JP5344839B2 - Method for manufacturing glass substrate for magnetic disk and method for manufacturing magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an inside diameter dimensional error of a glass substrate for a magnetic disk while a compression stress layer obtained by chemical strengthening is held. <P>SOLUTION: A chemical strengthening treatment liquid of a chemical strengthening treatment vessel 130 is brought into contact with a disk like glass substrate 102 having a circular hole in its center, so that partial ions contained in the glass substrate 102 are replaced with ions in the chemical strengthening treatment liquid to chemically strengthen the glass substrate 102. Thereby the compression stress layer having &lt;150 &mu;m thickness is formed on the inner peripheral end surface and the like of the surface of the glass substrate 102. Inner peripheral end surface polishing is then performed with &lt;5 &mu;m stock removal using an inner peripheral end surface polishing device by a shape transfer machining method. The polishing of the inner peripheral end surface is so performed that the compression stress layer formed on the inner peripheral end surface of the glass substrate 102 in the chemical strengthening step remains. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

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 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.

  In addition, with the increase in the density of magnetic recording media, 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 flying height is getting smaller. A magnetic head equipped with such a magnetoresistive element may cause a thermal asperity failure as an inherent failure. In thermal asperity failure, when the magnetic head passes over a minute convex or concave shape on the magnetic disk surface while flying, the magnetoresistive element is heated by adiabatic compression or contact of air, and a read error occurs. It is an obstacle.

  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 also required to be highly cleaned to completely remove dust and foreign matters.

  In addition to the smoothness and flatness of the magnetic disk surface, strict accuracy control is required for the inner diameter dimensional error in the circular hole provided in the center of the magnetic disk. This is because the dimensional error of the inner peripheral end surface of the magnetic disk directly affects the installation accuracy when the magnetic disk is fitted to the HDD spindle motor. In addition, if the inner diameter dimensional error is large, there is a possibility of inducing a mechanical error in stacking servo (writing servo information to the magnetic disk) performed before the magnetic disk is assembled in a magnetic disk device such as an HDD, There is a possibility of causing a mating failure with the spindle during disk stacking. The inner peripheral end surface of the magnetic disk has a smaller surface area than the main surface, and if the rotation center of the magnetic disk is displaced due to an inner diameter dimensional error, it becomes difficult to position the HDD head at the correct position on the HDD. Will not be able to record / play.

  Further, since data is read and written while the magnetic disk rotates at a high speed, it is necessary to prevent data on the magnetic disk from being blurred even at the high speed rotation. Therefore, it is particularly important to manage the accuracy of the inner diameter error of the magnetic disk substrate.

  Further, paying attention to the data access of the HDD, in order to accurately store / reproduce the data of the magnetic disk incorporated in the HDD, a servo pattern serving as a positioning index is written in advance on the magnetic disk. This servo pattern writing is executed by inserting a magnetic disk in a device called a servo writer. Then, the magnetic disk on which the servo pattern is written is once detached from the servo writer and is inserted into a spindle motor of the HDD as a product.

  If the inner diameter error of the magnetic disk is large, the position of the servo pattern and the recording / reproducing head of the HDD as a product will be shifted when the magnetic disk is installed in the HDD. Will not be done. Although a technique for adjusting alignment to correct such a positional relationship has been disclosed (for example, Patent Document 1), a fundamental solution for suppressing an inner diameter dimensional error has not been made.

In this way, the demand for higher recording density of magnetic disks is increasing further in recent years, and management of inner diameter dimensional errors that are more severe than those of conventional glass substrates for magnetic disks is required.
JP 2004-199841 A

  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. Such chemical strengthening treatment can improve the impact resistance and vibration resistance of the glass substrate, and can prevent the glass substrate from being damaged by the impact and vibration.

  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 immersing it in the molten salt (chemical strengthening treatment liquid) in a state where the glass substrate to be treated is stored in a glass substrate holder. The ion exchange is performed between the glass substrate and the molten salt.

  At this time, a phenomenon occurs in which the inner diameter of the glass substrate changes before and after the chemical strengthening step, that is, the inner diameter changes as the glass substrate expands toward the center of the inner diameter. This is because when the glass substrate is subjected to a chemical strengthening treatment, a compressive stress is generated on the surface of the glass substrate, and the dimensions of the glass substrate change due to the compressive stress.

  Further, the composition of the chemical strengthening treatment liquid changes with time. Specifically, in the chemical strengthening treatment, the ions contained in the chemical strengthening treatment liquid and the ions contained in the glass substrate are ion-exchanged, so that the chemical strengthening treatment proceeds as the chemical strengthening treatment proceeds. In the strengthening treatment liquid, ions contained in the ion-exchanged glass substrate increase. This change in composition contributes to changing the inner diameter of the glass substrate during chemical strengthening. The amount of change in the inner diameter is not negligible with respect to the inner diameter error of the glass substrate, which is more strictly demanded. Therefore, the glass substrate has a high inner diameter including the amount of change in the inner diameter in the chemical strengthening process. Dimensional accuracy is required.

  Furthermore, when the inner diameter of the glass substrate after the inner peripheral processing step also has a certain dimensional error, and the inner diameter of the glass substrate of the glass substrate before the chemical strengthening treatment is smaller or larger than a predetermined design value, Through chemical strengthening treatment under certain chemical strengthening treatment conditions, the dimensional accuracy is further deteriorated together with the dimensional error, and a large number of defective products are produced.

  The inventors of the present application have grasped the relationship between the chemical strengthening treatment condition and the amount of change (elongation) in the inner diameter of the glass substrate when the chemical strengthening treatment is performed under the chemical strengthening treatment condition, and the glass substrate before the chemical strengthening treatment. By performing chemical strengthening treatment under appropriate chemical strengthening treatment conditions based on the difference between the desired inner diameter dimension and the final inner diameter, and performing inner peripheral end face polishing with an appropriate machining allowance after the chemical strengthening treatment. In order to complete the present invention, it has been found that even if the inner diameter of the glass substrate before chemical strengthening treatment deviates from a predetermined design value, the final inner diameter dimensional accuracy of the glass substrate can be improved. It came.

  In view of such a problem, the present invention provides a method for producing a glass substrate for magnetic disk and a magnetic device capable of reducing an inner diameter dimensional error of the glass substrate for magnetic disk while retaining a compressive stress layer obtained by chemical strengthening. An object is to provide a method for manufacturing a disk.

Method of manufacturing a glass substrate for a magnetic disk according to the present invention is a process for producing a glass substrate for a magnetic disk to produce a disk-shaped glass substrate having a circular hole is formed in the center, Li inner diameter from the desired value is different The chemical strengthening treatment liquid is brought into contact with the glass substrate of the aluminosilicate glass containing ions, and a part of the ions contained in the glass substrate is replaced with ions in the chemical strengthening treatment solution, thereby forming a compressive stress layer and reducing the inner diameter. A chemical strengthening process for obtaining a glass substrate having an inner diameter smaller than a desired value, and polishing the inner peripheral end surface of the chemically strengthened glass substrate so as to leave a compressive stress layer, so that the inner diameter of the glass substrate is reduced. and a inner peripheral end face polishing process of adjusting to a desired value, the chemical strengthening treatment conditions in the chemical strengthening process, based on the relationship between the previously grasped chemical strengthening treatment conditions and the inner diameter of the variation of the glass substrate As the composition of the chemical strengthening treatment liquid used in the chemical strengthening step changes according to the number of treatments, the allowance for end face polishing in the inner peripheral end face polishing step is adjusted within a range of less than 5 μm. The inner diameter of the substrate is adjusted to a desired value .

According to the present invention, in addition to performing chemical strengthening treatment under predetermined chemical strengthening treatment conditions, the inner diameter of the glass substrate before chemical strengthening treatment is determined in advance in order to polish the inner peripheral end surface by appropriate machining allowance thereafter. Even if it deviates from the designed value, it is possible to realize an inner diameter dimension with a smaller error. In addition, it is good for the machining allowance in an inner peripheral end surface grinding | polishing process to be less than 5 micrometers. This is to reduce the machining allowance as much as possible so that the compressive stress layer formed by chemical strengthening can be retained to the maximum extent.

  The expansion caused by the chemical strengthening treatment can be grasped in advance by setting the chemical strengthening treatment conditions, but it cannot be as accurate as the polishing treatment of the inner peripheral end face. However, as in the present invention, in the last step after chemical strengthening, if a machining allowance that can be controlled with high accuracy is determined and end face polishing is performed, the desired shape can be approached with smaller errors.

  However, the polishing performed in the final stage needs to be performed within a range in which the compressive stress layer formed on the inner peripheral end face of the glass substrate remains in the chemical strengthening process. This is to prevent the effect of the chemical strengthening treatment from being lost.

  The thickness of the compressive stress layer formed in the above-described chemical strengthening step is preferably less than 150 μm.

  In the inner peripheral end face polishing step described above, the inner peripheral end face may be polished by shape transfer processing. This is because, according to the shape transfer processing, it is possible to significantly reduce the error of the inner diameter dimension as compared with, for example, polishing with a brush.

Further, in the magnetic disk producing method according to the present invention is to produce a glass substrate for a magnetic disk by a method according to any of the above, the surface of the magnetic disk glass substrate, and wherein the Turkey to form at least a magnetic layer To do.

  As described above, according to the present invention, it is possible to reduce the inner diameter dimensional error of the magnetic disk glass substrate while retaining the compressive stress layer obtained by chemical strengthening.

  Next, embodiments of a method for manufacturing a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk according to the present invention will be described in detail with reference to the accompanying drawings. In the figure, elements not directly related to the embodiment of the present invention are not shown. Similar elements are denoted by the same reference numerals.

(Adjustment of chemical strengthening treatment conditions in chemical strengthening process)
With the miniaturization, thinning, and high-density recording of magnetic disks, high smoothness and flatness of the inner peripheral surface of the glass substrate are required. The present embodiment focuses on the inner peripheral end surface of the glass substrate, particularly the amount of change in the chemical strengthening process, and aims to reduce the final inner diameter (ID) dimensional error of the glass substrate. Hereinafter, a glass disk substrate manufacturing system 200 capable of performing a series of steps including a chemical strengthening step will be described.

  FIG. 1 is a functional block diagram showing a glass disk substrate manufacturing system 200 according to the present embodiment. The manufacturing system 200 of the glass substrate 102 for magnetic disks of FIG. 1 is comprised including the inner peripheral end surface grinding apparatus 110, the chemical strengthening processing tank 130, and the inner peripheral end surface polishing apparatus 120. Here, in order to facilitate understanding, the manufacturing system 200 for a magnetic disk glass substrate is described with reference to the manufacturing process particularly for the inner peripheral end surface of the glass substrate 102. However, in the actual process, the surface of the glass substrate 102 and It goes without saying that the manufacturing process of the outer peripheral end face is also included.

  The inner peripheral end surface grinding device 110 functions as an inner peripheral processing device, and, for example, the inner peripheral end surface in a circular hole formed at the center of a disk-shaped glass substrate 102 made of multicomponent glass is ground by a grinding amount. To do. The inner peripheral end surface grinding device 110 can be configured in various forms as long as the inner peripheral end surface of the glass substrate 102 can be ground. For example, the inner peripheral end surface is chamfered (chamfer: chamfer). It is also possible to configure with a device.

  FIG. 2 is an explanatory diagram for explaining a grinding process of the inner peripheral end surface grinding apparatus 110. Here, as shown in FIG. 2A, the inner peripheral end surface 114 formed by the circular holes 112 of the disk-shaped glass substrate 102 is ground and chamfered.

  In the inner peripheral end surface grinding apparatus 110, as shown in FIG. 2B, an inner diameter grinding wheel 116 for grinding is inserted into the circular hole 112. The plurality of glass substrates 102 stacked in a cylindrical shape are sandwiched between two upper and lower bottom surfaces by a sandwiching member. The inner diameter grinding wheel 116 is a pulley-like rotary grinding wheel, and its outer periphery is a grinding surface.

  The glass substrate 102 and the inner diameter grinding wheel 116 are rotationally driven by a fixed driving means (not shown), and the inner diameter grinding wheel 116 is brought into contact with the inner peripheral end surface 114 of the cylindrical glass substrate 102 so that each glass is brought into contact with each other. The substrate 102 is subjected to uniform inner diameter processing. The rotation direction is set so as to be the opposite direction at each contact point. The inner peripheral end face 114 and the chamfer 114a as shown in FIG. 2C are formed by the grinding process of the inner peripheral end face. In addition, the outer peripheral end face can be ground simultaneously with the grinding of the inner peripheral end face 114.

  The inner peripheral end surface polishing apparatus 120 functions as an inner peripheral processing apparatus like the inner peripheral end surface grinding apparatus 110, and further polishes the inner peripheral end face 114 of the glass substrate 102 ground by the inner peripheral end surface grinding apparatus 110 by a polishing amount. To do.

  FIG. 3 is an explanatory diagram for explaining immersion of the glass substrate 102 in the chemical strengthening treatment liquid. Here, a glass substrate holder 132 made of a metal material and a treatment tank 134 containing a chemical strengthening treatment liquid are shown. The glass substrate holder 132 is provided with a holding portion 136 in which a plate-like thin plate is curved, and a plurality of protrusions are formed in a wave shape in the longitudinal direction on the surface on the bulging side. One glass substrate 102 is held in each V-shaped groove formed between the protrusions. And after all the glass substrates 102 which should be processed by one chemical strengthening are arrange | positioned, the glass substrate 102 is immersed in the processing tank 134 with the glass substrate holder 132 for a predetermined time.

  The temperature of the chemical strengthening treatment liquid is preferably set to about 100 to 150 ° C. lower than the glass transition point of the material of the glass substrate 102, and more preferably the temperature of the chemical strengthening treatment liquid itself is set to about 350 to 400 ° C. Is done. This is because when the temperature is set lower than 150 ° C from the glass transition point of the material of the glass substrate 102, the chemical strengthening treatment is not sufficiently performed, and when set higher than the temperature lower than 100 ° C, the glass substrate is warped in the chemical strengthening treatment. This is because it becomes easier.

  By such chemical strengthening treatment, a compressive stress layer is formed on the surface and the end face of the glass substrate 102. 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 less than 150 μm by adjusting the chemical strengthening treatment conditions for the chemical strengthening. This is because if the compressive stress layer is 150 μm or more, the production efficiency is unnecessarily deteriorated.

  FIG. 4 is a longitudinal sectional view for explaining the configuration of the inner peripheral end surface polishing apparatus 120. The inner peripheral end surface polishing device 120 is a device that polishes the inner peripheral end surface of the glass substrate 102 by shape transfer processing. The plurality of glass substrates 102 stacked in a cylindrical shape are fixed to the fixing portion 122 of the inner peripheral end surface polishing apparatus 120. One or both of the glass substrates 102 is arranged so that the glass substrate 102 and the polishing body 124 inserted into the circular hole of the glass substrate 102 are relatively rubbed with the center axis of the disk of the glass substrate 102 as the center of rotation. Is rotated to polish the inner peripheral end surface of the glass substrate 102.

  The inner peripheral end surface polishing apparatus 120 includes a body to be polished 12, a fixed portion 122, a polishing body 124, and a polishing driving unit 18, and a plurality of the objects to be polished 12 formed in a cylindrical shape are stacked. The inner peripheral end surface of the is polished.

  The object to be polished 12 is formed in a cylindrical shape by laminating a plurality of glass substrates 102. Each glass substrate 102 is chamfered at the outer peripheral end surface and the inner peripheral end surface in the grinding step, and as shown in the enlarged view of FIG. 4, for example, an inner peripheral end surface (T surface) 114 and a chamfer (C surface) 114a are formed. Has been. Further, the glass substrates 102 are laminated with a spacer 26 interposed therebetween. The spacer 26 is provided in order to prevent the chamfer 114a of the inner peripheral end surface of the glass substrate 102 from being left unpolished by the polishing brush and to prevent damage to the glass substrate or the like during polishing.

  The fixing portion 122 mainly includes a substrate case 30, a fastening cover 32, and a rotation holding base 34. The substrate case 30 serves to store the object to be polished 12. Specifically, the object to be polished 12 is fastened via the collar 36 by the substrate case 30 and the fastening cover 32 fitted to the substrate case 30. By tightening the substrate case 30 and the tightening cover 32, the arrangement of the glass substrates 102 as the object to be polished 12 can be maintained without being affected by the rotation of the fixing portion 122 and the rotation of the polishing body 124 described later. it can.

  In addition, the rotation holding table 34 can fix and hold the substrate case 30 and rotate the substrate case 30 in both forward and reverse directions. The rotation speed of the rotation holding table 34 can be adjusted, and an appropriate rotation speed can be selected according to the purpose of polishing.

  The polishing body 124 has a rotation axis that is orthogonal to the glass substrate 102 of the body 12 to be polished, coincides with the central axis of the inner hole of the body 12 to be polished, and serves as the rotation center of the polishing body 124. And a plurality of polishing cloths 126 provided on the side wall of the polishing body 140. The plurality of polishing cloths 126 may be formed of a soft polisher made of suede or velor, or a hard polisher such as hard velor, foamed resin, or pitch-impregnated suede. It is arranged to make a part. The polishing cloth 126 may be arranged so that the centers thereof are substantially equidistant from each other on an arbitrary circumference. That is, the polishing body 124 may have a configuration in which a plurality of polishing cloths 126 are arranged at substantially equal intervals around the central axis.

(Shape transfer processing)
The outer diameter of the polishing body 124 is formed in a curved surface along the inner diameter shape of the glass substrate 102, and conforms to the circumferential surface 150 of the inner diameter of the glass substrate 102. That is, the inner peripheral end face is polished by shape transfer processing. The polishing body 124 is brought into contact with the inner peripheral end surface of the object to be polished 12 with the same pressure, and a polishing liquid is supplied between the inner peripheral end surface of the object to be polished 12 and the polishing body 124. 4 is rotated in the direction of the arrow shown on the polishing body 124 in FIG. Here, the rotation around the rotation axis of the polishing body 124 is set as the rotation, but the movement is not limited to this operation, and the movement of the polishing body 124 in the direction of the rotation axis is also included.

  At this time, the glass substrate 102 may be fixed to the fixing portion 122 and not rotated. This is because the inner periphery of the glass substrate 102 and the outer periphery of the polishing body 124 are matched, so that a sufficient polishing speed can be obtained only by the rotation of the polishing body 124. However, this does not prevent the glass substrate 102 from being polished by rotating in the direction opposite to the rotation direction of the polishing body 124. Specifically, for example, the polishing body 124 may be fixed and only the glass substrate 102 may be rotated. Conversely, only the polishing body 124 may be rotated while the glass substrate 102 is fixed. You may rotate both relatively.

  Further, the polishing body 124 may polish the entire inner peripheral end surface of the object to be polished 12 by swinging slowly (stroke) in the direction of the rotation axis in the inner hole with respect to the glass substrate 102.

  Since the polishing cloth 126 of the polishing body 124 corresponds to the inner diameter of the glass substrate 102, that is, is formed in a curved surface having the same radius as the inner peripheral curved surface of the glass substrate 102, the polishing cloth 126 of the polishing body 124. Can be brought into surface contact with the inner peripheral end surface of the glass substrate 102 and can be pressed against the inner peripheral end surface with an equal predetermined pressing force. In this way, the inner peripheral end face can be polished smoothly, and a small and stable inner diameter roundness and concentricity and low inner diameter tolerance can be achieved. Further, since the polishing body 124 and the glass substrate 102 are in surface contact, the unit pressing force applied to each polishing cloth 126 is low, polishing heat can be suppressed, and deterioration of the inner peripheral end surface of the glass substrate 102 can be prevented.

  Here, the polishing pad 126 and the inner peripheral end surface of the glass substrate 102 are preferably in surface contact with each other by 50% or more, and more preferably by 60% or more. By making the surface contact 50% or more or 60% or more, when the polishing body 124 is rotated, it can be stably operated, and the polishing rate can be improved by increasing the ratio of the surface contact. Can do. In addition, by increasing the contact area between the polishing cloth 126 and the inner peripheral end surface of the object to be polished in this way, the polishing rate can be increased, and a glass substrate with better inner diameter roundness and concentricity can be obtained. Can be obtained.

  However, if the number of the polishing cloths 126 of the polishing body 124 is an odd number, the pressing force to the inner peripheral end face may be biased. Therefore, the polishing cloth 126 is an even number, and the pair of polishing cloths 126 are opposed to each other. It is desirable to place cloth 126. In FIG. 4, six polishing cloths 126 are arranged, and two pairs of each of the polishing cloths 126 are formed to face each other with the circular center of the polishing body 124 interposed therebetween. Therefore, the pressing force on the inner peripheral end face becomes uniform, and the inner diameter roundness and concentricity can be further reduced.

  Further, in the present embodiment, it has been described that the outer diameter of the polishing body 124 corresponds to the inner diameter of the glass substrate 102. However, when the outer diameter of the polishing body 124 and the inner diameter of the glass substrate 102 do not match, the polishing body 124. It is necessary to adjust the outer diameter of the. The polishing body 124 in the present embodiment moves the plurality of polishing cloths 126 described above in a direction perpendicular to the extending direction of the rotation axis, that is, expands / contracts the polishing body 124, so that the inner peripheral end surface of the glass substrate 102 You may press-contact to.

  Further, when the polishing body 124 is inserted into or extracted from the glass substrate 102, the outer diameter of the polishing body 124 is temporarily reduced in order not to damage the inner periphery of the glass substrate 102.

  In the polishing body 124, a polishing cloth 126 formed of a soft polisher made of suede or velor, or a hard polisher such as hard velor, foam resin, or pitch-impregnated suede is arranged to form a part of a cylindrical shape. May be. Further, the polishing body 124 may polish the entire inner peripheral end surface 114 of the glass substrate 102 by swinging slowly (stroke) in the direction of the rotation axis within the circular hole with respect to the glass substrate 102.

  Further, the nozzle 128 of the inner peripheral surface polishing apparatus 120 supplies a polishing liquid containing polishing abrasive grains between the polishing body 124 and the glass substrate 102. As this abrasive grain, although depending on the shape of the target end face, for example, normal abrasive grains such as alumina, cerium oxide, colloidal silica, etc. can be used. Further, the dispersion medium in which the abrasive grains are dispersed is not particularly limited, and water is preferable from the viewpoint of cost, but any dispersion medium used for normal polishing is preferably used. be able to.

  The chemical strengthening treatment tank 130 includes a treatment tank containing a chemical strengthening treatment liquid and a control unit thereof. In the chemical strengthening process, the chemical strengthening treatment bath 130 immerses the glass substrate 102 in a chemical strengthening treatment liquid in which a chemically strengthened salt is dissolved by heating, and some ions of the glass substrate (aluminosilicate glass containing Li ions), for example, Monovalent metal ions such as Li ions and Na ions are replaced with monovalent ions having a larger ion diameter than the above ions in the chemical strengthening treatment liquid, for example, Na ions and K ions. 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 Na ions and K ions, sodium nitrate, potassium nitrate, lithium nitrate and mixed molten salts thereof are preferably used, but are not limited to nitrates. , Sulfate, bisulfate, carbonate, halide and the like may be used.

FIG. 5 is an explanatory view showing an example of a change in the inner diameter dimensional error due to the chemical strengthening process. The glass substrate 102 that has finished the inner peripheral end surface polishing step by the inner peripheral end surface polishing apparatus 120 has an inner peripheral end surface 114 that faces the inner diameter of the circular hole 112, that is, the center of the circular hole 112, as shown in FIG. This distance d ₁ is finished to an inner diameter dimensional error within a predetermined range depending on the diameter of the polishing body 124, the concentration of the polishing liquid, and the polishing time. However, in the chemical strengthening step, as shown in FIG. 5B, a compressive stress layer 118 is formed, and the inner peripheral end surface 114 of the glass substrate 102 changes in the direction of decreasing the inner diameter, resulting in an inner diameter dimensional error. affect. Accordingly, the inner diameter decreases from d ₁ to d ₂ .

  Thus, in the chemical strengthening step, the amount of change in the inner diameter varies depending on the state of the chemical strengthening treatment liquid and the chemical strengthening treatment conditions. Further, the inner diameter of the glass substrate 102 after the inner peripheral processing step by the inner peripheral processing device such as the inner peripheral end surface grinding device 110 or the inner peripheral end surface polishing device 120 also has a certain dimensional error. Therefore, when the inner diameter of the glass substrate 102 after the inner peripheral processing step is smaller or larger than a predetermined design value, for example, it is combined with the dimensional error through chemical strengthening processing under a certain chemical strengthening processing condition. As a result, the dimensional accuracy of the inner diameter is further deteriorated and defective products are produced in large quantities.

  Accordingly, the inventors of the present application have grasped the relationship between the chemical strengthening treatment condition and the amount of change (elongation) in the inner diameter of the glass substrate 102 when the chemical strengthening treatment is performed under the chemical strengthening treatment condition. By performing chemical strengthening treatment under predetermined chemical strengthening processing conditions based on the difference between the inner diameter dimension of the previous glass substrate 102 and the desired value of the final inner diameter, and polishing the inner peripheral end face with a predetermined allowance, It has been found that even if the inner diameter of the glass substrate 102 before the chemical strengthening process deviates from a predetermined design value, the inner diameter dimensional accuracy of the glass substrate 102 can be improved.

More specifically, as shown in FIG. 5 (c), the glass substrate 102 whose inner diameter becomes dimension d ₂ by performing chemical strengthening treatment, by performing an inner peripheral end face polishing by more appropriate allowance , an inner diameter, is polished to the final desired dimension d _3. Such adjustment of the inner diameter dimensional error by changing the chemical strengthening treatment conditions and the machining allowance of the inner peripheral end face polishing is particularly effective when the glass substrate 102 is produced in a small amount.

(Method for producing glass substrate for magnetic disk)
If the manufacturing system of the glass substrate for magnetic disks mentioned above is used, the manufacturing method of the glass substrate for magnetic disks can be provided. Such a method of manufacturing a glass substrate for a magnetic disk involves chemically contacting a part of ions contained in the glass substrate 102 by bringing a chemical strengthening treatment liquid into contact with the disk-shaped glass substrate 102 having a circular hole formed in the center. It includes a chemical strengthening step for chemically strengthening the glass substrate by replacing with ions in the strengthening treatment liquid, and an inner peripheral end surface polishing step for polishing the inner peripheral end surface of the chemically strengthened glass substrate.

  In the inner peripheral end face polishing step, the inner peripheral end face of the glass substrate is polished so that the compressive stress layer formed on the inner peripheral end face of the glass substrate 102 in the chemical strengthening process remains.

  According to this embodiment, in addition to performing chemical strengthening treatment under predetermined chemical strengthening treatment conditions, the inner diameter of the glass substrate 102 before chemical strengthening treatment is then polished in order to polish the inner peripheral end surface by appropriate machining allowance. Even if it deviates from a predetermined design value, it is possible to realize an inner diameter dimension with a smaller error.

  If the said method is demonstrated more concretely, it is a premise that the internal diameter of the glass substrate before a chemical strengthening process is larger than a final desired shape. By the subsequent chemical strengthening step, the inner peripheral end surface of the glass substrate expands toward the center, and the inner diameter is temporarily smaller than the final desired shape. Further, by polishing the inner peripheral end face in the inner peripheral end face polishing step, the inner diameter increases again, and a desired dimension can be reached with a small error.

  In addition, it is conceivable to predict the expansion caused by the chemical strengthening process in advance and determine the chemical strengthening conditions, and to achieve the final desired shape only by such expansion. However, although the amount of change in the inner diameter due to the chemical strengthening treatment can be controlled by the chemical strengthening conditions, it cannot be as accurate as adjusting the machining allowance in the end surface polishing. Therefore, there is a possibility that the error becomes large only by predicting the amount of change by the chemical strengthening process. However, as in the embodiment of the present invention, after chemical strengthening, by further determining a machining allowance that can be controlled with high accuracy and performing end face polishing, it becomes possible to approach the desired shape with smaller errors. .

  Hereinafter, specific examples of the above-described embodiment will be described. In this example, a glass substrate for magnetic disk and a magnetic disk were manufactured through the following steps.

(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 with a grinding wheel from sheet glass formed by a fusion method, a downdraw method, or a float method. 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 the aluminosilicate glass, soda lime glass or the like can also be used.

  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).

(3) End surface grinding process And the inner peripheral end surface and the outer peripheral end surface were ground with a diamond grindstone, and predetermined chamfering was performed (forming).

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

(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 tank of neutral detergent, a pure water, and IPA (isopropyl alcohol) 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 the chemical strengthening step, 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.

  Thus, by immersing in the chemical strengthening solution, Li ions and sodium ions in the surface layer of the glass substrate are respectively replaced with sodium ions and potassium ions in the chemical strengthening solution, and the glass substrate is strengthened. At this time, the thickness of the compressive stress layer at the inner diameter of the glass substrate was less than about 150 μm.

(7) Inner peripheral end face polishing step Next, the end face of the glass substrate was subjected to mirror polishing by shape transfer processing. At this time, slurry (free abrasive grains) containing cerium oxide abrasive grains was used as the abrasive grains. By this inner peripheral end face polishing step, the end face of the glass substrate was processed into a mirror state that can prevent the generation of particles and the like. The machining allowance in this inner periphery polishing step was 5 μm or less.

以上のように、実施形態に記載した技術を本実施例に採用することにより、歩留まりを大きく向上させることができた。 [Example]
Compared with the case where the inner peripheral end face polishing is performed after the chemical strengthening step as in this example, and the comparative example in which the inner peripheral end face polishing is performed first and the chemical strengthening step is performed later, The result was able to be obtained. However, the number of samples of the glass substrate is 10,000.

As described above, by using the technique described in the embodiment in this example, the yield can be greatly improved.

  Then, the glass substrate which finished the chemical strengthening process was immersed in a 20 degreeC water tank, cooled, 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. Further, the glass substrate that had been washed with sulfuric acid was washed by sequentially immersing it in each washing tank of pure water and IPA (isopropyl alcohol). In addition, ultrasonic waves were applied to each cleaning tank.

  As described above, the first lapping step, the cutting step, the second lapping step, the inner peripheral end surface polishing step, the main surface polishing step, the chemical strengthening step, and the cooling step are performed, so that a flat and smooth, high-rigidity magnetic field is obtained. A glass substrate for disk was obtained.

(8) Precision cleaning step Next, the glass substrate for magnetic disk on 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.

(9) 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.

  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.

  INDUSTRIAL APPLICABILITY The present invention can be used in a method for manufacturing a glass substrate for a magnetic disk including a chemical strengthening process in which a part of a glass substrate is ion-exchanged for chemical strengthening and a method for manufacturing a magnetic disk.

It is the functional block diagram which showed the manufacturing system of the glass substrate for magnetic discs It is explanatory drawing for demonstrating the grinding process of an internal peripheral end surface grinding apparatus. It is explanatory drawing for demonstrating the immersion to the chemical strengthening process liquid of a glass substrate. It is a longitudinal cross-sectional view for demonstrating the structure of an inner peripheral end surface grinding | polishing apparatus. It is explanatory drawing which showed the example of a change of the internal diameter dimension error by a chemical strengthening process and inner peripheral end surface grinding | polishing.

Explanation of symbols

200 Glass substrate manufacturing system for magnetic disk 102 Glass substrate 110 Inner peripheral end surface grinding device 112 Circular hole 114 Inner peripheral end surface 120 Inner peripheral end surface polishing device 130 Chemical strengthening treatment tank

Claims (4)

A method of manufacturing a glass substrate for a magnetic disk for manufacturing a disk-shaped glass substrate having a circular hole formed in the center,
A chemical strengthening treatment liquid is brought into contact with a glass substrate of an aluminosilicate glass containing Li ions having an inner diameter different from a desired value, and some ions contained in the glass substrate are replaced with ions in the chemical strengthening treatment liquid. A chemical strengthening step of forming a compressive stress layer and changing the inner diameter to obtain a glass substrate having an inner diameter smaller than a desired value;
Polishing the inner peripheral end surface of the glass substrate subjected to chemical strengthening so that the compressive stress layer remains to be a mirror surface, and an inner peripheral end surface polishing step for adjusting the inner diameter of the glass substrate to a desired value,
While setting the chemical strengthening treatment conditions in the chemical strengthening step based on the relationship between the chemical strengthening treatment conditions grasped in advance and the amount of change in the inner diameter of the glass substrate,
As the composition of the chemical strengthening treatment liquid used in the chemical strengthening step changes depending on the number of treatments, the margin for end face polishing in the inner peripheral end face polishing step is adjusted within a range of less than 5 μm. A method for producing a glass substrate for a magnetic disk , wherein the inner diameter of the magnetic disk is adjusted to a desired value .   The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein a thickness of the compressive stress layer formed in the chemical strengthening step is less than 150 μm.   3. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein in the inner peripheral end face polishing step, the inner peripheral end face is polished by shape transfer processing. A glass substrate for a magnetic disk is produced by the method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 3 ,
A magnetic disk manufacturing method comprising forming at least a magnetic layer on a surface of the magnetic disk glass substrate.

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