WO2014175292A1

WO2014175292A1 - Magnetic disk-use glass substrate fabrication method and magnetic disk fabrication method

Info

Publication number: WO2014175292A1
Application number: PCT/JP2014/061342
Authority: WO
Inventors: 秀造徳光; 尚宏神谷
Original assignee: Hoya株式会社
Priority date: 2013-04-22
Filing date: 2014-04-22
Publication date: 2014-10-30
Also published as: SG11201508659PA; JP6081580B2; MY179113A; CN105122363B; JPWO2014175292A1; CN105122363A

Abstract

The present invention provides a fabrication method for a magnetic disk-use glass substrate on which ultraclean cleaning can be carried out without degrading, insofar as possible, the smooth surface obtained from precision polishing. In this magnetic disk-use glass substrate fabrication method, after the step in which the magnetic disk-use glass substrate has been given a mirror surface polish, the glass substrate is cleaned by being exposed to a cleaning solution that can etch the glass substrate and that contains at least guanidine or imidazole. In addition, the cleaning is performed while keeping the total quantity of sodium ions and potassium ions in the cleaning solution to under 200 ppm.

Description

Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk

The present invention relates to a method for manufacturing a glass substrate for a magnetic disk mounted on a magnetic disk device such as a hard disk drive (HDD) and a method for manufacturing a magnetic disk.

There is a magnetic disk as one of information recording media mounted on a magnetic disk device such as a hard disk drive (HDD). A magnetic disk is configured by forming a thin film such as a magnetic layer on a substrate, and an aluminum substrate has been conventionally used as the substrate. However, recently, in response to the pursuit of higher recording density, the ratio of the glass substrate capable of narrowing the distance between the magnetic head and the magnetic disk as compared with the aluminum substrate is gradually increasing. Further, the surface of the glass substrate is polished with high accuracy so as to increase the recording density so that the flying height of the magnetic head can be reduced as much as possible. In recent years, the demand for further increase in recording capacity of HDDs has only increased, and in order to realize this, it has become necessary to further improve the quality of glass substrates for magnetic disks. A clean glass substrate surface is required.

As described above, high smoothness on the surface of the magnetic disk is indispensable for reducing the flying height (flying height) necessary for increasing the recording density. In order to obtain high smoothness of the magnetic disk surface, it is necessary to polish the surface of the glass substrate with high precision because the surface of the substrate is highly smooth. However, this is not sufficient, and cleaning after polishing is not sufficient. Therefore, it is necessary to remove the adhered foreign matter on the substrate surface to obtain a clean substrate surface.
As a conventional method, for example, Patent Document 1 discloses a method of cleaning a substrate with an alkali (pH 8 to 13) after polishing using a polishing liquid containing a polyvalent amine. Patent Document 2 discloses a method of cleaning a substrate with an alkaline cleaner having a pH of 10 or more containing an alkaline agent and aldonic acids after polishing.

JP 2012-107226 A JP 2010-86563 A

In the current HDD, a recording density of about 500 gigabits per square inch has been achieved, and for example, about 320 gigabytes of information can be stored in one 2.5 inch type (65 mm diameter) magnetic disk. Although it is possible, there is a demand for further higher recording density, for example, 375 to 500 gigabytes, and further 1 terabyte. With the recent demand for larger capacity of HDDs, the demand for improvement of the substrate surface quality has become more severe than ever. In the next generation substrate for a magnetic disk of, for example, 375 to 500 gigabytes as described above, since the influence of the substrate on the media characteristics becomes large, not only the surface roughness of the substrate but also surface defects due to adhesion of foreign matters do not exist. In this regard, further improvement from the current product is required.

In the next generation substrate, the influence of the substrate on the media characteristics becomes large for the following reasons.
For example, the flying height of the magnetic head (the gap between the magnetic head and the surface of the medium (magnetic disk)) is greatly reduced (lower flying height). By doing so, the distance between the magnetic head and the magnetic layer of the medium is reduced, so that signals of smaller magnetic particles can be picked up, and high recording density can be achieved. In recent years, a function called DFH (Dynamic Flying Height) has been mounted on a magnetic head in order to achieve a lower flying height than before. This is a function of providing a heating unit such as a very small heater in the vicinity of the recording / reproducing element part of the magnetic head and projecting only the periphery of the recording / reproducing element part toward the medium surface. In the future, with this DFH function, it is expected that the gap between the element portion of the magnetic head and the medium surface will be extremely small, less than 2 nm or less than 1 nm. Under such circumstances, when the average roughness of the substrate surface was made extremely small, extremely small foreign matter (for example, a small one having a length in the in-plane direction of the main surface of about 10 to 40 nm) that did not cause a problem in the past. If there is a surface defect that is slightly convex due to adhesion or the like, it becomes a convex defect on the surface of the medium as it is, which increases the risk of collision of the magnetic head.

By the way, according to the study by the present inventors, even using various conventional precision polishing techniques including the method disclosed in the above patent document, precision cleaning techniques, or simply combining them, It has been found that low roughness after cleaning and high cleanliness cannot be compatible.
The demand for improving the substrate surface quality accompanying the recent demand for higher capacity HDDs has become more severe than ever, and there is a limit to the further improvement of the substrate surface quality by the conventional improvement methods. There is. Here, the alkaline agent refers to a substance that exhibits alkalinity when dissolved in water.

The present invention has been made to solve such a conventional problem. The object of the present invention is to perform a cleaning process without first degrading the smooth surface roughness obtained by precision polishing as much as possible. And, as a result, to provide a method for manufacturing a glass substrate for magnetic disk that can achieve low roughness (high smoothness). Second, glass for magnetic disk capable of performing highly clean cleaning It is to provide a method for manufacturing a substrate.

In order to increase the cleanliness of the substrate, it is necessary to clean and remove the foreign matter adhering to the substrate surface. To that end, cleaning with an alkaline chemical solution having a high pH (strong alkalinity) can achieve high cleanliness. preferable. This is because the surface of the glass is etched with an alkaline chemical solution having a high alkalinity, and even a fixed foreign substance can be removed by uprooting. However, with conventional alkali cleaning, the higher the alkalinity, the greater the etching effect on the glass, so that the alkali cleaning increases the surface roughness of the substrate and maintains the ultra-smooth surface roughness obtained by precision polishing. Can not do. Therefore, the present inventors sought a method for suppressing an increase in the surface roughness of the substrate while maintaining the cleaning power by alkali cleaning. As a result, it was ascertained that by using a specific alkaline agent, the increase in roughness can be specifically suppressed.
It was also found that not only the alkalinity of the alkali agent used for washing but also the kind of cation paired with OH ions greatly affects the amount of increase in roughness. Furthermore, it was found that the degree of surface roughness after cleaning varies depending on the type of organic alkali agent and the product lot, due to the influence of different amounts of sodium ions and potassium ions present in the cleaning liquid. Here, organic alkalis such as tetramethylammonium hydroxide (TMAH) originally contain neither sodium nor potassium ions, but sodium and potassium are inevitably mixed in industrial production processes. It was considered that this was involved in the surface roughness of the glass substrate.

Based on these findings, the present inventors completed the present invention as a result of intensive studies.
That is, the present invention has the following configuration.
(Configuration 1)
A method of manufacturing a glass substrate for a magnetic disk including a cleaning process of a glass substrate, wherein the cleaning process includes a process of bringing the glass substrate into contact with a cleaning liquid containing at least one of guanidine and imidazole. The relationship between the amount of increase in the surface roughness (Ra) of the glass substrate main surface after the cleaning treatment and the total concentration of sodium ions and potassium ions in the cleaning solution used for the cleaning treatment was determined in advance, Based on the relationship, the total concentration of sodium ions and potassium ions in the cleaning liquid is determined so that the increase in surface roughness (Ra) is 0.06 nm or less, and the total concentration of sodium ions and potassium ions in the cleaning liquid is determined. Cleaning the glass substrate whose main surface is mirror-polished under the condition that the concentration is equal to or less than the determined concentration. Method of manufacturing a glass substrate for a magnetic disk according to symptoms.

(Configuration 2)
A method for producing a glass substrate for a magnetic disk comprising a glass substrate cleaning treatment, wherein the glass substrate contains at least one of sodium and potassium in a glass component, and a cleaning liquid containing at least one of guanidine and imidazole. And performing a cleaning process on the glass substrate having a main surface mirror-polished while exchanging at least a part of the cleaning liquid so that the total amount of sodium ions and potassium ions in the cleaning liquid does not exceed 200 ppm. A method of manufacturing a glass substrate for a magnetic disk.

(Configuration 3)
A method for producing a glass substrate for a magnetic disk including a cleaning process for a glass substrate, wherein the cleaning process includes a process of bringing the glass substrate into contact with a cleaning liquid containing at least one of guanidine and imidazole, and sodium in the cleaning liquid A method for producing a glass substrate for a magnetic disk, wherein the cleaning treatment is performed while suppressing the total amount of ions and potassium ions to less than 200 ppm.

(Configuration 4)
4. The method for producing a glass substrate for a magnetic disk according to any one of Structures 1 to 3, wherein the glass substrate contains at least one of sodium and potassium in a glass component.
(Configuration 5)
The cleaning liquid further contains at least one substance among a surfactant, a chelating agent, and a dispersing agent, and the cleaning process is performed while suppressing the total amount of sodium ions and potassium ions in the cleaning liquid to less than 200 ppm. The manufacturing method of the glass substrate for magnetic discs in any one of the structures 1 thru | or 4.

(Configuration 6)
The difference between the surface roughness (Ra) of the glass substrate main surface after the cleaning treatment and the surface roughness (Ra) of the glass substrate main surface immediately before the cleaning treatment is within 0.06 nm. A method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 2 to 5.
(Configuration 7)
7. The method for producing a glass substrate for a magnetic disk according to any one of Structures 1 to 6, wherein the surface roughness (Ra) of the glass substrate main surface immediately before the cleaning treatment is 0.13 nm or less.

(Configuration 8)
The method for producing a glass substrate for a magnetic disk according to any one of Structures 1 to 7, wherein the pH of the cleaning liquid is 10 or more.
(Configuration 9)
9. The magnetic according to any one of configurations 1 to 8, wherein the cleaning process is a cleaning process performed after a final polishing process in a polishing process in which a main surface of the glass substrate is polished using polishing abrasive grains. A method for producing a glass substrate for a disk.
(Configuration 10)
The method for producing a glass substrate for a magnetic disk according to claim 9, wherein the polishing liquid used for the final polishing is alkaline.
(Configuration 11)
A magnetic disk manufacturing method comprising: forming at least a magnetic recording layer on a magnetic disk glass substrate manufactured by the method for manufacturing a magnetic disk glass substrate according to any one of Structures 1 to 10.

According to the present invention, a glass substrate for a magnetic disk capable of performing a cleaning process without degrading the smooth surface roughness obtained by precision polishing as much as possible and, as a result, achieving a low roughness (high smoothness). The manufacturing method of can be provided. Moreover, according to this invention, the manufacturing method of the glass substrate for magnetic discs which can implement highly clean washing | cleaning can be provided. According to the present invention, a high-quality glass substrate for a magnetic disk that can further reduce the roughness of the main surface of the substrate and reduce surface defects due to adhesion of foreign substances or the like from the conventional product at low cost. It is possible to manufacture. The glass substrate for a magnetic disk obtained by the present invention can be suitably used as a substrate for the next generation in which the demand for the surface quality of the substrate is particularly stricter than the present. Further, by using the glass substrate obtained by the present invention, a highly reliable magnetic disk capable of long-term stable operation even when combined with a magnetic head with an extremely low flying height design equipped with a DFH function is obtained. Can do.

It is sectional drawing of the glass substrate for magnetic discs. It is a whole perspective view of the glass substrate for magnetic discs. It is a longitudinal cross-sectional view which shows schematic structure of a double-side polish apparatus.

Hereinafter, embodiments of the present invention will be described in detail.
The glass substrate for a magnetic disk is usually a rough grinding step (rough lapping step), a shape processing step, a fine grinding step (fine lapping step), an end surface polishing step, a main surface polishing step (first polishing step, second polishing step). It is manufactured through a chemical strengthening process.
In manufacturing the magnetic disk glass substrate, first, a disk-shaped glass substrate (glass disk) is molded from molten glass by direct pressing. In addition to such a direct press, a glass substrate may be obtained by cutting into a predetermined size from a plate glass manufactured by a downdraw method or a float method. Next, grinding (lapping) is performed on the molded glass substrate in order to improve dimensional accuracy and shape accuracy. This grinding process usually uses a double-sided lapping machine to grind the main surface of the glass substrate using hard abrasive grains such as diamond. By grinding the main surface of the glass substrate in this way, a predetermined plate thickness and flatness are processed, and a predetermined surface roughness is obtained.

After finishing this grinding process, polishing is performed to obtain a highly accurate flat surface (mirror surface). As a method for polishing a glass substrate, it is preferable to use a polishing pad such as polyurethane while supplying a slurry (polishing liquid) containing a metal oxide abrasive such as cerium oxide or colloidal silica.

The polishing liquid in the present embodiment contains a pH adjusting agent for adjusting the pH of the polishing liquid and other additives as required in addition to the combination of the abrasive and water as a solvent. Also good.

Moreover, it is preferable that the said polishing liquid applied to a grinding | polishing process (especially final grinding | polishing process (after-mentioned 2nd grinding | polishing process)) adjusts, for example to the acidic region. For example, sulfuric acid is added to the polishing liquid to adjust the pH to a range of 2 to 4. The reason why the polishing liquid adjusted to the acidic region is preferably used is from the viewpoint of productivity and cleanliness.
Further, it is more preferable to apply the cleaning treatment of the present invention to the cleaning treatment performed after the polishing step of polishing the main surface of the glass substrate using a polishing liquid adjusted to an alkaline region containing colloidal silica abrasive grains. . When polishing on a glass substrate with acidity, some elements escape from the surface of the glass substrate due to the leaching action of the acid, so local unevenness is likely to occur in the etching action when performing alkaline cleaning thereafter. The roughness of the glass substrate surface after cleaning becomes large. Such a phenomenon is relatively difficult to occur when polishing is performed under conditions adjusted to be alkaline. Accordingly, when the glass substrate is cleaned using a strongly alkaline cleaning solution after the polishing step, polishing under alkaline conditions is preferable because the surface roughness can be made relatively lower than that during acidic polishing. From the viewpoint of reducing the difference from the pH of the cleaning liquid, the pH of the polishing liquid when polishing under alkaline conditions is preferably 10 or more, and more preferably 11 or more. Moreover, it is preferable to set it as 13 or less from a viewpoint of ease of handling.

As the abrasive grains such as colloidal silica contained in the polishing liquid, those having an average particle diameter of about 10 to 100 nm are preferably used from the viewpoint of polishing efficiency. In particular, in the present invention, the abrasive grains contained in the polishing liquid used in the final polishing step (second polishing step, which will be described later) have an average particle size of 10 from the viewpoint of further reducing the surface roughness. It is preferable to use a material having a thickness of about 40 nm, particularly a fine material having a size of about 10-20 nm. However, the finer the abrasive grain, the harder it is to remove once adsorbed to the glass substrate. When the cleaning treatment of the present invention is applied after polishing of ultrafine colloidal silica abrasive grains having an average particle diameter of 20 nm or less, the abrasive grains are cleaned and removed while maintaining a very low surface roughness. It is effective because it can be cleaned.

In the present invention, the average particle size is a point where the cumulative curve is 50% when the cumulative curve is obtained with the total volume of the powder population in the particle size distribution measured by the light scattering method as 100%. (Hereinafter referred to as “cumulative average particle diameter (50% diameter)”). In the present invention, the cumulative average particle diameter (50% diameter) is specifically a value obtained by measurement using a particle diameter / particle size distribution measuring apparatus.

Moreover, the colloidal silica abrasive grain produced | generated by hydrolyzing an organosilicon compound can be used for the colloidal silica abrasive grain used for this invention. Although such abrasive grains do not easily aggregate with each other, they easily adhere firmly to the glass substrate surface after the polishing step, and it is effective to apply the cleaning treatment according to the present invention.

In the present invention, the polishing method in the polishing step is not particularly limited. For example, the polishing pad and the glass substrate are brought into contact with the glass substrate and the polishing pad while supplying the polishing liquid containing the abrasive grains. The surface of the glass substrate may be polished in a mirror shape by relatively moving.
For example, FIG. 3 is a longitudinal sectional view showing a schematic configuration of a planetary gear type double-side polishing apparatus that can be used in a glass substrate polishing process. The double-side polishing apparatus shown in FIG. 3 meshes with the sun gear 2, the internal gear 3 arranged concentrically on the outer side, the sun gear 2 and the internal gear 3, and the sun gear 2 and the internal gear 3. An upper surface plate 5 and a lower surface plate 6 on which a carrier 4 that revolves and rotates according to rotation, and a polishing pad 7 that can hold the workpiece 1 held by the carrier 4 are attached, and an upper surface plate A polishing liquid supply unit (not shown) for supplying a polishing liquid is provided between 5 and the lower surface plate 6.

By such a double-side polishing apparatus, during polishing, the workpiece 1 held by the carrier 4, that is, the glass substrate is sandwiched between the upper surface plate 5 and the lower surface plate 6, and the upper and

lower surface plates

5, 6 are polished. While supplying the polishing liquid between the pad 7 and the workpiece 1, the carrier 4 revolves and rotates according to the rotation of the sun gear 2 and the internal gear 3, and the upper and lower surfaces of the workpiece 1 are moved. Polished.

Particularly, the polishing pad for finishing polishing is preferably a polishing pad (suede pad) of a soft polisher. The polishing pad preferably has an Asker C hardness of 60 to 80. The contact surface of the polishing pad with the glass substrate is preferably made of a foamed resin with an open foam pore, particularly foamed polyurethane. When polishing is performed in this manner, the surface of the glass substrate can be polished into a smooth mirror surface.

In one embodiment of the present invention, for example, in a cleaning process for cleaning a glass substrate with a cleaning liquid containing a cleaning agent, which is performed after the polishing process of the main surface of the glass substrate, the cleaning process has an etching property with respect to the glass substrate. It is characterized by including a treatment of bringing a glass substrate into contact with a cleaning liquid containing a specific alkaline agent, specifically, at least one of guanidine and imidazole.

As a result of searching for a method for suppressing an increase in the surface roughness of the substrate while maintaining the detergency due to the alkali cleaning, the present inventors have specifically increased the roughness by using a specific alkaline agent, that is, guanidine. I found out that it could be suppressed.
Although the above guanidine has a high alkalinity (for example, equivalent to KOH) and has a large effect of removing foreign substances due to the etching action on glass, there is little increase in the roughness of the substrate surface after cleaning. Therefore, by cleaning the glass substrate with a cleaning solution containing guanidine as an alkaline cleaner, low roughness (high smoothness) in the glass substrate after cleaning can be realized, and good cleanability can be obtained, and high cleanliness can be obtained. Can be achieved.

The content of guanidine in the cleaning liquid is not particularly limited, but is preferably in the range of 0.005 mol / liter to 1 mol / liter, for example. When the content of guanidine is less than 0.005 mol / liter, the etching rate is lowered, so that it takes time to obtain the foreign matter removing effect by the etching action on the glass, and the productivity may be deteriorated. On the other hand, if the content of guanidine is more than 1 mol / liter, sufficient alkali cleaning action can be obtained, but the etching rate by alkali increases, so when the glass composition contains sodium or potassium, the elution amount thereof is In some cases, it becomes necessary to frequently adjust sodium ions and potassium ions in the cleaning liquid. In addition, there may be variations in the inner and outer diameters of the substrate that require very strict management, resulting in deviation from a predetermined range. Moreover, since alkalinity becomes too strong, handling is also required.
In the case where the cleaning liquid is used in a circulating manner and Na ions or K ions in the cleaning liquid increase due to elution from the glass substrate, it is effective to add a chelating agent or the like that captures alkali metal ions.

In addition, as a result of searching for a method for suppressing the increase in the surface roughness of the substrate while maintaining the detergency by alkali cleaning, the present inventors can suppress the increase in roughness specifically by using imidazole. I found it.
The imidazole also has high alkalinity (e.g., equivalent to KOH), and has a small increase in the roughness of the substrate surface after cleaning, despite the large effect of removing foreign matter due to the etching action on glass. Therefore, by washing the glass substrate with a cleaning solution containing imidazole as an alkali cleaning agent, low roughness (high smoothness) in the glass substrate after washing can be realized, and good cleanability can be obtained and high cleanliness can be obtained. Can be achieved.

The content of imidazole in the cleaning liquid is not particularly limited, but is preferably in the range of 0.005 mol / liter to 1 mol / liter, for example. When the content of imidazole is less than 0.005 mol / liter, the etching rate becomes low, so that it takes time to obtain the foreign matter removing effect by the etching action on the glass, and the productivity is deteriorated. On the other hand, if the content of imidazole is more than 1 mol / liter, sufficient alkali cleaning action can be obtained, but the etching rate for glass becomes too fast, and there is a possibility that the increase in the roughness of the substrate surface after cleaning becomes large. .

The above organic alkali agents such as guanidine and imidazole are highly soluble in water, exhibit strong alkalinity when dissolved in water, and have a large foreign matter removing effect due to the etching action on glass, but the surface of the surface by etching is high. Roughness can be suppressed. Although this mechanism is not necessarily clear, it is considered as follows.
That is, in the case of potassium ions or sodium ions, bonding to OH groups on the glass substrate surface (external silanol groups or internal silanol groups generated by hydrolyzing siloxane bonds (O—Si—O bonds)) causes etching of the bonded portions. In order to selectively increase the rate, it is thought that the etching rate unevenness occurs on the glass substrate surface, leading to an increase in roughness. However, in the case of the above organic alkaline agent, etching is performed even when combined with OH groups on the glass surface. No rate increase is expected. Moreover, it is thought that there exists an effect which suppresses later combining Na ion and K ion because said organic alkaline agent has couple | bonded with OH group previously. Thereby, it is possible to suppress an increase in the roughness of the substrate surface after cleaning by performing the cleaning process while suppressing the contents of sodium ions and potassium ions contained in the cleaning liquid. Therefore, ultra-low roughness (high smoothness) in the glass substrate after cleaning can be realized, good cleaning properties can be obtained, and high cleanliness can be achieved.

In the present invention, the above guanidine is more effective than the above imidazole. This is presumed to be because the above-mentioned effects are large because the above-mentioned guanidine is more basic.
In the present invention, the guanidine and the imidazole may be used in combination.

Conventionally, it has been generally recognized that the increase in roughness of the glass substrate surface after alkali cleaning depends only on the alkalinity of the alkali agent, and that the increase in roughness increases with strong alkali. Found that the amount of increase in roughness has a great influence not only by the alkalinity of the alkali agent used for washing, but also by the type of cation paired with OH ions.

For example, when a strong alkali such as KOH or NaOH is used as the alkali agent, the effect of removing foreign matter by a good etching action can be obtained, but the roughness of the glass substrate surface after cleaning is greatly increased. According to the study by the present inventors, it has been found that in this case, not only the alkalinity of these alkali agents but also the presence of cations such as K ions and Na ions are involved in increasing the roughness of the substrate.

Therefore, the present inventors have found that it is preferable to perform the cleaning treatment while suppressing the total amount of Na ions and K ions in the alkaline cleaning liquid to less than 200 ppm. Thereby, the etching action by OH ions of the alkaline agent contained in the cleaning liquid is obtained, and on the other hand, by suppressing the abundance of Na ions and K ions in the cleaning liquid, the synergistic action of the alkali metal ions and OH ions. An increase in the roughness of the substrate can be suppressed. In particular, it is preferable to perform the cleaning treatment while suppressing the total amount of Na ions and K ions in the alkaline cleaning liquid to 100 ppm or less, more preferably 10 ppm or less, and even more preferably 1 ppm or less.
To control or control the content of sodium ions and potassium ions in the cleaning solution, measure the content of these ions in the cleaning solution by sampling the cleaning solution at the start of cleaning or at a predetermined timing during cleaning. However, when it can exceed the predetermined value, it can be adjusted by reducing the content of these ions by means such as addition of a chelating agent or the like for trapping the ions, dilution with water, or replacement of the washing solution. Further, when Na or K is contained in the glass substrate, the relationship between the cleaning time and the number of batches (the number of cleaning processes) and the concentration of Na ions and K ions in the cleaning liquid is previously grasped, and based on the grasped relationship. You may perform the process which adjusts content of Na ion and K ion.

In addition, when the above guanidine or imidazole is used, the effect of the presence of Na ions and K ions in the cleaning liquid is reduced due to the action of guanidine or imidazole binding to the OH group on the glass surface, as described above. It is considered that a foreign matter removing effect by the etching action can be obtained, and an increase in the roughness of the substrate surface after cleaning can be suppressed.

Further, when a glass substrate containing an alkali metal component such as sodium or potassium in the glass component is cleaned, the cleaning step is performed while suppressing the total amount of Na ions and K ions in the alkali cleaning solution by elution of the glass component to less than 200 ppm. Is preferred.
In addition, the content of Na ions and K ions in the cleaning liquid can be examined by, for example, an ion chromatography method or an ICP method using the cleaning liquid sampled from the cleaning tank.
Moreover, ppm means mass ppm (mass ratio expressed in parts per million).

Further, in order to prevent foreign matters removed from the substrate surface by the alkali cleaning agent from re-adhering to the substrate surface and improve the cleaning effect, the cleaning liquid contains an interface in addition to the guanidine or the imidazole. You may make it contain cleaning agents, such as an activator, a chelating agent, and a dispersing agent suitably.
Examples of the surfactant that can be preferably used in the present invention include anionic surfactants such as sodium alkyl sulfate ester, fatty acid sodium, and alkylaryl sulfonate, and nonionic surfactants such as polyoxyethylene alkyl ether and polyoxyethylene derivatives. Can be mentioned. Examples of the chelating agent include aminocarboxylic acids such as EDTA, organic acids such as citric acid, and salts thereof. Furthermore, examples of the dispersant include phosphates, sulfates, and polymer dispersants.

However, since these detergents such as surfactants, chelating agents, and dispersants are usually formulated with alkali salts (potassium salts, sodium salts, etc.), even when these detergents are included in the cleaning liquid, It is preferable to perform the washing treatment while keeping the total amount of sodium ions and potassium ions below 200 ppm. More preferably, the washing treatment is performed while the amount is suppressed to 100 ppm or less, and more preferably 10 ppm or less. In such a case, it is preferable to use a quaternary ammonium cation such as tetramethylammonium ion to form a quaternary ammonium salt. By using a quaternary ammonium salt, the amount added can be increased without increasing the amount of sodium ions or potassium ions. In addition, in the synthesis of the additive, when sodium or potassium is inevitably mixed as an impurity, it is preferable to use one that has been purified with an ion exchange resin or the like so that the amount of the ions is reduced. The same applies to magnesium ions and calcium ions.

The cleaning treatment is usually performed by, for example, contacting (for example, dipping) the glass substrate after the polishing step into a cleaning tank containing a cleaning liquid containing at least one of the guanidine and the imidazole and a necessary additive. . At this time, it is also preferable to apply ultrasonic waves in order to increase the cleaning effect. The liquid temperature of the cleaning liquid, the cleaning time, and the like can be set as appropriate.

In the present invention, the difference between the surface roughness (Ra) of the glass substrate main surface after the cleaning treatment and the surface roughness (Ra) of the glass substrate main surface immediately before the cleaning treatment may be within 0.06 nm. More preferably, it is 0.05 nm or less, more preferably 0.03 nm or less, and still more preferably 0.01 nm or less.
That is, according to the present invention, it is possible to suppress an increase in roughness of the substrate surface due to alkali cleaning.

Moreover, it is preferable that the surface roughness (Ra) of the glass substrate main surface immediately before the cleaning treatment is an ultra-smooth surface of 0.10 nm or less. According to the present invention, an increase in the surface roughness of the substrate due to alkali cleaning can be suppressed, so that the ultra-smooth substrate surface roughness obtained by the polishing process can be prevented from being deteriorated as much as possible.

In the present invention, it is preferable that the pH of the cleaning liquid is 10 or more. According to the present invention, even if the cleaning liquid has a high pH (strong alkali), since the increase in the roughness of the substrate surface is small, as a result, it is possible to perform highly clean cleaning while suppressing the increase in roughness. is there. More preferably, it is 11 or more. When the pH is less than 10, the etching rate becomes low, and thus it takes time to obtain the effect of removing foreign matter by the etching action on the glass, and the productivity may be deteriorated. On the other hand, if the pH is higher than 13, sufficient alkali cleaning action is obtained, but the etching rate by alkali increases, so when sodium or potassium is contained in the glass composition, the amount of elution increases and the amount in the cleaning liquid is increased. It may be necessary to frequently adjust sodium ions and potassium ions. In addition, there may be variations in the inner and outer diameters of the substrate that require very strict management, resulting in deviation from a predetermined range. Moreover, since alkalinity becomes too strong, handling is also required.

A preferred embodiment of the present invention is a method for manufacturing a glass substrate for a magnetic disk including a glass substrate cleaning process, wherein the cleaning process contacts the glass substrate with a cleaning liquid containing at least one of guanidine and imidazole. The amount of increase in surface roughness (Ra) of the main surface of the glass substrate after the cleaning process before the cleaning process and the total concentration of sodium ions and potassium ions in the cleaning liquid used for the cleaning process A relationship is obtained in advance, and based on the obtained relationship, a total concentration of sodium ions and potassium ions in the cleaning solution at which the increase amount of the surface roughness (Ra) is 0.06 nm or less is determined, and the cleaning solution The main surface is mirrored while maintaining the condition that the total concentration of sodium ions and potassium ions is not more than the determined concentration. A process for producing a glass substrate for a magnetic disk, which comprises carrying out the cleaning process of the polished the glass substrate.
According to such an embodiment, the cleaning process can be performed so that the amount of increase in the roughness of the glass substrate surface due to the cleaning becomes a predetermined value or less.

Another preferred embodiment of the present invention is a method for manufacturing a glass substrate for a magnetic disk including a glass substrate cleaning process, wherein the glass substrate contains at least one component of sodium and potassium in the glass component. And cleaning the glass substrate whose main surface is mirror-polished while using a cleaning solution containing at least one of guanidine and imidazole and changing the solution when the total amount of sodium ions and potassium ions in the cleaning solution exceeds 200 ppm. Is a method for manufacturing a glass substrate for a magnetic disk.

According to such an embodiment, even when, for example, a large amount of glass substrate is continuously washed and consequently washed in the same washing tank for a long time, the total amount of sodium ions and potassium ions in the washing solution is 200 ppm. If the amount exceeds the value, the total amount of sodium ions and potassium ions in the cleaning liquid can be suppressed to less than 200 ppm by exchanging the liquid with a new cleaning liquid, so that an increase in the roughness of the glass substrate surface can be suppressed.

Further, as another preferred embodiment of the present invention, there is provided a method for producing a glass substrate for a magnetic disk including a glass substrate cleaning process, wherein the cleaning process is performed on a cleaning liquid containing at least one of guanidine and imidazole. A method for producing a glass substrate for a magnetic disk, comprising the step of bringing a glass substrate into contact, wherein the cleaning treatment is performed while the total amount of sodium ions and potassium ions in the cleaning liquid is suppressed to less than 200 ppm.
According to such an embodiment, since the total amount of sodium ions and potassium ions in the cleaning liquid can be suppressed to less than 200 ppm, an increase in the roughness of the glass substrate surface can be suppressed.

Normally, the polishing process includes a first polishing process for removing scratches and distortions remaining in the lapping process as described above, and a glass substrate while maintaining a flat surface obtained in the first polishing process. Generally, it is performed through two stages of the second polishing step that finishes the surface roughness of the main surface into a smooth mirror surface (however, multistage polishing of three or more stages may be performed). It is preferable to apply the cleaning treatment of the present invention to at least the second polishing step in the subsequent stage, that is, the cleaning step performed after the final polishing step in the polishing step. In particular, it is preferable to apply the cleaning process of the present invention to a cleaning process performed after a polishing process for polishing a main surface of a glass substrate using a polishing liquid adjusted to an alkaline region containing abrasive grains of colloidal silica. is there. When polishing the glass substrate with acid, some elements are removed from the glass substrate surface by the leaching action with the acid, and then the etching action becomes uneven when the washing is performed with the alkali. The glass substrate surface is greatly roughened. Such a phenomenon is not observed when polishing is performed under conditions adjusted to be alkaline, and the glass substrate surface roughness can be relatively lowered.

In the present invention, the glass (the glass type) constituting the glass substrate is preferably an aluminosilicate glass. Amorphous aluminosilicate glass is more preferable. Such a glass substrate can be finished to a smooth mirror surface by mirror polishing the surface, and the strength after processing is good. As such an aluminosilicate glass, SiO ₂ is 58 wt% to 75 wt%, Al ₂ O ₃ is 5 wt% to 23 wt%, Li ₂ O is 3 wt% to 10 wt%, Na ₂ An aluminosilicate glass containing O as a main component in an amount of 4 wt% or more and 13 wt% or less (however, an aluminosilicate glass containing no phosphorus oxide) can be used. Further, for example, SiO ₂ is 62 wt% to 75 wt%, Al ₂ O ₃ is 5 wt% to 15 wt%, Li ₂ O is 4 wt% to 10 wt%, and Na ₂ O is 4 wt%. above 12 wt% or less, the ZrO ₂ 5.5 wt% to 15 wt% or less, while containing as the main component, the weight ratio of Na _₂ O / ZrO ₂ is 0.5 to 2.0, Al ₂ O ₃ An amorphous aluminosilicate glass containing no phosphorus oxide having a weight ratio of / ZrO ₂ of 0.4 or more and 2.5 or less can be obtained.

In addition, heat resistance may be required as a characteristic of next-generation substrates. Examples of the heat-resistant glass in this case are 50 to 75% SiO ₂ , 0 to 6% Al ₂ O ₃ , 0 to 2% BaO, and 0 to 3% Li ₂ O in terms of mol%. ZnO 0 to 5%, Na ₂ O and K ₂ O 3 to 15% in total, MgO, CaO, SrO and BaO 14 to 35% in total, ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂ in total 2 to 9%, molar ratio [(MgO + CaO) / (MgO + CaO + SrO + BaO)] in the range of 0.85 to 1 Further, a glass having a molar ratio [Al ₂ O ₃ / (MgO + CaO)] in the range of 0 to 0.30 can be preferably used.

In the present invention, the surface of the glass substrate after the polishing process has an arithmetic average surface roughness Ra of 0.20 nm or less, particularly 0.15 nm or less, more preferably 0.10 nm or less. Further, the maximum roughness Rmax is 2.0 nm or less, particularly 1.5 nm or less, more preferably 1.0 nm or less. In the present invention, Ra and Rmax are roughnesses calculated in accordance with Japanese Industrial Standard (JIS) B0601: 1982. These surfaces are preferably mirror surfaces.
Further, in the present invention, the surface roughness (for example, the maximum roughness Rmax, the arithmetic average roughness Ra) is measured by measuring the range of 1 μm × 1 μm with a resolution of 512 × 512 pixels using an atomic force microscope (AFM). It is practically preferable to obtain the surface roughness of the obtained surface shape.

In the present invention, it is preferable to perform chemical strengthening treatment before or after the polishing process. As a method of chemical strengthening treatment, for example, a low-temperature ion exchange method in which ion exchange is performed in a temperature range that does not exceed the temperature of the glass transition point, for example, a temperature of 300 degrees Celsius or more and 400 degrees Celsius or less is preferable. The chemical strengthening treatment is a process in which a molten chemical strengthening salt is brought into contact with a glass substrate, whereby an alkali metal element having a relatively large atomic radius in the chemical strengthening salt and a relatively small atomic radius in the glass substrate. This is a treatment in which an alkali metal element is ion-exchanged, an alkali metal element having a large ion radius is permeated into the surface layer of the glass substrate, and compressive stress is generated on the surface of the glass substrate. Since the chemically strengthened glass substrate is excellent in impact resistance, it is particularly preferable for mounting on a HDD for mobile use, for example. As the chemical strengthening salt, alkali metal nitric acid such as potassium nitrate or sodium nitrate can be preferably used.

As shown in FIGS. 1 and 2, the disk-shaped glass substrate having both

main surfaces

11, 11 and an outer peripheral side end surface 12 and an inner peripheral side end surface 13 therebetween as shown in FIG. 1 and FIG. 1 is obtained. The outer peripheral side end surface 12 includes chamfered

surfaces

12b and 12b between the side wall surface 12a and the main surfaces on both sides thereof. The inner peripheral side end face 13 has the same shape.

The present invention also provides a method for producing a magnetic disk using the above glass substrate for a magnetic disk. In the present invention, the magnetic disk is manufactured by forming at least a magnetic layer on the magnetic disk glass substrate according to the present invention. As a material for the magnetic layer, a hexagonal CoCrPt-based or CoPt-based ferromagnetic alloy having a large anisotropic magnetic field can be used. As a method of forming the magnetic layer, it is preferable to use a method of forming a magnetic layer on a glass substrate by a sputtering method, for example, a DC magnetron sputtering method. Further, by interposing an underlayer between the glass substrate and the magnetic layer, the orientation direction of the magnetic grains of the magnetic layer and the size of the magnetic grains can be controlled. For example, by using a hexagonal underlayer containing Ru or Ti, the easy magnetization direction of the magnetic layer can be oriented along the normal line of the magnetic disk surface. In this case, a perpendicular magnetic recording type magnetic disk is manufactured. The underlayer can be formed by sputtering as with the magnetic layer.

In addition, a protective layer and a lubricating layer may be formed in this order on the magnetic layer. As the protective layer, an amorphous hydrogenated carbon-based protective layer is suitable. For example, the protective layer can be formed by a plasma CVD method. Further, as the lubricating layer, a lubricant having a functional group at the end of the main chain of the perfluoropolyether compound can be used. In particular, it is preferable that the main component is a perfluoropolyether compound having a terminal hydroxyl group as a polar functional group. The lubricating layer can be applied and formed by a dip method.
By using the magnetic disk glass substrate obtained by the present invention, a highly reliable magnetic disk can be obtained.

Hereinafter, embodiments of the present invention will be specifically described with reference to examples. In addition, this invention is not limited to a following example. Further, a comparative example (reference example) for the embodiment of the present invention will be described together.
The following (1) rough lapping step (rough grinding step), (2) shape processing step, (3) fine lapping step (fine grinding step), (4) end surface polishing step, (5) main surface first polishing step, A glass substrate for magnetic disk was manufactured through (6) chemical strengthening step, (7) main surface second polishing step, and (8) cleaning treatment.

(1) Coarse lapping step First, a glass substrate made of a disc-shaped amorphous aluminosilicate glass having a diameter of 66 mmφ and a thickness of 1.0 mm was obtained from molten glass by direct pressing using an upper die, a lower die, and a barrel die. . In addition to such a direct press, a glass substrate may be obtained by cutting into a predetermined size from a plate glass manufactured by a downdraw method or a float method. As the aluminosilicate glass, glass containing SiO ₂ : 58 to 75% by weight, Al ₂ O ₃ : 5 to 23% by weight, Li ₂ O: 3 to 10% by weight, Na ₂ O: 4 to 13% by weight It was used.

Next, a lapping process was performed on the glass substrate in order to improve dimensional accuracy and shape accuracy. This lapping process was performed using a double-sided lapping apparatus. Specifically, a glass substrate held by a carrier was brought into close contact between the upper and lower surface plates, and the carrier was lapped by rotating the sun gear and the internal gear of the wrapping device to move the planetary gear.

(2) Shape processing step Next, after making a hole in the central portion of the glass substrate using a cylindrical grindstone, a predetermined chamfering process was performed on the outer peripheral end surface and the inner peripheral end surface. In general, a 2.5-inch HDD (hard disk drive) uses a magnetic disk having an outer diameter of 65 mm.

(3) Fine wrapping step This fine wrapping step was performed using a double-sided wrapping apparatus as described above. Specifically, a glass substrate held by a carrier was brought into close contact between upper and lower surface plates to which pellets in which diamond abrasive grains were fixed with a resin were attached.

(4) End face polishing process Next, the surface of the end face (inner periphery, outer periphery) of the glass substrate was polished by brush polishing while rotating the glass substrate.

(5) Main Surface First Polishing Step Next, the first polishing step was performed using the double-side polishing apparatus shown in FIG. In the double-side polishing apparatus, the glass substrate held by the carrier 4 is closely attached between the upper and lower

polishing surface plates

5 and 6 to which the polishing pad 7 is attached, and the carrier 4 is engaged with the sun gear 2 and the internal gear 3. The glass substrate is sandwiched between upper and

lower surface plates

5 and 6. Thereafter, the polishing liquid is supplied and rotated between the polishing pad and the polishing surface of the glass substrate, so that the glass substrate revolves while rotating on the

surface plates

5 and 6, and both surfaces are polished simultaneously. . Specifically, a hard polisher (hard foamed urethane) was used as the polisher, and the first polishing step was performed. As the polishing liquid, a polishing liquid in which 10% by weight of cerium oxide (average particle diameter (50% diameter) 1 μm) was dispersed in water as an abrasive was used. The load applied to the glass substrate surface was 100 g / cm ² and the polishing time was 15 minutes.
The glass substrate after the first polishing step was washed and dried.

(6) Chemical strengthening process Next, the glass substrate which finished the said washing | cleaning was chemically strengthened. For chemical strengthening, a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed was prepared, the chemical strengthening solution was heated and melted, and the cleaned and dried glass substrate was immersed to perform chemical strengthening treatment. The glass substrate after chemical strengthening was washed and dried.

(7) Main surface second polishing step Next, using the same double-side polishing apparatus as used in the first polishing step, the polisher is replaced with a soft polisher (suede) polishing pad (72 foam polyurethane with Asker C hardness). Then, the second polishing step was performed. This second polishing step is, for example, mirror polishing for finishing the surface roughness of the glass substrate main surface to a smooth mirror surface with an Rmax of about 2 nm or less while maintaining the flat surface obtained in the first polishing step. It is processing. The polishing liquid used was adjusted to acidity (pH = 2) by adding sulfuric acid to water in which 10% by weight of colloidal silica (average particle diameter (50% diameter) 15 nm) was dispersed as an abrasive. The load was 100 g / cm ² and the polishing time was 10 minutes.
Here, in order to investigate the surface roughness Ra after polishing, one substrate was extracted from the same lot, washed with water only for 1200 seconds, dried, and measured under the above conditions by AFM. .15 nm. However, a large amount of colloidal silica particles adhered to the surface of the substrate, which was a rejected product level.

(8) Cleaning process Next, the glass substrate which finished the said 2nd grinding | polishing process was implemented. Specifically, it is immersed for 600 seconds in a cleaning tank (liquid temperature: normal temperature) containing a cleaning liquid (pH 12.6) in which guanidine is added to pure water so as to have a concentration of 0.3 mol / liter as an alkaline cleaning agent. And washing with ultrasonic waves of 80 kHz. The cleaning liquid was used in a circulating manner.
At this time, the guanidine used did not contain Na ions or K ions (below the detection limit). In addition, when this washing | cleaning liquid was sampled and the density | concentration of Na ion and K ion was investigated using the ion chromatography method, neither was detected.
Thereafter, the glass substrate was immersed in another cleaning tank (pure water, room temperature), and ultrasonic cleaning was performed at 80 kHz for 300 seconds, followed by drying.

About 100 glass substrates (referred to as sample 1) obtained through each of the above steps, the surface roughness (Ra) of the main surface of the glass substrate after the cleaning process and immediately before the cleaning process (that is, the second polishing process). After completion, the surface roughness (Ra) of the main surface of the glass substrate was measured with an atomic force microscope (AFM), and the difference (ΔRa: value obtained by subtracting Ra before cleaning from Ra after cleaning) Are shown in Table 1. The value of the surface roughness is an average value of 100 manufactured glass substrates.
Moreover, the foreign material defect was evaluated with respect to another 100 glass substrate obtained on the same conditions. The main surface of the obtained glass substrate was observed with a laser type surface inspection apparatus, and the detected surface defects were analyzed with an SEM and an atomic force microscope (AFM). Table 2 shows the number of foreign matter defects (convex defects due to foreign matter adhesion). The count number is an average value of 100 manufactured glass substrates. In addition, as a measurement condition of the surface inspection device, by irradiating the main surface with a laser beam having a wavelength of 405 nm, a power of 80 mW, and a spot diameter of 6 μm, it is possible to observe a very small defect whose length in the main surface direction is about 10 to 40 nm. It is.
In Sample 1, a glass substrate for a magnetic disk having a substrate surface in which the increase in substrate surface roughness due to alkali cleaning was suppressed to 0.06 nm or less was obtained.

In addition, samples 2 to 6 were prepared in the same manner as sample 1 except that the addition amounts of KOH and guanidine in the cleaning solution were variously changed, and the cleaning solution having the alkali metal ion concentration in the cleaning solution shown in Table 1 was used. A glass substrate was produced. When the pH deviated from 12.6, the amount of guanidine added was finely adjusted so that the pH became 12.6.
Further, tetramethylammonium hydroxide (hereinafter abbreviated as “TMAH”) is added to the cleaning liquid as an alkali agent, and the amount of the addition is changed variously, and the cleaning liquid having the alkali metal ion concentration in the cleaning liquid shown in Table 1 Glass substrates of Samples 7 to 10 were produced in the same manner as Sample 1 except that it was used.
Further, glass substrates of

Samples

11 and 12 were produced in the same manner as Sample 1 except that a cleaning liquid obtained by adding KOH or NAOH, which is a conventional inorganic alkaline agent, to the cleaning liquid was used.

Furthermore, in addition to guanidine, the anionic surfactant (tetramethylammonium dodecylbenzenesulfonate (quaternary ammonium cation salt), hereinafter abbreviated as DBS) is added as a cleaning agent in addition to guanidine, and the addition amount is variously changed. Glass substrates of Samples 13 to 17 were prepared in the same manner as Sample 1 except that the cleaning solution having an alkali metal ion concentration in the cleaning solution shown in Table 1 was used. In addition to guanidine in the cleaning solution, poly (oxyethylene) nonylphenyl ether as a non-ionic surfactant as a cleaning agent, molecular weight 660.87 (10EO) (10EO indicates that the number of added moles of ethylene oxide is 10) Then, a glass substrate of Sample 18 was produced in the same manner as Sample 1 except that the cleaning solution having the alkali metal ion concentration in the cleaning solution shown in Table 1 was used.
In the above samples 1 to 18, the alkali metal ion concentration in the cleaning liquid was adjusted with Na ions or K ions. Even when the predetermined alkali metal ion concentration was adjusted by mixing Na ions and K ions, the results were almost the same as those shown in Tables 1 and 2 below, so it did not depend on the mixing ratio of Na ions and K ions. .

For the glass substrates of Samples 2 to 18 above, similarly to Sample 1, the surface roughness of the main surface was measured and foreign object defects were evaluated. The results are summarized in Tables 1 and 2 below.

From the results of Tables 1 and 2, the following can be understood.
1. According to the embodiment to which the cleaning liquid containing guanidine of the present invention is applied, an increase in the substrate surface roughness after the cleaning process can be suppressed. Further, addition of the above surfactant in addition to guanidine does not change the amount of increase in roughness after the cleaning treatment, but improves the cleaning properties.
2. On the other hand, when cleaning is performed using conventional KOH or NaOH, the substrate surface roughness after the cleaning process is greatly increased although good cleaning properties can be obtained. Further, when TMAH is added, not only the amount of increase in roughness is slightly larger than that of guanidine but also the number of foreign object defects is slightly increased.
The foreign matter count numbers in Sample 11 (KOH) and Sample 12 (NaOH) were 775 and 796, respectively. Although this result is equivalent to guanidine, since the increase in roughness after the cleaning treatment is large as described above, it is impossible to achieve both an increase in roughness due to cleaning and a cleaning property.
3. Further, it is preferable to use guanidine as the alkali agent rather than TMAH because the amount of increase in surface roughness can be reduced. Since guanidine is considered to have an effect of suppressing Na ions and K ions from approaching the silanol group by adsorbing to the silanol group on the glass substrate surface as described above, the effect of suppressing the increase in roughness than TMAH. Is considered high.
We further confirmed the advantages of guanidine. A continuous cleaning test for 20 batches was performed under the conditions of Sample 1 and Sample 7, and ΔRa was compared for the 20th batch of glass substrates. In both cases, ΔRa increased compared to the 1st batch, but in the 20th batch, ΔRa was smaller when guanidine was used. In the comparison in the results of the first batch (Table 1), both were almost equal, and it is considered that the increase in roughness was suppressed by the action of guanidine.
Further, in the second main surface polishing step, a glass substrate was prepared under the same conditions as Sample 1 except that the polishing liquid was made alkaline (pH = 12). ΔRa was 70% of Sample 1, Reduced. From this, it was confirmed that the liquid property of the polishing liquid used for the polishing treatment before the cleaning treatment of the present invention is preferably alkaline rather than acidic.

Further, the glass substrates of Samples 101 to 106 were the same as Sample 1 except that the amount of imidazole added in the cleaning solution was variously changed and the cleaning solution having the alkali metal ion concentration in the cleaning solution shown in Table 3 was used. Was made.
Further, tetramethylammonium hydroxide (hereinafter abbreviated as “TMAH”) was added as an alkaline agent to the cleaning liquid, and the amount of addition was changed variously to obtain an alkali metal ion concentration in the cleaning liquid shown in Table 3. Glass substrates of Samples 107 to 110 were produced in the same manner as Sample 101 except that it was used.
Further, glass substrates of Samples 111 and 112 were produced in the same manner as Sample 101, except that a cleaning liquid obtained by adding KOH or NAOH, which is a conventional inorganic alkaline agent, to the cleaning liquid was used.

Further, the sample 101 was used except that the DBS was added as a cleaning agent in addition to imidazole to the cleaning solution, and the addition amount was variously changed to use the cleaning solution having the alkali metal ion concentration in the cleaning solution shown in Table 3. In the same manner, glass substrates of Samples 113 to 117 were produced. Further, in addition to guanidine in the cleaning liquid, the nonionic surfactant was added as a cleaning agent, and the cleaning liquid having the alkali metal ion concentration in the cleaning liquid shown in Table 3 was used. A glass substrate of Sample 118 was produced.

For the glass substrates of the above samples 101 to 118, as in sample 1, the measurement of the surface roughness of the main surface and the evaluation of foreign matter defects were performed. The results are summarized in Tables 3 and 4 below.

The following can be seen from the results of Tables 3 and 4 above.
1. According to the embodiment to which the cleaning liquid containing imidazole of the present invention is applied, an increase in substrate surface roughness after the cleaning process can be suppressed. Further, addition of the above surfactant in addition to imidazole does not change the amount of roughness increase after the washing treatment, but the washing properties are improved.
2. On the other hand, when cleaning is performed using conventional KOH or NaOH, the substrate surface roughness after the cleaning process is greatly increased although good cleaning properties can be obtained. Further, when TMAH is added, not only the amount of increase in roughness is slightly larger than that of guanidine but also the number of foreign object defects is slightly increased.

(Manufacture of magnetic disk)
The following film formation steps were performed on the magnetic disk glass substrates obtained in Sample 1 and Sample 101 to obtain a magnetic disk for perpendicular magnetic recording.
That is, on the glass substrate, an adhesion layer made of a CrTi alloy thin film, a soft magnetic layer made of a CoTaZr alloy thin film, a seed layer made of NiW, an underlayer made of a Ru thin film, a perpendicular magnetic recording layer made of a CoCrPt alloy, carbon A protective layer and a lubricating layer were sequentially formed. The protective layer is for preventing the magnetic recording layer from deteriorating due to contact with the magnetic head, and is made of hydrogenated carbon, and provides wear resistance. The lubricating layer was formed by dipping a liquid lubricant of alcohol-modified perfluoropolyether.
The obtained magnetic disk was installed in an HDD equipped with a DFH head, and a load / unload durability test was conducted for one month while operating the DFH function in a high temperature and high humidity environment of 80 ° C. and 80% RH. There were no particular obstacles and good results were obtained.

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Sun gear 3 Internal gear 4 Carrier 5 Upper surface plate 6 Lower surface plate 7 Polishing pad 11

Main surface

12, 13 End surface of substrate

Claims

A method of manufacturing a glass substrate for a magnetic disk including a cleaning process for a glass substrate,
The cleaning treatment includes a treatment of bringing the glass substrate into contact with a cleaning solution containing at least one of guanidine and imidazole,
Obtaining in advance a relationship between the amount of increase in surface roughness (Ra) of the main surface of the glass substrate after the cleaning process before the cleaning process and the total concentration of sodium ions and potassium ions in the cleaning liquid used for the cleaning process Every
Based on the obtained relationship, determine the total concentration of sodium ions and potassium ions in the cleaning liquid in which the increase amount of the surface roughness (Ra) is 0.06 nm or less,
A glass substrate for a magnetic disk, wherein a cleaning process is performed on the glass substrate whose main surface is mirror-polished under a condition that the total concentration of sodium ions and potassium ions in the cleaning solution is equal to or less than the determined concentration. Production method.
A method of manufacturing a glass substrate for a magnetic disk including a cleaning process for a glass substrate,
The glass substrate contains at least one component of sodium and potassium in a glass component,
Using a cleaning solution containing at least one of guanidine and imidazole,
The magnetism is characterized in that the glass substrate whose main surface is mirror-polished is cleaned while replacing at least part of the cleaning solution so that the total amount of sodium ions and potassium ions in the cleaning solution does not exceed 200 ppm. A method for producing a glass substrate for a disk.
A method of manufacturing a glass substrate for a magnetic disk including a cleaning process for a glass substrate,
The cleaning treatment includes a treatment of bringing the glass substrate into contact with a cleaning solution containing at least one of guanidine and imidazole,
A method for producing a glass substrate for a magnetic disk, wherein the cleaning treatment is performed while the total amount of sodium ions and potassium ions in the cleaning liquid is suppressed to less than 200 ppm.
The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 3, wherein the glass substrate contains at least one of sodium and potassium in a glass component.
The cleaning liquid further contains at least one substance among a surfactant, a chelating agent, and a dispersing agent,
5. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the cleaning treatment is performed while a total amount of sodium ions and potassium ions in the cleaning liquid is suppressed to less than 200 ppm.
The difference between the surface roughness (Ra) of the glass substrate main surface after the cleaning treatment and the surface roughness (Ra) of the glass substrate main surface immediately before the cleaning treatment is within 0.06 nm. A method for producing a glass substrate for a magnetic disk according to claim 2.
7. The cleaning process according to claim 1, wherein the cleaning process is a cleaning process performed after a final polishing process in a polishing process in which a main surface of the glass substrate is polished using polishing abrasive grains. Manufacturing method of glass substrate for magnetic disk.
The method for producing a glass substrate for a magnetic disk according to claim 7, wherein the polishing liquid used for the final polishing is alkaline.
A method for producing a magnetic disk, comprising forming at least a magnetic recording layer on the glass substrate for a magnetic disk produced by the method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 8.