JP2006095636A - Glass substrate carrier for magnetic recording medium, method for manufacturing glass substrate for magnetic disk, and method for manufacturing magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate carrier which is especially useful in the case of manufacturing a magnetic disk for floating and moving a magnetic head at a small floating height of at most 10 nm, a method for manufacturing a glass substrate for a magnetic disk utilizing the same glass substrate carrier, and a method for manufacturing a magnetic disk utilizing the same glass substrate. <P>SOLUTION: The glass substrate carrier comprises a glass substrate holding portion 41 which has holding holes 41a for holding glass substrates therein and has a disk-like shape as a whole, a gear portion 42 provided along the outside periphery of the glass substrate holding portion, and engagement portions 41b, 42b for engaging the glass substrate holding portion with the gear portion. Glass substrates are held within the range inside the circle having a radius of the engagement portions nearest to an origin that is the center of the glass substrate holding portion. The glass substrate for the magnetic disk is manufactured by holding the glass substrate in the glass substrate carrier and by mirror-polishing the surface of the glass substrate by relatively moving the glass substrate and polishing cloth while bringing them into contact with each other. Further, the magnetic disk is manufactured by forming at least a magnetic layer on the glass substrate for the magnetic disk. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a glass substrate carrier for a magnetic recording medium such as a magnetic disk mounted on a magnetic disk device such as an HDD (hard disk drive), a method for manufacturing a magnetic disk, and a method for manufacturing a glass substrate for a magnetic disk.

Today, information recording technology, particularly magnetic recording technology, is required to undergo dramatic technological innovation with the rapid development of IT industry. For a magnetic disk mounted on an HDD or the like, a technology capable of realizing an information recording density of 40 Gbit / inch ² or more is required in response to a request for a high capacity.
Recently, a glass substrate has attracted attention as a magnetic disk substrate suitable for increasing the recording density. Since the glass substrate has higher rigidity than the metal substrate, it is suitable for high-speed rotation of the magnetic disk device, and since a smooth and flat surface is obtained, it is easy to reduce the flying height of the magnetic head. It is suitable for improving the S / N ratio of the recording signal and increasing the recording density.

  In order to achieve such a high recording density, it is necessary to improve the smoothness of the glass substrate surface. Usually, a glass substrate for a magnetic disk is manufactured by grinding and polishing the surface of a glass disk formed in a predetermined size. Usually, in this polishing process, a polishing apparatus is used to remove scratches and distortions remaining in the grinding process, so that a hard polisher is used as the polisher, and the glass disk surface is polished by the first polishing process and the first polishing process. In order to finish the resulting flat surface while maintaining the flat surface, the process is divided into a second polishing step in which the glass disk surface is polished with a soft polisher instead of a hard polisher. Patent Document 1 below discloses a polishing carrier used to hold a substrate for polishing a magnetic disk substrate or the like, and a polishing method using the polishing carrier.

JP 2000-288920 A

Recently, information recording density of 60 Gbit / inch ² or higher has been required for HDDs. This is partly related to the fact that HDDs have been installed in mobile phones, car navigation systems, digital cameras, etc., in addition to the need for conventional computer storage devices.
In these new applications, the housing space for mounting the HDD is significantly smaller than that of a computer, so it is necessary to downsize the HDD. For this purpose, it is necessary to reduce the diameter of the magnetic disk mounted on the HDD. For example, a 3.5-inch type or 2.5-inch type magnetic disk could be used in a computer application, but in the case of the new application, a smaller diameter, for example, a 0.8-inch type to a 1.8-inch type is used. A small-diameter magnetic disk such as an inch type is used. Even when the diameter of the magnetic disk is reduced in this way, it is necessary to store a certain amount of information capacity, which will increase the speed of information recording.

  Also, in order to effectively use the limited disk area, an HDD of LUL (Load Unload) method has been used instead of the conventional CSS (Contact Start and Stop) method. In the LUL system, the magnetic head is retracted to a ramp called a ramp located outside the magnetic disk when stopped, and the magnetic head starts to slide on the magnetic disk after the magnetic disk starts rotating during start-up operation. Recorded and played back by flying. During the stop operation, the magnetic head is retracted to the ramp outside the magnetic disk, and then the rotation of the magnetic disk is stopped. This series of operations is called LUL operation. This is because the magnetic disk for the LUL method does not require a contact sliding area (CSS area) with the magnetic head as in the CSS system, and the recording / reproducing area can be enlarged, which is preferable for high information capacity. .

  In order to improve the information recording density under such circumstances, it is necessary to reduce the spacing loss as much as possible by reducing the flying height of the magnetic head. In order to achieve an information recording density of 60 gigabits or more per square inch, the flying height of the magnetic head needs to be 10 nm or less. Unlike the CSS method, the LUL method does not make contact between the magnetic head and the magnetic disk surface, so there is no need to provide an irregular shape to prevent adsorption on the magnetic disk surface, and the magnetic disk surface must be extremely smooth. Is possible. Therefore, in the magnetic disk for LUL method, the flying height of the magnetic head can be further reduced compared to the CSS method, so that the S / N ratio of the recording signal can be increased and the recording capacity of the magnetic disk device can be increased. There is also an advantage of being able to contribute.

  Due to a further drop in the flying height of the magnetic head accompanying the recent introduction of the LUL method, it has become necessary to operate the magnetic disk stably even at an extremely low flying height of 10 nm or less. However, when the magnetic head flies over the magnetic disk surface with such an extremely low flying height, a problem that fly stiction failure frequently occurs. The fly stiction failure is a failure in which the flying posture of the magnetic head suddenly becomes unstable during recording / reproduction, resulting in abnormal fluctuations in the recording signal and the reproduction signal.

When such a fly stiction failure occurs, the HDI (Head Disk Interface) reliability at the time of flying of the magnetic head, for example, LUL durability is greatly deteriorated. In addition, the magnetic head may be dropped on the surface of the magnetic disk during the flight and attracted, and the magnetic disk may be destroyed.
For this reason, when the flying height of the magnetic head is, for example, an extremely low flying height of 10 nm or less, it is difficult to maintain the flying stability of the magnetic head, and there is a problem that a head crash failure is likely to occur.
These faults tend to occur after a short time after HDDs are shipped to the market and incorporated into personal computers (PCs), etc. (HDD failures). For this reason, the widespread use of glass substrates for magnetic disks that can achieve high recording density has been hindered.

  In view of these circumstances, the present inventor has a magnetic disk and a magnetic disk that can be safely recorded and reproduced without causing a crash failure and a fly stiction failure even when the flying height of the magnetic head flies at 10 nm or less. Efforts were made to develop glass substrates. For example, the polishing abrasive grains are refined to perform precise mirror polishing, or the polishing method disclosed in, for example, Patent Document 1 is used, but it has been found that these obstacles may not always be reliably prevented. .

  The present invention has been made to solve these problems, and an object of the present invention is to manufacture a magnetic recording medium such as a magnetic disk for flying a magnetic head with a low flying height of 10 nm or less. A glass substrate carrier for a magnetic recording medium, a method for manufacturing a glass substrate for a magnetic disk using the glass substrate carrier, or a method for manufacturing a magnetic disk using a glass substrate manufactured by the manufacturing method Is to provide.

The present inventor examined the cause of the problem, and found that there was a concave streak defect (hereinafter referred to as a concave defect) on the glass substrate surface (particularly the outer periphery) of the magnetic disk that caused the failure. did. When such a concave defect exists on the surface of the glass substrate, the same concave defect also occurs on the surface of a magnetic disk manufactured using this glass substrate.
According to the study of the present inventor, the reason why such a concave defect is formed on the surface of the glass substrate is considered as follows.
That is, if there is a scratch or the like on the surface of the polishing cloth (for example, polishing pad) used in the polishing process, the surface of the polishing cloth is not smooth when the polishing cloth is pressed against the glass substrate surface and polished. For this reason, a concave defect is also formed on the glass substrate surface.

Conventionally, in a glass substrate for a magnetic disk, removal of convex foreign matters that adversely affect a magnetic head flying above has been focused on. Since the concave shape does not collide with the upper magnetic head, there is a situation that it has not been regarded as a problem so much. The present inventor has convinced that this concave defect may cause the above problem. This is because the flying height of the magnetic head has been further reduced compared to the prior art, and it was thought that the concave defect, which has not been regarded as a problem in the past, may have an adverse effect on the magnetic head.
Therefore, the present inventor firstly maintains the mirror surface state of the mirror-polished glass substrate surface, and secondly, a concave defect that adversely affects the magnetic head when the magnetic head passes above with a low flying height of 10 nm or less. The present invention was completed by conducting research with a focus on not forming.
That is, the present invention has the following configuration.

(Configuration 1) In a polishing process of a glass substrate for a magnetic recording medium including a process of relatively moving a glass substrate and a polishing cloth in contact with each other, the glass substrate and the glass substrate are rotated while holding the glass substrate inside. A glass substrate carrier for moving a polishing cloth relative to the glass substrate carrier, the glass substrate carrier having a holding hole for holding the glass substrate inside and a disk-shaped glass substrate holding portion as a whole, and the glass substrate holding A gear part provided along the outer periphery of the part, and an engaging part for engaging the glass substrate holding part and the gear part, and when the center of the glass substrate holding part is the origin, The glass substrate carrier for a magnetic recording medium, wherein the glass substrate is held in a region inside the radius of the engaging portion closest to the origin.
(Structure 2) The engaging portion is made of a material harder than a material of a portion of the glass substrate holding portion that comes into contact with the glass substrate. It is a glass substrate carrier.
(Structure 3) The glass substrate carrier for a magnetic recording medium according to Structure 1 or 2, wherein a portion of the glass substrate holding portion that contacts the glass substrate is made of a resin material.

(Configuration 4) A disk-shaped glass substrate is held on the glass substrate carrier according to any one of Configurations 1 to 3, and the glass substrate and the polishing cloth are moved relative to each other while being brought into contact with each other to mirror the surface of the glass substrate. A method for producing a glass substrate for a magnetic disk, comprising a step of polishing.
(Configuration 5) A polishing surface plate provided with a sun gear at the center, an internal gear provided on an outer edge of the polishing surface plate, and the glass substrate carrier meshed with the sun gear and the internal gear. A method of manufacturing a glass substrate for a magnetic disk comprising a step of mirror polishing the surface of a glass substrate, wherein a polishing cloth is attached to the polishing surface plate, and a gear portion of the glass substrate carrier is connected to the sun gear. While meshing with the internal gear, holding the glass substrate on the glass substrate carrier, and rotating and driving at least one of the sun gear and the internal gear, the glass substrate and the polishing cloth are brought into contact with each other. 5. The method of manufacturing a glass substrate for a magnetic disk according to Configuration 4, wherein the surface of the glass substrate is mirror-polished by being relatively moved.
(Structure 6) A magnetic disk manufacturing method, wherein at least a magnetic layer is formed on a glass substrate for a magnetic disk obtained by the manufacturing method according to Structure 4 or 5.

The present invention is described in detail below.
A glass substrate carrier for a magnetic recording medium according to the present invention is a polishing process for a glass substrate for a magnetic recording medium, including a process of moving the glass substrate and a polishing cloth in contact with each other, as in Configuration 1. A glass substrate carrier that rotates while holding the glass substrate therein and relatively moves the glass substrate and the polishing cloth, and the glass substrate carrier has a holding hole for holding the glass substrate inside. And a glass substrate holding part having a disk shape as a whole, a gear part provided along the outer periphery of the glass substrate holding part, and an engaging part for engaging the glass substrate holding part and the gear part. When the center of the glass substrate holding portion is the origin, the glass substrate is held in a region inside the radius of the engaging portion that is closest to the origin. .

  FIG. 1 shows a configuration of an embodiment of the glass substrate carrier according to the present invention, where (a) is a plan view of a gear portion and (b) is a plan view of a glass substrate holding portion. In the glass substrate carrier of the present invention, the glass substrate holding portion and the gear portion provided along the outer periphery of the glass substrate holding portion are configured as separate members. And are integrated. Thus, the material suitable for each member can be used by comprising a glass substrate holding | maintenance part and a gear part by another member.

The gear part 42 shown to Fig.1 (a) comprises the annular | circular shape, and the tooth | gear 42a is formed in the outer peripheral part over the whole outer periphery. For convenience, in FIG. 1A, only a part of the outer periphery shows the teeth 42a. Further, on the inner peripheral portion of the gear portion 42, engagement convex portions 42 b that fit into engagement concave portions of a glass substrate holding portion described later are formed at a plurality of locations at substantially equal intervals.
The gear portion 42 is preferably made of a hard material so as to mesh with a sun gear and an internal gear in a double-side polishing apparatus described later, for example. The material of the gear part 42 is preferably a metal material, for example, stainless steel excellent in mechanical durability and wear resistance is preferable.

  On the other hand, the glass substrate holding portion 41 shown in FIG. 1 (b) has a disc shape as a whole, and there are a plurality of engaging recesses 41b fitted on the outer periphery of the engaging recesses 41b of the gear portion 42 described above. It is formed at approximately equal intervals in the place. The glass substrate holding part 41 has a plurality of holding holes 41a for holding the glass substrate. Then, when the center of the glass substrate holding portion 41 is the origin C, it is in a region inside the radius R1 of the engagement portion (here, the engagement recess 41b) closest to the origin C, that is, The holding hole 41a is provided in a region having A as the outer periphery so that the glass substrate is held. In the configuration of the present embodiment, the radius R1 to the engagement recess 41b with respect to the origin C is configured to be the same length.

In the glass substrate holding portion 41, it is preferable that at least a portion of the holding hole 41a that contacts the glass substrate is made of a resin material. Of course, from the viewpoint of moldability, it is preferable that the entire glass substrate holding portion 41 is made of a resin material. Examples of the resin material include resin materials such as aramid fiber, FRP (glass epoxy), and polycarbonate.
By engaging the engagement convex portion 42b and the engagement concave portion 41b, the glass substrate holding portion 41 is fitted to the gear portion 42 and integrated so that they do not move in the rotation direction. It is a glass substrate carrier.

Here, the configuration of the glass substrate carrier in which the conventional glass substrate holding portion and the gear portion are configured as separate members will be described.
FIG. 2A is a plan view showing a configuration of a gear portion of a conventional glass substrate carrier, and FIG. 2B is a plan view showing a configuration of a glass substrate holding portion. In addition, the same code | symbol is attached | subjected to the location equivalent to FIG. 1, and the overlapping description is abbreviate | omitted.
The configuration of the gear portion is substantially the same, but the glass substrate holding portion has a radius to the engagement recess 41b closest to the origin C when the center of the glass substrate holding portion 41 is the origin C. A part of the outermost holding hole 41a protrudes from a region inside R2, that is, a region having B as an outer periphery.

  In this way, the disk-shaped glass substrate is held on the glass substrate carrier of the present invention having a different configuration from the conventional glass substrate carrier, and the glass substrate and the polishing cloth are moved relative to each other while being in contact with each other. By mirror polishing, it is possible to suppress the occurrence of concave defects as seen on the glass substrate surface after the conventional mirror polishing process. As a result, magnetic disks manufactured using this glass substrate are HDD When mounted on the magnetic head, fly stiction failure can be prevented even in a low flying environment where the flying height of the magnetic head is 10 nm or less, and the flying stability of the magnetic head can be suitably maintained.

FIG. 3 is a longitudinal sectional view showing a schematic configuration of a planetary gear type double-side polishing apparatus.
The double-side polishing apparatus shown in FIG. 3 meshes with the sun gear 2, the internal gear 3 disposed concentrically on the outside thereof, the sun gear 2 and the internal gear 3, and responds to the rotation of the sun gear 2 and the internal gear 3. The upper surface plate 5 and the lower surface plate 6 to which the carrier 4 that revolves and rotates and the polishing cloth (for example, the polishing pad) 7 that can hold the workpiece 1 held by the carrier 4 are attached, A polishing liquid supply unit (not shown) for supplying a polishing liquid is provided between the surface plate 5 and the lower surface plate 6.
With such a double-side polishing apparatus, the workpiece 1 held on the carrier 4 (the glass substrate carrier of the present invention), that is, the glass substrate is held between the upper surface plate 5 and the lower surface plate 6 during mirror polishing. While the polishing liquid is supplied between the polishing cloth 7 of the upper and lower surface plates 5 and 6 and the workpiece 1, the carrier 4 revolves and rotates according to the rotation of the sun gear 2 and the internal gear 3, The upper and lower surfaces of the polished workpiece 1 are polished.

Examples of the glass for producing the glass substrate in the present invention include aluminosilicate glass and soda lime glass. Aluminosilicate glass is preferable because it can be made of chemically strengthened glass because high rigidity can be obtained. Alternatively, amorphous glass or crystallized glass including amorphous and crystals can be used.
Such glass, as an amorphous aluminosilicate _glass, SiO 2: 58-75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: _{3~10 wt%,} Na 2 O: _4~ It is preferably made of an aluminosilicate glass containing 13% by weight as a main component.
Furthermore, the composition of the glass _disc, SiO 2: _{62~75 wt%, Al} 2 O 3: _{5~15 wt%,} Li 2 O: _{4~10 wt%,} Na 2 O: _4~12 wt%, ZrO ₂ : While containing 5.5 to 15% by weight as a main component, the weight ratio of Na ₂ O / ZrO ₂ is 0.5 to 2.0, and the weight ratio of Al ₂ O ₃ / ZrO ₂ is 0.4 to An aluminosilicate glass of 2.5 is preferred.
Further, in order to eliminate protrusions on the glass disk surface caused by the undissolved material of ZrO ₂ , SiO ₂ is 57 to 74%, ZnO ₂ is 0 to 2.8%, Al ₂ O ₃ is 3 in terms of mol%. It is preferable to use a glass for chemical strengthening containing ˜15%, LiO ₂ ˜7-16% and Na ₂ O 4˜14%.

Such aluminosilicate glass is chemically strengthened to increase the bending strength, the depth of the compressive stress layer is deep, and the Knoop hardness is excellent. The chemical strengthening method is not particularly limited as long as it is a conventionally known chemical strengthening method, but chemical strengthening by a low-temperature ion exchange method is preferable in practice.
There is no particular limitation on the diameter size of the glass substrate according to the present invention. The thickness of the glass substrate is preferably about 0.1 mm to 1.5 mm. In particular, in the case of a magnetic disk composed of a thin substrate of about 0.1 mm to 0.9 mm, a glass substrate for a magnetic disk having high impact resistance can be provided.

  In the present invention, the magnetic disk is manufactured by forming at least a magnetic layer on the magnetic disk glass substrate according to the present invention. As the magnetic layer material, a hexagonal CoPt ferromagnetic alloy having a large anisotropic magnetic field can be used. As a method for forming the magnetic layer, a method of forming a magnetic layer on a glass substrate by sputtering, for example, DC magnetron sputtering can be used. Further, by interposing an underlayer between the glass substrate and the magnetic layer, the orientation direction of the magnetic grains of the magnetic layer and the size of the magnetic grains can be controlled. For example, by using a cubic base layer such as a Cr-based alloy, for example, the magnetization easy direction of the magnetic layer can be oriented along the magnetic disk surface. In this case, a magnetic disk of the in-plane magnetic recording system is manufactured. Further, for example, by using a hexagonal underlayer containing Ru or Ti, for example, the easy magnetization direction of the magnetic layer can be oriented along the normal of the magnetic disk surface. In this case, a perpendicular magnetic recording type magnetic disk is manufactured. The underlayer can be formed by sputtering as with the magnetic layer.

  In the present invention, a protective layer and a lubricating layer are preferably formed in this order on the magnetic layer. As the protective layer, an amorphous hydrogenated carbon-based protective layer is suitable. For example, the protective layer can be formed by a plasma CVD method. The thickness of the protective layer is preferably 30 angstroms to 80 angstroms. Further, as the lubricating layer, a lubricant having a functional group at the end of the main chain of the perfluoropolyether compound can be used. In particular, it is preferable that the main component is a perfluoropolyether compound having a terminal hydroxyl group as a polar functional group. The film thickness of the lubricating layer is preferably 5 angstroms to 15 angstroms. The lubricating layer can be applied and formed by a dip method.

  According to the present invention, a glass substrate carrier for a magnetic recording medium, which is particularly useful when manufacturing a magnetic recording medium such as a magnetic disk for flying a magnetic head with a low flying height of 10 nm or less, or To provide a method for producing a glass substrate for a magnetic disk comprising a step of mirror polishing the surface of a glass substrate using the glass substrate carrier, or a method for producing a magnetic disk using a glass substrate produced by the production method. it can.

Hereinafter, embodiments of the present invention will be specifically described with reference to examples. In addition, this invention is not limited to a following example.
Example 1
(1) Rough lapping step (rough grinding step), (2) Shape processing step, (3) Fine lapping step (fine grinding step), (4) End surface polishing step, (5) Main surface polishing step, (6 ) A glass substrate for a magnetic disk of this example was manufactured through a chemical strengthening step.

(1) Coarse lapping process First, a glass disk made of aluminosilicate glass having a diameter of 66 mmφ and a thickness of 1.5 mm was obtained from molten glass by direct pressing using an upper mold, a lower mold, and a body mold. In this case, in addition to the direct press, a glass disk may be obtained by cutting out from a sheet glass formed by a downdraw method or a float method with a grinding wheel. As the aluminosilicate _glass, SiO 2: _{58~75 wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: _{3~10 wt%,} Na 2 O: _4~13 chemical containing wt% Tempered glass was used. Next, a lapping process was performed on the glass disk in order to improve dimensional accuracy and shape accuracy. This lapping process was performed using a double-sided lapping machine and using abrasive grains having a particle size of # 400. Specifically, first, alumina abrasive grains of particle size # 400 are used, the load is set to about 100 kg, and the sun gear and the internal gear of the lapping device are rotated, so that both surfaces of the glass disk stored in the carrier are faced. Lapping was performed with an accuracy of 0 to 1 μm and a surface roughness (Rmax) of about 6 μm.

(2) Shape processing step Next, a cylindrical grindstone is used to make a hole in the center portion of the glass disk, and the outer peripheral end face is ground to a diameter of 65 mmφ. Chamfered. The surface roughness of the end surface of the glass disk at this time was about 4 μm in Rmax. In general, a 2.5-inch HDD (hard disk drive) uses a magnetic disk having an outer diameter of 65 mm.
(3) Fine lapping step Next, the grain size of the abrasive grains was changed to # 1000 and the surface of the glass disk was lapped so that the surface roughness was about 2 μm in Rmax and about 0.2 μm in Ra. The glass disk which finished the said lapping process was immersed in each washing tank (ultrasonic application) of neutral detergent and water sequentially, and ultrasonic cleaning was performed.
(4) End face polishing step Next, the surface roughness of the end face (inner circumference, outer circumference) of the glass disk was polished to about 1 μm at Rmax and about 0.3 μm at Ra while rotating the glass disk by brush polishing. And the surface of the glass disk which finished the said end surface grinding | polishing was water-washed.

(5) Main surface polishing step Next, a first polishing step for removing scratches and distortions remaining in the lapping step described above was performed using the double-side polishing apparatus shown in FIG. In this case, the glass substrate carrier of the present invention having the configuration shown in FIG. 1 was used. The material of the gear part of the glass substrate carrier is stainless steel (SUS316), and the material of the glass substrate holding part is FRP (glass epoxy). In the double-side polishing apparatus, the glass substrate (the glass disk) held by the glass substrate carrier is brought into close contact between the upper and lower polishing surface plates 5 and 6 to which the polishing pad 7 is attached, and the gear portion of the glass substrate carrier is connected to the sun. The glass substrate is engaged with the gear 2 and the internal gear 3, and the glass substrate is clamped by the upper and lower surface plates 5 and 6. Thereafter, the polishing liquid is supplied and rotated between the polishing pad 7 and the polishing surface of the glass substrate, so that the glass substrate revolves while rotating on the surface plates 5 and 6, and both surfaces are polished simultaneously. is there. Specifically, a hard polisher (hard foamed urethane) was used as the polisher, and the first polishing step was performed. As polishing conditions, the polishing liquid was RO water in which cerium oxide (average particle size 1.3 μm) was dispersed as an abrasive, and the polishing time was 15 minutes. The glass substrate after the first polishing step was sequentially immersed in each cleaning bath of neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying), ultrasonically cleaned, and dried. .

  Subsequently, the same double-side polishing apparatus as that used in the first polishing step was used, and the second polishing step was performed by replacing the polisher with a polishing pad of soft polisher (suede). Also in this case, the glass substrate carrier of the present invention having the configuration shown in FIG. 1 was used as in the first polishing step. This second polishing step is, for example, mirror polishing for finishing the surface roughness of the glass substrate main surface to a smooth mirror surface with an Rmax of about 6 nm or less while maintaining the flat surface obtained in the first polishing step. It is processing. The polishing conditions were RO water in which cerium oxide (average particle size 0.8 μm) was dispersed as the polishing liquid, and the polishing time was 5 minutes. The glass substrate after the second polishing step was sequentially immersed in each cleaning bath of neutral detergent, pure water, pure water, IPA, and IPA (steam drying), ultrasonically cleaned, and dried.

(6) Chemical strengthening process Next, the chemical strengthening process was performed to the glass substrate which finished the said washing | cleaning. The chemical strengthening treatment was performed by preparing a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed, heating the chemical strengthening solution to 380 ° C., and immersing the cleaned and dried glass substrate for about 4 hours. . The glass substrate after chemical strengthening was sequentially immersed in each of washing tanks of sulfuric acid, neutral detergent, pure water, pure water, IPA, and IPA (steam drying), ultrasonically cleaned, and dried.
Further, when the surface roughness of the main surface of the glass substrate obtained through the above steps was measured with an atomic force microscope (AFM), it had an ultra-smooth surface with Rmax = 2.13 nm and Ra = 0.20 nm. A glass substrate was obtained. The obtained glass substrate had an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.635 mm.
Thus, 100 glass substrates for magnetic disks of this example were obtained. The main surface of the obtained glass substrate was subjected to visual inspection and precise inspection using light reflection / scattering / transmission. As a result, none of the glass substrates had a concave defect on the main surface and was finished to a good mirror surface.

Next, the following film formation process was performed on the magnetic disk glass substrate obtained in this example to obtain a magnetic disk.
A seed layer, an underlayer, a magnetic layer, a protective layer, and a lubricating layer were sequentially formed on the glass substrate using a single wafer sputtering apparatus.
As the seed layer, a first seed layer made of a CrTi thin film (film thickness: 30 nm) and a second seed layer made of an AlRu thin film (film thickness: 40 nm) were formed. The underlayer was a CrW thin film (film thickness: 10 nm) and was provided in order to improve the crystal structure of the magnetic layer. In addition, this CrW thin film is comprised by the composition ratio of Cr: 90at% and W: 10at%.
The magnetic layer is made of a CoPtCrB alloy and has a thickness of 20 nm. The contents of Co, Pt, Cr, and B in this magnetic layer are Co: 73 at%, Pt: 7 at%, Cr: 18 at%, and B: 2 at%.
The protective layer is for preventing the magnetic layer from deteriorating due to contact with the magnetic head, and is made of hydrogenated carbon having a thickness of 5 nm, and wear resistance is obtained. The lubricating layer is formed by perfluoropolyether liquid lubricant by dipping and has a thickness of 0.9 nm.

Next, the obtained magnetic disk was evaluated as follows.
[Reliability evaluation]
When the obtained magnetic disk was evaluated for glide characteristics, the touchdown height was 4.5 nm. Touchdown height lowers the flying height of the flying head in order (for example, lowers the rotational speed of the magnetic disk), finds the flying height that starts to contact the magnetic disk, and determines the flying height of the magnetic disk. In order to measure the capability, normally, an HDD that requires a recording density of 60 Gbit / inch ² or more is required to have a touchdown height of 5 nm or less.

  The obtained magnetic disk was mounted on a load / unload hard disk drive (HDD) having a maximum recording density of 60 gigabits per square inch. The flying height of the magnetic head mounted on this hard disk drive is 10 nm, and an NPAB slider (negative pressure slider) is adopted as the slider. The reproducing element is a magnetoresistive effect type reproducing element. When this hard disk drive was tested, there was no head crash failure or fly stiction failure, and recording and reproduction could be performed safely. The load / unload operation was repeated 600,000 times, but there was no failure. It is said that a normally used HDD needs to be used for about 10 years in order for the number of load / unload operations to exceed 600,000 times. From this, it can be seen that the magnetic disk of this embodiment can guarantee high reliability.

(Comparative example)
In the (5) main surface polishing step of Example 1, a polishing treatment was performed using the glass substrate carrier having the configuration shown in FIG. The material of the gear part and the glass substrate holding part of the glass substrate carrier is the same as that of the first embodiment.
Except this point, 100 glass substrates for magnetic disks were obtained in the same manner as in Example 1. When the main surface of the obtained glass substrate was observed in detail, there was a substrate in which a concave defect was observed on the main surface. In particular, many concave defects were observed on the outer peripheral side of the main surface of the glass substrate. In addition, when the surface of the polishing pad used for the polishing process was observed, scratches were observed, which is considered to be one of the causes of the concave defects on the glass substrate surface.

Further, a magnetic disk was manufactured in the same manner as in Example 1 using the glass substrate in which the concave defect was recognized.
When the glide characteristic of the obtained magnetic disk was evaluated, the touchdown height was 5.4 nm. Furthermore, when tested for LUL durability, it failed due to a head crash after 300,000 LUL operations.

It is a top view of the glass substrate carrier which concerns on this invention. It is a top view of the glass substrate carrier of a prior art example. It is a longitudinal cross-sectional view which shows schematic structure of a double-side polish apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Workpiece 2 Sun gear 3 Internal gear 4 Glass substrate carrier 5 Upper surface plate 6 Lower surface plate 7 Polishing cloth (polishing pad)
41 Glass substrate holding part 41a Holding hole 42 Gear part

Claims (6)

In the polishing process of the glass substrate for a magnetic recording medium including the process of relatively moving the glass substrate and the polishing cloth in contact with each other, the glass substrate and the polishing cloth are rotated while holding the glass substrate inside. A relatively moving glass substrate carrier,
The glass substrate carrier has a holding hole for holding the glass substrate therein and has a disk-shaped glass substrate holding portion as a whole, a gear portion provided along the outer periphery of the glass substrate holding portion, and the glass substrate An engaging portion that engages the holding portion and the gear portion, and when the center of the glass substrate holding portion is the origin, it is inside the radius of the engaging portion that is closest to the origin A glass substrate carrier for a magnetic recording medium, characterized in that the glass substrate is held in the region.   2. The glass substrate carrier for a magnetic recording medium according to claim 1, wherein the engaging portion is made of a material harder than a material of a portion of the glass substrate holding portion that contacts the glass substrate. .   3. The glass substrate carrier for a magnetic recording medium according to claim 1, wherein a portion of the glass substrate holding portion that comes into contact with the glass substrate is made of a resin material.   A disk-shaped glass substrate is held on the glass substrate carrier according to any one of claims 1 to 3, and the surface of the glass substrate is mirror-polished by relatively moving the glass substrate and a polishing cloth in contact with each other. The manufacturing method of the glass substrate for magnetic discs characterized by including a process.   Using a polishing platen provided with a sun gear at the center, an internal gear provided on the outer edge of the polishing platen, and the glass substrate carrier meshed with the sun gear and the internal gear, A method of manufacturing a glass substrate for a magnetic disk including a step of mirror polishing a surface of a substrate, wherein a polishing cloth is attached to the polishing surface plate, and a gear portion of the glass substrate carrier is connected to the sun gear and the internal gear. The glass substrate is held on the glass substrate carrier, and at least one of the sun gear and the internal gear is rotationally driven to move the glass substrate and the polishing cloth in contact with each other. The method for producing a glass substrate for a magnetic disk according to claim 4, wherein the surface of the glass substrate is mirror-polished. 6. A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer on a glass substrate for a magnetic disk obtained by the manufacturing method according to claim 4 or 5.

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