JP3512702B2 - 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, a method of manufacturing a substrate thereof, and the like.

[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 occupied by the glass substrate, which can make the distance between the magnetic head and the magnetic disk narrower than that of aluminum, has been gradually increasing. The glass substrate, which tends to increase in number, is generally chemically strengthened to increase its strength so that it can withstand impact when mounted on a magnetic disk drive. 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 is changed from a thin film head to a magnetoresistive head (MR head),
It is shifting to a giant (large) magnetoresistive head (GMR head), and is responding to higher recording density.

[0004]

As described above, high smoothness of the magnetic disk surface is indispensable in order to reduce the flying height required for high recording density. In addition, when the MR head is used, high smoothness is required on the surface of the magnetic recording medium due to the problem of thermal asperity. In this thermal asperity, if there is an abnormal projection on the surface of the magnetic disk, the MR head is affected by this projection and heat is generated in the MR head, and this heat changes the resistance value of the head and causes electromagnetic conversion. This is a phenomenon that causes a malfunction.
The abnormal projection referred to in the present invention has a surface roughness Ra of 0.
When it is about 1 to 0.7 nm, Rmax / Ra is 20
It means a protrusion as described above.

As described above, demands for high smoothness of the surface of the magnetic disk have been increasing day by day both for lowering the flying height and for preventing the generation of thermal asperity. In order to obtain such a high smoothness of the magnetic disk surface, a highly smooth substrate surface is required after all, but it is no longer necessary to increase the recording density of the magnetic disk simply by polishing the substrate surface with high accuracy. Has reached the stage where it cannot be realized. In other words, no matter how highly accurately polished, high smoothness cannot be obtained if foreign matter is attached 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. On the other hand, the above-mentioned glass substrate having a high smoothness was obtained through a polishing process using abrasive grains of cerium oxide and a polishing process using colloidal silica abrasive grains. It was found that it is useful not only for the 2.5-inch glass substrate mounted on the hard disk of a personal computer but also for a desktop computer, and the demand for the 3-inch and 3.5-inch glass substrate is rapidly increasing. . Under such circumstances, it has become a problem in terms of cost to carry out the polishing process using different polishing abrasive grains, and a glass having the same high smoothness as the conventional one can be obtained by using cerium oxide abrasive grains. A substrate manufacturing method is required. However, it has been found that the above-mentioned foreign substances cannot be ignored after the polishing step using cerium oxide abrasive grains.

[0006] This kind of foreign matter is subjected to a normal cleaning process (neutral detergent, water, water, etc.) performed after a precision polishing process using a polishing abrasive such as cerium oxide so that the surface roughness Ra is about 1.0 nm or less. It cannot be removed by ultrasonic cleaning or scrub cleaning with IPA (isopropyl alcohol) or the like, and the protrusion height (Rmax) is about 10 nm. This type of foreign matter is caused by a precision polishing process using polishing abrasive grains such as cerium oxide, and is considered to be mainly polishing residue (protrusion). These days, for example,
A glass substrate having an ultra-smooth surface roughness of Rmax of 3 nm or less and Ra of 0.3 nm or less has been demanded, and in such a situation, this kind of polishing residue or the like becomes a problem. When thin films such as magnetic films are laminated with this kind of polishing residue etc. adhering to the glass substrate, protrusions are formed on the surface of the magnetic disk, which is a factor that prevents low flying height and prevention of thermal asperity. become.

An object of the present invention is to prevent such a polishing residue from remaining on the glass substrate. Another object is to manufacture an information recording medium with a high yield by using a glass substrate from which polishing residue or the like which is a sub-film defect is removed.

[0008]

The present invention has been made in view of the above-mentioned objects, and has the following configuration.

(Structure 1) In a method of manufacturing a glass substrate for an information recording medium, which has a step of polishing a main surface of a glass substrate, at least the main surface is washed with sulfuric acid after the step of polishing the main surface, When the surface roughness of the glass substrate was measured by an atomic force microscope (AFM), Ra = 0.1 to 0.7 nm, Rmax / Ra <20.
A method of manufacturing a glass substrate for an information recording medium, comprising:

(Structure 2) A step of polishing the main surface of the glass substrate, and a chemistry for strengthening the glass substrate by replacing some of the ions contained in the glass substrate with ions having a larger ion diameter than the ions. In a method of manufacturing a glass substrate for an information recording medium, which comprises a strengthening step, and a step of cleaning at least the main surface with sulfuric acid after the polishing step and before the chemical strengthening step. Manufacturing method of glass substrate for recording medium.

(Structure 3) The method for manufacturing a glass substrate for an information recording medium according to Structure 2, wherein pre-cleaning with an alkali is performed before cleaning with the sulfuric acid.

(Structure 4) In the method for manufacturing a glass substrate for an information recording medium, which has a step of polishing the main surface of the glass substrate, at least the main surface is washed with a cleaning liquid showing alkalinity after the step of polishing the main surface. And the process of
And a step of washing at least the main surface with sulfuric acid, the method for manufacturing a glass substrate for an information recording medium.

(Structure 5) The glass substrate for an information recording medium according to any one of Structures 1 to 4, wherein the polishing abrasive grains used in the step of polishing the main surface are cerium oxide. Method.

(Structure 6) In the method for manufacturing a glass substrate for an information recording medium having a step of polishing the main surface of a glass substrate, the polishing abrasive grains used in the step of polishing the main surface are cerium oxide, A method of manufacturing a glass substrate for an information recording medium, comprising a step of washing at least the main surface with sulfuric acid after the step of polishing the main surface.

(Structure 7) The method for manufacturing a glass substrate for an information recording medium according to Structure 6, wherein pre-cleaning with an alkali is performed before cleaning with the sulfuric acid.

(Structure 8) After the main surface is washed with sulfuric acid, some of the ions contained in the glass substrate are replaced with ions having an ion diameter larger than the ions, so that the glass substrate is chemically strengthened. 8. The method for manufacturing a glass substrate for an information recording medium according to any one of configurations 4 to 7, characterized by performing the steps.

(Structure 9) In the step of polishing the main surface,
9. The method for manufacturing a glass substrate for an information recording medium according to any one of configurations 2 to 8, wherein the surface roughness Ra of the glass substrate is polished to 1.0 to 0.1 nm or less.

(Structure 10) The production of the glass substrate for an information recording medium according to any one of Structures 2 to 9, wherein the sulfuric acid used in the sulfuric acid cleaning step has a concentration of 25% by volume or more. Method.

(Structure 11) The method for manufacturing a glass substrate for an information recording medium according to any one of Structures 1 to 10, wherein the glass substrate for an information recording medium is a glass substrate for a magnetic disk.

(Structure 12) The method for manufacturing a glass substrate for an information recording medium according to Structure 11, wherein the glass substrate for an information recording medium is a glass substrate for a magnetic disk for a magnetoresistive head.

(Structure 13) An information recording medium 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 structures 1 to 12. Production method.

(Structure 14) The method for manufacturing an information recording medium according to Structure 13, wherein the recording layer is a magnetic layer.

The method of manufacturing the glass substrate for an information recording medium of the present invention will be described below.

The method for producing a glass substrate for an information recording medium of the present invention is a method for producing a glass substrate for an information recording medium, which comprises a step of precision polishing the main surface, and after the polishing step,
The method is characterized by having a step of cleaning the glass substrate with sulfuric acid.

By carrying out the sulfuric acid cleaning after the polishing step in this way, polishing residues (protrusions) and the like (residual) caused by the polishing step can be effectively removed. This kind of polishing residue, etc., is a normal cleaning process (neutral detergent, water,
It cannot be removed by ultrasonic cleaning such as IPA or scrub cleaning.

The concentration of sulfuric acid used for washing with sulfuric acid is preferably 25% by volume or more. If the sulfuric acid concentration is less than 25% by volume, the effect of dissolving and removing the polishing residue with sulfuric acid is weak,
This is not preferable because it becomes difficult to remove the abnormal protrusion. The concentration of sulfuric acid is more preferably 50% or more, and further preferably 75% or more. The cleaning effect improves as the concentration of sulfuric acid increases. The temperature condition for washing with sulfuric acid is 40 ° C. or higher and the glass transition point or lower, preferably 60 ° C. or higher and 120 ° C. or lower. The cleaning effect improves as the temperature of sulfuric acid increases.

The step of washing with sulfuric acid is carried out during the manufacturing process of the glass substrate for an information recording medium, especially when the surface roughness Ra is 1.0 nm.
It is preferably performed after the precision polishing step of the main surface for the purpose of reducing roughness below. This is because, as will be described later, cerium oxide or the like used in the precision polishing process easily causes polishing residue and the like. The step of washing with sulfuric acid is effective in removing the polishing residue even if it is performed after the polishing step other than the precision polishing step.

In the case where the chemical strengthening step is involved, it is preferable that the step of 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 (protrusions) in the precision polishing step can be dissolved and removed by washing with sulfuric acid. 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. Will result in a sub-film defect. When precision polishing is performed after the chemical strengthening step, it is preferable to wash with sulfuric acid even after the precision polishing after the chemical strengthening step.

The step of washing with sulfuric acid is preferably performed in a wet state immediately after the polishing step. This is because if the sulfuric acid cleaning is performed in a wet state immediately after the polishing step, the above-mentioned polishing residue and the like are before drying and firmly adhering, so that the above-mentioned polishing residue and the like can be effectively removed. .

In the present invention, it is preferable to carry out pre-cleaning with an alkali before carrying out the sulfuric acid cleaning of the present invention. 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 due to the gentle etching effect. As the cleaning liquid used for the alkaline cleaning, an aqueous solution having an alkalinity such as sodium hydroxide, potassium hydroxide, and ammonia can be used.

In the present invention, the polishing abrasive grains used in the precision polishing step of the main surface include cerium oxide, zirconium oxide, aluminum oxide, manganese oxide, colloidal silica and the like. The sulfuric acid cleaning of the present invention is particularly effective for cleaning after precision polishing with cerium oxide as polishing abrasive grains.

In the present invention, the type, size and thickness of the glass substrate are not particularly limited. As the material of the glass substrate, for example, aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass,
Examples thereof include chain silicate glass and glass ceramics such as crystallized glass.

Of these, aluminosilicate glass is preferable because it has relatively strong resistance to sulfuric acid and is easily chemically strengthened. Among them, as aluminosilicate glass, SiO ₂ : 58 to 75% by weight, Al ₂ O ₃ : 5 to 23
% By weight, Li ₂ O: 3 to 10% by weight, Na ₂ O: 4 to 13
Glass for chemical strengthening that contains wt% as a main component, T
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 to 15 mol%, Si
O ₂ : Chemical strengthening glass containing 35 to 60 mol% is preferable. Aluminosilicate glass with such a composition is cleaned with silica hydrofluoric acid (has an etching effect)
Although the foreign substances can be removed by this method, the surface roughness of the glass becomes rough due to this cleaning (etching action), so the sulfuric acid cleaning of the present invention is suitable for such glass.
Further, the aluminosilicate glass or the like having the above-mentioned composition is chemically strengthened to increase the bending strength, the depth of the compression stress layer is deep, and the Knoop hardness is also excellent.

In the present invention, 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 and vibration resistance. Here, the chemical strengthening method is not particularly limited as long as it is a conventionally known chemical strengthening method, but for example, low temperature type chemical strengthening in which ion exchange is performed in a region not exceeding the transition temperature from the viewpoint of the glass transition point is preferable. . Examples of the alkali molten salt used for the chemical strengthening include potassium nitrate, sodium nitrate, and nitrates obtained by mixing them. Various forms are conceivable as a means for holding the glass substrate during the chemical strengthening, but the point is that the chemical strengthening treatment liquid can be brought into contact with the glass substrate in a predetermined state and liquid sagging does not occur. Is preferred.

The glass substrate for an information recording medium according to the above-mentioned manufacturing method of the present invention can be used as a glass substrate for a magnetic recording medium, a glass substrate for a magneto-optical disc, a disc substrate for electron optics such as an optical disc. In particular, it can be suitably used as a magnetic disk substrate for a magnetoresistive head for recording / reproducing with a magnetoresistive head (including a large magnetoresistive head).

Next, a method for manufacturing the information recording medium of the present invention will be described.

The method for producing an information recording medium of the present invention is characterized by forming at least a recording layer such as a magnetic layer on the glass substrate for an information recording medium obtained in the present invention.

In the present invention, particularly in the case of a magnetic recording medium,
Since it is possible to prevent the above-mentioned polishing residues (protrusions) that cause thermal asperity or head crash from remaining on the glass substrate, a magnetic recording medium having a magnetic layer formed on the glass substrate can be manufactured with high yield. can do. Further, the function of the magnetoresistive head can be fully brought out. Further, the performance can be sufficiently obtained as a CoPt-based magnetic recording medium that can be suitably used for the magnetoresistive head.

Similarly, on the recording / reproducing surface of the magnetic recording medium, the convex portion formed by the above-mentioned polishing residue (protrusion) or the like causing the thermal asperity does not occur, and the head crash occurs at a higher level. It can be prevented.

Further, the above-mentioned polishing residue (protrusion) or the like which causes thermal asperity does not cause a defect in a film such as a magnetic layer and cause an error.

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

The underlayer in the magnetic recording medium 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, NiAl / Cr, NiAl / CrMo, N
Examples include multilayer underlayers such as iAl / CrV.

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, C containing Co as a main component is used.
oCrTa, CoPtCr, CoNiPt, CoNi
CrPt, CoNiCrTa, CoCrPtTa, Co
Examples of the magnetic thin film include CrPtB and CoCrPtSiO. The magnetic layer includes a magnetic film and a non-magnetic film (for example, Cr,
A multilayer structure (for example, CoPtCr / CrMo / CoP) that is divided by CrMo, CrV, etc. to reduce noise.
tCr, CoCrPtTa / CrMo / CoCrPtT
a) or the like).

As a magnetic layer for a magnetoresistive head (MR head) or a large magnetoresistive head (GMR head), a Co-based alloy is used, and Y, Si, a rare earth element, 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, as the magnetic layer, magnetic particles of Fe, Co, FeCo, CoNiPt, etc. are dispersed in a non-magnetic film made of ferrite, iron-rare earth, SiO ₂ , BN or the like. It may be a granular structure or the like. The magnetic layer may be either in-plane type or 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 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 instead of the protective layer. For example, instead of the above-mentioned protective layer, colloidal silica fine particles are dispersed and applied on a Cr film diluted with an alcohol solvent on a Cr film, and further baked to form a silicon oxide (SiO ₂ ) film. You may form.

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

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

[0053]

EXAMPLES The present invention will be described in more detail based on the following examples.

Example 1

(1) Roughing Step First, a glass substrate made of aluminosilicate glass cut into a disk shape having a diameter of about 100 mmφ and a thickness of 3 mm from a sheet glass formed by the downdraw method was ground with a relatively coarse diamond. Grinding was performed with a grindstone to form a diameter of about 100 mmφ and a thickness of 1.5 mm. In this case, instead of the down draw method, the molten glass, upper mold,
A disk-shaped glass body may be obtained by direct pressing using a lower mold and a barrel mold. Alternatively, 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
% By weight, Li ₂ O: 3 to 10% by weight, Na ₂ O: 4 to 13
Glass for chemical strengthening containing wt% as a main component (for example, SiO ₂ : 63.5 wt%, Al ₂ O ₃ : 14.2 wt%, Na ₂ O: 10.4 wt%, Li ₂ O: 5 .4 wt%, ZrO _2: 6.0 wt%, Sb ₂ O _3: 0.4 wt%, As ₂ O _3: using 0.1 wt% content to aluminosilicate glass).

Then, both surfaces 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 B0601) to about 10 μm.

Next, using a cylindrical grindstone, a hole having a diameter of 25 mmφ was made in the central portion of the glass substrate, and the outer peripheral end face was also ground to a diameter of 95 mmφ, and then the outer peripheral end face and the inner peripheral face were chamfered with a predetermined chamfer. Processed. 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 processing step Next, the surface roughness of the end face of the glass substrate is 1 μm in 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 that 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, alumina abrasive grains having a grain size of # 400 are used, and 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 the polisher (polishing powder), and the first polishing step was carried out 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 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 been subjected to 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 (Polytex: manufactured by Speed Fam Co.), and the second polishing step was performed. Carried out. This second polishing step is intended to reduce the roughness of, for example, a surface roughness Ra of 1.0 to 0.3 nm or less, while maintaining the flat surface obtained in the first polishing step described above. Is. The polishing conditions were the same as in the first polishing step except that the polishing liquid was cerium oxide (particle size 1.0 μm) + water, the load was 100 g / cm ² , the polishing time was 5 minutes, and the removal amount was 5 μm. did.

(6) Sulfuric acid cleaning Next, the glass substrate was washed with concentrated sulfuric acid (96%) at a temperature of 60 ° C.
Washed with, polishing residue (protrusion) by cerium oxide polishing
Was dissolved and removed. The sulfuric acid cleaning method was performed by immersing a plurality of glass substrates held in sulfuric acid stored in a cleaning tank (about 6 minutes). Thus, by removing the polishing residue (protrusion) before the chemical strengthening in the next step, it is possible to prevent the sub-film defect. 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 adhered to the glass substrate,
Foreign substances unnecessary for the chemical strengthening are mixed in the chemical strengthening treatment liquid, and the foreign substances adhere to the glass substrate during the chemical strengthening, resulting in a sub-film defect. The occurrence of such a sub-film defect can be prevented by the above-mentioned sulfuric acid cleaning.

The glass substrate that has been cleaned with sulfuric acid is cleaned. This cleaning step means precision cleaning, and its purpose is to remove contaminants such as organic components adhering to the glass substrate and particles. The process from the cleaning process to the packaging in the case was performed under the environment of clean air supplied by the clean booth.
First, for the first cleaning, the glass substrate is washed with neutral detergent, neutral detergent, pure water, pure water, IPA (isopropyl alcohol),
Each IPA (steam drying) cleaning tank was sequentially immersed and cleaned. Ultrasonic waves were applied to each cleaning tank.

(7) Chemical Strengthening Step Next, the glass substrate having undergone the cleaning step was chemically strengthened. The chemical strengthening is performed by placing the chemical strengthening treatment liquid in a chemical strengthening treatment tank and immersing the glass substrate held by the holding member in the chemical strengthening treatment liquid. In addition, the holding member of the glass substrate is formed by connecting three support columns having a plurality of V grooves formed at equal intervals in the arrangement direction of the glass substrate with connecting members at both end surfaces thereof. Each of the plurality of glass substrates is supported and held at three points by V grooves in the same plane of the three columns, and a plurality of glass substrates are arranged in the extending direction of the columns.

The columns and the connecting members of the holding member of this embodiment are made of SUS316 which is an austenitic stainless alloy having excellent corrosion resistance in the high temperature range required for chemical strengthening. Further, 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
Etc. are suitable. Further, since the chemical strengthening treatment liquid of this embodiment is circulated through the filter, the chemical strengthening treatment liquid is kept clean.

As a concrete 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. About 3 washed glass substrates
It was dipped for a time. During this dipping, in order to chemically strengthen the entire surface of the glass substrate, a plurality of glass substrates were held by a holding member so that the end faces were held.

As described above, 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 by the immersion treatment in the chemical strengthening solution.
The glass substrate is strengthened by being replaced with potassium ions.

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

The glass substrate which has been subjected to the chemical strengthening is
It was immersed in a water bath at 0 ° C., rapidly cooled and maintained for about 10 minutes. This makes it possible to remove defective products containing minute cracks.

The surface roughness of the main surface of the glass substrate obtained through the above steps was measured by an atomic force microscope (AFM). Rmax was 2.81 nm and Ra was 0.24 n.
m and Rq were 0.30 nm. Further, upon close inspection of the glass surface, no abnormal protrusions causing thermal asperity were observed.

(8) Magnetic Disk Manufacturing Process Using an in-line type sputtering device on both sides of the glass substrate for magnetic disk obtained through the above-mentioned steps,
NiAl seed layer, CrMo underlayer, CoCrPtT
A magnetic layer and hydrogenated carbon protective layer were sequentially formed, and a perfluoropolyether lubricating layer was formed by the dipping method to obtain a magnetic disk.

When a glide test was performed on the obtained magnetic disk, a hit (a head scratches a projection on the surface of the magnetic disk) or a crash (a head collides with a projection on the surface of the magnetic disk) was found. I couldn't do it. It was also confirmed that no defect was generated in the film such as the magnetic layer due to the protrusion that causes thermal asperity.

A reproduction test was conducted on the magnetic disk of the present example which had been subjected to the glide test, using a magnetoresistive head. It was confirmed that the thermal asperity caused a malfunction in reproduction of all the plurality of samples (500 sheets). I couldn't do it.

Comparative Example 1 A glass substrate was prepared in the same manner as in Example 1 except that washing with sulfuric acid was not carried out after the polishing step. The surface roughness of the main surface of the obtained glass substrate was measured with an atomic force microscope (AFM).
The Rmax was 11.0 nm, the Ra was 0.30 nm, and the Rq was 0.40 nm. In addition, when the surface of the glass substrate was inspected in detail, abnormal protrusions that were considered to be polishing residue were observed.

Next, a magnetic disk having the same film structure as that of Example 1 was manufactured and a glide test and a reproduction test by a magnetoresistive head were carried out. Malfunction of was confirmed.

Example 2 A glass was prepared in the same manner as in Example 1 except that the washing with sulfuric acid described in Example 1 was performed with a 6 wt% sodium hydroxide aqueous solution (50 ° C., 30 minutes). A 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 3.70 nm, Ra was 0.27 nm, and Rq was 0.35 n.
It was m. Further, when the surface of the glass substrate was inspected in detail, no abnormal protrusions that could cause thermal asperity were observed.

Next, a magnetic disk having the same film structure as in Example 1 was manufactured and a glide test and a reproduction test by a magnetoresistive head were carried out. No malfunction was observed.

Example 3 A glass substrate was produced in the same manner as in Example 2 except that the third polishing step was performed after the second polishing step in Example 1. In this third polishing step, the surface roughness Ra is 0.3.
The purpose is to reduce the roughness so that the thickness becomes 0.1 nm or less. The polishing conditions for the third polishing step are: colloidal silica (average particle size: 100 nm) + water as the polishing liquid, a load of 25 to 100 g / cm ² , and a polishing time of 5 to 2
It was the same as the second polishing step, except that the removal amount was 0 to 5 μm for 0 minutes. When the surface roughness of the main surface of the obtained glass substrate was measured by an atomic force microscope (AFM), R
max is 2.0 nm, Ra is 0.15 nm, and Rq is 0.
It was 19 nm. Further, when the surface of the glass substrate was inspected in detail, no abnormal protrusions that could cause thermal asperity were observed.

Next, a magnetic disk having the same film structure as in Example 1 was prepared and a glide test and a reproduction test by a magnetoresistive head were carried out. No malfunction was observed.

As in Embodiments 2 and 3, pre-cleaning with alkali is performed before cleaning with sulfuric acid to disperse the polishing agent used in the polishing process and adhering to the glass substrate, thereby providing a gentle etching effect. This is preferable because the polishing agent can be removed efficiently.

Reference Example Instead of the concentrated sulfuric acid described in Example 1, the concentration was 20% by volume.
A glass substrate was produced in the same manner as in Example 1 except that the washing with dilute sulfuric acid (60 ° C., 6 minutes) was performed. The surface roughness of the main surface of the obtained glass substrate was measured with an atomic force microscope (A
When measured by FM, the Rmax was 10 nm, the Ra was 0.3 nm, and the Rq was 0.35 nm. In addition, when the surface of the glass substrate was inspected in detail, abnormal protrusions that were considered to be polishing residue were observed.

Next, a magnetic disk having the same film structure as in Example 1 was prepared and a glide test and a reproduction test using a magnetoresistive head were carried out. Malfunction of was confirmed.

Examples 4 to 6 The sulfuric acid washing conditions described in Example 1 were changed to a concentration of 75% by volume.
(60 ° C.) (Example 4), the concentration is 50% by volume (120
C.) (Example 5) and the concentration was 25% by volume (110.degree. C.) (Example 6), and a glass substrate was produced in the same manner as in Example 1. The surface roughness of the main surface of the obtained glass substrate was measured by an atomic force microscope (AFM). In Example 4, Rmax = 2.95 nm and Ra = 0.24.
nm, Rq = 0.31 nm, in Example 5, Rmax =
4.51 nm, Ra = 0.40 nm, Rq = 0.49n
m, in Example 6, Rmax = 5.83 nm, Ra =
It was 0.58 nm and Rq = 0.71 nm. Also,
Upon close inspection of the glass substrate surface, no abnormal protrusions that could cause thermal asperity were observed.

Next, a magnetic disk having the same film structure as in Example 1 was manufactured and a glide test and a reproduction test by a magnetoresistive head were carried out. As a result, a glide defect due to an abnormal protrusion and a reproduction due to thermal asperity were performed. No malfunction was observed.

Examples 7 to 9 Instead of the aluminosilicate glass used in Example 1, soda lime glass (Example 7), aluminoborosilicate glass (Example 8) and crystallized glass (Example 9) were used. A glass substrate and a magnetic disk were produced in the same manner as in Example 1 except for the above.

As a result, the same surface roughness as that of Example 1 was obtained on the glass substrate, and no abnormal protrusions causing the thermal asperity were observed. Further, in the glide test on the magnetic disk and the reproducing test using the magnetoresistive head, neither gliding failure due to abnormal protrusions nor reproducing malfunction due to thermal asperity was observed.

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

For example, the sulfuric acid cleaning of the present invention is not limited to cleaning after the final polishing step such as the above-mentioned second polishing step and third polishing step for the purpose of reducing the surface roughness, but also scratches remaining in the lapping step. Needless to say, it can be also used as a first polishing step for the purpose of removing strain and distortion, a lapping step for the purpose of improving the dimensional accuracy and shape accuracy of the substrate, and cleaning after the end surface polishing step.

[0097]

As described above, according to the present invention, it is possible to obtain a glass substrate for an information recording medium having no polishing residue or the like remaining on the glass substrate. Further, if an information recording layer or the like is manufactured using this glass substrate for information recording medium, an information recording medium without a sub-film defect can be obtained.

Particularly in the case of a magnetic recording medium, a low flying height without head crash can be realized. Furthermore, in the case of a magnetic recording medium that is electromagnetically converted by a magnetoresistive head, since there is no protrusion that causes thermal asperity, it is possible to prevent deterioration of the reproducing function due to thermal asperity. In addition, manufacturing defects due to protrusions that cause thermal asperity can be avoided,
Higher quality magnetic recording media can be obtained with high yield.

Claims (10)

(57) [Claims] 1. A main surface of a glass substrate is treated with an acid as polishing abrasive grains.
Magnetic disk having a step of polishing with cerium oxide and a step of chemically strengthening the glass substrate by substituting some ions contained in the glass substrate with ions having a larger ion diameter than the ions. A method for manufacturing a glass substrate for a magnetic disk, comprising a step of washing at least the main surface with sulfuric acid having a concentration of 25% by volume or more after the polishing step and before the chemical strengthening step . Method for manufacturing glass substrate. 2. A main surface of a glass substrate is treated with an acid as polishing abrasive grains.
Magnetic disk having a step of polishing with cerium oxide and a step of chemically strengthening the glass substrate by replacing some of the ions contained in the glass substrate with ions having a larger ion diameter than the ions. In the method for manufacturing a glass substrate for use , after the polishing step and before the chemical strengthening step, there is a step of washing at least the main surface with sulfuric acid having a concentration of 25% by volume or more, and the step of washing with the sulfuric acid. Is a method for manufacturing a glass substrate for a magnetic disk, which is performed in a wet state immediately after the polishing step. 3. Cerium oxide is used as a main surface with abrasive grains.
In the method for manufacturing a glass substrate for a magnetic disk, which includes a step of precisely polishing the glass substrate, after the polishing step, there is a step of washing the glass substrate with sulfuric acid having a concentration of 25% by volume or more. The method is a method for manufacturing a glass substrate for a magnetic disk , wherein the step is performed in a wet state immediately after the polishing step. 4. Cerium oxide is used as a main surface for polishing abrasive grains.
In a method for manufacturing a glass substrate for a magnetic disk, which has a step of precision polishing using the glass substrate, after the polishing step, the glass substrate is washed with sulfuric acid having a concentration of 25% by volume or more for the purpose of removing polishing residues caused by the polishing step. Magnetic disk characterized by having steps
Of manufacturing glass substrate for automobile. 5. In the step of washing with sulfuric acid, Ra = 0.1 to 0.7 nm and Rmax / Ra <2 when the surface roughness of the glass substrate is measured by an atomic force microscope (AFM).
0 to object (surface roughness Ra 0.1~0.7nm der
In the case of the above, projections (polishing residue) such that Rmax / Ra is 20 or more are performed for the purpose of preventing the glass substrate from remaining. 5) The method according to any one of claims 1 to 4, Manufacturing method of glass substrate for magnetic disk . 6. The step of washing with sulfuric acid is performed by thermal
5. The magnetic disk according to claim 1, which is carried out for the purpose of preventing polishing residues (protrusions) that cause asperity from remaining on the glass substrate.
Manufacturing method of glass substrate for disk . 7. Prior to washing with the sulfuric acid, process for producing a glass substrate for a magnetic disk according to any one of claims 1 to 6, characterized in that the pre-cleaning with an alkali. 8. polishing the main surface, any one of claims 1 to 7, characterized in that polishing the surface roughness Ra of the glass substrate to be equal to or less than 1.0~0.1nm A method of manufacturing a glass substrate for a magnetic disk according to . 9. glass substrate for a magnetic disk, a magnetic disk according to any one of claims 1 to 8, characterized in that a glass substrate for a magnetic disk for a magnetic resistive head
Of manufacturing glass substrate for automobile. 10. The magnet according to any one of claims 1 to 9.
A method of manufacturing a magnetic disk , comprising forming at least a magnetic layer on a glass substrate obtained by the method of manufacturing a glass substrate for an air disk .