JP3534220B2 - Method for manufacturing glass substrate for information recording medium and method for manufacturing information recording medium - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording medium used as a recording medium for information processing equipment and a method for manufacturing a substrate thereof.

[0002]

2. Description of the Related Art A magnetic disk is one of the information recording media of this type. A magnetic disk is constructed by forming a thin film such as a magnetic layer on a substrate, and an aluminum or glass substrate has been used as the substrate. However, in recent years, in response to the pursuit of higher recording density, the ratio of the glass substrate that can make the distance between the magnetic head and the magnetic recording medium narrower than that of aluminum is gradually increasing.

The glass substrate, which tends to increase in number, is generally chemically strengthened so as to increase its strength so as to withstand impact when mounted on a magnetic disk driver. In addition, the surface of the glass substrate is highly accurately polished so that the flying height of the magnetic head can be lowered as much as possible to realize a high recording density. On the other hand, not only the glass substrate but also the magnetic head can be connected to the magnetic resistance (MR
Head) and is responding to higher recording densities.

[0004]

As described above, high flatness of the magnetic disk surface is indispensable for achieving the low flying height required for high recording density. In addition, when an MR head is used, high flatness is required on the surface of the magnetic recording medium due to the problem of TA (thermal asperity). In this thermal asperity, if there is a protrusion on the surface of the magnetic disk, the MR head is affected by the protrusion and heat is generated in the MR head. This heat changes the resistance value of the head and causes electromagnetic conversion. This is a phenomenon that causes a malfunction.

As described above, the demand for high flatness of the surface of the magnetic disk is increasing day by day both for lowering the flying height and for preventing the occurrence of thermal asperity. In order to obtain such a high flatness of the magnetic disk surface, a highly flat substrate surface is eventually required, but it is no longer necessary to polish the substrate surface with high accuracy. Is reaching the stage where it cannot be realized. In other words, no matter how highly accurately polished, high flatness cannot be obtained even if foreign matter adheres to the substrate. Of course, although foreign substances have been removed from the past, the foreign substances on the substrate, which have been allowed in the past, are now regarded as a problem at the level of high density.

Examples of this type of foreign matter include extremely fine iron powder, stainless steel pieces, which cannot be removed by ordinary washing,
Examples thereof include glass chips. When a thin film such as a magnetic film is laminated with these particles of iron powder or the like adhering to the glass substrate, a protrusion is formed on the surface of the magnetic disk, which reduces flying height and thermal asperity. It becomes an obstacle.

An object of the present invention is to prevent such particles of fine iron powder or the like from adhering to a glass substrate.

[0008]

Means for Solving the Problems The present invention has been made in view of the above-mentioned objects, and when the cause of adhesion of fine iron powder, glass chips, and stainless steel pieces to a glass substrate is earnestly investigated, chemical During the chemical strengthening of the glass substrate, the iron powder generated from various manufacturing equipment or construction equipment, which is placed around the chemical strengthening processing equipment in the strengthening processing liquid, is mixed into the chemical strengthening processing liquid. It was found that the mixed metal powder such as iron powder adheres to the glass substrate.

The first structure of the present invention is to bring some of the ions contained in the glass substrate into contact with the chemical strengthening treatment liquid so that some of the ions in the treatment liquid have an ion diameter larger than that of the ions. In a method for manufacturing a glass substrate for a magnetic recording medium, which comprises a chemical strengthening step of strengthening a glass substrate by substituting into, a means for trapping minute particles present in the chemical strengthening treatment liquid is provided. Manufacturing method of glass substrate for recording medium.

A second structure of the present invention is the glass substrate for an information recording medium according to the above structure 1, characterized in that the means for capturing the minute metal pieces is a filter for filtering the circulating chemical strengthening treatment liquid. Manufacturing method.

A third structure of the present invention is characterized in that the minute metal piece is minute iron powder and the capturing means is a magnet arranged so as to come into contact with the chemical strengthening treatment liquid.
A method for producing the glass substrate for an information recording medium described.

A fourth structure of the present invention is the method for manufacturing a glass substrate for an information recording medium according to the above structures 1 to 3, wherein the glass substrate for an information recording medium is a glass substrate for a magnetic disk. A fifth structure of the present invention is the method for manufacturing a glass substrate for an information recording medium according to the structure 4, wherein the glass substrate for a magnetic disk is a glass substrate used for a magnetic disk for a magnetoresistive head.

A sixth structure of the present invention is characterized in that at least a recording layer is formed on a glass substrate obtained by the method for manufacturing a glass substrate for an information recording medium according to any one of the structures 1 to 5. Method for manufacturing information recording medium.

A seventh structure of the present invention is the method for manufacturing an information recording medium according to the structure 6, wherein the recording layer is a magnetic layer.

As the chemical strengthening method of the present invention, low temperature type chemical strengthening in which ion exchange is carried out in a region not exceeding the glass transition temperature is preferable. As the alkali molten salt used as the chemical strengthening treatment solution, potassium nitrate, sodium nitrate, nitrate mixed with these, or the like can be used. Further, as the glass substrate, aluminosilicate glass containing zirconia, soda lime glass, or crystallized glass can be used.

The particles include metal particles such as iron powder and stainless steel, metal oxides, and glass chips. It is effective that these particles can be suitably removed if they have a size of several microns or more.

A filter or the like is used as a means for capturing the minute particles of the present invention. Any filter can be used as long as it can supply the chemically strengthened treatment liquid by filtration, and for example, a micro-sieve (a wire net having holes formed by etching) can be used. In this case, since the chemical strengthening treatment liquid is heated to a high temperature, a martensitic or austenitic stainless alloy having excellent corrosion resistance is preferable. Further, as a means for capturing other particles, a magnet or the like may be arranged so as to come into contact with the chemical strengthening treatment solution, particularly when the particles are fine iron powder. Further, the capturing means may be fixed or may be moved. The information recording medium glass substrate according to the manufacturing method of the present invention includes a magnetic recording medium glass substrate, an optical recording medium glass substrate, a magneto-optical recording medium glass substrate, and the like. In particular, the magnetic disk for a magnetoresistive head and the method for manufacturing the substrate thereof have remarkable effects.

Next, the magnetic recording medium of the present invention will be described. The magnetic recording medium of the present invention comprises at least a magnetic layer formed on the glass substrate for a magnetic recording medium of the present invention.

According to the present invention, particles that cause thermal asperity or head crash do not adhere, so that when a magnetic recording medium is manufactured by forming a magnetic layer or the like on a glass substrate, No protrusions formed on the main surface due to particles that cause thermal aspherity occur, and head crashes can be prevented at a higher level. In particular, for a magnetic recording medium that is reproduced by a magnetoresistive head, the function of the magnetoresistive head can be sufficiently obtained. Further, C which can be suitably used for a magnetoresistive head
The performance of the magnetic recording medium such as the oPt system can be sufficiently obtained.

Similarly, even on the recording / reproducing surface of the magnetic recording medium, a convex portion formed by particles that cause thermal asperity does not occur, and head crash can be prevented at a higher level.

Further, particles that cause thermal aspherity do not cause defects in the film such as the magnetic layer and cause errors.

The magnetic recording medium usually has a predetermined flatness and surface roughness, and on the glass substrate for a magnetic disk, the surface of which is chemically strengthened if necessary, an underlayer, a magnetic layer, a protective layer, The lubricating layer is sequentially laminated to manufacture.

The underlayer in the magnetic recording medium of the present invention is
It is selected according to the magnetic layer.

As the underlayer, for example, Cr, Mo, T
Examples thereof include an underlayer made of at least one material selected from nonmagnetic metals such as a, Ti, W, V, B and Al. In the case of the magnetic layer containing Co as a main component, it is preferable to use Cr alone or a Cr alloy from the viewpoint of improving the magnetic characteristics. The base layer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are laminated. For example, Cr / Cr, Cr / CrMo, Cr / CrV, Cr
V / CrV, Al / Cr / CrMo, Al / Cr / C
Examples include multilayer underlayers such as r, Al / Cr / CrV, and Al / CrV / CrV.

The material of the magnetic layer in the magnetic recording medium of the present invention is not particularly limited.

As the magnetic layer, for example, CoPt, CoCr, CoNi, CoNiCr, C containing Co as a main component is used.
oCrTa, CoPtCr, CoNiPt, CoNi
CrPt, CoNiCrTa, CoCrTaPt, Co
Examples include magnetic thin films such as CrPtSiO. The magnetic layer includes a magnetic film and a non-magnetic film (for example, Cr, CrMo, Cr
Multi-layer structure (for example, CoPtCr / CrMo / CoPtCr, CoC) divided by V etc. to reduce noise
rTaPt / CrMo / CoCrTaPt, etc.).

As a magnetic layer for a magnetoresistive head (MR head) or a large magnetoresistive head (GMR head), a Co alloy is used, and Y, Si, rare earth elements, Hf, and G are used.
Also included are impurity elements selected from e, Sn, and Zn, or those containing oxides of these impurity elements.

In addition to the above, the magnetic layer has a structure in which magnetic particles such as Fe, Co, FeCo and CoNiPt are dispersed in a non-magnetic film made of ferrite, iron-rare earth, SiO2, BN or the like. It may be a granular material or the like. Further, the magnetic layer may be in either an inner surface type or a vertical type recording format.

The protective layer in the magnetic recording medium of the present invention is not particularly limited.

Examples of the protective layer include a Cr film, a Cr alloy film, a carbon film, a zirconia film, and a silica film. These protective films can be continuously formed with an underlayer, a magnetic layer and the like by an in-line type sputtering device. Also,
These protective films may be a single layer, or may be a multi-layer structure composed of the same or different types of films.

In the present invention, another protective layer may be formed on the protective layer or in place of the protective layer. For example, instead of the above protective layer, tetraalkoxylane is diluted with an alcoholic solvent on a Cr film, colloidal silica fine particles are dispersed and applied, and further baked to form a silicon oxide (SiO2) film. You may.

The lubricating layer in the magnetic recording medium of the present invention is not particularly limited.

The lubricating layer is prepared by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon, and coating it on the surface of the medium by a dipping method, a spin coating method or a spraying method, and if necessary. It is formed by heat treatment.

[0034]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1

(1) Roughing Step First, a glass substrate made of aluminosilicate glass cut out from a sheet glass formed by the downdraw method into a disc shape having a diameter of 96 mmφ and a thickness of 3 mm with a grinding wheel,
Diameter 96 with a relatively coarse diamond wheel
It was molded into mmφ and a thickness of 1.5 mm. In this case, instead of the downdraw method, the molten glass may be directly pressed using an upper die, a lower die and a barrel die to obtain a disc-shaped glass body. Alternatively, it may be formed by the float method.

As an aluminosilicate glass, SiO2 is 57 to 74%, ZnO2 is 0 to 2.8%, Al2O3 is 3 to 15%, and LiO2 is 7 to 7 in mol%.
Glass for chemical strengthening containing 16% as a main component and 4% to 14% Na2O (eg, SiO2:
67.0%, ZnO2: 1.0%, Al2O3: 9.0%,
A glass for chemical strengthening containing LiO2: 12.0% and Na2O: 10.0% as main components was used.

Then, both sides of the glass substrate were ground one by one with a diamond grindstone having a finer grain size than that of the grindstone. The load at this time was about 100 kg. As a result, the surface roughness of both surfaces of the glass substrate is Rmax (JIS
(Measured with B 0601) to a thickness of about 10 μm.

Next, a hole is made in the central portion of the glass substrate using a cylindrical grindstone, the outer peripheral end face is also ground to a diameter of 95 mmφ, and then the outer peripheral end face and the inner peripheral face are subjected to predetermined chamfering. did. At this time, the surface roughness of the end surface of the glass substrate was about 4 μm in Rmax.

(2) End face mirror surface finishing step Next, the surface roughness of the end face of the glass substrate is 1 μm as Rmax by brush polishing while rotating the glass substrate.
It was polished to about 0.3 μm with Ra.

The surface of the glass substrate which had been subjected to the above-mentioned end face mirror finishing was washed with water.

(3) Sanding (Wrapping) Step Next, the glass substrate was sanded. This sanding step aims to improve dimensional accuracy and shape accuracy.
The sanding process was performed using a lapping device, and was performed twice by changing the grain size of the abrasive grains to # 400 and # 1000.

Specifically, first, using alumina abrasive grains having a grain size of # 400, the load L is set to about 100 kg,
By rotating the adder gear and the adder gear, the surface precision of both surfaces of the glass substrate housed in the carrier is 0 to 1 μm,
Lapping was performed so that the surface roughness (Rmax) was about 6 μm.

Next, the grain size of the alumina abrasive grains was adjusted to # 1000.
The surface roughness (Rmax) 2μ
It was about m.

The glass substrate that had been sanded was washed by sequentially immersing it in a washing bath of neutral detergent and water.

(4) First Polishing Step Next, a first polishing step was performed. This first polishing step is intended to remove the scratches and strains remaining in the sanding step described above, and was performed using a polishing apparatus.

More specifically, a hard polisher (cerium pad MHC15: manufactured by Speedfam) was used as a polisher (polishing powder), and the first polishing step was carried out under the following polishing conditions.

Polishing liquid: cerium oxide + water load: 300 g / cm ² (L = 238 kg) Polishing time: 15 minutes Removal amount: 30 μm Lower surface plate rotation speed: 40 rpm Upper surface plate rotation speed: 35 rpm Inner gear rotation speed: 14 rpm Outer gear rotation speed: 29 rpm

The glass substrate which has undergone the first polishing step is
Immerse in each cleaning bath of neutral detergent, pure water, pure water, IPA (isopropyl alcohol), IPA (steam drying),
Washed.

(5) Second Polishing Step Next, using the polishing apparatus used in the first polishing step, the polisher was changed from a hard polisher to a soft polisher (Porelax: manufactured by Speed Fam Co.), and the second polishing step was performed. Carried out. The polishing conditions were the same as in the first polishing step, except that the load was 100 g / cm ² , the polishing time was 5 minutes, and the removal amount was 5 μm.

The glass substrate that has undergone the second polishing step is
It was washed by sequentially immersing it in each of a neutral detergent, a neutral detergent, pure water, pure water, IPA (isopropyl alcohol) and IPA (steam drying). Ultrasonic waves were applied to each cleaning tank.

(6) Chemical Strengthening Step Next, the glass substrate which has undergone the grinding, polishing and cleaning steps is subjected to chemical strengthening. The chemical strengthening is performed by storing the chemical strengthening treatment liquid in the chemical strengthening treatment tank and immersing the holding means holding the glass substrate in the chemical strengthening treatment tank. At this time, the treatment liquid in the chemical strengthening treatment tank is circulated by a pump, and is filtered in a clean state by a stainless mesh of about 1 micron mesh provided in the middle of the circulation path and is supplied to the treatment tank in a clean state. There is. This filter, a stainless steel net, generates dust from manufacturing equipment and construction equipment, iron powder that floats in the atmosphere and falls into the chemical treatment tank, stainless steel pieces, or glass chips generated by rubbing the glass substrate onto the glass substrate. It can be prevented from adhering.

Under such an environment, chemical strengthening was performed as follows. Potassium nitrate (60%) and sodium nitrate (4
(0%) was prepared, the chemical strengthening solution was heated to 400 ° C. in the chemical strengthening treatment tank, and the cleaned glass substrate preheated to 300 ° C. was immersed for about 3 hours. At the time of this immersion, in order to chemically strengthen the entire surface of the glass substrate, a plurality of glass substrates were housed in a holder so as to be held by the end faces.

As described above, by performing the immersion treatment in the chemical strengthening solution, the lithium ion and the sodium ion in the surface layer of the glass substrate are converted into the sodium ion in the chemical strengthening solution,
The glass substrate is strengthened by being replaced with potassium ions.

The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 to 200 μm.

The glass substrate after the above-mentioned chemical strengthening is
It was immersed in a water bath at 0 ° C., rapidly cooled and maintained for about 10 minutes.

After the quenching, the glass substrate is heated to about 40.degree.
It was dipped in sulfuric acid heated to, and washed while applying ultrasonic waves.

The surface roughness Ra of the glass substrate obtained through the above steps was 0.5 to 1 nm. Further, when the glass surface was closely inspected, no particles causing the thermal aspherity were found. In particular,
No iron powder of 3-5 microns or more was observed.

(7) Magnetic Disk Manufacturing Process A texture layer, a Cr underlayer, and a CrMo underlayer formed by sputtering of AlN are formed on both surfaces of the glass substrate for a magnetic disk obtained through the above-mentioned steps by using an in-line type sputtering device. , CoPtCrTa magnetic layer and C protective layer were sequentially formed to obtain a magnetic disk.

A glide test was carried out on the obtained magnetic disk, and no hits (the head scratched the projections on the magnetic disk surface) or crashes (the head collided with the projections on the magnetic disk surface) were not observed. . It was also confirmed that particles causing the thermal asperity did not cause defects in the film such as the magnetic layer.

Incidentally, a glide test was carried out for comparison with this embodiment, which was chemically strengthened with a clean chemical strengthening treatment liquid as in the present invention, and a comparative example, which was chemically strengthened without using a trapping means. It turned out that the example had far fewer defectives.

A reproduction test was conducted on the magnetic disk of the present example which had completed the glide test, using a magnetoresistive head. It was confirmed that the reproduction error due to the thermal asperity occurred for all of a plurality of samples (500 sheets). I was not able to admit.

Examples 2 to 3 Glass for magnetic disk was prepared in the same manner as in Example 1 except that soda lime glass (Example 2) and soda aluminosilicate glass (Example 3) were used in place of the aluminosilicate glass. A substrate and a magnetic disk were obtained.

As a result, the same thing as in Example 1 was confirmed. .

Example 4 Al (film thickness 50 Å) / Cr (100) was formed on both surfaces of the magnetic disk glass substrate obtained in Example 1.
0 angstrom) / CrMo (100 angstrom) underlayer, CoPtCr (120 angstrom) / CrMo (50 angstrom) / Co
A magnetic layer made of PtCr (120 Å),
A Cr (50 Å) protective layer was formed by an in-line type sputtering device.

The above substrate was dipped in an organic silicon compound solution (mixture of water, IPA and tetraethoxysilane) in which fine silica particles (grain size 100 Å) were dispersed,
A protective layer made of SiO2 having a texture function is formed by firing, and the protective layer is further subjected to a dip treatment with a lubricant made of perfluoropolyether to form a lubricating layer. Got

When a glide test was conducted on the obtained magnetic disk, no hit or crush was observed. It was also confirmed that no defect was generated in the film such as the magnetic layer. Furthermore, as a result of a reproduction test using a magnetoresistive head, no malfunction of reproduction due to thermal asperity was observed.

Example 5 Al / Cr / Cr was used as the underlayer and CoNiCr was used as the magnetic layer.
A magnetic disk for a thin film head was obtained in the same manner as in Example 4 except that Ta was used.

It was confirmed that the magnetic disk was the same as in Example 4.

Although the present invention has been described with reference to the preferred embodiments, the present invention is not necessarily limited to the above embodiments.

A filter was used as a means for trapping particles in the chemical strengthening treatment liquid. For example, if only iron powder is trapped, a magnet or the like is placed in the chemical strengthening treatment liquid or the inner wall of the chemical strengthening tank. It may be inscribed in or embedded in.

[0072]

As described above, according to the present invention, it is possible to prevent metal pieces such as iron powder or metal oxide pieces from adhering to the glass substrate during the chemical strengthening. Particles that cause ferritity are not generated, and it is possible to prevent deterioration of the reproduction function due to thermal aspherity.

Further, it is possible to avoid defects due to particles that cause thermal aspherity, and it is possible to obtain a higher quality magnetic recording medium with a high yield.

   ─────────────────────────────────────────────────── ─── Continued front page       (56) Reference JP-A-5-32431 (JP, A)                 JP-A-7-155712 (JP, A)                 JP-A-8-64572 (JP, A)                 JP-A-4-162627 (JP, A)                 JP 62-237991 (JP, A)

Claims (4)

(57) [Claims] 1. A glass substrate by bringing a glass substrate into contact with a chemical strengthening treatment liquid to replace some of the ions contained in the glass substrate with ions in the treatment liquid having an ion diameter larger than the ions. In a method of manufacturing a glass substrate for a magnetic disk , which includes a chemical strengthening step for strengthening a thermal asperity (TA: Thermal Asperit
To prevent degradation of the playback function by y), thermal
Causes of asperity (TA: Thermal Asperity)
To prevent the adhered particles from sticking to the glass substrate
, The magnetoresistive f, characterized in that a means for capturing fine particles present in the chemical strengthening treatment solution
Magnetic disk used for magnetic discs
Method of manufacturing a glass substrate for a click. 2. A means for capturing fine particles comprises:
2. The magnetoresistive head according to claim 1, which is a filter for filtering the circulating chemical strengthening treatment liquid.
For manufacturing a glass substrate for a magnetic disk used for a magnetic disk . 3. A fine metal piece, which is one of the fine particles, is fine iron powder, and the capturing means is a magnet arranged so as to come into contact with the chemical strengthening treatment liquid. The magnetic disk reproduced by the described magnetoresistive head.
A method of manufacturing a glass substrate for a magnetic disk used for a disk . 4. A magnetic Di according to any one of claims 1 to 3
Magnetic, which comprises forming at least a magnetic layer on a glass substrate obtained by the manufacturing method of a glass substrate for disk
Used for magnetic disks reproduced by air resistance type heads
Manufacturing method of magnetic disk .