JP2002133649A - Substrate for information recording medium and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the flying height of a substrate for information recording medium to be made smaller without a head crash or a thermal asperity. SOLUTION: After a substrate work, a lapping work, the first and the second polisher works and then a final polishing work are conducted in polishing process. In this case, the final polishing work is conducted using final polishing abrasive materials produced by removing completely CeO2 polishing particles with particle diameters over 3 μm from CeO2 polishing particles with particle diameters from 0.1 μm to 3 μm through a wet classification by a natural sedimentation and making the content of particles having diameters from 1 μm to 3 μm to 10 wt.% or less and then producing the final polishing abrasive (final abrasive material) with the content of fluorine in the CeO2 polishing particles less than 1 wt.% preferably. The requested information recording medium substrate is produced through a texture treatment, a chemical strengthening and a final cleaning treatment after the completion of the above final polishing work.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate for an information recording medium and a method for manufacturing the same, and more particularly, to a substrate for an information recording medium used in an information recording apparatus represented by a hard disk drive (hereinafter referred to as "HDD"). And its manufacturing method.

[0002]

2. Description of the Related Art In recent years, the progress of information technology has been remarkable, and various information recording devices for storing information have been actively developed. "HDD").

An HDD records and reproduces information by sliding a magnetic head over a data zone formed on a disk substrate.
(ntact Start Stop) method and ramp load method.

In the CSS method, uniform fine irregularities of about several tens of nm, which are called CSS zones, are mainly provided along the inner or outer circumference of the disk substrate. Glide over the data zone,
When the disk substrate stops or starts, it slides on the CSS zone of the disk substrate.

In the ramp load method, the magnetic head glides on the disk substrate while the disk substrate is rotating, and the magnetic head is stored in a predetermined storage position when the disk substrate stops.

Therefore, in either of the above-mentioned CSS type or ramp-load type driving systems, while the disk substrate is rotating, the magnetic head is slightly lifted from the disk substrate, and a gap of several tens of nm (hereinafter, referred to as a distance) from the magnetic head. ,
While maintaining the “flying height”, the glide will occur on the surface of the disk substrate.

By the way, with the recent increase in the amount of information storage, a small HDD having a large storage capacity has been demanded. Therefore, it is necessary to increase the data zone density. Therefore, it is required to reduce the flying height in order to cope with such a high data zone density.

Further, in recent years, a drive method called a contact method in which a magnetic head and a disk substrate are always in contact has been studied, and the disk substrate material is relatively small and thin. Easy glass materials have come to be widely used.

On the other hand, in the HDD, when a magnetic head gliding on a disk substrate comes into contact with the disk substrate, it is called a texture process in order to avoid applying an excessive resistance to the magnetic head. Fine irregularities are formed on the surface of a disk substrate. For example, after fine polishing is performed using an abrasive containing free abrasive grains having an average particle diameter of 0.3 μm to 3.0 μm, silica hydrofluoric acid is used. (Japanese Patent Laid-Open No. 2000-132829) has been proposed.

In the prior art, since the etching treatment is performed using silica hydrofluoric acid having a lower etching rate (lower etching power) than a hydrofluoric acid aqueous solution containing hydrofluoric acid or potassium fluoride, the surface roughness is reduced. It is considered that control can be performed with high accuracy.

[0011]

However, according to the experimental results of the present inventors, precision polishing using an abrasive (free abrasive) having an average particle diameter of 0.3 μm to 3.0 μm is performed according to the above-mentioned conventional technology. Even if the polishing is performed, when the polishing slurry contains a polishing slurry having a large particle diameter of 3 μm or more, even if the amount is extremely small, the projection height is large due to the etching treatment after the polishing treatment. It was found that linear or dot-like abnormal projections were formed.

If the abnormal projection on the substrate collides with the magnetic head, a head crash may occur, or thermal asperity in which the magnetic head detects an abnormal signal and malfunctions due to heat generated by the collision may occur. .

[0013] On the other hand, for polishing a glass substrate, rare earth oxides having excellent polishing efficiency, particularly cerium oxide-based abrasive grains starting from natural ore are preferably used. It is technically and economically difficult to completely remove abrasive particles having a large particle size of 3 μm or more even if dry classification is performed on the system abrasive particles as is as the powder raw material.

That is, in the case of the cerium oxide-based abrasive grains, for example, a bastnasite-based abrasive obtained by subjecting a rare earth mineral containing cerium as a main component to a predetermined chemical treatment, followed by firing, pulverization, and dry classification. Abrasives and the like are known, but even if an attempt is made to classify a large amount of powdery abrasives by the dry classification, it is difficult to classify only abrasives having a large particle size of 3 μm or more with high accuracy due to turbulence of air flow and the like. In addition, if a large particle size of 3 μm or more is to be completely removed, the yield is greatly reduced, and the productivity is deteriorated.

The present invention has been made in view of such circumstances, and provides an information recording medium substrate capable of further reducing the flying height without causing a head crash or thermal asperity, and a method of manufacturing the same. The purpose is to do.

[0016]

As described in the section of [Problems to be Solved by the Invention], according to the experimental results of the present inventors, an abrasive having an average particle diameter of 0.3 μm to 3.0 μm is used. Even if precision polishing is performed by using the polishing agent, if the polishing agent contains a polishing agent having a large particle diameter of 3 μm or more, even if the amount is extremely small, the polishing treatment after the polishing treatment may result. It has been found that a linear or dot-like abnormal projection having a large projection height occurs.

Further, it has been found that the smaller the average particle size of the polishing agent is, the more minute irregularities are formed on the glass substrate, and therefore, it is preferable to reduce the average particle size of the polishing agent to the extent that the glass substrate is not damaged. Also got.

The present invention has been made on the basis of such findings and the like. The method of manufacturing a substrate for an information recording medium according to the present invention comprises subjecting a glass substrate to precision polishing using an abrasive. Thereafter, in a method for manufacturing an information recording medium substrate, which performs a predetermined etching process to manufacture an information recording medium substrate, the abrasive grains contained in the abrasive have an average particle diameter of 0.1 μm to 3 μm. In addition, the maximum particle size is less than 3 μm.

As a typical abrasive material, natural cerium oxide (CeO ₂ ) is widely used, but the abrasive material generally contains about several percent of a fluorine component as an impurity. .

Then, through experiments and research conducted by the present inventors,
It has been found that when the fluorine content in the abrasive is excessively high, the polishing accuracy becomes coarse, and it is preferable to suppress the fluorine content to a low level in order to perform a highly accurate polishing treatment.

Therefore, in the method for producing a substrate for an information recording medium of the present invention, it is preferable to use an abrasive having a fluorine content of 1 wt% or less.

The fluorine content in the polishing slurry can be easily reduced to 1 wt% or less by washing the polishing slurry with acid or water.

Further, in order to reduce the flying height, it is desirable to reduce the maximum projection height of the projections on the substrate surface. From this viewpoint, the content of the abrasive grains having a particle size of 1 μm to 3 μm is reduced. It is preferable that the content is 10 wt% or less of the solid content.

According to the inventor's intensive research, the abrasive grains are adjusted to a suspension in a liquid agent, and then subjected to wet classification such as spontaneous sedimentation or centrifugation to obtain a difference in gravity between the particle diameters of the abrasive grains. It has been found that abrasive grains having a large particle diameter of 3 μm or more can be reliably and completely removed by utilizing such a gravity difference.

Therefore, in the method of manufacturing a substrate for an information recording medium according to the present invention, a suspension is prepared by dispersing the abrasive grains in a liquid material, and then wet classification is performed. It is characterized by producing an agent.

In addition, the abrasive grains that have been subjected to wet classification agglomerate,
Alternatively, from the viewpoint of avoiding the generation of bacteria in the polishing agent, it is preferable to subject the supernatant to a polishing treatment within a predetermined time after collecting the supernatant.

Further, it is necessary to form a compressed layer on the substrate by the above-mentioned polishing treatment, and to subject the substrate on which the compressed layer is formed to a texture treatment. For this purpose, the abrasive grains are at least more than the glass substrate. Has a predetermined hardness of high hardness,
Further, it is preferably a polyhedral shape.

By subjecting a substrate on which a fine compression layer is formed to a texture process (etching process), a large number of fine irregularities are formed on the substrate surface. In order to form the film, it is preferable that the etching treatment is performed with an alkaline aqueous solution after treating with an acidic aqueous solution.

Further, the information recording medium substrate according to the present invention is manufactured by the above-mentioned manufacturing method, and the contour plane corresponding to 50% of the total area of the cross-sectional curve on the cut surface of the substrate surface is used as a reference line. 0.4 from the reference line
%, The height to the contour plane is 2 nm to 7 nm.

That is, the surface shape of the substrate surface is generally evaluated based on the surface roughness Ra (JIS B0601). The smaller the number is, the smaller the number is, and the larger the number of small protrusions is, the larger the number is without the high protrusions. Therefore, it is not suitable as an index for evaluating abnormal protrusions.

Therefore, in the present invention, when a contour plane corresponding to 50% of the total area of the cross-sectional curve on the cut surface of the substrate surface is set as the reference line, the contour line is 0.4% of the total area from the reference line.
%, Which is equivalent to 0.4% of the total area, so that the flying height of the magnetic head and the occurrence of head crash and thermal asperity are avoided. Height up to isosurface is 2nm ~ 7
Since the thickness is set to nm, an information recording medium substrate capable of reducing the flying height can be obtained.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail.

FIG. 1 is a manufacturing process diagram of an information recording medium including a method for manufacturing an information recording medium substrate according to the present invention. The information recording medium substrate is formed by a substrate processing step 1 → polishing step 2 → texture processing step. The information recording medium is manufactured through 3 → chemical strengthening process 4 → finish cleaning process 5 and then the information recording medium is manufactured by laminating a multilayer film on a substrate in a film forming process 6.

Hereinafter, each of the above steps will be sequentially described.

(1) Substrate Processing Step In the substrate processing step 1, a sheet-like glass material is ground using a grindstone such as a diamond grindstone to produce a glass substrate having a predetermined donut shape.

The substrate material of the glass substrate is not particularly limited, and the surface processing is easy, the elasticity and the rigidity are high.
High-strength glass or crystallized glass can be used, but inorganic glass that can be easily eluted with acid and can form a good texture, for example, an alkali metal oxide such as LiO ₂ or an alkaline earth such as MgO. It is preferable to use an alumina silicate-based glass containing a metal oxide and Al ₂ O ₃ or the like.

(2) Polishing Step The polishing step 2 includes a lapping process, a first polisher process,
The second polishing process and the finish polishing process are performed in four stages.

That is, first, using a lapping device, lapping is performed with abrasive grains such as alumina having a predetermined abrasive grain size, and then an abrasive in which free abrasive grains are dispersed in a polishing liquid is mixed with a hard polisher. Then, the first polisher is processed, and the second polisher is processed by replacing the hard polisher with the soft polisher.

Next, a suspension is prepared by suspending abrasive grains having an average particle diameter of 0.1 μm to 3 μm in a liquid material, and then the suspension is subjected to a wet classification treatment such as a natural sedimentation treatment or a centrifugal separation treatment. And the supernatant is fractionated to completely remove abrasive grains having a particle size of 3 μm or more, thereby producing a finish polishing abrasive having a maximum particle size of less than 3 μm (hereinafter referred to as “finish polishing agent”).

The reason why the abrasive grains having a size of 3 μm or more were completely removed as described above is that even a very small amount of abrasive grains having a size of 3 μm or more is contained as described in the section of “Problems to be Solved by the Invention”. This is because there is a possibility that an abnormal projection having a large projection height may occur in the texture processing described later.

In this embodiment, the average particle size is 0.1%.
The reason why the abrasive grains having a size of 3 μm to 3 μm were used is as follows.

That is, when the average particle size exceeds 3 μm, the surface roughness Ra of the glass substrate becomes large, and it becomes impossible to perform desired precision polishing. On the other hand, from the viewpoint of performing the desired precision polishing, the average particle size is preferably smaller, but when the average particle size is less than 0.1 μm, the abrasive grains are locally aggregated,
Apparently, the surface of the glass substrate is polished by the abrasive grains having a large particle diameter, and therefore, the glass substrate is damaged or the polishing rate is reduced, which causes a decrease in productivity. Therefore, in the present embodiment, abrasive grains having an average particle diameter of 0.1 μm to 3 μm are used.

Further, among the particle diameters of the abrasive grains contained in the finishing abrasive, the content of the abrasive grains having a particle diameter of 1 μm to 3 μm is set to 10 wt% or less of the total solid content.

That is, when the content of the abrasive grains having a particle size of 1 μm to 3 μm exceeds 10 wt% of the total solid content, the viscosity of the suspended finish abrasive becomes too high, so that the slurry containing the abrasive is contained. There is a possibility that the supply of the finished abrasive from the tank to the polishing machine becomes difficult, or the finished abrasive does not move smoothly in the pipe, and the settle / agglomeration of the finished abrasive occurs in the pipe. For this reason, in the present embodiment, a particle size of 1
The abrasive content in the range of μm to 3 μm was adjusted to be 10 wt% or less of the total solid content.

As a method for adjusting the content of abrasive grains having a particle size of 1 μm to 3 μm to 10 wt% or less of the total solid content, the content of the abrasive grains having a particle size of 1 μm to 3 μm is previously adjusted to 10 wt% or more, for example, 15 wt% or less. It can be easily obtained by setting the content to 30 wt% and wet-classifying such free abrasive grains.

As a typical abrasive raw material, natural CeO ₂ is widely used. However, this type of abrasive material contains metal fluoride as an impurity, It is preferable to adjust the content of fluorine therein to 1 wt% or less.

That is, free abrasive grains used as an abrasive are obtained by pulverizing a sintered body which has been subjected to a firing treatment, and when, for example, natural CeO ₂ is used as a raw material for free abrasive grains,
CeO ₂ usually contains 6 wt% to 8 wt% of a fluorine component in the form of metal fluoride.

However, the lower the fluorine content in the CeO ₂ abrasive grains, the less the hard portions formed in the subsequent baking treatment, so that the abrasive itself becomes softer and the glass substrate becomes more uniform and finer. A compression layer is formed. In other words, when the fluorine content is large, the polished surface of the glass substrate becomes rough, the maximum projection height Rp becomes large, and abnormal projections are likely to occur. For this reason, the fluorine content in the polishing agent is preferably adjusted to 1 wt% or less.

As a method for reducing the fluorine content, natural CeO ₂ can be easily obtained by washing with acid or water, and a commercially available first-grade or special-grade high-purity CeO ₂ or the like can be used. Can be used.

The finished abrasive can be easily obtained by irradiating the separated supernatant liquid with ultrasonic waves or stirring vigorously, or by crushing and dispersing loose abrasive grains by impinging a high-pressure jet stream on the inner wall. Desired adjustment can be performed.

Then, finish polishing is performed using the above-mentioned finishing abrasive and a suede type polishing pad.

In this case, if the suspension is wet-classified and used within a predetermined time T1 (for example, 40 hours), free abrasive grains are prevented from agglomerating and bacteria are generated in the finishing abrasive. Therefore, it is preferable to use the finishing abrasive within the predetermined time T1.

The abrasive grains contained in the finishing abrasive are
In order to form a very fine surface compression layer on the surface of a glass substrate, it is required that the hardness is at least higher than that of the glass substrate (Knoop hardness of 500 or more), but if such a condition is satisfied, it is particularly limited. Is not something like Ce
Rare earth oxides such as O ₂ , ZrO ₂ , MnO ₂ , TiO ₂ , F
e ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , diamond and the like can be used. However, from the viewpoint of obtaining excellent polishing efficiency, it is preferable to use rare earth oxides, particularly CeO ₂ -based abrasive grains.

Further, it is preferable that the abrasive grains have a polyhedral shape.

That is, in the fine compressed layer necessary for forming fine irregularities on the glass substrate, the corners of the free abrasive grains are pressed against the surface of the glass substrate, and thus local stress is applied to the glass substrate. It is considered to be formed. Therefore, when the shape of the abrasive grains is spherical, it is difficult to form a compressed layer suitable for a desired etching process because the local stress is not applied. For this reason, the shape of the abrasive grains is preferably a polyhedral shape.

The polishing pad used for polishing is not particularly limited, and a nonwoven fabric or a foam can be used. It is preferable to use a layer (NAP layer) in which an opening is formed by finishing the surface of the continuous foam layer and a suede pad formed from the base layer, since the glass substrate is unlikely to be damaged. It is preferable to improve the homogeneity by finishing the pad surface before polishing, since an extremely fine compressive stress layer can be formed more uniformly.

(4) Texture Processing Step Texture processing step 3 includes a cleaning step and a drying step.

First, in the cleaning step, the polished glass substrate is cleaned using an acidic aqueous solution and an alkaline aqueous solution.

That is, in the acidic aqueous solution, some components in the glass are eluted and SiO ₂ which is a skeleton component of the glass is eluted.
It will be rich. Since SiO ₂ is soluble in an alkaline aqueous solution, if the glass substrate 1 is washed with an acidic aqueous solution and then washed with an alkaline aqueous solution, the surface of the glass substrate 1 is easily etched.

The acidic aqueous solution is not particularly limited, but hydrofluoric acid having a strong etching action on glass,
A strong acid such as sulfuric acid, hydrochloric acid, nitric acid, sulfamic acid, or phosphoric acid is preferable in promoting the etching treatment of the surface of the glass substrate.

The alkaline aqueous solution is not particularly limited either, and potassium hydroxide, sodium hydroxide, ammonia,
Any chemical solution can be used as long as it is an alkaline raw material that dissolves in water, such as tetramethyl hydride. Also,
It is also preferable to add a surfactant or a chelating agent in order to enhance the cleaning effect. For example, RBS25 manufactured by Chemical Products can be used.

The concentrations of the acidic aqueous solution and the alkaline aqueous solution are not particularly limited, and the concentration required for performing the texture treatment can be appropriately selected in consideration of the chemical resistance of the glass substrate.

The cleaning time and the cleaning temperature are not particularly limited and are appropriately determined according to the concentration of the chemical solution and the etching rate of the glass substrate. The washing temperature is preferably set to 70 ° C. or lower.

In the present embodiment, the cleaning method is performed by immersing the glass substrate in an acidic aqueous solution or an alkaline aqueous solution. In this case, the cleaning may be performed while irradiating the glass substrate with ultrasonic waves. Further, the irradiation of such an ultrasonic wave may be performed under a constant frequency, or simultaneously irradiating a plurality of different frequencies,
Alternatively, the frequency may be changed over time. The output of the ultrasonic wave is not particularly limited, but generally, the lower the frequency and the higher the output, the stronger the damage to the glass substrate. Therefore, it is preferable to determine in consideration of such points.

As a cleaning method, a shower method, a jet method, or the like may be used in addition to the immersion method described above. In this case, it is preferable that a sponge or the like is brought into contact with the glass substrate to rub the glass substrate.

Next, the process proceeds to a drying step, and the washed glass substrate is dried.

The drying method is not particularly limited, either.
Glass substrate 1 in isopropyl alcohol (IPA) vapor
For example, an IPA vapor drying method in which the glass substrate is immersed, and a spin drying method in which the glass substrate is rotated at a high speed to remove the washing water.

Many fine irregularities without abnormal projections are formed on the surface of the glass substrate thus textured.

(4) Chemical strengthening treatment step In the chemical strengthening treatment step 4, a glass substrate is placed on a molten salt adjusted to a predetermined temperature, for example, a molten salt composed of a mixed solution of potassium nitrate (KNO ₃ ) and sodium nitrate (NaNO ₃ ). After immersion for a predetermined time, a chemical strengthening process is performed in which Li ⁺¹ and Na ⁺¹ in the chemical components of the glass substrate are ion-exchanged into K ⁺¹ having a large ionic radius. By performing such a chemical strengthening treatment, the surface compressive stress is increased, and thereby, even if the magnetic disk is rotated at a high speed, it can be prevented from being damaged.

Then, the glass substrate is gradually cooled to room temperature, and the molten salt attached to the glass substrate is washed away in pure water.

(5) Finish Cleaning Step In the finish cleaning step 5, the glass substrate is immersed in an alkaline aqueous solution and, if necessary, washed with alkali while irradiating ultrasonic waves to remove iron powder or the like adhered to the glass substrate. Impurities, that is, residual foreign matters are removed by etching.

As the alkaline aqueous solution, potassium hydroxide, sodium hydroxide, ammonia, tetramethyl hydride and the like can be used as in the case of the above-mentioned texture treatment.

(6) Film Forming Step In the film forming step 6, a seed layer, an underlayer, a magnetic layer, and a protective layer are sequentially laminated on a glass substrate by using a well-known sputtering method. A lubricating layer is formed on the surface of the substrate, whereby an information recording medium is manufactured.

As the seed layer, NiAl, NiAlR
u, NiAlNd, NiAlTa, or the like can be used, and CrMo, Cr, CrV, or the like can be used as the underlayer.

The magnetic layer is made of CoP to ensure excellent information recording / reproducing characteristics and film adhesion.
Cobalt-based alloys such as tCr and CoPtCrTa can be used. As the protective layer, a carbon-based material such as hydrogenated carbon can be used, and as the lubricating layer, a liquid lubricant such as perfluoroether can be used.

The information recording medium substrate manufactured as described above uses the contour plane corresponding to 50% of the total area of the cross-sectional curves on the cut surface of the substrate surface as a reference line. The height from the line to the contour plane corresponding to 0.4% of the total area is 2 nm to 7 nm, whereby the flying height can be further reduced without causing a head crash or thermal asperity.

That is, in order to secure a stable glide of the magnetic head and reduce the flying height, it is necessary to prevent the occurrence of abnormal projections as described above. Conventionally, the surface shape of the glass substrate is evaluated. As a representative index, surface roughness Ra (JIS B 0601) is known.

However, the surface roughness Ra is calculated as an integrated average value of a roughness curve obtained by cutting off a surface waviness component longer than a predetermined wavelength from a cross-sectional curve of an object to be measured (a glass substrate in the present embodiment). You.

Therefore, even if high protrusions are formed, the surface roughness Ra is reduced if the number of protrusions is small, and the surface roughness Ra is increased if a large number of small protrusions are formed without the high protrusions. That is, when the surface shape of the glass substrate is evaluated based on the surface roughness Ra, the surface roughness Ra may be within an allowable range even if there is a risk of head crash or thermal asperity due to having a high protrusion. Therefore, the surface shape of the glass substrate is changed to the surface roughness Ra.
However, the shape evaluation cannot be performed with high accuracy even if the evaluation is made in the above.

Therefore, in the present embodiment, the concept of the bearing ratio BR and the bearing height BH is introduced, and the shape of the glass substrate is evaluated using the bearing height BH.

That is, as shown in FIG. 2, a cross-sectional curve S, which is a profile obtained by cutting the surface at a plane perpendicular to the surface of the glass substrate, is obtained, and a bearing ratio between the maximum value and the minimum value of the cross-sectional curve S is determined. When defined as BR, the contour surface indicating the average line of the total area of the sectional curve S is a bearing ratio BR.
Is 50%, and the maximum value of the cross-sectional curve S indicates the case where the bearing ratio BR is 0%.

Therefore, the bearing ratio BR is 50
% Is defined as the bearing height BH, the surface shape of the glass substrate becomes the bearing height B.
In this embodiment, the bearing ratio BR is 50% to 0.4% in the height direction, that is, BH04 is 2 nm to 7 nm.
Is set to

That is, when the BH04 is less than 2 nm, the flight stability of the magnetic head is sharply reduced, which may cause a head crash or thermal asperity. On the other hand, if the BH04 exceeds 7 nm, the probability of the magnetic head colliding with the projection increases when the flying height is reduced, and head crash and thermal asperity are more likely to occur. Therefore, in the present embodiment, BH04 is set to 2 nm to 7 nm in consideration of the demand for narrowing the flying height.
nm.

In consideration of a mechanism that causes a head crash or thermal asperity on the disk substrate, a larger bearing height BH (a distance in the height direction of the bearing ratio BR) can be evaluated with higher accuracy. If the bearing height BH is too large, noise factors that do not affect head crash etc. are emphasized,
Sensitivity deteriorates. For this reason, in this embodiment, the bearing height BH is set to BH04 (the bearing ratio BR is set to 50).
% To 4% in the height direction).

As described above, according to the present embodiment, by setting BH04 to 2 nm to 7 nm, the flying height can be further reduced without causing a head crash or thermal asperity. A substrate can be obtained.

[0086]

Next, embodiments of the present invention will be described specifically.

[First Embodiment] The present inventors consider that a different B
A number of glass substrates having H04 were prepared, and the relationship between BH04 and head crash was examined.

That is, the glass substrate, the polishing method, and the etching method were variously changed, and glass substrates having different BH04 were produced.

More specifically, by changing the particle size of the abrasive particles and the hardness of the polishing pad, or by changing the amount of etching by changing the combination of the composition of the glass substrate and the concentration of the etching solution, the BH04 is removed. A number of different glass substrates were made.

Next, a pressure of 26.7 kPa (200 Torr)
A fixed point levitation test of the magnetic head was performed under reduced pressure. That is, since the flying height between the magnetic head and the glass substrate decreases with a decrease in pressure, contact between the magnetic head and the glass substrate is likely to occur under reduced pressure. Tested gender.

FIG. 3 is a diagram showing test results of the fixed point levitation test. The horizontal axis indicates BH04 (nm), and the vertical axis indicates the time until a head crash occurs.

As apparent from FIG. 3, in the fixed-point levitation test under reduced pressure, when BH04 is 2 nm or more, the time required for head crash to occur is 60 to 100 hours, whereas when BH04 is less than 2 nm. To become and,
A sudden drop in flight stability caused a head crash within 20 hours, so BH04 was at least 2n
It was confirmed that at least m was required.

[Second Embodiment] The inventors of the present invention
O ₂ : 67 mol%, Al ₂ O ₃ : 10 mol%, Li ₂ O: 7 mol
_{l%, Na 2 O: 9mol} %, MgO: 3mol%, CaO: 4
Aluminosilicate glass having a chemical composition of mol% was subjected to grinding using a diamond grindstone to produce a donut-shaped glass substrate having an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 1.0 mm.

Then, using a lapping apparatus, using alumina abrasive grains having an abrasive grain size of # 400, a surface roughness Ra of 2 was obtained.
Lapping to about μm, then
Lapping was performed using alumina abrasive grains having an abrasive grain size of # 1000 so that the surface roughness Ra was about 0.7 μm.

Next, the glass substrate thus wrapped is immersed in a pure water bath and washed, and then a hard polisher is used as a polishing pad and CeO ₂ abrasive particles having an average particle size of 2 μm ( First polisher processing is performed by using an abrasive obtained by dispersing Mitsui Kinzoku Mining Co., Ltd. (trade name: “Mirek”) in water, and thereafter, a soft polisher is used as a polishing pad instead of a hard polisher, and an average A second polisher process is performed using an abrasive in which CeO ₂ abrasive grains (trade name “Mirek”, manufactured by Mitsui Mining & Smelting Co., Ltd.) having a particle size of 0.5 μm to 1 μm are dispersed in water to obtain a sheet thickness of 0. 6
mm, and the surface of the glass substrate was polished until the surface roughness Ra became about 0.1 μm.

Next, the free abrasive grains are mixed with water in a tank of 0.1 m ³ , the free abrasive grains are suspended in water to form a suspension, and the suspension is subjected to a predetermined settling time T1. And the particles having a particle size of 3 μm or more were allowed to settle naturally.

Here, as for the free abrasive grains, "Mirek" manufactured by Mitsui Kinzoku Mining Co., Ltd. was used as in the case of the first and second polisher processing. 5μ
m and Example 7 were 0.1 μm (polyhedral shaped synthetic cerium oxide).

In Example 8, after sintering a rare earth basic sulfate mainly composed of CeO ₂ abrasive grains having an average particle diameter of 0.5 μm, dry classification was performed to obtain free abrasive grains.

Further, in Examples 9 and 10, the average particle diameter was 0.1.
CeO ₂ using ammonium fluoride or hydrofluoric acid as a rare earth basic sulfate mainly composed of 5 μm CeO ₂ abrasive grains
_A fluorine component was introduced into ₂ , and thereafter firing treatment and dry classification were performed to obtain free abrasive grains. Specifically, the concentration of ammonium fluoride or hydrofluoric acid, the processing temperature, and the processing time were varied so that the fluorine content was 1 wt% (Example 9) and 3w.
The free abrasive grains of t% (Example 10) were adjusted.

The CeO ₂ abrasive grains are obtained by pulverizing a sintered body which has been dried and then fired, so that the shape is not spherical but polyhedral having corners.

The natural settling time T1 was 24 hours (Examples 1, 5 to 7), 16 hours (Example 2), 8 hours (Example 3), and 4 hours (Examples 4, 8 to 10). Wet classification is performed by setting four types, and the natural sedimentation time T1
The test pieces of Examples having different abrasive grain contents having particle diameters of 1 to 3 μm were prepared by changing the average particle diameter. That is, the first embodiment
In the case of -10, the content of abrasive grains having a particle size of 1 to 3 μm is previously set to 10 w
By performing wet classification at t% or more and varying the treatment time (natural sedimentation time T1) of the wet classification, an example test piece having a particle size of 1 to 3 μm and a different abrasive content was prepared.

Next, the supernatant of the suspension was collected to prepare an abrasive, and within a predetermined time T2 after the collection, a suede-type polishing pad (Kanebo Co., Ltd .; trade name "B") was used as the polishing pad within a predetermined time T2.
ELLATRIX "), and a final finish polishing was performed to produce a glass substrate having a homogenized surface.

The predetermined time T2 is 2 hours (Examples 1 to 3).
Example 4 and Example 7), 40 hours (Example 5), 6
Each was set to 0 hour (Example 6).

Next, the glass substrate thus polished is shower-washed with pure water to remove abrasives (free abrasive grains) adhering to the surface of the glass substrate.
The glass substrate was immersed in a 3 wt% hydrofluoric acid solution (temperature: 50 ° C.) for 2.5 minutes and irradiated with ultrasonic waves having a frequency of about 48 kHz and an output of 1 W / cm ² .

Thereafter, the glass substrate was immersed in sodium hydroxide of pH 11 (temperature: 40 ° C.) for 2.5 minutes, and irradiated with ultrasonic waves having a frequency of about 48 kHz and an output of 1 W / cm ² .

Next, the glass substrates were successively immersed in three pure water tanks arranged side by side and washed with pure water to remove the alkaline aqueous solution attached to the surface of the glass substrates, and then the glass substrates were placed in an isopropyl alcohol bath. Soak for 2 minutes and frequency about 48
After irradiating an ultrasonic wave of kHz and an output of 1 W / cm ^2, the substrate was dried in isopropyl alcohol vapor for 1 minute.

Thereafter, the reagent-grade sodium nitrate and the reagent-grade potassium nitrate were mixed at a volume ratio of 40:60 to prepare a molten salt at a temperature of 380 ° C., and glass was immersed in the molten salt to prepare a molten salt. Hold for a time, thereby allowing Li in the glass substrate
Chemical strengthening treatment for ion exchange of ⁺¹ and Na ⁺¹ into K ⁺¹ having a large ionic radius was performed.

Next, the glass substrate thus subjected to the chemical strengthening treatment was immersed in a pure water bath to wash away the molten salt adhering to the surface of the glass substrate.

Then, the glass substrate was immersed in a sodium hydroxide solution having a pH of 11 (temperature: 40 ° C.) for 2.5 minutes and irradiated with ultrasonic waves having a frequency of about 48 kHz and an output of 1 W / cm ² . Next, the glass substrate is lifted out of the sodium hydroxide solution and sequentially immersed in three pure water baths to wash the glass substrate with alkali. Thereafter, the glass substrate is immersed in an isopropyl alcohol bath for 2 minutes to obtain a frequency of about 48 kHz.
After irradiating ultrasonic waves of z and output of 1 W / cm ^2, the substrate was dried in isopropyl alcohol vapor for 1 minute, thereby producing a substrate for an information recording medium.

Next, a NiAl film as a seed layer and a CrMo as an underlayer are formed on the surface of the information recording medium substrate thus formed by using a well-known sputtering method.
A film, CoCrPt as a magnetic layer, and a C-based film as a protective layer are sequentially laminated, and a perfluoropolyether as a lubricating layer is formed on the surface of the protective film by an immersion method.
Test pieces of Examples 1 to 10 were produced.

The present inventors have found that the average particle size is 0.5 μm.
CeO ₂ abrasive grains (Mirake) are dry-classified to a particle size of 3 μm
After most of the above abrasive grains were removed, the CeO ₂ abrasive grains were dispersed in water, the final polishing agent was adjusted by forcible stirring, and the final polishing was performed using the final polishing agent. As in the case of Nos. 1 to 10, texture treatment → chemical strengthening treatment → finish cleaning → film formation treatment was performed to prepare a test piece of Comparative Example 1.

Also, as in Comparative Example 1, finish polishing was performed using CeO ₂ abrasive grains obtained by dry classification, and the same texture treatment as in Examples 1 to 10 was performed. Instead, a texture treatment was performed using 0.3% silicic hydrofluoric acid, and then a chemical strengthening treatment, a finish cleaning, and a film formation treatment were performed as in the above Examples 1 to 10, to produce a test piece of Comparative Example 2. .

Further, the present inventors assumed that the average particle size was 0.5 μm
The CeO ₂ abrasive grains (Mirake) are dispersed in water in the form of powder without classifying to prepare a finishing abrasive, and finish polishing is performed using the finishing abrasive. In the same manner as in the above, a texture test, a chemical strengthening process, a finish cleaning, and a film forming process were performed to prepare a test piece of Comparative Example 3.

Furthermore, the present inventors used spherical colloidal silica (trade name “COMPOL”, manufactured by Fujimi Incorporated) as abrasive grains contained in the finishing abrasive, and carried out the same wet classification as described above. After that, a finish abrasive was prepared, and then a texture treatment, a chemical strengthening treatment, a finish cleaning, and a film formation treatment were performed in the same manner as described above, thereby producing a test piece of Comparative Example 4.

Then, after the finish cleaning step for each of the test pieces, the maximum projection height Rp, the number of projections, and BH04
To check the surface shape of the glass substrate, and then perform a fixed-point levitation test and continuous seek test after manufacturing the information recording medium to observe the presence or absence of scratches and head crashes on the information recording medium, and check the medium characteristics did.

Table 1 shows the measurement results for each test piece.

[0117]

[Table 1]

In Table 1, the particle size of abrasive grains for calculating particles of 3 μm or more and 1 to 3 μm was measured using a scanning electron microscope (S-4500, manufactured by Hitachi, Ltd.).
The Blaine diameter was measured according to JIS R 5201 (1955), and the Blaine diameter was defined as the average particle diameter.

[0119] The measurement region of maximum projection height Rp and the number of protrusions and 20 [mu] m × 20 [mu] m, the number of protrusions indicates the number of protrusions having a 10nm or more projection height in the measurement area, 0.01 mm ² per Converted to and displayed. still,
The maximum projection height Rp and the number of projections were measured using a tapping mode of an atomic force microscope (manufactured by Digital Instruments, Inc., trade name: “Nanoscope a”).

BH04 was obtained by calculating the height of the bearing ratio BR from 50% to 0.4% from the sectional curve of the glass substrate.

The fixed point levitation test was performed at a pressure of 26.7 kPa.
The test was performed under a reduced pressure (200 Torr) for 24 hours, and the presence or absence of a scratch on the magnetic head and the information recording medium and the presence or absence of a head crash were observed with an optical microscope (manufactured by Nikon Corporation). The continuous seek test was performed at a flying height of 15 nm and a rotation speed of 1
The operation was performed at 66.7 s ^-1 (10,000 rpm) for 1,000 hours, and the presence or absence of a head crash was observed with the optical microscope.

As is clear from Table 1, in Comparative Example 1, since the finish abrasive was obtained by dry classification, high-precision classification was not carried out. As a result, the maximum protrusion height Rp was as large as 15.6 nm, and 27 abnormal protrusions with a diameter of 10 nm or more were generated at 27 / 0.01 mm ^2.
No. 4 was also as large as 7.5 nm, and it was recognized that the information recording medium was scratched although no head crash occurred.

In Comparative Example 2, texture treatment was performed using silica hydrofluoric acid instead of hydrofluoric acid in Comparative Example 1, and the maximum projection height Rp was as large as 13.8 nm.
16 abnormal protrusions of 10 nm or more / 0.01 mm ²
BH04 was as large as 7.1 nm, and the information recording medium was found to be damaged as in Comparative Example 1.

In Comparative Example 3, since the abrasive material was not subjected to the wet classification, the particle size of the free abrasive grains was large, and the polished surface was so rough that the desired precision polishing could not be carried out. In the fixed point levitation test, a head crash occurred and the information recording medium was found to be damaged.

Further, in Comparative Example 4, since the final polishing was performed using spherical colloidal silica, a desired texture could be formed even by performing a texturing process with hydrofluoric acid and sodium hydroxide after the polishing process. For this reason, the maximum protrusion height is as small as 1.5 nm, and the BH04 is as small as 1.2 nm, which lowers the flight stability of the magnetic head. In the fixed point levitation test, the magnetic head and the information recording medium are damaged. It was confirmed that a head crash occurred.

On the other hand, in Examples 1 to 10, finishing abrasives having a maximum particle size of less than 3 μm and a particle size of 1 μm to 3 μm of 10 wt% or less were produced by wet classification by a natural sedimentation method. Since the finish polishing is performed using the finish abrasive, the maximum projection height Rp is 10 n
m or less, and thus there are no protrusions exceeding 10 nm (the number of protrusions is “0”), and BH04 also has 3.1 nm to 4.5 n.
m was within the range of 2 nm to 7 nm, and no abnormality was observed in the fixed point levitation test or the continuous seek test.

Further, when comparing Example 4 with Examples 8 to 10, since the abrasive contains 6 wt% of the fluorine component in Example 4, the maximum projection height Rp is
Although it is better than that of Example No. 3, it shows a relatively large value of 7.5 nm, whereas Examples 8 to 10 show that the fluorine content is reduced to 0 wt% to 3 wt%. Rp was as low as 3.0 nm to 6.5 nm, and thus it was confirmed that the maximum protrusion height Rp can be suppressed by reducing the fluorine content in the abrasive.

In Examples 2, 5 and 6, only the predetermined time T2 until the start of use after wet classification of loose abrasive particles was changed, but in Example 6, the maximum projection height Rp exceeded 5 nm. On the other hand, in Examples 2 and 5, the maximum protrusion height Rp can be suppressed to be substantially uniform at 5 nm or less, and therefore, it is confirmed that the predetermined time T2 is preferably set within 40 hours. Was done. This is considered to be because the predetermined time T2 of Example 6 was 60 hours, which was a long time until the start of use, so that abrasive grains were aggregated and bacteria were generated in the finished abrasive.

[0129]

As described above in detail, the method of manufacturing a substrate for an information recording medium according to the present invention is characterized in that a glass substrate is precisely polished using an abrasive, and then a predetermined etching process is performed. In the method for producing a substrate for an information recording medium for producing a substrate for a recording medium, the abrasive grains contained in the abrasive have an average particle diameter of 0.1 μm to 3 μm and a maximum particle diameter of less than 3 μm, and The content of abrasive grains having a particle size of 1 μm to 3 μm should be 10% or less of the total solid content, and more preferably, the content of the fluorine component contained in the abrasive should be 1 wt%.
By doing the following, it is possible to manufacture an information recording medium substrate capable of further reducing the flying height without causing abnormal projections on the substrate.

[0130] Further, after the above-mentioned abrasive grains are dispersed in a liquid material to prepare a suspension, wet classification is performed, and then the supernatant is separated to produce the above-mentioned abrasive. The grains can be completely removed.

The abrasive grains have a predetermined hardness at least higher than that of the glass substrate and have a polyhedral shape, so that a desired compression layer is formed on the substrate surface.
Texture processing can be facilitated.

In the predetermined etching process, a desired texture can be efficiently formed on the substrate surface by performing an etching process using an acidic aqueous solution and then performing an etching process using an alkaline aqueous solution.

Further, the information recording medium substrate according to the present invention is a substrate for an information recording medium having a large number of fine irregularities formed on the substrate surface, which is manufactured by the above-described manufacturing method, and has a cross-sectional curve at a cut surface of the substrate surface. When a contour plane corresponding to 50% of the total area is used as a reference line, the height from the reference line to a contour plane corresponding to 0.4% of the total area is 2 nm.
When the contour surface corresponding to 50% of the total area of the fine irregularities represented by the cross-sectional curve of the substrate surface is set as a reference line, the area is 0.4% of the total area from the reference line.
Since the height up to the contour plane corresponding to is 2 nm to 7 nm, it is possible to obtain an information recording medium substrate that can further reduce the flying height while avoiding the occurrence of head crash and thermal asperity.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of an information recording medium including an information recording medium substrate.

FIG. 2 is a diagram showing a relationship between a substrate diameter and a bearing ratio BR and a bearing height BH.

FIG. 3 is a diagram showing a relationship between BH04 and head crash.

[Description of Signs] 2 Polishing process

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 5/73 G11B 5/73 (72) Inventor Atsushi Kurachi 3-5-5 Doshomachi, Chuo-ku, Osaka-shi, Osaka No. 11 Inside Nippon Sheet Glass Co., Ltd. (72) Koichi Suzuki 3-5-11 Doshomachi, Chuo-ku, Osaka City, Osaka Prefecture AA08 AB03 AC03 BB04 BB10 BB11 BB16 5D006 CB04 CB07 5D112 AA02 AA24 BA03 GA14 GA27 GA30

Claims (8)

[Claims] 1. A method for manufacturing a substrate for an information recording medium, wherein a precision polishing process is performed on a glass substrate using an abrasive, and then a predetermined etching process is performed to manufacture the substrate for an information recording medium. The abrasive grains contained in the powder have an average particle diameter of 0.1 μm
A method for producing a substrate for an information recording medium, wherein the maximum particle size is less than 3 μm. 2. The method for manufacturing a substrate for an information recording medium according to claim 1, wherein the content of the fluorine component contained in the polishing agent is 1 wt% or less. 3. The content of abrasive grains having a particle size of 1 μm to 3 μm is as follows:
3. The method for producing a substrate for an information recording medium according to claim 1, wherein the amount is 10 wt% or less of the total solid content. 4. The polishing agent according to claim 1, wherein said abrasive is dispersed in a liquid material to form a suspension, and then wet classification is performed, and then the supernatant is collected to produce said abrasive. A method for manufacturing a substrate for an information recording medium according to claim 3. 5. The method for producing a substrate for an information recording medium according to claim 4, wherein the produced abrasive is subjected to a polishing treatment within a predetermined time after the supernatant is collected. 6. The information recording medium according to claim 1, wherein the abrasive has a predetermined hardness higher than at least a glass substrate, and has a polyhedral shape. Method of manufacturing substrates. 7. The method according to claim 1, wherein the predetermined etching process is performed by performing an etching process using an acidic aqueous solution and then performing an etching process using an alkaline aqueous solution.
The method for manufacturing a substrate for an information recording medium according to any one of the above. 8. A substrate for an information recording medium having a large number of fine irregularities formed on a surface of a substrate, wherein the substrate is manufactured by the method according to any one of claims 1 to 7, and is formed on a cut surface of the surface of the substrate. When a contour plane corresponding to 50% of the total area of the cross-sectional curve is used as a reference line, a height from the reference line to a contour plane corresponding to 0.4% of the total area is 2 nm to 7 nm. A substrate for an information recording medium, comprising: