WO2013099585A1

WO2013099585A1 - Method for manufacturing glass substrate for information storage medium

Info

Publication number: WO2013099585A1
Application number: PCT/JP2012/082015
Authority: WO
Inventors: 葉月中江
Original assignee: コニカミノルタ株式会社
Priority date: 2011-12-28
Filing date: 2012-12-11
Publication date: 2013-07-04
Also published as: JPWO2013099585A1

Abstract

This method involves a step (S60) in which, while supplying to the surface of a glass substrate a polishing liquid containing, as abrasive grains, any of cerium oxide, zirconium oxide and zirconium silicate, the surface of the glass substrate is roughly polished by sliding contact with a polishing pad, a step (S65) in which, after the glass substrate has been removed from the polishing pad, the surface of the glass substrate is acid-washed while supplying an acidic cleaning liquid to the surface of the glass substrate, and a step (S70) for forming a compressive stress layer on the surface of the glass substrate after acid washing. When the glass substrate is removed from the polishing pad, said removal is performed with the glass substrate in a state in contact with the liquid having a 0.5-10w% abrasive grain concentration.

Description

Manufacturing method of glass substrate for information recording medium

The present invention relates to a method for manufacturing a glass substrate for information recording media, and in particular, manufacturing a glass substrate for information recording media mounted as part of an information recording medium in an information recording device such as a hard disk drive (HDD). Regarding the method.

Information recording devices such as hard disk drives are built in various devices such as computers. Such an information recording apparatus is equipped with an information recording medium such as a magnetic disk formed in a disk shape. The information recording medium is manufactured by forming a magnetic recording layer for magnetic recording on the main surface of a glass or aluminum substrate.

A glass substrate used for manufacturing an information recording medium is referred to as an information recording medium glass substrate (hereinafter also simply referred to as a glass substrate). A method for manufacturing a glass substrate for an information recording medium is disclosed in, for example, Japanese Patent Application Laid-Open No. 2010-165420 (Patent Document 1).

Information storage devices such as hard disk drives are expanding their usage and usage environment year by year. The demands on information recording devices for increasing capacity, impact resistance, heat resistance, and the like tend to increase year by year. With this trend, various things are required also for the glass substrate for information recording media. For example, in order to achieve an increase in capacity of an information recording medium, a glass substrate is required to have high cleanliness and high smoothness. Furthermore, in addition to the improvement of impact resistance, the glass substrate is required not to deteriorate in characteristics under various usage environments.

In order to improve impact resistance as a glass substrate, chemical strengthening treatment (also referred to as ion exchange treatment) is generally performed. In the chemical strengthening treatment, ions on the surface layer of the glass substrate (glass base plate) are exchanged for ions having an ion radius larger than the ions. By forming the compressive stress layer on the surface of the glass substrate, it becomes possible to improve the impact resistance as the glass substrate.

Generally, the chemical strengthening treatment is performed after the precision polishing process for the glass base plate. In recent years, as the demand for high smoothness of a glass substrate increases, a precision polishing step may be performed after the chemical strengthening treatment. In this case, in order to improve the smoothness of the surface of the glass substrate, the chemical strengthening treatment is performed after the rough polishing process is performed using cerium oxide or zirconium oxide. After the chemical strengthening treatment, precision polishing is performed using colloidal silica or the like. By performing a precision polishing step after the chemical strengthening treatment, the surface of the glass substrate can have a high smoothness with a surface roughness of 1 to 2 mm.

On the other hand, various cleaning methods are being studied in order to increase the cleanliness of the surface of the glass substrate. For example, in order to increase the cleanliness of the surface of the glass substrate, the abrasive grains remaining on the surface of the glass substrate are washed away using a cleaning liquid containing a strong acid or HF after the rough polishing step. After performing rough polishing on the surface of the glass substrate, polishing abrasive grains remaining on the surface of the glass substrate are washed away (referred to as a rinsing step).

JP 2010-165420 A

Assume that after the rinsing process is performed on the glass substrate after the rough polishing process, the glass substrate is subjected to acid cleaning, and further the chemical strengthening treatment is performed on the glass substrate after the acid cleaning. The present inventors have found that some of the glass substrates obtained in this way are inferior in impact resistance. Specifically, the present inventors conducted a drop impact test under a certain condition (for example, a high temperature and high humidity state) on an information recording apparatus in which the glass substrate is mounted as an information recording medium. It was found that the impact resistance of the glass substrate obtained was lowered.

The present invention is a glass for an information recording medium capable of suppressing the impact resistance of the obtained glass substrate from being lowered even when a chemical strengthening treatment is performed after the rough polishing step and before the precision polishing step. An object is to provide a method for manufacturing a substrate.

A method for producing a glass substrate for an information recording medium according to the present invention provides a polishing machine including a polishing pad, and a glass base plate containing a polishing liquid containing any one of cerium oxide, zirconium oxide, or zirconium silicate as abrasive grains. A step of performing rough polishing by sliding the polishing pad against the surface of the glass base plate while removing the glass base plate after the rough polishing from the polishing pad, While supplying an acidic cleaning liquid to the surface of the glass base plate, acid cleaning is performed on the surface of the glass base plate, and alkali metal ions contained in the glass base plate after the acid cleaning are included. Forming a compressive stress layer on the surface of the glass base plate by ion exchange with a chemically strengthened salt having an ionic radius larger than the ionic radius, and When the glass base plate after the rough polishing is removed from the polishing pad, the glass base plate is in contact with a liquid having a concentration of the polishing abrasive grains of 0.5 w% to 10 w%. Removed from the polishing pad.

Preferably, the cleaning liquid used in the acid cleaning step includes sulfuric acid and / or hydrofluoric acid. Preferably, the chemical strengthening salt used in the step of forming the compressive stress layer includes sodium ions and potassium ions.

According to the present invention, even when the chemical strengthening treatment is performed after the rough polishing step and before the precision polishing step, the information recording medium capable of suppressing the impact resistance of the obtained glass substrate from being lowered. A method for producing a glass substrate for use can be obtained.

It is a perspective view which shows an information recording device provided with the glass substrate manufactured by using the manufacturing method of the glass substrate for information recording media in embodiment. It is a top view which shows the glass substrate manufactured by the manufacturing method of the glass substrate for information recording media in embodiment. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. It is a top view which shows the information recording medium provided with the glass substrate manufactured by the manufacturing method of the glass substrate for information recording media in embodiment as an information recording medium. FIG. 5 is a cross-sectional view taken along line VV in FIG. 4. It is a flowchart figure which shows each process of the manufacturing method of the glass substrate for information recording media in embodiment. It is sectional drawing which shows the double-side polish machine used for the rough polishing process of the manufacturing method of the glass substrate for information recording media in embodiment. It is a flowchart figure which shows each process of the manufacturing method of the glass substrate for information recording media in a comparative example. It is a figure which shows the experimental condition and experimental result of the experiment example performed regarding embodiment.

Embodiments and examples based on the present invention will be described below with reference to the drawings. In the description of the embodiments and the examples, when the number, amount, and the like are referred to, the scope of the present invention is not necessarily limited to the number, amount, and the like unless otherwise specified. In the description of the embodiment and each example, the same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated.

[Embodiment]
(Information recording device 30)
First, the information recording device 30 will be described with reference to FIG. FIG. 1 is a perspective view showing the information recording apparatus 30. The information recording apparatus 30 includes the glass substrate 1 manufactured by the method for manufacturing a glass substrate for information recording medium (hereinafter also simply referred to as a glass substrate) in the embodiment as the information recording medium 10.

Specifically, the information recording device 30 includes an information recording medium 10, a housing 20, a head slider 21, a suspension 22, an arm 23, a vertical shaft 24, a voice coil 25, a voice coil motor 26, a clamp member 27, and a fixing screw. 28. A spindle motor (not shown) is installed on the upper surface of the housing 20.

An information recording medium 10 such as a magnetic disk is rotatably fixed to the spindle motor by a clamp member 27 and a fixing screw 28. The information recording medium 10 is rotationally driven by this spindle motor at, for example, several thousand rpm. Although details will be described later with reference to FIGS. 4 and 5, in the information recording medium 10, a compression stress layer 12 (see FIG. 5) and a magnetic recording layer 14 (see FIGS. 4 and 5) are formed on the glass substrate 1. To be manufactured.

The arm 23 is attached so as to be swingable around the vertical axis 24. A suspension 22 formed in a leaf spring (cantilever) shape is attached to the tip of the arm 23. A head slider 21 is attached to the tip of the suspension 22 so as to sandwich the information recording medium 10.

A voice coil 25 is attached to the opposite side of the arm 23 from the head slider 21. The voice coil 25 is clamped by a magnet (not shown) provided on the housing 20. A voice coil motor 26 is constituted by the voice coil 25 and the magnet.

A predetermined current is supplied to the voice coil 25. The arm 23 swings around the vertical axis 24 by the action of electromagnetic force generated by the current flowing through the voice coil 25 and the magnetic field of the magnet. As the arm 23 swings, the suspension 22 and the head slider 21 also swing in the direction of the arrow AR1. The head slider 21 reciprocates on the front and back surfaces of the information recording medium 10 in the radial direction of the information recording medium 10. A magnetic head (not shown) provided on the head slider 21 performs a seek operation.

While the seek operation is performed, the head slider 21 receives a levitation force due to the air flow generated as the information recording medium 10 rotates. Due to the balance between the levitation force and the elastic force (pressing force) of the suspension 22, the head slider 21 travels with a constant flying height with respect to the surface of the information recording medium 10. By the traveling, the magnetic head provided on the head slider 21 can record and reproduce information (data) on a predetermined track in the information recording medium 10. The information recording apparatus 30 on which the glass substrate 1 is mounted as a part of the members constituting the information recording medium 10 is configured as described above.

(Glass substrate 1)
FIG. 2 is a plan view showing glass substrate 1 manufactured by the method for manufacturing a glass substrate for information recording medium according to the present embodiment. 3 is a cross-sectional view taken along the line III-III in FIG.

As shown in FIGS. 2 and 3, the glass substrate 1 (glass substrate for information recording medium) used as a part of the information recording medium 10 (see FIGS. 4 and 5) has a main surface 2, a main surface 3, It has the inner peripheral end surface 4, the hole 5, and the outer peripheral end surface 6, and is formed in a disk shape as a whole. The hole 5 is provided so as to penetrate from one main surface 2 toward the other main surface 3. A chamfer 7 is formed between the main surface 2 and the inner peripheral end surface 4 and between the main surface 3 and the inner peripheral end surface 4. Between the main surface 2 and the outer peripheral end surface 6 and between the main surface 3 and the outer peripheral end surface 6, a chamfered portion 8 (chamfer portion) is formed.

The size of the glass substrate 1 is, for example, 0.8 inch, 1.0 inch, 1.8 inch, 2.5 inch, or 3.5 inch. The thickness of the glass substrate is, for example, 0.30 mm to 2.2 mm from the viewpoint of preventing breakage. In the present embodiment, the glass substrate has an outer diameter of about 64 mm, an inner diameter of about 20 mm, and a thickness of about 0.8 mm. The thickness of the glass substrate is a value calculated by averaging the values measured at a plurality of arbitrary points to be pointed on the glass substrate.

(Information recording medium 10)
FIG. 4 is a plan view showing an information recording medium 10 provided with a glass substrate 1 as an information recording medium. FIG. 5 is a cross-sectional view taken along the line VV in FIG.

4 and 5, the information recording medium 10 includes a glass substrate 1, a compressive stress layer 12, and a magnetic recording layer 14. The compressive stress layer 12 is formed so as to cover the

main surfaces

2 and 3, the inner peripheral end face 4, and the outer peripheral end face 6 of the glass substrate 1. The magnetic recording layer 14 is formed so as to cover a predetermined region on the

main surfaces

2 and 3 of the compressive stress layer 12. By forming the compressive stress layer 12 on the inner peripheral end face 4 of the glass substrate 1, a hole 15 is formed inside the inner peripheral end face 4. The information recording medium 10 is fixed to a spindle motor provided on the housing 20 (see FIG. 1) using the holes 15.

In the information recording medium 10 shown in FIG. 5, the magnetic recording layer 14 is formed on both the compressive stress layer 12 formed on the main surface 2 and the compressive stress layer 12 formed on the main surface 3 (both sides). Is formed. The magnetic recording layer 14 may be provided only on the compression stress layer 12 (one side) formed on the main surface 2, or on the compression stress layer 12 (one side) formed on the main surface 3. It may be provided.

The magnetic recording layer 14 is formed by spin-coating a thermosetting resin in which magnetic particles are dispersed on the compressive stress layer 12 on the

main surfaces

2 and 3 of the glass substrate 1 (spin coating method). The magnetic recording layer 14 may be formed by a sputtering method or an electroless plating method performed on the compressive stress layer 12 on the

main surfaces

2 and 3 of the glass substrate 1.

The thickness of the magnetic recording layer 14 is about 0.3 μm to 1.2 μm for the spin coating method, about 0.04 μm to 0.08 μm for the sputtering method, and about 0.05 μm to about the electroless plating method. 0.1 μm. From the viewpoint of thinning and high density, the magnetic recording layer 14 is preferably formed by sputtering or electroless plating.

As a magnetic material used for the magnetic recording layer 14, a Co-based alloy or the like containing Ni or Cr as a main component is added for the purpose of adjusting the residual magnetic flux density. Is preferably used.

In order to improve the sliding of the magnetic head, the surface of the magnetic recording layer 14 may be thinly coated with a lubricant. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon.

The magnetic recording layer 14 may be provided with a base layer or a protective layer as necessary. The underlayer in the information recording medium 10 is selected according to the type of magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni.

The underlayer provided on the magnetic recording layer 14 is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

Examples of the protective layer for preventing wear and corrosion of the magnetic recording layer 14 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be formed continuously with an in-line type sputtering apparatus together with the underlayer and the magnetic film. These protective layers may be a single layer, or may have a multilayer structure composed of the same or different layers.

Another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, tetraalkoxylane is diluted with an alcohol-based solvent on a Cr layer, and then colloidal silica fine particles are dispersed and applied, followed by baking to form a silicon oxide (SiO ₂ ) layer. It may be formed.

(Glass substrate manufacturing method)
Next, the manufacturing method S100 of the glass substrate (glass substrate for information recording media) in this Embodiment is demonstrated using the flowchart figure shown in FIG. The glass substrate manufacturing method S100 in the present embodiment includes a plate-like glass forming step S10, a first lapping step S20, a cut-out forming step S30, a second lapping step S40, an end surface polishing step S50, a rough polishing step S60, and a cleaning step S65. , A chemical strengthening step S70, a precision polishing step S80, and a scrub cleaning step S90.

The magnetic thin film forming step S200 is performed on the glass substrate obtained through the scrub cleaning step S90. Through the magnetic thin film forming step S200, the information recording medium 10 (see FIGS. 4 and 5) is obtained. Hereinafter, the details of the steps S10 to S90 constituting the glass substrate manufacturing method S100 will be described in order.

(Plate-shaped glass forming step S10)
First, in the glass sheet forming step S10, a glass sheet is manufactured using a known glass forming method such as a direct press method, a float method, a down draw method, a redraw method, or a fusion method using molten glass as a material. Among these, the direct press method can be directly molded from a melted glass into a target glass molded product, and thus is suitable for producing a large amount of plate-like glass having the same shape. In the direct press method, molten glass is supplied to a press mold and pressed with a press mold while the glass is in a softened state to form a sheet glass.

For example, amorphous glass can be used as the material of the glass base plate. When amorphous glass is used, chemical strengthening can be appropriately performed, and a glass substrate for an information recording medium excellent in flatness of the main surface and substrate strength can be provided.

(First lapping step S20)
In the first lapping step S20, lapping (grinding) is performed on the surface of the sheet glass. The lapping process is performed using alumina free abrasive grains by a double-sided lapping apparatus using a planetary gear mechanism. Specifically, the lapping platen is pressed from above and below on both sides of the plate glass, a grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relatively to perform lapping. Do. By this lapping process, a sheet glass having a flat main surface can be obtained.

(Cut-out molding step S30)
In the cut-out forming step S30, the plate glass is cut using a diamond cutter, and a disk-shaped glass base plate is cut out from the plate glass. In the cut-out forming step S30, a cylindrical diamond drill is used to form an inner hole at the center of the glass base plate to form an annular glass base plate (coring process). Thereafter, the inner peripheral end face and the outer peripheral end face are ground with a diamond grindstone and subjected to predetermined chamfering (forming, chamfering).

(Second wrapping step S40)
In the second lapping step S40, lapping is performed on both main surfaces of the obtained glass base plate in the same manner as in the first lapping step. By performing the second lapping step S40, the fine uneven shape formed on the main surface in the cut-out and forming step S30, which is the previous step, can be removed in advance, and the rough polishing step S60 to be performed later can be performed in a short time. Can be completed.

(End face polishing step S50)
In the end face polishing step S50, the inner peripheral end face and the outer peripheral end face of the glass base plate are polished using a polishing brush having a spiral brush bristle material. While supplying the polishing slurry between the polishing brush and each end face of the glass base plate, the polishing brush is rotated in contact with each end face. With the glass base plate immersed in the polishing liquid, the polishing brush may be rotated in contact with each end face.

(Rough polishing step S60)
The glass base plate whose inner peripheral end face and outer peripheral end face are polished has its main surface roughly polished in a plurality of times. For example, the main surface is polished twice in the first and second rough polishing steps. By gradually increasing the finishing accuracy of the glass base plate, a glass base plate having a highly smooth and flat surface can be obtained. When rough polishing is performed in two steps, the first rough polishing step is mainly intended to remove scratches and distortions remaining on the main surface in the lapping step described above, and the second rough polishing step It is intended to finish in a mirror shape.

Referring to FIG. 7, the rough polishing step S60 is performed on both main surfaces of the glass base plate so as to efficiently obtain the surface roughness of the glass base plate finally required in the subsequent precision polishing step S80. In contrast, this is a step of performing rough polishing using a polishing slurry. It does not specifically limit as a grinding | polishing method employ | adopted at this process, It is possible to grind | polish using a double-side polisher.

In this embodiment, a double-side polishing machine 40 shown in FIG. 7 was used. The double-side polishing machine 40 includes a lower surface plate 41 and an upper surface plate 42 that are provided opposite to each other in the vertical direction.

Polishing pads

43 and 44 are fixed to opposing surfaces of the lower surface plate 41 and the upper surface plate 42, respectively.

The glass base plate 1 is held in the holding hole of the carrier 45 and is sandwiched between the lower surface plate 41 and the upper surface plate 42. The lower surface plate 41 and the upper surface plate 42 are rotated by a drive source (not shown). The rotation drive of the lower surface plate 41 and the upper surface plate 42 is controlled by the control device 48. In a state where the glass base plate 1 is held by the holding holes of the carrier 45, the first main surface and the second main surface of the glass base plate 1 are simultaneously polished by the upper and

lower polishing pads

43 and 44. At the time of polishing, polishing slurry is supplied from the abrasive supply device 46. In FIG. 7, the abrasive supply device 46 is one place, but is not limited thereto, and the position and the number thereof can be arbitrarily configured.

In the rough polishing step S60, the polishing liquid (polishing slurry) used may contain cerium oxide, zirconium oxide, zirconium silicate or the like as abrasive grains. The concentration of cerium oxide in the polishing liquid is, for example, about 5% to 10%. The machining allowance for the surface of the glass base plate to be polished is, for example, 10 μm to 30 μm. By rough polishing, the surface undulation and roughness of the glass base plate can be kept low. By rough polishing, the shape of the inner peripheral end face and the outer peripheral end face of the glass base plate can be adjusted. The surface Ra of the glass base plate after rough polishing is, for example, about 3 to 10 mm. As described above, the main surface of the glass base plate 1 is roughly polished. After the rough polishing, the glass base plate 1 is acid cleaned using sulfuric acid or hydrofluoric acid.

(Washing step S65)
Referring again to FIG. 6, after the rough polishing step S60, the glass base plate 1 is subjected to a cleaning process using an acidic cleaning liquid. The purpose of this cleaning treatment is to remove from the surface of the glass base plate 1 any of cerium oxide, zirconium oxide, or zirconium silicate used as a polishing slurry in the rough polishing step S60, which is the previous step. .

Specifically, after removing the glass substrate 1 after the rough polishing from the polishing pad used in the rough polishing step S60, the surface of the glass substrate 1 is etched using a cleaning liquid containing sulfuric acid or hydrofluoric acid. Wash while. A polishing slurry such as cerium oxide, zirconium oxide, or zirconium silicate adhering to the surface of the glass base plate is appropriately removed by a strongly acidic cleaning solution such as sulfuric acid and / or hydrofluoric acid.

In the glass substrate manufacturing method S100 of the present embodiment, a so-called rinse process is not performed after the rough polishing process S60 and before the cleaning process S65. When removing the glass base plate 1 after rough polishing from the polishing pad, the glass base plate 1 is removed from the polishing pad as it is with the polishing liquid sufficiently adhered thereto. The glass base plate 1 is removed from the polishing pad of the double-side polishing machine while in contact with a polishing liquid (or other liquid) having a polishing abrasive concentration of 0.5 w% or more and 10 w% or less. Thereafter, the glass base plate 1 is cleaned using an acidic cleaning solution.

The cleaning liquid used in the cleaning step S65 varies depending on the chemical resistance of the glass base plate, but a concentration of about 1% to 30% is preferable for sulfuric acid, and 0.2% to 5% for hydrofluoric acid. A concentration of about is preferred. Cleaning using these cleaning liquids may be performed while applying ultrasonic waves in a cleaning machine in which an aqueous solution is stored. The frequency of the ultrasonic wave used at this time is preferably 78 kHz or higher.

(Chemical strengthening step S70)
After the cleaning step S65, the glass base plate 1 is chemically strengthened. As the chemical strengthening liquid, for example, a mixed liquid of potassium nitrate (60%) and sodium sulfate (40%) can be used. The chemical strengthening liquid is heated to, for example, 300 ° C. to 400 ° C. The cleaned glass base plate 1 is preheated to 200 ° C. to 300 ° C., for example. The glass base plate 1 is immersed in the chemical strengthening solution for 3 hours to 4 hours, for example.

The immersion is preferably performed in a state of being housed in a holder so that the plurality of glass base plates 1 are held at their respective end faces so that both main surfaces of the glass base plate 1 are chemically strengthened. . By immersing the glass base plate 1 in the chemical strengthening solution, the alkali metal ions (lithium ions and sodium ions) on the surface layer of the glass base plate 1 are chemically strengthened salts having relatively large ionic radii in the chemical strengthening solution ( Sodium ion and potassium ion). Thereby, a compressive stress layer having a thickness of, for example, 50 μm to 200 μm is formed on the surface layer of the glass base plate 1.

The surface of the glass base plate 1 is strengthened by the formation of the compressive stress layer, and the glass base plate 1 has good impact resistance. The glass base plate 1 subjected to the chemical strengthening treatment is appropriately washed. For example, the glass base plate 1 is further cleaned with pure water or IPA (isopropyl alcohol) after being cleaned with sulfuric acid.

(Precision polishing step S80)
After the chemical strengthening step S70, a precision polishing process is performed on the glass base plate 1. The precision polishing step S80 is intended to finish the main surface of the glass base plate 1 in a mirror shape. In the precision polishing step S80, as in the above-described rough polishing step S60, the glass substrate 1 is precisely polished using a double-side polishing machine (see FIG. 7).

In the fine polishing step S80 and the rough polishing step S60, the composition of the polishing abrasive grains contained in the polishing liquid (slurry) used and the polishing pad used are different. In the precision polishing step S80, the particle size of the abrasive grains in the polishing liquid supplied to the surface of the glass base plate 1 on which the compressive stress layer is formed is made smaller than in the rough polishing step S60, and the hardness of the polishing pad is increased. Soften.

The polishing pad used in the precision polishing step S80 is, for example, a soft foam resin polisher. As the polishing liquid used in the precision polishing step S80, for example, colloidal silica having a finer particle size than the cerium oxide abrasive used in the rough polishing step S60 is used. The particle size (primary) of the colloidal silica used in the precision polishing step S80 is preferably 15 nm to 80 nm. Precision polishing using colloidal silica increases the smoothness of the surface of the glass base plate.

(Scrub cleaning step S90)
After the precision polishing step S80, a scrub cleaning process is performed on the glass base plate 1. Specifically, after the glass base plate 1 after the precision polishing is removed from the polishing pad used in the precision polishing step S80, the glass base plate on which the compressive stress layer is formed while supplying a cleaning solution to the surface of the glass base plate 1 Scrub cleaning is performed on the surface of the plate 1 using a scrub cleaning device.

The glass base plate 1 may be temporarily stored in water after being removed from the polishing pad of the double-side polishing machine. By storing in water, it is possible to reduce the amount of foreign matter such as polishing grits or free abrasive grains adhering to the glass base plate 1 after precision polishing while preventing the surface of the glass base plate 1 from drying after precision polishing. it can. After the glass base plate 1 is stored in water for a predetermined time, the glass base plate 1 is set in a scrub cleaning device, and the glass base plate 1 is scrubbed.

As the scrub cleaning, for example, a cleaning liquid such as a detergent or pure water is used. The pH of the cleaning solution used for scrub cleaning is preferably 9.0 or more and 12.2 or less. Within this range, the ζ potential can be easily adjusted and scrub cleaning can be performed efficiently. As scrub cleaning, both scrub cleaning with a detergent and scrub cleaning with pure water may be performed. By using a detergent and pure water, the glass base plate 1 can be more appropriately cleaned. The glass base plate 1 may be further rinsed with pure water between scrub cleaning with a detergent and scrub cleaning with pure water.

After the scrub cleaning, the glass base plate 1 may be further subjected to ultrasonic cleaning. After scrub cleaning with detergent and pure water, ultrasonic cleaning with chemicals such as sulfuric acid aqueous solution, ultrasonic cleaning with pure water, ultrasonic cleaning with detergent, ultrasonic cleaning with IPA, and / or steam drying with IPA Further, it may be performed.

The glass substrate manufacturing method S100 in the present embodiment is configured as described above. By using glass substrate manufacturing method S100, glass base plate 1 of the present embodiment shown in FIGS. 2 and 3 can be obtained.

(Magnetic thin film forming step S200)
Magnetic recording layers are formed on both main surfaces (or one of the main surfaces) of the glass base plate 1 that has been subjected to the scrub cleaning process. The magnetic recording layer includes, for example, an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoFeZr alloy, an orientation control underlayer made of Ru, a perpendicular magnetic recording layer made of a CoCrPt alloy, a protective layer made of a C system, and an F system. Are formed by sequentially forming the lubricating layer. By forming the magnetic recording layer, the information recording medium 10 shown in FIGS. 4 and 5 can be obtained.

(Action / Effect)
As described at the beginning, in order to achieve both high smoothness and impact resistance on the surface of the glass substrate, chemical strengthening treatment may be performed after the rough polishing step and before the precise polishing step. Also in the manufacturing method of the glass substrate in the present embodiment, chemical strengthening step S70 is performed after rough polishing step S60 and before precision polishing step S80.

Referring to FIG. 8, here, when the chemical strengthening step S70 is performed after the rough polishing step S60 and before the fine polishing step S80 as in the glass substrate manufacturing method S101 in the comparative example, the rough polishing is performed. Assume that a rinsing step S62 is performed as a pre-step of the cleaning step S65 between the step S60 and the chemical strengthening step S70. The rinsing step S62 is performed by supplying a rinsing cleaning liquid between the polishing pad and the glass base plate before the glass base plate is removed from the polishing pad of the double-side polishing machine.

Suppose that a glass substrate manufactured using the glass substrate manufacturing method S101 of the comparative example is mounted on a hard disk, and a drop test is performed on the hard disk in a high-temperature and high-humidity environment. In this case, the drop impact resistance of the hard disk provided with the glass substrate manufactured using the glass substrate manufacturing method S101 is the same as that of the glass substrate manufactured using the glass substrate manufacturing method S100 of the present embodiment. Lower than the hard disk provided.

The inventors investigated this substrate and found that there was unevenness in the thickness of the compressive stress layer on the surface of the glass substrate manufactured using the glass substrate manufacturing method S101. When the hard disk is placed in a high-temperature and high-humidity environment, the distribution of the thickness unevenness of the compressive stress layer is increased, so that the glass substrate manufactured using the glass substrate manufacturing method S101 of the comparative example is mounted. As a hard disk, the drop impact resistance is reduced.

The cause of the uneven distribution in a high temperature and humidity environment is considered as follows. The compressive stress layer is gradually relaxed when the temperature is high, but the rate of relaxation varies depending on how the stress layer enters. Specifically, the relaxation rate proceeds faster as the internal stress is weaker. Since the thickness depends on internal stress, the thinner the thickness, the faster the relaxation. Therefore, when the stress relaxation is accelerated in a high-temperature and high-humidity environment, the unevenness of the compressive stress layer becomes more remarkable.

The present inventors have intensively studied which process causes the uneven thickness of the compressive stress layer, and the occurrence of the uneven thickness of the compressive stress layer is caused by the rough polishing process and the cleaning process. It was found that this was caused by a rinsing process performed during the period.

As in the manufacturing method S101 of the glass substrate of the comparative example, the rinsing step removes polishing abrasive grains remaining on the surface of the glass base plate after performing rough polishing with a liquid called slurry containing polishing abrasive grains. Done for. In general, it has been considered that a high cleanliness can be achieved by carrying out this rinsing step and then carrying out washing with an acidic washing solution.

Here, by performing the rinsing step, the concentration (amount) of abrasive grains adhering to the glass base plate decreases. On the other hand, the pressure applied from the polishing machine (polishing pad) to the surface of the glass base plate is a substantially constant value during the rinsing process. Accordingly, as the amount of abrasive grains remaining on the surface of the glass base plate in the rinsing step is gradually reduced, the dispersion of the pressure on the abrasive grains of the polishing pad is reduced, and the abrasive grains are removed from the polishing pad. The pressure applied to each grain (same for both primary and secondary particles) increases, and the pressure acting on the glass base plate of each grain of the abrasive grains gradually increases.

As the concentration of the polishing abrasive grains decreases, each abrasive grain comes into strong contact with the surface of the glass base plate. In order to obtain a high cleanliness for the glass base plate, acid cleaning with sulfuric acid or HF is performed in the cleaning step after the rough polishing step. At this time, when a small amount of abrasive grains strongly adheres to the surface of the glass base plate, the surface of the glass substrate is preferentially eroded by the cleaning liquid prior to the removal of the deposits. As a result, the surface shape of the preferentially eroded glass base plate exhibits irregularities. In the chemical strengthening step S70, which is a subsequent step, ion exchange is not performed uniformly in the unevenly formed portions, and the thickness of the formed compressive stress layer becomes uneven.

Therefore, when the hard disk mounted with the glass substrate manufactured using the glass substrate manufacturing method S101 of the comparative example as described above is placed in a high temperature and high humidity environment, the thickness distribution of the compressive stress layer is uneven. As a result, the drop impact resistance of the hard disk on which the glass substrate is mounted is reduced.

As in the glass substrate manufacturing method S100 of the present embodiment, the abrasive grains remaining on the surface of the glass base plate are removed after the glass base plate is removed from the polishing pad of the double-side polishing machine without rinsing. In this case, the surface of the glass base plate hardly receives pressure from the abrasive grains. Therefore, in this case, the abrasive grains hardly adhere firmly to the surface of the glass base plate, and the abrasive grains can be easily removed from the surface of the glass base plate.

The uneven thickness of the compressive stress layer as described above due to the rinsing process is not detected by the optical inspection machine, unlike the general unevenness. Since the unevenness of the thickness of the compressive stress layer as described above occurs locally, it does not affect the surface roughness of the glass base plate. Even if a glass substrate having uneven thickness of the compressive stress layer is incorporated in the hard disk, it does not cause a collision with the magnetic head, so there is no problem when it is used in a normal environment. However, when such a hard disk is placed in a hot and humid environment, as described above, the drop impact resistance is reduced.

On the other hand, in the glass substrate manufacturing method S100 in the present embodiment, after the rough polishing step S60 is performed, the cleaning step S65 is performed without performing the rinse step. Since the abrasive grains do not adhere firmly to the surface of the glass base plate, the surface of the glass substrate is not preferentially affected by the cleaning liquid prior to the removal of the deposits in the cleaning step S65. As a result, the surface shape of the glass base plate does not exhibit irregularities, and ion exchange is performed uniformly in the chemical strengthening step S70 which is a subsequent step. Therefore, according to the glass substrate manufacturing method S100 in the present embodiment, the impact resistance of the obtained glass substrate is obtained even when the chemical strengthening treatment is performed after the rough polishing step and before the precision polishing step. It is possible to suppress the decrease.

[Experimental example]
Referring to FIG. 9, the following experiment based on Examples 1 to 6 and Comparative Examples 1 and 2 was performed on the above-described embodiment. In Examples 1 to 6 and Comparative Examples 1 and 2, the process up to the end surface polishing step S50 (see FIG. 6) was performed in the same manner as in the above-described embodiment.

Example 1
In the rough polishing step S60 of Example 1, rough polishing was performed using a polishing slurry having a cerium oxide concentration of 10 w%. A foamed urethane pad was used as the polishing pad. The machining allowance for the surface of the glass base plate was 20 μm. Thereafter, the glass substrate was removed from the polishing pad in a state where the glass substrate was brought into contact with a solution containing 8.0% by weight of cerium oxide (polishing abrasive grains) (the rinsing step was not performed).

In cleaning step S65 of Example 1, 5% sulfuric acid was used as a cleaning liquid, and cleaning was performed while applying an ultrasonic wave of 80 kHz. After washing with ultrasonic waves, the glass base plate was dried with IPA vapor.

In the chemical strengthening step S70 of Example 1, a mixture of Na nitrate and nitric acid K at a ratio of 5: 5 (molar ratio) was prepared as a chemically strengthened salt. The glass substrate was immersed in a chemically strengthened salt heated to 400 ° C., and ion exchange was performed for 6 hours. After removing the glass substrate from the chemically strengthened salt, the glass substrate was quenched and washed with warm water to remove nitrate from the surface of the glass substrate. The subsequent steps are the same as those in the above embodiment.

(Example 2)
In the rough polishing step S60 of Example 2, as in Example 1 described above, rough polishing was performed using a polishing slurry having a cerium oxide concentration of 10 w%. Then, the glass substrate was removed from the polishing pad in the state which made the glass substrate contact the solution containing cerium oxide (abrasive grain) 5.0w% (the rinse process is not implemented). In the cleaning step S65, 1% concentration hydrofluoric acid was used as the cleaning liquid, and cleaning was performed in the same manner as in Example 1 described above. In the chemical strengthening step S70, as in Example 1 described above, a chemical strengthening salt prepared by mixing Na nitrate and nitric acid K at a ratio of 5: 5 (molar ratio) is prepared and subjected to chemical strengthening treatment. It was.

(Example 3)
In the rough polishing step S60 of Example 3, as in Example 1 described above, rough polishing was performed using a polishing slurry having a cerium oxide concentration of 10 w%. Thereafter, the glass substrate was removed from the polishing pad in a state where the glass substrate was brought into contact with a solution containing 0.5 w% of cerium oxide (polishing abrasive grains) (the rinsing step was not performed). In the cleaning step S65, 1% concentration sulfuric acid was used as the cleaning liquid, and cleaning was performed in the same manner as in Example 1 described above. In the chemical strengthening step S70, as in Example 1 described above, a chemical strengthening salt prepared by mixing Na nitrate and nitric acid K at a ratio of 5: 5 (molar ratio) is prepared and subjected to chemical strengthening treatment. It was.

(Example 4)
In the rough polishing step S60 of Example 4, as in Example 1 described above, rough polishing was performed using a polishing slurry having a cerium oxide concentration of 10 w%. Thereafter, the glass substrate was removed from the polishing pad in a state where the glass substrate was brought into contact with a solution containing 0.5 w% of cerium oxide (polishing abrasive grains) (the rinsing step was not performed). In the cleaning step S65, 30% sulfuric acid was used as the cleaning liquid, and cleaning was performed in the same manner as in Example 1 described above. In the chemical strengthening step S70, as in Example 1 described above, a chemical strengthening salt prepared by mixing Na nitrate and nitric acid K at a ratio of 5: 5 (molar ratio) is performed. It was.

(Example 5)
In the rough polishing step S60 of Example 5, as in Example 1 described above, rough polishing was performed using a polishing slurry having a cerium oxide concentration of 10 w%. Thereafter, the glass substrate was removed from the polishing pad in a state where the glass substrate was brought into contact with a solution containing 10.0 w% of cerium oxide (polishing abrasive grains) (the rinsing step was not performed). In the cleaning step S65, 5% concentration hydrofluoric acid was used as the cleaning liquid, and cleaning was performed in the same manner as in Example 1 described above. In the chemical strengthening step S70, as in Example 1 described above, a chemical strengthening salt prepared by mixing Na nitrate and nitric acid K at a ratio of 5: 5 (molar ratio) is prepared and subjected to chemical strengthening treatment. It was.

(Example 6)
In the rough polishing step S60 of Example 6, similarly to Example 1 described above, rough polishing was performed using a polishing slurry having a cerium oxide concentration of 10 w%. Thereafter, the glass substrate was removed from the polishing pad in a state where the glass substrate was brought into contact with a solution containing 0.5 w% of cerium oxide (polishing abrasive grains) (the rinsing step was not performed). In the cleaning step S65, 1% concentration sulfuric acid was used as the cleaning liquid, and cleaning was performed in the same manner as in Example 1 described above. In the chemical strengthening step S70, nitric acid K was prepared as a chemically strengthened salt, and the chemical strengthening treatment was performed in the same manner as in Example 1 described above.

(Comparative Example 1)
In the rough polishing step S60 of Comparative Example 1, as in Example 1 described above, rough polishing was performed using a polishing slurry having a cerium oxide concentration of 10 w%. Then, the glass substrate was removed from the polishing pad in a state where the glass substrate was brought into contact with a solution containing 0.01 w% cerium oxide (polishing abrasive grains) (rinsing step was performed). In the cleaning step S65, 5% concentration sulfuric acid was used as the cleaning liquid, and cleaning was performed in the same manner as in Example 1 described above. In the chemical strengthening step S70, as in Example 1 described above, a chemical strengthening salt prepared by mixing Na nitrate and nitric acid K at a ratio of 5: 5 (molar ratio) is prepared and subjected to chemical strengthening treatment. It was.

(Comparative Example 2)
In the rough polishing step S60 of Comparative Example 2, as in Example 1 described above, rough polishing was performed using a polishing slurry having a cerium oxide concentration of 10 w%. Then, the glass substrate was removed from the polishing pad in the state which made the glass substrate contact the solution containing cerium oxide (abrasive grain) 5.0w% (the rinse process is not implemented). In the cleaning step S65, 3% concentration sodium hydroxide was used as the cleaning liquid, and cleaning was performed in the same manner as in Example 1 described above. In the chemical strengthening step S70, as in Example 1 described above, a chemical strengthening salt prepared by mixing Na nitrate and nitric acid K at a ratio of 5: 5 (molar ratio) is prepared and subjected to chemical strengthening treatment. It was.

(Impact resistance test results)
A magnetic recording layer was formed on the glass substrates obtained in Examples 1 to 6 and Comparative Examples 1 and 2, and each was incorporated into a hard disk. The hard disk corresponding to each of Examples 1 to 6 and Comparative Examples 1 and 2 was allowed to stand for 96 hours at 200 ° C. in an RH 80% environment. Thereafter, the hard disks corresponding to each of Examples 1 to 6 and Comparative Examples 1 and 2 were dropped, and the drop impact resistance was evaluated.

When the glass substrate was cracked when the load was 1100 G, the evaluation was B. When a crack occurred in the glass substrate when the load was 1200 G, the evaluation was A. When a crack occurred in the glass substrate when the load was 1300 G, the evaluation was S. Even when the load was 1300 G, when the glass substrate did not crack, it was evaluated as an evaluation SS.

From the results shown in FIG. 9, it is considered that the chemically strengthened salt used for the chemical strengthening treatment should contain at least sodium ions. This is because when the chemically strengthened salt contains sodium ions, the compressive stress layer is stably formed. It is considered that the ratio of potassium ion to sodium ion does not particularly affect the impact resistance of the glass substrate.

As shown in Comparative Example 1, when removing the glass substrate from the polishing pad, when the glass substrate is removed while contacting the cerium oxide (polishing abrasive grains) with a solution of less than 0.01 w% by performing a rinsing step, It can be seen that the drop impact resistance deteriorates. As shown in Comparative Example 2, when removing the glass substrate from the polishing pad, even when the rinsing step is not performed, the polishing liquid is applied to the surface of the glass base plate by using a strong base (alkaline) cleaning liquid. It can be seen that since the ion exchange is not performed well in the remaining portion, the drop impact resistance deteriorates.

As mentioned above, although embodiment and each Example based on this invention were described, embodiment and each Example disclosed this time are illustrations in all points, and are not restrictive. The technical scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Glass substrate (glass base plate), 2, 3 main surface, 4 inner peripheral end surface, 5,15 hole, 6 outer peripheral end surface, 7,8 chamfer, 10 information recording medium, 12 compressive stress layer, 14 magnetic recording layer , 20 housing, 21 head slider, 22 suspension, 23 arm, 24 vertical axis, 25 voice coil, 26 voice coil motor, 27 clamp member, 28 fixing screw, 30 information recording device, 40 double-side polishing machine, 41 lower surface plate, 42 Upper surface plate, 43, 44 polishing pad, 45 carrier, 46 abrasive supply device, 48 control device.

Claims

A polishing machine including a polishing pad is prepared, and a polishing liquid containing any one of cerium oxide, zirconium oxide, or zirconium silicate as abrasive grains is supplied to the surface of the glass base plate, and the surface of the glass base plate is supplied. A process of performing rough polishing by sliding the polishing pad against,
Removing the glass base plate after the rough polishing from the polishing pad, and then performing acid cleaning on the surface of the glass base plate while supplying an acidic cleaning solution to the surface of the glass base plate; ,
A compression stress layer is formed on the surface of the glass base plate by ion exchange of alkali metal ions contained in the glass base plate after the acid cleaning with a chemically strengthened salt having an ionic radius larger than the ion radius. And comprising the steps of:
When removing the glass substrate after the rough polishing from the polishing pad, the glass substrate is in contact with a liquid having a concentration of the abrasive grains of 0.5 w% to 10 w%. Removed from the polishing pad of
A method for producing a glass substrate for an information recording medium.
The cleaning liquid used in the acid cleaning step includes sulfuric acid and / or hydrofluoric acid,
The manufacturing method of the glass substrate for information recording media of Claim 1.
The chemical strengthening salt used in the step of forming the compressive stress layer includes sodium ions and potassium ions.
The manufacturing method of the glass substrate for information recording media of Claim 1 or 2.