JP5371667B2 - Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a glass substrate for a magnetic disk using a polishing liquid, which reliably removes contamination adhered to the glass substrate in a polishing step even in a condition of using a comparatively dilute chemical solution in a cleaning step after the polishing step in order to improve surface roughness, and which suppresses an increase in pH due to repetition of the polishing steps even when pH of the polishing liquid is set in a weakly acidic region in order to achieve low roughness. <P>SOLUTION: In the method for manufacturing the glass substrate for the magnetic disk by polishing a main surface of the glass substrate, the polishing liquid to be used in the polishing step includes two or more components containing a substance exhibiting a chelating action to the contamination adhering to the glass substrate and a substance exhibiting a dispersing action thereto, and the substances are also included in a cleaning liquid used in a cleaning step achieved after the polishing step. The polishing liquid includes an acidic substance to adjust pH to a predetermined value, and a buffer component composed of an acidic weak acid and an alkaline weak acid salt, and is a buffer solution at the predetermined pH. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk used as a recording medium for a computer or the like, and a method for manufacturing a magnetic disk.

  In recent years, with the advancement of information technology, information recording technology, particularly magnetic recording technology, has made remarkable progress. An aluminum substrate has been widely used as a substrate for a magnetic recording medium such as an HDD (Hard Disk Drive) which is one of the magnetic recording media. However, with the miniaturization, thinning, and high recording density of magnetic disks, glass substrates that are superior in substrate surface flatness and substrate strength compared to aluminum substrates are gradually being replaced.

  In order to effectively use the main surface of the magnetic disk, an LUL (Load UnLoad) method has been used instead of the conventional CSS (Contact Start Stop) method. The CSS system is a system in which a magnetic head is brought into contact with a CSS zone provided on the main surface of the magnetic disk and retracted, and the LUL system is a system in which the magnetic head is retracted to a ramp (inclined portion) provided outside the magnetic disk. It is. The CSS zone cannot only be used as a recording area, but also has to have a certain surface roughness to prevent the magnetic head from being attracted. However, by adopting the LUL method, the entire surface of the magnetic disk can be used as a recording area, and it is not necessary to provide an uneven shape on the surface, and the surface of the magnetic disk can be extremely smoothed.

  Further, as the magnetic recording technology has been increased in density, the magnetic head has been changed from a thin film head to a magnetoresistive head (MR head) and a large magnetoresistive head (GMR head). However, the GMR head has high sensitivity and high recording density, and if the head and the substrate are separated from each other, information on adjacent recording bits is picked up. Therefore, it is necessary to keep the flying height of the magnetic head low. .

  Under these circumstances, the flying height of the magnetic head is required to be reduced, and the flying height of the magnetic head from the substrate is narrowed to about 8 nm.

  If the flying height of the magnetic head is reduced, a head crash failure or thermal asperity failure may occur. The head crash failure is a failure in which the magnetic head collides with the convex portion of the magnetic disk and is damaged. Thermal asperity failure means that the magnetoresistive element is heated by adiabatic compression or contact of air when the magnetic head passes over a minute convex or concave shape on the magnetic disk surface while flying. This is a failure that causes a read error. Therefore, for a magnetic head equipped with a magnetoresistive element, the magnetic disk surface is required to have extremely high smoothness and flatness, that is, low roughness.

  In particular, recently, as described in Patent Document 1, in order to further improve the recording density, the perpendicular magnetic recording method is becoming the main method. In the case of this perpendicular magnetic recording medium, since the recording density is higher than in the case of the in-plane magnetic recording method, the influence of the roughness of the glass substrate is more likely to appear. For this reason, the glass substrate is required to have even lower roughness.

  Further, in order to achieve lower roughness in the above situation, it is necessary to pay attention to the process of determining the surface roughness of the glass substrate, and it is necessary to appropriately adjust the pH of the polishing liquid (slurry). There is. That is, there is a correlation between the pH of the polishing liquid and the polishing rate. For example, in an aluminosilicate glass, the polishing rate basically tends to be higher on the acidic side. However, if the polishing process is repeated, there is a problem that the pH of the polishing liquid increases and the polishing rate decreases.

  Therefore, conventionally, in order to suppress an increase in pH of the polishing liquid, one kind of buffering material such as tartaric acid has been added to the polishing liquid.

  On the other hand, as a new phenomenon associated with a decrease in the surface roughness of the glass substrate, a problem of an increase in surface roughness that has occurred through an interface between polishing and cleaning, which has not been a problem in the past, has become apparent. In a glass substrate having a surface roughness (Ra) after polishing of 0.15 nm or less after polishing, a tendency to greatly increase the surface roughness is confirmed when combined with alkali immersion after acid immersion. The lower the pH of the acid, that is, the stronger the acidity, the greater the roughness increase due to subsequent alkali soaking.

  In addition, cleaning with an alkaline chemical solution is always performed for cleaning after polishing. That is, there is a problem that the lower the pH of the polishing liquid in the polishing process, the greater the increase in surface roughness due to subsequent cleaning. Therefore, in the case of a glass substrate having a low surface roughness, the pH of the polishing liquid is changed from a conventional pH of about 2 to a weakly acidic region of pH 3 to 4 or more in order to suppress an increase in surface roughness that occurs through an interface between polishing and cleaning. I had to set it.

JP 2005-44464 A

  By the way, immediately after completion of polishing in the final polishing step, when the contamination is firmly attached to the glass substrate, the contamination cannot be easily removed from the glass substrate even if chemical cleaning is performed thereafter. At present, the surface roughness of the glass substrate is about 0.1 nm Ra, but when the substrate is cleaned with a chemical such as a strong alkali or strong acid after the final polishing in which the roughness is built, the substrate roughness is reduced. There is a problem that it rises greatly.

  Further, even if the polishing liquid is set to a weakly acidic region having a pH of 3 to 4 or more, it is necessary to suppress an increase in the pH of the polishing liquid caused by repeated use of the polishing liquid. However, in the weakly acidic region at pH 3 and 4 or more, the pH of the polishing liquid is large due to the additive amount of the additive species, that is, the difference in additive concentration, due to the influence of the liquidity of the additive species. A problem that fluctuated was developed.

  In trend, the weakly acidic region where the acidity of the polishing liquid is weaker, the additive concentration must be reduced. However, when the added concentration is small, the buffering action is weakened.

  Therefore, in order to realize low roughness, the present invention can reliably remove the contaminants adhering to the glass substrate in the polishing step even in a relatively dilute chemical solution condition in the cleaning step after the polishing step. An object of the present invention is to provide a method for producing a glass substrate for a magnetic disk and a method for producing a magnetic disk using a polishing liquid that can suppress an increase in pH caused by repeated use of the polishing liquid even when the pH of the liquid is in a weakly acidic region. To do.

  In order to solve the above-described problems and achieve the above object, the present invention aims to reduce the total amount of contaminants adhering to the glass substrate, reducing the adhesion force of contaminants adhering to the glass substrate, and polishing process. In the cleaning step, at least one type of the same chemical solution is used, so that the contamination adhered in the polishing step can be easily removed in the cleaning step.

  First, regarding the reduction of the total amount of contamination and the reduction of adhesion force, it is necessary to stably disperse the contamination that is difficult to remove by cleaning in the polishing liquid. About this, it carries out by the combination of 2 or more components of the substance which shows a chelating action, and the substance which shows a dispersion | distribution action with respect to the target contamination.

  Next, in order to make it easier to remove the contaminants attached in the polishing process in the cleaning process, the same substance as that added to the cleaning process is added to the polishing liquid used in the polishing process.

  That is, an additive species that effectively acts on the contamination species adhering to the glass substrate can be added to the abrasive to suppress the adhesion amount and adhesion force of the contamination to the glass substrate. Thereafter, contamination that adheres to the glass substrate can be easily removed by performing chemical cleaning including the same substance as the abrasive additive species in the cleaning step.

  In the cleaning process, the alkali process, the acid process, and the alkali process are basically performed in three orders. In all three processes, the same additive species is added. , The ability to remove contamination can be increased.

  Further, in the present invention, in order to achieve the above object, a buffer composition is obtained by combining two arbitrary components that form a combination exhibiting a buffering action, and the target pH is obtained by changing the ratio of the two components added. Allows buffer composition. As a result, the amount of addition can be freely set without being restricted by the fact that the pH varies depending on the concentration of addition as in the case where there is only one buffer component.

  In particular, in the weak acid region where the pH of the polishing liquid is about 4, it was conventionally impossible to add a large amount of a buffer component, but a combination of the two components enabled a large amount of addition, and the pH stability of the polishing liquid increased. As a result, an increase in the pH of the polishing liquid caused by repeated use of the polishing liquid could be significantly suppressed.

  That is, the present invention has any one of the following configurations.

[Configuration 1]
A polishing pad is pressed against both main surfaces of a disk-shaped glass substrate, and the glass substrate and the polishing pad are relatively moved while supplying a polishing liquid containing an abrasive between the glass substrate and the polishing pad. In the manufacturing method of manufacturing the glass substrate for a magnetic disk by polishing the main surface of the glass substrate, the polishing liquid is made up of a substance that exhibits a chelating action and a substance that exhibits a dispersing action on contaminants attached to the glass substrate. It contains two or more components, and these substances are buffer components composed of two components, a weak acid showing acidity and a weak acid salt showing alkalinity, and are also included in a cleaning liquid in a cleaning process performed after the polishing process. To do.

[Configuration 2 ]
The polishing pad is pressed against both main surfaces of the disk-shaped glass substrate, and the glass substrate and the polishing pad are relatively moved while supplying a polishing liquid containing an abrasive between the glass substrate and the polishing pad. In the manufacturing method of manufacturing the glass substrate for magnetic disk by polishing the main surface of the glass substrate, the polishing liquid comprises an acidic substance for bringing the pH of the polishing liquid into a weakly acidic region , and a weak acid and an alkalinity indicating acidity. And a buffer solution consisting of two components of the weak acid salt shown, and is a buffer solution in a weakly acidic region , and the buffer component consisting of two components is also included in the cleaning solution in the cleaning step performed after the polishing step It is characterized by.

[Configuration 3 ]
In the method for producing a glass substrate for a magnetic disk having Configuration 1 or Configuration 2 , the buffer component is acetic acid, malic acid, malonic acid, succinic acid, citric acid, tartaric acid, phosphoric acid, phosphinic acid, phosphonic acid, pyrophosphoric acid , Tripolyphosphoric acid, hydroxyethanephosphonic acid (HEDP), aminotrimethylenephosphonic acid (NTMP), and any combination of these salts.

[Configuration 4 ]
At least a magnetic layer is formed on the surface of the glass substrate obtained by the method for producing a glass substrate for a magnetic disk having any one of Structures 1 to 3 .

[Configuration 5 ]
In the method of manufacturing a magnetic disk having Configuration 4 , the magnetic disk is a magnetic disk for perpendicular magnetic recording system, the magnetic layer is composed of a plurality of layers, and at least one layer is a soft magnetic layer. To do.

  In the present invention, the polishing liquid used in the polishing step contains two or more components of a substance exhibiting a chelating action and a substance exhibiting a dispersing action on contaminants attached to the glass substrate, and these substances are implemented after the polishing process. Since it is also included in the cleaning liquid in the cleaning process, the total amount of contamination adhering to the glass substrate is reduced and the adhesion of contamination adhering to the glass substrate is reduced, and contamination adhering in the polishing process is also cleaned. It can be easily removed in the process.

  That is, the present invention provides a magnetic disk glass that can reliably remove contaminants adhering to the glass substrate in the polishing process even under relatively dilute chemical conditions in the cleaning process after the polishing process in order to improve the surface roughness. A substrate manufacturing method and a magnetic disk manufacturing method can be provided.

  In the present invention, in the polishing step for polishing the main surface of the glass substrate, the polishing liquid is a buffer composed of two components: an acidic substance for obtaining a predetermined pH, a weak acid showing acidity, and a weak acid salt showing alkalinity. Since it is a buffer solution with a predetermined pH, it can be freely added without the restriction that the pH fluctuates depending on the concentration of addition as in the case of one buffer component. It became possible to set to.

  In particular, in the weak acid region where the pH of the polishing liquid is about 4, it was conventionally impossible to add a large amount of a buffer component. However, the combination of two components enabled the addition of a large amount, and the stability of the pH of the polishing liquid increased. As a result, it was possible to significantly suppress the increase in the pH of the polishing liquid that occurs with the repetition of the polishing process.

  That is, the present invention provides a magnetic disk glass using a polishing liquid that can suppress an increase in pH caused by repeated use of the polishing liquid even when the pH of the polishing liquid is in a weakly acidic region in order to realize low roughness. A substrate manufacturing method and a magnetic disk manufacturing method can be provided.

  Embodiments for carrying out the present invention will be described below.

  In the present invention, the polishing liquid used in the polishing process for polishing the main surface of the glass substrate for magnetic disks is one of a substance that exhibits a chelating action and a substance that exhibits a dispersing action against contaminants that adhere to the glass substrate in the polishing process. By containing more than the components, it is possible to stably disperse contaminants that are difficult to remove easily by washing in the polishing liquid, and to reduce the total amount of contaminants and adhesion.

  Contaminants that are difficult to remove by washing are metallic and organic foreign matters such as Fe. It is considered that at least the outermost layer of the metallic contamination such as Fe exists in a hydroxide state. When these metal hydroxides are brought into contact with glass, they are adsorbed on the substrate with a large surface area with respect to the particle diameter, so that removal by washing becomes difficult. Since these metal hydroxides have a particle size of 3 μm or less, they can be treated as colloids, and these hydroxides can be regarded as hydrophobic colloids. In order to stably disperse the hydrophobic colloid, a component forming a so-called “protective colloid” may be added.

  Moreover, in this invention, these components are also contained in the washing | cleaning liquid used in the washing | cleaning process implemented after a grinding | polishing process. That is, in the cleaning process, contamination that adheres to the glass substrate can be more easily removed by performing chemical cleaning including the same substance as the abrasive additive species.

  The cleaning process is basically performed in three steps: alkaline process, acid process, and alkaline process. In all three processes, the same additive species is added to remove contamination. The ability can be further enhanced.

Further, in the present invention, the polishing liquid used in the polishing step for polishing the main surface of the glass substrate for magnetic disk ensures the stability of the polishing rate. It is preferable that a buffer solution having a predetermined pH is included, including an acidic substance for adjusting the pH and a buffer component composed of two components of a weak acid exhibiting acidity and a weak acid salt exhibiting alkalinity.

  The buffer component is a buffer composition in which two arbitrary components are combined so as to exhibit a buffering action, and a buffer solution composition having a predetermined pH can be obtained by changing the composition ratio of the two components. Thus, the amount of addition can be freely set without being subjected to the restriction that the pH varies depending on the concentration of addition as in the case of one buffer component. In particular, in the weak acid region where the pH of the polishing liquid is about 4, conventionally, a large amount of addition was impossible, but by combining two components, a large amount of addition is possible, and the stability of the pH of the polishing liquid is increased. An increase in the pH of the polishing liquid caused by repeated use of the polishing liquid accompanying the repetition of the polishing process can be greatly suppressed.

  In addition, by setting the pH of the polishing liquid to a weak acid region of about 4, it is possible to suppress an increase in surface roughness even if cleaning with an alkaline chemical solution is performed in the cleaning step after polishing.

  The composition of the buffer solution is a combination that exhibits a buffering action that is established by a combination of any weak acid that exhibits acidity and any weak acid salt that exhibits alkalinity. Examples include acetic acid, malic acid, malonic acid, succinic acid, citric acid, tartaric acid, phosphoric acid, phosphinic acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid, hydroxyethanephosphonic acid (HEDP), aminotrimethylenephosphonic acid (NTMP) And a composition in which any one of these salts is arbitrarily combined.

  Furthermore, for the purpose of increasing the polishing rate in the weakly acidic region of pH 3 to 4, a component capable of shifting the ζ potential of the polishing liquid and the glass substrate to the isoelectric point side may be further added. This is presumably because the ζ potential of the glass substrate and the polishing liquid is shifted to the isoelectric point, resulting in an increase in the interaction between the two and an increase in the polishing rate. As a measure for increasing the polishing rate, an electrolyte of about 1 wt% is added so that the ζ potential of the polishing liquid is within 25 mV in absolute value. As a result, the addition of this electrolyte can confirm an increase in the abrasive particle diameter (D50 value).

  Embodiments of a magnetic disk glass substrate and a magnetic disk manufacturing method to which the present invention is applied will be described below. This glass substrate for magnetic disk and magnetic disk are 0.8 inch type disk (inner diameter 6 mm, outer diameter 21.6 mm, plate thickness 0.381 mm), 1.0 inch type disk (inner diameter 7 mm, outer diameter 27.4 mm, It is manufactured as a magnetic disk having a predetermined shape such as a plate thickness of 0.381 mm) and a 1.8 inch type magnetic disk (inner diameter of 12 mm, outer diameter of 48 mm, plate thickness of 0.508 mm). Further, it may be manufactured as a 2.5 inch type disc or a 3.5 inch type disc.

(1) Shape processing step and first lapping step First, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper die, a lower die, and a barrel die to obtain an amorphous plate glass. The aluminosilicate glass is a glass containing an alkali metal element having a network-like glass skeleton made of SiO and a structure containing aluminum as a modifying ion. In addition to direct pressing, a disk-shaped glass substrate for a magnetic disk may be obtained by cutting a sheet glass formed by a downdraw method or a float method with a grinding wheel. As the aluminosilicate _glass, SiO 2: 58 to 75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: 3 to 10 _wt%, Na 2 O: 4 to 13 principal component weight% Chemically strengthened glass contained as

  Next, both main surfaces of the plate glass were lapped to form a disk-shaped glass base material. The lapping process is a grinding process in which a lapping platen is pressed against the main surface of the sheet glass and roughed.

(2) Cutting process (coring, forming)
Next, an inner hole was formed in the center using a cylindrical diamond drill (coring). Then, the inner peripheral end face and the outer peripheral end face were ground with a diamond grindstone and subjected to predetermined chamfering (forming).

(3) End surface polishing process Next, the end surface of the glass substrate was mirror-polished by a brush polishing method. By this end surface polishing step, the end surface of the glass substrate was processed into a mirror surface state capable of preventing generation of particles and the like.

(4) Second Lapping Step Next, a second lapping process was performed on both main surfaces of the obtained glass substrate in the same manner as in the first lapping step. By performing this second lapping step, it is possible to remove in advance the fine unevenness formed on the main surface in the cutting step and end surface polishing step, which are the previous steps, and shorten the subsequent polishing step on the main surface. Will be able to be completed in time.

  In the second lapping step, # 1000 is selected as the grain size of the abrasive grains, the flatness of the main surface is 3 μm, the surface roughness Rmax is about 2 μm, and the arithmetic average roughness Ra is about 0.2 μm (Rmax and Ra are According to Japanese Industrial Standard (JIS) B0601). Rmax and Ra were measured with an atomic force microscope (AFM) (Digital Instruments Nanoscope). The flatness is measured by a flatness measuring device, and is the distance (height difference) between the highest part and the lowest part of the substrate surface in the vertical direction (direction perpendicular to the surface).

(5) 1st grinding | polishing process of a main surface First, the 1st grinding | polishing process was given as a grinding | polishing process of a main surface. The primary purpose of this first polishing step is to polish the main surface in advance prior to the second polishing step (mirror polishing step), which is the next step, and to remove scratches and distortions remaining on the main surface in the lapping step described above. To do.

  In the first polishing step, 100 to 200 glass substrates were polished at once by a double-side polishing apparatus capable of polishing. This double-side polishing apparatus performs polishing by sandwiching the multiple glass substrates with an upper surface plate and a lower surface plate through a polishing cloth and relatively moving them by a planetary gear mechanism. A hard resin polisher was used as the polishing cloth in the first polishing step. As the abrasive, cerium oxide abrasive grains were used, and those having a maximum particle size of 3.5 μm, an average value of 1.1 μm, and a D50 value of 1.1 μm were mixed in water.

  The glass substrate which finished this 1st grinding | polishing process was immersed in each washing tank of neutral detergent, a pure water, and IPA (isopropyl alcohol) one by one, and was wash | cleaned.

(6) Chemical strengthening process Next, the glass substrate which finished the above-mentioned lapping process and the 1st grinding | polishing process was chemically strengthened. For chemical strengthening, a chemical strengthening solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared, and the chemically strengthened solution is heated to 375 ° C., and the cleaned glass substrate is preheated to 300 ° C. And was immersed in the chemical strengthening solution for about 3 hours. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, it was performed in a state of being housed in a holder so that a plurality of glass substrates were held at the end surfaces.

  Thus, by immersing in a chemical strengthening solution, the lithium ion and sodium ion of the surface layer of a glass substrate are each substituted by the sodium ion and potassium ion in a chemical strengthening solution, and a glass substrate is strengthened. The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 μm to 200 μm.

  The glass substrate that had been subjected to the chemical strengthening treatment was immersed in a 20 ° C. water bath and rapidly cooled, and maintained for about 10 minutes. And the glass substrate which finished quenching was immersed in the concentrated sulfuric acid heated at about 40 degreeC, and was wash | cleaned. Further, the glass substrate after the sulfuric acid cleaning was cleaned by immersing in a cleaning bath of pure water and IPA (isopropyl alcohol) sequentially.

(7) Second polishing step for main surface Next, a second polishing step was performed as a polishing step for the main surface. The purpose of this second polishing step is to finish the main surface into a mirror surface. In the second polishing step, mirror polishing of the main surface was performed using a soft foam resin polisher, specifically, foamed polyurethane, as the polishing cloth, using the same double-side polishing apparatus as in the first polishing step.

  As an abrasive, colloidal silica abrasive grains having a particle diameter of 30 nm are prepared, water, sulfuric acid as a total dissociating inorganic acid, and any weak acid that exhibits acidity and any weak acid that exhibits alkalinity as a buffering composition. Using a combination that exhibits a buffer action established by the combination of salts, acetic acid, malic acid, malonic acid, succinic acid, citric acid, tartaric acid, phosphoric acid, phosphinic acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid, hydroxyethanephosphonic acid ( HEDP), aminotrimethylene phosphonic acid (NTMP) and any combination of these salts, ie acetic acid and acetate, citric acid and citrate, tartaric acid and tartrate, phosphoric acid and One of phosphate, tartaric acid and phosphate, citric acid and phosphate was used.

  The content of silica in the polishing liquid is preferably 5 to 40% by weight. In this example, it was 10% by weight. The balance in the polishing liquid is ultrapure water.

(8) Cleaning step after mirror polishing treatment The glass substrate that has finished the second polishing step is immersed in a cleaning solution that is a 0.01 to 5 wt% KOH aqueous solution or a 3 to 5 wt% NaOH aqueous solution to obtain an alkali. Washing was performed.

  This cleaning liquid has a buffering composition contained in the polishing liquid used in the second polishing step, that is, a component having a buffering action formed by a combination of any weak acid showing acidity and any weak acid salt showing alkalinity. It is included. These components include acetic acid, malic acid, malonic acid, succinic acid, citric acid, tartaric acid, phosphoric acid, phosphinic acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid, hydroxyethanephosphonic acid (HEDP), aminotrimethylenephosphonic acid ( NTMP) and any combination of these salts, and the same components as those contained in the polishing liquid.

  Cleaning was performed by applying ultrasonic waves. Furthermore, it wash | cleaned by immersing in each washing tank of neutral detergent, a pure water, a pure water, IPA, and IPA (steam drying) sequentially. Note that ultrasonic waves were applied to each cleaning tank.

(9) Inspection step of glass substrate for magnetic disk The glass substrate for magnetic disk manufactured as described above was inspected. When the roughness of the glass substrate surface was measured with an AFM (atomic force microscope), Ra (ave) had a similar value, and there was no tendency.

  In addition, the surface of each glass substrate of an Example was a clean mirror surface state. There were no foreign objects on the surface that could hinder the flying of the magnetic head or cause thermal asperity failure. That is, a flat and smooth high-rigidity glass substrate for a magnetic disk was obtained.

  Using the magnetic disk glass substrate manufactured as described above, a perpendicular magnetic recording type magnetic disk was manufactured.

(10) Magnetic disk manufacturing process On both surfaces of the glass substrate obtained through the above-described processes, an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoTaZr-based alloy, an underlayer made of Ru, and a CoCrPt group on the surface of the glass substrate A perpendicular magnetic recording disk was manufactured by sequentially forming a perpendicular magnetic recording layer made of an alloy, a protective layer made of hydrogenated carbon, and a lubricating layer made of perfluoropolyether. Although this configuration is an example of a configuration of a perpendicular magnetic disk, a magnetic layer or the like may be configured as an in-plane magnetic disk.

(11) Magnetic disk inspection process The magnetic disk manufactured as described above was inspected. When a head crash test was carried out by flying over a magnetic disk using an inspection head having a flying height of 10 nm, the magnetic head was in contact with foreign matter or the like in any of the magnetic disks made of the glass substrates of the above examples. There was no crash failure.

  Next, when a head crush test using an inspection head having a flying height of 8 nm was performed, no crush failure occurred in any of the magnetic disks made of the glass substrates of the above examples. Note that Ra (max) -Ra (min) is considered to be 0.02 or less.

  Next, with respect to the magnetic disk made of the glass substrate of the example, the flying height is 8 nm, the reproducing element portion is a magnetoresistive element, the recording element portion is a single magnetic pole element, and recording is performed by a perpendicular recording method. When a reproduction test was performed, it was confirmed that information was recorded and reproduced normally. The thermal asperity signal was not detected in the reproduction signal. Recording and reproduction could be performed at 100 gigabits per square inch.

  Next, a glide height test was performed on the magnetic disk made of the glass substrate of the example. In this test, when the flying height of the inspection head is gradually lowered, the flying height is checked to determine the contact between the testing head and the magnetic disk. As a result, in the magnetic disk of this example, no contact occurred even when the flying height was 4 nm from the inner edge portion to the outer edge portion of the magnetic disk. At the outer edge portion of the magnetic disk, the glide height was 3.7 nm.

  As mentioned above, although the suitable Example of this invention was described, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  The present invention is applied to a method of manufacturing a glass substrate for a magnetic disk used as a recording medium of a computer or the like and a method of manufacturing a magnetic disk.

Claims (5)

A polishing pad is pressed against both main surfaces of a disk-shaped glass substrate, and the glass substrate and the polishing pad are relatively moved while supplying a polishing liquid containing an abrasive between the glass substrate and the polishing pad. Then, in the manufacturing method of polishing the main surface of the glass substrate and manufacturing a glass substrate for a magnetic disk,
The polishing liquid contains two or more components of a substance exhibiting a chelating action and a substance exhibiting a dispersing action on contaminants attached to the glass substrate, and these substances are composed of two components of a weak acid showing acidity and a weak acid salt showing alkalinity. A method for producing a glass substrate for a magnetic disk , which is a buffer component and is also contained in a cleaning liquid in a cleaning process performed after a polishing process. A polishing pad is pressed against both main surfaces of a disk-shaped glass substrate, and the glass substrate and the polishing pad are relatively moved while supplying a polishing liquid containing an abrasive between the glass substrate and the polishing pad. Then, in the manufacturing method of polishing the main surface of the glass substrate and manufacturing a glass substrate for a magnetic disk,
The polishing liquid contains an acidic substance for bringing the pH of the polishing liquid into a weakly acidic region, and a buffer component composed of two components of a weak acid showing acidity and a weak acid salt showing alkalinity, and the buffering solution in the weakly acidic region includes: The buffer component consisting of the two components is also contained in a cleaning liquid in a cleaning process performed after the polishing process . The buffer component includes acetic acid, malic acid, malonic acid, succinic acid, citric acid, tartaric acid, phosphoric acid, phosphinic acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid, hydroxyethanephosphonic acid (HEDP), aminotrimethylenephosphonic acid ( NTMP) and any combination of any of these salts.
Claim 1 or claim 2 Symbol mounting method of manufacturing a glass substrate for a magnetic disk, characterized in that. A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer on a surface of a glass substrate obtained by the method for manufacturing a glass substrate for a magnetic disk according to any one of claims 1 to 3 . The magnetic disk is a magnetic disk for perpendicular magnetic recording system,
The magnetic disk manufacturing method according to claim 4 , wherein the magnetic layer includes a plurality of layers, and at least one layer is a soft magnetic layer.