JP5036323B2 - Method for manufacturing glass substrate for magnetic disk, method for manufacturing magnetic disk, and glass substrate holder - Google Patents

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk including a chemical strengthening step and a cooling step, a method for manufacturing a magnetic disk, and a glass substrate holder.

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

  As the magnetic recording technology increases 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). The amount is getting smaller.

  More specifically, in an LMR (horizontal magnetic recording) type or PWR (perpendicular magnetic recording) type HDD, after the HDD is activated, the magnetic head travels completely on the magnetic disk or travels in a pseudo-contact manner to the magnetic head. Read and write information using the leakage flux of That is, when writing information, the magnetic film on the disk is magnetized by the leakage magnetic flux generated by passing a current through the induction coil of the magnetic head, and when reading information, the leakage magnetic flux from the magnetized magnetic disk is read. Is detected by a magnetic head induction coil or MR / GMR / TMR element and converted into an induced current.

  In order to achieve the demand for higher recording density in recent years, it is essential to make the flying height of the magnetic head with respect to the magnetic disk smaller. In other words, by suppressing the spread of the leakage magnetic flux between the magnetic head and the magnetic disk, the magnetization area formed on the magnetic disk can be reduced, and the number of magnetization areas existing per unit area can be increased. Is possible. In this way, high recording density is achieved.

  However, in HDDs, it is necessary to move the magnetic head and magnetic disk relative to each other at a high speed of several tens of m / sec, and how the flying height is reduced to several tens of nanometers or less. One big solution is to hold it below.

  One of the problems to be solved is an evaluation index representing the surface shape of the magnetic disk represented by surface waviness. If the factor has partial non-uniformity, the flying or pseudo-flying of the magnetic head is hindered, and it becomes difficult to stably maintain the flying height between the magnetic disks.

  A magnetic head equipped with a magnetoresistive element such as MR / GMR / TMR may cause a thermal asperity failure as an inherent failure. Thermal asperity failure is caused when a magnetoresistive element is heated by adiabatic compression or contact of air when a magnetic head passes over a minute convex or concave shape on the surface of a magnetic disk, causing a read error. It is an obstacle. To increase the recording density, it is essential to reduce the flying height. However, if the magnetic disk has surface waviness, there is a problem that the flying height cannot be reduced in order to avoid thermal asperity failure.

  Therefore, for such a magnetic head, 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 also required to be highly cleaned to completely remove dust and foreign matters.

  Such a glass substrate for a magnetic disk is formed through a plurality of processes. First, a single wafer is cut into a disk shape, and an inner hole is formed to form a glass substrate. Thereafter, the outer peripheral end surface and the inner peripheral end surface of the cut glass substrate are chamfered, and both end surfaces are polished. Subsequently, the main surface of the glass substrate is also polished, and finally the glass substrate that has been polished is subjected to a chemical strengthening treatment.

  The chemical strengthening step for performing this chemical strengthening treatment is performed by, for example, heating and melting a molten salt of an alkali salt, and storing and holding the glass substrate to be treated in a glass substrate holder in the molten salt (chemical strengthening treatment liquid). It is performed by dipping and ion exchange. Here, the glass substrate holder is used because the entire surface of the glass substrate is uniformly immersed in the chemical strengthening treatment liquid.

And if the chemical strengthening process of a glass substrate is completed, a glass substrate will be cooled in the state hold | maintained at the glass substrate holder. However, since the temperature of the chemical strengthening treatment liquid is as high as about 400 ° C., the glass substrate is distorted or warped when it is simply cooled while being held on the glass substrate holder. In order to solve such a problem, a technique is known in which the freezing point of the chemical strengthening treatment liquid is lowered and the warpage generated in the glass substrate is reduced (for example, Patent Document 1).
JP 2001-192239 A

  On the other hand, recently, a perpendicular magnetic recording method is being adopted in order to further improve the recording density. In the case of this perpendicular magnetic recording medium, the influence of the processing accuracy of the glass substrate tends to appear more conspicuously than in the case of the in-plane magnetic recording method. For this reason, the glass substrate is required to have lower roughness, flatness, and shape accuracy.

  As described above, when the glass substrate holder is cooled while being held by the glass substrate holder, the local portion of the glass substrate and the portion where the chemical strengthening treatment liquid remains locally in the glass substrate are compared with other portions. The cooling rate is different (temperature distribution is different), which gives a physical force to the glass substrate in the form of reaction, resulting in local drag, distortion and warpage, and also chipping and cracking. End up.

  Such a region with a different cooling rate can be formed between the portion in contact with the glass substrate holder and the other portion in the glass substrate based on the difference in heat capacity between the holding portion of the glass substrate holder and the glass substrate. This is due to the difference in temperature change. Therefore, a glass substrate having a relatively high surface area ratio, i.e., a thinner plate thickness, exhibits more pronounced distortion and warpage.

  Moreover, if the chemical strengthening treatment solution is solidified while adhering to the substrate and the solidified portion cannot be cleaned in the subsequent cleaning process, and the portion remains, the cause is that the flatness of the glass substrate is significantly deteriorated. It becomes.

  The deterioration of the flatness of the glass substrate based on such a cooling process has been an allowable range in the past, but the glass substrate has become thinner due to the recent miniaturization of the magnetic disk, and in the perpendicular magnetic recording system, the glass substrate has become thinner. Since unevenness on the surface of the substrate is increased by a surface layer such as a magnetic layer, flatness is required more strictly than in the past.

  As a result of earnestly examining the above problems, the inventors of the present application have configured the glass substrate holder so that the chemical strengthening treatment liquid remaining locally on the main surface, in particular, the glass substrate can be quickly taken out. Thus, the present inventors have found that the chemical strengthening treatment liquid can be removed quickly and reliably, and have completed the present invention.

  The present invention has been made in view of the above-mentioned problems of the conventional glass substrate cooling process, and the object of the present invention is to prevent the glass substrate from being distorted, warped, cracked, and chipped, and has a low A novel and improved method for producing a magnetic disk glass substrate, a method for producing a magnetic disk, and a glass substrate holder that are excellent in roughness and flatness.

In order to solve the above-described problems, according to one aspect of the present invention, a chemical strengthening of a glass substrate is performed by immersing a disk-shaped glass substrate in a chemical strengthening treatment solution in which a chemically strengthened salt is dissolved by heating and performing ion exchange. A method of manufacturing a glass substrate for a magnetic disk, comprising: a strengthening step; and a cooling step of cooling the glass substrate heated by the chemical strengthening step in a state where the glass substrate holder is held by the glass substrate holder. The yarn is formed by stretching a plurality of yarns in a substantially V shape so as to have elasticity, and the yarn contacts the boundary portion between the main surface and the outer peripheral chamfer of the glass substrate, and the glass substrate is placed on both sides by point contact. The temperature change of the whole glass substrate in a cooling process is equalized by hold | maintaining from the above, The manufacturing method of the glass substrate for magnetic discs characterized by the above-mentioned is provided.

  With this configuration, the contact area between the glass substrate and the holding unit can be minimized, the chemical strengthening treatment liquid can be prevented from solidifying between the glass substrate and the holding unit, and the temperature change of the entire glass substrate can be made uniform. It becomes possible. Therefore, it is possible to prevent the glass substrate from being distorted or warped. The holding unit can also hold the glass substrate only by point contact.

The holding part of the glass substrate holder is preferably pressed and fixed by elasticity.

At least the yarn may be brought into contact with the boundary between the lowermost main surface of the outer periphery of the glass substrate and the outer peripheral chamfer.

Angle between the main surface and the thread of the glass substrate may be less than 45 °.

  The chamfered surface is formed with an inclination of 45 ° with respect to the main surface. Therefore, by setting the angle formed by the main surface and the thread to less than 45 °, the glass substrate and the thread do not make a surface contact or a line contact with the chamfered surface or the main surface, but only point contact with the boundary portion. It is possible to keep the contact area between the glass substrate and the holding portion to a minimum.

The angle formed between the main surface of the glass substrate and the thread is preferably equal on both sides.

  The yarn may be a metal wire. Since the metal wire is strong in environmental resistance and has a low coefficient of thermal expansion, it does not deform even at high temperatures in chemical strengthening. In addition, since there is little deterioration over time, appropriate elasticity (tension) can be maintained. Therefore, the number of complicated maintenance operations can be reduced, and a glass substrate excellent in low roughness and flatness can be supplied stably.

  The boundary part may be formed of a curved surface, and the holding part may be in point contact with the curved surface of the boundary part. With such a configuration, even if the glass substrate is slightly inclined and contacts the holding portion, the point contact with the boundary portion is maintained, and the contact area between the glass substrate and the holding portion can be kept to a minimum.

  Also provided is a method of manufacturing a magnetic disk including a step of forming at least a magnetic layer on the surface of a glass substrate obtained by the method of manufacturing a glass substrate for a magnetic disk.

In order to solve the above-mentioned problems, according to another aspect of the present invention, a glass-like glass substrate is immersed in a chemical-strengthening treatment solution in which a chemically strengthened salt is dissolved by heating, and ion exchange is performed to chemically strengthen the glass substrate. After that, a glass substrate holder used for cooling a glass substrate heated in chemical strengthening, wherein the glass substrate holder stretches a plurality of threads in a substantially V shape so as to have elasticity. The holding part is formed of the glass in the cooling process by holding the glass substrate from both sides by point contact with the yarn contacting the boundary between the main surface of the glass substrate and the outer peripheral chamfered surface. A glass substrate holder is provided, characterized in that the temperature change of the entire substrate is made uniform .

The holding part is formed by curving a thin plate so as to be wavy in the longitudinal direction, and stretching a plurality of threads in a substantially V shape between U-shaped groove portions between the protruding portions of the undulating thin plate It is good to be done. It should be noted that the components corresponding to the technical idea in the method for manufacturing a glass substrate for magnetic disk described above and the description thereof can be applied to the method for manufacturing a magnetic disk and a glass substrate holder.

  As described above, according to the present invention, it is possible to keep the cooling rate of the entire glass substrate uniform by minimizing the contact area between the glass substrate and the holding portion, and to prevent the glass substrate from being distorted or warped. It is possible to maintain excellent flatness.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  The glass substrate for magnetic disks is formed through a plurality of processes. In the final stage, a chemical strengthening process and a cooling process are performed. The glass substrate is held by the glass substrate holder during the chemical strengthening process and / or the cooling process. Hereinafter, in order to facilitate understanding of the embodiment of the present invention, the chemical strengthening process and the cooling process which are the premise thereof will be described in detail.

(Chemical strengthening process)
In the chemical strengthening step, the chemical strengthening treatment tank immerses the glass substrate in a chemical strengthening treatment solution in which the chemically strengthened salt is dissolved by heating, and a part of ions of the glass substrate (aluminosilicate glass containing Li ions), for example, Li ions And monovalent metal ions such as Na ions are substituted with monovalent ions having a larger ion diameter than the above ions in the chemical strengthening treatment liquid, such as Na ions, K ions, Ag ions, and the like. By such an ion exchange method, a compressive stress layer is formed on the surface of the glass substrate, and it is possible to obtain a large mechanical strength in which cracks and cracks are unlikely to occur.

  As the chemical strengthening treatment liquid (treated molten salt) containing such Na ions and K ions, sodium nitrate, potassium nitrate, silver nitrate and mixed molten salts thereof are preferably used, but are not limited to nitrates. Sulfates, bisulfates, carbonates, halides and the like may be used.

  The temperature of the chemical strengthening treatment liquid is preferably set to be about 50 to 150 ° C. lower than the strain point of the material of the glass substrate, and more preferably the temperature of the chemical strengthening treatment liquid itself is set to about 350 to 400 ° C. The This is because when the temperature is set lower than 150 ° C. than the strain point of the glass substrate material, chemical strengthening is not sufficiently performed, and when set higher than 50 ° C., the glass substrate is likely to be distorted in the chemical strengthening process. is there.

  By such chemical strengthening, a compressive stress layer is formed on the surface and end face of the glass substrate. The compressive stress layer formed on the end face, particularly the inner peripheral end face, causes deformation of the inner peripheral end face in the present embodiment, and the amount of expansion (elongation) is grasped as the amount of change. The thickness of the compressive stress layer is preferably 20 to 250 μm by adjusting the chemical strengthening treatment conditions for the chemical strengthening. This is because if it is less than 20 μm, the strength of the glass substrate may be reduced, and if it exceeds 250 μm, the production efficiency is unnecessarily deteriorated.

(Cooling process)
After the chemical strengthening process using the chemical strengthening treatment liquid is completed, a plurality of glass substrates are held on the glass substrate holder pulled up from the chemical strengthening treatment liquid. In this cooling step, it is preferable to cool the glass substrate without the chemical strengthening treatment liquid on the main surface, but a large amount of molten liquid is caused by the surface tension at the contact point between the glass substrate and the holding portion for holding the glass substrate. May remain. When the solution is solidified in the cooling process, a difference in thermal expansion occurs between the contact point with the holding part of the glass substrate and the non-contact part (non-contact part), and the expanded state is maintained only at the contact point with the holding part. Since it is condensed later than the other parts, distortion and warping are caused.

  FIG. 1 is an explanatory diagram for explaining the cause of such distortion and warpage. Here, glass substrate 10 is held in a slot formed by a plurality of holding portions 110 of glass substrate holder 100. The distortion and warpage are caused by the temperature distribution in the plane of the glass substrate, and the temperature distribution is caused by the difference in temperature change between the glass substrate 10 and the holding unit 110. This difference in temperature change is caused by the difference in the amount of heat released to the surrounding medium (amount of movement) due to the volume (heat capacity) and surface area of the housing. Therefore, the glass substrate having a larger surface area with respect to the volume, Compared with a glass substrate holder that requires a predetermined housing strength and inevitably increases in volume, it is easier to be cooled. In this way, a difference in temperature change occurs between the glass substrate and the holding part.

  When the difference in temperature change as described above occurs, the heat energy is transferred from the glass substrate holder 100 to the glass substrate 10 via the holding unit 110. Accordingly, in the contact region 112 of the glass substrate 10 with the holding portion 110, thermal energy acts in a direction that hinders cooling, and the contact portion 114 around the contact point of the glass substrate 10 lags behind the other non-contact portion 116. Temperature decreases. Accordingly, the temperature distribution and the temperature change transition in the surface of the glass substrate 10 are not uniform.

  FIG. 2 is a longitudinal sectional view taken along the line AA ′ of FIG. 1 for explaining a contact state of the holding unit 110 arranged to hold the bottom surface of the glass substrate 10. Since the glass substrate 10 is merely placed on the holding unit 110 and is not fixed at all, the glass substrate 10 has play in the direction perpendicular to the main surface of the glass substrate in the holding unit 110. However, the holding part 110 formed with the V-shaped groove according to the present embodiment abuts on the bottom surface of the glass substrate 10 at the two contact areas 112 due to the action of gravity, and is filled with the chemical strengthening treatment liquid 118 around the periphery. The Therefore, in the holding part 110 arrange | positioned at the bottom face of the glass substrate 10, a contact area with the glass substrate 10 becomes very large, and the movement of the thermal energy in a cooling process increases in connection with it. Such a difference in temperature change with the holding unit 110 causes a difference in thermal expansion within the surface of the glass substrate 10 and causes distortion and warpage.

  FIG. 3 is a cross-sectional view taken along the line BB ′ of FIG. 1 for explaining the contact state of the holding unit 110 arranged to hold the side surface of the glass substrate 10. Also in this case, since the glass substrate 10 is not fixed to the holding unit 110, the glass substrate 10 is inclined and contacts only one side of the holding unit 110. Therefore, the contact area 112 is also one point on one side. In the holding part 110 arranged on such a side surface, the chemical strengthening treatment liquid 118 does not remain due to gravity, but only a minute chemical strengthening treatment liquid 118 due to surface tension remains as shown in FIG.

  In this case, since the contact area with the holding part 110 is small and the amount of the remaining chemical strengthening treatment liquid 118 is also small, it seems that distortion and warping at first glance are reduced. However, distortion and warpage can also occur when temperature changes differ between the front and back surfaces of the glass substrate 10. This is equivalent to the mechanism of distortion due to the difference in thermal expansion between the contact portion with the holding portion 110 and other portions, and the object is merely replaced by the front side and the back side of the outer peripheral end surface of the glass substrate 10.

  FIG. 4 is a cross-sectional view for explaining that the glass substrate 10 is distorted due to a temperature change difference between the front and back sides. The glass substrate 10 has a surface 120 and a surface 122. In FIG. 4, the surface 122 side of the outer peripheral end surface of the glass substrate 10 is in contact with the holding unit 110. Accordingly, the surface 122 side has a slower cooling rate than the surface 120 side and maintains a state of thermal expansion. Therefore, only the surface 122 side extends in the substrate radial direction as shown in FIG. Warpage that becomes a concave shape occurs. When the undulation due to this warp is measured through an optical flat for measuring interference fringes, the value reaches 8 nm. Therefore, in order to prevent distortion and warpage, it can be understood that the temperature change difference between the front and back surfaces of the glass substrate 10 must be taken into account as well as the temperature change difference between the glass substrate 10 and the holding unit 110.

  The inventor of the present application pays attention to the fact that the cause of distortion and warpage is caused by the movement of heat due to the large contact area between the glass substrate and the holding part, and the chemical strengthening locally remaining on the main surface of the glass substrate. By configuring the glass substrate holder so that the processing liquid can be quickly removed, the chemical strengthening processing liquid can be quickly and reliably removed from the main surface, and the contact area between the glass substrate and the holding part can be minimized. This makes it possible to eliminate distortion and warpage of the glass substrate. Here, the glass substrate holder 200 of this embodiment used for the cooling process after a chemical strengthening process is demonstrated first.

(Glass substrate holder 200)
FIG. 5 is a perspective view showing the configuration of the glass substrate holder 200. The glass substrate holder 200 includes a holding unit 210 and a fixing unit 220, and holds the glass substrate 10 at least during the cooling process.

  Such a glass substrate holder 200 may be used in combination with a chemical strengthening process preceding the cooling process, or only the cooling process may be used. In other words, chemical strengthening may be performed while the glass substrate 10 is held in the glass substrate holder 200, and then the cooling process may be performed while maintaining the state where the glass substrate 10 is held. The heated glass substrate 10 may be transferred to the glass substrate holder 200 to perform the cooling process. The chemical strengthening process assumes that the entire glass substrate 10 is chemically strengthened. However, when only a part of the glass substrate 10, for example, an end face (including a chamfered surface) is chemically strengthened, only the main surface is chemically strengthened. You can also.

  The holding part 210 is formed by bending a plate-like thin plate 212 as a base, and a plurality of protrusions are formed on the surface of the bulging side so that the protrusions are wavy in the longitudinal direction. A thread 214 is stretched in a V shape in a U-shaped groove formed between the protrusions. Then, the glass substrate 10 is placed on the V-shaped thread 214.

  The thread 214 may be formed of a metal wire. Since the metal wire is strong in environmental resistance and has a low coefficient of thermal expansion, it does not deform even at high temperatures in chemical strengthening. In addition, since there is little deterioration due to aging, appropriate elasticity (tension) can be maintained over a long period of time. Therefore, the number of complicated maintenance operations can be reduced, and a glass substrate excellent in low roughness and flatness can be supplied stably.

  6 and 7 are longitudinal sectional views showing in detail the structure in which the holding unit 210 holds the glass substrate 10. Here, FIG. 6A shows the holding unit 210 on the bottom surface of the glass substrate holder 200, and FIG. 7 shows the holding unit 210 on the side surface. As shown in FIG. 6A, the thread 214 formed by being stretched on the plate material 212 is composed of the main surface 12 of the glass substrate 10 and the chamfered surface 16 formed between the main surface 12 and the end surface 14. Are formed so that the cross-sectional shape including the contact point at the two boundary portions 18 is substantially V-shaped. Such a structure of the holding portion 210 is similarly formed on the side surface (see FIG. 7).

  With this configuration, the chemical strengthening treatment liquid remaining locally on the glass substrate 10, particularly on the main surface 12, can be quickly taken out, and the chemical strengthening treatment liquid can be quickly and reliably removed from the main surface 12. Accordingly, the glass substrate 10 and the holding unit 210 are more reliably in contact with each other only with a point.

  Further, by forming the thread 214 in a substantially V shape as shown in FIG. 6A, even if the glass substrate 10 is slightly tilted from the direction perpendicular to the holding part 210, the point contact with the boundary part 18 is maintained. Therefore, even if the glass substrate 10 is appropriately arranged on the glass substrate holder 200, the contact area between the glass substrate 10 and the holding unit 210 can be kept to a minimum.

  Further, the angle 20 formed by the main surface 12 and the yarn 214 at the contact point between the yarn 214 stretched in a substantially V shape and the boundary portion 18 may be less than 45 °.

  The chamfered surface 16 of the present embodiment is formed with an inclination of 45 ° with respect to the main surface 12. Therefore, by setting the angle 20 formed between the main surface 12 and the yarn 214 to be less than 45 °, the glass substrate 10 and the yarn 214 do not face or line contact with the chamfer 16 or the main surface 12. Only point contact.

  Furthermore, it is desirable that the angle 20 formed by the main surface 12 and the thread 214 is 22.5 ° as shown in FIG. By setting the angle 20 formed between the main surface 12 and the thread 214 to 22.5 °, the angle 22 formed between the chamfered surface 16 and the thread 214 is also 22.5 °, and the main surface 12 and the chamfered surface 16 and the thread are aligned. The contact angle with 214 becomes uniform. Accordingly, since the surface tension between the main surface 12 and the chamfered surface 16 and the yarn 214 can be minimized, the remaining chemical strengthening treatment liquid can be reduced.

  In this way, the chemical strengthening treatment liquid locally remaining on the main surface 12 of the glass substrate 10 is quickly taken out, so that the chemical strengthening treatment liquid can be quickly and reliably removed from the main surface 12. It is possible to prevent the chemical strengthening treatment liquid from being solidified. Moreover, the movement of the heat | fever between the glass substrate 10 and the holding | maintenance part 210 is suppressed by reducing a contact area. Thus, it is possible to make the temperature change of the entire glass substrate 10 uniform, and it is possible to prevent the glass substrate 10 from being distorted or warped.

  Here, if held at the boundary between the chamfered surface 16 and the end surface 14 of the glass substrate 10, the yarn 214 intersects at a shallow angle, so the chemical strengthening treatment liquid cannot be taken out due to its surface tension, Many chemical strengthening processing liquids remain and solidify. Therefore, it is very important in the present embodiment that the yarn 214 abuts on the boundary portion 18 between the main surface 12 and the chamfered surface 16 as described above.

  Further, the thread 214 may be stretched so as to have elasticity. By giving elasticity to the holding part 210, the rigidity is reduced as compared with the conventional rigid holding part, the expansion and contraction of the glass substrate 10 can be absorbed, and the reaction force applied to the glass substrate 10 is reduced. .

  In addition, it is possible to mitigate the transmission of the glass substrate 10 to the glass substrate 10 due to the impact when the glass substrate 10 is arranged on the glass substrate holder 200, the movement of the glass substrate holder 200, and the like. No need to spend Furthermore, on the side surface of the glass substrate 10, as shown in FIG. 7, the glass substrate 10 is pressed and fixed by the elasticity of the holding portion 210, and it can be prevented from vibrating due to play in the glass substrate holder 200.

  The boundary portion 18 is formed of a curved surface having a radius of curvature (1 / R) of 5 (= 1 / 0.200 mm) to 200 (= 1 / 0.005 mm), and the yarn 214 is formed on the curved surface of the boundary portion 18. You may make point contact. With this configuration, even if the glass substrate 10 is slightly tilted and abuts against the thread 214, the point contact with the boundary portion 18 is maintained, and the contact area between the glass substrate 10 and the holding portion 210 can be kept to a minimum. It becomes.

  The fixing part 220 includes two holding fixing parts 222 for fixing the holding part 210 and four reinforcing plates 224 connected to the holding fixing part 222 in order to increase the strength of the holding fixing part 222. The

  As described above, in the method for manufacturing a magnetic disk glass substrate according to this embodiment, the glass substrate 10 is cooled in a state where the glass substrate 10 is held by the holding portion 210 of the glass substrate holder 200. At this time, the chemical strengthening treatment liquid adhering to the main surface of the glass substrate 10 is quickly taken out along the yarn 214, and the chemical strengthening treatment liquid is quickly and reliably removed from the main surface 12.

  With this configuration, the cooling rate of the entire glass substrate 10 can be made uniform, and distortion and warpage of the glass substrate can be prevented. Therefore, a magnetic disk glass substrate having excellent flatness can be produced, yield can be increased, and high productivity can be stably obtained.

  Further, not only in the cooling step described above, but also in the chemical strengthening step in the previous step, a difference in heating rate occurs between the portion in contact with the glass substrate holder 200 and the other non-contact portion, Local distortion and warping occur. Such distortion or warpage becomes a minute convex or concave shape on the magnetic disk surface and causes the above-described thermal asperity failure.

  Also in the chemical strengthening step, the glass substrate 10 and the holding unit 210 are insulated by minimizing the contact area between the glass substrate 10 and the holding unit 210 by using the glass substrate holder 200 of the present embodiment. It becomes possible to make the whole temperature change uniform. Accordingly, it is possible to prevent the glass substrate from being distorted or warped even in the chemical strengthening step. Here, it is assumed that the entire glass substrate 10 is chemically strengthened, but the glass substrate 10 is partially targeted for chemical strengthening, for example, only the end surface 14 (which may include the chamfered surface 16). You can also.

  In this way, it is possible to alleviate the obstruction of the magnetic head slider's flying and pseudo-levitation running characteristics in LMR (horizontal magnetic recording) and PWR (perpendicular magnetic recording) type HDDs, and to realize a higher recording density.

  Hereinafter, examples of the chemical strengthening process and the cooling process for performing the above-described chemical strengthening will be described.

[Example 1]
In this example, a glass substrate for magnetic disk and a magnetic disk were manufactured through the following steps. In particular, in (6) the chemical strengthening step and the cooling step, the chemical strengthening step and the cooling step according to the present embodiment are applied.

(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. In addition, the glass for chemical strengthening was used as aluminosilicate glass. 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 fusion method, 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 In addition to aluminosilicate glass, soda lime glass can be used as the glass.

  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 on both sides of the plate glass from above and below, the grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relative to each other for 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, a circular hole was formed in the center of the glass substrate to obtain a donut-shaped glass substrate (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) 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.

(4) End surface polishing process Next, the end surface of the glass substrate was mirror-polished by a brush polishing method. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used. 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.

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

  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.

  Next, a second polishing step was performed as the main surface polishing step. 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 foamed resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the polishing liquid, cerium oxide abrasive grains finer than the cerium oxide abrasive grains used in the first polishing step were used.

  The glass substrate which finished this 2nd grinding | polishing process was immersed in each washing | cleaning tank of neutral detergent, a pure water, and IPA sequentially, and was wash | cleaned. Note that ultrasonic waves were applied to each cleaning tank.

(6) Chemical strengthening process and cooling process Next, the glass substrate which finished the above-mentioned lapping process and polishing process was chemically strengthened. By performing chemical strengthening in this way, a high compressive stress can be generated in the surface layer portion of the magnetic disk substrate, and the impact resistance can be improved.

  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 is heated to 300 ° C. The sample was preheated and immersed in a chemical strengthening solution for about 3 hours. In the immersion, the glass substrate holder in the present embodiment was applied. Such glass substrate holders hold a plurality of glass substrates at their end faces. Therefore, the entire surface of the glass substrate can be chemically strengthened.

  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.

  When the glass substrate holder according to the present embodiment is used in such a chemical strengthening process, no heat transfer occurs between the glass substrate immersed in the chemical strengthening solution and the glass substrate holder, so that a glass substrate with good flatness is obtained. Generated.

  Subsequently, the glass substrate after the chemical strengthening step was cooled by being immersed in a 20 ° C. water bath while being held in the glass substrate holder of the present embodiment, and maintained for about 10 minutes. And the glass substrate which finished cooling was immersed in the concentrated sulfuric acid heated at about 40 degreeC, and was wash | cleaned. Furthermore, the glass substrate that had been subjected to the sulfuric acid cleaning was sequentially immersed and cleaned in each of pure water and IPA cleaning tanks. In addition, ultrasonic waves were applied to each cleaning tank.

  Since the glass substrate holder according to the present embodiment does not cause heat transfer between the glass substrate and the glass substrate holder even in such a cooling process, a glass substrate with a better flatness is generated.

[Comparison]
Here, the magnetic disk generated according to the present embodiment is compared with a conventional comparative example (one that has been cooled without using the glass substrate holder of the present invention), and determined as defective due to cracks, chipping, warping, or the like. The incidence of those that were made was compared. Such cracks, chips, and defective products are measured visually or using a measuring device with respect to 100,000 samples.

  As described above, a flat, smooth, high-rigidity glass substrate for a magnetic disk is obtained by performing the first lapping step, the cutting step, the second lapping step, the end surface polishing step, the main surface polishing step, and the chemical strengthening step. Obtained.

(7) Precision cleaning process Next, the glass substrate for magnetic disks in which the texture was formed was precisely cleaned. This is to remove abrasive residues and foreign iron-based contaminants that cause head crush and thermal asperity failure, and to obtain a glass substrate with a smooth surface and a clean surface. As a precision cleaning process, a water rinse cleaning and an IPA cleaning process were performed after cleaning with an alkaline aqueous solution.

(8) 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.

  The obtained magnetic disk was confirmed to be free from defects in the film such as the magnetic layer due to foreign matter. In addition, when the glide test was performed, no hit (the head bited against the protrusion on the surface of the magnetic disk) or crash (the head collided with the protrusion on the surface of the magnetic disk) was not recognized. Furthermore, when a reproduction test was conducted with a magnetoresistive head, no malfunction of reproduction due to thermal asperity was found.

  Further, when the glass substrate for the magnetic disk is manufactured using the glass substrate holder of the present embodiment and the glass substrate manufactured by the method of the comparative example is each a magnetic disk, It was found that the magnetic disk manufactured using the glass substrate manufactured according to the embodiment has a smaller head crash rate.

  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.

  In addition, each process in the manufacturing method of the glass substrate for magnetic disks of this specification does not necessarily need to process in time series along the order described in the specification, and the process (in parallel or separately performed ( For example, parallel processing or object processing) may be included.

  The present invention is applicable to a method for manufacturing a glass substrate for a magnetic disk including a chemical strengthening step or a subsequent cooling step, a method for manufacturing a magnetic disk, and a glass substrate holder.

It is explanatory drawing for demonstrating the cause of distortion and curvature. It is a longitudinal cross-sectional view in FIG. 1 AA 'line for demonstrating the contact state of the holding | maintenance part arrange | positioned so that the bottom face of a glass substrate may be hold | maintained. It is a cross-sectional view in FIG. 1BB 'line for demonstrating the contact state of the holding part arrange | positioned so that the side surface of a glass substrate may be hold | maintained. It is a cross-sectional view for explaining that a glass substrate is distorted by a temperature change difference between the front and back sides. It is the perspective view which showed the structure of the glass substrate holder. It is the longitudinal cross-sectional view which showed in detail the structure where a holding | maintenance part hold | maintains a glass substrate. It is the longitudinal cross-sectional view which showed in detail the structure where a holding | maintenance part hold | maintains a glass substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Glass substrate 100 ... Glass substrate holder 110, 210 ... Holding part 112 ... Contact area 114 ... Contact part 116 ... Non-contact part 118 ... Chemical strengthening process liquid 200 ... Glass substrate holder 214 ... Yarn

Claims (10)

A chemical strengthening step of chemically strengthening the glass substrate by immersing a disc-shaped glass substrate in a chemical strengthening treatment solution in which a chemically strengthened salt is dissolved by heating, and ion exchange, and a glass substrate heated by the chemical strengthening step A cooling step of cooling in a state of being held in a glass substrate holder, and a manufacturing method of a glass substrate for a magnetic disk comprising:
The holding part of the glass substrate holder is formed by stretching a plurality of threads in a substantially V shape so as to have elasticity,
The yarn comes into contact with the boundary between the main surface of the glass substrate and the outer chamfered surface, and the glass substrate is held from both sides by point contact, thereby uniformizing the temperature change of the entire glass substrate in the cooling step. A method for producing a glass substrate for a magnetic disk, comprising: The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the holding portion of the glass substrate holder presses and fixes the glass substrate by the elasticity.   3. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein at least the yarn is brought into contact with a boundary portion between a lowermost main surface of the outer periphery of the glass substrate and the outer peripheral chamfered surface. . Wherein the angle between the yarn and the main surface of the front Symbol glass substrate is less than 45 °, the manufacturing method of the glass substrate according to any one of claims 1 to 3. 5. The method of manufacturing a glass substrate for a magnetic disk according to claim 4, wherein the angle formed between the main surface of the glass substrate and the yarn is equal on both sides. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the yarn is a metal wire. The boundary portion is formed by a curved surface, the holding unit is characterized in that in point contact with the curved surface of the boundary portion, it claims 1-6 or method of manufacturing a glass substrate for a magnetic disk according to the.   The method for producing a magnetic disk according to claim 1, comprising a step of forming at least a magnetic layer on the surface of the glass substrate obtained by the method for producing a glass substrate for a magnetic disk. . In order to cool a glass substrate heated in the chemical strengthening after chemical strengthening of the glass substrate by immersing a disk-shaped glass substrate in a chemical strengthening treatment solution in which a chemically strengthened salt is dissolved by heating and exchanging ions. A glass substrate holder used for
The glass substrate holder includes a holding portion formed by stretching a plurality of threads in a substantially V shape so as to have elasticity,
The holding portion is configured such that the yarn contacts the boundary portion between the main surface and the outer peripheral chamfer of the glass substrate, and holds the glass substrate from both sides by point contact, so that the entire glass substrate in the cooling step is A glass substrate holder characterized by uniformizing temperature changes . The holding portion bends the thin plate so as to have a wave shape in the longitudinal direction, and the plurality of threads are stretched in a substantially V shape in a U-shaped groove portion between the protruding portions on the bulging side of the wavy thin plate. The glass substrate holder according to claim 9, wherein the glass substrate holder is formed.

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