JP2009059427A - Method for manufacturing glass substrate for magnetic disk, method for manufacturing magnetic disk, and apparatus for measuring substrate thickness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic disk glass substrate manufacturing method for efficiently manufacturing a glass substrate without discarding a glass substrate whose, for example, substrate thickness has been measured as test of the glass substrate, and to provide a method for manufacturing a magnetic disk, and an apparatus for measuring a substrate thickness. <P>SOLUTION: The magnetic disk glass substrate manufacturing method includes a polishing step of polishing a main surface of a circular glass substrate 1 (3), and a test step of testing the polished glass substrate 1. The test step includes measuring a shape of the glass substrate 1 (3) in a non-contact manner while holding the glass substrate 1 (3) in water. The glass substrate 1 (3) used in the test is returned to the manufacturing process. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk, a method for manufacturing a magnetic disk, and a plate thickness measuring apparatus, and measures the plate thickness of a glass substrate for a magnetic disk, etc., for which plate thickness accuracy and surface smoothness are required with high accuracy. The present invention relates to a method of manufacturing a glass substrate for a magnetic disk including a step of performing, a method of manufacturing a magnetic disk, and a plate thickness measuring device used in a step of measuring the plate thickness.

  There is a magnetic disk as a magnetic recording medium mounted on an HDD (Hard Disk Drive) which is one of the magnetic recording media. As a magnetic disk, a structure in which a film such as NiP (nickel phosphorus) is deposited on a metal substrate made of an aluminum-magnesium alloy, or a base layer, magnetic layer, protective layer, lubrication on a substrate such as a glass substrate or a ceramic substrate. Some have a configuration in which layers are sequentially stacked.

  In recent years, with the miniaturization, thinning, and high-density recording of magnetic disks, glass substrates that have superior substrate surface flatness compared to metal substrates such as aluminum substrates have been used.

  By the way, in the glass substrate, in order to achieve further high density recording, it is necessary to further improve the smoothness of the substrate surface, and strict dimensional accuracy is required for the glass substrate.

  In the manufacturing process of the magnetic disk glass substrate, the dimension of the glass substrate is measured for each process or after a plurality of processes in response to the demand for such dimensional accuracy. Here, since the main surface of the magnetic disk glass substrate is polished to a mirror surface, it is avoided that a measuring jig is brought into contact with the main surface when measuring the dimensional accuracy. A precision measuring instrument is used as a measuring instrument for performing such high-precision measurement. Specifically, an accuracy of 0.1 μm is required as the accuracy of the plate thickness required for the magnetic disk glass substrate.

Regarding such dimensional accuracy, an apparatus for measuring the thickness of a substrate in a non-contact manner has been proposed (see Patent Document 1). In this measuring apparatus, by supporting the outer peripheral edge of the disc, the disc is supported in a state in which contact scratches are unlikely to occur on both sides of the disc.
Japanese Patent Laid-Open No. 8-147691

  However, when measuring the thickness of the glass substrate for a magnetic disk, for example, when measuring the thickness of the glass substrate after the polishing process, the abrasive grains remaining on the substrate surface are removed and dried. It was measured in the state.

  However, if the removal of the abrasive grains is not complete, the abrasive grains remaining on the substrate surface will be firmly fixed on the substrate surface, resulting in a defective product, even if it is a good product before the measurement. It was difficult to return to the manufacturing process to make a product. That is, in the conventional manufacturing process, the glass substrate whose thickness was measured was discarded as a defective product without returning to the manufacturing process.

  Further, the main surface of the glass substrate for magnetic disks is required to have surface smoothness in angstrom units, and in order to achieve this requirement, the number of abrasive grains adhering to the glass substrate surface is not limited. A value close to zero is required. In order to satisfy such requirements, when measuring the plate thickness, the glass substrate must be washed to sufficiently remove the abrasive grains, and the production efficiency in the production process is remarkably reduced accordingly. There was a problem.

  The present invention has been made in view of the above points, and a method for manufacturing a glass substrate for a magnetic disk capable of efficiently manufacturing a glass substrate without discarding, for example, a glass substrate whose thickness has been measured as an inspection of the glass substrate. Another object of the present invention is to provide a magnetic disk manufacturing method and a plate thickness measuring apparatus.

  The method for manufacturing a glass substrate for a magnetic disk according to the present invention includes a polishing step for polishing a main surface of a disk-shaped glass substrate, and an inspection step for inspecting the polished glass substrate. In the method, the inspection step includes a step of measuring the shape of the glass substrate in a non-contact state while holding the glass substrate in water, and returning the inspected glass substrate to the manufacturing step. And

  According to this manufacturing method, since it can test | inspect without drying a glass substrate, generation | occurrence | production that a glass substrate becomes defective by drying can be prevented. Thereby, the inspected glass substrate can be returned to the production line, and the yield in the production process of the magnetic disk glass substrate can be improved.

  The method for producing a glass substrate for a magnetic disk according to the present invention also includes a polishing step for polishing the main surface of a disk-shaped glass substrate and a measurement step for measuring the plate thickness of the glass substrate after polishing. In the method for manufacturing a glass substrate, the measuring step is performed such that light is incident obliquely on one of the main surfaces of the glass substrate while the glass substrate is held in water. An irradiation step of irradiating; a light receiving step of receiving reflected light from the one surface of the glass substrate held in the water; and a reflected light from the other surface; and the glass based on the two reflected lights. And calculating the thickness of the substrate, and returning the glass substrate on which the thickness has been measured to the manufacturing process.

  According to this manufacturing method, since the plate thickness can be measured without drying the glass substrate, it is possible to prevent the glass substrate from being defective due to drying. Thereby, the measured glass substrate can be returned to the manufacturing line, and the yield in the manufacturing process of the glass substrate for magnetic disks can be improved.

  In the method for manufacturing a glass substrate for a magnetic disk according to the present invention, it is preferable that in the irradiation step, the light is irradiated to the glass substrate in water from outside the water tank. In this case, it is not necessary to install an irradiating means for irradiating light for measurement and a light receiving means for receiving reflected light from the glass substrate in the water, so that measurement is performed using more highly accurate irradiating means and light receiving means. It can be performed.

  The method for producing a magnetic disk of the present invention comprises a polishing step for polishing the main surface of a disk-shaped glass substrate, a measurement step for measuring the plate thickness of the polished glass substrate, and a main surface of the glass substrate. A magnetic recording layer forming step of forming a magnetic recording layer made of a magnetic thin film, wherein the measuring step includes holding the glass substrate in water in a state where the glass substrate is in the main state. An irradiation step of irradiating light so as to be incident obliquely on one surface of the surface, reflected light from the one surface of the glass substrate held in the water, and from the other surface A light receiving step for receiving reflected light and a calculation step for calculating a plate thickness of the glass substrate based on the two reflected lights, wherein the glass substrate on which the plate thickness is measured is returned to the manufacturing step. And

  According to this manufacturing method, since the plate thickness can be measured without drying the glass substrate, it is possible to prevent the glass substrate from being defective due to drying. Thereby, the measured glass substrate can be returned to the manufacturing line, and the yield in the manufacturing process of the glass substrate for magnetic disks can be improved. Thus, the yield in the manufacturing process of a magnetic disk using this magnetic disk glass substrate can be improved.

  In the method of manufacturing a magnetic disk according to the present invention, it is preferable that in the irradiation step, the light is irradiated to the glass substrate in water from outside the water tank. In this case, it is not necessary to install an irradiating means for irradiating light for measurement and a light receiving means for receiving reflected light from the glass substrate in the water, so that measurement is performed using more highly accurate irradiating means and light receiving means. It can be performed.

  The plate thickness measuring device of the present invention is a plate thickness measuring device for measuring the plate thickness of a plate-like glass substrate, and includes a water tank, a holding means for holding the glass substrate inside the water tank, and the water tank. Irradiation means for irradiating light so as to be incident obliquely with respect to one of the main surfaces of the glass substrate held inside, reflected light from the one surface of the glass substrate, It is characterized by comprising light receiving means for receiving reflected light from the other surface and calculation means for calculating the plate thickness of the glass substrate based on the two reflected lights.

  According to this configuration, since the thickness of the glass substrate can be measured without drying, it is possible to prevent the glass substrate from being defective due to drying. Thereby, the measured glass substrate can be returned to the production line, and the yield of the glass substrate can be improved. Thus, the yield in the manufacturing process of the magnetic disk using this glass substrate can be improved.

  In the plate thickness measuring apparatus according to the present invention, the irradiating unit and the light receiving unit are provided outside the water tank, and a part of the water tank is provided with a transmission unit that transmits the light and the reflected light. It is preferable. In this case, it is not necessary to install an irradiating means for irradiating light for measurement and a light receiving means for receiving reflected light from the glass substrate in the water, so that measurement is performed using more highly accurate irradiating means and light receiving means. It can be performed.

  According to the present invention, a method for manufacturing a glass substrate for a magnetic disk, a method for manufacturing a magnetic disk, and a plate thickness that can efficiently manufacture a glass substrate without discarding the glass substrate whose thickness is measured, for example, as an inspection of the glass substrate. A measuring device can be provided.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
The magnetic disk manufacturing method according to the present invention is for manufacturing a magnetic disk mounted on, for example, a hard disk drive (HDD). This magnetic disk is a recording medium capable of performing high-density information signal recording and reproduction by, for example, a perpendicular magnetic recording method. Moreover, the manufacturing method of the glass substrate for magnetic discs which concerns on this invention manufactures the glass substrate used for the said magnetic disc.

  This glass substrate for a magnetic disk has an outer diameter of 15 to 30 mm, an inner diameter of 5 to 12 mm, and a plate thickness of 0.35 to 0.5 mm. For example, “0.8 inch type magnetic disk” (inner diameter of 6 mm, outer 21.6 mm diameter, plate thickness 0.381 mm), “1.0 inch type magnetic disk” (inner diameter 7 mm, outer diameter 27.4 mm, plate thickness 0.381 mm), etc. . Further, it may be manufactured as a magnetic disk such as a “2.5 inch magnetic disk” or a “3.5 inch magnetic disk”. Here, the “inner diameter” is the inner diameter of the circular hole at the center of the glass substrate.

  FIG. 1 is a perspective view showing the configuration of a magnetic disk glass substrate 1 (hereinafter simply referred to as a glass substrate) manufactured by the method for manufacturing a magnetic disk glass substrate according to the present invention.

  The method for producing a glass substrate 1 according to the present invention is a method for producing a glass substrate for a magnetic disk, which produces a glass substrate 1 having a circular hole (center hole) 2 in the center as shown in FIG. Since the glass substrate 1 is made of glass, it can achieve excellent smoothness by mirror polishing, has high hardness, and high rigidity, and thus has excellent impact resistance. In particular, a magnetic disk used for a hard disk drive mounted on a portable (carried) or in-vehicle information device is required to have high impact resistance. It is highly useful to use. Although glass is a brittle material, the breaking strength can be improved by a strengthening treatment such as chemical strengthening.

  As a glass preferable as the material of such a glass substrate 1, an aluminosilicate glass can be mentioned. This is because the aluminosilicate glass can realize an excellent smooth mirror surface and can increase the breaking strength by, for example, chemical strengthening. Moreover, as glass preferable as a material of such a glass substrate 1, crystallized (amorphous) glass can be mentioned.

As the aluminosilicate glass, SiO ₂ : 62 to 75 wt%, Al ₂ O ₃ : 5 to 15 wt%, Li ₂ O: 4 to 10 wt%, Na ₂ O: 4 to 12 wt% ZrO ₂ : 5.5 to 15 wt% as a main component, and the weight ratio of Na ₂ O to ZrO ₂ is 0.5 to 2.0, and Al ₂ O ₃ and ZrO ₂ A chemically strengthened glass having a weight ratio of 0.4 to 2.5 is preferred.

Further, in such a glass substrate 1, in order to eliminate the protrusion of the glass substrate surface undissolved product of ZrO ₂ occurs causes a SiO ₂ 57 to 74 [mol%], the ZrO ₂ 0 to 2.8 Use chemically strengthened glass containing [mol%], Al ₂ O _{3 3} to 15 [mol%], LiO ₂ 7 to 16 [mol%], Na ₂ O 4 to 14 [mol%]. Is preferred. The aluminosilicate glass having such a composition has an increased bending strength, a deep compressive stress layer, and an excellent Knoop hardness when chemically strengthened.

  Moreover, the material which comprises the glass substrate 1 manufactured in this invention is not necessarily limited to what was mentioned above. That is, as the material of the glass disk, in addition to the aluminosilicate glass described above, for example, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or crystallized glass Examples thereof include glass ceramics.

  FIG. 2 is a flowchart showing the manufacturing process of the magnetic disk including the manufacturing process of the glass substrate 1 according to the embodiment of the present invention. As shown in FIG. 2, in the method for manufacturing glass substrate 1 according to the present embodiment, glass disk 3 (FIG. 1) is formed by a press method or the like in the glass disk forming step of step ST11. In the lapping process of step ST12, the shape of the glass disk 3 is adjusted and the main surface is lapped. In the lapping process, processing is performed using a double-sided lapping apparatus and alumina abrasive grains, and the dimensional accuracy and shape accuracy of the glass disk 3 are set to predetermined ones. Here, the outer peripheral side end surface portion and the inner peripheral side end surface portion (the inner end surface of the center hole 2 (FIG. 1)) of the glass disk 3 may be polished.

  Next, in step ST13, a first polishing process is performed as a main surface polishing process (polishing process) of the glass disk 3. This first polishing step is mainly intended to remove scratches and distortions remaining on the main surface in the lapping step described above. This process can be performed using a planetary gear mechanism using a double-side polishing apparatus and a hard resin polisher. As the abrasive, cerium oxide abrasive grains are preferably used. Incidentally, the main surface of the glass disk 3 means two surfaces (the front surface 3a and the back surface 3b (FIG. 1)) of the glass disk 3.

  Next, in step ST14, a second polishing process is executed as a mirror polishing process of the main surface of the glass disk 3. The purpose of this second polishing step is to finish the main surface into a mirror surface. This step can be performed using a planetary gear mechanism using a double-side polishing apparatus and a soft foam resin polisher. As the abrasive, it is preferable to use fine cerium oxide abrasive grains as compared with the cerium oxide abrasive grains used in the first polishing step.

  Next, out of the glass disks 3 for which the second polishing process has been completed, one glass disk 3 is extracted every predetermined number (for example, 100), and an inspection process for the shape of the glass disk 3 is performed. In the case of this embodiment, as the inspection of the shape of the glass disk 3, the plate thickness is measured (plate thickness measuring step described later: step ST19). Incidentally, the inspection of the shape of the glass disk 3 is a concept including not only the inspection of the thickness of the glass disk 3 but also the inspection of the surface roughness and the like. Therefore, the inspection of the shape of the glass disk 3 is not limited to the measurement of the plate thickness described in the present embodiment, but includes, for example, the case where the surface roughness of the glass disk 3 is measured.

  In the inspection process of the glass disk 3, in step ST15, the number of glass disks 3 for which the second polishing process has been completed is counted. The extraction is not performed until the count result becomes “100”, and the process proceeds from step ST15 to the chemical strengthening process (step ST16) which is the next process in the manufacturing process. On the other hand, when the count result is “100”, one glass disk 3 that has finished the second polishing step is extracted, and the process proceeds to step ST19 to measure the plate thickness. If the count result is “100” and one glass disk 3 is extracted for the plate thickness inspection, the count value is reset.

  The plate thickness measuring step (step ST19) is a step of measuring the plate thickness with an accuracy of 0.1 μm by accurately measuring the plate thickness of the glass disk 3 in a non-contact manner. In this plate thickness measuring step, a plate thickness measuring apparatus 10 shown in FIGS. 3A and 3B is used. That is, as shown in FIGS. 3A and 3B, first, the glass disk 3 after the second polishing step is immersed in water, and the inner peripheral side end face portion (center hole) of the glass disk 3 is immersed in the water. 3 on the inner end face of 2) is supported at three points by the supporting members 9a, 9b and 9c. The support members 9a, 9b and 9c are provided at the tip of the arm 8 extending from the outside to the inside of the water tank 11, and are stored in the water tank 11 by supporting the center hole 2 of the glass disk 3. The glass disk 3 is held in water.

  As shown in FIGS. 3B and 4, a laser beam is emitted from the light emitting portion 20 a of the sensor 20 (FIG. 3B) provided outside the water tank 11 with respect to the held glass disk 3. The first reflected light LB1 irradiated with LA and reflected on one surface 3a of the main surface of the glass disk 3 and the reflected light LB2 from the other surface 3b of the main surface of the glass disk 3 are detected by the sensor. The light receiving unit 20b receives light. Incidentally, the reflected light LB2 from the other surface 3b of the main surface is a glass disc via one surface (first surface) 3a of the main surface of the glass disc 3, as shown in FIG. The laser beam LA1 incident on the inside of the glass disk 3 means the reflected light reflected by the back surface (second surface) 3c of the other surface 3b inside the glass disk 3. In the sensor 20 (FIG. 3B), the distance from the sensor 20 to the one surface 3a and the distance from the sensor 20 to the other surface 3b are determined based on the light receiving positions of the received reflected lights LB1 and LB2. Each is detected, and the plate thickness of the glass disk 3 is obtained from these differences. That is, in the case of the present embodiment, the sensor 20 uses a light emitting element (semiconductor laser) as the light emitting unit 20a, and uses a light position detecting element (PSD (Position Sensitive Detector)) as the light receiving unit 20b, and in an oblique direction on the measurement target. The diffuse reflection component reflected on the light is received by the light receiving unit 20b, and the distance from the sensor 20 to the measurement object (one surface 3a, the other surface 3b) is detected based on the light receiving position. As the sensor 20, for example, LK-G15 (trade name) manufactured by Keyence Corporation can be used, but various sensors using the same measurement principle or other measurement principles can be used.

  Since the high-precision sensor 20 is generally difficult to immerse in water, in the present embodiment, the sensor 20 is installed outside the water tank 11, and the sensor 20 allows the sensor 20 to enter the water from the outside. The laser beam LA is irradiated toward the head.

  A transmission plate 13 is provided in the window 12 (FIG. 3B) through which the laser light LA and the reflected light LB1 and LB2 of the water tank 11 are transmitted. The transmission plate 13 has a Waviness (Wq: root mean square height of waviness curve) of 5 [nm] or less, and is made of a glass plate that transmits laser light.

  The transmission plate 13 is adapted to fit into a window portion 12 formed on the side surface portion of the water tank 11, and a seal member (not shown) is provided between the periphery of the transmission plate 13 and the window portion 12. It seals so that the water in the water tank 11 may not leak.

  Using the plate thickness measuring apparatus 10 having such a configuration, the plate thickness of the glass disk 3 is measured and calculated, and the plate thickness measuring step (step ST19) is executed. In this plate thickness measurement process, the surface of the glass disk 3 after the second polishing process is simply washed, and then the glass disk 3 is immersed in a water tank 11 containing water. As described above, the glass disk 3 is supported at three points on its inner peripheral side end face (center hole 2) in the water tank 11. Thus, by supporting the center hole 2 at three points, the glass disk 3 can be stably held even in water. Further, in the water tank 11, the glass disk 3 is supported so that the first surface 3 a faces the window 12 provided with the transmission plate 13.

  In this state, the laser light LA is emitted from the light emitting portion 20a of the sensor 20 provided outside the water tank 11 to the first surface 3a of the glass disk 3 from the oblique direction via the transmission plate 13, and the first The reflected light LB1 reflected on the first surface 3a is received by the light receiving unit 20b. Further, the laser beam LA irradiated to the first surface 3a of the glass disk 3 is transmitted through the first surface 3a and is incident on the second surface 3c facing the first surface 3a. 2 is reflected by the second surface 3c, is transmitted through the first surface 3a, and is received by the light receiving portion 20b of the sensor 20. Based on the reflected light LB1 from the first surface 3a and the reflected light LB2 from the second surface 3c, the sensor 20 calculates the glass disk plate based on the phase difference between them. Calculate the thickness.

  And based on this measurement result, the quality of the glass disk 3 is determined to be good (step ST20). The glass disk 3 determined to be non-defective is returned to the production line, and a chemical strengthening step (step ST16) subsequent to the second polishing step (step ST14) is performed. In this chemical strengthening process, the glass disk 3 that has not been extracted for the plate thickness measurement process (step ST19) and the glass disk 3 that has been determined to be non-defective in the plate thickness measurement process (step ST19) are chemically strengthened. It becomes the object of.

  In the chemical strengthening step (step ST16), a chemical strengthening solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) was prepared, and this chemical strengthening solution was heated to 400 ° C and preheated to 300 ° C. The cleaned glass disk 3 is immersed for about 3 hours. During the immersion, in order to chemically strengthen the entire surface of the glass disk 3, they are accommodated in a holder so that the plurality of glass disks 3 are held by the end faces.

  Thus, by immersing in the chemical strengthening solution, the lithium ions and sodium ions in the surface layer of the glass disk 3 are respectively replaced with sodium ions and potassium ions in the chemical strengthening solution, and the glass disk 3 is strengthened. The glass disk 3 that has been subjected to chemical strengthening is immersed in a 20 ° C. water bath to be rapidly cooled and maintained for about 10 minutes.

  Next, the glass disk 3 that has been rapidly cooled is immersed in concentrated sulfuric acid heated to about 40 ° C. to perform a cleaning step (step ST17). Further, the glass disk 3 that has been subjected to the sulfuric acid cleaning is subjected to pure water, IPA. (Isopropyl alcohol) and steam-dried cleaning baths are sequentially immersed in the cleaning. In addition, an ultrasonic wave is applied to each washing tank.

  A final inspection process (step ST18) is performed on the surface of the glass disk 3 obtained through the above processes. In this inspection process, the surface roughness of the glass disk 3 is measured with an atomic force microscope (AFM), which is a type of scanning probe microscope (SPM). According to industrial standard (JIS) B0601. The mirror surface state is confirmed by both observation with an electron microscope and observation with an optical microscope.

  On the other hand, in the plate thickness measurement process (step ST19) for measuring the plate thickness of the glass disk 3 described above, was the glass disk 3 determined to be defective determined to be defective because the plate thickness was greater than a specified value? If it is determined whether or not (step ST21) is larger than the specified value (step ST21: YES), the process proceeds to step ST22, and the entire lot from which the glass disk 3 has been extracted in step ST15 is returned to the lapping process. The lot reprocessing is performed, and the process returns to the lapping step (step ST12). As a result, for a lot (including the glass disk 3 subjected to the sampling inspection) whose plate thickness is greater than the specified value, the lapping process is performed again so that the plate thickness falls within the specified value. As described above, it is presumed that the same result is obtained with respect to the glass disk 3 of the same lot as the glass disk 3 subjected to the sampling inspection and not subjected to the sampling inspection. 3 is again subjected to the lapping step.

  The glass disk 3 that has been subjected to the lapping process again proceeds again to the first polishing step (step ST13), the second polishing step (step ST14), and the extracted one sheet to the plate thickness measurement step (step ST19). Processing in each step is performed. And when it determines with a non-defective product in the plate thickness measurement process performed again, about the glass disk 3 by which the subsequent chemical strengthening process (step ST16) was performed about the lot, and the plate thickness measurement was performed Is also returned to the production line and sent to the chemical strengthening process.

  On the other hand, if the measurement result of the plate thickness measurement step (step ST19) is smaller than the standard thickness, a negative result is obtained in step ST21, so that the process moves from step ST21 to step ST23. The measured glass disk 3 is discarded, and in step ST24, lot error processing is executed for the glass disk 3 in the same lot as the discarded glass disk 3. In this lot error processing, for example, the thickness of the glass disks 3 of all the lots is measured, the ones within the standard are returned to the production line, and the non-standard ones are discarded, A disposal process is performed.

  Thus, in the manufacturing process of the glass substrate of this Embodiment demonstrated above, about the non-defective product whose plate | board thickness is within a specification about the glass disc 3 rotated by the plate | board thickness measurement process (step ST19). Is returned to the production line, even if it is a non-standard defective product, if the plate thickness is larger than the standard and can be made a good product by re-wrapping, it is returned to the production line and re-wrapped. The

  After the manufacturing of the glass substrate 1 for a magnetic disk is performed by the processes described above (steps ST11 to ST24), a magnetic recording layer made of a magnetic thin film in step ST30 is formed on the manufactured glass substrate 1. Thus, a magnetic disk is manufactured.

  An example of the magnetic recording layer forming process in step ST30 will be described. On both main surfaces of the glass substrate 1 manufactured by the manufacturing process of the glass substrate 1 in the above-described steps ST11 to ST24, a Ni-Ta alloy first underlayer, Ru no. (2) An underlayer, a Co—Cr—Pt—B alloy magnetic layer, and a hydrogenated carbon protective layer are sequentially formed. Then, an alcohol-modified perfluoropolyether lubricating layer is formed by a dip method. In this way, a magnetic disk for the perpendicular magnetic recording system can be manufactured. The method for forming the magnetic recording layer is not limited to this, and other various methods and materials can be applied.

  In the magnetic disk manufacturing method described above, the glass disks 3 flowing through the production line are sequentially extracted every predetermined number, and the thickness of the extracted glass disks 3 is measured by an inspection process. In the inspection process for measuring the plate thickness, the glass disk 3 to be inspected is immersed in the water stored in the water tank 11. And from the sensor 20 installed in the air outside the water tank 11, the first surface 3 a of the glass disk 3 supported in the water of the water tank 11 through the transmission plate 13 provided on the side surface of the water tank 11. Is irradiated with a laser beam LA.

  The sensor 20 is a high-precision type that is difficult to install in water, and is installed outside the water tank 11 (in the air). A high flatness transmission plate 13 is provided on the side surface of the water tank 11 on the optical path of the laser beam LA emitted from the sensor 20. As the transmission plate 13 is smoother, the measurement accuracy of the plate thickness is improved. In this embodiment, the Waviness (Wq) is 5 nm or less. Thereby, it is possible to obtain the measurement accuracy capable of maintaining the accuracy of the glass disk 3 that requires accuracy of 0.1 μm unit.

  As described above, the thickness of the glass disk 3 can be measured with high accuracy while supporting the glass disk 3 in water, so that the main surface becomes dirty as compared with the case where the glass disk 3 is dried and measured as in the prior art. Can be avoided. As a result, the glass disk 3 after measurement is kept in a good state, and the glass disk 3 determined to have a good inspection result is directly returned to the production line to be completed as a product. Can do.

  Thus, according to the above manufacturing method, the yield can be improved in manufacturing the glass substrate 1 by returning the glass disk 3 determined to be non-defective by the inspection to the manufacturing line and completing it as a product. Therefore, the manufacturing yield of magnetic disks manufactured using this glass substrate 1 can be improved.

  In the above-described embodiment, the case where the measurement method of irradiating the laser beam LA from the outside of the water tank is applied to the inspection process performed after the second polishing process has been described, but the present invention is limited to this. Instead, it can also be applied to the plate thickness measurement process at other timings.

  In the above-described embodiment, the case where the thickness of the glass disk 3 is measured in a non-contact manner in the manufacturing process of the magnetic disk glass substrate has been described, but the present invention is not limited to this. When measuring the surface roughness of the glass disk 3 using an atomic force microscope without contact, or when irradiating the surface of the glass disk 3 with light and inspecting the surface roughness based on the nature of the scattered light The present invention can be applied to various inspections that can be inspected in water among the inspection steps for evaluating the glass disk 3 in a non-contact manner.

  Moreover, although the case where the sensor 20 is installed outside the water tank 11 (in the air) has been described in the above-described embodiment, the present invention is not limited to this, and a sensor that can be installed in water is used. For example, the water tank 11 may be installed in the water (underwater).

  The present invention is applicable, for example, when measuring the thickness of a glass disk in a manufacturing process of a glass substrate for a magnetic disk.

The perspective view which shows the glass substrate manufactured in the manufacturing method of the glass substrate for magnetic discs concerning embodiment of this invention 1 is a flowchart showing a manufacturing process of a magnetic disk including a manufacturing process of a glass substrate for a magnetic disk according to an embodiment of the present invention. Sectional drawing which shows the plate | board thickness measuring apparatus used for the manufacturing process of FIG. Sectional view showing laser light and its reflected light on a glass disk

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Center hole 3 Glass disk 3a 1st surface 3b 2nd surface 8 Arm 9a, 9b, 9c Support member 11 Water tank 12 Window part 13 Transmission plate 20 Sensor 20a Light emission part 20b Light-receiving part LA Laser beam LB1, LB2 reflected light

Claims (7)

A method for producing a glass substrate for a magnetic disk comprising a polishing step for polishing a main surface of a disk-shaped glass substrate, and an inspection step for inspecting the glass substrate after polishing,
The inspection process includes
Including the step of measuring the shape of the glass substrate in a non-contact manner while holding the glass substrate in water;
A method of manufacturing a glass substrate for a magnetic disk, comprising returning the inspected glass substrate to a manufacturing process. A method for producing a glass substrate for a magnetic disk, comprising: a polishing step for polishing a main surface of a disk-shaped glass substrate; and a measurement step for measuring a plate thickness of the glass substrate after polishing,
The measurement step includes
An irradiation step of irradiating light so as to be obliquely incident on one of the main surfaces of the glass substrate with the glass substrate held in water,
A light receiving step for receiving reflected light from the one surface of the glass substrate held in the water and reflected light from the other surface;
And calculating a thickness of the glass substrate based on the two reflected lights,
A method for producing a glass substrate for a magnetic disk, wherein the glass substrate on which the plate thickness has been measured is returned to the production process.   3. The method for manufacturing a glass substrate for a magnetic disk according to claim 2, wherein, in the irradiation step, the light is irradiated to the glass substrate in water from outside the water tank. A polishing step for polishing the main surface of the disk-shaped glass substrate, a measuring step for measuring the plate thickness of the polished glass substrate, and a magnetic recording layer made of a magnetic thin film on the main surface of the glass substrate A magnetic disk manufacturing method including a magnetic recording layer forming step,
The measurement step includes
An irradiation step of irradiating light so as to be obliquely incident on one of the main surfaces of the glass substrate while holding the glass substrate in water,
A light receiving step for receiving reflected light from the one surface of the glass substrate held in the water and reflected light from the other surface;
And calculating a thickness of the glass substrate based on the two reflected lights,
A method of manufacturing a magnetic disk, wherein the glass substrate on which the plate thickness has been measured is returned to the manufacturing process.   5. The method of manufacturing a magnetic disk according to claim 4, wherein, in the irradiation step, the light is irradiated to the glass substrate in water from outside the water tank. A plate thickness measuring device for measuring the thickness of a plate-like glass substrate,
A tank,
Holding means for holding the glass substrate in the water tank;
Irradiation means for irradiating light so as to be incident obliquely on one surface of the main surfaces of the glass substrate held inside the water tank;
A light receiving means for receiving reflected light from the one surface of the glass substrate and reflected light from the other surface;
A plate thickness measuring apparatus comprising: a calculating unit that calculates a plate thickness of the glass substrate based on the two reflected lights. The irradiation means and the light receiving means are provided outside the water tank,
The plate thickness measuring apparatus according to claim 6, wherein a part of the water tank is provided with a transmission part that transmits the light and the reflected light.

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