[Title of Invention]

METHOD FOR PRODUCING SUBSTRATE, METHOD FOR PRODUCING MAGNETIC DISK, AND POLISHING APPARATUS

[Technical Field]

[0001] The present invention relates to a method for producing a substrate including substrate polishing processing, a method for producing a magnetic disk, and a polishing apparatus for polishing a substrate.

[Background Art]

[0002] Nowadays, in order to record data, hard disk drives (HDDs) are incorporated in personal computers, DVD (Digital Versatile Disc) recording apparatuses, and the like.

A magnetic disk obtained by providing a magnetic layer on a substrate is used in a hard disk drive, and magnetic recording information is recorded in, or read from, the magnetic layer with a magnetic head that is made to fly slightly above the surface of the magnetic disk. In order to increase storage capacity of hard disk drives, magnetic recording density has been increased. In order to enable the increase in the magnetic recording density, surface unevenness of main surfaces of a substrate for use as a substrate of a magnetic disk is minimized as much as possible, Therefore, high precision polishing is performed in the production of a substrate used for a magnetic disk.

[0003] A polishing apparatus, for example, polishes the main surfaces of a substrate with polishing pads while holding the substrate between upper and lower surface plates provided with the polishing pads and rotating the upper and lower surface plates. At this time, a polishing liquid is supplied between the polishing pads and the main surfaces of the substrate. The polishing liquid contains polishing abrasive particles, such as colloidal silica, having a small particle size. For example, the polishing liquid is supplied onto the main surfaces of the substrate from a polishing liquid tank through a plurality of through holes that are formed so as to pass through the upper surface plate. The substrate held between the upper and lower surface plates moves between the upper and lower surface plates in such a manner as to revolve around the central axis of rotation of the upper surface plate while rotating on its axis. For this reason, the plurality of through holes, which are formed in the upper surface plate and through which the polishing liquid is supplied, are provided dispersed in a region where the substrate moves (see FIG. 2 of PTL 1 , for example).

[Citation List]

[Patent Literature]

[0004] [PTL1 ]: Japanese Patent No. 6371310

[Summary of Invention]

[Technical Problem]

[0005] Incidentally, in recent years, in order to increase storage capacity of data centers for cloud computing, there is demand for further increases in storage capacity of HDD apparatuses compared with conventional ones.

With respect to present-day magnetic disks, the flying height of a magnetic head above a magnetic disk is minimized, and many magnetic disks are installed in an HDD apparatus, but this is not enough for the above-described increases in storage capacity of HDD apparatuses. To address this issue, it is conceivable to increase the number of magnetic disks installed in an HDD apparatus. In order to increase the number of magnetic disks, reducing the thickness of a substrate, which has the largest thickness in each magnetic disk, is effective. In this case, since the thickness of the substrate is reduced, it is also necessary to reduce the thickness of a carrier, which is used when holding the substrate between upper and lower surface plates and polishing the substrate, in accordance with the thickness of the substrate. However, a reduction in the thickness of the carrier reduces the rigidity of the carrier and leads to bending deformation, and consequently, there are cases where an end of the carrier is caught in an opening of a through hole in the upper surface plate through which the polishing liquid is supplied, and causes damage to a polishing pad that is provided around the opening. As a result, the substrate may have polishing blemishes, non-uniform polishing, or the like, and high precision polishing cannot be realized. That is to say, during polishing, the opening of the through hole, through which the polishing liquid is supplied, constitutes an obstacle and prevents the substrate held by the carrier from being precisely polished.

[0006] In view of this, an object of the present invention is to provide a method for producing a substrate with which, during polishing of main surfaces of a substrate, an opening of a through hole through which a polishing liquid is supplied does not constitute an obstacle, and precision polishing of the substrate can be realized; a method for producing a magnetic disk; and a polishing apparatus.

[Solution to Problem]

[0007] An aspect of the present invention is a method for producing a substrate including substrate polishing processing. This production method includes the polishing processing including;

a step of polishing main surfaces of a substrate with polishing pads while holding the substrate between an upper surface plate and a lower surface plate that are provided with the polishing pads and rotating the upper surface plate and the lower surface plate; and

a step of, during polishing of the main surfaces, supplying a polishing liquid to an inner circumferential face of a center hole of the upper surface plate through which a central axis of rotation of the upper surface plate passes and allowing the polishing liquid to descend along the inner circumferential face, thereby supplying the polishing liquid between the substrate and the polishing pads through a gap between the upper surface plate and the lower surface plate.

The inner circumferential face is provided with a descending velocity control means that suppresses descending velocity of the polishing liquid.

[0008] It is preferable that no openings for supplying the polishing liquid except for an opening of the center hole are provided in a lower opposing surface of the upper surface plate that opposes the lower surface plate.

[0009] It is preferable that the center hole has an inclined portion where the inner circumferential face is inclined with an angle of at least 0 degrees and less than 90 degrees with respect to a lower opposing surface of the upper surface plate that opposes the lower surface plate so that a hole cross-sectional area of the center hole increases toward the lower opposing surface, the inclined portion being provided along a circumference of the opening.

[0010] It is preferable that the inner circumferential face includes an uneven portion as the descending velocity control means.

[001 1] It is preferable that the uneven portion includes a groove-like depressed portion extending on the inner circumferential face.

[0012] It is preferable that the substrate is held in an inner hole formed in a plate-shaped carrier,

the carrier is arranged relative to the upper surface plate so that, during polishing of the main surfaces, the carrier is held between the upper surface plate and the lower surface plate in a state in which the carrier holds the substrate, and an outer circumferential portion of the carrier receives the polishing liquid flowing down from an opening of the center hole of the upper surface plate while passing through a position that is nearer to the central axis of rotation than a position of an edge of the opening, the carrier includes an outer frame portion that forms an outer circumference of the carrier and a flat plate portion that is surrounded by the outer frame portion,

the outer frame portion and a portion of the flat plate portion on a circumference thereof are located nearer to the central axis of rotation than the position of the edge of the opening, and

the outer frame portion bulges relative to the flat plate portion.

[0013] It is preferable that polishing of the substrate is started in a state in which the polishing liquid has been contained in at least a portion of the gap between the upper surface plate and the lower surface plate before the polishing of the substrate is started.

[0014] It is preferable that, before the polishing of the substrate is started, the polishing liquid has been supplied to, for example, sprinkled on, the carrier disposed on the lower surface plate and to a region of the lower surface plate that comes into contact with the substrate held by the carrier.

[0015] It is preferable that the substrate is a disk-shaped plate sewing as a base of a substrate for a magnetic disk.

[0016] Another aspect of the present invention is a method for producing a magnetic disk, including a step of performing the polishing processing of the above-described method for producing a substrate, and a step of forming a magnetic film on a surface of the substrate after the polishing processing.

For example, this production method includes:

a step of polishing main surfaces of a substrate with polishing pads while holding the substrate between an upper surface plate and a lower surface plate that are provided with the polishing pads and rotating the upper surface plate and the lower surface plate;

a step of, during polishing of the main surfaces, supplying a polishing liquid to an inner circumferential face of a center hole of the upper surface plate through which a central axis of rotation of the upper surface plate passes and allowing the polishing liquid to descend along the inner circumferential face while suppressing descending velocity of the polishing liquid using a descending velocity control means provided on the inner circumferential face, thereby supplying the polishing liquid between the substrate and the polishing pads through a gap between the upper surface plate and the lower surface plate; and

a step of producing a magnetic disk by forming a magnetic film on a surface of the substrate that has been polished.

[0017] Another aspect of the present invention is a polishing apparatus for polishing a substrate. This polishing apparatus includes:

an upper surface plate and a lower surface plate that are provided with polishing pads and configured to hold main surfaces of a substrate from opposite sides;

a rotating mechanism configured to rotate the upper surface plate and the lower surface plate relative to the substrate held between the upper surface plate and the lower surface plate in order to polish the main surfaces; a polishing liquid supply mechanism configured to supply a polishing liquid to an inner circumferential face of a center hole of the upper surface plate through which a central axis of rotation of the upper surface plate passes during polishing of the main surface; and

a descending velocity control means provided on the inner circumferential face and configured to suppress descending velocity of the polishing liquid descending along the inner circumferential face,

wherein the center hole is configured such that the polishing liquid with the descending velocity being suppressed by the descending velocity control means is supplied between the substrate and the polishing pads through a gap between the upper surface plate and the lower surface plate.

[0018] It is preferable that no openings for supplying the polishing liquid except for an opening of the center hole are provided in a lower opposing surface of the upper surface plate that opposes the lower surface plate.

[0019] It is preferable that the center hole has an inclined portion where the inner circumferential face is inclined at least 0 degrees and less than 90 degrees with respect to a lower opposing surface of the upper surface plate that opposes the lower surface plate so that a hole cross-sectional area of the center hole increases toward the lower opposing surface, the inclined portion being provided along a circumference of the opening.

[0020] It is preferable that at least a portion of the inner circumferential face includes an uneven portion as the descending velocity control means.

[0021] It is preferable that the uneven portion includes a groove-like depressed portion extending on the inner circumferential face.

[Advantageous Effects of the Invention]

[0022] According to the method for producing a substrate, the method for producing a magnetic disk, and the polishing apparatus, during polishing of main surfaces of a substrate, an opening of a through hole through which a polishing liquid is supplied does not constitute an obstacle, and precision polishing of the substrate can be realized. [Brief Description of Drawings]

[0023] FIG. 1 is an exploded perspective view of a polishing apparatus according to an embodiment of the invention.

FIG. 2 is a cross-sectional view of the polishing apparatus shown in FIG. 1.

FIGS. 3 A and 3B are diagrams each showing a descending velocity control portion that is used in a method for producing a substrate according to an embodiment of the invention.

FIG. 4 is a diagram for illustrating the configuration of a carrier that is used in the method for producing a substrate according the embodiment, and the arrangement of the carrier and an upper surface plate.

[Description of Embodiments]

[0024] Hereinafter, a method for producing a substrate, a method for producing a magnetic disk, and a polishing apparatus will be described in detail.

[0025] As described above, when polishing main surfaces of a substrate with polishing pads while holding the substrate between upper and lower surface plates provided with the polishing pads and rotating the upper and lower surface plates, an opening of a through hole through which a polishing liquid is supplied constitutes an obstacle to the movement of the carrier holding the substrate and causes damage to the polishing pad around the opening, thereby making it difficult to realize high precision polishing. Therefore, in an embodiment of the invention, the opening of the through hole through which the polishing liquid is supplied is disposed at a position different from a conventional position. Specifically, the polishing liquid is supplied to an inner circumferential face of a center hole of the upper surface plate through which the central axis of rotation of the upper surface plate passes and is allowed to flow and descend along the surface of the inner circumferential face and then flow into a gap between the upper surface plate and the lower surface plate from an opening of the center hole on a lower opposing surface side of the upper surface plate that opposes the lower surface plate. The polishing liquid is then supplied between the substrate and the polishing pads through this gap. That is to say, the polishing liquid is allowed to flow and descend along the surface of the inner circumferential face of the center hole and supplied to the gap between the upper surface plate and the lower surface plate. However, troubles are likely to occur as follows: it is difficult for the polishing liquid descending along the inner circumferential face to change its flowing direction at the opening of the center hole so as to flow along the lower opposing surface of the upper surface plate, and most of the polishing liquid flows down to an upper opposing surface side of the lower surface plate, and only a small amount of the polishing liquid flows along the lower opposing surface of the upper surface plate. It was found that such troubles can be explained by the following reason: since the polishing liquid descends along the inner circumferential face at a high descending velocity, the polishing liquid does not change its flowing direction along the lower opposing surface of the lower upper surface plate, and most of the polishing liquid is likely to flow down to the upper opposing surface side of the lower surface plate. Thus, in the present embodiment, a descending velocity control means that suppresses the descending velocity of the polishing liquid is provided on the inner circumferential face of the center hole. The wording “a descending velocity control means is provided” includes providing, for example, an uneven portion including a depressed portion and/or a protruding portion, etc., or an inclined portion, on the inner circumferential face of the center hole, and furthermore, also includes directing an outlet of a pipe for supplying the polishing liquid to the inner circumferential face in a horizontal direction (circumferential direction of the inner circumferential face), an upward direction that is orthogonal to the horizontal direction, or a direction that is inclined with respect to the horizontal direction or the upward direction, in order to increase the period of time for which the polishing liquid flowing along the inner circumferential face is in contact with the inner circumferential face and thereby suppress the descending velocity. In this manner, an appropriate amount of polishing liquid can be supplied to the upper opposing surface of the lower surface plate and, furthermore, to the lower opposing surface of the upper surface plate. Moreover, since an opening of a hole for supplying the polishing liquid is not provided in a region of the lower opposing surface of the upper surface plate that comes into contact with the substrate, the carrier does not cause damage to the polishing pad that is located around an edge of the opening. Thus, precision polishing of the substrate can be realized. In the following description, a glass plate G is used as a substrate to be polished, but it should be construed that the substrate is not limited to a glass substrate, and may also be a substrate made of a metal such as an aluminum alloy or a silicon substrate.

[0026] FIG. 1 is an exploded perspective view of a polishing apparatus (double-side polishing apparatus). FIG. 2 is a cross-sectional view of the polishing apparatus. A polishing apparatus 1 shown in FIG. 1 has a pair of upper and lower surface plates, that is, an upper surface plate 40 and a lower surface plate 60. An annular glass plate G is sandwiched between the upper surface plate 40 and the lower surface plate 60, and the upper surface plate 40 and the lower surface plate 60 are rotated to thereby move the glass plate G and each surface plate relative to each other. Thus, both main surfaces of the glass plate G can be polished. Note that a polishing liquid containing polishing abrasive particles is supplied between the glass plate G and polishing pads provided on the respective surface plates.

The upper surface plate 40 has a center hole 42 through which the central axis of rotation of the upper surface plate 40 passes. Furthermore, as a rotating mechanism configured to rotate the upper surface plate 40 and the lower surface plate 60 for the purpose of polishing the main surfaces, a rotating shaft 44 that rotates the upper surface plate 40 and a rotating shaft 64 that rotates the lower surface plate 60 are connected to the upper surface plate 40 and the lower surface plate 60, respectively, and a driving motor 50 is connected to the rotating shafts 44 and 64. Hereinafter, the upper surface plate 40 and the lower surface plate 60 may be collectively referred to simply as surface plates.

[0027] The configuration of the polishing apparatus 1 will be more specifically described with reference to FIGS. 1 and 2. In FIG. 2, the rotating shaft 44 is not shown.

In the polishing apparatus 1 , polishing pads 10 are attached to an upper opposing surface of the lower surface plate 60 and a lower opposing surface of the upper surface plate 40. The polishing pads 10 shown in FIG. 1 have a sheet-like shape. For example, a foamed urethane resin or the like can be used for the polishing pads 10.

The carrier 30 has a holding hole in which a circular plate-shaped glass plate G is held when the glass plate G is held between the upper surface plate 40 and the lower surface plate 60 and the main surfaces of the glass plate G are polished. Specifically, the carrier 30 has teeth portions 31 that are provided at an outer circumferential portion thereof and that engage with a sun gear 61 and an internal gear 62, as well as one or more holding holes (inner holes) 32, each for accommodating and holding a glass plate G. The sun gear 61 , the internal gear 62 provided in an outer edge, and the circular plate-shaped carrier 30 together constitute a planetary gear mechanism with a central axis CTR at its center. The circular plate-shaped carrier 30 engages with the sun gear 61 on an inner circumferential side, engages with the internal gear 62 on an outer circumferential side, and accommodates and holds one or more glass plates G. The carrier 30 serving as a planetary gear revolves on the lower surface plate 60 while rotating around its axis, and thus the glass plate G and the lower surface plate 60 are moved relative to each other. For example, when the sun gear 61 rotates in the counterclockwise direction, the carrier 30 rotates in the clockwise direction, and the internal gear 62 rotates in the counterclockwise direction. As a result, relative motion occurs between the polishing pad 10 provided on the lower surface plate 60 and the glass plate G. Similarly, the glass plate G and the upper surface plate 40 may be moved relative to each other.

[0028] While the above-described relative motion is occurring, the upper surface plate 40 is pressed against the glass plate G held by the carrier 30 (i.e., pressed in the vertical direction) with a predetermined pressure, and thus, the polishing pad 10 is pressed against the glass plate G.

A polishing liquid supply mechanism is provided which is configured to supply the polishing liquid to an inner circumferential face 42a of the center hole 42 of the upper surface plate 40, through which the central axis CTR of rotation of the upper surface plate 40 passes, during polishing of the main surfaces of the glass plate G. The polishing apparatus 1 includes, as the polishing liquid supply mechanism, a supply tank 71 in which the polishing liquid is stored, a pump (not shown) that supplies the polishing liquid from the supply tank 71 to the inner circumferential face 42a of the center hole 42 of the upper surface plate 40, and one or more pipes 72. In the thus configured polishing apparatus 1, a descending velocity suppressing portion 42b that suppresses the descending velocity of the polishing liquid descending along the inner circumferential face 42a is provided on the inner circumferential face 42a of the center hole 42.

[0029] Since the polishing apparatus 1 is configured as described above, in the method for producing a substrate including the substrate polishing processing, the main surfaces of the glass plate G are polished with the polishing pads 10 while the glass plate G is held between the upper surface plate 40 and the lower surface plate 60, which are provided with the polishing pads 10, and the upper surface plate 40 and the lower surface plate 60 are rotated. During polishing of the main surfaces of the glass plate G, the polishing liquid is supplied to the inner circumferential face 42a of the center hole 42 of the upper surface plate 40, through which the central axis CTR of rotation of the upper surface plate 40 passes, and is allowed to descend along the inner circumferential face 42a and supplied between the glass plate G and the polishing pads 10 through the gap between the upper surface plate 40 and the lower surface plate 60. Since the descending velocity suppressing portion 42b is provided on the inner circumferential face 42a, the descending velocity of the polishing liquid can be suppressed. Thus, the amount of polishing liquid that separates from the inner circumferential face 42a at the opening of the center hole

42 and flows downward can be reduced, and accordingly the amount of polishing liquid that is supplied to the lower opposing surface of the upper surface plate 40 is increased. Thus, the amount of polishing liquid that is supplied between the polishing pad 10 provided on the upper surface plate 40 and the glass plate G is increased, and precision polishing can be realized. Therefore, it is preferable that no openings for supplying the polishing liquid except for the opening of the center hole 42 are provided on the side of the surface of the upper surface plate 40 that polishes the glass plate G. This prevents the occurrence of a situation where an end of the carrier 30 is caught in the opening and causes damage to the polishing pad that is provided around the opening. Therefore, polishing blemishes and non-uniform polishing do not occur, and high precision polishing can be realized.

Note that, according to the present invention, since the polishing liquid can be supplied through the gap between the upper surface plate 40 and the lower surface plate 60 with high efficiency as described above, the size of the gap can be reduced. Therefore, the present invention is preferably used in the case where the size of the gap is 1 mm or less, more preferably in the case where the size of the gap is 0.7 m or less, and even more preferably in the case where the size of the gap is 0.6 m or less.

[0030] The size of the gap between the upper surface plate 40 and the lower surface plate 60 depends on the thickness of the glass plate G. In the case where the glass plate G is to be used as a substrate of a magnetic disk of an HDD apparatus, the thickness of the glass plate G is set to be, for example, 0.7 mm or less, or more preferably 0.6 m or less, in order to increase the number of magnetic disks installed in the HDD apparatus. The gap between the upper surface plate 40 and the lower surface plate 60 that is determined based on the thickness of the glass plate G as described above is extremely narrow. According to the foregoing embodiment, the polishing liquid can be efficiently supplied to the lower opposing surface of the upper surface plate 40 and the upper opposing surface of the lower surface plate 60 that demarcate this narrow gap.

[0031] FIG. 3 A is a diagram showing a preferred embodiment of the descending velocity control portion 42b. The descending velocity control portion 42b shown in FIG. 3 A is an inclined portion 42c, which is an inclined surface that is inclined with an inclination angle Q of at least 0 degrees and less than 90 degrees with respect to the lower opposing surface of the upper surface plate 40. That is to say, the inclined portion 42c where the inner circumferential face 42a is inclined with an inclination angle Q of at least 0 degrees and less than 90 degrees with respect to the lower opposing surface of the upper surface plate 40 so that the hole cross-sectional area of the center hole 42 increases toward the lower opposing surface of the upper surface plate 40 is provided along the circumference of the opening of the center hole 42. The inner circumferential face 42a along which a polishing liquid S flows due to surface tension constitutes the inclined portion 42c, which reduces the descending velocity of the polishing liquid S, and thus, a velocity component along the horizontal direction is produced. For this reason, the amount of polishing liquid S that separates from the inner circumferential face 42a at the opening of the center hole 42 and flows downward can be reduced, and accordingly the amount of polished liquid S that is supplied to the lower opposing surface of the upper surface plate 40 is increased. Thus, the amount of polishing liquid S that is supplied between the polishing pad 10 provided on the upper surface plate 40 and the glass plate G is increased, making it possible to perform precise polishing while suppressing non-uniform polishing and the like. From the standpoint of increasing the amount of polishing liquid S that is supplied to the lower opposing surface of the upper surface plate 40, it is preferable that the inclination angle Q of the inclined portion 42c with respect to the lower opposing surface of the upper surface plate 40 is 15 degrees to 75 degrees. Moreover, from the standpoint of reducing the descending velocity of the polishing liquid S and thereby increasing the amount of polishing liquid S that is supplied to the lower opposing surface of the upper surface plate 40, it is preferable that the length of the inclined portion 42c in a thickness direction of the upper surface plate 40 is 3 mm or more in terms of the length of the center hole 42 in the thickness direction of the upper surface plate 40. Although there is no particular upper limit to the above-described length, it is more preferable to set the above-described length to be 10 cm or less, for example, in order to prevent the area of the upper surface plate 40 from being excessively reduced by the inclined portion 42c. Moreover, although the inclined portion 42c is a surface with a fixed inclination angle 0 as described above, the inclination angle Q of another embodiment may vary, and, for example, the inclined portion 42c may be a curved surface that is rounded so that the inclination angle Q decreases downward, or may have a rounded shape with a predetermined radius of curvature. This radius of curvature is 3 mm to 50 mm, for example.

[0032] FIG. 3B is a diagram showing another preferred embodiment of the descending velocity control portion 42b. The descending velocity control portion 42b shown in FIG. 3B is an uneven portion 42d. The uneven portion 42d includes a protruding wall or a protrusion, a depression, or the like, and it is sufficient that the uneven portion 42d is uneven to such an extent that the descending velocity of the polishing liquid S is reduced. In other words, it is sufficient that the uneven portion 42d is a protruding portion and/or a depressed portion. The uneven portion 42d shown in FIG. 3B includes two depressions.

Moreover, according to another embodiment, the uneven portion 42d includes a groove-like depressed portion extending on the inner circumferential face 42a. With regard to the groove, side walls on both sides of the groove may be parallel surfaces or non-parallel surfaces, and there is no particular limitation on the cross-sectional shape of the groove. Also, the number of grooves is not limited to one, and a plurality of grooves may be provided. The width of the groove is 0.5 mm to 50 mm, for example. In the case where a plurality of grooves are provided, although there is no limitation on the distance between the grooves, the distance between the grooves is 0.5 mm to 10 mm, for example. Moreover, the depth of the groove is 0.5 mm to 30 mm, for example. The groove may go around, or may be interrupted midway without going around, the inner circumferential face 42a. Moreover, the extending direction of the groove may be parallel to or inclined with respect to the lower opposing surface.

According to another embodiment, the uneven portion 42d includes a ridge-like protruding portion extending on the inner circumferential face 42a. Side walls of on both sides of the protruding portion may be parallel surfaces or may be non-parallel surfaces, and there is no particular limitation on the cross-sectional shape of the protruding portion. Also, the number of protruding portions is not limited to one, and a plurality of protruding portions may be provided. The width of the protruding portion is 0.5 mm to 50 mm, for example. In the case where a plurality of protruding portions are provided, although there is no particular limitation on the distance between the protruding portions, the distance between the protruding portions is 0.5 mm to 10 mm, for example. Moreover, the height of the protruding portion is 0.5 mm to 30 mm, for example.

[0033] FIG. 4 is a diagram for illustrating the configuration of the carrier 30 according to another embodiment and the arrangement of the carrier 30 and the upper surface plate 40. As shown in FIG. 1, the carrier 30 is a plate-shaped member that holds the glass plate G in the holding hole (inner hole) 32. According to the embodiment shown in FIG. 4, the carrier 30 is arranged relative to the upper surface plate 40 so that, during polishing of the main surfaces of the glass plate G, the carrier 30 is held between the upper surface plate 40 and the lower surface plate 60 in a state in which it holds the glass plate G, and an outer circumferential portion of the carrier 30 receives the polishing liquid flowing down from the opening of the center hole 42 while passing through a position that is nearer to the central axis CTR of rotation than the position of an edge of the opening of the center hole 42. At this time, the outer circumferential portion of the carrier 30 includes an outer frame portion 34 that forms the outer circumference of the carrier 30 and a flat plate portion 36 that is surrounded by the outer frame portion 34. A portion of each of the outer frame portion 34 and the flat plate portion 36 on its circumference is located nearer to the central axis CTR of rotation than the position of the edge of the opening. The outer frame portion 34 bulges relative to the flat plate portion 36 (the outer frame portion 34 protrudes in the direction of the normal to the plane of the flat plate portion 36). Since the outer frame portion 34 bulges in this manner, the polishing liquid S flowing down onto the carrier 30 is less likely to flow to the outside of the carrier 30 and is more likely to be supplied between the polishing pad 10 provided on the lower surface plate 60 and the glass plate G. Thus, non-uniform polishing is unlikely to occur during polishing of the glass plate G that is in contact with the lower surface plate 60, and precision polishing can be performed. The outer frame portion 34 and the flat plate portion 36 of this carrier 30 may be configured as a single member or may be configured by combining a plurality of members.

Note that in the case where the gap between the upper surface plate 40 and the lower surface plate 42 is narrow, and the polishing liquid S overflows from this gap, the polishing liquid S flowing along the inner circumferential face 42a is pushed out of the gap and cannot easily enter the gap. In such a case, when the carrier 30 has the configuration having the outer frame portion 34 and the flat plate portion 36, the outer frame portion 34 makes it unlikely that the polishing liquid S leaks, and therefore, polishing can be efficiently performed. It is preferable to use this carrier 30 in the case where the size of the gap is 1 mm or less, more preferably in the case where the size of the gap is 0.7 mm or less, and even more preferably in the case where the size of the gap is 0.6 mm or less.

[0034] In the foregoing embodiment, since the polishing liquid S is supplied from the opening of the center hole 42, the farther away from the central axis CTR of rotation of the upper surface plate 40 and the lower surface plate 60, the smaller the amount of polishing liquid S that is supplied from the opening of the center hole 42 at an initial stage of polishing. For this reason, in order to efficiently perform polishing of a glass plate G that is located away from the central axis CTR of rotation at the initial stage of polishing, according to an embodiment, it is preferable to start polishing the glass plate G in a state in which the polishing liquid S has been contained in at least a portion of the gap between the upper surface plate 40 and the lower surface plate 60 before the polishing of the glass plate G is started. For example, it is preferable that the polishing liquid S has been supplied to the carrier 30, which is disposed on the lower surface plate 60, and a region of the lower surface plate 60 that is in contact with the glass plate G, which is held by the carrier

30, before polishing of the glass plate G is started. Although there is no particular limitation on the method for supplying the polishing liquid S, sprinkling, for example, can be adopted.

[0035] For example, the glass plate G is a disk-shaped plate serving as the base of a substrate for a magnetic disk. Since the main surfaces of substrates for magnetic disks have an extremely low surface roughness, the method for producing a glass plate in which the above-described polishing, with which precision polishing can be performed without non-uniform polishing, is beneficial when a disk-shaped plate serving as the base of a substrate for a magnetic disk is to be polished.

A magnetic disk is produced by forming a magnetic film on a surface of a glass plate that has been produced according to the foregoing embodiment.

[0036] While the method for producing a substrate, the method for producing a magnetic disk, and the polishing apparatus of the present invention have been described in detail above, the present invention is not limited to the foregoing embodiments, and various modifications and changes can of course be made to the present invention without departing from the gist of the present invention.

[List of Reference Numerals]

[0037] 1 Polishing apparatus

10 Polishing pad

30 Carrier

31 Teeth portions

32 Holding hole

40 Upper surface plate

42 Lower surface plate

42a Inner circumferential face

42b Descending velocity suppressing portion

42c Inclined portion

42d Uneven portion

44, 64 Rotating shaft

50 Driving motor

60 Lower surface plate

61 Sun gear

62 Internal gear

71 Supply tank

72 Pipe