JP5259224B2 - Method for manufacturing glass substrate for magnetic disk and method for manufacturing magnetic disk - Google Patents

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk 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. As a substrate for magnetic recording media such as HDD (Hard Disk Drive), which is one of the magnetic recording media, a substrate replacing the aluminum substrate that has been widely used with the miniaturization, thinning, and high-density recording of magnetic disks. A glass substrate excellent in flatness and substrate strength of the main surface has been used.

Magnetic disks are required to have a high recording density, and in recent years, the information recording density of magnetic disks has been increased to about 200 Gbit / inch ² . Along with this increase in recording density, the magnetic head has been changed from a thin film head to a magnetoresistive head (MR head) and a giant magnetoresistive head (GMR head), and the magnetic head substrate (magnetic disk). The flying height from the center is narrowed to about 20 nm to 5 nm. Thus, by reducing the flying height (magnetic spacing) of the magnetic head from the magnetic disk, the spacing loss can be improved and the SN ratio (signal noise ratio) can be improved. High recording density can be achieved.

  A magnetic head equipped with the magnetoresistive element may cause a head crash or a thermal asperity failure as an inherent failure. The head crash is a failure that is physically damaged when the magnetic head collides with a protrusion on the surface of the magnetic disk. Thermal asperity failure means that the magnetoresistive element is heated by adiabatic compression or contact of air when the magnetic head passes while flying over a minute convex or concave shape on the magnetic disk surface. This is a failure that causes a read error.

  Therefore, for a magnetic head equipped with a magnetoresistive element, the surface of the magnetic disk is required to have extremely high smoothness and flatness. Further, if the magnetic layer is formed with dust and foreign matters attached, convex portions are formed. Therefore, the glass substrate is required to be highly cleaned to completely remove dust and foreign matters.

  Since glass substrates for magnetic disks are mass-produced at low cost, several tens to several hundreds of glass substrates are transported in a state of being housed in one holder, and immersed in a washing tank as they are for cleaning. Even when cleaning is performed using a plurality of cleaning tanks, cleaning is performed by sequentially moving each tank while being accommodated in the holder. A method of performing processing in units of a constant processing time (tact time) while flowing an article is called a tact method.

  In the process of cleaning the glass substrate, even if dust or foreign matter adhering to the glass substrate is removed by cleaning, when removing the glass substrate from the cleaning liquid, the dust or foreign matter remaining in the cleaning liquid may reattach to the glass substrate. is there. Therefore, in the cleaning process, it is necessary not only to remove dust from the glass substrate but also to reduce the number of dust and foreign matters contained in the cleaning liquid in order to prevent re-adhesion. Such a cleaning liquid is normally circulated for effective use of resources, and the cleaning liquid is filtered to collect dust and foreign matters when circulating.

  As a technique for grasping the number of particles in the cleaning liquid, for example, in Patent Document 1, the number of particles in the cleaning liquid is measured at regular intervals, and the measured number of particles adheres to the hard disk substrate by linear calculation. A technique for estimating the number of particles for obtaining the number of particles is disclosed. According to Patent Document 1, the number of particles adhering to the hard disk substrate can be estimated without newly installing an appearance test apparatus.

Further, in Patent Document 2, in a method of circulatingly supplying a cleaning liquid and filtering at the time of circulating supply, the amount of particles mixed before or during the cleaning process is detected by a particle counter, and the detected particles are detected. A technique for generating a detection signal within a predetermined amount or more than a predetermined amount depending on the amount is also disclosed. According to Patent Document 2, an operator can be informed of an inappropriate cleaning state, and the cleaning liquid can be managed in an appropriate cleaning state, so that the cleaning performance and the yield can be improved.
JP-A-2005-185773 JP-A-11-233478

  In the cleaning process, after the glass substrate is immersed and cleaned in the cleaning liquid as described above, the glass substrate is dried by bringing the vapor of a liquid mainly composed of a water-soluble solvent into contact with the glass substrate. Since the glass substrate is washed with a plurality of cleaning liquids prior to the drying treatment, it has been considered that the glass substrate after the drying treatment does not have particles attached thereto, or the amount of attachment thereof is extremely small.

  However, when the glass substrate after drying was inspected, adhesion of particles was confirmed. Moreover, it turned out that the adhesion amount varies for every holder in which the glass substrate is accommodated. If particles adhere to the glass substrate in this way, even in a magnetic disk manufactured using such a glass substrate, the smoothness and flatness of the main surface will vary, making it difficult to stabilize the quality. Become.

  In view of such problems, the present invention prevents the adhesion of particles to the glass substrate in the cleaning process, thereby reducing variations in the surface state of the glass substrate after cleaning and capable of stabilizing the quality. It aims at providing the manufacturing method of the glass substrate for disks, and the manufacturing method of a magnetic disk.

  As a result of intensive studies on the above problems, the present inventors have focused on the adhesion of particles to the glass substrate in the drying process after the cleaning process in the cleaning process. As a result of further studies, the inventors have conceived that particles are present in a liquid mainly composed of a water-soluble solvent used in the drying process. Therefore, appropriately controlling the amount of particles in the liquid and preventing the particles from adhering to the glass substrate is effective for improving the non-defective rate of the glass substrate, and hence the non-defective rate of the magnetic disk. I thought it was.

  However, the drying process is a process of drying by bringing a vapor of a water-soluble solvent (for example, isopropyl alcohol) into contact with a glass substrate, and it is extremely difficult to measure particles in the vapor. As a result of further studies, it was found that the amount of adhered particles (residual amount) on the glass substrate and the conductivity of the water-soluble solvent are in a certain proportional relationship, and the present invention has been completed.

  In order to solve the above problems, a typical configuration of a method for manufacturing a glass substrate for a magnetic disk according to the present invention is a method for manufacturing a glass substrate for a magnetic disk including a glass substrate cleaning step. And the drying process and the measurement process, the cleaning process is a process of immersing the glass substrate in the cleaning liquid and cleaning, and the drying process is a liquid whose main component is a water-soluble solvent having a boiling point lower than that of water, It is a process of drying the glass substrate by bringing the steam into contact with the cleaned glass substrate, and the measurement process measures the electrical resistance value of the liquid in the drying process, and when the electrical resistance value is below a predetermined value, It is a process for determining that the content of particles contained in the liquid exceeds an allowable value.

  With the above configuration, the content of particles in the liquid can be easily grasped without performing an operation such as sampling and inspecting the liquid. In the cleaning process, the glass substrate is cleaned using a plurality of types of cleaning liquids in a plurality of cleaning tanks. For this reason, in the drying process of drying the glass substrate after cleaning, the cleaning liquid in the cleaning process that adheres to the glass substrate and the holder in which the glass substrate is stored is a liquid used for the drying process (hereinafter referred to as “drying”). It will be mixed in a solvent for use. Since such cleaning liquid contains particles such as fine dust and abrasives scraped during the polishing process, as the drying process is performed, particles accumulate in the drying solvent and exceed an allowable value. Here, the allowable value is an upper limit value of the allowable value of the content of particles contained in the drying solvent.

  When the drying solvent in which particles are accumulated as described above is vaporized, the accumulated particles rise together with the vapor, reattach to the glass substrate after cleaning, and contaminate the glass substrate. In particular, when the content of particles contained in the drying solvent exceeds the allowable value, the amount of particles that re-adhere to the glass substrate after cleaning is large, so the flatness and smoothness of the glass substrate surface are significantly reduced. And quality standards cannot be met. As a result, the non-defective product rate of the glass substrate decreases, and when a magnetic disk is manufactured using such a glass substrate, the quality of the final product becomes unstable. Therefore, it is necessary to appropriately grasp the content of particles contained in the drying solvent and replace the drying solvent as appropriate.

  Here, since the particles contained in the drying solvent each have a specific electrical conductivity (the reciprocal of the electrical resistance value), the electrical resistance value of the drying solvent is such that particles are accumulated in the drying solvent. The value changes. Therefore, by measuring the electrical resistance value of the drying solvent, it is possible to grasp the content of particles contained in the drying solvent from the amount of change in the measured value. As a result, when the electric resistance value becomes a predetermined value or less, it can be determined that the content of particles contained in the drying solvent exceeds the allowable value, and the drying solvent can be replaced as appropriate. become.

The predetermined value is preferably 300 MΩ · cm ² . By setting the predetermined value in this way, it can be easily determined whether or not the particles in the drying solvent exceed the allowable value. A drying solvent having an electric resistance value of a predetermined value of 300 MΩ · cm ² or less has a particle content that exceeds an allowable value. Therefore, when a drying treatment is performed on a glass substrate using such a drying solvent, cleaning is performed. The amount of particles that reattach to the subsequent glass substrate increases.

  Said washing | cleaning process is good in it being a process performed after the last grinding | polishing process of the said glass substrate for magnetic discs.

  The glass substrate is washed multiple times in the manufacturing process. However, the drying process is not performed in the cleaning other than the cleaning process after the final polishing process. This is because, if the glass substrate is dried during the manufacturing process, particles such as fine dust and abrasives scraped by polishing adhere firmly to the glass substrate, and adversely affect the subsequent manufacturing process. It is. Therefore, the present invention is particularly effective in a cleaning process performed after the final polishing process of the glass substrate, that is, a cleaning process including a drying process.

  The water-soluble solvent is preferably isopropyl alcohol.

  Since isopropyl alcohol (IPA) has a low boiling point, it can be vaporized at a lower temperature than water. Moreover, since isopropyl alcohol has high hydrophilicity, it is easily dissolved in water, and when the vapor comes into contact with water, a water-alcohol mixture is formed. Accordingly, since the boiling point of water drops due to azeotropy, water attached to the glass substrate can be easily dried by bringing the vapor of isopropyl alcohol into contact with the glass substrate.

  A method of manufacturing a magnetic disk according to the present invention is characterized in that at least a magnetic layer is formed on the surface of a glass substrate for a magnetic disk manufactured using any one of the manufacturing methods described above.

  Since the glass substrate for a magnetic disk manufactured by applying the present invention has extremely good flatness and smoothness, the magnetic disk manufactured using such a glass substrate also has good smoothness and flatness. Therefore, even in the case of a perpendicular magnetic disk in which the recording density is increased and the flying height of the magnetic head is small, a signal reading error can be prevented.

  As described above, according to the present invention, it is possible to appropriately grasp the content of particles contained in a liquid by measuring the electrical resistance value of the liquid (drying solvent) used in the drying process. . And based on this, by controlling the content of particles, it is possible to prevent the particles from adhering to the glass substrate in the cleaning process. Therefore, it is possible to provide a method for manufacturing a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk that can reduce variations in the surface state of the glass substrate after cleaning and stabilize the quality.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiment are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  First, the glass substrate for magnetic disks according to the present embodiment will be described, and then the cleaning process will be described. FIG. 1 is a view for explaining a glass substrate for a magnetic disk according to the present embodiment, and FIG. 1 (a) is a perspective view of the glass substrate for a magnetic disk. The magnetic disk glass substrate 100 has a disk shape, and an inner hole is formed at the center thereof. Since the main surface 110 is an area for recording and reproducing information, the main surface 110 is substantially smooth for the recording head to fly.

  FIG.1 (b) is XX sectional drawing of Fig.1 (a). The magnetic disk glass substrate 100 is interposed between a main surface 110 serving as an information recording / reproducing area, an end surface 120 orthogonal to the main surface 110, and the main surface 110 and the end surface 120. And a chamfered surface 130. In addition, since the boundary between the end surface 120 and the chamfered surface 130 may become unclear due to an end surface polishing process described later, in the present embodiment, the end surface 120 and the chamfered surfaces 130 on both sides constitute a single curved surface. Including the case of doing.

  If particles or foreign matter adhere to the magnetic disk glass substrate 100, particularly its main surface 110, before the magnetic disk film forming process, a smooth magnetic layer cannot be formed on the glass substrate in the film forming process, and the final product The yield rate of a certain magnetic disk is reduced.

  FIG. 2 is a schematic view of a holder and a cleaning tank in which a glass substrate is stored. As shown in FIG. 2, a plurality of glass substrates 100 are arranged in a holder 200 and immersed in a cleaning tank 210 supplied with a cleaning liquid 220 together with the holder 200 while being suspended from an arm 202. Then, particles adhering to the glass substrate 100 are removed by the water flow of the cleaning liquid 220 in the cleaning tank 210 and the movement by the rhythmic part (not shown) of the cleaning tank 210. Although not shown in FIG. 2, the cleaning tank 210 is equipped with an ultrasonic vibration device, and cleaning is performed by applying ultrasonic vibration to more effectively remove particles adhering to the glass substrate 100. can do.

  FIG. 3 is a diagram for explaining the details of the cleaning process. As shown in FIG. 3, the cleaning process is roughly divided into three processes: a cleaning process, a drying process, and a measurement process. In the present embodiment, a cleaning process using five types of cleaning liquids using five cleaning tanks 210 is given as an example, but the present invention is not limited to this. Further, in the cleaning process, the glass substrate 100 is accommodated in the plurality of holders 200, but the holder 200 and the arm 202 are not shown in FIG. 3 for easy understanding.

  The above five cleaning tanks 210 (210a to 210e) are supplied with different cleaning liquids 220 (220a to 220e) from the cleaning liquid supply unit (not shown) and the IPA tank 280, depending on the purpose of cleaning. By providing a plurality of the cleaning tanks 210 in the cleaning process, it is possible to sequentially perform cleaning using two or more types of cleaning liquids having at least different components for each cleaning tank.

  As the cleaning liquid 220, sulfuric acid, organic acid, alkaline aqueous solution, neutral aqueous solution, surfactant, chelating agent, distilled water (pure water), isopropyl alcohol (hereinafter referred to as “IPA”), or the like can be used properly. In FIG. 3, the acid cleaning tank 210a has an acidic solution 220a, the pure water cleaning tank 210b has pure water 220b, the neutral detergent cleaning tank 210c has a neutral detergent solution 220c, and the pure water cleaning tank 210d has a pure water cleaning tank 210d. The pure water 220d is supplied to the IPA cleaning tank 210e as IPA 220e as the cleaning liquid 220.

  The cleaning liquid 220 removes dust adhering to the glass substrate and floats in the cleaning liquid. The cleaning liquid 220 supplied from the cleaning liquid supply unit is used while being replenished with a new one while being filtered or distilled and reused.

  In particular, the drying solvent 240 (IPA) used for the drying process is recycled after being dehydrated and distilled after use. Further, the IPA 220e used in the IPA cleaning tank 210e is also reused. The used IPA is first discharged to the waste liquid tank 260. The water content in IPA after use (the amount of water contained in IPA) is about 5 wt%. Such IPA is fed to a dehydrating distillation apparatus 270 and regenerated by dehydrating distillation. The water content of the IPA after the regeneration treatment is preferably 0.5 wt% or less. The IPA after the regeneration processing is supplied to the IPA tank 280, and is supplied from the IPA tank 280 to the IPA cleaning tank 210e and the drying processing tank 230. At this time, the water content of IPA is preferably 1 wt% or less.

  The IPA tank 280 is also supplied with unused IPA from the IPA storage tank 290, and replenishes what is insufficient only with the IPA after the regeneration process. The water content of this unused IPA is 0.1 wt% or less. Thus, by reusing the IPA used for the cleaning process and the drying process, it is possible to reduce the cost of the IPA.

  In the cleaning process, the plurality of glass substrates 100 are stored side by side in a holder 200 (not shown), and are first put into the acid cleaning tank 210a and cleaned in the acidic solution 220a for a certain period of time. When the cleaning is completed, the glass substrate 100 is moved from the acid cleaning tank 210a to the pure water cleaning tank 210b together with the holder 200 (not shown). Then, cleaning is performed in the same manner as described above, and after the cleaning in the pure water cleaning tank 210b is completed, the liquid moves to the neutral detergent cleaning tank 210c. The neutral detergent cleaning tank 210c, the pure water cleaning tank 210d, and the IPA cleaning tank 210e are also cleaned in the same manner as described above. The five cleaning tanks 210 are each provided with an ultrasonic vibration device (not shown) for each of the cleaning tanks 210. In the cleaning process in each cleaning tank 210, ultrasonic vibration is applied for cleaning. .

  The glass substrate 100 that has been cleaned in the above-described five cleaning tanks 210 and has completed the cleaning process moves together with the holder 200 (not shown) to the drying process tank 230 that performs the drying process. A drying solvent 240 mainly composed of IPA, which is a water-soluble solvent having a lower boiling point than water, is supplied from the IPA tank 280 to the drying treatment tank 230. And the temperature of the drying solvent 240 is raised to the boiling point vicinity with the heating apparatus (not shown) with which the drying processing tank 230 is equipped, and the drying solvent 240 is vaporized. In addition, a resistance measuring device 250 is connected to the drying treatment tank 230.

  In the drying process, the glass substrate 100 comes into contact with the vaporized drying solvent 240 in the upper part of the drying process tank 230. Here, the cleaning liquid 220 in the cleaning process is attached to the glass substrate 100 and the holder 200 in which the glass substrate 100 is accommodated. When the cleaning liquid 220 comes into contact with the vaporized drying solvent 240, a water-alcohol mixture is formed. Therefore, the boiling point of water drops due to azeotropy, and the cleaning liquid 220 adhering to the glass substrate 100 can be easily dried.

  In particular, as described above, when the water-soluble solvent that is the main component of the drying solvent 240 is IPA, the boiling point thereof is lower than that of water, so that water can be vaporized at a temperature lower than the boiling point. In addition, since IPA has high hydrophilicity, it is easy to dissolve in water, and when IPA vapor is brought into contact with the glass substrate 100, there is an advantage that it tends to be a water-alcohol mixture.

  In the above drying process, if the cleaning liquid 220 in the cleaning process adhering to the glass substrate 100 and the holder 200 in which the glass substrate 100 is stored is dropped before drying, the drying liquid in the drying process tank 230 is dried. It will be mixed in the solvent 240. Since the cleaning liquid 220 contains particles such as fine dust and abrasives scraped off during the polishing process, these particles are mixed in the drying solvent 240, and as the drying process is performed, the drying solvent 240 contains particles. Will be accumulated.

  When the drying solvent 240 in which particles are accumulated is vaporized as described above, the particles also rise together with the vaporized drying solvent 240 and are reattached to the glass substrate 100. As a result, the flatness and smoothness of the surface of the glass substrate 100 are lowered, and the flatness and smoothness of the surface of the magnetic disk manufactured using the glass substrate 100 are also lowered. For this reason, it is necessary to appropriately grasp the content of particles contained in the drying solvent 240 used in the drying process and to replace the drying solvent as appropriate.

  Therefore, in the measurement process, the electrical resistance value of the drying solvent 240 is measured by the resistance measuring device 250. The resistance measurement device 250 may include a resistance value measurement unit 250a, a predetermined value setting unit 250b, a predetermined value determination unit 250c, and a predetermined value notification unit 250d. With such a configuration, a predetermined value of the electric resistance value is set in advance in the predetermined value setting unit 250b, the resistance value measuring unit 250a measures the electric resistance value of the drying solvent 240, and whether the measured value is equal to or less than the predetermined value. Measurement processing can be smoothly performed such that the predetermined value determination unit 250c determines that the predetermined value is less than or equal to the predetermined value, and the predetermined value notification unit 250d notifies by voice or the like.

  It is considered that most of the particles mixed in the drying solvent 240 are the abrasive used in the polishing process and the fine dust removed by the polishing. Since each of these particles has a specific electrical conductivity (the reciprocal of the electrical resistance value), the electrical resistance value of the drying solvent 240 varies depending on the content of the particles.

Therefore, an allowable value of the content of particles in the drying solvent 240 is set, an electrical resistance value of the drying solvent 240 at the allowable value is measured in advance, and the value is set as a predetermined value in the predetermined value setting unit 250b. . For example, in the present embodiment, the predetermined value is set to 300 MΩ · cm ² . This is because when the glass substrate after the cleaning process is inspected, it is necessary to keep the content of particles in the drying solvent 240 within about 13,000 in order to maintain the quality of the glass substrate, that is, the allowable value is This is because there are 13,000 and the electric resistance value at this time is 300 MΩ · cm ² . The predetermined value can be appropriately changed according to the allowable value of the content of particles in the drying solvent 240, that is, the quality required for the glass substrate.

And the resistance value measurement part 250a measures the electrical resistance value of the solvent 240 for drying at the time of the drying process in a washing | cleaning process. When the electrical resistance value is 300 MΩ · cm ² or less, the predetermined value determination unit 250 c exceeds the allowable value of the particle content in the drying solvent 240 and exceeds 300 MΩ · cm ^2. It can be determined that the particle content is within an allowable value.

  As a result of the measurement, when the content of the particles in the drying solvent 240 exceeds the allowable value, the predetermined value notification unit 250d notifies a warning by a screen display or sound. By monitoring the electrical resistance value, the worker can detect in advance that the time for replacement of the drying solvent 240 is approaching, and can perform replacement without delay when a warning is notified.

  With the above configuration, the content of the particles in the drying solvent 240 can be easily grasped without performing an operation such as sampling and inspecting the drying solvent 240 in the drying processing tank 230, and the drying The solvent can be changed as appropriate. In addition, the measurement process may be measured constantly, for example, intermittently or at a predetermined timing. In addition, by setting a plurality of predetermined electric resistance values with respect to the particle content, the particle content can be grasped step by step.

  In addition, the cleaning step may be performed after the final polishing step of the magnetic disk glass substrate. As will be described later, the glass substrate 100 is cleaned a plurality of times in the manufacturing process, but the drying process is not performed in the cleaning other than the cleaning process after the final polishing process. This is because if the glass substrate 100 is dried during the manufacturing process, the particles adhere firmly to the glass substrate 100 and adversely affect the subsequent manufacturing process. Note that the cleaning process in the cleaning process can also be applied as cleaning after the first polishing process or the chemical strengthening process.

  As described above, according to the method for manufacturing a magnetic disk glass substrate according to the present invention, by preventing particles from adhering to the glass substrate in the cleaning process, the variation in the surface state of the glass substrate after the cleaning process is reduced. The quality of the glass substrate can be stabilized.

  Moreover, since the flatness and smoothness of a glass substrate for a magnetic disk manufactured by applying the present invention are extremely good, the smoothness and flatness are good even in a magnetic disk manufactured using such a glass substrate. Therefore, the flying stability of the magnetic head when writing to the magnetic disk is improved, the head crash failure and thermal asperity failure are reduced, and the flying height of the magnetic head can be reduced. Can contribute.

(Example)
Embodiments of a method for manufacturing a magnetic disk to which the present invention is applied will be described below. The glass substrate 100 for magnetic disk and the magnetic disk are 0.8 inch type disk (inner diameter 6 mm, outer diameter 21.7 mm, plate thickness 0.381 mm), 1.0 inch type disk (inner diameter 7 mm, outer diameter 27.4 mm). , Plate thickness 0.381 mm), 1.8 inch type magnetic disk (inner diameter 12 mm, outer diameter 48 mm, plate thickness 0.508 mm) and the like. 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 Examples of the material of the glass substrate 100 in this embodiment include soda lime glass, aluminosilicate glass, borosilicate glass, and crystallized glass. Among these, aluminosilicate glass is preferable. is there. Since the aluminosilicate glass is smooth and has high rigidity, the magnetic spacing, particularly the flying height of the magnetic head, can be more stably reduced. Aluminosilicate glass can obtain high rigidity and strength by chemical strengthening.

First, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper mold, a lower mold, and a body mold to obtain an amorphous plate glass. In addition, the glass for chemical strengthening was used as aluminosilicate glass. In addition to direct pressing, a disk-shaped glass substrate 100 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. This lapping process was performed using alumina free abrasive grains with a double-sided lapping apparatus using a planetary gear mechanism. Specifically, the lapping platen is pressed from above and below on both sides of the plate glass, a grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relatively to perform lapping. went. By this lapping process, a glass base material having a flat main surface was obtained.

(2) Cutting process (coring, forming)
Next, the glass base material was cut using a diamond cutter, and a disk-shaped glass substrate was cut out from the glass base material. Next, using a cylindrical diamond drill, an inner hole was formed in the central portion of the glass substrate to obtain an annular glass substrate 100 (coring). Then, the inner peripheral end face and the outer peripheral end face 120 were ground with a diamond grindstone and subjected to predetermined chamfering (forming).

(3) Second Lapping Step Next, the second lapping process was performed on both main surfaces 110 of the obtained glass substrate 100 in the same manner as in the first lapping step. By performing this second lapping step, the fine irregularities formed on the main surface in the cutting step and end surface polishing step, which are the previous steps, can be removed in advance, and the subsequent polishing step for the main surface 110 can be performed. It can be completed in a short time.

(4) End surface polishing step Next, end surface polishing of the outer periphery of the glass substrate 100 is performed. First, the end surface 120 is polished independently prior to the chamfered surface 130. The polishing method may be, for example, a method of simultaneously polishing a plurality of glass substrates 100 with a brush, but the machining allowance increases. Therefore, for example, a single wafer polishing method may be used.

  Subsequently, the chamfered surface 130 was mirror-polished. Thereby, the difference of the surface roughness in the perimeter of the outer periphery of the chamfered surface 130 of one glass substrate 100 became the range of 0.001 micrometer or less. And the glass substrate 100 which finished the end surface grinding | polishing process was washed with water. By this end face polishing step, the end face 120 of the glass substrate 100 was processed into a mirror state that can prevent the precipitation of sodium and potassium.

  In this embodiment, it has been described that the chamfered surface 130 is polished after the end portion is polished. However, this order is arbitrary, and the end face 120 may be polished after the chamfered surface 130 is polished first.

  Next, regarding the inner peripheral end surface, a glass substrate block in which a large number of sheets are laminated may be formed, and the chamfered inner peripheral end portion may be simultaneously polished with a brush roll. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used.

(5) Main surface polishing step As the main surface polishing step, first, a first polishing step was performed. The first polishing step is mainly intended to remove scratches and distortions remaining on the main surface 110 in the lapping step described above. In the first polishing step, the main surface 110 was polished using a hard resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains were used.

  The glass substrate 100 which finished this 1st grinding | polishing process was immersed in each washing tank of neutral detergent, a pure water, and IPA (isopropyl alcohol) sequentially, and was wash | cleaned.

  Next, a second polishing step was performed as the main surface polishing step. The purpose of the second polishing step is to finish the main surface 110 in a mirror shape. In the second polishing step, mirror polishing of the main surface 110 was performed using a soft foam resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains finer than the cerium oxide abrasive grains used in the first polishing step were used.

(6) Cleaning step The glass substrate 100 after the second polishing step is sequentially immersed in an acid cleaning tank 210a, a pure water cleaning tank 210b, a neutral detergent cleaning tank 210c, a pure water cleaning tank 210d, and an IPA cleaning tank 210e. Then, washing treatment was performed with the acidic solution 220a, the pure waters 220b and 220d, the neutral detergent solution 220c, and the IPA 220e. Note that an ultrasonic wave was applied to each cleaning tank 210. Then, the glass substrate 100 was brought into contact with the vaporized drying solvent 240 at the top of the drying treatment tank 230 to perform a drying treatment.

In addition, the resistance measuring device 250 is connected to the drying treatment tank 230 that performs the drying treatment, and the electrical resistance value of the drying solvent 240 in the drying treatment tank 230 is intermittently measured at a predetermined interval. . Then, by setting an electric resistance value with respect to an allowable value of the content of particles in the drying solvent 240 in advance, if the measured electric resistance value is equal to or less than a predetermined value, the particles in the drying solvent 240 are It can be judged that the content of exceeds the allowable value. The predetermined value is preferably 300 MΩ · cm ² . This is because when the predetermined value is 300 MΩ · cm ² or less, the content of particles in the drying solvent 240 exceeds the allowable value. Such a predetermined value can be set according to the allowable value of the content of particles in the drying solvent 240.

  With the above configuration, the content of the particles in the drying solvent 240 can be easily grasped without performing an operation such as sampling and inspecting the drying solvent 240 from the drying treatment tank 230. Therefore, it is possible to replace the drying solvent 240 in which particles are accumulated in an allowable amount or more as appropriate, and to reduce particles on the glass substrate 100 during the drying process in the cleaning process.

[Evaluation]
The effectiveness of this embodiment in the magnetic disk manufactured by the above process will be described. FIG. 4 is a graph showing the relationship between the resistance value and the number of particles in the drying solvent in Examples and Comparative Examples. Here, in the examples, using a predetermined value (300MΩ · cm ²⁾ drying solvent 240 is greater than the electrical resistance in 2680.0MΩ · cm ^2, the comparative example, electric resistance 184.0MΩ A drying solvent 240 having a cm ² (predetermined value of 300 MΩ · cm ² or less) was used. The number of particles in the dry solvent was measured using a laser particle counter (LPC) for the dry solvents used in the examples and comparative examples.

As shown in FIG. 4, the drying solvent 240 used in the example had an electric resistance value of 2680.0 MΩ · cm ² and a number of particles of 2918.0. On the other hand, the drying solvent 240 used in the comparative example had an electric resistance value of 184.0 MΩ · cm ² and a number of particles of 13646.2. From this, it can be seen that the electrical resistance value of the drying solvent 240 and the number of particles are inversely proportional. Thereby, it can be understood that the number of particles in the drying solvent 240 can be grasped by measuring the electric resistance value of the drying solvent 240.

  Therefore, in the cleaning process, the content of the particles contained in the drying solvent 240 is properly grasped, and the content is an allowable value (the upper limit value of the allowable content of the particles contained in the drying solvent). When the value exceeds the value, it is necessary to replace the drying solvent 240. Thereby, the amount of particles adhering to the glass substrate 100 during the cleaning process can be reduced, and the high-quality glass substrate 100 with high flatness and smoothness can be manufactured.

(7) Chemical strengthening process Next, the glass substrate 100 which finished the above-mentioned lapping process and 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 400 ° C., and the cleaned glass substrate 100 is heated to 300 ° C. This was done by preheating and immersing in a chemical strengthening solution for about 3 hours. In this immersion, in order to chemically strengthen the entire surface of the glass substrate 100, the plurality of glass substrates 100 were stored in a holder so that the glass substrate 100 was held by the end surface 120.

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

  The glass substrate 100 that had been subjected to the chemical strengthening treatment was immersed in a water bath at 20 ° C. for rapid cooling and maintained for about 10 minutes. And the glass substrate 100 which finished quenching was immersed in the concentrated sulfuric acid heated at about 40 degreeC, and was wash | cleaned. Furthermore, the glass substrate 100 that had been subjected to the sulfuric acid cleaning was sequentially immersed and cleaned in each cleaning tank of pure water and IPA (isopropyl alcohol). In addition, ultrasonic waves were applied to each cleaning tank.

  As described above, by applying the first lapping step, the cutting step, the end surface polishing step, the second lapping step, the first and second polishing steps, and the chemical strengthening step, a flat and smooth high-rigidity magnetic disk glass A substrate 100 was obtained.

(8) Magnetic disk manufacturing process (film formation process)
On both surfaces of the glass substrate 100 obtained through the above-described steps, 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 perpendicular magnetic made of a CoCrPt-based alloy on the surface of the glass substrate 100. A perpendicular magnetic recording disk was manufactured by sequentially forming a recording layer, 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.

  Thus, by manufacturing the magnetic disk as the final product using the glass substrate 100 having high flatness and smoothness, the magnetic disk can also obtain high flatness and smoothness. Therefore, it is possible to improve the flying stability of the magnetic head when writing to the magnetic disk. As a result, the head crash failure and the thermal asperity failure can be reduced and the flying height of the magnetic head can be reduced, thereby contributing to the realization of a high recording density.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, 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 can be used in a method for manufacturing a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk.

It is a figure explaining the glass substrate for magnetic discs concerning this embodiment. It is a general-view figure of the holder and cleaning tank in which a glass substrate is stored. It is a figure explaining the detail of a washing process. It is a figure which shows the relationship between a resistance value and the number of particles in an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Glass substrate, 110 ... Main surface, 120 ... End surface, 130 ... Chamfering surface, 200 ... Holder, 202 ... Arm, 210 ... Cleaning tank, 210a ... Acid cleaning tank, 210b ... Pure water cleaning tank, 210c ... Neutral Detergent washing tank, 210d ... pure water washing tank, 210e ... IPA washing tank, 220 ... washing liquid, 220a ... acidic solution, 220b ... pure water, 220c ... neutral detergent solution, 220d ... pure water, 220e ... IPA, 230 ... drying Treatment tank, 240 ... drying solvent, 250 ... resistance measuring device, 250a ... resistance value measuring unit, 250b ... predetermined value setting unit, 250c ... predetermined value judging unit, 250d ... predetermined value notifying unit, 260 ... waste liquid tank, 270 ... Dehydration distillation apparatus, 280 ... IPA tank, 290 ... IPA storage tank

Claims (2)

In the method for manufacturing a glass substrate for a magnetic disk including a glass substrate cleaning step,
The cleaning step is a step performed after the final polishing step of the magnetic disk glass substrate, and includes a cleaning process, a drying process, a measurement process, and an exchange process .
The cleaning process is a process of immersing and cleaning the glass substrate in a cleaning liquid,
The drying process
Vaporizing a liquid mainly composed of isopropyl alcohol , which is a water-soluble solvent having a lower boiling point than water, and bringing the vapor into contact with the washed glass substrate, thereby drying the glass substrate.
The measurement process includes
Measure the electrical resistance value of the liquid in the drying process,
When the electric resistance value was 300MΩ · cm ² or less, Ri process of determining der and content of particles contained in the liquid exceeds the allowable value,
The replacement process, when the electric resistance value measured by the measurement process was 300MΩ · cm ² or less, a magnetic disk, wherein the processing der Rukoto exchanging isopropyl alcohol which is a main component of the liquid Method for manufacturing glass substrate. A method for producing a magnetic disk, comprising forming at least a magnetic layer on a surface of a glass substrate for a magnetic disk produced using the production method according to claim 1 .

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