JP2002358632A - Substrate for information recording medium and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a magnetic disk surely and stably drivable even when a flying height is made lower than heretofore in order to deal with the trend toward a high density of data zones. SOLUTION: After a compression layer and non-compression layer are formed on a glass substrate in a polishing process step 4, the glass substrate undergoes etching treatment in an acidic solution where a hydrofluoric acid and fluoride salt are made to coexist in a texturing treatment process step 5 (first surface treatment 5a). In such a case, the acidic solution prepared to 0.3 to 0.98, more preferably 0.56 to 0.93 in the ratio X of the sum of the concentrations per mol each of the hydrofluoric acid and hydrogen ions to the sum of the concentrations per mol each of the hydrofluoric acid and fluoride ions is used as the etchant. A layer changed in properties is thereafter removed by using an alkaline solution (second surface treatment 5b) and the magnetic disk substrate is manufactured through a chemical strengthening treatment process step 6 and finishing cleaning process step 7.

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 magnetic disk substrate.
A Start Stop method and a ramp load method are known.

In the CSS method, uniform fine irregularities of about several tens of nanometers called a CSS zone are provided mainly along the inner or outer periphery of the magnetic disk substrate, and the magnetic head is driven while the magnetic disk substrate is rotating. Glide over the data zone of the substrate and glide over the CSS zone of the magnetic disk substrate when the magnetic disk substrate stops or starts.

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

Therefore, in either of the CSS system and the ramp load system, while the magnetic disk substrate is rotating, the magnetic head is slightly lifted from the magnetic disk substrate, and a gap of several tens nm from the magnetic head ( In the HDD, the magnetic head gliding on the magnetic disk substrate comes into contact with the magnetic disk substrate while maintaining the flying height. However, it is necessary to prevent the magnetic head from being loaded with an excessive resistance.
After performing precision polishing using an abrasive containing 3.0 μm free abrasive grains, and etching with silica hydrofluoric acid, a number of minute projections called textures are formed on the surface of the magnetic disk substrate. The technique is known (JP-A-2000-132829).

In the prior art, the surface of the magnetic disk substrate is etched with silica hydrofluoric acid, so that polishing marks (abrasion marks) formed by the abrasive remain as projections, thereby causing the surface of the magnetic disk substrate to be damaged. Many small protrusions (textures) are formed. Moreover, since silicon hydrofluoric acid has a lower etching rate and weaker etching power than a hydrofluoric acid aqueous solution containing hydrofluoric acid or potassium fluoride, the surface roughness can be controlled with high precision.

[0008]

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. In order to cope with such a high data zone density, a low flying height (for example, 10 n
m or less flying height).

On the other hand, when the flying height is reduced, the air layer between the magnetic head and the magnetic disk is narrowed, so that the flying stability of the magnetic head is reduced.

Therefore, in order to realize a stable low flying height, it is necessary to completely remove minute foreign matters adhering to the magnetic disk substrate to avoid collision of the magnetic head with the foreign matters. Needless to say, it is necessary to improve the quality of the above texture to improve the flying stability of the magnetic head, and for that purpose, the height of the fine protrusions is made as low as possible and the density is increased. In addition, it is necessary to suppress variations in the height of the protrusion.

However, in the above-mentioned prior art, even if precision polishing is performed using an abrasive (free abrasive) having an average particle diameter of 0.3 μm to 3.0 μm, the polishing rate of silica hydrofluoric acid is low, so that the polishing rate is low. When the magnetic disk is driven at a flying height of 10 nm or less as described above, a magnetic head may be moved to the abnormal protrusion by forming a linear or dot-like abnormal protrusion having a large protrusion height in the etching process after the process. There is a problem that a collision may cause a so-called head crash or thermal asperity.

In addition, in the above-mentioned prior art, the surface roughness Ra
However, there is a problem that the flying stability of the magnetic head at a low flying height cannot be completely dealt with.

The present invention has been made in view of such circumstances, and it is possible to reliably and stably operate even if the flying height is made lower than before in order to cope with a higher data zone density. An object of the present invention is to provide an information recording medium substrate that can be driven and a method for manufacturing the same.

[0014]

In the technical field of information recording media, it is considered that further higher density of data zones will be required in the future, but in order to realize such higher density of data zones. As described above, it is necessary to further reduce the flying height, and for that purpose, it is necessary to further reduce the height of the minute projections formed on the substrate surface.

It is considered that the etching depth from the substrate surface may be reduced in order to reduce the height of the minute projections. However, when the etching depth is reduced, the compression layer (polishing) formed by polishing is required. Many of the scars remain and the compressed layer cannot be sufficiently removed. Therefore, when the compressed layer is exposed to a high temperature by a chemical strengthening process, a sputtering process, or the like that is performed after the minute projections are formed, heat is generated. Small projections grow due to relaxation expansion, and as a result, abnormal projections having a large projection height are generated, and the magnetic head may collide with the abnormal projections, causing thermal asperity or head crash.

That is, in order to obtain a desired flying stability suitable for lowering the flying height, while suppressing the height of the fine projections, the variation in the height of the projections which may be caused by the above-mentioned relaxation expansion is suppressed. There is a need to. That is, in order to avoid the formation of abnormal protrusions having a high protrusion height, it is considered necessary to increase the etching depth as much as possible and sufficiently remove the compressed layer.

The present inventors have conducted intensive studies from such a viewpoint. As a result, it has been found that an alkali compound is added to hydrofluoric acid to generate a fluoride salt, and a surface treatment is performed with an acidic solution containing the fluoride salt. Thereby, the surface roughness Ra of the substrate surface can be surely reduced, and the height of the projections can be uniformly reduced. Moreover, even after performing a heat treatment such as a chemical strengthening treatment, relaxation expansion due to heat is caused. Therefore, it has been found that fine protrusions having a low protrusion height can be formed at a high density.

The present invention has been made based on such findings, and the method for manufacturing a substrate for an information recording medium according to the present invention comprises the steps of: In the method for manufacturing an information recording medium substrate which performs a surface treatment to manufacture an information recording medium substrate, the surface treatment is performed using an etching solution in which hydrofluoric acid and a fluoride salt coexist. I have.

According to the experimental results of the present inventors, when the addition amount of the alkali compound to hydrofluoric acid is small, there is no difference from the case of etching with hydrofluoric acid alone. It was found that when excessively added to the hydrofluoric acid, the number of the fine projections became small and a desired high-density texture could not be formed. Therefore, it is considered that there is an optimum range for the amount of the alkali compound added to hydrofluoric acid.

Therefore, the present inventors have further revised from this viewpoint.
After diligent research on hydrofluoric acid and fluoride ions,
Hydrofluoric acid and hydrogen ions for the sum of the concentrations per mole each
, The ratio X of the sum of the concentrations per mole is 0.3 to 0.1.
98, preferably 0.56 to 0.93.
The use of the chilling liquid allows the
The maximum height from the average value of the protrusion heights (hereinafter referred to as the “maximum protrusion height
Rp) shows little difference before and after the heat treatment.
In addition, the maximum projection height Rp is 3.6 n even after the heat treatment.
m and a projection height of 2 nm or more is 150
Pieces / 100μm ^Two(10μm × 10μm) or more
It is possible to obtain an information recording medium substrate having
The desired flying stability even at low flying heights
Was obtained.

That is, in the method for manufacturing a substrate for an information recording medium according to the present invention, the sum of the concentration of the hydrofluoric acid and the hydrogen ion per mole of each of the concentrations of the hydrofluoric acid and the fluoride ion is preferably Is characterized in that the etching solution is prepared so that the ratio X becomes 0.3 to 0.98, preferably 0.56 to 0.93.

According to the above-described manufacturing method, even if a heat treatment such as a chemical strengthening treatment or a sputtering treatment is performed, the maximum projection height of the minute projections after the heat treatment can be suppressed to less than 3.6 nm, and A desired information recording medium substrate having high-density minute projections can be manufactured, and therefore, an information recording medium substrate having excellent flying stability even under a low flying height can be obtained.

The above-mentioned fluoride salt is formed by replacing a cation of an alkali compound with a hydrogen ion of hydrofluoric acid. When the cation is a divalent cation,
A precipitate is formed with hydrofluoric acid, which is not preferable.

Therefore, the etching solution is preferably a solution in which the hydrogen ions have been replaced with monovalent cations.

Further, it is preferable that the monovalent cation is an alkylammonium ion which does not easily form a precipitate even when reacted with another chemical substance in a solution. Also,
When the monovalent cation is an ammonium ion, a precipitate is generated between the monovalent cation and the silicon-based compound eluted from the glass substrate, which is not preferable.

When the surface of a glass substrate is treated with the above-mentioned acidic etching solution, some of the components constituting the glass substrate are eluted into the acidic solution. A deteriorated layer is formed. Then, such altered layer can be removed by performing a surface treatment with an alkaline solution.

Therefore, in the method of manufacturing a substrate for an information recording medium according to the present invention, it is preferable that the surface treatment is performed by performing a first surface treatment with the etching solution and then performing a second surface treatment with an alkaline solution. .

That is, after the first surface treatment is performed, the deteriorated layer is removed by performing the second surface treatment with an alkaline solution, preferably an alkaline solution having a pH of 12 or more, and the surface layer of the glass substrate is removed. Can be cured.

Further, as a result of further intensive studies by the present inventors, a pretreatment using an acidic solution having a pH of 4 or less as a treatment liquid before performing the above-mentioned surface treatment allows the surface of the glass substrate to be treated. Has found that a larger number of microprojections can be formed.

Therefore, a method of manufacturing a substrate for an information recording medium according to the present invention is characterized in that at least one pre-treatment is performed with an acidic solution (preferably having a pH of 4 or less) before performing the surface treatment. .

According to the above-described manufacturing method, more fine projections can be formed on the surface of the glass substrate.
The information recording medium can be started more smoothly,
An information recording medium substrate with further improved flying stability under low flying height can be manufactured.

Further, since such a pretreatment is also performed with an acidic solution, an altered layer is formed on the surface of the glass substrate as in the case of the surface treatment described above.

Therefore, it is preferable to perform at least one first pretreatment using an acidic solution before performing the surface treatment, and then perform a second pretreatment using an alkaline solution.

The abrasive used for precision polishing is preferably a free abrasive having an average particle size of 0.01 μm to 3 μm.

According to the above manufacturing method, the compression depth of the compression layer formed on the surface of the glass substrate by precision polishing using the above-mentioned free abrasive grains can be set to 2 nm to 15 nm. Can be obtained. When the compression depth is less than 2 nm, the height of the fine projections becomes too low, which hinders the texture shape. On the other hand, when the compression depth exceeds 15 nm, the compression layer is not discrete and the abrasive grains are rubbed. It is not preferable because it becomes a continuous shape along the mark and a mountain-like shape is formed instead of a fine protrusion by etching.

Furthermore, the present inventors have conducted intensive studies to effectively obtain a texture having a desired projection height and the desired number of projections. As a result, the content of the SiO ₂ component in the glass composition was excessively increased. This makes it difficult to form minute projections. On the other hand, when the content of the Al ₂ O ₃ component is excessively increased, minute projections are easily formed. However, the probability of formation of abnormal projections increases, which causes head crash and thermal asperity. It was found that there was a risk of causing

[0037] That is, it is desirable to use a glass substrate having a composition ratio of SiO ₂ component and Al ₂ O ₃ component has a certain relationship, specifically, the content of SiO _2, Al ₂
The difference between the content of O ₃ and ５３ is 53% to 6% by mole%.
It is desirable to use a glass substrate having a relationship of 6%, preferably 58% to 64%.

The glass substrate used for the information recording medium substrate is preferably an aluminosilicate-based glass material having excellent water resistance and mechanical strength. , SiO ₂ : 63% to 70
_{%, Al 2 O 3: 4} % ~11%, Li 2 O: 5% ~11
%, Na ₂ O: 6% to 14%, K ₂ O: 0% to 2%, Ti
_{O 2: 0% ~5%,} ZrO 2: 0% ~2.5%, MgO:
0% to 6%, CaO: 1% to 9%, SrO: 0% to 3
% And BaO: 0% to 2% (however, MgO, CaO,
SrO and BaO preferably have a total composition of 2% to 15%).

Further, the information recording medium substrate according to the present invention is characterized in that the information recording medium substrate has a glass substrate on which a large number of fine projections are formed, and is manufactured by any one of the above-described manufacturing methods. And the height of the projections of 2 nm or more is 150/100 μm ^2.
As described above, the maximum projection height from the average of the projection heights is less than 3.6 nm.

According to the information recording medium substrate, the fine projections are manufactured by the above manufacturing method, and the height of the fine projections is 150 protrusions / 100 μm ² or more of 2 nm or more, and the maximum height of the projections is 3. Since it is less than 6 nm, even when driven at a low flying height of 10 nm or less, good flying stability can be maintained without causing head crash, thermal asperity, and the like.

[0041]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view of a main part of a magnetic disk substrate as an information recording medium substrate manufactured by the manufacturing method of the present invention. The magnetic disk substrate 1 is made of an aluminosilicate glass material and has a thickness of 2 nm or more. The number of the micro projections 2 having a projection height of not less than 150/100 μm ² ,
Moreover, the maximum projection height Rp, which is the maximum height from the average value of the projection heights, is formed to be less than 3.6 nm.

That is, in the field of HDDs, it is necessary to reduce the flying height between the magnetic head and the magnetic disk to 10 nm or less in order to cope with a further increase in data zone density in the future. It is necessary to ensure flying stability even when driven at a height.

Also, it is necessary to prevent the magnetic head and the magnetic disk from sticking to each other to cause trouble at the time of starting. For this purpose, it is necessary to form a large number of minute projections 2 on the surface of the magnetic disk substrate 1.

That is, in order to drive the magnetic disk smoothly and stably even when the flying height is 10 nm or less, it is necessary to form many small projections 2 having a low and uniform projection height. In this embodiment, assuming that such a requirement is satisfied, the magnetic disk substrate 1 has 15 micro-projections 2 having a projection height of 2 nm or more.
0/100 μm ² or more, and the maximum projection height Rp, which is the maximum height from the average of the projection heights, is 3.6 n.
m.

Next, a method for manufacturing the magnetic disk substrate 1 will be described.

FIG. 2 is a manufacturing process diagram showing one embodiment (first embodiment) of a method of manufacturing the magnetic disk substrate 1. The magnetic disk substrate 1 is formed in a substrate processing step 3 →
It is manufactured through a polishing step 4 → a texture processing step 5 → a chemical strengthening processing step 6 → a finish cleaning step 7.

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

(1) Substrate Processing Step 3 In the substrate processing step 3, first, a glass substrate serving as a material of a magnetic disk substrate is manufactured by a well-known float method, and is formed into a sheet.

The glass substrate is, specifically, SiO ₂ : 6
3 mol% to 70 mol%, Al ₂ O ₃ : 4 mol% to 11 mol%,
Li ₂ O: 5 mol% to 11 mol%, Na ₂ O: 6 mol% to 1
_{4mol%, K 2 O: 0mol} % ~2mol%, TiO 2: 0mol%
_{~5mol%, ZrO 2: 0mol%} ~2.5mol%, MgO:
0 mol% to 6 mol%, CaO: 1 mol% to 9 mol%, Sr
O: 0 mol% to 3 mol%, BaO: 0 mol% to 2 mol% (however, the total of MgO, CaO, SrO and BaO is 2 mol%
% To 15 mol%) of aluminosilicate glass.

The reason for setting the above composition range will be described below.

Although SiO ₂ is a main component constituting glass, if its content is less than 63 mol%, the durability of the glass is deteriorated. On the other hand, if its content exceeds 70 mol%, the viscosity becomes too large and the glass is melted. Becomes difficult. For this reason,
In the present embodiment, the content of SiO ₂ is set to 63 mol% to 70 mol%.
mol%.

Al ₂ O ₃ is a component that increases the ion exchange rate during the chemical strengthening treatment and improves the water resistance of the glass, and is easily eluted with an acidic aqueous solution, and therefore promotes etching with an acidic aqueous solution. It is a component that does.
However, if the content is less than 4 mol%, the desired effect cannot be exhibited, while the content is 11 mol%.
If it exceeds, the viscosity becomes too large and the devitrification resistance decreases,
Melting becomes difficult. For this reason, in the present embodiment, Al
The content of ₂ O ₃ was set at 4 mol% to 11 mol%.

Li ₂ O is an alkali metal oxide, and is ion-exchanged with an alkali metal ion having a large ionic radius during chemical strengthening treatment to form a large compressive stress layer to improve the mechanical strength and to improve the mechanical strength during melting of the glass. It is a component that enhances solubility, and is also easily eluted with an acidic aqueous solution, and therefore promotes etching with respect to an acidic aqueous solution. However, if the content is less than 5 mol%, the surface compressive stress after ion exchange becomes insufficient, and the viscosity increases, making melting difficult. On the other hand, if the content exceeds 11 mol%, the chemical durability deteriorates. Therefore, in the present embodiment, the content of Li ₂ O is set to 5 mol% to 1 mol%.
It was set to 1 mol%.

Na ₂ O, like Li ₂ O, is also an alkali metal oxide, is ion-exchanged with an alkali metal ion having a large ionic radius during chemical strengthening treatment, increases the solubility during glass melting, and increases the acidity. It is a component that is easily eluted with an aqueous solution and therefore promotes etching with an acidic aqueous solution. However, if the content is less than 6 mol%, the surface compression stress after ion exchange is insufficient, and the viscosity increases, making melting difficult. If the content exceeds 14 mol%, the chemical durability becomes poor. Getting worse. Therefore, in the present embodiment, the content of Na ₂ O is set to 6 mol% to 14 mol%.
mol%.

K ₂ O is also an alkali metal oxide, a component that enhances the solubility during glass melting and promotes elution in an acidic aqueous solution, and promotes etching in an acidic aqueous solution. However, if its content exceeds 2 mol%, the chemical durability deteriorates. For this reason, in this embodiment, the content of K ₂ O is set to 0 mol% to ₂ mol.
%.

Since TiO ₂ is a component for improving the water resistance of glass, it is added as necessary. However, if its content exceeds 5 mol%, the liquidus temperature of the glass increases, and the devitrification resistance is lowered. Getting worse. Therefore, in this embodiment, TiO ₂
Was set to 0 mol% to 5 mol%.

ZrO ₂ , like TiO ₂ , is a component that improves the water resistance of glass, and is therefore added as necessary. However, if its content exceeds 2.5 mol%, fine crystals are formed when the glass is melted. There is a risk of precipitation. Therefore, in the present embodiment, the content of ZrO ₂ is set to 0 mol% to 2.5 mol%.
Set to.

MgO is an alkaline earth metal oxide,
Enhances the solubility of the glass and promotes etching for acidic aqueous solutions. Further, it is appropriately added to adjust the viscosity characteristics and expansion coefficient for forming glass. However, if the content exceeds 6 mol%, the liquidus temperature of the glass increases, and the devitrification resistance deteriorates. Therefore, in this embodiment, the content of MgO is set to 0 mol% to 6 mol%.

CaO, like MgO, is an alkaline earth metal oxide, enhances the solubility of glass, and promotes etching with an acidic aqueous solution. Further, it is appropriately added to adjust the viscosity characteristics and expansion coefficient for forming glass. It is necessary to contain at least 1 mol% or more in order to exhibit the intended action and effect. If the content exceeds 9 mol%, the liquidus temperature of the glass increases, and the devitrification resistance deteriorates. . Therefore, in the present embodiment, C
The content of aO was set to 1 mol% to 9 mol%.

SrO and BaO, like CaO and MgO, are also alkaline earth metal oxides, are components that increase the solubility of glass, and promote etching of acidic aqueous solutions. Further, it is appropriately added to adjust the viscosity characteristics and expansion coefficient for forming glass. However, Sr
When the O content exceeds 3 mol% and the BaO content exceeds 2 mol%, the specific gravity of the glass substrate becomes too heavy, which is not preferable. Therefore, in this embodiment, the SrO content is set to 0 mol%.
The contents of l% to 3 mol% and the content of BaO were set to 0 mol% to 2 mol%, respectively.

In the present embodiment, the above-mentioned alkaline earth metal oxides, ie, MgO, CaO, MgO,
SrO and BaO are SiO ₂ , Al ₂ O ₃ , and Li ₂ O
Although the content is determined according to the content of, in the present embodiment, the content of these alkaline earth metal oxides,
It is prepared so as to be 2 mol% to 15 mol% in total.

That is, when the total amount of these alkaline earth metal oxides is less than 2 mol%, the desired action and effect of accelerating the etching with respect to the acidic solution cannot be exerted, while the total amount of the alkaline earth metal oxides is 15 mol%. %, The devitrification resistance deteriorates or the specific gravity becomes too heavy, which is not preferable for the magnetic disk substrate 1. Therefore, in the present embodiment, the content of the alkaline earth metal oxide is set to a total of 2 mol% to 15 mol%.

Further, in the present embodiment, the composition and composition are such that the SiO ₂ content and the Al ₂ O ₃ content have the relationship of the equation (1).

SiO _2- (1/2) Al ₂ O ₃ = 53 mol% to 66 mol%, preferably 58% to 64% (1) That is, polishing marks are formed on the surface of the glass substrate in the polishing step 4 described later. A large number of compressed layers are formed, and in the subsequent texture processing step 5, the non-compressed layer is etched more to form a large number of microprojections 2. However, when the content of SiO ₂ becomes excessively large, compressive strain is caused by polishing marks. The difference in the etching rate in the depth direction of the glass substrate between the compressed layer where the cracks are generated and the non-compressed layer where no polishing marks are formed is reduced, and as a result, the minute projections 2 are hardly formed, and the minute projections 2 are formed. However, the maximum projection height Rp becomes excessively small.

[0066] On the other hand, when the content of Al ₂ O ₃ comes increased, the etching of the non-compressed layer Al ₂ O ₃ is contained many Al ₂ O ₃ component from it easily eluted to acidic aqueous solution As a result, abnormal protrusions having a maximum protrusion height Rp of 3.6 nm or more are easily formed.

Therefore, when the difference between the SiO ₂ content and the Al ₂ O ₃ content becomes large, the fine projections 2 having a small projection height are formed, but the number of projections is also reduced. And the start of the magnetic disk may be hindered. On the other hand, the SiO ₂ content and A
When the difference from the l ₂ O ₃ content is reduced, the number of projections increases, but abnormal projections are formed, and therefore thermal asperity and head crash are likely to occur.

Therefore, in the present embodiment, the height of the protrusions of 2 nm or more is 150 protrusions / 100 μm ² or more, and the maximum protrusion height is set so that the appropriate minute protrusions 2 are formed on the surface of the glass substrate. The SiO ₂ content and the Al ₂ O are set so that the microprojections 2 having an Rp of less than 3.6 nm are formed.
_{3 The} components are prepared so that the relationship with the content satisfies the above formula (1).

Then, the surface of the glass substrate thus formed into a sheet by the float method is ground by using a grindstone such as a diamond grindstone, and then the end surface of the glass substrate is polished (mirror finish). A glass substrate is formed into a predetermined donut shape.

(2) Polishing Step 4 In the polishing step 4, first, a lapping device is used to perform a lapping process with abrasive grains having a predetermined grain size such as alumina.

Next, the lapping-processed glass substrate is precisely polished using an abrasive in which free abrasive grains are dispersed in a polishing liquid.

That is, in the polishing step 4, as shown in FIG. 3, loose abrasive grains are loaded on the glass substrate 10 by precision polishing to form polishing marks.
Forms a surface in which the compressed layer 9 in which compression strain is caused by the polishing marks and the non-compressed layer 8 in which the polishing marks are not formed are mixed.
In the present embodiment, the compression depth H of the compression layer 9 is 2
Precision polishing is performed by selecting the particle size of the free abrasive grains so as to be in the range of nm to 15 nm.

That is, the compression depth H of the compression layer 9 is 2 nm.
If it is less than the above, the height of the minute projections 2 formed by the etching process described later becomes too low, which hinders the formation of texture. On the other hand, if the compression depth H exceeds 15 nm, the compression layer will not be discrete but will be continuous along the scratch marks of the abrasive grains, and will be mountain-shaped when an etching process described later is performed.

Therefore, in the present embodiment, precision polishing is performed with free abrasive grains so that the compression depth H of the compression layer 9 becomes 2 nm to 15 nm. And, as described above, the compression depth H is 2 nm.
In order to perform precision polishing so as to have a thickness of up to 15 nm, the particle diameter of the free abrasive grains is preferably 0.01 μm to 3 μm.

The type of the free abrasive grains is not particularly limited, but in order to obtain the excellent surface smoothness required for the information recording medium substrate, cerium oxide (CeO ₂ ), manganese oxide, zirconia oxide, Titania oxide, SiO ₂ ,
Preferably, diamond abrasive grains are used.

The polishing method is not particularly limited. If a double-side polishing machine in which a suede-type polishing pad made of artificial leather is attached to the upper surface plate and the lower surface plate is used, both surfaces can be precisely polished at low cost. Can be.

(3) Texture Processing Step 5 Next, the processing proceeds to the texture processing step 5, where the first and second surface treatments 5a and 5b are performed.

First, in the first surface treatment 5a, an alkaline compound is added to hydrofluoric acid to prepare an acidic solution in which hydrofluoric acid and a fluoride salt coexist, and etching is performed using the acidic solution.

That is, in the compression layer 9, the densified SiO
_{Since 2} prevents the elution of other components, etching becomes difficult, and as a result, a remarkable difference occurs in the etching rate between the compressed layer 9 and the non-compressed layer 8. That is, as shown in FIG. 4A, the compressed layer 9 and the non-compressed layer 8 are both etched, but the etching rate of the compressed layer 9 is lower than that of the non-compressed layer 8, so that the surface of the glass substrate 10 Indicates that a large number of microprojections 2 are formed corresponding to the compression layer 9 (in the figure, the phantom lines indicate the surface of the glass substrate 10 before the etching process).

Specifically, the acidic solution is represented by the following formula (2)
An alkali compound is added to hydrofluoric acid such that the ratio X defined by the formula is in the range of 0.3 to 0.98, preferably 0.56 to 0.93. The first surface treatment 5a is performed by using this.

X = [[HF] + [H ⁺ ]] / [[HF] + [F ⁻ ]] (2) Here, [HF] is the weight concentration per mole of hydrofluoric acid in the etching solution. (Wt% / mol), [H ⁺ ] is the weight concentration per mole of hydrogen ions (wt% / mol) in the etching solution.
mol), [F ^-] 1 of fluoride ion in the etching solution
It is a weight concentration per mol (wt% / mol).

That is, when the etching process is performed only with hydrofluoric acid, the number of the microprojections 2 is proportional to the hydrofluoric acid concentration, and when the concentration of hydrofluoric acid is reduced, the number of the microprojections 2 decreases. When the concentration of hydrofluoric acid is increased, the number of projections of the minute projections 2 increases. Further, the magnetic disk substrate 1 is usually subjected to a chemical strengthening process after the texturing process is performed, thereby increasing the surface compressive stress and improving the mechanical strength. Since the heat treatment is performed in the molten salt in the atmosphere, the minute protrusions 2 relax and expand due to heat, and the protrusion height gradually increases. As a result, there is a possibility that thermal asperity or head crash of the magnetic head may be caused.

Therefore, in the present embodiment, in order to solve such a problem, the ratio X is set to 0.3 to 0.98, preferably 0.1 to 0.9.
An acidic solution in which a hydrofluoric acid and a fluoride salt coexist is prepared by adding an alkali compound to hydrofluoric acid so as to be in the range of 56 to 0.93, and the first surface treatment is performed using the acidic solution as an etching solution. 5a is going on.

The reason why the ratio X is limited to the above range will be described below.

In a solution, most of hydrofluoric acid is dissociated into hydrogen ions and fluorine ions, and the hydrogen ions are replaced with cations of an alkali compound to form a fluoride salt.
As a result, an etching solution in which hydrofluoric acid and a fluoride salt coexist is produced. However, if the ratio X exceeds 0.98, the content of the hydrofluoric acid becomes excessive because the addition amount of the alkali compound is small. There is no difference from the case where only the etching is performed, so that an abnormal protrusion having a high protrusion height of 3.6 nm or more is formed, and it is difficult to uniformly form the minute protrusion 2 having a low protrusion height.

On the other hand, when the etching solution is prepared so that the ratio X is less than 0.3, the amount of the alkali compound added becomes too large, and therefore, the etching rate of the compressed layer 9 and the non-compressed layer 8 is almost zero. As a result, the projection density of the minute projections 2 decreases.

Therefore, in this embodiment, the amount of the alkali compound added is adjusted so that the ratio X becomes 0.3 to 0.98, preferably 0.56 to 0.93, and an etching solution is prepared. ing.

The alkali compound to be added to hydrofluoric acid is not particularly limited, but has a monovalent cation such as tetramethylammonium hydroxide (hereinafter referred to as “TMAH”) or trimethylammonium hydroxide. Preference is given to using alkylammonium hydroxides. That is, in the case of an alkali compound having a divalent cation,
The reaction with hydrofluoric acid is not preferable because a precipitate is formed. Further, even in the case of an alkali compound having a monovalent cation, for example, when ammonium fluoride is used, SiO ₂ contained in the glass substrate 10 reacts with ammonium fluoride to cause a precipitate ((NH ₄₎ it is not preferable to generate the ₂ SiF _6). On the other hand, even if the alkylammonium hydroxide reacts with another chemical substance in a solution, a precipitate is hardly formed, and therefore, it is most preferable to use the alkylammonium hydroxide as an alkali compound.

After completion of the first surface treatment 5a in this way, in the second surface treatment 5b, alkali cleaning is performed using an alkaline solution. That is, the first surface treatment 5
As shown in FIG. 4 (a), as shown in FIG. 4 (a), a microprojection 2 having a large projection height is formed in a portion where a deep and large indentation is applied, and a projection is formed in a portion where the degree of indentation is shallow or small. Small projections 2 with a small height are formed,
When the surface treatment is performed with the acidic etching solution as described above, a component rich in SiO ₂ is eluted, and as a result, a soft altered layer 11 having a small thickness, a small mechanical strength, and a small mechanical strength is formed on the surface of the glass substrate 10. It is formed.

Therefore, in the second surface treatment 5b, as shown in FIG. 4 (b), the deteriorated layer 11 is removed by performing alkali washing with an alkaline solution, and the surface layer is hardened.

Here, the kind of the alkaline solution is not particularly limited, but it is preferable that the pH is 12 or more in order to efficiently and completely remove the deteriorated layer 11 in a short time. Sodium hydroxide or the like can be used.

The processing time and the processing temperature in the first and second surface treatments 5a and 5b are not particularly limited, and are appropriately determined according to the concentration of the chemical solution and the etching rate of the glass substrate 10. In consideration of the above, it is preferable to set the processing time to 1 minute to 20 minutes and the processing temperature to 70 ° C. or less.

In the present embodiment, the treatment is performed by dipping the glass substrate 10 in an etching solution or an alkaline solution. In this case, the cleaning may be performed while applying ultrasonic waves to the glass substrate 10. Further, the application of the ultrasonic wave may be performed under a constant frequency, a plurality of different frequencies may be simultaneously applied, or the frequency may be changed with time. Also, the output of the ultrasonic wave is not particularly limited, but generally, the lower the frequency and the higher the output, the more the glass substrate 1
Since the damage to 0 becomes stronger, it is preferable to determine in consideration of such points.

As a treatment method, in addition to the above-described immersion method, a shower method, a jet method, or the like may be used. In this case, it is also preferable to rub the glass substrate 10 by bringing a sponge or the like into contact therewith. .

(4) Chemical Strengthening Step 6 Next, as described above, the first and second surface treatments 5a,
After cleaning and drying the glass substrate 10 on which 5b has been applied,
The chemical strengthening process 6 is performed.

The drying method is not particularly limited. For example, an IPA vapor drying method in which the glass substrate 10 is immersed in isopropyl alcohol (IPA) vapor, a glass substrate 10
Can be used at high speed to remove the washing water.

Then, in the chemical strengthening treatment step 6, a molten salt adjusted to a predetermined high temperature, for example, potassium nitrate (KN
The glass substrate 10 is immersed in a molten salt composed of a mixture of O ₃ ) and sodium nitrate (NaNO ₃ ) for a predetermined time, and Li ⁺ and Na ⁺ in the chemical components of the glass substrate 10 are ion-exchanged to K ⁺ having a large ionic radius. Execute the chemical strengthening process. 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, breakage can be prevented.

(5) Finish Cleaning Step 7 In the finish cleaning step 7, the glass substrate 10 is immersed in an alkaline solution and, if necessary, is subjected to alkaline cleaning while irradiating ultrasonic waves to thereby fix the iron fixed to the glass substrate 10. The impurities such as powder, that is, the remaining foreign matter are removed by etching, and the production of the magnetic disk substrate 1 is completed.

As the alkaline solution, potassium hydroxide, sodium hydroxide, ammonia, tetramethylammonium hydroxide and the like can be used.

The magnetic disk substrate 1 thus manufactured is laminated with a multilayer film in a film forming process thereafter, whereby a magnetic disk as an information recording medium is manufactured. That is, in the film forming process, a seed layer, an underlayer, a magnetic layer, and a protective layer are sequentially laminated on the glass substrate 10 by using a well-known sputtering method, and then a lubricating layer is formed on the surface of the protective layer by an immersion method. Thus, an information recording medium is manufactured.

In the above-described manufacturing method, even when the glass substrate 10 is exposed to a high-temperature atmosphere by a chemical strengthening process, a sputtering process, or the like, since the thermal expansion is suppressed, abnormal projections are formed. Can be avoided, and the minute projections 2 having a projection height of 2 nm or more
The magnetic disk substrate 1 having 50 protrusions / 100 μm ² or more and a maximum protrusion height Rp of less than 3.6 nm can be manufactured.

Therefore, even if the magnetic disk is driven at a low flying height of 10 nm or less, a magnetic disk which does not cause head crash or thermal asperity and does not impair the flying stability of the magnetic head can be obtained.

Further, since a large number of minute projections 2 are formed on the substrate surface of the magnetic disk substrate 1 at a high density, the magnetic head and the magnetic disk do not adhere to each other and are not damaged at the time of restart. Even during driving, smooth driving can be ensured.

FIG. 5 is a manufacturing process diagram showing a second embodiment of the method for manufacturing the magnetic disk substrate 1. The substrate processing step 3, the polishing step 4, the chemical strengthening step 6, and the finish cleaning step 7 shown in FIG. 5 are performed in the same manner as in the first embodiment. However, in the second embodiment, the texture processing step 5 'is performed instead of the texture processing step 5 performed in the first embodiment.

In the texture processing step 5 ′, the first and second surface processing steps 5 c and 5 d are performed in the same manner as in the first embodiment, but before this, the first pre-processing 5 a uses the acidic solution. Then, a second pretreatment 5b is performed using an alkaline solution. As a result, the number of the fine protrusions 2 is increased, and the texture is further densified.

More specifically, in the first pretreatment 5a ', surface treatment is performed with an acidic solution, and as shown in FIG.
A step D is formed on the surface of 0. That is, similarly to the first embodiment, the polishing step 4 in the second embodiment also.
The compression layer 12 and the non-compression layer 13 are formed by the above, but since the compression layer 12 is formed by densifying SiO ₂ having excellent acid resistance, it is hardly etched, and the non-compression layer 13 is selectively formed. Etching is performed, and as a result, a step D is formed on the surface of the glass substrate 20.

The acidic solution is not particularly limited.
In order to form a desired step D, the solution is preferably a solution having a pH of 4 or less, specifically, sulfuric acid, nitric acid, hydrochloric acid,
One or more selected from phosphoric acid can be used.

After the completion of the first pretreatment 5a 'in this way, in the second pretreatment 5b', alkali cleaning is performed using an alkaline solution. That is, the first preprocessing 5
Due to a ′, a step D is formed on the surface of the glass substrate 20 as described above. However, since a component rich in SiO ₂ , which is a glass component, elutes, the mechanical strength is weak on the surface of the glass substrate 20. The soft altered layer 14 is formed.

Therefore, in the subsequent second pretreatment 5b ', as shown in FIG. 6 (b), the deteriorated layer 14 is removed by performing alkali washing with an alkaline solution, and the surface layer is hardened.

Then, as in the first embodiment, a first surface treatment 5c 'is performed using an acidic solution obtained by adding an alkali compound to hydrofluoric acid as an etching solution. As a result, FIG. As shown, a large number of microprojections 2 and altered layer 16 are formed.

Next, the first surface treatment 5
After the completion of c ', in the subsequent second surface treatment 5d', the altered layer 16 is removed with an alkaline solution, and then the magnetic disk substrate 1 is subjected to a chemical strengthening process 6 and a finish cleaning process 7.
Is manufactured.

As described above, in the second embodiment, the first
Before and after performing the surface treatment 5c '
By performing steps a ′ and 5b ′, a step D is formed to form the microprojections 2 to some extent, and then, as in the first embodiment, the first and second surface treatments 5c ′ , 5
By performing d ', it is possible to manufacture the magnetic disk substrate 1 having a large number of minute projections 2 with a higher density while reducing the height of the projections.

[0113]

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

[First Embodiment] The inventors of the present invention
O ₂ : 67 mol%, Al ₂ O ₃ : 10 mol%, Li ₂ O: 7.
_{5mol%, Na 2 O: 8.5mol} %, MgO: 3.0mol
%, CaO: aluminosilicate glass having a chemical composition of 4.0 mol% is melted by a float method, formed into a sheet shape, and then subjected to a grinding process using a diamond grindstone. Surface) was mirror-finished 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 0.6 mm.

As is apparent from the above chemical composition, the present glass substrate is made of an alkaline earth metal oxide (MgO and C
The content of aO) is adjusted to a total of 7 mol%, and is in the range of 2 mol% to 15 mol% within the scope of the present invention.
Also, {SiO _2- (1/2) Al ₂ O ₃ } is adjusted to 61 mol%, which is a preferred range of the present invention from 58 mol% to 6 mol%.
It is within the range of 4 mol%.

[0116] Then, using abrasive CeO ₂ abrasive grains are dispersed in a polishing liquid and (CeO ₂ abrasive grains having a grain size of 1.2 [mu] m) the polishing pad of suede type made artificial leather polishing the glass substrate Then, a compression layer was formed by randomly applying polishing marks (abrasion marks) to the surface of the glass substrate, and then shower-washing with pure water to roughly remove abrasives attached to the surface of the glass substrate (precision). Polishing).

When the surface properties of the glass substrate were observed with an atomic force microscope after the precision polishing, the surface roughness Ra was 0.1.
44 nm, maximum protrusion height Rp is 19.1 nm, 2 nm to
The number of microprojections having a projection height of 3 nm was 22/100 μm ² (10 μm × 10 μm).

Next, as described in Examples 1 to 3 and Comparative Examples 1 to 3, the first and second surface treatments were performed on the glass substrate polished in this manner. Was performed to etch the substrate surface, and then a chemical strengthening treatment was performed to evaluate the surface properties of the glass substrate before and after the chemical strengthening treatment.

(Example 1) The present inventors first set a temperature of 5
Hydrofluoric acid (HF) concentration maintained at 0 ° C is 0.030 wt%
And the TMAH (N (CH ₃ ) ₄ OH) concentration is 0.010 wt.
% And a mixture of hydrofluoric acid and TMAH is prepared so that the ratio X becomes 0.927, and an acidic solution in which hydrofluoric acid and tetramethylammonium fluoride (fluoride salt) coexist is prepared. did.

That is, the ratio X is defined by the equation (2) as described above.

X = [[HF] + [H ⁺ ]] / [[HF] + [F ⁻ ]] (2) And the molecular weight of hydrofluoric acid is 20, and the molecular weight of TMAH is 9
Therefore, ([HF] + [F ⁻ ]) is 1.5 × 10
^-3 (= 0.030 / 20) and ([HF] +
[H ⁺ ]) is 1.39 × 10 ⁻³ (1.5 × 10 ⁻³ −0.
11 × 10 ⁻³ (= 0.010 / 91), and when these numerical values are substituted into Expression (2), the ratio X becomes 0.927. That is, the ratio X is within the range of the present invention from 0.3 to 0.3.
The amount of hydrofluoric acid and TMAH was adjusted so as to be 0.98 (preferably 0.56 to 0.93), and an acidic solution as an etching solution was prepared.

Next, the present inventors consider that the frequency is 48 KHz,
The glass substrate was immersed in the etching solution for 2.5 minutes while irradiating ultrasonic waves having an output of 1 kW / cm ² , and then immersed in a pure water bath to sufficiently wash (first surface treatment). . Next, the glass substrate is immersed in a potassium hydroxide (KOH) aqueous solution having a pH of 12 for 2.5 minutes to remove the altered layer (second surface treatment), and then the glass substrate is immersed in a pure water bath. The washing operation was repeated three times, and further dried in IPA vapor for 1 minute, thereby producing a test piece having a large number of microprojections formed on a glass substrate, and observing the surface properties of the test piece with an atomic force microscope.

Next, reagent grade 1 sodium nitrate and reagent 1
To prepare a molten salt heated to 380 ° C. at a temperature of 380 ° C. and immersed in the molten salt for 3 hours, thereby holding the glass substrate. Li ⁺ and Na ⁺ inside are converted to K ^{+ with} a large ion radius.
Was subjected to a chemical strengthening treatment for ion exchange.

Thereafter, the step of immersing the test piece subjected to the chemical strengthening treatment in a pure water bath was repeated three times, and after the molten salt attached to the surface of the glass substrate was washed away,
After drying in PA vapor for 1 minute, the surface properties of the test piece were observed again with an atomic force microscope.

(Example 2) The present inventors prepared 0.030 wt% hydrofluoric acid and 0.040 wt%
And TMAH was mixed so that the ratio X became 0.707, and an acidic solution in which hydrofluoric acid and tetramethylammonium fluoride (fluoride salt) coexisted was produced.

That is, in this case, [HF] is 1.5
× 10 ⁻³ (= 0.030 / 20), [F ⁻ ] is 0, and [H ⁺ ] is 0.44 × 10 ⁻³ (= 0.040 / 20).
91), the ratio X is 0.707 according to equation (2). That is, also in the second embodiment, the ratio X is within the range of the present invention in the range of 0.3 to 0.98 (preferably 0.56
~ 0.93), the amount of hydrofluoric acid and TMAH was adjusted to prepare an acidic solution as an etching solution.

Next, using the etching solution (acid solution) prepared above, the first and second surface treatments were performed by the same method and procedure as in Example 1 to form a large number of fine projections on the glass substrate. The prepared test piece was prepared, and its surface properties were observed with an atomic force microscope.

Next, a chemical strengthening treatment was performed by the same method and procedure as in Example 1, the test piece was washed in a pure water bath, dried, and the surface properties of the test piece after the chemical strengthening treatment were measured by an atomic force microscope. Was observed.

(Example 3) The present inventors prepared 0.030 wt% hydrofluoric acid maintained at a temperature of 50 ° C and 0.060 wt%.
And TMAH was mixed so that the ratio X became 0.561, to prepare an acidic solution in which hydrofluoric acid and tetramethylammonium fluoride (fluoride salt) coexisted.

That is, in this case, ([HF] + [F
^- ]) Is 1.5 × 10 ⁻³ (= 0.030 / 20),
([HF] + [H ⁺ ]) is 0.84 × 10 ⁻³ (1.5 ×
Since it is 10 ⁻³ −0.66 × 10 ⁻³ (= 0.060 / 91), the ratio X is 0.561 from Expression (2).
That is, in Example 3, the ratio X is within the range of the present invention.
The mixing amount of hydrofluoric acid and TMAH was adjusted so as to be 3 to 0.98 (preferably 0.56 to 0.93) to prepare an acidic solution as an etching solution.

Next, using the prepared etching solution (acid solution), the first and second surface treatments were performed by the same method and procedure as in Example 1 to form many fine projections on the glass substrate. The prepared test piece was prepared, and its surface properties were observed with an atomic force microscope.

Next, a chemical strengthening treatment was carried out in the same manner and procedure as in Example 1, the test piece was washed in a pure water bath, dried, and the surface properties of the test piece after the chemical strengthening treatment were examined with an atomic force microscope. Was observed.

(Comparative Example 1) The present inventors maintained a temperature of 50 ° C. on a precision-polished glass substrate.
Using a 1 wt% hydrofluoric acid solution as an etchant,
After performing the surface treatment described above, a second surface treatment was performed by the same method and procedure as in Example 1, and the surface properties of the test piece were observed with an atomic force microscope.

Next, a chemical strengthening treatment was performed by the same method and procedure as in Example 1, the test piece was washed in a pure water bath, dried, and the surface properties of the test piece after the chemical strengthening treatment were measured by an atomic force microscope. Was observed.

(Comparative Example 2) The present inventors maintained a temperature of 50.degree.
Using a 1 wt% hydrofluoric acid solution as an etchant,
After performing the surface treatment described above, a second surface treatment was performed by the same method and procedure as in Example 1, and the surface properties of the test piece were observed with an atomic force microscope.

Next, a chemical strengthening treatment was performed by the same method and procedure as in Example 1, the test piece was washed in a pure water bath, dried, and the surface properties of the test piece after the chemical strengthening treatment were examined by an atomic force microscope. Was observed.

(Comparative Example 3) The present inventors have found that the ratio X is 0.
0.030 which was maintained at a temperature of 50 ° C. so as to be 100
An acidic solution was prepared by mixing wt% of hydrofluoric acid and 0.500 wt% of ammonium fluoride (NH ₄ F) as a fluoride salt.

That is, in this case, [HF] is 1.5
× 10 ⁻³ (= 0.030 / 20), [H ⁺ ] is 0, and the molecular weight of ammonium fluoride is 37. Therefore, [F ⁻ ] is 13.5 × 10 ⁻³ (= 0.500). / 3
7), and the ratio X is 0.100 from Expression (2). That is, in this comparative example, the mixing amount of hydrofluoric acid and ammonium fluoride was adjusted so that the ratio X was out of the range of the present invention, and an acidic solution as an etching solution was prepared.

Next, using the etching solution (acid solution) prepared above, the first and second surface treatments were performed by the same method and procedure as in Example 1 to form a large number of fine projections on the glass substrate. The prepared test piece was prepared, and its surface properties were observed with an atomic force microscope.

Next, a chemical strengthening treatment was performed by the same method and procedure as in Example 1, the test piece was washed in a pure water bath, dried, and the surface properties of the test piece after the chemical strengthening treatment were examined by an atomic force microscope. Was observed.

Table 1 shows the composition of the chemical solution used in each of the above Examples and Comparative Examples, and Table 2 shows the surface properties of each of the Examples and Comparative Examples before and after the chemical strengthening treatment.

In the observation of the above surface properties, measurement was performed in a tapping mode using a Nanoscope IIIa manufactured by Digital Instruments as an atomic force microscope.

[0143]

[Table 1]

[0144]

[Table 2]

As is clear from Tables 1 and 2, Comparative Example 1 performed the first surface treatment only with hydrofluoric acid.
Since the hydrofluoric acid concentration is as small as 0.015 wt%, the maximum protrusion height Rp before the chemical strengthening treatment is as small as 3.1 nm, but the number of the fine protrusions is as small as 80/100 μm ^2, and after the chemical strengthening treatment. It was found that the maximum projection height Rp increased to 3.6 nm due to relaxation expansion due to heat, which could cause thermal asperity and head crash.
Moreover, even after the chemical strengthening treatment, the number of protrusions is 12
Since it is as small as 0 pieces / 100 μm ² , when it is used for a magnetic disk, adhesion to a magnetic head is likely to occur, and it may be difficult to start smoothly.

In Comparative Example 2, as in Comparative Example 1, the first surface treatment was performed using only hydrofluoric acid. However, since the hydrofluoric acid concentration was as high as 0.030 wt%, the first surface treatment was performed before the chemical strengthening treatment. Although the number of microprojections is as large as 400/100 μm ² , the maximum projection height Rp is also as high as 3.8 nm, and the number of the microprojections is 500/10 after chemical strengthening treatment.
Although it is increased to 0 μm ² , the maximum protrusion height Rp is further increased to 4.1 nm due to relaxation expansion by heat, and there is a possibility that thermal asperity or head crash may occur.

In Comparative Example 3, since a large amount of ammonium fluoride was contained in the solution, the SiO ₂ contained in the glass substrate 10 reacted with the ammonium fluoride to precipitate ((NH ₄ ) ₂ to generate the SiF _6), 45 or number of projections is in front chemical reinforcement / 100 [mu] m ^2, very small and 40/100 [mu] m ² after chemical strengthening treatment, also of CeO ₂ imparted with indentations microparticles of glass substrate It was not able to be completely removed from the surface, so that it was confirmed that dirt was conspicuous on the surface of the glass substrate, and that abnormal projections having a high maximum projection height Rp were generated.

On the other hand, in Examples 1 to 3, the first surface treatment was carried out using an acidic etching solution whose ratio X was adjusted to 0.56 to 0.93 which is a preferable range of the present invention. Thus, the magnetic disk substrate 1 having a microprojection with a maximum projection height Rp of less than 3.6 nm and a projection count of 150/100 μm ² or more is hardly changed before and after the chemical strengthening treatment. It turned out that it can be manufactured.

[Second Embodiment] The present inventors have proposed the first embodiment.
A glass substrate having the same composition as in Example 1 was prepared and precision polished, and the precision polished glass substrate was subjected to first and second surface treatments before the first and second surface treatments were performed. A treated test piece was prepared (Examples 5 to 7), and the surface properties of the test piece (Example 4) subjected to only the first and second surface treatments were compared.

(Example 4) The present inventors prepared 0.025 wt% of hydrofluoric acid and 0.010 wt% of
And TMAH was mixed so that the ratio X became 0.912, and an acidic solution in which hydrofluoric acid and tetramethylammonium fluoride (fluoride salt) coexisted was produced.

That is, in this case, ([HF] + [F
^- ]) Is 1.25 × 10 ⁻³ (= 0.025 / 20), and ([HF] + [H ⁺ ]) is −0.11 × 10 ⁻³ (=
0.010 / 91), the ratio X
Is 0.912. That is, in the fourth embodiment, the ratio X is in the range of 0.3 to 0.98 (preferably 0.5
The amount of hydrofluoric acid and TMAH was adjusted so as to be 6 to 0.93) to prepare an acidic solution as an etching solution.

Next, using the prepared etching solution (acid solution), the first and second surface treatments were performed by the same method and procedure as in Example 1 to form a large number of fine projections on the glass substrate. The prepared test piece was prepared, and its surface properties were observed with an atomic force microscope.

Next, a chemical strengthening treatment was performed by the same method and procedure as in Example 1, the test piece was washed in a pure water bath, dried, and the surface properties of the test piece after the chemical strengthening treatment were examined by an atomic force microscope. Was observed.

(Example 5) The present inventors first set the temperature
An aqueous solution of hydrofluoric acid with a pH of 3.1 maintained at 0 ° C. (0.00
5 wt%), then a frequency of 48 KHz and an output of 1
While irradiating ultrasonic waves of kW / cm ^2, the glass substrate which has been precisely polished is immersed in the hydrofluoric acid aqueous solution for 5 minutes.
Pretreatment was performed.

Next, the glass substrate was immersed in an aqueous solution of potassium hydroxide (KOH) having a pH of 12 for 2.5 minutes, and then washed by immersing the glass substrate in a pure water bath.
This was repeated twice, and then dried in IPA vapor for 1 minute to remove the altered layer, and the second pretreatment was performed.

Thereafter, etching treatment is performed using the same acidic solution as in Example 4 (first surface treatment).
Next, a second surface treatment was performed in the same manner and procedure as in Example 4 to prepare a test piece having a large number of microprojections formed on a glass substrate, and the surface properties were observed with an atomic force microscope.

Next, a chemical strengthening treatment was carried out in the same manner and procedure as in Example 4, the test piece was washed in a pure water bath, dried, and the surface properties of the test piece after the chemical strengthening treatment were examined with an atomic force microscope. Was observed.

Example 6 The present inventors prepared an aqueous sulfuric acid solution (0.5 wt%) having a pH of 1 and maintained at a temperature of 50 ° C., and then irradiated with ultrasonic waves having a frequency of 48 KHz and an output of 1 kW / cm ^2. While the precision polished glass substrate is
The sample was immersed in the aqueous sulfuric acid solution for 1 minute to perform a first pretreatment.

Thereafter, a second pretreatment, a first and a second surface treatment were sequentially performed in the same manner and procedure as in Example 5 to produce a test piece having a large number of microprojections formed on a glass substrate.
The surface properties were observed with an atomic force microscope.

Next, a chemical strengthening treatment was carried out in the same manner and procedure as in Example 5, the test piece was washed in a pure water bath, dried, and the surface properties of the test piece after the chemical strengthening treatment were examined with an atomic force microscope. Was observed.

(Example 7) The present inventors reported that the pH was 4.1.
A phthalic acid standard solution (C ₆ H ₄ (COOH) ₂ ) was prepared, and the glass substrate, which had been precisely polished while being irradiated with ultrasonic waves having a frequency of 48 KHz and an output of 1 kW / cm ² , was treated with the phthalic acid standard solution for 5 minutes. The first pretreatment was performed by immersion.

Thereafter, the second pretreatment, the first and second surface treatments were sequentially performed in the same manner and procedure as in Example 5 to produce a test piece having a large number of microprojections formed on a glass substrate.
The surface properties were observed with an atomic force microscope.

Next, a chemical strengthening treatment was performed by the same method and procedure as in Example 5, the test piece was washed in a pure water bath, dried, and the surface properties of the test piece after the chemical strengthening treatment were measured by an atomic force microscope. Was observed.

Table 3 shows the composition of the chemical solution used in each of the above Examples, and Table 4 shows the surface properties before and after the chemical strengthening treatment in each of the Examples.

In the observation of the above surface properties, a nanoscope IIIa manufactured by Digital Instruments Co., Ltd. was used as an atomic force microscope in the same manner as in the first embodiment, and the measurement was performed in a tapping mode.

[0166]

[Table 3]

[0167]

[Table 4]

Comparing the fourth embodiment with the fifth to seventh embodiments, when the first and second pre-processings are performed, the fineness is smaller than when the first and the second pre-processings are not performed. It can be seen that the number of projections of the projections 2 is increased, so that the density of the fine projections can be further increased, and smooth driving at a low flying height is more suitable. Moreover, the maximum projection height Rp after the chemical strengthening treatment is 3.
Since the diameter is suppressed to less than 6 nm, no abnormal protrusion occurs, and even when the magnetic head glides on the magnetic disk at a low flying height, it is possible to avoid thermal asperity and head crash.

[0169]

As described above in detail, the method of manufacturing a substrate for an information recording medium according to the present invention comprises the steps of: subjecting a glass substrate to a precision polishing treatment using an abrasive, followed by a surface treatment; In the method for manufacturing an information recording medium substrate for manufacturing a substrate, the surface treatment is performed using an etching solution in which hydrofluoric acid and a fluoride salt coexist, and each of the hydrofluoric acid and fluoride ions The ratio X of the sum of the concentration of each of the hydrofluoric acid and hydrogen ions to the sum of the concentrations per mole is 0.3 to 0.98, preferably 0.56 to 0.98.
Since the etching solution is prepared so as to be 0.93, the maximum projection height after the heat treatment can be reduced even if heat treatment such as chemical strengthening treatment or sputtering treatment is performed. A desired information recording medium substrate having minute projections (texture) formed at a high density can be manufactured, and therefore, an information recording medium substrate having excellent flying stability even under a low flying height can be obtained.

The etching solution is a solution in which the hydrogen ions have been replaced by monovalent cations, and the monovalent cations are composed of alkylammonium ions. Is not generated, and a desired etching process can be performed smoothly.

In the surface treatment, the first surface treatment is performed with the etching solution, and then the second surface treatment is performed with an alkaline solution. A soft deteriorated layer having low target strength can be easily removed, and the chemical durability of the surface layer can be enhanced.

Further, by performing at least one pretreatment with an acidic solution having a pH of 4 or less before performing the surface treatment, and performing a second pretreatment using an alkaline solution after performing the first pretreatment. By performing the pre-treatment, a larger number of fine protrusions can be formed on the surface of the glass substrate, which makes it possible to start the magnetic disk smoothly and more reliably, and to stably fly under a low flying height. The properties are further improved.

In the glass substrate, the difference between the content of SiO ₂ and half of the content of Al ₂ O ₃ is 53% to 66%, preferably 58% to 64% by mol%. By having a composition component, a moderate fine protrusion, that is, 2 nm
The height of the projections is 150/100 μm ² or more, and the maximum height of the projections can be effectively contributed to the formation of minute projections of less than 3.6 nm.

More preferably, the glass substrate is preferably an aluminosilicate-based glass material having excellent water resistance and mechanical strength.
_{2: 63% ~70%, Al} 2 O 3: 4% ~11%, Li
₂ O: 5% to 11%, Na ₂ O: 6% to 14%, K ₂ O:
_{0% ~2%, TiO 2:} 0% ~5%, ZrO 2: 0% ~
2.5%, MgO: 0% to 6%, CaO: 1% to 9%,
SrO: 0% to 3%, and BaO: 0% to 2% (however,
MgO, CaO, SrO, and BaO are 2% to 1 in total.
5%), the height of moderate fine protrusions, that is, protrusions of 2 nm or more is 150/100.
It can effectively contribute to the formation of microprojections having a size of not less than μm ² and a maximum projection height of less than 3.6 nm.

Further, the average particle size is 0.01 μm to 3 μm
When precision polishing is performed with free abrasive grains, the compression depth of the compression layer formed on the surface of the glass substrate can be set to 2 nm to 15 nm, so that the desired texture shape can be obtained.

Further, the information recording medium substrate according to the present invention is manufactured by the above-described manufacturing method, and the fine projections have a projection height of 2 nm or more of 150 projections / 100 μm.
A m ² or more, and by the maximum protrusion height is less than 3.6 nm, to obtain a substrate for an information recording medium capable of be driven by the following low flying height 10nm to secure the flying stability be able to.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a main part of an embodiment of a magnetic disk substrate 1 as an information recording medium substrate according to the present invention.

FIG. 2 is a manufacturing process diagram showing one embodiment (first embodiment) of a method for manufacturing a magnetic disk substrate.

FIG. 3 is a cross-sectional view of the glass substrate precisely polished in a polishing step 4.

FIG. 4 is a cross-sectional view of a glass substrate showing a surface treatment in a texture processing step 5, in which (a) shows a surface of the glass substrate 10 before an etching process by a virtual line;
(B) shows a state in which the deteriorated layer 8 has been removed by alkali washing.

FIG. 5 is a manufacturing process diagram showing a second embodiment of the method for manufacturing the magnetic disk substrate 1.

FIG. 6 is a cross-sectional view of a glass substrate showing a surface treatment in a texture processing step 5 ′ according to the second embodiment;
(A) shows a step D formed on the surface of the glass substrate 20 by slightly etching the portion of the non-compressed layer 13.
(B) shows a state in which the altered layer 14 has been removed by alkali washing, and (c) shows a state in which
This shows a state in which a large number of smile protrusions 2 and altered layer 16 are formed, and FIG.
Is a state in which is removed.

[Explanation of symbols]

 5, 5 'texture processing step 5a, 5c' first surface treatment 5b, 5d 'second surface treatment 5a' first pretreatment 5b 'second pretreatment

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuhiro Saito 4-7-28 Kitahama, Chuo-ku, Osaka-shi, Osaka F-term in Nippon Sheet Glass Co., Ltd. 5D006 CB04 CB06 CB07 5D112 AA02 BA03 BA08 BA09 GA09 GA14 GA27

Claims (15)

[Claims] 1. A method of manufacturing a substrate for an information recording medium, comprising: performing a precision polishing process on a glass substrate using an abrasive, and then performing a surface treatment to manufacture a substrate for an information recording medium. A method for producing a substrate for an information recording medium, wherein the method is performed using an etching solution in which hydrofluoric acid and a fluoride salt coexist. 2. The ratio X of the sum of the concentration of each of the hydrofluoric acid and hydrogen ions to the sum of the concentrations of each of the hydrofluoric acid and fluoride ions per mole is 0.3 to 0.98. The method for manufacturing a substrate for an information recording medium according to claim 1, wherein the etching solution is prepared as described above. 3. The method according to claim 2, wherein the etching solution is prepared so that the ratio X is 0.56 to 0.93. 4. The information recording medium substrate according to claim 1, wherein the etching solution is a solution in which the hydrogen ions are replaced with monovalent cations. Production method. 5. The method according to claim 4, wherein the monovalent cation is an alkyl ammonium ion. 6. The surface treatment according to claim 1, wherein after the first surface treatment is performed with the etching solution, the second surface treatment is performed with an alkaline solution. The method for manufacturing the information recording medium substrate according to the above. 7. The method for manufacturing a substrate for an information recording medium according to claim 1, wherein at least one pretreatment is performed with an acidic solution before the surface treatment is performed. 8. The method according to claim 1, wherein at least one first pretreatment is performed with an acidic solution before the surface treatment is performed, and then a second pretreatment is performed using an alkaline solution. A method for manufacturing a substrate for an information recording medium according to claim 6. 9. The method for manufacturing a substrate for an information recording medium according to claim 7, wherein the pH of the acidic solution is 4 or less. 10. The glass substrate has a difference between the content of SiO ₂ and half the content of Al ₂ O ₃ of 5% by mol%.
The method for manufacturing a substrate for an information recording medium according to any one of claims 1 to 9, wherein the content is 3% to 66%. 11. The glass substrate according to claim 1, wherein the difference between the content of SiO _{2 and} the content of Al ₂ O ₃ is 5% by mol%.
The method for manufacturing a substrate for an information recording medium according to claim 10, wherein the content is 8% to 64%. 12. The glass substrate according to claim 1, wherein the glass substrate is made of SiO
_{2: 63% ~70%, Al} 2 O 3: 4% ~11%, Li
₂ O: 5% to 11%, Na ₂ O: 6% to 14%, K ₂ O:
_{0% ~2%, TiO 2:} 0% ~5%, ZrO 2: 0% ~
2.5%, MgO: 0% to 6%, CaO: 1% to 9%,
SrO: 0% to 3%, and BaO: 0% to 2% (however,
MgO, CaO, SrO, and BaO are 2% to 1 in total.
The method for manufacturing a substrate for an information recording medium according to any one of claims 1 to 9, characterized in that: 13. The abrasive has an average particle size of 0.01 μm.
2. The method for producing a substrate for an information recording medium according to claim 1, wherein the abrasive grains are loose abrasive grains having a size of from 3 to 3 [mu] m. 14. An information recording medium substrate in which a large number of fine projections are formed on a surface of a glass substrate, wherein the substrate is manufactured by the manufacturing method according to claim 1. Description: Information recording medium substrate. 15. The microprojection, wherein the height of the projections of 2 nm or more is 150/100 μm ² or more, and the maximum projection height from the average value of the projection heights is less than 3.6 nm. The information recording medium substrate according to claim 14, wherein