WO2013145461A1

WO2013145461A1 - Method for producing hdd glass substrate

Info

Publication number: WO2013145461A1
Application number: PCT/JP2012/082492
Authority: WO
Inventors: 大士梶田
Original assignee: コニカミノルタ株式会社
Priority date: 2012-03-28
Filing date: 2012-12-14
Publication date: 2013-10-03

Abstract

Provided is a method that is for producing an HDD glass substrate having a thermally assisted recording method and that is able to suppress a decrease in compressive stress of the glass substrate surface during high-temperature film formation processing. The method for producing an HDD glass substrate having a thermally assisted recording method and having an amount of magnetic head floatation of no greater than 3 nm is provided with: a step for forming the glass substrate (1); and a step for contacting the glass substrate (1) to a chemical strengthening treatment liquid. The concentration of alkaline earth metals contained in the chemical strengthening treatment liquid (100) is 50-10,000 ppb inclusive.

Description

Manufacturing method of glass substrate for HDD

The present invention relates to a method for manufacturing a glass substrate for an HDD (Hard Disk Drive), and more particularly to a method for manufacturing a glass substrate used for an HDD having a magnetic head flying height of 3 nm or less.

In recent years, with a dramatic increase in the storage capacity of HDDs, it has become indispensable to reduce the recording area per bit of the medium. In proportion to the reduction in the recording area of the medium, the size of the magnetic particles for recording must be reduced, and the energy to maintain the direction of magnetization recorded in one direction is reduced due to the reduction in size, making it more susceptible to thermal energy. There is a problem.

Therefore, in order to stabilize the magnetization direction, it is necessary to change the magnetic particles to an Fe—Pt magnetic material having a high magnetic anisotropy energy. This Fe—Pt-based magnetic material needs to be subjected to high-temperature heat treatment during film formation in the manufacturing process for forming the recording medium. Therefore, it is indispensable to manufacture a glass substrate with high heat resistance that can withstand high-temperature heat treatment. Conventional techniques relating to high-temperature heat treatment of Fe—Pt magnetic materials are described in, for example, Ketsutsu et al., “FePtCu high-density HDD medium material”, Toshiba Review 57, No. 9, September 2002, p54-p57 (Non-patent Document 1). It is disclosed.

By the way, in addition to the improvement in recording density, HDDs are currently required to have impact resistance as the number of portable applications such as notebook personal computers and external HDDs increases. In order to improve the mechanical strength of the glass substrate and improve the impact resistance, there is a method of subjecting the glass substrate to chemical strengthening treatment. By so-called ion exchange method, the alkali element near the surface (surface layer) of the glass substrate is replaced with another alkali element having a diameter larger than that of the alkali element, and by the substitution, a compressive strain is generated on the surface of the glass substrate, A chemical strengthening layer (also referred to as a compressive stress layer) is formed. For example, Japanese Unexamined Patent Application Publication No. 2002-121051 (Patent Document 1) discloses a conventional technique related to a chemical strengthening treatment of a glass substrate.

JP 2002-121051 A

As a technique for realizing high-density recording equivalent to 1 Tb / in ² in an HDD information recording medium, a heat-assisted recording method is promising. However, in the heat-assisted recording method, it is necessary to perform the film forming process on the main surface of the glass substrate at a high temperature. Therefore, even if a glass substrate that has been chemically strengthened to improve impact resistance is used, the compressive stress layer relaxes during the heat treatment at high temperatures, resulting in variations in the compressive stress. There was a problem that shape change occurred.

The present invention has been made in view of the above problems, and its main purpose is heat-assisted recording, which can suppress a change in shape of the glass substrate due to a change in compressive stress on the surface of the glass substrate during the high-temperature film forming process. It is providing the manufacturing method of the glass substrate for HDD of a system.

The method for manufacturing a glass substrate for HDD according to the present invention is a method for manufacturing a glass substrate for HDD of a thermally assisted recording method in which the flying height of the magnetic head is 3 nm or less, and a step of molding the glass substrate and a chemical strengthening treatment And a step of bringing the glass substrate into contact with the liquid, and the concentration of the alkaline earth metal contained in the chemical strengthening treatment liquid is 50 ppb or more and 10,000 ppb or less.

In the above production method, the temperature of the chemical strengthening treatment liquid is preferably 450 ° C. or higher.

According to the method for manufacturing a glass substrate for HDD of the present invention, it is possible to suppress a change in shape of the glass substrate due to a change in compressive stress on the surface of the glass substrate during the high-temperature film forming process.

It is a perspective view which shows HDD provided with the glass substrate manufactured by the manufacturing method of the glass substrate for HDD in embodiment. It is a perspective view which shows the glass substrate obtained by the manufacturing method of the glass substrate in embodiment. It is a perspective view which shows the information recording medium provided with the glass substrate obtained by the manufacturing method of the glass substrate in embodiment. It is a flowchart which shows the manufacturing method of the glass substrate in embodiment. It is a schematic diagram which shows the state before ion exchange of the glass substrate which contacts a chemical strengthening process liquid. It is a schematic diagram which shows the state after ion exchange of the glass substrate which contacts a chemical strengthening process liquid. It is a figure which shows the experimental condition and experimental result of an Example and a comparative example.

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.

[Hard Disk Drive 30]
With reference to FIG. 1, first, a hard disk drive 30 which is an example of an information recording apparatus will be described. FIG. 1 is a perspective view showing the hard disk drive 30. The hard disk drive 30 includes the information recording medium 10. The information recording medium 10 is manufactured using the glass substrate 1 manufactured by the method for manufacturing a glass substrate for HDD (hereinafter also simply referred to as a glass substrate) in the embodiment.

Specifically, the hard disk drive 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. Is provided. 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 formed by applying a magnetic material to the glass substrate 1 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. The information recording medium 10 is manufactured by forming a magnetic recording layer on the glass substrate 1.

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 hard disk drive 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.

The flying height at which the magnetic head provided on the head slider 21 floats with respect to the surface of the information recording medium 10 is called flying height. In the hard disk drive 30 of the present embodiment, the flying height is 3 nm or less. That is, the distance between the information recording medium 10 in the thickness direction of the information recording medium 10 and the magnetic head when the information recording medium 10 is rotated is 3 nm or less.

The glass substrate 1 of the present embodiment is used for a heat-assisted recording type HDD capable of reducing the recording area of a medium. In order to improve the read / write function in a minute recording area, the distance between the magnetic head and the medium is reduced, and a flying height of 3 nm or less is defined as described above. As a result, the read / write characteristics of the hard disk drive 30 can be improved and the recording density can be improved as compared with the conventional case.

[Glass substrate 1 / information recording medium 10]
FIG. 2 is a perspective view showing the glass substrate 1 used for the information recording medium 10 (see FIG. 3). FIG. 3 is a perspective view showing the information recording medium 10 provided with the glass substrate 1. With reference to FIG. 2 and FIG. 3, the glass substrate 1 obtained by the manufacturing method of the glass substrate for information recording media based on this Embodiment and the information recording medium 10 provided with the glass substrate 1 are demonstrated.

As shown in FIG. 2, a glass substrate 1 (information recording medium glass substrate) used for the information recording medium 10 has an annular disk shape with a circular hole 1H formed in the center. When the glass substrate 1 has a disc shape, the glass substrate 1 is suitable as the glass substrate 1 of the information recording medium 10 assembled to the hard disk drive 30, for example. The circular disk-shaped glass substrate 1 has a front main surface 1A, a back main surface 1B, an inner peripheral end surface 1C, and an outer peripheral end surface 1D.

The size of the disk-shaped glass substrate 1 is not particularly limited, and may be a small-diameter disk having an outer diameter of 3.5 inches, 2.5 inches, 1.8 inches, or less, for example. The thickness of the glass substrate 1 may be as thin as 2 mm, 1 mm, 0.8 mm, 0.635 mm, or less. The thickness of the glass substrate 1 is a value calculated by averaging thickness values measured at a plurality of arbitrary points on the glass substrate 1.

As shown in FIG. 3, the information recording medium 10 is configured by forming a magnetic film on the front main surface 1A of the glass substrate 1 and forming a magnetic thin film layer 2 including a magnetic recording layer. Is done. In FIG. 3, the magnetic thin film layer 2 is formed only on the front main surface 1A, but the magnetic thin film layer 2 may also be formed on the back main surface 1B.

The magnetic thin film layer 2 is formed by spin-coating a thermosetting resin in which magnetic particles are dispersed on the front main surface 1A of the glass substrate 1 (spin coating method). The magnetic thin film layer 2 may be formed on the front main surface 1A of the glass substrate 1 by a sputtering method or an electroless plating method.

The film thickness of the magnetic thin film layer 2 formed on the front main surface 1A of the glass substrate 1 is about 0.3 μm to 1.2 μm in the case of the spin coating method, about 0.04 μm to 0.08 μm in the case of the sputtering method, In the case of the electroless plating method, the thickness is about 0.05 μm to 0.1 μm. From the viewpoint of thinning and high density, the magnetic thin film layer 2 is preferably formed by sputtering or electroless plating.

The magnetic material used for the magnetic thin film layer 2 is not particularly limited, and a conventionally known material can be used. However, in order to obtain a high coercive force, Co having high crystal anisotropy is basically used for the purpose of adjusting the residual magnetic flux density. A Co-based alloy to which Ni or Cr is added is suitable. Further, as a magnetic layer material suitable for heat-assisted recording, an FePt-based material may be used.

Further, a lubricant may be thinly coated on the surface of the magnetic thin film layer 2 in order to improve the sliding of the magnetic recording head. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon.

Furthermore, if necessary, an underlayer or a protective layer may be provided. The underlayer in the information recording medium 10 is selected according to the 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.

Also, the underlayer is not limited to a single layer, and may have a multi-layer 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 thin film layer 2 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 continuously formed together with an underlayer, a magnetic film and the like by an in-line type sputtering apparatus. In addition, these protective layers may be a single layer, or may have a multilayer structure including 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, tetraalkoxysilane 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 of the glass substrate (glass substrate for information recording media) in this Embodiment is demonstrated using the flowchart shown in FIG. FIG. 4 is a flowchart showing a method for manufacturing a glass substrate in the embodiment.

The glass substrate manufacturing method in the present embodiment includes a forming step (step S10), a first lapping step (step S20), a shape processing step (step S30), an inner peripheral polishing step (step S40), and a second lapping step ( Glass obtained through step S50), outer periphery polishing step (step S60), first main surface polishing step (step S70), second main surface polishing step (step S80), and chemical strengthening step (step S90). A magnetic film forming step (step S100) may be performed on the substrate (corresponding to the glass substrate 1 in FIG. 2). The information recording medium 10 is obtained by the magnetic film forming step (step S100).

Hereinafter, each of these steps S10 to S100 will be described in order. In the following, simple cleaning that is appropriately performed between steps S10 to S100 is not described.

(Molding process)
In the forming step (step S10), the glass material constituting the glass substrate is melted. As a glass raw material that is a raw material of the glass substrate, oxides, carbonates, nitrates, hydroxides, and the like corresponding to the raw materials of the respective components constituting the glass substrate 1 were weighed to a desired ratio and sufficiently mixed with powder. Prepared ingredients are prepared. This blended raw material is put into a platinum crucible or the like in an electric furnace heated to 1300 to 1550 ° C., for example, 1400 ° C., and melted, and further clarification and stirring are performed.

For example, general aluminosilicate glass is used as the glass material. The aluminosilicate glass is composed of 58 mass% to 75 mass% SiO ₂ , 5 mass% to 23 mass% Al ₂ O ₃ , 3 mass% to 10 mass% Li ₂ O, and 4 mass% to 13 mass. % Na ₂ O as a main component. The glass material is not limited to aluminosilicate glass, and may be any material such as soda lime glass or borosilicate glass.

The melted glass material is cast into a preheated mold and slowly cooled into a glass block. Subsequently, after being held at a temperature in the vicinity of the glass transition point for 1 to 3 hours, it is gradually cooled to remove strain. The obtained glass block is sliced into a disk shape and cut out using a core drill with concentric inner and outer circumferences. Or after pouring molten glass on a lower mold | type, it press-molds with an upper mold | type and a lower mold | type, and you may shape | mold into a disk shape. In this way, a disk-shaped glass blank (glass base material) is formed. The glass blank material may be formed by cutting out sheet glass (plate glass) formed by a downdraw method or a float method.

(First wrapping process)
Next, in the first lapping step (step S20), a lapping process is performed on both main surfaces of the formed glass blank material for the purpose of improving dimensional accuracy and shape accuracy. The two main surfaces of the glass blank material are the main surface that becomes the front main surface 1A and the main surface that becomes the back main surface 1B in FIG. Also called).

The lapping process is performed using a double-sided lapping device using a planetary gear mechanism. Specifically, the lapping platen is pressed from above and below on both main surfaces of the glass blank material, the grinding liquid is supplied onto both main surfaces, and the glass blank material and lapping platen are moved relative to each other for lapping. Processing is performed. By the lapping treatment, the approximate parallelism, flatness, thickness, etc. of the glass substrate are preliminarily adjusted, and a glass base material having an approximately flat main surface is obtained. For example, by using a grinding fluid containing alumina abrasive grains of particle size # 400 (particle size of about 40 to 60 μm) and setting the load of the upper surface plate to about 100 kg, the surface accuracy of both surfaces of the glass blank material is 0 μm to 1 μm. The surface roughness Rmax may be finished to about 6 μm.

(Shaping process)
Next, in the shape processing step (step S30), a coring (inner peripheral cut) process is performed on the center portion of the glass blank material using a cylindrical diamond drill. By the coring process, an annular glass substrate having a hole in the center is obtained. Thereafter, the inner peripheral end face and the outer peripheral end face opposed to the hole in the central part are ground with a diamond grindstone so that the outer diameter is 65 mm and the inner diameter (the diameter of the circular hole 1H in the central part) is 20 mm. Processing is performed. The surface roughness of the end surface of the glass substrate at this time is about 2 μm in Rmax. In general, a glass substrate having an outer diameter of 65 mm is used for a 2.5-inch hard disk.

(Inner grinding process)
Next, in the inner peripheral polishing step (step S40), mirror polishing by brush polishing is performed on the inner peripheral end surface of the glass substrate. Specifically, by supplying a polishing liquid containing an abrasive to the polishing brush, placing the polishing brush in contact with the inner peripheral end surface of the glass substrate, and applying the polishing brush while rotating the glass substrate The inner peripheral end face of the glass substrate is polished.

As the above-mentioned abrasive, it is preferable to use one or more selected from the group consisting of cerium oxide, zirconium oxide, and aluminum oxide. The polishing brush is preferably made of one or more selected from the group consisting of aramid fibers, polybutylene terephthalate, and polypropylene.

(Second wrapping process)
Next, in the second lapping process (step S50), the lapping process is performed on both main surfaces of the glass substrate in the same manner as in the first lapping process (step S20). By performing this second lapping step, it is possible to remove in advance the fine irregularities such as fine scratches and protrusions formed on both main surfaces of the glass substrate in the coring or end face processing in the previous step. It is possible to shorten the polishing time of the main surface in the subsequent process.

(Outer periphery polishing process)
Next, in the outer peripheral polishing step (step S60), the outer peripheral end surface of the glass substrate is subjected to mirror polishing by brush polishing. Specifically, by supplying a polishing liquid containing an abrasive to the polishing brush, placing the polishing brush in contact with the outer peripheral end surface of the glass substrate, and applying the polishing brush while rotating the glass substrate, The outer peripheral end surface of the glass substrate is polished. Said abrasive | polishing agent and polishing brush are selected similarly to the abrasive | polishing agent and polishing brush used in the case of grinding | polishing of the internal peripheral end surface of a glass substrate.

(First main surface polishing process)
Next, a first main surface polishing step (step S70) is performed as a rough polishing step which is a first step in the main surface polishing step of the glass substrate. The main purpose of the first main surface polishing step is to correct warpage of the glass substrate while removing scratches remaining on the main surface of the glass substrate in the lapping step described above. In the first main surface polishing step, the main surface is polished by a double-side polishing apparatus having a planetary gear mechanism. For example, polishing is performed using a polishing pad such as hard velor, urethane foam, or pitch-impregnated suede. As the abrasive, general cerium oxide abrasive grains are used.

(Second main surface polishing step)
Next, a second main surface polishing step (step S80) is performed as a precision polishing step which is the second step of the main surface polishing step of the glass substrate. In the second main surface polishing step, when coating the main surface of the glass substrate, or when separating the glass substrate, etc., the fine defects generated on the main surface of the glass substrate are eliminated to finish it in a mirror shape, And it aims at eliminating the curvature of a glass substrate and finishing to desired flatness. In the second main surface polishing step, the main surface is polished by a double-side polishing apparatus having a planetary gear mechanism. For example, polishing is performed using a polishing pad which is a soft polisher made of suede or velor. As the abrasive, general colloidal silica finer than the cerium oxide used in the first main surface polishing step is used.

(Chemical strengthening process)
Next, in the chemical strengthening step (step S90), the glass substrate that has finished the main surface polishing step described above is chemically strengthened. After the glass substrate is washed, a chemical strengthening treatment liquid containing a chemical strengthening salt is prepared, and the glass substrate is brought into contact with the chemical strengthening treatment liquid by immersing the glass substrate (precursor) in the chemical strengthening treatment liquid. To chemically strengthen the glass substrate. For example, on both main surfaces of the glass substrate, a compressive stress layer may be formed in a range from the glass substrate surface to about 150 μm to improve the rigidity of the glass substrate. In this way, a glass substrate corresponding to the glass substrate 1 shown in FIG. 2 is obtained. By applying chemical strengthening treatment before any polishing step, the compressive stress layer may be removed from the main surface of the glass substrate after polishing, but even in this case, the inner peripheral side and the outer peripheral side end surface of the glass substrate The compressive stress layer remains after polishing.

(Magnetic film forming process)
Finally, in the magnetic film forming step (step S100), the glass substrate that has been subjected to the chemical strengthening treatment is washed with at least one of water, acid, and alkali, and then the glass corresponding to the glass substrate 1 shown in FIG. The magnetic thin film layer 2 is formed by forming a magnetic film on both main surfaces (or one of the main surfaces) of the substrate. The magnetic thin film layer 2 is made of 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. The lubricating layer is formed by sequentially forming a film. By forming the magnetic thin film layer, a perpendicular magnetic recording disk corresponding to the information recording medium 10 shown in FIG. 3 can be obtained.

The information recording medium in the present embodiment is an example of a perpendicular magnetic disk composed of a magnetic thin film layer. The magnetic disk may be composed of a magnetic layer or the like as a so-called in-plane magnetic disk.

(Details of “Chemical Strengthening Process” in Step S90)
Details of the “chemical strengthening step” in step S90 will be described below. As the alkali molten salt contained in the chemical strengthening treatment liquid, potassium nitrate, sodium nitrate or a nitrate mixed with these, potassium sulfate, sodium sulfate or a sulfate mixed with these can be used.

As a result of the chemical strengthening treatment, alkali metal ions (for example, lithium ions and sodium ions when using aluminosilicate glass) present on the surface of the glass substrate precursor are compared to these ions contained in the chemical strengthening treatment liquid. Thus, the ions are replaced with sodium ions and potassium ions having a large ion radius (ion exchange method). Due to the strain caused by the difference in ion radius, compressive stress is generated around the ion-exchanged region, and both main surfaces of the glass substrate precursor are strengthened in that region.

FIG. 5 is a schematic view showing a state before ion exchange of the glass substrate 1 in contact with the chemical strengthening treatment liquid 100. The term “contact with the chemical strengthening treatment liquid” includes all aspects such as a case where the glass substrate is immersed in the chemical strengthening treatment liquid and a case where the chemical strengthening treatment liquid is sprayed on the glass substrate. FIG. 5 schematically shows an aspect in which the surface layer portion of the glass substrate 1 is in contact with the chemical strengthening treatment liquid 100 and the surface layer portion contains lithium ions. The chemical strengthening treatment liquid 100 is a potassium nitrate solution, and the chemical strengthening treatment liquid 100 contains potassium ions.

The chemical strengthening treatment liquid 100 of the present embodiment further contains a certain amount of alkaline earth metal Be, Mg, Ca, Sr or Ba. In FIG. 5, calcium ions are shown as an example of an alkaline earth metal. The concentration of the alkaline earth metal contained in the chemical strengthening treatment liquid 100 is 50 ppb or more and 10,000 ppb or less.

When a predetermined amount of alkaline earth metal is contained in the chemically strengthened salt, the alkaline earth metal in the chemically strengthened salt appropriately inhibits the ion exchange of the alkali metal ions. While relaxing the exchange rate, alkali metal ions are penetrated deep into the glass substrate to increase the thickness of the compressive stress layer, and the gradient of the compressive stress layer (change in compressive stress intensity from the surface layer to the deep part) is moderated. It becomes possible. When the alkaline earth metal is not contained in the chemically strengthened salt, the gradient of the compressive stress layer formed by ion exchange of alkali metal ions is increased.

When manufacturing the information recording medium 10 of the heat-assisted recording method, it is necessary to perform a film formation process of the magnetic film on the main surface of the glass substrate at a high temperature. Heat is transferred to the extreme surface layer of the glass substrate with respect to the temperature rise of several minutes during film formation. When the compressive stress layer is formed by concentrating on a region where the depth of the surface layer of the glass substrate is small, alkali metal ions easily move during heating, and the compressive stress in the compressive stress layer easily changes. For this reason, relaxation of the compressive stress layer, that is, a phenomenon in which the compressive stress acting in the compressive stress layer on the surface of the glass substrate changes and the compressive strain is partially eliminated causes a change in the shape of the glass substrate.

In the manufacturing method of the present embodiment, it is possible to form a compressive stress layer having a gentle gradient compressive stress up to a deeper position of the glass substrate by containing an alkaline earth metal in the chemically strengthened salt. Since the amount of heat transferred to a deep position inside the glass substrate during heating is small, the compression stress in the compressive stress layer is hardly lowered at a deep position inside the glass substrate. Therefore, it is possible to suppress a change in the compressive stress layer during the high-temperature film forming process in the film forming process.

If the concentration of the alkaline earth metal (Be, Mg, Ca, Sr, Ba) in the chemical strengthening treatment solution is less than 50 ppb, the effect of suppressing the change of the compressive stress layer in the film forming process cannot be sufficiently obtained. On the other hand, when the concentration of the alkaline earth metal exceeds 10,000 ppb, the content of the alkaline earth metal is increased with respect to the alkali metal, so that it is difficult to obtain a desired compressive stress layer thickness. Therefore, an optimal compressive stress layer can be formed by setting the concentration of the alkaline earth metal contained in the chemical strengthening treatment liquid to 50 ppb or more and 10,000 ppb or less.

Moreover, the chemical strengthening treatment liquid exhibits the effect of alkaline earth metal more remarkably as the temperature is higher. This is because if the chemical strengthening treatment liquid is at a high temperature, the ion exchange rate is improved, so that a compressive stress layer is likely to be formed on the surface layer of the glass substrate. This is because a compressive stress layer having a small gradient of compressive stress can be formed deeper in the glass substrate. Specifically, the temperature of the chemical strengthening treatment liquid 100 is desirably 450 ° C. or higher.

FIG. 6 is a schematic diagram showing a state after the ion exchange of the glass substrate 1 in contact with the chemical strengthening treatment liquid 100. In FIG. 5, lithium ions existing on the surface layer of the glass substrate 1 come out into the chemical strengthening treatment liquid 100, and potassium ions present in the chemical strengthening treatment liquid 100 enter the glass substrate 1 after lithium ions come out. Then, ion exchange is performed. Lithium ions have a relatively small ionic radius and a low bonding strength, and therefore easily come out of the glass substrate 1. When potassium ions enter the glass substrate 1, the potassium ions have a relatively large ionic radius, so that compressive stress is generated in the glass substrate 1. Thereby, the strength of the glass substrate 1 is increased, and the glass substrate 1 having improved mechanical strength that is less likely to be damaged such as generation of cracks is produced.

Alkaline earth metals such as calcium ions contained in the chemical strengthening treatment solution 100 have characteristics that inhibit ion exchange of alkali metal ions and make it difficult for ion exchange to proceed. An alkaline earth metal that hinders the chemical strengthening treatment is intentionally contained in the chemical strengthening treatment liquid 100, and the chemical strengthening treatment is performed under conditions where ion exchange is unlikely to occur. A compressive stress layer having a gentle compressive stress gradient to a deeper position in the substrate 1 can be formed.

The alkali metal ions at a deep position away from the surface layer of the glass substrate 1 are not easily affected by heating in the subsequent heat treatment process, and are difficult to move even when heated. Therefore, in the deep position of the glass substrate 1, the fall of the compressive stress in a post process becomes difficult to occur. That is, changes in the compressive stress layer during the high-temperature film formation process in the film formation process can be suppressed.

In addition, even when alkaline earth metals such as Mg and Ca contained in the chemical strengthening treatment liquid 100 are precipitated as some salt on the surface of the glass substrate 1, the salt may be removed in the subsequent cleaning of the glass substrate 1. If possible, there will be no problem in the subsequent process. Further, when the main surface of the glass substrate 1 is polished after the ion exchange, naturally, no problem due to the salt occurs.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

<Example 1-3 and Comparative Example 1-6>
A predetermined amount of the raw material powder was weighed into a platinum crucible, mixed, and then heated to 1550 ° C. in an electric furnace for melting. After the raw material was sufficiently melted, a platinum stirring blade was inserted into the glass melt and stirred for 1 hour. Thereafter, the stirring blade was taken out and allowed to stand for 30 minutes, and then a glass block was obtained by pouring the glass melt into a jig. Thereafter, the glass block was held in the vicinity of the glass transition point of each glass for 2 hours, and then slowly cooled to remove strain. The obtained glass block was sliced into a disc shape having a thickness of about 1.5 mm and an outer diameter of 2.5 inches, and the inner and outer circumferences were concentrically cut out using a cutter. Then, rough polishing and precision polishing of both main surfaces were performed, and ion exchange treatment was performed by immersing in a 500 ° C. potassium nitrate chemical strengthening treatment solution containing a prescribed amount of Ca for 1 hour. Thereafter, cleaning was performed to prepare glass substrates for information recording media of Examples and Comparative Examples.

The compression stress layer was evaluated for the produced glass substrate for information recording medium. The sample was taken out from the glass substrate after ion exchange by cutting 1 mm in width, and the thickness of the compressive stress layer was evaluated from the cross-sectional direction of the taken out sample. A polarimeter (Shinko Seiki Co., Ltd.) was used as the measuring device.

Further, after that, a film formation process of Fe—Pt alloy was performed on the glass substrate at 600 ° C. for 3 minutes, and then the compression stress layer was evaluated and subjected to shape inspection. The shape inspection was judged based on whether or not the glass substrate was deformed. The presence / absence of deformation was determined by measuring the flatness of the glass substrate using a white light interference type surface shape measuring device Optiflat (manufactured by Phase Shift Technology). The flatness of the glass substrate before film formation was all 5 μm or less.

FIG. 7 is a diagram showing experimental conditions and experimental results of Example 1-3 and Comparative Example 1-6. In the result of the shape inspection shown in FIG. 7, the case where the flatness is 5 μm or less is evaluated as “no deformation”, the case where the flatness is more than 5 μm and less than 10 μm is evaluated as “small deformation”, and the flatness is 10 μm or more. Was evaluated as “large deformation”.

As shown in FIG. 7, in Example 1-3 in which the Ca concentration in the chemical strengthening treatment solution was 50 ppb or more and 10000 ppb or less, a compressive stress layer having a thickness of 140 to 150 μm was obtained after ion exchange. The thickness of the stress layer did not change. On the other hand, in Comparative Example 1-3 in which the Ca concentration in the chemical strengthening treatment liquid is less than 50 ppb and in Comparative Example 4-6 in which the Ca concentration exceeds 10,000 ppb, the compressive stress after ion exchange is compared with Example 1-3. The thickness of the layer was small, and the thickness of the compressive stress layer was further reduced after film formation.

For the glass substrate of Example 1-3 in which the thickness of the compressive stress layer did not change after film formation, no deformation was observed in the shape inspection. On the other hand, in the glass substrate of Comparative Example 1-6 in which the thickness of the compressive stress layer was changed after the film formation, it was confirmed by the shape inspection that the glass substrate was deformed.

As described above, in the glass substrate chemically strengthened with the Ca concentration contained in the chemical strengthening treatment liquid being 50 ppb or more and 10,000 ppb or less, a deep compressive stress layer is obtained by the chemical strengthening treatment, and the film is formed in a high temperature atmosphere. Later, the compressive stress layer did not change, and it was shown that there was no problem with the glass substrate shape.

Further, Be, Mg, Sr and Ba, which are alkaline earth metals other than Ca, were similarly evaluated, but the same tendency as in the case of Ca was obtained.

As described above, the embodiment of the present invention has been described. However, it should be considered that the embodiment and example disclosed this time are examples in all respects and are not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 glass substrate, 10 information recording medium, 30 hard disk drive, 100 chemical strengthening treatment liquid.

Claims

A method of manufacturing a glass substrate for HDD of a thermally assisted recording method in which the flying height of a magnetic head is 3 nm or less,
Forming a glass substrate;
A step of bringing the glass substrate into contact with a chemical strengthening treatment liquid,
The manufacturing method of the glass substrate for HDD whose density | concentration of the alkaline-earth metal contained in the said chemical strengthening process liquid is 50 ppb or more and 10,000 ppb or less.
The manufacturing method of the glass substrate for HDD of Claim 1 whose temperature of the said chemical strengthening process liquid is 450 degreeC or more.