JP2002109727A - Method for manufacturing information recording medium and glass board of it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a glass board for an information recording medium, which has perfect smoothness, by completely removing residue in grinding with strong acid treatment and preventing surface roughness caused by the strong acid treatment. SOLUTION: In a method for manufacturing a glass board for an information recording medium, main surface of the glass board is ground with abrasive grains, and then strong acid treatment is performed. Following material is used as an abrasive grain, that is, the content of a cause material, which reacts with a component of treatment liquid used at the strong acid treatment and then generates a component to erode the glass board surface, is equal or less than a predetermined value. Before the strong acid treatment, abrasive grains for grinding, which adhere to main surface of the glass board, are removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art There is a magnetic disk as one of information recording media as a recording medium of an information processing device. A magnetic disk is formed 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 capable of making the distance between the magnetic head and the magnetic disk narrower than aluminum has been gradually increasing. Further, the surface of the glass substrate is polished with high precision to achieve a high recording density so that the flying height of the magnetic head can be reduced as much as possible.

As described above, high smoothness of the surface of a magnetic disk is indispensable for a low flying height required for a high recording density. In order to obtain high smoothness of the magnetic disk surface, a substrate surface with high smoothness is ultimately required, but it is no longer possible to achieve high recording density of the magnetic disk simply by polishing the substrate surface with high precision. I have done it. That is, no matter how high the polishing accuracy, high smoothness cannot be obtained if foreign matter adheres to the substrate. Of course, foreign matter has been conventionally removed, but foreign matter on the substrate, which has been conventionally allowed, is considered to be a problem at today's high-density level.

On the other hand, the above-mentioned glass substrate having high smoothness is obtained by precision polishing using cerium oxide abrasive grains. However, after the polishing step using cerium oxide abrasive grains, there is a problem that the surface roughness cannot be reduced due to the remaining foreign matter (polishing residue) that cannot be removed by ordinary cleaning. And sulfuric acid cleaning (Japanese Patent Application No. 2000-93).
No. 304).

[0005]

However, when a treatment of washing with sulfuric acid is carried out after the polishing of cerium oxide, the effect of removing the unpolished residue was recognized, but it was found that a new problem occurred. That is, it was found that a concave defect was observed in the glass substrate that had been subjected to the above treatment.

SUMMARY OF THE INVENTION The present invention has been made under the above-mentioned background, and completely removes polishing residue by a strong acid treatment, and at the same time, prevents the occurrence of surface roughness due to the strong acid treatment to provide a high defect-free smoothness. It is an object of the present invention to provide a method for manufacturing a glass substrate for an information recording medium and a method for manufacturing an information recording medium, which can manufacture a glass substrate for an information recording medium having:

[0007]

Means for Solving the Problems As means for solving the above-mentioned problems, a first means is a method comprising polishing a main surface of a glass substrate using abrasive grains, and then performing a strong acid treatment. A method for producing a glass substrate for a recording medium, wherein the content of a causative substance that generates a component that erodes the glass substrate surface by reacting with a processing liquid component used in the strong acid treatment as the polishing abrasive grain is reduced. A method for manufacturing a glass substrate for an information recording medium, characterized by using a glass substrate having a predetermined amount or less. The second means includes a step of removing abrasive grains adhering to the main surface of the glass substrate before performing the strong acid treatment on the glass substrate for an information recording medium according to the first means. It is a manufacturing method. The third means is
A method for producing a glass substrate for an information recording medium, comprising a step of performing a strong acid treatment after polishing the main surface of the glass substrate with polishing abrasive grains, wherein the polishing abrasive grains are used in the strong acid treatment. When the content of the causative substance that generates a component that erodes the glass substrate surface by reacting with the liquid component exceeds a predetermined amount, the polishing grinder attached to the glass substrate main surface before performing the strong acid treatment. A method for producing a glass substrate for an information recording medium, comprising a step of removing particles. A fourth means is the glass for an information recording medium according to the second or third means, wherein the removing step is at least one selected from water polishing, tape polishing, and scrub cleaning. This is a method for manufacturing a substrate.
According to a fifth aspect, in the glass substrate for an information recording medium according to any one of the first to fifth aspects, the causative substance is fluorine and the content thereof is 5% by weight or less. It is a manufacturing method. A sixth means is the method for manufacturing a glass substrate for an information recording medium according to any one of the first to fifth means, wherein the abrasive grains are cerium oxide. A seventh means is the method for manufacturing a glass substrate for an information recording medium according to any one of the first to sixth means, wherein the strong acid is sulfuric acid. Eighth means is the method for producing a glass substrate for an information recording medium according to the seventh means, wherein the concentration of the sulfuric acid is 30% by weight or less. The ninth means is an information recording apparatus according to any one of the first to eighth means, wherein after a main surface of the glass substrate is treated with a strong acid, a chemical strengthening step for strengthening the glass substrate is performed. This is a method for manufacturing a glass substrate for a medium. A tenth means is characterized in that at least a recording layer is formed on an information recording medium glass substrate manufactured by the method for manufacturing an information recording medium glass substrate according to any one of the first to ninth means. This is a method for manufacturing an information recording medium.

[0008] The above means have been made based on the following facts that were first clarified as a result of the research of the present inventors. That is, the present inventors have thoroughly investigated the phenomenon in which the surface of a glass substrate is roughened due to a concave defect when a process of cleaning with sulfuric acid is performed after polishing using an abrasive. As a result, it was found that the surface roughness due to the concave defect was greatly affected by the type of the abrasive. That is, it was found that concave defects were remarkably generated in some types of abrasives, and were hardly found in other types of abrasives.

[0009] Therefore, the composition of the abrasive was examined in detail to trace components. Heretofore, it was not considered that the components of the abrasive were problematic, so the detailed components of the abrasive were almost unknown. As a result, it has been found that the abrasive that causes the concave defect commonly contains a causative substance that generates a component that reacts with a strong acid and erodes the glass. For example, it has been found that certain cerium oxide abrasives known as general abrasive grains include fluorine (fluoride), phosphorus (oxo acid salt), and the like.

For this reason, when sulfuric acid cleaning is performed in a state where abrasive grains are adhered to the surface of the glass substrate, “fluoride + sulfuric acid → hydrogen fluoride + sulfate” or “phosphorus oxoacid salt + sulfuric acid → phosphoric acid + It has been found that a reaction called "sulfate" occurs, and a concave defect is formed by the etching action of HF (hydrogen fluoride) or phosphoric acid at the portion where the abrasive has adhered, and the surface becomes rough. The present invention has been made based on this new elucidated fact.

That is, as in the first means, the content of a causative substance which generates a component which reacts with a processing solution component used in strong acid treatment to generate a component which erodes the glass substrate surface is used as the polishing abrasive used. By using what is below the fixed amount,
The concave defect due to the above-described etching action can be prevented.

Further, as in the second means, the content of a causative substance which generates a component which reacts with a processing solution component used in the strong acid treatment to generate a component which erodes the glass substrate surface is used as the polishing abrasive used. When the amount exceeds the fixed amount, a concave defect due to the above-described etching action can be prevented by providing a step of removing abrasive grains attached to the main surface of the glass substrate before performing the strong acid treatment.

The strong acid as used herein means one having a pKa (acid dissociation index) of 3 or less, for example, hydrochloric acid (HCl),
Nitric acid (HNO ₃ ), perchloric acid (HClO ₄ ), sulfuric acid (H ₂
SO ₄ ), chlorous acid, chloric acid, hydrobromic acid, hydroiodic acid, iodic acid, thiocyanic acid, amidosulfuric acid, chromic acid,
Phosphinic acid, phosphonic acid, phosphoric acid, diphosphoric acid, tripolyphosphoric acid, sulfurous acid, disulfuric acid, selenic acid, selenous acid, arsenic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, trifluoroacetic acid, picric acid, malonic acid, Refers to oxalic acid and the like. The strong acid treatment refers to, for example, an act of performing cleaning, surface treatment, and the like of a glass substrate.

[0014] The term "predetermined amount or less" means that the caustic substance contained in the abrasive grains reacts with sulfuric acid and the glass substrate is not locally etched, or even if the glass substrate is etched, the magnetic head in the glide test. This means that there is no crash or hit, and no error occurs in the recording / reproducing test in which a signal at the time of reproduction cannot be read.

As in the second and third means, before the strong acid treatment,
Since the abrasive grains adhering to the glass substrate are removed, a causative substance such as fluorine (fluoride) or phosphorus (oxo acid salt) contained in the abrasive grains reacts with a strong acid (eg, sulfuric acid). Thus, it is possible to reliably prevent the glass substrate from being locally etched. The causative substances are fluorine (F),
And phosphorus (P).

In the third means, exceeding the predetermined amount means that the abrasive grains adhered to the main surface of the glass substrate are not removed before the strong acid treatment is performed. The range in which the caustic substance reacts with the strong acid to locally etch the glass substrate, causing the magnetic head to crash or hit in a glide test, or an error in which a read signal cannot be read during a read / write test. .

Since the abrasive grains on the glass substrate after the use of the abrasive grains are strongly adhered, it is difficult to remove them by a usual cleaning method (ultrasonic cleaning with a neutral detergent, water, IPA, etc.). However, for example, as described in the fourth means, the abrasive grains are removed by a mechanical action such as water polishing (the concentration of the abrasive grains is 0), tape polishing, scrub cleaning and the like. As a result, the strong acid and the abrasive grains do not come into contact with each other, so that the occurrence of concave defects can be reliably prevented.

Examples of substances having an etching effect on a glass substrate include hydrogen fluoride, phosphoric acid, and alkali. Hydrogen fluoride and alkali are S
Phosphorus has the function of cutting the glass network forming oxides of i-O, Al-O, BO and PO, and phosphoric acid is the glass network-forming oxidation of glass component PO in the glass containing phosphorus oxides. Works to cut things.

Usually, polishing abrasive grains such as cerium oxide contain more than 5% by weight of fluorine and more than 0.1% by weight of phosphorus. When a strong acid treatment is performed after the polishing step, even a very small amount of fluorine or phosphorus contained in the abrasive grains reacts with the strong acid, so that hydrogen fluoride (HF) has a strong etching effect on the glass substrate. And phosphoric acid are generated, so that the glass substrate is etched at a portion where the abrasive locally remains.

For the reasons described above, the content of fluorine contained in the abrasive grains is preferably 5% by weight or less. In order to prevent concave defects, it is desirable to use abrasive grains preferably containing less than 3% by weight, more preferably containing no fluorine. However, in this case, considering the manufacturing cost and the like, the content of fluorine contained in the abrasive grains is preferably about 1 to 3% by weight for practical use. When the glass component contains an oxide of phosphorus, the content of phosphorus in the abrasive grains is desirably 0.1% by weight or less for the above-described reason.

Examples of abrasive grains used in the step of polishing a glass substrate include cerium oxide, zirconium oxide, aluminum oxide, manganese oxide, and colloidal silica. In particular, when cerium oxide is used as abrasive grains, the effects of the present invention are remarkably exhibited.

As described in the seventh means, among the strong acids, sulfuric acid is preferable because it does not corrode the glass substrate and is suitable for cleaning abrasives and foreign substances. Also,
As described in the eighth means, the concentration of sulfuric acid used for cleaning sulfuric acid is preferably 30% by weight or less. If it exceeds 30% by weight, the probability that fluorine or phosphorus reacts with sulfuric acid increases, and the incidence of concave defects increases. The temperature condition of sulfuric acid is 40 ° C. or more and the boiling point or less, preferably 60 ° C. or more and 1
20 ° C. or less. As the temperature of sulfuric acid increases, the cleaning effect improves. More preferably, the content is 15% by weight or less.

The step of strong acid treatment (particularly, washing with sulfuric acid) comprises:
It is preferably performed during the manufacturing process of the glass substrate for an information recording medium, particularly after the precision polishing process of the main surface for the purpose of reducing the surface roughness Ra to 1.0 nm or less.
This is because, as will be described later, cerium oxide or the like used in the precision polishing process tends to cause polishing residue and the like. The sulfuric acid cleaning step is effective in removing polishing residues and the like even if it is performed after a polishing step other than the precision polishing step.

When a chemical strengthening step is involved, it is preferable that the step of performing a strong acid treatment (in particular, washing with sulfuric acid) is performed after the precision polishing step of the main surface and before the chemical strengthening step. This is because the polishing residue (protrusion) in the precision polishing step can be dissolved and removed by the sulfuric acid cleaning. If chemical strengthening is performed with the polishing residue remaining on the glass substrate, foreign substances unnecessary for chemical strengthening will be mixed into the chemical strengthening treatment liquid, and foreign substances will adhere to the glass substrate during chemical strengthening. This causes a sub-film defect. When precision polishing is performed after the chemical strengthening step, it is preferable to perform sulfuric acid cleaning even after the precision polishing after the chemical strengthening step.

In the above-mentioned means, it is preferable to perform pre-cleaning with an alkali before performing the sulfuric acid cleaning. By performing pre-cleaning with an alkali, the polishing agent used in the polishing step and attached to the glass substrate can be dispersed, and the polishing agent can be efficiently removed by a gentle etching effect. As the cleaning liquid used for the alkali cleaning, any aqueous solution having an alkalinity such as sodium hydroxide, potassium hydroxide, or ammonia can be used.

In the above means, the type of the glass substrate,
The size, thickness and the like are not particularly limited. Examples of the material of the glass substrate include, for example, aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or glass ceramic such as crystallized glass. Can be

Of these, aluminosilicate glass is preferred because of its relatively high resistance to sulfuric acid and the ease of chemical strengthening. Among them, as the aluminosilicate glass, SiO ₂ : 58 to 75% by weight, Al ₂ O ₃ : 5 to 23
Wt%, Li ₂ O: 3~10 wt%, Na ₂ O: 4~13
Glass for chemical strengthening containing, by weight,
iO _2: 5~30 mol%, CaO: 1~45 mol%, M
gO + CaO: 10 to 45 _{mol%, Na 2 O + Li 2} O:
3 to 30 mol%, Al ₂ O _3: 0~15 mol%, Si
Glass for chemical strengthening containing O ₂ : 35 to 60 mol% is preferred.

Aluminosilicate glass or the like having such a composition is cleaned using silica hydrofluoric acid (has an etching action).
However, the cleaning (etching action) reduces the surface roughness of the glass. Therefore, the sulfuric acid cleaning of the present invention is suitable for such glass.
Further, the aluminosilicate glass or the like having the above-described composition is enhanced in bending strength by chemical strengthening, has a deep compressive stress layer, and is excellent in Knoop hardness.

In the above means, the surface of the glass substrate may be subjected to a chemical strengthening treatment by a low-temperature ion exchange method for the purpose of improving impact resistance, vibration resistance and the like. here,
The chemical strengthening method is not particularly limited as long as it is a conventionally known chemical strengthening method. For example, low-temperature chemical strengthening in which ion exchange is performed in a region not exceeding a transition temperature from the viewpoint of a glass transition point is preferable. Examples of the alkali molten salt used for chemical strengthening include potassium nitrate and sodium nitrate, and nitrates obtained by mixing them. Various means are conceivable as means for holding the glass substrate during chemical strengthening, but the point is that the chemical strengthening treatment liquid can come into contact with the glass substrate in a predetermined state and does not cause liquid dripping. Is preferred.

The glass substrate for an information recording medium according to the above means can be used as a glass substrate for a magnetic recording medium, a glass substrate for a magneto-optical disk, and a disk substrate for an electro-optical disk such as an optical disk. In particular, it can be suitably used as a magnetic disk substrate for a magnetoresistive head for recording and reproducing with a magnetoresistive head (including a giant magnetoresistive head).

Further, in the method of manufacturing an information recording medium according to the above-described means, in particular, in the case of a magnetic recording medium, it is possible to prevent the occurrence of a concave portion which causes a head crash or an error during recording / reproducing. A magnetic recording medium on which a magnetic layer or the like is formed can be manufactured with high yield.

The magnetic recording medium usually has a predetermined flatness and surface roughness, and has an underlayer, a magnetic layer, a protective layer, It is manufactured by sequentially laminating a lubricating layer.

The underlayer in the magnetic recording medium is selected according to the magnetic layer. As the underlayer, for example, Cr, M
An underlayer made of at least one or more materials selected from nonmagnetic metals such as o, Ta, Ti, W, V, B, and Al. In the case of a magnetic layer containing Co as a main component,
From the viewpoint of improving the magnetic properties, it is preferable that the material is Cr alone or a Cr alloy. The underlayer is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked.
For example, Cr / Cr, Cr / CrMo, Cr / CrV,
CrV / CrV, NiAl / Cr, NiAl / CrM
o, a multi-layer underlayer of NiAl / CrV or the like.

The material of the magnetic layer in the magnetic recording medium is not particularly limited. As the magnetic layer, for example, CoPt, CoCr, CoNi, CoNiCr,
CoCrTa, CoPtCr, CoNiPt, CoN
iCrPt, CoNiCrTa, CoCrPtTa, C
Magnetic thin films such as oCrPtB and CoCrPtSiO can be used. The magnetic layer is formed by replacing the magnetic film with a non-magnetic film (for example, C
r, CrMo, CrV, etc.) to reduce the noise (for example, CoPtCr / CrMo / C)
oPtCr, CoCrPtTa / CrMo / CoCrP
tTa).

As a magnetic layer corresponding to a magnetoresistive head (MR head) or a giant magnetoresistive head (GMR head), a Co-based alloy is made of Y, Si, a rare earth element, Hf, G
An impurity element selected from e, Sn, and Zn, or an element containing an oxide of these impurity elements is also included.

As the magnetic layer, in addition to the above, magnetic particles such as Fe, Co, FeCo, and CoNiPt are dispersed in a nonmagnetic film made of ferrite, iron-rare earth, SiO ₂ , BN, or the like. A granular structure may be used. Further, the magnetic layer may be of any of an in-plane type and a vertical type.

The protective layer in the magnetic recording medium 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 apparatus. Further, these protective films may have a single-layer structure or a multi-layer structure composed of the same or different films.

In the above means, 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, colloidal silica fine particles are dispersed and applied on a Cr film after diluting tetraalkoxysilane with an alcohol-based solvent, and then fired to form a silicon oxide (SiO 2) film. You may.

The lubricating layer in the magnetic recording medium is not particularly limited. The lubricating layer is formed, for example, by diluting perfluoropolyether, which is a liquid lubricant, with a solvent such as freon, applying the dip method, spin coating method, or spray method on the medium surface, and performing heat treatment as necessary. I do.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a glass substrate for an information recording medium, a method for manufacturing a glass substrate for an information recording medium, a method for manufacturing an information recording medium, and an information recording medium according to embodiments will be described in detail below. (Example 1) The method for manufacturing an information recording medium according to Example 1 includes (1) a roughening process, (2) an end surface mirror polishing process, (3) a sanding (lapping) process, and (4) a first process. Polishing step, (5) second polishing step, (6) water polishing step, (7)
It has a chemical strengthening step and (8) a magnetic disk manufacturing step. Hereinafter, these steps will be described in detail.

(1) Roughening Step First, a glass substrate made of aluminosilicate glass having a diameter of about 100 mmφ and a thickness of 3 mm cut out from a sheet glass formed by a downdraw method with a grinding wheel is removed from a relatively rough diamond. It was formed into a diameter of about 100 mmφ and a thickness of 1.5 mm by grinding with a grindstone. In this case, instead of the downdraw method, the molten glass is
A disk-shaped glass body may be obtained by direct pressing using a lower mold and a body mold. Further, it may be formed by a float method.

As the aluminosilicate glass, SiO ₂ : 58 to 75% by weight, Al ₂ O ₃ : 5 to 23
Wt%, Li ₂ O: 3~10 wt%, Na ₂ O: 4~13
A glass for chemical strengthening containing as a main component weight% (aluminosilicate glass containing no oxide of phosphorus such as P ₂ O ₅ ) was used.

Next, both surfaces of the glass substrate were ground one by one with a diamond grindstone having a finer grain size than the grindstone. The load at this time was about 100 kg. As a result, the surface roughness of both surfaces of the glass substrate can be reduced to Rmax (JIS
(Measured with B0601).

Next, a hole having a diameter of 25 mm was made in the center of the glass substrate using a cylindrical grindstone, and the outer peripheral end surface was also ground to a diameter of 95 mmφ. Then, predetermined chamfers were formed on the outer peripheral end surface and the inner peripheral surface. Processed. At this time, the surface roughness of the end face of the glass substrate was about 4 μm in Rmax.

(2) Step of Mirroring the End Surface Next, the surface roughness of the end surface of the glass substrate is adjusted to 1 μm by Rmax while rotating the glass substrate by brush polishing.
Polished to about 0.3 μm with Ra. The surface of the glass substrate that had been subjected to the end surface mirror finishing was washed with water.

(3) Sanding (Wrapping) Step Next, the glass substrate was sanded. This sanding step aims at improving dimensional accuracy and shape accuracy.
The sanding process was performed using a lapping device, and was performed twice while changing the grain size of the abrasive grains to # 400 and # 1000. More specifically, first, by using alumina abrasive grains having a grain size of # 400, setting the load L to about 100 kg, and rotating the internal rotation gear and the external rotation gear, both surfaces of the glass substrate housed in the carrier can be subjected to surface accuracy. 0 to 1 μm, surface roughness (Rma
x) Lapping was performed to about 6 μm.

Next, the particle size of the alumina abrasive grains was changed to # 1000.
Perform lapping instead of surface roughness (Rmax) 2μ
m. After finishing the sanding process,
Washing was performed by sequentially immersing each in a washing tank of a neutral detergent and water.

(4) First Polishing Step Next, a first polishing step was performed. This first polishing step is for removing scratches and distortions remaining in the above sanding step, and was performed using a polishing apparatus. For details, use a hard polisher (cerium pad MH) as a polisher (polishing powder).
C15: manufactured by Rodelnita), and the first polishing step was performed under the following polishing conditions.

Polishing liquid: cerium oxide (particle size: 1.3 μm)
(Free abrasive grains) + water Load: 300 g / cm ² (L = 238 kg) Polishing time: 15 minutes Removal amount: 30 μm Lower platen rotation speed: 40 rpm Upper platen rotation speed: 35 rpm Inner gear rotation speed: 14 rpm Outer gear rotation speed ： 29rpm

The glass substrate after the first polishing step is
Immerse in each washing tank of neutral detergent, pure water, pure water, IPA (isopropyl alcohol), IPA (steam drying) sequentially,
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 (Polytex: manufactured by Speed Fam), and the second polishing step was performed. Carried out. The second polishing step aims at reducing the roughness of, for example, the surface roughness Ra of about 1.0 to 0.3 nm or less while maintaining the flat surface obtained in the first polishing step described above. It is. The polishing conditions were such that the polishing liquid was cerium oxide (particle diameter: 1.0 μm, fluorine content: 6.3% by weight, phosphorus content:
0.2% by weight) + water, 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.

(6) Water Polishing Step Next, the supply of the polishing liquid was switched to water, and water polishing was performed for 2 minutes. The same polishing pad as used in the second polishing step was used, and the load was 30 g / cm ² .

(7) Washing with sulfuric acid Next, the glass substrate was washed with sulfuric acid (20% by weight) at a temperature of 70 ° C. The sulfuric acid cleaning method involves immersing a plurality of glass substrates held in sulfuric acid contained in a cleaning tank (about 3 times).
Min) I went. As described above, by reliably removing the polishing residue before the chemical strengthening in the next step, a sub-film defect can be prevented. In particular, it is important to perform this sulfuric acid cleaning before chemical strengthening. In other words, if chemical strengthening is performed with the polishing residue from cerium oxide polishing remaining on the glass substrate, foreign substances unnecessary for chemical strengthening will be mixed into the chemical strengthening treatment solution, and the glass substrate will be damaged during chemical strengthening. When a foreign substance adheres to the substrate, a sub-film defect occurs. The occurrence of such sub-film defects can be prevented by the above-described sulfuric acid cleaning.

The glass substrate which has been washed with sulfuric acid is washed. This cleaning step means precision cleaning, and is intended to remove dirt, particles, and the like made of organic components attached to the glass substrate. The process from this washing step to packing in a case was performed in an environment of clean air supplied by a clean booth.
First, the first cleaning is to clean the glass substrate with neutral detergent, neutral detergent, pure water, pure water, IPA (isopropyl alcohol),
It was immersed in each washing tank of IPA (steam drying) in order and washed. In addition, ultrasonic waves were applied to each cleaning tank.

(7) Chemical Strengthening Step Next, the glass substrate after the cleaning step was chemically strengthened. The chemical strengthening is performed by putting the chemical strengthening treatment liquid into the chemical strengthening treatment tank and immersing the glass substrate held by the holding member in the chemical strengthening treatment liquid. Note that the holding member for the glass substrate is formed by connecting three pillars having a plurality of V-grooves formed at equal intervals in the direction in which the glass substrates are arranged, with connecting members at both end surfaces thereof. The plurality of glass substrates are supported and held at three points by V-grooves in the same plane of the three columns, and are arranged in the direction in which the columns extend.

Each support and connecting member of the holding member of this embodiment is made of SUS316, which is an austenitic stainless steel alloy having excellent corrosion resistance in a high temperature range required for chemical strengthening. The chemical strengthening treatment tank is made of austenitic stainless alloy SUS304. The materials of the chemical strengthening treatment tank and the holding means may be the same or different.
Other stainless alloys include, for example, SUS316L
And the like are preferred. Further, since the chemical strengthening treatment liquid of the present embodiment is circulated through the filter, the chemical strengthening treatment liquid is kept clean.

As a specific method of chemical strengthening, a chemical strengthening solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) was prepared, and this chemical strengthening solution was heated to 400 ° C. and preheated to 300 ° C. Approximately 3 cleaned glass substrates
It was carried out by soaking for a time. At the time of this immersion, in order to chemically strengthen the entire surface of the glass substrate, a plurality of glass substrates were held by holding members so as to be held at end faces.

As described above, by performing the immersion treatment in the chemical strengthening solution, the lithium ions and the sodium ions on the surface layer of the glass substrate become the sodium ions in the chemical strengthening solution,
The glass substrate is strengthened by being respectively substituted by 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 which has been chemically strengthened is
It was immersed in a water bath at a temperature of 10 ° C., rapidly cooled, and maintained for about 10 minutes. This makes it possible to remove defective products containing minute cracks. Further, the glass substrate that had been chemically strengthened was subjected to sulfuric acid washing, a neutral detergent, pure water, IPA, and a washing / drying step of IPA (steam drying). Note that these cleaning steps are ultrasonic cleaning in which ultrasonic waves are applied.

The surface roughness of the main surface of the glass substrate obtained through the above steps was measured by an atomic force microscope (AFM), and it was found that Rmax was 6.5 to 9.3 nm and Ra was 0.6.
０．９0.9 nm. Further, when the glass surface was inspected in detail, no defect in the concave portion was observed (100 defects were observed after observing 100 substrates).

(8) Magnetic Disk Manufacturing Process On both surfaces of the magnetic disk glass substrate obtained through the above-described processes, an in-line sputtering device is used.
NiAl seed layer, CrMo underlayer, CoCrPtT
a A magnetic layer and a hydrogenated carbon protective layer were sequentially formed, and a perfluoropolyether lubricating layer was formed by dipping to obtain a magnetic disk.

When a glide test was performed on the obtained magnetic disk, no hit (the head hits a protrusion on the surface of the magnetic disk) or crash (the head hit the protrusion on the surface of the magnetic disk) was not recognized. . (100 out of 100 OK) Also, in the recording / reproducing test, no error that a signal at the time of reproduction cannot be read did not occur (100 out of 100 OK).

(Examples 2 to 3) Scrub cleaning (condition: using a surfactant and cleaning with a sheet-fed washing machine using a roller) instead of water polishing in the above-described embodiment (Example 2) Polishing with a tape-type texturing device (condition: polishing with a single-wafer-type tape-type texturing device that presses a tape against a rotated substrate while supplying diamond abrasive grains using a nylon-based tape (Example 3) A glass substrate was produced in the same manner as in Example, except that ()) was performed.

The surface roughness of the main surface of the obtained glass substrate was measured by an atomic force microscope (AFM). In Example 2, Rmax was 6.6 to 8.9 nm, and Ra was 0.1 to 0.9 mm.
In the third embodiment, Rmax is 6 to 0.9 nm.
It was 4-9.2 nm and Ra was 0.6-0.8 nm.
Further, when the surface of the glass substrate was subjected to a precision inspection, no defect in the concave portion was observed (100 defects were observed after observing 100 substrates).

When a glide test was performed on the obtained magnetic disk, no hit (the head touches a protrusion on the magnetic disk surface) or crash (the head collides with the protrusion on the magnetic disk surface) was not recognized. . (100 out of 100 OK) Also, in the recording / reproducing test, no error that a signal at the time of reproduction cannot be read did not occur (100 out of 100 OK).

(Examples 4 and 5) Further, the cerium oxide abrasive used in the second polishing step of the above example was changed to high-purity cerium oxide (fluorine content = 0% by weight). A glass substrate was produced in the same manner as in Example 2 (scrub cleaning) (Example 4). In addition, the polishing substrate used in the second polishing step was made of high-purity cerium oxide (fluorine content: 0% by weight), and a glass substrate was similarly prepared except that scrub cleaning was not performed before cleaning with strong acid (sulfuric acid). Fabricated (Example 5).

The surface roughness of the main surface of the obtained glass substrate was measured by an atomic force microscope (AFM). As a result, although the polishing rate was slightly lowered, both Examples 4 and 5 had Rmax of 5.3 to 7.0. 5 nm, Ra was 0.5 to 0.8 nm, and the result was smaller than the surface roughness of the glass substrate obtained in Example 2. Further, when the surface of the glass substrate was subjected to a precision inspection, no defect in the concave portion was observed (100 defects were observed after observing 100 substrates). As compared with Example 5, the cleaning performance (cleaning time and cleaning performance) is higher when a step of forcibly removing the abrasive from the glass substrate is performed before the strong acid treatment as in Example 4. Thus, it is possible to reliably prevent the remaining abrasive.

A glide test was performed on the obtained magnetic disk. As a result, no hit (the head touches a protrusion on the surface of the magnetic disk) or crash (the head hits a protrusion on the surface of the magnetic disk) was not recognized. (100 out of 100 OK). Further, in the recording / reproducing test, there was no error that a signal at the time of reproducing could not be read (100 out of 100 OK).

Comparative Example 1 Next, for comparison, water polishing was not performed before cleaning with sulfuric acid, and the cleaning conditions for sulfuric acid were 95%.
Example 1 except that concentrated sulfuric acid at 96 ° C and 96% by weight was used.
In the same manner as in the above, a glass substrate was produced. When the surface roughness of the main surface of the obtained glass substrate was measured by an atomic force microscope (AFM), Rmax was 8.1 to 11.3 nm, and R
a was 0.6 to 0.9 nm. In addition, when the surface of the glass substrate was subjected to a precision inspection, a defect of a concave portion having a size of about several μm to several mm and a depth of about 6 to 10 nm was observed (37 out of 100).

Next, a magnetic disk having the same film configuration as in Example 1 was manufactured, and a glide test and a recording / reproducing test were performed. An error that the signal at the time could not be read was confirmed in 19 out of 100 sheets.

Example 6 A glass substrate and a magnetic disk were produced in the same manner as in Example 1 except that crystallized glass was used instead of the aluminosilicate glass used in Example 1. In addition, the crystallized glass used in this example was SiO ₂ : 65 to 83% by weight, Li ₂ O: 8 to 1
3 wt%, Al ₂ O _3: 0~7 wt%, K ₂ O: 0~7 wt%, MgO: 0.5 to 3.5 wt%, ZnO: 0 to 5
Wt%, P ₂ O _5: 1~4 wt%, PbO: 0 to 5 wt%
Of the composition range was used. As a result, the same surface roughness as that of Example 1 was obtained on the glass substrate, and no concave portion causing a head crash or a recording / reproducing error was observed. In a glide test on a magnetic disk and a reproduction test using a magnetoresistive head, no head crash or an error during reproduction was recognized.

(Comparative Example 2) Next, for comparison, Example 6 was used.
The glass was used in the same manner as in Example 6 except that the crystallized glass used in Example 1 was not used, and that water polishing was not performed before washing with sulfuric acid, and that the washing conditions for sulfuric acid were 95 ° C. and 96% by weight of concentrated sulfuric acid. A substrate and a magnetic disk were manufactured. As a result, defects in the concave portions due to the reaction of fluorine or phosphorus contained in the abrasive with sulfuric acid were observed, and crashes and errors during reproduction were also confirmed in the glide test and the recording / reproducing test.

[0073]

As described above, the present invention relates to a method for producing a glass substrate for an information recording medium, comprising the steps of polishing the main surface of a glass substrate using abrasive grains and then performing a strong acid treatment. As the abrasive grains, a substance that causes a component that causes a component that reacts with a processing liquid component used in the strong acid treatment to generate a component that erodes the glass substrate surface is equal to or less than a predetermined amount. This allows
Manufacture of a glass substrate for an information recording medium capable of manufacturing a glass substrate for an information recording medium having high smoothness without defects by simultaneously removing polishing residue by a strong acid treatment and preventing surface roughness due to the strong acid treatment. It is possible to provide a method and a method for manufacturing an information recording medium.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G059 AA09 AB03 AB09 AB11 AC03 BB12 HB03 HB13 HB14 HB23 5D112 AA02 BA03 BA09 GA09 GA14 GA27 GA30

Claims (10)

[Claims] 1. A method for manufacturing a glass substrate for an information recording medium, comprising a step of polishing a main surface of a glass substrate using abrasive grains and then subjecting the glass substrate to a strong acid treatment. Manufacturing a glass substrate for an information recording medium, wherein the content of a causative substance that generates a component that erodes the surface of the glass substrate by reacting with a processing liquid component used in the process is not more than a predetermined amount. Method. 2. A method for manufacturing a glass substrate for an information recording medium according to claim 1, further comprising a step of removing abrasive grains attached to the main surface of the glass substrate before performing the strong acid treatment. . 3. A method for producing a glass substrate for an information recording medium, comprising a step of performing a strong acid treatment after polishing a main surface of a glass substrate using polishing abrasive grains, wherein said polishing abrasive grains are used as said strong acid treatment. When the content of the causative substance that generates a component that erodes the glass substrate surface by reacting with the processing liquid component used in the case exceeds a predetermined amount, it adheres to the glass substrate main surface before performing the strong acid treatment. A method for manufacturing a glass substrate for an information recording medium, comprising a step of removing polishing abrasive grains. 4. The production of a glass substrate for an information recording medium according to claim 2, wherein the removing step is at least one selected from water polishing, tape polishing, and scrub cleaning. Method. 5. The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein the causative substance is fluorine, and the content thereof is 5% by weight or less. . 6. The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein the abrasive grains are cerium oxide. 7. The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein the strong acid is sulfuric acid. 8. The method for producing a glass substrate for an information recording medium according to claim 7, wherein the concentration of the sulfuric acid is 30% by weight or less. 9. The information recording medium according to claim 1, wherein after a main surface of the glass substrate is treated with a strong acid, a chemical strengthening step is performed to strengthen the glass substrate. A method for manufacturing a glass substrate. 10. An information recording medium, wherein at least a recording layer is formed on an information recording medium glass substrate manufactured by the method for manufacturing an information recording medium glass substrate according to claim 1. Manufacturing method.