JP5755952B2 - Inspection and sorting method for HDD glass substrate, manufacturing method of HDD information recording medium, and HDD glass substrate - Google Patents

Description

  The present invention relates to a method for inspecting and sorting a glass substrate for HDD and a method for manufacturing an information recording medium for HDD.

  An information recording medium such as a magnetic disk is mounted as an HDD (Hard Disk Drive) on a computer or the like. An information recording medium is manufactured by forming a magnetic thin film layer including a recording layer using properties such as magnetism, light, or magnetomagnetism on the surface of a substrate. As the recording layer is magnetized by the magnetic head, predetermined information is recorded on the information recording medium.

  Conventionally, an aluminum substrate has been used as a substrate for an information recording medium. However, as the recording density is improved, it is gradually being replaced by a glass substrate that is superior in smoothness and strength of the substrate surface as compared with an aluminum substrate.

  In order to improve mechanical strength, this glass substrate is generally subjected to chemical strengthening treatment. This chemical strengthening treatment is to replace the ions (for example, Li, Na ions) in the glass substrate with those having a larger ionic radius (for example, Na ions, K ions), thereby giving an internal stress. It is a process to strengthen. By the substitution, a compressive strain is generated on the surface of the glass substrate, and a chemically strengthened layer is formed.

As the above chemical strengthening treatment, e.g. in KNO ₃ and NaNO ₃ and mixed powder was heated to 300 to 400 ° C. chemical strengthening solution obtained by liquefaction of, by holding the glass substrate using a fixing jig (Patent Document 1).

  However, even when the chemical strengthening treatment step is performed, when the magnetic recording medium is used in a severe thermal fluctuation environment, the shape of the glass substrate is deformed due to the stress variation due to the chemical strengthening layer, and the magnetic recording medium It may cause a change in shape with time, and may cause an HDD read error. In particular, since the flying height of the recording head has become smaller with the recent increase in recording density, strict evaluation of the chemical strengthening layer has become more important than ever.

  As evaluation with respect to a chemical strengthening layer, the chemical strengthening layer was confirmed by the amount of change of an alkali component by analysis of a scanning analytical electron microscope such as SEM-EDX, for example. FIG. 1 shows the content of lithium oxide in the depth direction of the glass substrate by the above-described analysis with respect to the ion exchange state of the chemically strengthened glass substrate. However, for this analysis and confirmation, the glass substrate must be broken and inspected one by one, and it has been difficult to uniformly evaluate the entire substrate. In addition, it is possible to evaluate the chemically strengthened layer by using a polarimeter or to observe the cross section by using a polarizing microscope, but the entire main surface of the substrate cannot be evaluated uniformly, and chemical strengthening is performed on the entire surface of the substrate. Variations in layer thickness could not be confirmed.

Japanese Patent No. 3165558

  The present invention has been made in view of the above prior art, and the problem to be solved is that the variation of the chemically strengthened layer is made uniform over the entire substrate without destroying the glass substrate subjected to the chemical strengthening step. It is an object of the present invention to provide an inspection / sorting method for glass substrates for HDDs that can be evaluated in the same manner. Furthermore, with this inspection / sorting method, an HDD that generates less read errors even when used for a long period of time. It is an object of the present invention to provide a manufacturing method capable of manufacturing a business information recording medium.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies in the manufacturing process of a glass substrate for HDD, paying attention to the phase difference generated due to variations in internal stress caused by chemical strengthening provided by the chemical strengthening process. It was. As a result, the chemical strengthening process is followed by an inspection / sorting process, the glass substrate that has been chemically strengthened is irradiated with white light, and the transmitted light has a constant phase difference, and there is no variation. As a result, it was found that the HDD glass substrate excellent in the uniformity of internal stress can be detected without breaking. Furthermore, an information recording medium using a glass substrate obtained by such an inspection / sorting process has little variation in residual stress, and variation in internal stress even when used for a long time in a harsh environment. It has been found that the deformation due to the above does not occur, and it is possible to suppress the occurrence of reading errors.

  That is, according to the present invention, in the step of inspecting and sorting the HDD glass substrate having a compressive stress layer applied to the surface layer by the chemical strengthening step, the radial direction of the HDD glass substrate is 0.5 mm from the radial end of the central hole. And measuring the phase difference from the outer diameter end of the glass substrate for HDD to a position of 0.5 mm, and selecting the phase difference having a maximum value of less than 5.0 nm. This is an inspection / sorting method for HDD glass substrates.

  In the inspection / sorting method of the glass substrate for HDD, the maximum value of the phase difference is less than 4.0 nm in the case of the glass substrate for HDD in which the thickness of the compressive stress layer is 20 μm or more. It is preferable to select

  Further, in the inspection / sorting method of the glass substrate for HDD, in the case of the glass substrate for HDD in which the thickness of the compressive stress layer is less than 20 μm, the maximum value of the phase difference is less than 3.0 nm. It is preferable to select.

  The inspection / sorting method described above is particularly preferably used in the step of inspecting / sorting a glass substrate for HDD having a surface layer provided with a compressive stress layer of 20 μm or more by a chemical strengthening step.

 According to another aspect of the present invention, there is provided a method for manufacturing an HDD information recording medium, wherein a magnetic layer is provided only on a glass substrate selected by the above-described HDD glass substrate inspection / sorting method.

  According to the present invention, inspection and selection of a glass substrate for HDD that can uniformly evaluate the variation of internal stress due to the chemical strengthening over the entire substrate without destroying the glass substrate subjected to the chemical strengthening step. In addition, a magnetic layer is provided only on a glass substrate for HDD selected by this inspection / sorting method to produce an HDD information recording medium, which can be used in a harsh environment for a long time. Even in this case, it is possible to provide an HDD information recording medium in which occurrence of reading errors is suppressed.

It is a figure which shows the ion exchange state of the glass substrate for HDD which performed the chemical strengthening process. It is a figure which shows the measurement analysis range in the inspection / sorting method of the glass substrate for HDD which concerns on this embodiment. It is a manufacturing process figure explaining the process in manufacture of the glass substrate for HDD. It is a top view which shows the glass substrate for HDD manufactured by the manufacturing method of the glass substrate for HDD which concerns on this embodiment. It is the schematic which shows the process of the direct press method in the manufacturing method of the glass substrate for HDD which concerns on this embodiment. It is a schematic sectional drawing which shows the process of the float method in the manufacturing method of the glass substrate for HDD which concerns on this embodiment. It is a schematic sectional drawing which shows an example of the grinding | polishing apparatus used at the rough grinding | polishing process and the precision grinding | polishing process in the manufacturing method of the glass substrate for HDD which concerns on this embodiment. It is a partial cross section perspective view which shows the magnetic disc which is an example of the magnetic recording medium using the glass substrate for HDD manufactured by the manufacturing method of the glass substrate for HDD which concerns on this embodiment. It is a figure showing the result of the error yield in the inspection / sorting method of the glass substrate for HDD concerning this embodiment. It is a figure showing the result of the error yield in the inspection / sorting method of the glass substrate for HDD concerning this embodiment.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

  The inspection / sorting method of the HDD glass substrate according to the present embodiment is a process of inspecting / sorting the HDD glass substrate having a compressive stress layer applied to the surface layer by the chemical strengthening step, in the radial direction of the HDD glass substrate. The phase difference from the position 0.5 mm from the diameter end of the center hole to the position 0.5 mm from the outer diameter end of the glass substrate for HDD is selected to be less than 5.0 nm. .

  Moreover, the phase measurement process by the inspection / sorting method for the glass substrate for HDD according to the present embodiment is not particularly limited except that it is provided after the chemical strengthening process, and may be performed between any processes. .

  As a manufacturing method of the glass substrate for HDD, in addition to the phase measurement process and the chemical strengthening process, there are a method including a disk machining process, an edge polishing process, a double-side grinding process, a double-side polishing process, a cleaning process, a shape inspection process, and the like. Can be mentioned. And each said process may be performed in this order, and the order of a grinding | polishing process (secondary grinding | polishing process) and a washing | cleaning process may be replaced. Furthermore, a method including steps other than these may be used. For example, you may provide what performs an end surface grinding | polishing process between a double-sided grinding process and a grinding | polishing process.

  In particular, the cleaning process may be performed before or after the polishing process, and may be performed once before and after the polishing process.

  First, the chemical strengthening step in the production method of the present invention will be described in detail.

<Chemical strengthening process>
If the chemical strengthening process in the manufacturing method of this invention is a well-known method, it will not specifically limit. Specifically, the process etc. which immerse the glass base plate which gave the disk processing process etc. which are mentioned later in a chemical strengthening process liquid are mentioned, for example. By soaking, a chemically strengthened layer can be formed on the surface of the glass base plate. And by forming a chemical strengthening layer, impact resistance, vibration resistance, heat resistance, etc. can be improved.

In the present invention, the compressive stress layer applied to the chemical strengthening step is a layer having a compressive stress value of 2 kg / mm ² or more. The compressive stress is too strong, there are cases where the flatness is deteriorated, the compression stress value is preferably 2 kg / mm ² or more 15 kg / mm ² or less. In addition, although the thickness of the compressive stress layer by the chemical strengthening process applied to the conventional glass substrate for HDD was 100-200 micrometers, in recent years, the request | requirement with respect to the flatness of a glass substrate becomes severer, and the compressive stress layer of The thickness is preferably 50 μm or less.

  The chemical strengthening step involves immersing the glass base plate in a heated chemical strengthening treatment solution to convert alkali metal ions such as lithium ions and sodium ions contained in the glass base plate into alkali ions such as potassium ions having a larger ion radius. It is carried out by an ion exchange method that substitutes metal ions. Due to the strain caused by the difference in ion radius, compressive stress is generated in the ion-exchanged region and the surface of the glass base plate is strengthened.

In this embodiment, it is thought that a strengthening layer is suitably formed by this chemical strengthening process by using the glass composition as described above as a glass base plate that is a raw material of the glass substrate. Specifically, among Li ₂ O, Na ₂ O, and K ₂ O, which are alkali components of the glass base plate, the content of Na ₂ O is large, and the sodium ions of Na ₂ O are chemically strengthened. This is thought to be because it is easily exchanged for potassium ions contained in. Further, since the polishing agent used in the polishing step before the chemical strengthening step, here the rough polishing step, is an abrasive having the above composition, the alkaline earth metal adhering to the surface of the glass base plate is used. The amount is small and the chemical strengthening is considered to be uniform.

  The chemical strengthening treatment liquid is not particularly limited as long as it is a chemical strengthening treatment liquid used in the chemical strengthening step in the method for producing a glass substrate for a magnetic information recording medium. Specifically, for example, a melt containing potassium ions, a melt containing potassium ions and sodium ions, and the like can be given.

  Examples of these melts include melts obtained by melting potassium nitrate, sodium nitrate, potassium carbonate, sodium carbonate, and the like. Among these, it is preferable to use a combination of a melt obtained by melting potassium nitrate and a melt obtained by melting sodium nitrate from the viewpoint of low melting point and preventing deformation of the glass base plate. At that time, a melt obtained by melting potassium nitrate and a melt obtained by melting sodium nitrate are preferably mixed in approximately the same amount.

  Next, the inspection / sorting step in the production method of the present invention will be described in detail.

<Inspection / sorting process>
The inspection / selection step is performed after the chemical strengthening step described above, and may be performed a plurality of times as long as it is after the chemical strengthening step.

  FIG. 2A is a manufacturing process diagram illustrating a process in manufacturing a conventional glass substrate for HDD. The conventional glass substrate manufacturing method does not have the inspection / selection stage by phase measurement as in the present invention, and cannot examine the uniformity of internal stress due to chemical strengthening, and the internal stress due to chemical strengthening for each substrate. There was variation in

  In addition, when a chemical strengthening process is performed on a glass substrate, the glass substrate may be warped depending on variations in internal stress. Even if precision polishing is performed after the chemical strengthening treatment, it is difficult to correct such variations.

  On the other hand, FIG. 2 (b) is a manufacturing process diagram of the glass substrate for HDD of the present invention. As described above, since the inspection / selection process is performed after the chemical strengthening treatment process, the internal due to chemical strengthening is performed. It is possible to confirm the uniformity of stress. Further, FIG. 2 (c) shows that the first inspection / selection process is performed after the chemical strengthening treatment process, and the second inspection / selection process is performed after the double-side polishing process. By performing the inspection / sorting process, it is possible to perform more strict inspection / sorting.

  The compressive stress layer applied to the chemical treatment process can be regarded as an optical “strain layer”, and birefringence with different effective refractive index occurs in the direction perpendicular to the direction parallel to the optical axis with respect to the transmitted light. . Therefore, there is a difference in propagation speed between TE polarized light having parallel electric field components and TM polarized light having electric field components perpendicular to the lattice lines, and a phase difference (also referred to as retardation) appears in the transmitted light. Such birefringence in the thickness direction and the planar direction of the glass substrate can measure the thickness of the compressive stress layer by cutting out a slice from the glass substrate and measuring the phase difference of the cross section. However, when the compressive stress due to chemical strengthening is uniformly generated in the plane direction of the glass substrate, birefringence does not occur when the phase difference is measured by transmitted light from the surface direction of the glass substrate. No retardation is detected. However, when there is a variation in the compressive stress, the variation can be detected as a phase difference.

  Specifically, the chemically strengthened glass substrate is irradiated with white light, and the amount of transmitted light phase difference at a plurality of locations on the glass substrate is measured. By measuring the phase difference, it is possible to evaluate variations in internal stress.

  The phase difference in the present invention can be measured using PA-100 (manufactured by Photonic Lattice). The phase difference measurement / analysis position in the present invention is a position 0.5 mm from the diameter end of the central hole of the HDD glass substrate and a position 0.5 mm from the outer diameter end of the HDD glass substrate.

  FIG. 3 is a cross-sectional view of the glass substrate, and is a diagram showing the phase difference measurement analysis position of the present invention. In general, a glass substrate for HDD having an outer diameter of 65 mm and an inner diameter of the center hole of 20 mm is used. Moreover, when the end surface processing step is performed, the width of the end surface is 0.15 mm, and it is preferable to measure the phase difference of the compressive stress layer on the main surface of the glass substrate excluding these. The reason for not measuring the phase difference of the end face is that light may not be transmitted due to the edge of the end face, and it is not possible to distinguish the dark part due to the edge or the dark part due to birefringence on the element side. This is because a higher numerical value is measured.

  If the maximum value of the phase difference measured as described above is less than 5.0 nm, a glass substrate having a small internal strain can be inspected and selected. That is, if the phase difference obtained by this phase measurement step is not in such a range, it can be determined that the compression stress value balance is poor in the glass substrate. Then, by removing the glass substrate with a poor compressive stress value balance from the HDD glass substrate on which the magnetic film is subsequently formed, a glass substrate without an internal strain to which the compressive stress layer is uniformly applied is more reliably produced. be able to.

  In the phase measurement process of the present invention, the measurement time is significantly shorter than that of other stress measurements, and a glass substrate can be measured over a wide range. Other general stress measuring devices include a polarimeter and the like, but since the measuring range is in units of several millimeters, productivity deteriorates.

Moreover, when the layer whose compressive stress value is 2 kg / mm ² or more is 20 μm or more by the chemical strengthening step, it is preferable to select the layer having the maximum value of the phase difference at the measurement range position of 4.0 nm. In the inspection / sorting step of the glass substrate having a compressive stress layer of 20 μm or more, it is possible to sort a glass substrate with a lower error frequency by using such a retardation range as a sorting standard.

On the other hand, when the layer having a compressive stress value of 2 kg / mm ² or more by the chemical strengthening step is less than 20 μm, it is preferable to select one having a maximum phase difference of 3.0 nm or less at the measurement range position. . In the inspection / sorting step of the glass substrate having a compressive stress layer of less than 20 μm, it is possible to sort a glass substrate with a lower error frequency by using such a retardation range as a sorting standard.

  Next, the disk processing step in the manufacturing method of the present invention will be described in detail.

<Disk processing process>
In the disk processing step, a through-hole 10a is formed at the center part from a glass base plate formed from a glass material having a predetermined composition so that the inner periphery and the outer periphery are concentric as shown in FIG. This is a process of processing into a disk-shaped glass base plate 10. Specifically, processing is performed using a direct press method, a float method, or the like.

(Direct press method)
FIG. 5 is a schematic view showing a processing step of the glass base plate by the direct press method.

  FIG. 5A shows a lower mold 3 and an upper mold 4 constituting the mold. The upper die 4 is in contact with the lower die 3 so as to surround the molding surface when the mold is clamped, and is provided with a stopper for regulating the interval between the molding surfaces. FIG. 5B shows a casting process, and the molten glass flow 6 flowing out from the outflow pipe 5 is supplied to the center of the lower mold forming surface. In addition, as shown to Fig.5 (a) etc., the upper surface in which the molding surface of the lower mold | type 3 is formed is flat (except the part which shape | molds the thick part of a glass blank). In the next cutting step shown in FIG. 5C, the molten glass is cut with the cutting blade 7 to obtain the gob 2 on the lower mold surface. Subsequently, in FIG. 5 (d), the gob is pressed by the upper mold 4 and the lower mold 3. At the time of mold clamping, the interval between the upper and lower mold forming surfaces is regulated by the stopper. The gob 2 is pressurized by the upper and lower molds, and is spread out in the cavity formed by the upper and lower molds, and is molded into the glass base plate 10 that is a press-molded product. The peripheral edge of the molded product does not contact either the upper mold 4 or the lower mold 3 and remains on the glass base plate 10 as a free surface. After press molding, the upper die 4 is separated from the glass base plate 10 on the lower die 3 and retracts upward. The outer diameter of the press-formed product 1 is measured using optical means by a non-contact measurement method, for example, when the molded product is released from the upper die 4 and is on the lower die 3. After the outer diameter measurement, as shown in FIG. 5 (e), after the glass base plate 10 is cooled to a temperature that does not deform even when a force for taking out is applied, the glass base plate 10 is taken out from the lower mold 3. .

  The surface roughness Ra of the glass base plate taken out as described above is preferably 10 μm or less and Rmax is 50 μm or less. If the surface roughness Ra or the maximum height roughness Rz of the glass base plate after the cutting process is too high, grinding damage is large, and if it is too low, the grinding process cannot be performed.

  Further, in the glass base plate taken out as described above, the surface undulation of the surface that comes into contact with the mold first, that is, the surface that comes into contact with the lower mold, is larger than the surface that comes into contact with the mold later, that is, the surface that comes into contact with the upper mold. I know that. This is because the coefficient of thermal expansion of the glass is different between the surface that comes into contact with the mold first and the surface that comes into contact with the mold later, so that the stress balance is lost and different undulations occur on each surface. That is, the ratio of the surface undulation Wa1 of the surface with a large undulation to the surface undulation Wa2 of the surface with a small undulation is 1: 1.5 to 1: 2.5.

(Float method)
FIG. 6 is a cross-sectional view showing a processing step by the float method.

  The float process step includes a cutting step in which a cut line is made on one side of a glass material formed in a plate shape on a molten metal and cut along the cut line. In the cutting step, after forming a cut line on the surface of the glass base plate that is in contact with the molten metal of the glass material, the cutting line is advanced in the thickness direction of the glass base plate to form a disk-shaped glass base plate. To cut out.

  FIG. 6A is a cross-sectional view of the plate-like glass material 1.

  As the glass material, a plate-shaped glass material manufactured by a float process is used. The float method is, for example, a method in which a molten liquid obtained by melting a glass material is poured onto molten tin and solidified as it is. In the obtained glass base plate, one surface is a free surface of glass (hereinafter referred to as a free surface) and the other surface (hereinafter referred to as a contact surface) is an interface between glass and tin. High smoothness. And as the thickness, a 0.95 mm thing is mentioned, for example. In addition, the surface roughness, for example Ra, of a glass base plate or a glass substrate can be measured using a general surface roughness measuring machine.

  For this reason, the glass material has a surface in contact with the molten metal and the other surface. In the case of the glass material 1 shown in FIG. 6A, the upper surface is the contact surface 1A and the lower surface is the free surface 1B.

  A cut line is formed on the contact surface 1A of the glass material 1 to draw a curve that forms a substantially peripheral edge of a region to be a glass substrate for a magnetic disk. In the present embodiment, as shown in FIG. 6 (b), circular cutting lines 8 and 9 are formed on the contact surface 1A of the glass material 1 with the glass cutter 15 to draw the disc-shaped outer peripheral side and inner peripheral side, respectively. To do.

  In this case, the outer peripheral side and inner peripheral cut lines 8 and 9 are formed obliquely with respect to the thickness direction of the glass plate. Further, in the present embodiment, the cut lines 8 and 9 are formed obliquely outward from the contact surface 1A of the glass material 1 toward the free surface 1B side, and when viewed in the cross-sectional view of FIG. The incisors 8 and 8 and the incisors 9 and 9 are formed in a C-shape. Further, in the present embodiment, the cut lines 8 and 9 are formed obliquely outward from the contact surface 1A of the glass material 1 toward the free surface 1B, but the present invention is not limited thereto, and for example, the contact surface 1A of the glass material 1 Incisions 8 and 9 are formed obliquely inward from the free surface 1B side, and when viewed in FIG. It is also possible to advance the cutting line so that the inner part surrounded by the cutting line is extracted upward.

  Next, as shown in FIG.6 (c), the said cut lines 8 and 9 formed in the contact surface 1A of the glass raw material 1 are advanced toward the free surface 1B side. Thereby, the inner region 10 a surrounded by the cut line 8 is separated from the glass material 1. The inner portion 10b surrounded by the cut line 9 is separated from the region 10a surrounded by the cut line 8.

  As means for advancing the cut lines 8 and 9 formed on the contact surface 1A of the glass material 1 in this way toward the free surface 1B side, means for causing a difference in thermal expansion in the glass material 1, for example, the glass material 1 A method of heating one side is preferred. By heating the glass material 1, a difference in thermal expansion occurs in the thickness direction of the glass material 1, and the glass material can be easily cut into a target disk shape.

  Subsequently, as shown in FIG. 6 (d), the inner regions 10a and 10b surrounded by the cut line 8 are pushed downward, and further, the region 10b surrounded by the cut line 9 is pushed out, so that a circle is formed at the center. A disk-shaped glass base plate 10 having holes is obtained.

  Moreover, it is preferable that the surface roughness Ra of the glass base plate after the cutting step is 5 nm to 50 nm and the maximum height roughness Rz is 20 nm to 100 nm. If the surface roughness Ra or the maximum height roughness Rz of the glass base plate after the cutting process is too high, grinding damage is large, and if it is too low, the grinding process cannot be performed.

  Moreover, in the glass base plate after the said cutting process, it turns out that the surface waviness of a free surface is large compared with a molten metal contact surface. This is thought to be because, in the float process, the occurrence of waviness can be suppressed because the interface in contact with the molten metal is more stable than the interface with air. That is, the ratio of the surface undulation Wa1 of the surface with a large undulation to the surface undulation Wa2 of the surface with a small undulation is 1: 1.2 to 1: 3.0. The free surface waviness Wa is 1 to 5 nm, and the molten metal contact surface waviness Wa is 0.6 to 3 nm.

  Further, the disk processing step of the present invention may include a step of polishing the corner (end surface) of each cut line after the cutting step. By this end surface polishing step, cracks on the glass substrate caused by the cut lines can be reduced.

  In this disk processing step, for example, the outer diameter r1 is 2.5 inches (about 64 mm), 1.8 inches (about 46 mm), 1 inch (about 25 mm), 0.8 inches (about 20 mm), etc., and the thickness is It is processed into a disk-shaped glass base plate having a thickness obtained by adding about 0.3 mm to the thickness of the finally produced glass substrate. If the thickness is exceeded, the machining allowance increases and the production efficiency deteriorates. Since the thickness of the finally manufactured glass substrate is determined, the thickness to be processed in the disk processing step is determined by calculating backward from the thickness.

<Double-side grinding process>
The double-side grinding step is a step of processing the glass base plate to a predetermined plate thickness. Specifically, the process etc. which grind | polish both surfaces of a glass base plate (double-sided grinding) are mentioned. By processing in this way, the parallelism, flatness and thickness of the glass base plate can be adjusted.

  The grinding apparatus used in the double-side grinding process is not particularly limited as long as it is a grinding apparatus used for manufacturing a glass substrate. Specifically, there is a grinding apparatus 11 as shown in FIG. FIG. 7 is a schematic cross-sectional view showing an example of a grinding apparatus used in a double-side grinding step in the method for manufacturing a glass substrate for magnetic information recording media according to the embodiment of the present invention.

  A grinding apparatus 11 as shown in FIG. 7 is an apparatus capable of simultaneous grinding on both sides. The grinding apparatus 11 includes an apparatus main body 11a and a coolant supply unit 11b that supplies coolant, which is a coolant, to the apparatus main body 11a.

  The apparatus main body 11a includes a disk-shaped upper surface plate 12 and a disk-shaped lower surface plate 13, and they are arranged vertically spaced apart so that they are parallel to each other. Then, the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13 rotate in directions opposite to each other.

  In order to grind both the front and back surfaces of the glass base plate 10 on the opposing surfaces of the disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13, fixed abrasive grains 14 containing diamond particles are provided. Yes. The fixed abrasive grains 14 containing diamond particles used in this double-side grinding process may be in the form of pellets by bonding a plurality of diamond particles with a resin, or by bonding or electrodeposition using a resin, You may use the sheet-like thing which adhered the diamond particle to the lower surface plate 13 planarly.

  A carrier may be sandwiched between the fixed abrasive 8 and the surface plates 12 and 13. The carrier revolves in the same direction as the lower surface plate 13 with respect to the center of rotation of the surface plates 12 and 13 while rotating while holding the plurality of glass base plates 10. The disk-shaped upper surface plate 12 and the disk-shaped lower surface plate 13 can be operated by separate driving. In the grinding apparatus 11 operating in this manner, the coolant 17 is supplied between the fixed abrasive grains 14 and the glass base plate 10 and between the fixed abrasive grains 14 and the glass base plate 10, whereby the glass base material is supplied. The plate 10 can be ground.

  The coolant supply unit 11 b includes a container in which a coolant 17 is placed and a pon 16. That is, the coolant 17 in the container is supplied into the surface plates 12 and 13 by the pump 16 and circulated. The facets from which the ground surfaces of the upper and lower surface plates 12 and 13 are cut off, which are generated during the circulation, are removed from the respective ground surfaces. Specifically, when the coolant 17 is circulated, the coolant is filtered with a filter provided in the lower surface plate 13, and the facet is retained in the filter.

  Further, when the arithmetic average roughness Ra of the glass base plate is measured at a plurality of locations, the difference between the minimum value and the maximum value of Ra obtained is preferably about 0.01 to 0.4 μm.

  When the double-side grinding process is performed, polishing performed in the rough polishing process described later can be efficiently performed. Further, the surface roughness Ra of the glass base plate used in the polishing step performed by the double-side grinding process is preferably 0.5 μm or less, and more preferably 0.3 μm or less. When the surface roughness Ra is larger than 0.5 μm, a large undulation may remain even after the subsequent polishing step. Further, the maximum height roughness Rz is preferably 3 μm or less. This is to facilitate the polishing process.

  Moreover, it is preferable that the removal allowance of the glass base plate in the said double-sided grinding process is 50 micrometers or more and 200 micrometers or less. In some cases, the advance allowance cannot sufficiently remove the undulation from 50 μm. When the advance allowance is larger than 200 μm, the processing time becomes long, and the efficiency of the manufacturing method is deteriorated.

  Furthermore, in the double-sided grinding step of the present invention, the number of glass base plates to be ground must be plural, specifically 80 or more, and more preferably 100 or more. When the number of glass substrates to be ground is less than 80, undulation removal cannot be performed efficiently. This is because a further change in internal stress occurs due to a further worsening of the upper and lower processing balance, resulting in a deterioration in flatness. When the flatness is deteriorated, the processing rate is affected and the processing cannot be performed.

  Moreover, this double-side grinding process may be performed once or twice or more. For example, when it is performed twice, the parallelism, flatness and thickness of the glass base plate are preliminarily adjusted in the first double-side grinding step (first double-side grinding step), and the second double-side grinding step (second double-side grinding step) ), The parallelism, flatness and thickness of the glass base plate can be finely adjusted.

<Double-side polishing process>
The double-side polishing step is intended to remove the scratches and distortions remaining in the double-side grinding step described above by polishing the main surface of the glass base plate with a polishing slurry containing cerium oxide. The double-side polishing step may be divided into a rough polishing step (primary polishing step) and a fine polishing step (secondary polishing step), and is performed using the following polishing method.

(Rough polishing process)
The polishing apparatus used in the rough polishing step is not particularly limited as long as it is a polishing apparatus used for manufacturing a glass substrate.

  The surface to be polished in the rough polishing step is a main surface. The main surface is a surface parallel to the surface direction of the glass base plate.

  Next, the abrasive | polishing agent used in the grinding | polishing process of this invention contains a cerium oxide as a main component. The content of cerium oxide is preferably 3 to 15% by mass with respect to the total amount of the polishing slurry. By setting it as such a range, the glass substrate for magnetic information recording media with higher smoothness can be manufactured.

  The polishing slurry is a liquid in which the abrasive, dispersant, etc. are dispersed in water, that is, a slurry liquid. In the state where the abrasive is dispersed in water, even if the alkaline earth metal is contained in the water, the alkaline earth metal is dissolved, so that it hardly adheres to the surface of the glass base plate and is included in the abrasive. Alkaline earth metal tends to adhere to the surface of the glass base plate. For this reason, the use of an abrasive containing a small amount of alkaline earth metal can sufficiently suppress the adhesion of alkaline earth metal to the polished glass base plate.

(Precision polishing process)
The precision polishing process is a mirror polishing process that finishes a smooth mirror surface having a surface roughness (Rmax) of about 6 nm or less, for example, while maintaining the flat and smooth main surface obtained in the rough polishing process. The precision polishing step is performed, for example, by using a polishing apparatus similar to that used in the rough polishing step and replacing the polishing pad from a hard polishing pad to a soft polishing pad. The surface to be polished in the precision polishing step is the main surface, similar to the surface to be polished in the rough polishing step.

  Further, as the abrasive used in the precision polishing step, an abrasive that causes fewer scratches even if the abrasiveness is lower than the abrasive used in the rough polishing step is used. Specifically, for example, a polishing agent containing silica-based abrasive grains (colloidal silica) having a particle diameter lower than that of the polishing agent used in the rough polishing step. The average particle diameter of the silica-based abrasive is preferably about 20 nm. And the polishing slurry liquid containing the said abrasive | polishing agent is supplied to a glass base plate, a polishing pad and a glass base plate are slid relatively, and the surface of a glass base plate is mirror-polished.

<Glass base plate composition>
First, each component of a glass base plate is further explained in full detail.

_{First, SiO 2, Al 2 O 3} , and _B 2 _{O 3} is a framework component of the glass workpiece. Li ₂ O, Na ₂ O, and K ₂ O are alkali components of the glass base plate. MgO, CaO, BaO, SrO, and ZnO are alkaline earth components of the glass base plate.

  Next, the skeleton component of the glass base plate will be described.

As the skeleton component of the glass workpiece to be used in the present embodiment, as described above, SiO ₂ is 58 to 70 wt%, _Al 2 _{O 3} is 12 to 18 _wt%, B 2 _{O 3} is 0-3 wt% (However, 0 is included), and the total thereof, that is, the total of SiO ₂ , Al ₂ O _3, and B ₂ O ₃ is 72 to 85 mass%.

SiO ₂ is a component that forms a glass skeleton (matrix). If the content of SiO ₂ is too small, the glass structure becomes unstable and the chemical durability is deteriorated, and the viscosity characteristics at the time of melting are deteriorated, which may impair the moldability. If the content of SiO ₂ is too large, with the productivity becomes poor meltability decreases, sufficient rigidity may become impossible to obtain. Therefore, the content of SiO ₂ is preferably 58 to 70% by mass.

Al ₂ O _{3 is} also a component that forms a skeleton of glass, and contributes to improvement of durability and strength and surface hardness of glass. If the content of Al ₂ O ₃ is too small, the durability and strength may not be sufficient as a glass substrate for a magnetic information recording medium. Further, when the content of Al ₂ O ₃ is too large, intensified devitrification tendency of the glass, it may stable glass formation is difficult. Therefore, the content of Al ₂ O ₃ is preferably 12 to 18% by mass.

B ₂ O ₃ has the effect of improving the chemical durability by improving the meltability and improving the productivity and stabilizing the glass structure by entering the glass skeleton. However, B ₂ O ₃ tends to volatilize when melted, and the glass component ratio tends to become unstable. Further, since the strength is lowered, the hardness is lowered, the glass substrate is easily damaged, the fracture toughness value is reduced, and the substrate tends to be damaged. For these reasons, the content of B ₂ O ₃ is preferably 3% by mass or less. _Further, it is possible to a composition that does not contain B 2 _{O 3.} In the _above, the 0 wt% in the content of 0-3 wt% B 2 _{O 3,} which means that may include aspects that do not contain B 2 _{O 3.} In addition, the notation of “0 mass%” in the glass composition of the present application document is in agreement with this, and means that it may include an embodiment not containing the component (hereinafter, the same notation is agreed).

Then, the total amount of SiO ₂ and _Al 2 _{O 3} and _B 2 _{O 3} w (FMO) is preferably 70 to 85 wt%. This is to stabilize the glass structure. If the total amount is too small, the glass structure tends to become unstable. Moreover, when there is too much this total amount, the viscosity characteristic at the time of a fusion | melting will deteriorate, and there exists a tendency for productivity to fall.

  Next, the alkali component of the glass base plate will be described.

As an alkaline component of the glass base plate used in the present embodiment, as described above, Li ₂ O is 1 to 8% by mass, Na ₂ O is ₂ to 13% by mass, and K ₂ O is 0.2 to ₂ % by mass. And the sum thereof, that is, the sum of Li ₂ O, Na ₂ O and K ₂ O is 3.2 to 23% by mass.

Li ₂ O has a unique property among alkali metal elements, and has a function of improving the solubility of the glass, while greatly improving the Young's modulus by improving the ion filling rate in the glass structure. Has an effect. Li 2 _O content is too small, there is a tendency that it is impossible to exhibit sufficient effect on improvement of the improvement and the Young's modulus of solubility. Further, the content of Li 2 _O, is too large, as described above, there are cases where the surface of the recording layer of the information recording medium serving as a trigger of a very small and thin reaction precipitates. Therefore, the content of Li ₂ O, is preferably 1 to 8 wt%.

Na 2 _O has an effect of lowering the melting temperature of the glass, the effect of increasing the coefficient of linear expansion. Further, it is considered to be a component that greatly affects the effect of chemical strengthening in the chemical strengthening process. That is, when the content of Na ₂ O is too small, not only does the melting temperature tend not to be sufficiently lowered, but the strength cannot be sufficiently increased by the chemical strengthening step. On the other hand, if the content of Na ₂ O is too large, the amount of elution increases and the recording layer may be adversely affected. Therefore, the content of Na ₂ O is preferably _{2 to} 13% by mass. In addition, this content is more than the content in a general glass substrate.

K 2 _O is, have the effect of lowering the melting temperature of the glass, the effect of increasing the coefficient of linear expansion. When the content of K ₂ O is too small, there is a tendency that the melting temperature cannot be lowered sufficiently. On the other hand, when the content of K ₂ O is too large, not only does the amount of elution increase and the recording layer may be adversely affected, but there is a tendency that the strength cannot be sufficiently increased by the chemical strengthening step. This is thought to be due to the fact that the chemical strengthening process replaces potassium ions instead of sodium ions of Na ₂ O to form a strengthened layer and inhibits this exchange. Therefore, the content of K ₂ O is preferably 0.2 to 2% by mass.

Then, Li ₂ O, Na ₂ O and _{K 2} O to the total amount w of (R2 O) is preferably a 3.2 to 23 wt%. If the total amount is too small, there is a tendency that the melting temperature cannot be lowered sufficiently. If the total amount is small, the content of Na ₂ O is also small, and chemical strengthening is sufficiently exerted. It tends to be difficult. On the other hand, if the total amount is too large, the amount of elution increases and the recording layer may be adversely affected.

  In addition, MgO, CaO, BaO, SrO, and ZnO, which are alkaline earth components of the glass base plate, have the effect of improving the meltability as well as increasing the thermal expansion coefficient and rigidity. The total amount w (MgO + CaO + BaO + SrO + ZnO) of MgO, CaO, BaO, SrO and ZnO is preferably 1 to 10% by mass. If the total amount is too small, the effect of improving rigidity and improving meltability tends to be insufficient. Moreover, when there is too much this total amount, there exists a tendency for a chemical structure to fall while glass structure becomes unstable and melt productivity falls.

Moreover, as a glass base plate, you may contain components other than the above. Specifically, for example, ZrO ₂ or cerium oxide may be contained. Then, the content of ZrO _2, is preferably from 0 to 5 wt%. Moreover, as content of a cerium oxide, 0-2 mass% is preferable. In addition, cerium oxide has an effect which suppresses generation | occurrence | production of a fine unevenness | corrugation when grind | polishing a glass base plate using the abrasive | polishing agent containing a cerium oxide.

  And the magnetic recording medium using the glass substrate for magnetic information recording media manufactured by the manufacturing method of the glass substrate for magnetic information recording media concerning the above-mentioned embodiment is explained.

  FIG. 8 is a partial cross-sectional perspective view showing a magnetic disk as an example of a magnetic recording medium using the glass substrate for magnetic information recording medium manufactured by the method for manufacturing a glass substrate for magnetic information recording medium according to the present embodiment. is there. The magnetic disk D includes a magnetic film 102 formed on the main surface of a circular glass substrate 101 for a magnetic information recording medium. For the formation of the magnetic film 102, a known method is used. For example, a formation method (spin coating method) for forming a magnetic film 102 by spin-coating a thermosetting resin in which magnetic particles are dispersed on a glass substrate 101 for a magnetic information recording medium, or a glass substrate for a magnetic information recording medium Examples include a formation method (sputtering method) for forming the magnetic film 102 on the substrate 101 by sputtering, a formation method (electroless plating method) for forming the magnetic film 102 on the glass substrate 101 for magnetic information recording medium by electroless plating, and the like. It is done.

  The thickness of the magnetic film 102 is about 0.3 to 1.2 μm when the spin coating method is used, and is about 0.04 to 0.08 μm when the sputtering method is used. In some cases, the thickness is about 0.05 to 0.1 μm. From the viewpoint of thinning and densification, film formation by sputtering is preferable, and film formation by electroless plating is preferable.

  The magnetic material used for the magnetic film 102 can be any known material and is not particularly limited. The magnetic material is preferably, for example, a Co-based alloy based on Co having high crystal anisotropy in order to obtain a high coercive force, and Ni or Cr added for the purpose of adjusting the residual magnetic flux density. More specifically, CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, CoCrPtSiO, and the like whose main component is Co can be given.

The magnetic film 102 has a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa, etc.) divided by a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) in order to reduce noise. May be. Magnetic material used for the magnetic layer 102, in addition to the magnetic material, ferrite or iron - may be a rare earth, also, Fe in a non-magnetic film made of _SiO 2, BN, etc., Co, FeCo, CoNiPt and the like A granular material having a structure in which the magnetic particles are dispersed may be used. In addition, for recording on the magnetic film 102, either an inner surface type or a vertical type recording format may be used.

  In order to improve the sliding of the magnetic head, the surface of the magnetic film 102 may be thinly coated with a lubricant. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.

  Furthermore, an underlayer or a protective layer may be provided on the magnetic film 102 as necessary. The underlayer in the magnetic disk D is appropriately selected according to the magnetic film 102. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. For example, in the case of the magnetic film 102 containing Co as a main component, the material of the underlayer is preferably Cr alone or a Cr alloy from the viewpoint of improving magnetic characteristics.

  Further, the underlayer is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked. Examples of such an underlayer having a multilayer structure include multilayer underlayers such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, and NiAl / CrV. Examples of the protective layer that prevents wear and corrosion of the magnetic film 102 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be continuously formed with the underlayer and the magnetic film 102 by an in-line sputtering apparatus. These protective layers may be a single layer, or may be a multi-layer structure composed of the same or different layers.

Note that another protective layer may be formed on the protective layer or instead of the protective layer. For example, instead of the protective layer, a SiO ₂ layer may be formed on the Cr layer. Such a SiO ₂ layer is formed by dispersing and applying colloidal silica fine particles in a tetraalkoxysilane diluted with an alcohol-based solvent on the Cr layer and further baking.

  In such a magnetic recording medium based on the glass substrate 101 for magnetic information recording medium according to this embodiment, the glass substrate 101 for magnetic information recording medium is formed with the above-described composition. It can be done with high reliability.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
Using a glass substrate, a glass substrate is manufactured using a float method, and in accordance with the method shown in FIG. 3B, a disk processing step, a double-side grinding step, a double-side polishing step, a chemical strengthening treatment step, and a final cleaning step are performed. The glass substrate was manufactured 1000 times. In addition, in the chemical strengthening process, it manufactured so that the compressive-stress layer of a glass substrate main surface might be set to 30 micrometers.

  And the phase difference of each board | substrate was measured.

  Next, a 500-cycle heat shock test was performed on the glass substrate with 5 ° C./50% RH × 30 minutes and 80 ° C./90% RH × 30 minutes as one cycle.

(Error yield test)
When the magnetic film was formed on the 1000 glass substrates manufactured as described above and then mounted on the hard disk, the error occurrence rate was obtained, and the relationship with the phase difference due to each occurrence rate is shown in FIG.

  In the following error determination, when the error occurrence rate is 5% or more, it is represented as “x” as an unacceptable performance. If the error rate is less than 5%, it is expressed as Δ, if the error rate is less than 3%, it is indicated as ◯, and if the error rate is less than 1%, it is indicated as ◎.

  The results of the evaluation of Example 1 are shown in Table 1.

(Example 2)
Using a glass substrate, a glass substrate is prepared using the float method, and according to the method of FIG. 3C (however, the first phase difference measurement is not performed), the disk processing step, the double-side grinding step, and the chemical strengthening The treatment process, the cleaning process, the double-side polishing process, and the final cleaning process were performed, and 1000 glass substrates were manufactured. In the double-side polishing step after the chemical strengthening treatment step, the glass substrate main surface was manufactured so that the compressive stress layer was 10 μm.

  And the phase difference of each board | substrate was measured.

  Next, a 500-cycle heat shock test was performed on the glass substrate with 5 ° C./50% RH × 30 minutes and 80 ° C./90% RH × 30 minutes as one cycle.

(Error yield test)
When 1000 glass substrates manufactured as described above were formed and then mounted on a hard disk, the error occurrence rate was determined, and the relationship with the phase difference due to each occurrence rate is shown in FIG.

  The results of the evaluation of Example 2 are shown in Table 2.

  Based on the above results, by selecting a glass substrate having a maximum phase difference of less than 5 nm, an error rate of 5 can be obtained regardless of whether the thickness of the compressive stress layer is 10 μm or 30 μm. % Could be achieved.

  In addition, in order to reduce the error yield to less than 3%, it is clear that in the case of a glass substrate having a compressive stress layer of 30 μm, it is sufficient to select one having a maximum phase difference of less than 4 nm. . Further, it has been found that when the compressive stress layer is a glass substrate having a thickness of 10 μm, it is sufficient to select one having a maximum phase difference of less than 3 nm.

DESCRIPTION OF SYMBOLS 1 Glass plate 2 Gob 3 Lower mold 4 Upper mold 5 Outflow pipe 6 Molten glass 7 Cutting blade 8,9 Cutting line 10 Glass substrate 11 Grinding machine 12 Upper surface plate 13 Lower surface plate 14 Fixed abrasive 15 Glass cutter 16 Pump 101 Magnetic information Glass substrate for recording medium

Claims (7)

In the process of inspecting / selecting the glass substrate for HDD with a compressive stress layer applied to the surface layer by the chemical strengthening process,
In the radial direction of the glass substrate for HDD, the glass substrate for HDD in a range from a position 0.5 mm from the diameter end of the central hole to a position 0.5 mm from the outer diameter end of the glass substrate for HDD. The maximum value of the phase difference of the transmitted light based on the difference in propagation speed between the polarized light parallel to the electric field component and the polarized light perpendicular to the electric field component of the transmitted light transmitted from the surface direction is less than 5.0 nm. A method for inspecting and selecting a glass substrate for HDD, wherein a certain one is selected. In the process of inspecting and selecting a glass substrate for HDD having a compressive stress layer of less than 20 μm on the surface layer by a chemical strengthening process,
2. The inspection / sorting method for a glass substrate for HDD according to claim 1, wherein the maximum value of the phase difference is less than 3.0 nm.   2. The inspection / sorting method for a glass substrate for HDD according to claim 1, wherein the inspection / sorting of the glass substrate for HDD having a compressive stress layer of 20 [mu] m or more applied to the surface layer by a chemical strengthening step.   A method for producing an HDD information recording medium, comprising providing a magnetic layer only on a glass substrate selected by the inspection / sorting method for an HDD glass substrate according to claim 1. A glass substrate for HDD to have a compressive stress layer in the surface layer,
In the radial direction of the glass substrate for HDD, it was transmitted from the surface direction of the glass substrate for HDD in a range from a position 0.5 mm from the diameter end of the center hole to a position 0.5 mm from the outer diameter end . The maximum value of the amount of phase difference of the transmitted light based on the difference between the propagation speed of polarized light parallel to the electric field component of transmitted light and polarized light perpendicular to the electric field component is less than 5.0 nm. Glass substrate.   The HDD glass substrate according to claim 5, wherein the compressive stress layer has a thickness of 20 μm or more. The compressive stress layer has a thickness of less than 20 μm;
6. The glass substrate for HDD according to claim 5, wherein the maximum value of the phase difference is less than 3.0 nm.

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