Glass substrate manufacturing method and glass substrate

Abstract

To provide a technique for more reliably separating an annular glass substrate from a glass blank in a method for manufacturing a glass substrate for a magnetic disc.SOLUTION: A method for manufacturing an annular glass substrate (1) includes: forming a separation line (C1) including plural defects (D) along a circle (C1) on a glass blank (20) by radiating a laser beam (L) along a predetermined circle (C1) onto a surface (20a) of the glass blank (20); and separating an outside portion (21) and an inside portion (22) of the glass blank (20), on which the separation line (C1) is formed, from each other by heating the outside portion (21) of the separation line (C1) at higher temperature than the inside portion (22). The separation line (C1) includes a first region, in which two adjacent defects are periodically formed at a first interval, and a second region, in which two adjacent defects are formed at an interval shorter than the first interval.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing an annular glass substrate by processing the shape of the substrate using laser light, a method for manufacturing an annular glass substrate manufactured by the manufacturing method, and a method for manufacturing a glass substrate for a magnetic disk. [Background technology]

[0002] Nowadays, hard disk drives for recording data are used in personal computers, notebook personal computers, DVD (Digital Versatile Disc) recording devices, cloud computing data centers, etc. Hard disk drives use magnetic disks in which a magnetic layer is provided on a circular non-magnetic glass substrate for magnetic disks.

[0003] Conventionally, in such a manufacturing method of a glass substrate for a magnetic disk, a technique for separating an annular glass substrate from a glass plate is known (Patent Document 1). In this technique, first, a surface of a glass plate that is the base of a glass substrate is irradiated with a laser beam along a predetermined annular shape to form a defect along the predetermined annular shape. As a result, an outer portion and an inner portion with respect to the predetermined annular shape are formed on the surface of the glass plate. Then, the outer portion of the glass plate is heated at a higher temperature than the inner portion, so that the outer portion of the glass plate thermally expands relative to the inner portion, and a gap is formed between the outer portion and the inner portion. As a result, the outer portion and the inner portion of the glass plate can be separated. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 022510 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above-mentioned technique, even if the outer portion of the raw glass plate is heated to a higher temperature than the inner portion, the gap is not formed between the outer portion and the inner portion, and the outer portion and the inner portion cannot be separated from each other. Even if a gap is formed between the outer portion and the inner portion, and the outer portion and the inner portion can be separated from each other, chipping may occur on at least a part of the end face of the outer portion and the end face of the inner portion.

[0006] The present invention has been made to solve the above-mentioned problems, and has an object to provide a technique for more reliably separating a circular glass substrate from a raw glass plate in a manufacturing method of a glass substrate for a magnetic disk. [Means for solving the problem]

[0007] According to a first aspect of the present invention, there is provided a method for producing an annular glass substrate, comprising the steps of: irradiating a surface of a raw glass plate with a laser beam along a predetermined circle to form a separation line including a plurality of defects on the raw glass plate along the predetermined circle; and heating a portion of the raw glass plate having the separation line formed thereon at an outer side of the separation line to a higher temperature than a portion of the raw glass plate having the separation line formed thereon, thereby separating the outer portion from the inner portion. A method for manufacturing an annular glass substrate is provided, wherein the separation line includes a first region in which two adjacent defects are formed periodically with a first distance between them, and a second region in which two adjacent defects are formed with a distance shorter than the first distance between them.

[0008] In the method for manufacturing an annular glass substrate according to the first aspect of the present invention, a length of the second region may be 12.5% ​​or less of a circumferential length of the predetermined circle.

[0009] In the method for manufacturing an annular glass substrate according to the first aspect of the present invention, the interval shorter than the first interval may be 70% or less of the first interval.

[0010] In the method for manufacturing an annular glass substrate according to the first aspect of the present invention, the circumferential length of the predetermined circle does not have to be an integral multiple of the first interval.

[0011] In the method for manufacturing an annular glass substrate according to the first aspect of the present invention, the method may further include irradiating the surface of the glass plate with a laser beam along a second circle that is concentric with the predetermined circle and has a diameter shorter than that of the predetermined circle, thereby forming a second separation line including a plurality of defects along the second circle on the inside of the separation line of the glass plate, The second separation line may include a third region in which two adjacent defects are periodically formed with a second interval therebetween, and a fourth region in which two adjacent defects are formed with an interval shorter than the second interval, The second spacing may be smaller than the first spacing.

[0012] In the method for manufacturing an annular glass substrate according to the first aspect of the present invention, the separation line may be formed by irradiating the laser light at a constant period along the predetermined circle so as to go around the circle more than once.

[0013] According to a second aspect of the present invention, there is provided a method for producing an annular glass substrate, comprising the steps of: irradiating a surface of a raw glass plate with a laser beam along a predetermined circle to form a separation line including a plurality of defects on the raw glass plate along the predetermined circle; and heating a portion of the raw glass plate having the separation line formed thereon at an outer side of the separation line to a higher temperature than a portion of the raw glass plate having the separation line formed thereon, thereby separating the outer portion from the inner portion. A method for manufacturing an annular glass substrate is provided, wherein the plurality of defects include a plurality of first defects formed periodically at predetermined intervals on the specified circle, and a second defect located between at least one pair of adjacent first defects.

[0014] In the method for manufacturing an annular glass substrate according to the second aspect of the present invention, the separation line may be formed by irradiating the laser light at a constant period along the predetermined circle so as to go around the circle more than once.

[0015] In the method for manufacturing an annular glass substrate according to the second aspect of the present invention, the plurality of defects may include a plurality of the second defects each located between a plurality of sets of two adjacent first defects, The second defects may be formed when the laser light is irradiated along the predetermined circle for more than one revolution, and may be formed periodically at the predetermined intervals.

[0016] In the method for manufacturing an annular glass substrate according to the second aspect of the present invention, the predetermined interval may be set such that the circumferential length of the predetermined circle is not an integer multiple of the predetermined interval.

[0017] According to a third aspect of the present invention, there is provided a method for producing an annular glass substrate, comprising the steps of: irradiating a surface of a raw glass plate with a laser beam along a predetermined circle to form a separation line including a plurality of defects on the raw glass plate along the predetermined circle; and heating a portion of the raw glass plate having the separation line formed thereon at an outer side of the separation line to a higher temperature than a portion of the raw glass plate having the separation line formed thereon, thereby separating the outer portion from the inner portion. the plurality of defects are formed at predetermined intervals by irradiating the glass plate with the laser light at a constant relative speed in an irradiated area between the laser light and the glass plate along the predetermined circle at a constant period exceeding one revolution, the plurality of defects include a plurality of first defects formed by irradiation of the laser light in a first revolution and at least one second defect formed when the laser light is irradiated more than one revolution, There is provided a method for manufacturing a ring-shaped glass substrate, wherein the predetermined interval is determined such that the at least one second defect does not overlap with the plurality of first defects.

[0018] In the method for producing an annular glass substrate according to the first, second and third aspects of the present invention, the glass plate may be a glass plate produced by an overflow downdraw method.

[0019] According to a fourth aspect of the present invention, there is provided an annular glass substrate, Two major surfaces; an outer peripheral end surface connecting outer edges of the two main surfaces; a plurality of grooves, a first region, and a second region are formed on the outer peripheral end surface, each of the grooves extending in a thickness direction of the annular glass substrate; In the first region, two adjacent grooves are periodically formed at a first interval, A circular glass substrate is provided in which two adjacent grooves are formed in the second region at a distance shorter than the first distance.

[0020] In the ring-shaped glass substrate according to the fourth aspect of the present invention, the length of the second region may be 12.5% ​​or less of the length of the outer edge.

[0021] In the ring-shaped glass substrate according to the fourth aspect of the present invention, the interval shorter than the first interval may be 70% or less of the first interval.

[0022] The annular glass substrate according to the fourth aspect of the present invention may further include an inner peripheral end surface that is concentric with the outer peripheral end surface and is formed on the inside of the outer peripheral end surface, A plurality of grooves, a third region, and a fourth region each extending in a thickness direction of the annular glass substrate may be formed on the inner peripheral end surface, In the third region, two adjacent grooves may be periodically formed with a second interval therebetween, In the fourth region, two adjacent grooves may be formed at an interval shorter than the second interval, The second interval may be less than the first interval.

[0023] According to a fifth aspect of the present invention, there is provided a method for producing a glass substrate for a magnetic disk, the method including a process for polishing at least a main surface of the annular glass substrate according to the fourth aspect of the present invention. Effect of the Invention

[0024] According to the present invention, in the method for manufacturing a glass substrate for a magnetic disk, it is possible to more reliably separate the annular glass substrate from the raw glass plate. [Brief description of the drawings]

[0025] [Figure 1] 1 is a perspective view of a circular glass substrate manufactured by the manufacturing method of the present embodiment. FIG. [Diagram 2] 3 is a flowchart showing a flow of a method for manufacturing an annular glass substrate according to the present embodiment. [Diagram 3] 11A to 11C are diagrams illustrating irradiation of laser light in an outer separation line forming step. [Figure 4] 1A is a view of a glass plate on which an outer parting line has been formed, viewed from a direction perpendicular to the main surface, and FIG. 1B is an enlarged view of a portion of the outer parting line. [Diagram 5] FIG. 4 is a diagram illustrating heating in the first separation step. [Figure 6] FIG. 2 is a diagram illustrating separation by heating in the first separation step. [Figure 7] FIG. 2 is a perspective view of a circular glass plate extracted in a first separation step. [Figure 8] 11A to 11C are diagrams illustrating irradiation of laser light in an inner separation line forming step. [Figure 9] 1A is a view of a circular glass plate on which an inner parting line has been formed, viewed from a direction perpendicular to the main surface, and FIG. 1B is an enlarged view of a portion of the inner parting line. [Figure 10] FIG. 11 is a diagram illustrating heating in the second separation step. [Figure 11] FIG. 4 is a diagram illustrating separation by heating in the second separation step. [Figure 12]1A is a partially enlarged view of the outer peripheral end face of the annular glass substrate developed on a plane, and FIG. 1B is a partially enlarged view of the inner peripheral end face of the annular glass substrate developed on a plane. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] First, the annular glass substrate manufactured by the manufacturing method of this embodiment will be described with reference to FIG.

[0027] The glass substrate 1 is a circular thin glass substrate with a hole formed coaxially in the center, and is used, for example, as a substrate for a magnetic disk. The size of the glass substrate 1 is not limited, but it is a size suitable for a magnetic disk with a nominal diameter of, for example, 2.5 inches or 3.5 inches. In the case of a glass substrate for a magnetic disk with a nominal diameter of 2.5 inches, for example, the outer diameter (diameter) is 55 to 70 mm, the diameter of the center hole (diameter, also called the inner diameter) is 19 to 20 mm, and the plate thickness is 0.2 to 0.8 mm. In the case of a glass substrate for a magnetic disk with a nominal diameter of 3.5 inches, for example, the outer diameter is 85 to 100 mm, the diameter of the center hole is 24 to 25 mm, and the plate thickness is 0.2 to 0.8 mm.

[0028] The glass substrate 1 has a pair of opposing main surfaces 11a, 11b, an outer peripheral end surface 12, and an inner peripheral end surface 13 that defines a central hole. The main surface 11a is an annular surface having two concentric circles as an outer edge and an inner edge. The main surface 11b has the same shape as the main surface 11a and is concentric with the main surface 11a. The outer peripheral end surface 12 is a surface that connects the outer edge of the main surface 11a to the outer edge of the main surface 11b. The inner peripheral end surface 13 is a surface that connects the inner edge of the main surface 11a to the inner edge of the main surface 11b. A chamfered surface may be formed at the above-mentioned connection portion. When a magnetic disk is manufactured using the glass substrate 1, a magnetic layer is formed on the main surfaces 11a and 11b.

[0029] Next, a flow of a method for manufacturing an annular glass substrate according to one example of this embodiment will be described with reference to Fig. 2. The method for manufacturing an annular glass substrate according to this embodiment includes an outer separation line forming step (S10), a first separation step (S20), an inner separation line forming step (S30), and a second separation step (S40).

[0030] In the outer separation line forming step (S10), a laser beam is applied to the surface of the glass plate which is the material for the glass substrate 1, thereby forming a circular outer separation line including a plurality of defects in the glass plate. In the first separation step (S20), a portion of the glass plate outside the outer separation line is heated at a higher temperature than the inner portion, thereby separating the outer portion from the inner portion. In this way, a circular glass plate is extracted. In the inner separation line forming step (S30), a laser beam is applied to the surface of the circular glass plate extracted in the first separation step S20, thereby forming a circular inner separation line including a plurality of defects in the circular glass plate. In the second separation step (S40), a portion of the circular glass plate outside the inner separation line is heated at a higher temperature than the inner portion, thereby separating the outer portion from the inner portion. In this way, an annular glass substrate is manufactured.

[0031] Next, each step of the method for manufacturing the ring-shaped glass substrate according to one example of this embodiment will be described in detail with reference to FIGS.

[0032] In the outer separation line forming step (S10), as shown in FIG. 3, a laser beam L is irradiated onto a glass plate 20 that has been prepared in advance and has a rectangular shape or the like.

[0033] The raw glass plate 20 that is the material of the glass substrate 1 can be made of aluminosilicate glass, soda-lime glass, borosilicate glass, or the like. In particular, amorphous aluminosilicate glass can be suitably used because it can be chemically strengthened as necessary and can produce a magnetic disk glass substrate that is excellent in the flatness of the main surface and strength of the substrate. The raw glass plate 20 is manufactured, for example, by a float method or an overflow downdraw method and has a certain plate thickness. Alternatively, the raw glass plate 20 may be a glass plate obtained by press-molding a lump of glass using a mold. Note that the present invention is preferably applied to the raw glass plate 20 manufactured by the overflow downdraw method. Although the reason is not necessarily clear, it is presumed that one of the factors is that a large glass plate manufactured by the overflow downdraw method has a relatively large difference in residual stress depending on the position in its plane (i.e., the residual stress variation in the in-plane direction is relatively large). In the overflow downdraw method, molten glass is dropped vertically by gravity and stretched to a predetermined thickness to form a high-quality sheet glass, so the longer the drop distance, the higher the building required. However, because a tall building is technically difficult and expensive, the drop distance is practically limited. For this reason, the glass must be stretched and cooled over a shorter distance than in the float method, but since stretching and cooling are parameters that greatly affect the residual stress of the glass after forming, the residual stress variation in the in-plane direction becomes large. If the residual stress variation in the in-plane direction of a large glass plate is large, the residual stress variation between the multiple glass plates 20 after it is divided into individual pieces becomes large. In addition, depending on the size of the glass plate 20 after division, the residual stress variation in the plane of one glass plate 20 may also become large. In the present invention, it is assumed that a separation line consisting of intermittent defects is formed and cracks are generated between the multiple defects, but it has been found that the residual stress has a large effect on the formation of the cracks. That is, depending on the magnitude and in-plane distribution of the residual stress in the raw glass plate 20, cracks may or may not easily occur.Therefore, even if separation is successful for one raw glass plate 20, separation may not be successful for another raw glass plate 20. For this reason, by applying the present invention to the raw glass plates 20 manufactured by the overflow downdraw method, even when there is a large variation in residual stress between the plurality of raw glass plates 20 as described above, or when there is a large variation in residual stress within each raw glass plate 20, it is possible to stably separate a large number of raw glass plates 20 without error.

[0034] The laser light source and optical system 30 is a device that emits laser light L, and for example, a solid-state laser such as a YAG laser, a Yb:YAG laser, a Nd:YAG laser, a YVO laser, or a Nd:YVO laser is used. The wavelength of the laser light can be in the range of 1000 nm to 1100 nm, for example. The laser light L is a pulsed laser. In this embodiment, the pulse width of the laser light L is 10 -10 It is preferable that the pulse width is 100 picoseconds or less. The light energy of the laser light L can be appropriately adjusted according to the pulse width and the repetition frequency of the pulse width, but is, for example, 1 W or more in average output during the irradiation time. The frequency can be, for example, 1 kHz to 1000 kHz.

[0035] The laser irradiation method may be, for example, to irradiate the glass plate 20 with a laser light source and an optical system 30, with the laser light L appropriately adjusted so as to form a focal point on the surface and / or inside of the glass plate 20. Such irradiation of the laser light L forms a continuous focal point along the thickness direction of the glass plate 20 at one point on the circle C1. This continuous focal point is also called a focal line. Therefore, the light energy is concentrated linearly along the thickness direction of the glass plate 20, and a part of the glass plate 20 is turned into plasma, so that a defect D extending in the thickness direction of the glass plate 20 can be formed. Here, the defect D includes at least one of a hole formed in the glass plate 20, a crack developing from the hole, and a modified glass part (hereinafter referred to as a modified glass part). The hole may be a through hole penetrating the glass plate 20 in the thickness direction of the glass plate 20 by abrasion, or may be a hole that does not penetrate the glass plate 20. The modified glass part may be present over the entire thickness direction of the glass plate 20. It is preferable that these defects extend substantially perpendicular to the main surface 20a of the raw glass plate 20 (at an angle of 85 to 95 degrees), since this makes it easier to reduce the amount of material to be removed in a later process. Other methods of irradiating the laser beam include a method that utilizes self-convergence of a beam based on the Kerr effect, a method that utilizes a Gaussian-Bessel beam together with an axicon lens, a method that utilizes a line-focused beam formed by an aberration lens, and a method that uses a doughnut-shaped laser beam and a spherical lens. In any case, as long as the above-mentioned linear defect D can be formed, the irradiation conditions of the laser beam L are not particularly limited.

[0036] The laser light L is preferably applied to the glass plate 20 by a burst pulse method in which a plurality of light pulse groups are intermittently generated, with each unit being a light pulse group that is configured to generate pulsed light pulses continuously at a fixed time interval. In this case, the light energy of one pulse in one light pulse group may be modulated. By using the burst pulse laser light, the defect D can be efficiently formed.

[0037] The laser light L is irradiated while the laser light L is moved at a constant speed relative to the glass plate 20 fixed on the stage T. For example, the stage T and the glass plate 20 may be moved at a constant speed to draw a circle while the irradiation position of the laser light L is fixed, or may be rotated at a constant speed around the central axis. Here, the relative speed between the laser light L and the glass plate 20 (relative speed at the irradiation position of the laser light L) may be, for example, 10 to 1000 (mm / sec). The laser light L is intermittently irradiated at a constant period in a counterclockwise direction shown by the arrow in FIG. 3 along a circle C1 planned on the glass plate 20. In other words, the laser light L is sequentially irradiated to a plurality of locations on the circle C1 that are spaced apart at a constant interval (hereinafter also referred to as a pitch). The pitch is determined by the period of pulse irradiation of the laser light L and the relative speed between the laser light L and the glass plate 20, and may be, for example, 1 to 20 μm. Then, the laser light L is irradiated, for example, until it goes around the circle C1 once, that is, until it passes the position on the circle C1 where the laser light L was first irradiated. As a result, a circular outer parting line L1 is formed on the glass plate 20 by a plurality of defects D periodically arranged at a certain interval along the circle C1, such as defect D1 by the first pulse irradiation, defect D2 by the second pulse irradiation, defect D3 by the third pulse irradiation, defect D4 by the fourth pulse irradiation, etc. In the following description, the interval between two defects D means the distance between the centers of the two defects D. The circle C1 is an example of a predetermined circle in the present invention, and the outer parting line L1 is an example of a parting line in the present invention.

[0038] Here, the pitch of the defects D is determined by the period of pulse irradiation of the laser light L and the relative speed of the laser light L and the glass plate 20. It is preferable that the pitch of the defects D is not adjusted to be 1 / n (n is an integer) of the circumference of the circle C1. In other words, it is preferable that the period of pulse irradiation of the laser light L and the relative speed of the laser light L and the glass plate 20 are adjusted so that the circumference of the circle C1 is not an integer multiple of the pitch of the defects D. In this way, the defects D can be formed during the second round of irradiation of the laser light L so as not to overlap with the defects D formed during the first round of irradiation of the laser light L. In other words, the defects D can be formed between two adjacent defects D formed during the first round of irradiation of the laser light L during the second round of irradiation. In other words, it is preferable that the pitch of the defects D is adjusted so that the defects D formed during the second round of irradiation do not overlap with the defects D formed during the first round of irradiation (are located between two adjacent defects D formed during the first round of irradiation). As an example, as shown in FIG. 4(b), the defect Dn formed by the last pulse irradiation (i.e., the second round irradiation) of the laser light L is formed between two adjacent defects D4 and D5 without overlapping with the defect D4 formed by the fourth pulse irradiation (i.e., the first round irradiation) or the defect D5 formed by the fifth pulse irradiation (i.e., the first round irradiation) of the laser light L. Similarly, the defect Dn-1 formed by the second round irradiation is formed between the defect D3 and the defect D4 formed by the first round irradiation, the defect Dn-2 formed by the second round irradiation is formed between the defect D2 and the defect D3 formed by the first round irradiation, and the defect Dn-3 formed by the second round irradiation is formed between the defect D1 and the defect D2 formed by the first round irradiation. The interval between the defect Dn-4 and the defect Dn-3 is smaller than the interval between the defect Dn-4 and the defect Dn-3. In other words, in Figure 4(b), defects D1 to Dn are formed in this order counterclockwise around circle C1 at approximately constant intervals, but in the (counterclockwise) region from defect Dn-4 to defect D5, the distance between two adjacent defects D is shorter than in the (counterclockwise) region from defect D5 to defect Dn-4.It is preferable that the interval between two adjacent defects D in the (counterclockwise) region from defect Dn-4 to defect D5 is 70% or less of the interval between two adjacent defects D in the (counterclockwise) region from defect D5 to defect Dn-4. This is because the region where defects D are consecutive at short intervals is likely to trigger the formation of cracks along the outer separation line L1 in the first separation step (S20) described later. It is also possible to irradiate the laser light L only once so that defects D are formed at a shorter pitch than in this embodiment, but in this case, it is not possible to easily form cracks by intentionally creating an area on the circle C1 where the pitch of defects D is different (shorter). In addition, the number of defects D formed will increase, and productivity will also deteriorate. In addition, it is preferable that the length of the region from defect Dn-4 to defect D5 (the sum of the intervals between two adjacent defects D from defect Dn-4 to defect D5) is 12.5% ​​or less of the circumference of the circle C1. It is also preferable that the length exceeds 12.5%, in addition to the productivity being deteriorated, chipping may increase. The reason for this is not entirely clear, but it is speculated that if the ratio of the region where the interval between two adjacent defects D is short on the circumference of the circle C1 becomes too large, the region will come off the outer portion 21 (see FIG. 6) first in the first separation step (S20) described later, and will be easily inclined with respect to the outer portion 21, and the edge will get caught when coming off the outer portion 21, causing chipping. From the above viewpoint, 10% or less is more preferable, 5% or less is even more preferable, and 1% or less is most preferable. The lower limit is, for example, 0.01%, and if it is less than 0.01%, the effect of the present invention described later may not be obtained. Here, the distance between defect Dn-4 (the last defect of the first round) and defect D1 (the first defect of the first round) is usually very short compared to the circumference of the circle C1. For this reason, if the ratio of the second region of the present invention described later (the length of the region from defect Dn-4 to defect Dn) to the circumference of the circle C1 is sufficiently small (for example, 0.01% or less), it may be substantially ignored. That is, the region irradiated with the laser light L for more than one revolution along the circle C1 may be defined as a second region of the present invention, which will be described later.

[0039] Moreover, it is preferable that the region where the interval between two adjacent defects D is short is one place on the circumference of the circle C1. By gathering the regions where the interval between two adjacent defects D is short in one place, it is possible to suppress the occurrence of separation failure and chipping. Although the reason for this is not clear, it is presumed that gathering the regions where the interval between two adjacent defects D is short in one place forms a place where distortion concentrates on the circular outer separation line L1 during the first separation step (S20) described later, and cracks and gaps are likely to form from that point. In addition, gathering the regions where the interval between two adjacent defects D is short in one place has the advantage of efficiently forming the regions where the interval between two adjacent defects D is short.

[0040] The region from defect D caused by the last irradiation in the first round to defect D caused by the last irradiation in the second round (for example, the counterclockwise region from defect Dn-4 to defect Dn shown in FIG. 4(b)) is the second region of the present invention, and the region in which defects D are successively spaced at equal intervals (for example, the counterclockwise region from defect D5 to defect Dn-4 shown in FIG. 4(b)) is the first region of the present invention. The interval between defect D4 and defect D5 is an example of the first interval of the present invention. The first interval can be, for example, 1 to 20 μm. The interval between defect D4 and defect Dn, and the interval between defect Dn and defect D5 are examples of intervals shorter than the first interval of the present invention. Defects D1, D2, D3, ..., Dn-6, Dn-5, and Dn-4 formed during the first round of irradiation of laser light L are examples of the first defect of the present invention, and defects Dn-3, Dn-2, Dn-1, and Dn formed during the second round of irradiation of laser light L are examples of the second defect of the present invention.

[0041] Next, in the first separation step (S20), the glass plate 20 is heated to extract the part inside the outer parting line L1 from the glass plate 20 on which the outer parting line L1 has been formed. When the glass plate 20 is heated, for example, as shown in FIG. 5, a heater 40 is placed outside the outer parting line L1 to heat the outer part 21 of the glass plate 20 outside the outer parting line L1. It is preferable not to place a heater inside the outer parting line L1. In this case, the inner part 22 inside the outer parting line L1 is also indirectly heated by thermal conduction through the space or through the glass plate 20, but the outer part 21 of the glass plate 20 is heated at a higher temperature than the inner part 22. Therefore, the amount of thermal expansion of the outer part 21 of the glass plate 20 can be made larger than the amount of thermal expansion of the inner part 22. As a result, the outer part 21 of the glass plate 20 thermally expands toward the outside of the outer parting line L1 as shown in FIG. 6. Specifically, the outer portion 21 thermally expands relative to the inner portion 22 so that the inner diameter of the outer portion 21 becomes larger than the outer diameter of the inner portion 22. As a result, cracks are generated along the outer separation line L1, and the circular glass plate 22 is formed (although at this point, the glass plate remains integrated). Next, the outer portion 21 is further heated, and a gap is formed at the interface between the outer portion 21 and the inner portion 22 of the glass plate 20, and the outer portion 21 and the inner portion 22 can be separated. In other words, the circular glass plate 22 can be extracted from the rectangular glass plate 20 as shown in FIG. 7. The outer peripheral end surface of the circular glass plate 22 ultimately corresponds to the outer peripheral end surface 12 of the annular glass substrate 1. The state in which a gap is formed at the interface between the outer part 21 and the inner part 22 includes not only a state in which a measurable space is formed at any position between the outer part 21 and the inner part 22, but also a state in which the opposing surfaces of the outer part 21 and the inner part 22 are not physically or chemically bonded to each other even if a measurable space is not obtained. In other words, the state in which a gap is formed at the interface includes a state in which a crack is formed at the interface between the outer part 21 and the inner part 22 and the two are in contact with each other.

[0042] Next, in the inner separation line forming step (S30), as shown in FIG. 8, an inner separation line is formed by irradiating laser light L along a predetermined circle C2 onto the main surface 22a of the circular glass plate 22 separated in the first separation step (S20).

[0043] The laser beam L is irradiated while moving the laser beam L at a constant speed relative to the circular glass plate 22 fixed on the stage T, as in the outer parting line forming step (S10). For example, the stage T and the circular glass plate 22 may be moved at a constant speed to draw a circle while keeping the irradiation position of the laser beam L fixed, or may be rotated at a constant speed around the central axis. The laser beam L is irradiated intermittently at a constant period in a counterclockwise direction indicated by the arrow in FIG. 8 along a circle C2 set on the main surface 22a of the circular glass plate 22. In other words, the laser beam L is irradiated sequentially at a plurality of locations on the circle C2 spaced apart at a constant interval. The laser beam L is irradiated until it goes around the circle C2 once, that is, until it passes the position on the circle C2 where the laser beam L was first irradiated. As a result, in the circular raw glass plate 22, a circular inner separation line L2 as shown in Fig. 9(a) is formed by a plurality of defects D periodically arranged at regular intervals along the circle C2, such as defect D1 by the first pulse irradiation, defect D2 by the second pulse irradiation, defect D3 by the third pulse irradiation, defect D4 by the fourth pulse irradiation, etc. The circle C2 is an example of the second circle of the present invention, and the inner separation line L2 is an example of the second separation line of the present invention.

[0044] Here, it is preferable that the pulse irradiation period of the laser is not adjusted to be 1 / m (m is an integer) of the circumference of the circle C2. In other words, it is preferable that the pulse irradiation period of the laser light L and the relative speed of the laser light L and the glass plate 20 are adjusted so that the circumference of the circle C2 is not an integer multiple of the pitch of the defects D. In this way, the defect D can be formed during the second round of irradiation of the laser light L so as not to overlap with the defect D formed during the first round of irradiation of the laser light L. In other words, the defect D can be formed between two adjacent defects D formed during the first round of irradiation of the laser light L during the second round of irradiation. In other words, it is preferable that the pitch of the defects D is adjusted so that the defect D formed during the second round of irradiation does not overlap with the defect D formed during the first round of irradiation (is located between two adjacent defects D formed during the first round of irradiation). As an example, as shown in FIG. 9(b), the defect Dm formed by the last pulse irradiation (i.e., the second round irradiation) of the laser light L is formed between two adjacent defects D4 and D5 without overlapping with the defect D4 formed by the fourth pulse irradiation (i.e., the first round irradiation) or the defect D5 formed by the fifth pulse irradiation (i.e., the first round irradiation) of the laser light L. Similarly, the defect Dm-1 formed by the second round irradiation is formed between the defect D3 and the defect D4 formed by the first round irradiation, the defect Dm-2 formed by the second round irradiation is formed between the defect D2 and the defect D3 formed by the first round irradiation, and the defect Dm-3 formed by the second round irradiation is formed between the defect D1 and the defect D2 formed by the first round irradiation. The interval between the defect Dm-4 and the defect Dm-4 is smaller than the interval between the defect Dm-4 and the defect Dm-3 and the interval between the defect Dm-5 and the defect Dm-4. In other words, in Figure 9(b), defects D1 to Dm are formed in this order counterclockwise around circle C2 at approximately constant intervals, but in the (counterclockwise) region from defect Dm-4 to defect D5, the distance between two adjacent defects D is shorter than in the (counterclockwise) region from defect D5 to defect Dm-4.It is preferable that the interval between two adjacent defects D in the (counterclockwise) region from defect Dm-4 to defect D5 is 70% or less of the interval between two adjacent defects D in the (counterclockwise) region from defect D5 to defect Dm-4. This is because the region where defects D are successively spaced at short intervals is likely to trigger the formation of cracks along the inner separation line L2 in the second separation step (S40) described later. In addition, it is preferable that the length of the (counterclockwise) region from defect Dm-4 to defect D5 (the sum of the intervals between two adjacent defects D from defect Dm-4 to defect D5) is 12.5% ​​or less of the circumference of circle C2. Note that if it exceeds 12.5%, productivity may deteriorate and chipping may increase. The reason for this is not entirely clear, but it is speculated that if the ratio of the area where the interval between two adjacent defects D is short on the circumference of the circle C2 becomes too large, the area will come off the outer portion 23 (see FIG. 11) first in the second separation step (S40) described later, and will be easily inclined with respect to the outer portion 23, and the edge will get caught when coming off the outer portion 23, causing chipping. From the above viewpoint, 10% or less is more preferable, 5% or less is even more preferable, and 1% or less is most preferable. The lower limit is 0.01%, and if it is less than 0.01%, the effect of the present invention described later may not be obtained. In addition, the interval (second interval) defined by the defect D1 and the defect D2 formed in the inner separation line forming step (S30) may be the same as the interval (first interval; see FIG. 4(b)) defined by the defect D1 and the defect D2 formed in the outer separation line forming step (S10), but is preferably smaller than the first interval. Moreover, the second interval is more preferably 10 to 80% of the first interval. If it exceeds 80%, the smaller the radius of the separating circle, the more difficult it is to ensure a temperature difference between the inside and outside of the circle, which may increase costs, such as requiring a powerful heater. If it is smaller than 10%, a pulse laser with an extremely high frequency is required, which may increase costs.

[0045] The region from defect D caused by the last irradiation in the first round to defect D caused by the last irradiation in the second round (for example, the counterclockwise region from defect Dm-4 to defect Dm shown in FIG. 9(b)) is the third region of the present invention, and the region in which defects D are successively spaced at equal intervals (for example, the counterclockwise region from defect D5 to defect Dm-4 shown in FIG. 9(b)) is the fourth region of the present invention. The interval between defect D4 and defect D5 is an example of the second interval of the present invention. The interval between defect D4 and defect Dm, and the interval between defect Dm and defect D5 are examples of intervals shorter than the second interval of the present invention. Defects D1, D2, D3, ..., Dm-6, Dm-5, and Dm-4 formed during irradiation of the laser light L in the first round are examples of the first defect of the present invention, and defects Dm-3, Dm-2, Dm-1, and Dm formed during irradiation of the laser light L in the second round are examples of the second defect of the present invention. Note that defects D1 to D6 shown in Figure 9(b) are an example of the third defect of the present invention, defect Dm is an example of the fourth defect of the present invention, and the distance between defect D1 and defect D2 is an example of the second specified distance of the present invention.

[0046] Next, in the second separation step (S40), the circular glass plate 22 is heated to extract the part inside the inner parting line L2 from the circular glass plate 22 on which the inner parting line L2 has been formed. When heating the circular glass plate 22, for example, as shown in FIG. 10, a heater 40 is placed outside the inner parting line L2 to heat the outer part 23 of the circular glass plate 22 outside the inner parting line L2. It is preferable not to place a heater inside the inner parting line L2. In this case, the inner part 24 inside the inner parting line L2 is also indirectly heated by heat conduction through the space or through the circular glass plate 22, but the outer part 23 of the circular glass plate 22 is heated at a higher temperature than the inner part 24. Therefore, the amount of thermal expansion of the outer part 23 of the circular glass plate 22 can be made larger than the amount of thermal expansion of the inner part 24. As a result, as shown in Fig. 11, the outer portion 23 of the circular glass plate 22 thermally expands toward the outside of the inner separation line L2. Specifically, the outer portion 23 thermally expands relative to the inner portion 24 so that the inner diameter (inner diameter) of the outer portion 23 becomes larger than the outer diameter (outer diameter) of the inner portion 24. As a result, a gap is formed at the interface between the outer portion 23 and the inner portion 24 of the circular glass plate 22, and the outer portion 23 and the inner portion 24 can be separated. In other words, by extracting the inner portion 24 from the circular glass plate 22, it is possible to manufacture an annular glass substrate 1 with a hollowed-out center portion as shown in Fig. 1. The inner peripheral end face of the outer portion 23 of the circular glass plate 22 corresponds to the inner peripheral end face 13 of the annular glass substrate 1. In the second separation step (S40), the state in which a gap is formed at the interface between the outer portion 23 and the inner portion 24 includes not only a state in which a measurable space is formed at any position between the outer portion 23 and the inner portion 24, but also a state in which the opposing surfaces of the outer portion 23 and the inner portion 24 are not physically or chemically bonded to each other even if a measurable space is not obtained. In other words, the state in which a gap is formed at the interface includes a state in which a crack is formed at the interface between the outer portion 23 and the inner portion 24 and the two are in contact with each other.

[0047] In the case of manufacturing a glass substrate for a magnetic disk, although not shown in the drawings, after the second separation step (S40), post-processing including a chamfered surface forming step, an end surface polishing step, a main surface grinding step, a main surface polishing step, etc. may be further performed. A cleaning step may be added before or after each step as appropriate. Among these processes, steps other than the main surface polishing step may be omitted as appropriate.

[0048] In the chamfered surface forming step, a chamfer is formed on the inner peripheral end surface 13 and / or the outer peripheral end surface 12 of the annular glass substrate 1 using, for example, a shaped grindstone.

[0049] In the edge polishing process, the inner peripheral edge 13 and / or the outer peripheral edge 12 of the annular glass substrate 1 are mirror-finished by, for example, brush polishing. At this time, a polishing liquid containing fine particles of cerium oxide, zirconium oxide, or the like as free abrasive grains is used. By polishing the edge, the occurrence of thermal asperities can be prevented.

[0050] In the main surface grinding step, a double-sided grinding machine equipped with a planetary gear mechanism is used to perform grinding on the main surfaces 11a, 11b of the annular glass substrate 1. The grinding allowance is, for example, about several μm to several hundred μm. The double-sided grinding machine has an upper surface plate and a lower surface plate, and the annular glass substrate 1 is sandwiched between the upper surface plate and the lower surface plate. The annular glass substrate 1 and the surface plates are moved relatively to each other to grind the main surfaces 11a, 11b of the annular glass substrate 1. As the surface plate, for example, one having a grinding pad attached thereto containing fixed abrasive particles, such as diamond abrasive particles fixed by resin, can be used.

[0051] In the main surface polishing step, the main surfaces 11a, 11b ground in the main surface grinding step are polished. The removal amount by polishing is, for example, about 0.1 μm to 100 μm. The main surface polishing is intended to remove scratches and distortions remaining on the main surfaces 11a, 11b by grinding with fixed abrasive grains, adjust waviness and microwaviness, make the surface mirror-finished, reduce roughness, etc. For the main surface polishing, for example, a polishing liquid containing cerium oxide, zirconia, silica, etc. as free abrasive grains can be used. The main surface polishing step may be carried out in two or more separate steps. For example, it can be carried out in separate steps of a first main surface polishing (rough polishing) using a polishing liquid containing cerium oxide or zirconia, and a second main surface polishing using a polishing liquid containing silica.

[0052] Next, the appearance of the outer peripheral end face 12 and the inner peripheral end face 13 of the annular glass substrate 1 manufactured according to the manufacturing process described above will be described with reference to Figures 12(a) and (b). Note that Figure 12(a) corresponds to the portion of the outer peripheral end face 12 shown in Figure 4(b), and Figure 12(b) corresponds to the portion of the inner peripheral end face 13 shown in Figure 9(b).

[0053] As shown in FIG. 12(a), a plurality of grooves G are formed on the outer peripheral end surface 12 of the annular glass substrate 1, each extending in the thickness direction of the glass substrate 1. Each groove is formed by leaving a part or a trace of a defect D formed in the outer separation line forming step (S10) on the outer peripheral end surface 12 in the first separation step (S20). In the present invention, the groove includes not only a groove that extends without interruption in the thickness direction of the glass substrate 1, but also a groove that is interrupted halfway in the thickness direction of the glass substrate 1. The width of the groove in the circumferential direction is, for example, 2 to 10 μm. In FIG. 12(a), the grooves G1 to Gn correspond to the defects D1 to Dn shown in FIG. 4(b), respectively. The outer peripheral end face 12 has a first region in which the grooves G are formed in ascending order from groove G5 to groove Gn-4 at a first interval S1, and a second region in which two adjacent grooves G are formed at an interval shorter than the first interval S1 from groove Gn-4 to groove G5. In the outer peripheral end face 12, the circumferential length of the second region is, for example, 12.5% ​​or less of the circumferential length of the outer peripheral end face 12. In addition, in FIG. 12(a), the interval between two adjacent grooves G in the second region is 70% or less of the interval between two adjacent grooves G in the first region.

[0054] As shown in FIG. 12(b), a plurality of grooves G extending in the thickness direction of the glass substrate 1 are formed on the inner peripheral end surface 13 of the annular glass substrate 1, similarly to the outer peripheral end surface 12. Each groove is formed by leaving a part or a trace of the defect D formed in the inner separation line forming step (S30) on the inner peripheral end surface 13 by the second separation step (S40). The width of the groove in the circumferential direction is, for example, 2 to 10 μm. In FIG. 12(b), the grooves G1 to Gm correspond to the defects D1 to Dm shown in FIG. 9(b), respectively. The inner peripheral end surface 13 has a third region in which the grooves G are formed in ascending order with the second interval S2 between them, from the groove G5 to the groove Gm-4, and a fourth region in which the adjacent two grooves G are formed with the interval shorter than the second interval S2 between them, from the groove Gm-4 to the groove G5. The second interval S2 is shorter than the first interval S1 at the outer circumferential end face 12, and is, for example, 10 to 80% of the first interval S1.

[0055] According to the manufacturing method according to the above-mentioned aspect of the present invention, in the outer separation line forming step (S10), the laser light L is irradiated intermittently at a constant cycle until it goes around the circle C1 once, that is, until it passes the position on the circle C1 where the laser light L was initially irradiated. As a result, a plurality of defects D1 to Dn are formed in this order in a counterclockwise direction along the circle C1 at approximately constant intervals. At this time, on the circle C1, there are formed an area where two adjacent defects D are periodically arranged at an approximately constant interval (for example, the counterclockwise area from defect D5 to defect Dn-4 in FIG. 4(b)) and an area where two adjacent defects D are arranged at an interval shorter than the constant interval (for example, the counterclockwise area from defect Dn-4 to defect D5 in FIG. 4(b)). Therefore, even if local distortion occurs in the raw glass plate 20 due to differences in thermal histories during the manufacturing process, when the outer portion 21 is heated at a higher temperature than the inner portion 22 in the first separation step (S20), two adjacent defects D with a short distance between them (e.g., defects D4 and Dn in FIG. 4(b)) are more likely to be connected by a crack than two equally spaced defects D (e.g., defects D5 and D6 in FIG. 4(b)). In other words, a crack or gap is more likely to form between two adjacent defects D with a short distance between them than between two equally spaced defects D. Since glass is a brittle material, once a crack occurs, it has the property of easily propagating. Therefore, the crack or gap always stably extends along the circumference of the circle C1 from the crack or gap formed between two adjacent defects D with a short distance between them, so that the crack or gap can be reliably formed around the entire circumference of the circle C1 between the outer portion 21 and the inner portion 22. Therefore, the outer portion 21 and the inner portion 22 of the glass plate 20 can be separated reliably.

[0056] Furthermore, in the inner separation line forming step (S30), as in the outer separation line step (S10), the irradiation of the laser light L is performed intermittently at a constant cycle until the laser light L has traveled around the circle C2 once, that is, until the laser light L has passed the position on the circle C2 where the laser light L was initially irradiated. As a result, a plurality of defects D1 to Dm are formed in this order in a counterclockwise direction along the circle C2 at approximately constant intervals. At this time, a region is formed on the circle C2 where two adjacent defects D are periodically arranged at approximately constant intervals (for example, the counterclockwise region from defect D5 to defect Dm-4 in FIG. 9(b)) and a region is formed where two adjacent defects D are arranged at an interval shorter than the constant interval (for example, the counterclockwise region from defect Dm-4 to defect D5 in FIG. 9(b)). Therefore, even if local distortion occurs in the circular glass plate 22 due to differences in thermal histories during the manufacturing process, when the outer portion 23 of the circular glass plate 22 is heated at a higher temperature than the inner portion 24 in the second separation step (S40), two adjacent defects D with a short distance between them (e.g., defects D4 and Dm in FIG. 9(b)) are more likely to be connected by a crack than two equally spaced defects D (e.g., defects D5 and D6 in FIG. 9(b)). In other words, a crack or gap is more likely to form between two adjacent defects D with a short distance between them than between two equally spaced defects D. Therefore, a crack or gap is always stably formed from a crack or gap formed between two adjacent defects D with a short distance between them along the circumference of the circle C2, so that a crack or gap can be reliably formed around the entire circumference of the circle C2 between the outer portion 23 and the inner portion 24 of the circular glass plate 22. Therefore, the outer portion 23 and the inner portion 24 of the circular glass plate 22 can be separated reliably.

[0057] That is, according to the manufacturing method according to the embodiment of the present invention, the annular glass substrate 1 can be reliably separated from the raw glass plate 20 through the above-mentioned steps.

[0058] Furthermore, according to the manufacturing method of the present invention, in the outer separation line forming step (S10), the laser light L is irradiated until it completes one revolution along the circle C1 without changing the period of pulse irradiation of the laser light L and the relative speed between the laser light L and the glass plate 20. In other words, there is no need to change the setting of the period of pulse irradiation of the laser light L or the setting of the relative speed. Therefore, it is possible to form, by a simple method, a region where two adjacent defects D are periodically arranged at an approximately constant interval and a region where two adjacent defects D are arranged at an interval shorter than the constant interval.

[0059] Furthermore, in the inner separation line forming step (S30), the laser light L is irradiated until it completes one revolution along the circle C2 without changing the period of the pulse irradiation of the laser light L and the relative speed between the laser light L and the glass plate 20. In other words, there is no need to change the setting of the period of the pulse irradiation of the laser light L or the setting of the relative speed. Therefore, it is possible to form, by a simple method, a region where two adjacent defects D are periodically arranged at an approximately constant interval and a region where two adjacent defects D are arranged at an interval shorter than the constant interval.

[0060] In addition, according to the manufacturing method of the present invention, it is possible to extract (i.e., cut out) a desired disk-shaped glass substrate from a raw glass plate without using a release line. The release line is a dividing line that is provided so as to be able to divide the region outside the separation line in order to make it easier to take out a glass portion of a desired closed shape from the glass plate that is the base material, and is formed, for example, to include a plurality of defects like the above-mentioned separation line. This eliminates the need to heat the outside of the separation line to form a gap inside and outside the separation line, but there are some disadvantages. Since the manufacturing method of the present invention does not use a release line, it is possible to prevent the generation of unnecessary glass debris, and the remaining part (unnecessary part) after separation is easy to handle. In addition, it is very difficult to cut out a desired disk-shaped glass substrate from a raw glass plate. The reasons for this include that glass is generally difficult to heat and has a small linear expansion coefficient, and is easily caught inside and outside the separation line in the same way that a circular manhole does not fall. According to the manufacturing method of the present invention, it is possible to cut out a desired disk-shaped glass substrate from a raw glass plate more reliably by a simple method.

[0061] (Example) The outer separation line forming step (S10) of this embodiment was carried out under different conditions as shown in Table 1 below. The first separation step (S20) of this embodiment was carried out under the same conditions on the glass plate on which the outer separation line L1 was formed, and the defect occurrence rate was verified. As the raw glass plate 20, a square glass plate material having a length and width of 110 mm and a plate thickness of 0.7 mm, obtained by dividing a glass plate manufactured by the overflow downdraw method, was used. The outer separation line L1 having a diameter of 98 mm was formed on the raw glass plate 20. The irradiation of the laser light L was carried out so that defects D were continuously formed at a predetermined interval without changing the period of pulse irradiation of the laser light L and the relative speed between the laser light L and the raw glass plate 20. The total occurrence rate of separation failure and chipping was taken as the defect occurrence rate (%). The defect occurrence rate (%) was calculated by carrying out the first separation step (S20) 1000 times or more for each condition. In Table 1 below, "predetermined interval" means the interval between two adjacent defects D formed by two successive pulse irradiations. Also, "the interval between the first defect and the first defect of the second round" means the interval between the defect D formed by the first irradiation of the first round and the defect D formed by the first irradiation of the second round, such as the interval between defect D1 and defect Dn-3 shown in FIG. 4(b). Also, in "defect occurrence rate (rank)", the defect occurrence rate of Comparative Example 1 is used as the standard (denoted as "C") to take the ratio, and the defect occurrence rate of 95% or more and less than 100% of Comparative Example 1 is denoted as "B", and the defect occurrence rate of less than 95% of Comparative Example 1 is denoted as "A". In other words, the lowest defect occurrence rate is the best, and the next best is "A".

[0062] [Table 1]

[0063] From the results shown in Table 1, it can be seen that when the interval between the first defect and the first defect on the second circumference is 70% or less of the predetermined interval (Examples 2 to 4), the defect occurrence rate is lower and better than when it exceeds 70% (Example 1). It can also be seen that when the ratio of the second region to the circumferential length is 12.5% ​​or less (Examples 5 to 8), the defect occurrence rate is lower and better than when it exceeds 12.5% ​​(Example 9). When the outer peripheral end surface of the circular glass plate (diameter 98 mm, plate thickness 0.7 mm) separated by the first separation step (S20) was observed with a laser microscope, multiple grooves extending in the thickness direction were present, and in each example, a first region and a second region were formed. The width of each groove was 3 μm.

[0064] Next, the inner separation line forming step (S30) of this embodiment was carried out on the non-defective circular glass plate obtained by further manufacturing under the conditions of Example 4 in Table 1 above, while changing the conditions as shown in Table 2 below. Then, the second separation step (S40) of this embodiment was carried out on the circular glass plate on which the inner separation line L2 was formed under the same conditions, and the defect occurrence rate was verified. In the inner separation line forming step (S30), an inner separation line L2 with a diameter of 24 mm was formed on a circular glass plate with a diameter of 98 mm. The irradiation of the laser light L was carried out so that defects D were continuously formed at a predetermined interval without changing the period of pulse irradiation of the laser light L and the relative speed between the laser light L and the circular glass plate. The total occurrence rate of separation failure and chipping was taken as the defect occurrence rate (%). The defect occurrence rate (%) was calculated by carrying out the second separation step (S40) more than 1000 times for each condition. In Table 2 below, the meanings of "predetermined interval" and "interval between the first defect and the first defect of the second round" are the same as those in Table 1 above. In addition, for "defect occurrence rate (rank)", the defect occurrence rate of Comparative Example 2 is used as the standard (denoted as "C") to calculate the ratio, and a defect occurrence rate less than 95% of that of Comparative Example 2 is denoted as "A".

[0065] [Table 2]

[0066] As shown in Table 2 above, the defect rates of both Examples 10 and 11 were ranked "A". However, when compared in detail, Example 11, in which the predetermined interval was smaller than the predetermined interval (10 μm) in the outer separation line forming step (S10), was slightly better. When the inner peripheral end surface of the annular glass substrate (outer diameter 98 mm, inner diameter 24 mm, plate thickness 0.7 mm) separated by the second separation step (S40) was observed with a laser microscope, a plurality of grooves extending in the thickness direction were present, and in each Example, a third region and a fourth region were formed. The width of each groove was 3 μm.

[0067] Furthermore, a non-defective annular glass substrate obtained by further manufacturing under the conditions of Examples 10 and 11 in Table 2 above was subjected to the chamfered surface forming process, end surface polishing process, main surface grinding process, main surface polishing process, and cleaning process of this embodiment in sequence to obtain a glass substrate for magnetic disk having an outer diameter of 97 mm, an inner diameter of 25 mm, and a plate thickness of 0.5 mm.

[0068] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the claims. Modifications of the above embodiment will be described below.

[0069] In the above embodiment, in the outer separation line forming step (S10) and the inner separation line forming step (S30), the laser light L is intermittently irradiated at a constant cycle until it has completed one revolution along the circle C1 and the circle C2, but this is not limited thereto. For example, the laser light L may be irradiated only one revolution along the circle C1 and the circle C2 at a constant cycle while changing the speed of movement or rotation of the stage T. In this case, if the speed of the stage T is low, the interval between two adjacent defects D becomes narrow, but if the speed of the stage T is high, the interval between two adjacent defects D becomes wide. Therefore, in the outer separation line forming step (S10), the speed of the stage T may be increased to form a first region in which two adjacent defects are periodically formed with a first interval therebetween, and the speed of the stage T may be decreased to form a second region in which two adjacent defects are periodically formed with an interval shorter than the first interval therebetween. Similarly, in the inner separation line forming step (S30), the speed of the stage T may be increased to form a third region in which two adjacent defects are periodically formed with a second interval therebetween, and the speed of the stage T may be decreased to form a fourth region in which two adjacent defects are periodically formed with an interval shorter than the second interval. In this case, the interval shorter than the first interval is preferably 70% or less of the first interval. In this way, the defects D are successively spaced at intervals sufficiently shorter than the first interval, which may trigger the formation of cracks in the subsequent separation step (S20), and separation failures and chipping are likely to be reduced. In addition, the interval shorter than the second interval is preferably 70% or less of the second interval for the same reason as above. In addition, for the same reason as in the above embodiment, the second region is preferably one place on the circumference of the circle C1, and the fourth region is preferably one place on the circumference of the circle C2. The length of the second region is preferably 12.5% ​​or less of the circumference of the circle C1, and the length of the fourth region is preferably 12.5% ​​or less of the circumference of the circle C2.

[0070] Alternatively, the laser light L may be irradiated along the circle C1 and the circle C2 for only one revolution while changing the irradiation period, while keeping the speed of movement or rotation of the stage T constant. In this case, if the irradiation period of the laser light L is short, the interval between two adjacent defects D will be narrow, whereas if the irradiation period of the laser light L is long, the interval between two adjacent defects D will be wide. Therefore, in the outer separation line forming step (S10), the irradiation period of the laser light L may be lengthened to form a first region in which two adjacent defects are periodically formed with a first interval therebetween, and the irradiation period of the laser light L may be shortened to form a second region in which two adjacent defects are periodically formed with an interval shorter than the first interval. Similarly, in the inner separation line forming step (S30), a third region in which two adjacent defects are periodically formed with a second interval may be formed by lengthening the irradiation period of the laser light L, and a fourth region in which two adjacent defects are periodically formed with an interval shorter than the second interval may be formed by shortening the irradiation period of the laser light L. In this case, the interval shorter than the first interval is preferably 70% or less of the first interval for the same reason as above. Also, the interval shorter than the second interval is preferably 70% or less of the second interval for the same reason as above. Also, for the same reason as in the above embodiment, the second region is preferably one place on the circumference of the circle C1, and the fourth region is preferably one place on the circumference of the circle C2. Also, the length of the second region is preferably 12.5% ​​or less of the circumference of the circle C1, and the length of the fourth region is preferably 12.5% ​​or less of the circumference of the circle C2.

[0071] In the above embodiment, the inner separation line forming step (S30) is performed after the first separation step (S20), but this is not limited thereto. For example, the inner separation line forming step (S30) may be performed before the first separation step (S20) after the outer separation line forming step (S10), or the inner separation line forming step (S30) may be performed before the outer separation line forming step (S10). Furthermore, the outer separation line L1 and the inner separation line L2 may be formed simultaneously by simultaneously performing the outer separation line forming step (S10) and the inner separation line forming step (S30). In this case, the laser light L is irradiated along the circle C1 and the circle C2 at the same time.

[0072] In the above embodiment, in the outer separation line forming step (S10) and the inner separation line forming step (S30), the laser light L is irradiated while the glass plate on the stage T is moved or rotated by fixing the irradiation position of the laser light L and moving or rotating the stage T at a constant speed, but the present invention is not limited to this. For example, the laser light source and an optical system such as a micromirror device provided in the optical system 30 may be driven to periodically deflect the light beam, so that the glass plate fixed to the stage T is irradiated with the laser light L while moving it.

[0073] In the above embodiment, in the outer separation line forming step (S10) and the inner separation line forming step (S30), the multiple defects D are formed counterclockwise along the circles C1 and C2, but they may also be formed clockwise along the circles C1 and C2.

[0074] In the above embodiment, in the first separation step (S20) and the second separation step (S40), the heater 40 is disposed outside the separation line, and the heater 40 is not disposed inside the separation line, but this is not limited to this. If the portion outside the separation line can be heated to a higher temperature than the portion inside to an extent that separation is possible, the heater may be disposed inside the separation line to heat the inner portion.

[0075] In the above embodiment, the glass substrate is described as a magnetic disk glass substrate, but the present invention is not limited to this and can be applied to an annular glass substrate for any purpose, for example, a disk-shaped glass substrate without an inner circumferential circle (circular hole) such as a semiconductor substrate. In this case, the method for manufacturing the disk-shaped glass substrate includes: forming a separation line including a plurality of defects along a predetermined circle on the glass plate by irradiating a laser beam along a predetermined circle on the surface of the glass plate; and heating the outer part of the separation line of the glass plate on which the separation line is formed at a higher temperature than the inner part of the separation line to separate the outer part from the inner part, and the separation line includes a first region where two adjacent defects are periodically formed with a first interval therebetween, and a second region where two adjacent defects are formed with an interval shorter than the first interval. [Explanation of symbols]

[0076] 1 Glass substrate 11a,11b Main surface 12 Outer peripheral end face 13 Inner periphery end face 20 Glass plate 21 Outer part 22 Inner part (circular glass plate) 23 Outer part 24 Inner part 30 Laser light source and optical system 40 Heater L Laser light D1~Dn Defects G1~Gn Groove C1, C2 yen L1 outer separation line L2 inner separation line

Claims

1. A method for manufacturing a glass substrate, comprising the steps of: irradiating a surface of a raw glass plate with a laser beam along a predetermined circle to form a separation line including a plurality of defects on the raw glass plate along the predetermined circle; and heating the outer portion of the raw glass plate having the separation line formed thereon at a higher temperature than the inner portion of the raw glass plate having the separation line formed thereon, thereby separating the outer portion from the inner portion of the raw glass plate. A method for manufacturing a glass substrate, wherein the separation line includes a first region in which two adjacent defects are formed periodically with a first interval between them, and a second region in which two adjacent defects are formed with an interval shorter than the first interval.

2. The method for manufacturing a glass substrate according to claim 1 , wherein a length of the second region is equal to or less than 12.5% ​​of a circumferential length of the predetermined circle.

3. The method for manufacturing a glass substrate according to claim 1 , wherein the interval shorter than the first interval is 70% or less of the first interval.

4. The method for manufacturing a glass substrate according to claim 1 , wherein the perimeter of the predetermined circle is not an integer multiple of the first interval.

5. A method for manufacturing a glass substrate as described in any one of claims 1 to 4, wherein the separation line is formed by irradiating the laser light at a constant period so as to extend more than one revolution around the specified circle.

6. A method for manufacturing a glass substrate, comprising the steps of: irradiating a surface of a raw glass plate with a laser beam along a predetermined circle to form a separation line including a plurality of defects on the raw glass plate along the predetermined circle; and heating the outer portion of the raw glass plate having the separation line formed thereon at a higher temperature than the inner portion of the raw glass plate having the separation line formed thereon, thereby separating the outer portion from the inner portion of the raw glass plate. A method for manufacturing a glass substrate, wherein the plurality of defects include a plurality of first defects formed periodically at predetermined intervals on the specified circle, and a second defect located between at least one pair of adjacent first defects.

7. The method for manufacturing a glass substrate according to claim 6 , wherein the separation line is formed by irradiating the laser light at a constant period along the predetermined circle so as to go around the circle more than once.

8. the plurality of defects includes a plurality of the second defects each located between a plurality of sets of two adjacent first defects, 8. The method for manufacturing a glass substrate according to claim 7, wherein the second defects are formed when the laser light is irradiated along the predetermined circle for more than one revolution, and are formed periodically at the predetermined intervals.

9. 9. The method for manufacturing a glass substrate according to claim 6, wherein the predetermined interval is set so that the circumferential length of the predetermined circle is not an integral multiple of the predetermined interval.

10. A method for manufacturing a glass substrate, comprising the steps of: irradiating a surface of a raw glass plate with a laser beam along a predetermined circle to form a separation line including a plurality of defects on the raw glass plate along the predetermined circle; and heating the outer portion of the raw glass plate having the separation line formed thereon at a higher temperature than the inner portion of the raw glass plate having the separation line formed thereon, thereby separating the outer portion from the inner portion of the raw glass plate. the plurality of defects are formed at predetermined intervals by irradiating the glass plate with the laser light at a constant relative speed in an irradiated portion between the laser light and the glass plate along the predetermined circle at a constant period exceeding one revolution, the plurality of defects include a plurality of first defects formed by irradiation of the laser light in a first revolution and at least one second defect formed when the laser light is irradiated more than one revolution, The method for manufacturing a glass substrate, wherein the predetermined interval is determined such that the at least one second defect does not overlap with the plurality of first defects.

11. The method for producing a glass substrate according to any one of claims 1 to 10, wherein the raw glass plate is a raw glass plate produced by an overflow downdraw method.

12. A glass substrate comprising: Two major surfaces; an outer peripheral end surface connecting outer edges of the two main surfaces; the outer peripheral end surface includes a first region and a second region, A plurality of grooves extending in a thickness direction of the glass substrate are formed in each of the first region and the second region, In the first region, two adjacent grooves are periodically formed at a first interval, In the second region, two adjacent grooves are formed at a distance shorter than the first distance.

13. The glass substrate according to claim 12 , wherein the length of the second region is 12.5% ​​or less of the length of the outer edge.

14. The glass substrate according to claim 12 or 13, wherein the interval shorter than the first interval is 70% or less of the first interval.

15. The glass substrate according to claim 12, further comprising a hole located inside the outer peripheral end face and an inner peripheral end face formed along the hole.

16. The inner peripheral end surface includes a third region and a fourth region, A plurality of grooves extending in a thickness direction of the glass substrate are formed in each of the third region and the fourth region, In the third region, two adjacent grooves are periodically formed at a second interval, 16. The glass substrate according to claim 15, wherein in the fourth region, two adjacent grooves are formed at an interval shorter than the second interval.

17. The glass substrate of claim 16, wherein the second spacing is shorter than the first spacing.

18. A glass substrate comprising: Two major surfaces; an outer peripheral end surface connecting outer edges of the two main surfaces; a hole formed on the inner side of the outer circumferential end surface and an inner circumferential end surface formed along the hole, the inner peripheral end surface includes a third region and a fourth region, A plurality of grooves extending in a thickness direction of the glass substrate are formed in each of the third region and the fourth region, In the third region, two adjacent grooves are periodically formed at a second interval, In the fourth region, two adjacent grooves are formed at a distance shorter than the second distance.

19. The glass substrate according to claim 12, wherein the main surface of the glass substrate is formed by an overflow downdraw method.

20. A method for manufacturing a glass substrate, comprising at least a process of polishing the main surface of the glass substrate according to any one of claims 12 to 19.

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