JP2009006422A - Manufacturing method of glass substrate for magnetic disc, manufacturing method of magnetic disc, and polishing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent reduction of a matching degree of an upper surface plate and a lower surface plate generated due to the entry of polishing liquid into a gap between the lower surface plate and a lower surface plate supporting part and aggregation of polishing agent in the gap. <P>SOLUTION: A planetary gear type polishing device is provided with a polishing liquid supply part for supplying the polishing liquid between the upper surface plate and the lower surface plate. The polishing device is provided with a sealing means 15 between a sun gear 30 and the lower surface plate 10 to prevent entering of the polishing liquid into the gap between the lower surface plate 10 and the lower surface plate supporting part 12. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk including a step of polishing a glass substrate while supplying a polishing liquid, a method for manufacturing a magnetic disk, and a polishing apparatus for polishing both or one side of an object to be polished.

2. Description of the Related Art Conventionally, a polishing apparatus is known that uses a substrate (particularly a glass substrate) used for a photomask for lithography, a magnetic disk, a liquid crystal display, or the like as an object to be polished and polishes both surfaces or one surface thereof.
This type of polishing apparatus sets an object to be polished in a work holding hole of a carrier and sandwiches the object between an upper surface plate and a lower surface plate to polish both surfaces or one surface of the object to be polished. A planetary gear type is often used.

  The planetary gear type polishing device is engaged with the sun gear, the internal gear concentrically arranged on the outer side, the sun gear and the internal gear, and revolves and rotates according to the rotation of the sun gear and the internal gear. Carrier, an upper surface plate and a lower surface plate capable of sandwiching an object to be polished held from above and below, and a polishing liquid supply unit for supplying a polishing liquid between the upper surface plate and the lower surface plate Yes.

During polishing, the object to be polished held by the carrier is sandwiched between the upper surface plate and the lower surface plate, and the polishing liquid is supplied between the polishing surface (polishing pad) of the upper and lower surface plates and the object to be polished. The carrier revolves and rotates according to the rotation of the gear and the internal gear.
In such a polishing apparatus, a donut-shaped region between the sun gear and the internal gear and sandwiched between the upper surface plate and the lower surface plate is an actual polishing region. The polishing liquid is supplied to this donut-shaped polishing region through a polishing liquid supply hole formed in the upper surface plate.

Various polishing liquids in which fine polishing particles such as cerium oxide and silica (silicon dioxide) are dispersed in a liquid such as water and an alkaline solution are selectively used according to the purpose of polishing. .
At this time, the polishing liquid supplied between the upper surface plate and the lower surface plate is discharged through a groove provided in a lower surface plate supporting portion that supports the lower surface plate (for example, Patent Document 1).

  In recent years, the recording density of magnetic disks has been improved. In order to improve the recording density, it is necessary to reduce the spacing cross. Specifically, it is necessary to reduce the distance between the magnetic disk and the recording head. For example, in a recent HDD, the distance between the magnetic disk and the recording head is 10 nm or less.

  In the case of a perpendicular magnetic recording type magnetic disk, it is necessary to further reduce the distance between the magnetic disk and the recording head, but in order to reduce the distance between the magnetic disk and the recording head, it is necessary to There is a need to produce magnetic disks with reduced surface roughness. And in order to manufacture such a magnetic disk, it is necessary to reduce the surface roughness of the glass substrate for magnetic disks which is the board | substrate.

JP 2001-319505 A (FIG. 1)

However, it has been found that even when sufficiently fine abrasive particles are selected so that a desired surface roughness can be obtained, a surface roughness exceeding the allowable level occurs on the substrate.
As a result of investigation by the present inventor, the occurrence of surface roughness exceeding the allowable level is caused by the fact that the abrasive in the polishing liquid discharged through the groove of the lower surface plate support part supporting the lower surface plate is the lower surface plate and the lower surface plate. It was found that this was because it entered between the support part and aggregated here.

  In the polishing apparatus described in Patent Document 1, a groove is formed in a lower platen support portion that supports the lower platen. FIG. 3 shows this portion in detail. That is, a groove 203 (reference number in Patent Document 1) for discharging the polishing solution radially from the center of a lower surface plate support section 202 (reference number 2 in Patent Document 1) that supports the lower surface plate 201 (reference number 2 in Patent Document 1). (None) are formed. Part of the polishing liquid supplied between the lower surface plate and the upper surface plate flows from the center hole 201a of the lower surface plate 201 through the groove 203 of the lower surface plate support portion 202 and returns to the storage portion outside the apparatus. ing.

  By the way, in the planetary gear type polishing apparatus, the sun gear normally protrudes from a hole formed in the center of the lower surface plate, so that the polishing liquid is discharged from this hole into the groove of the lower surface plate support portion. However, in this case, the polishing liquid flowing in the groove 203 of the lower surface plate support portion enters the gap between the lower surface of the lower surface plate 201 and the upper surface of the bank portion 204 of the lower surface plate support portion, and the abrasive is aggregated here. Sometimes. Then, once the abrasive is agglomerated, the abrasive is accumulated and agglomerated with the core as the core, and the lower surface plate is partially lifted (raised).

When the lower surface plate partially lifts from the lower surface plate support part, when polishing while applying pressure by the upper surface plate, the pressure applied to the polished material acts strongly on the raised surface of the lower surface plate and the lower surface plate and upper surface plate The degree of match is shifted.
In this way, if a polished object such as a glass substrate for a magnetic disk is polished in a state where the degree of matching between the lower surface plate and the upper surface plate is shifted, polishing with a uniform pressure applied to the entire polished material cannot be performed. There is a problem that a desired surface roughness cannot be obtained.
In particular, when manufacturing a magnetic disk, a further reduction in the flying height of the magnetic head is required in order to achieve a high recording density. To achieve this, it is extremely high compared to the glass substrate for a magnetic disk. Smoothness is required. This smoothness has strict requirements not only on the roughness of the main surface of the glass substrate but also on the shape of the edge of the substrate.
Specifically, for example, as the roughness (Ra) of the main surface of the glass substrate, severe conditions such as 0.3 nm or less are required, and abrasive grains are provided between the lower surface plate and the lower surface plate support part. The present inventor has found that the above requirement cannot be achieved even by entering.

  The present invention has been considered in view of the above circumstances, and a magnetic disk glass substrate having a desired surface roughness is polished by polishing a magnetic disk glass substrate in a state in which the degree of matching between the lower surface plate and the upper surface plate is maintained. By providing a method for producing a glass substrate for a magnetic disk that can be obtained, and by preventing the polishing liquid from entering the gap between the lower surface plate support part and the lower surface plate and aggregating the abrasive here, An object of the present invention is to provide a polishing apparatus that can prevent the distance between the lower surface plate and the upper surface plate from partially changing and improve the degree of matching between the lower surface plate and the upper surface plate.

  In order to achieve the above object, a method for producing a glass substrate for a magnetic disk according to the present invention supplies a polishing liquid between an upper surface plate and a lower surface plate that sandwich a glass substrate as an object to be polished, and the glass substrate In the method of manufacturing a glass substrate for a magnetic disk using a polishing apparatus for polishing the substrate, the method includes a polishing step of polishing the glass substrate while maintaining the degree of coincidence between the lower surface plate and the upper surface plate.

In the present invention, it is preferable that in the polishing step, the glass substrate is polished while preventing the polishing liquid from entering the gap between the lower surface plate and the lower surface plate supporting portion that supports the lower surface plate.
Moreover, it is preferable that the average particle diameter of the abrasive grain which the said polishing liquid contains is 3 micrometers or less, and it is preferable that the abrasive grain is silicon dioxide.
In the polishing step, polishing is preferably performed so that the surface roughness (Ra) of the glass substrate is 0.3 nm or less.

  The magnetic disk manufacturing method of the present invention is a method including a step of forming at least a magnetic layer on the surface of the magnetic disk glass substrate manufactured by the method for manufacturing a magnetic disk glass substrate.

In order to achieve the above object, the polishing apparatus of the present invention includes an upper surface plate and a lower surface plate that sandwich an object to be polished, a lower surface plate support portion that supports the lower surface plate, the upper surface plate and a lower surface plate, In a polishing apparatus provided with a polishing liquid supply unit for supplying a polishing liquid between
Sealing means is provided for preventing the polishing liquid from entering the gap between the lower surface plate and the lower surface plate support portion.

  If the polishing apparatus is configured in this way, the polishing liquid does not enter the gap between the lower surface plate and the lower surface plate support portion and the abrasive does not aggregate, so that the degree of matching between the lower surface plate and the upper surface plate can be maintained. . Therefore, if polishing is performed using this polishing apparatus, a polished product having a desired surface roughness can be obtained.

When the polishing apparatus is a planetary gear type polishing apparatus in which a sun gear protrudes from a hole formed in the center of the lower surface plate, the sealing means is provided between the lower surface plate and the sun gear. It is preferable.
It is preferable to provide at least one or more through holes penetrating from the approximate center of the lower surface plate to the outer peripheral surface in the lower surface plate. In this case, the sealing means is located more centrally than the entrance of the upper surface of the lower surface plate. It is preferable to provide in.

In the polishing apparatus of the present invention, the sealing means is preferably a V-ring having a V-shaped cross section, and the V-ring is particularly preferably attached via a flange member.
When a V-ring is used as the sealing means, the area of the portion in contact with the rotating portion of the sealing means can be reduced, so that the wear of the sealing means is small even if the polishing apparatus is operated for a long time. As a result, it is possible to polish a polished object having a reduced surface roughness over a long period of time.
Further, when the V-ring is attached via the flange member, the V-ring can be easily attached and detached, and maintenance can be performed in a short time.

In the polishing apparatus of the present invention, the sealing means may be a shielding member formed at the lower end of the outer periphery of the lower surface plate.
If it does in this way, the polishing liquid which tries to enter into the gap | interval of both from the outer peripheral surface side of a lower surface plate and a lower surface plate support part can be interrupted | blocked.

According to the present invention, since it is possible to reliably prevent the polishing liquid from entering the gap between the lower surface plate and the lower surface plate support portion, it is possible to prevent the abrasive from aggregating in the gap between the lower surface plate and the lower surface plate support portion.
Therefore, it is possible to obtain a polished product with reduced surface roughness, for example, a magnetic disk glass substrate with a high yield. Further, since the glass substrate can be polished without changing the degree of coincidence between the lower surface plate and the upper surface plate, the shape of the end portion of the glass substrate for a magnetic disk can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Description of polishing apparatus]
First, a polishing apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 is a cross-sectional view of a polishing apparatus, and FIG. 2 is an enlarged cross-sectional view for explaining a main part of FIG.
As shown in these drawings, the polishing apparatus includes a planetary gear type polishing processing unit including a lower surface plate 10, an upper surface plate 20, a sun gear 30, an internal gear 40, a carrier 50, a polishing liquid supply unit 60, and the like. It has.

The lower surface plate 10 is a disk member having an annular horizontal upper surface, and a polishing pad 11 is attached to the upper surface. The lower surface of the lower surface plate 10 is fixed to a lower surface plate support 12 that can rotate about a vertical axis A (a vertical axis that passes through the center of the polishing portion). The lower surface plate support unit 12 is linked to the lower surface plate rotation drive unit 13, and rotates according to the drive to rotate the lower surface plate 10.
The lower surface plate 10 may be fixed so as not to rotate.

The upper surface plate 20 is a disk member having an annular horizontal lower surface, and a polishing pad 21 is attached to the lower surface facing the lower surface plate 10. The upper surface of the upper surface plate 20 is fixed to an upper surface plate support portion 22 that can rotate about the vertical axis A. The upper surface plate support unit 22 is linked to the upper surface plate rotation driving unit 23, and rotates according to the drive to rotate the upper surface plate 20.
Further, the upper surface plate 20 and the upper surface plate support portion 22 are supported so as to be movable up and down along the vertical axis A, and are moved up and down in accordance with the drive of the upper surface plate lifting and lowering drive portion 24 via a connector (not shown). Is done.
The upper surface plate 20 may be fixed so as not to rotate.

The sun gear 30 is rotatably provided at the center position of the polishing unit, and is rotated through a drive shaft 32 in accordance with the drive of the sun gear rotation drive unit 31. However, when rotating the internal gear 40, the sun gear 30 may be fixed so as not to rotate.
Moreover, although the sun gear 30 of the present embodiment is a spur gear in which a tooth row is integrally formed on a side surface portion, it may be a pin gear or the like.

The internal gear 40 is a ring-shaped gear having a tooth row on the inner peripheral side, and is arranged concentrically outside the sun gear 30. The internal gear 40 of the present embodiment is fixed so as not to rotate, but is rotatable about the vertical axis A and rotates according to the drive of an internal gear rotation drive unit (not shown). You may do it.
Further, in the internal gear, a pin gear or the like may be used in addition to the spur gear.

The carrier (planetary gear) 50 is a thin plate-like disk member having a tooth row on the outer peripheral portion, and one or a plurality of workpiece holding holes 50a for holding an object to be polished are formed.
The carrier 50 may be of a double carrier type in which a holder for the object to be polished is loosely inserted into a hole formed in the carrier.

A plurality of carriers 50 are usually arranged in the polishing portion. These carriers 50 mesh with the sun gear 30 and the internal gear 40 and rotate while revolving around the sun gear 30 according to the rotation of the sun gear 30 or the internal gear 40.
That is, the upper and lower surfaces of the object to be polished are polished by holding the object to be polished held by the carrier 50 between the upper surface plate 20 and the lower surface plate 10 and revolving and rotating the carrier 50 in this state.

  In such a polished portion, the outer diameters of the upper surface plate 20 and the lower surface plate 10 are usually smaller than the inner diameter of the internal gear 40, and between the sun gear 30 and the internal gear 40 and above A donut-shaped region sandwiched between the surface plate 20 and the lower surface plate 10 is an actual polishing region.

The polishing liquid supply unit 60 supplies a polishing liquid storage unit 61 that stores the polishing liquid, and supplies the polishing liquid stored in the polishing liquid storage unit 61 to a polishing region between the upper surface plate 20 and the lower surface plate 10. And a plurality of tubes 62 serving as polishing liquid supply paths.
The polishing liquid reservoir 61 is formed in an annular shape on a horizontal plane, and is provided above the upper surface plate support 22 via a plurality of support members 63.

  A plurality of through holes 22 a, 20 a, and 21 a communicating with each other are formed in the upper surface plate support portion 22, the upper surface plate 20, and the polishing pad 21, and the upper ends of the tubes 62 are connected thereto. Thereby, the polishing liquid stored in the polishing liquid storage part 61 is supplied to the polishing region between the upper surface plate 20 and the lower surface plate 10 through the tube 62 and the through holes 22a, 20a, and 21a.

[Polishing liquid]
As the polishing liquid, one in which fine abrasive particles are dispersed in a liquid is generally used.
The abrasive particles are, for example, silicon carbide, aluminum oxide, cerium oxide, zirconium oxide, manganese oxide, colloidal silica, and the like, and are appropriately selected according to the material of the object to be polished, the processed surface roughness, and the like.
These abrasive particles are dispersed in a liquid such as water, an acidic solution, or an alkaline solution to obtain a polishing liquid.
Further, the size of the abrasive particles (abrasive abrasive grains) is not limited, but the present polishing apparatus uses an abrasive particle having a small particle diameter to provide an extremely smooth object to be polished (especially a magnetic disk). It is suitable when obtaining a glass substrate for use. In particular, when polishing grains having an average particle diameter of 3 μm or less are used, this polishing apparatus is particularly suitable when extremely smoothness is required for an object to be polished.

[Polished object]
The present invention is useful for planar polishing using a flat substrate as an object to be polished. Surface polishing includes double-side polishing and single-side polishing.
As such an object to be polished, an information recording medium such as a photomask blank substrate for forming a photomask used for lithography, a substrate for forming a liquid crystal display device, a magnetic disk, an optical disk, or a magneto-optical disk is formed. For example, a semiconductor wafer or the like.

Examples of the shape of the object to be polished include a rectangle, a circle, a disk, and a block shape.
Examples of the material of the object to be polished include glass, crystallized glass, silicon, compound semiconductors (such as silicon carbide and GaAs), metals (such as aluminum, titanium, and platinum), and carbon.
In particular, it is useful for polishing glass substrates for magnetic disks whose surface roughness affects device performance.
In particular, the present invention is particularly suitable when the surface roughness (Ra) is 0.3 nm or less, preferably 0.2 nm or less, more preferably 0.1 nm or less (measured by AFM). . In particular, a glass substrate for a magnetic disk is mentioned as a suitable example.

Next, the main part of the polishing apparatus according to this embodiment will be described with reference to FIG.
In the planetary gear type polishing apparatus in which the sun gear protrudes from the hole formed in the center of the lower surface plate, the polishing liquid flows between the lower surface plate and the sun gear. Therefore, according to the present invention, the sealing liquid is sealed between the lower surface plate and the sun gear so that the polishing liquid does not enter the gap between the lower surface plate and the lower surface plate support portion.
[Sealing means]
As shown in FIGS. 1 and 2, a flange member 14 is provided in the center hole of the lower surface plate 10 of the polishing apparatus. The flange member 14 is formed to be positioned below the sun gear 30 and supports the drive shaft 32 via a bearing.
Further, a stepped portion 14a having a higher center side is formed on the inner peripheral side of the flange member 14, and a peripheral groove 14b is formed on the outer peripheral side thereof. A seal ring so-called V-ring 15 having a V-shaped cross section is attached to the stepped portion 14 a of the flange member 14. The V-ring 15 is in contact with the lower surface of the sun gear 30 so that the polishing liquid does not enter between the lower surface plate 10 and the sun gear 30.
As the ring for sealing, in addition to the V-ring, for example, an O-ring can be used. However, considering the contact area with the lower surface of the sun gear 30, it is preferable to use a V-ring that has a small contact area and can be used for a long time.
Further, the number of the staircase portions and the V rings can be plural.
In this way, the polishing liquid enters the gap between the lower surface plate and the lower surface plate support portion, and the abrasive does not aggregate here. The surface roughness of the polished article is not reduced.

Further, an inlet 16 a of the through hole 16 is formed in the circumferential groove 14 b of the flange member 14. The through-hole 16 is connected to an inlet 16 a formed in the flange member 14 and is provided so as to penetrate in the radial direction inside the lower surface plate 10. The outlet 16 b of the through hole 16 is provided on the outer peripheral surface of the lower surface plate 10. The number of through holes 16 is not limited to one, and a plurality of through holes 16 may be provided radially.
When such a through hole 16 is provided, the polishing liquid flowing into the center side of the lower surface plate 10 is collected in the circumferential groove 14 b of the flange member 14 and is discharged out of the lower surface plate 10 through the through hole 16. . Accordingly, since only a small amount of polishing liquid flows between the lower surface plate 10 and the sun gear 30, sufficient sealing can be performed even if the sealing ring is simple. Further, the polishing liquid supplied at the time of polishing and flowing to the center side of the lower platen can be discharged from almost the center of the lower platen. Accordingly, since the amount of polishing liquid flowing toward the sealing means can be reduced, the sealing means can be simplified.

In the embodiment shown in FIGS. 1 and 2, since the flange member 14 is separately provided and coupled to the lower surface plate 10, an O-ring 17a, a connecting surface between the lower surface plate 10 and the flange member 14, and a through hole connecting portion are provided. 17b is provided. In this way, it is possible to prevent the polishing liquid from leaking from the joint surface and the through hole connecting portion, and to reliably prevent the polishing liquid from entering the gap between the lower surface plate 10 and the lower surface plate support portion 12.
The flange member 14 may be formed integrally with the lower surface plate 10.

A shielding member 18 is provided at the outer peripheral lower end of the lower surface plate 10 over the entire circumference.
The shielding member 18 is provided with a plate-like member suspended from the lower end of the lower surface plate 10 and covers the boundary between the lower surface plate 10 and the lower surface plate support portion 12. In this way, the polishing liquid discharged from the polishing surface of the lower surface plate 10 and the outlet 16 b of the through hole 16 is prevented from entering the gap between the lower surface plate 10 and the lower surface plate support portion 12.
Thus, by preventing the polishing liquid from entering the gap between the lower surface plate 10 and the lower surface plate support portion 12 from the outer peripheral direction, the polishing liquid completely enters the gap between the lower surface plate 10 and the lower surface plate support portion 12. Can be prevented.

  Although not shown, the discharged polishing liquid is collected in the tank via a predetermined recovery path, and then again returned to the polishing liquid reservoir 61 via a reduction path intervening with a pump and a filter. Sent to.

Although one embodiment of the polishing apparatus of the present invention has been described, the present invention is not limited to this embodiment.
For example, depending on the form of the polishing apparatus, only the sealing means formed between the lower surface plate 10 and the sun gear 30 is provided on the inner peripheral side of the lower surface plate 10, or provided at the lower end of the lower surface plate 12 on the outer peripheral side of the lower surface plate. Alternatively, only sealing means comprising the shielding member 18 may be employed.

[Method of manufacturing glass substrate for magnetic disk]
Next, an embodiment according to the method for producing a glass substrate for a magnetic disk of the present invention will be described.
First, in a state where the rotation of the lower surface plate 10, the upper surface plate 20, and the sun gear 30 (internal gear 40) is stopped, the upper surface plate 20 is raised and the lower surface plate 10 and the upper surface plate 20 are separated. In this state, a magnetic disk glass substrate is set in the work holding hole 50a of the carrier 50.

The upper surface plate 20 is lowered, the glass substrate for magnetic disk held by the carrier 50 is sandwiched between the upper surface plate 20 and the lower surface plate 10, and the polishing liquid is supplied from the polishing liquid supply unit 60 to the polishing region, and the lower surface plate 10. The upper surface plate 20 and the sun gear 30 (internal gear 40) are rotated to start polishing.
The carrier 50 holding the magnetic disk glass substrate rotates while revolving around the sun gear 30 according to the rotation operation of the sun gear 30 (internal gear 40).

In the present embodiment, the polishing liquid that has flowed to the center side of the lower surface plate 10 during polishing is collected in the circumferential groove 14b and discharged to the outside of the lower surface plate 10 through the through hole 16 from the inlet 16a formed in the circumferential groove 14b. To do. At this time, the V-ring prevents the polishing liquid from entering between the lower surface plate 10 and the sun gear 30 from entering.
Further, the polishing liquid that has flowed to the outer peripheral side of the lower surface plate 10 and the polishing liquid discharged from the outlet 16 b through the through hole 16 are blocked by the shielding member 18, and the gap between the lower surface plate 10 and the lower surface plate support portion 12. It is discharged outside without entering.
In the embodiment of the present invention, the magnetic disk glass substrate is manufactured by such a manufacturing method including a polishing step.

〔Example〕
Below, an example which manufactures the glass substrate for magnetic discs using the polish device concerning the present invention is explained.
In this example, a glass substrate for a magnetic disk and a perpendicular magnetic recording disk were manufactured through the following steps (1) to (10).
(1) Shape processing step First, a multicomponent glass substrate made of amorphous glass was prepared. The glass type of the glass is aluminosilicate glass, and the specific chemical composition is 63.5 wt% for SiO ₂ , 14.2 wt% for Al ₂ O _3, 10.4 wt% for Na ₂ O, Li ₂ O. Was 5.4% by weight, ZrO ₂ was 6.0% by weight, Sb ₂ O ₃ was 0.4% by weight, and As ₂ O ₃ was 0.1% by weight.
This glass substrate was formed by a direct press method to obtain a disk-shaped glass substrate. And the hole was made in the center part of the glass substrate using the grindstone, and it was set as the disk-shaped glass substrate which has a circular hole in the center part. Further, the outer peripheral end face and the inner peripheral end face were chamfered.

(2) End face polishing step Subsequently, the surface roughness of the end face (inner circumference, outer circumference) of the glass substrate by brush polishing while rotating the glass substrate is about 1.0 μm at the maximum height (Rmax), arithmetic average roughness The thickness (Ra) was polished to about 0.3 μm.

(3) Grinding Step Subsequently, the surface of the glass substrate was ground by using # 1000 abrasive grains so that the flatness of the main surface was 3 μm, Rmax was about 2 μm, and Ra was about 0.2 μm. Here, the flatness is a distance (height difference) in the vertical direction (direction perpendicular to the surface) between the highest portion and the lowest portion of the substrate surface, and was measured by a flatness measuring device. Rmax and Ra were measured with an atomic force microscope (AFM) (Digital Instruments Nanoscope).

(4) Pre-polishing step Subsequently, the pre-polishing step was performed using a polishing apparatus capable of polishing both main surfaces of 100 to 200 glass substrates at a time. A hard polisher was used for the polishing pad. A polishing pad previously containing zirconium oxide and cerium oxide was used.
The polishing liquid in the preliminary polishing step was prepared by mixing water with cerium oxide polishing abrasive grains having an average particle diameter of 1.1 μm. The abrasive grains having a grain diameter exceeding 4 μm were previously removed. When the polishing liquid was measured, the maximum value of the abrasive grains contained in the polishing liquid was 3.5 μm, the average value was 1.1 μm, and the D50 value was 1.1 μm.
In addition, the load applied to the glass substrate was 80 to 100 g / cm ^2, and the removal thickness of the surface portion of the glass substrate was 20 to 40 μm.

(5) Mirror polishing process Subsequently, the mirror polishing process was implemented using the polisher concerning the above-mentioned embodiment. A soft polisher was used for the polishing pad.
The polishing liquid in the mirror polishing step was prepared by adding sulfuric acid and tartaric acid to ultrapure water, and further adding colloidal silica particles having a grain diameter of 40 nm. At this time, the sulfuric acid concentration in the polishing liquid was set to 0.15% by weight, and the pH value of the polishing liquid was set to 2.0. The concentration of tartaric acid was 0.8% by weight, and the content of colloidal silica particles was 10% by weight. The electrical conductivity of the polishing liquid was measured and found to be 6 mS / cm.
In the mirror polishing process, the pH value of the polishing liquid was not changed and could be kept almost constant. In this example, the polishing liquid supplied to the surface of the glass substrate was collected using a drain, cleaned by removing foreign substances with a mesh filter, and then reused by supplying it to the glass substrate again.
The polishing speed in the mirror polishing process is 0.25 μm / min, and it has been found that an advantageous polishing speed can be realized under the above-described conditions. The polishing speed was determined by dividing the amount of reduction in glass substrate thickness (processing allowance) required for finishing to a predetermined mirror surface by the required polishing time.

(6) Cleaning step after mirror polishing treatment Subsequently, the glass substrate was immersed in an aqueous NaOH solution having a concentration of 3 to 5 wt% to perform alkali cleaning. Cleaning was performed by applying ultrasonic waves. Furthermore, it wash | cleaned by immersing in each washing tank of neutral detergent, a pure water, a pure water, and isopropyl alcohol (steam drying) one by one. When the surface of the glass substrate after cleaning was observed with an AFM (Nanoscope manufactured by Digital Instruments), the maximum peak height (Rp) was 1.8 nm, and the arithmetic average roughness (Ra) was 0.25 nm. Moreover, adhesion of colloidal silica abrasive grains was not confirmed. Also, no foreign matter such as stainless steel or iron was found. Furthermore, the end shape was also good.

(7) Chemical strengthening treatment step Subsequently, a washed glass substrate preheated to 300 ° C. in a chemically strengthened salt obtained by mixing potassium nitrate (60%) and sodium nitrate (40%) and heating to 375 ° C. Chemical strengthening treatment was performed by immersion for 3 hours. By this treatment, lithium ions and sodium ions on the surface of the glass substrate are respectively replaced with sodium ions and potassium ions in the chemically strengthened salt, and the glass substrate is chemically strengthened.
In addition, the thickness of the compressive stress layer formed on the surface of the glass substrate was about 100 to 200 μm. After carrying out the chemical strengthening, the glass substrate was immersed in a 20 ° C. water bath, quenched, and maintained for about 10 minutes.

(8) Cleaning step after chemical strengthening Subsequently, the glass substrate after the rapid cooling is immersed in sulfuric acid heated to about 40 ° C. and washed while applying ultrasonic waves to complete the production of the glass substrate for the magnetic disk. did.

(9) Magnetic disk manufacturing process Subsequently, on the glass substrate for a magnetic disk manufactured as described above, an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoTaZr-based alloy, and an underlayer made of Ru on the surface of the glass substrate A perpendicular magnetic recording disk was manufactured by sequentially forming a perpendicular magnetic recording layer made of a CoCrPt-based alloy, a protective layer made of hydrogenated carbon, and a lubricating layer made of perfluoropolyether.

(10) Magnetic Disk Inspection Process Subsequently, the magnetic disk manufactured as described above was inspected.
First, a head crash test was carried out in which a flying head was floated on a magnetic disk using an inspection head having a flying height of 8 nm. As a result, the magnetic head did not come into contact with a foreign object or the like, and no crash failure occurred.
Next, a recording / reproducing test by a perpendicular recording method was performed using a magnetic head in which the reproducing element portion was a magnetoresistive element, the recording element portion was a single magnetic pole element, and the flying height was 8 nm. It was confirmed that information was recorded and reproduced normally. At this time, recording / reproduction could be performed at 100 gigabits per square inch without detecting a thermal asperity signal as a reproduction signal.
Next, a glide height test of the magnetic disk was performed. In this test, the flying height of the inspection head is gradually decreased, and the flying height at which the inspection head and the magnetic disk come into contact is confirmed. As a result, in the magnetic disk according to this example, no contact occurred even when the flying height was 4 nm from the inner edge portion to the outer edge portion of the magnetic disk. At the outer edge portion of the magnetic disk, the glide height was 3.7 nm.

[Comparative example]
A glass substrate for a magnetic disk was manufactured in the same manner as in the example except that the conventional polishing apparatus not provided with the sealing means was used for the mirror polishing process.
As a result, each time the batch was repeated, the surface roughness of the glass substrate after the mirror polishing treatment was rough, and the end shape was also deteriorated.

The present invention relates to a photomask blank substrate for forming a photomask used for lithography, a substrate for forming a liquid crystal display device, a substrate for forming an information recording medium such as a magnetic disk, an optical disk, a magneto-optical disk, It can be effectively used for polishing a semiconductor wafer or the like.
In particular, it can be suitably used for polishing an object whose surface roughness is important, such as a magnetic disk glass substrate.

It is sectional drawing of a grinding | polishing apparatus. It is an expanded sectional view for demonstrating the principal part of the grinding | polishing apparatus shown in FIG. It is a figure for demonstrating the discharge path of the polishing liquid in the conventional grinding | polishing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Lower surface plate 11 Polishing pad 12 Lower surface plate support part 13 Lower surface plate rotation drive part 14 Flange part 14b Circumferential groove 15 V ring 16 Through hole 18 Shielding member 20 Upper surface plate 21 Polishing pad 22 Upper surface plate support part 22a Through hole 23 Upper Surface plate rotation drive unit 24 Upper surface plate lift drive unit 30 Sun gear
31 Sun gear rotation drive unit 32 Sun gear drive shaft
40 Internal gear 50 Carrier 50a Workpiece holding hole 60 Polishing liquid supply part 61 Polishing liquid storage part

Claims (9)

In a method of manufacturing a glass substrate for a magnetic disk using a polishing apparatus that supplies a polishing liquid between an upper surface plate and a lower surface plate that sandwich a glass substrate that is an object to be polished, and polishes the glass substrate,
A method for producing a glass substrate for a magnetic disk, comprising a polishing step of polishing a glass substrate while maintaining a degree of coincidence between the lower surface plate and the upper surface plate.   The polishing process is characterized in that the glass substrate is polished while preventing the polishing liquid from entering a gap between the lower surface plate and a lower surface plate support part that supports the lower surface plate. Item 2. A method for producing a glass substrate for a magnetic disk according to Item 1.   The method for producing a glass substrate for a magnetic disk according to claim 1 or 2, wherein an average particle diameter of the abrasive grains contained in the polishing liquid is 3 µm or less.   4. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the abrasive grains are silicon dioxide.   The said grinding | polishing process grind | polishes so that the surface roughness (Ra) of a glass substrate may be 0.3 nm or less, The manufacture of the glass substrate for magnetic discs as described in any one of Claims 1-4 characterized by the above-mentioned. Method.   A method for producing a magnetic disk comprising the step of forming at least a magnetic layer on the surface of a glass substrate for a magnetic disk produced by the method according to claim 1. An upper surface plate and a lower surface plate that sandwich an object to be polished, a lower surface plate support unit that supports the lower surface plate, and a polishing liquid supply unit that supplies a polishing liquid between the upper surface plate and the lower surface plate In the polishing machine
A polishing apparatus comprising a sealing means for preventing the polishing liquid from entering a gap between the lower surface plate and the lower surface plate support portion. The polishing apparatus is a planetary gear type polishing apparatus in which a sun gear protrudes from a hole formed in the center of the lower surface plate,
The polishing apparatus according to claim 7, wherein the sealing means is provided between the lower surface plate and the sun gear.   The polishing apparatus according to claim 7 or 8, wherein at least one through-hole penetrating from an approximately center of the lower surface plate to an outer peripheral surface is provided in the lower surface plate.

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