medium manufactured by the method for manufacturing a disk-shaped glass substrate for a magnetic recording medium according to any one of claims 1 to 6.

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