JP2010238298A - Method for manufacturing glass substrate for magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a glass substrate for a magnetic disk, the method acquiring a pure glass substrate for a magnetic disk with little US (ultrasonic) damage by controlling rupture energy of cavitation more precisely. <P>SOLUTION: The method for manufacturing a glass substrate for a magnetic disk includes a cleaning step of ultrasonically cleaning a glass substrate for a magnetic disk, wherein the method further includes a foreign substance-measuring step of measuring the size of a foreign substance remaining on the glass substrate for a magnetic disk before the cleaning process. In the cleaning process, sound pressure and frequency of ultrasonic waves used in the ultrasonic cleaning are adjusted in accordance with the size of the foreign substance. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk used in a magnetic disk device such as a hard disk drive (hereinafter referred to as “HDD”).

  There is a magnetic disk as a magnetic recording medium mounted on a hard disk drive device (HDD device). A magnetic disk is manufactured by laminating a magnetic layer or a protective layer on a substrate, a glass substrate, or a ceramic substrate on which a NiP film is deposited on a metal plate made of an aluminum-magnesium alloy or the like. Conventionally, an aluminum alloy substrate has been widely used as a substrate for a magnetic disk. However, with recent downsizing, thinning, and high-density recording of magnetic disks, surface flatness and A glass substrate having excellent strength with a thin plate has been used.

  Such a glass substrate for a magnetic disk includes a shape processing step and a first lapping step (first grinding step); an end shape processing step (a coring step for forming a hole, an end (an outer peripheral end and an inner peripheral end) Chamfering step (chamfered surface forming step)); end surface polishing step (outer peripheral end portion and inner peripheral end portion); second lapping step (second grinding step); main surface polishing step (first step) 1 and 2nd grinding | polishing process); It manufactures through processes, such as a chemical strengthening process.

  The glass substrate for a magnetic disk obtained through the above-described steps is required to have a highly clean surface free from contamination so that the magnetic film formed on the substrate does not peel off. For this reason, ultrasonic cleaning is used to clean the magnetic disk glass substrate (Patent Document 1). In this ultrasonic cleaning, a magnetic disk glass substrate is immersed in a cleaning liquid, and ultrasonic vibration is applied to the cleaning liquid. At this time, particles such as water molecules in the cleaning liquid vibrate at high speed, water is rapidly vaporized and bubbles are generated, and these bubbles are rapidly condensed and disappeared. It becomes the state of. This is called cavitation, and contaminants are decomposed by this phenomenon and easily dispersed in the cleaning liquid, so that cleaning can be performed effectively.

JP 7-313946 A

  In such ultrasonic cleaning, the size of cavitation and the energy at the time of rupture affect the cleaning power. That is, the larger the cavitation burst energy, the greater the cleaning power. However, if the burst energy of cavitation is excessively increased, damage (ultrasonic damage (US damage)) of the glass substrate for magnetic disk due to the burst energy occurs. Such damage to the glass substrate for a magnetic disk causes a data read / write error of the magnetic disk obtained by using this.

  The present invention has been made in view of the above points, and more precisely controls the burst energy of cavitation to obtain a clean glass substrate for a magnetic disk with little US damage. The purpose is to provide.

  The method for manufacturing a glass substrate for magnetic disk of the present invention is a method for manufacturing a glass substrate for magnetic disk including a cleaning step of ultrasonically cleaning the glass substrate for magnetic disk, and the glass for magnetic disk before the cleaning step. A foreign matter measuring step for measuring the size of the foreign matter remaining on the substrate, wherein the ultrasonic pressure and frequency used in the ultrasonic cleaning are adjusted according to the size of the foreign matter in the cleaning step. And

  According to this method, it is possible to perform cleaning with a sound pressure that does not cause US damage to the glass substrate for magnetic disks and at a frequency with high cleaning power. It is possible to obtain a clean glass substrate for a magnetic disk with a small amount of the magnetic disk.

  In the method for manufacturing a magnetic disk glass substrate of the present invention, it is preferable that the step immediately before the cleaning step is a main surface polishing step of polishing the main surface of the magnetic disk glass substrate.

  In the method for producing a glass substrate for magnetic disk of the present invention, it is preferable that the step immediately before the cleaning step is a chemical strengthening step for chemically strengthening the glass substrate for magnetic disk.

  In the manufacturing method of the glass substrate for magnetic disks of this invention, it is preferable that the time from the process just before the said washing | cleaning process to the said washing | cleaning process is less than 1 hour.

  In the method for manufacturing a glass substrate for a magnetic disk of the present invention, when the size of the foreign matter to be removed is mainly 1.0 μm or less, the frequency of the ultrasonic wave is 80 kHz to 120 kHz, and the sound pressure of the ultrasonic wave Is preferably 1.5 mV to 2.5 mV.

  In the method for manufacturing a glass substrate for a magnetic disk of the present invention, when the size of the foreign matter to be removed is mainly greater than 1.0 μm, the frequency of the ultrasonic wave is set to 40 kHz to 80 kHz, and the ultrasonic wave Is preferably set to 1.0 mV to 2.0 mV.

  The method for manufacturing a magnetic disk glass substrate of the present invention includes a cleaning step of ultrasonically cleaning the magnetic disk glass substrate, and measures the size of foreign matter remaining on the magnetic disk glass substrate before the cleaning step. In the cleaning step, the sound pressure and frequency of the ultrasonic wave used in the ultrasonic cleaning are adjusted according to the size of the foreign material, so that the rupture energy of cavitation is controlled more precisely. A clean glass substrate for a magnetic disk with little US damage can be obtained.

It is a figure which shows the relationship between a foreign material residual rate and time. It is a figure which shows typically the ultrasonic cleaning apparatus used in manufacture of the glass substrate for magnetic discs concerning embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Currently, in ultrasonic cleaning for glass substrates for magnetic disks, the frequency of ultrasonic waves is usually about 28 kHz to 40 kHz. When ultrasonic waves of about 28 kHz to 40 kH are used, strong cavitation occurs. However, it is known that when the frequency of ultrasonic waves is 80 kHz or higher, the lower limit of the sound pressure in the liquid at which cavitation can occur is increased, and cavitation is less likely to occur. This is thought to be because liquid resonance is less likely to occur as the frequency of the ultrasonic wave increases. Further, when the frequency of the ultrasonic wave is increased, the acceleration of the vibration of particles such as water molecules caused by the ultrasonic wave increases in proportion to the square of the frequency, so that a strong detergency based on the vibration of the particle can be obtained.

  As described above, when a frequency higher than the frequency of ultrasonic waves that are normally used is used, a strong detergency can be obtained, but it is considered that damage to the glass substrate for a magnetic disk also increases. In addition, as the frequency of the ultrasonic wave increases, it has an effect of generating weak cavitation many times (temporal effect) and an effect of suppressing cleaning unevenness by shortening the wavelength (spatial effect). Although it is known that the size of a foreign material becomes small, the size of the foreign material on which each frequency has an effect is not actually specified.

  As a result of studying a method of obtaining a high cleaning effect against foreign matter by using a frequency higher than the frequency of ultrasonic waves normally used, and reducing damage to the magnetic disk glass substrate, It has been found that it is only necessary to adjust three relationships between the size of the foreign matter, the frequency of the ultrasonic wave (frequency higher than the frequency of the ultrasonic wave normally used), and the sound pressure of the ultrasonic wave.

  Specifically, a foreign substance existing on the surface of the substrate in this state is spin-dried or IPA (isopropyl alcohol) dried on the glass substrate surface in which a foreign substance of less than 1.0 μm and a foreign substance exceeding 1.0 μm are present. The surface is observed with SEM for the size and shape from the results, and the frequency of ultrasonic waves that can remove the foreign matter with high detergency according to the size of the foreign matter, and the glass substrate for the magnetic disk It was found that there is an ultrasonic sound pressure (mV) that can completely suppress damage. Here, the size of the foreign matter refers to the maximum length of the foreign matter.

  That is, the essence of the present invention is a method for manufacturing a magnetic disk glass substrate including a cleaning step of ultrasonically cleaning the magnetic disk glass substrate, and remains on the magnetic disk glass substrate before the cleaning step. A foreign matter measuring step for measuring the size of the foreign matter, and in the cleaning step, by adjusting the sound pressure and frequency of the ultrasonic wave used in the ultrasonic cleaning according to the size of the foreign matter, more precise cavitation It is to obtain a clean glass substrate for a magnetic disk with little US damage by controlling the burst energy. As a result, it is possible to bring out the cleaning effect of the physical action using ultrasonic waves to the limit while suppressing damage to the glass substrate for magnetic disk, so that ultrasonic waves using ultrasonic waves with a frequency of 28 kHz to 40 kHz are used. Compared with cleaning, it is possible to obtain a glass substrate for a magnetic disk with high quality.

  The method for manufacturing a glass substrate for a magnetic disk according to the present invention measures the size of foreign matter remaining on the glass substrate for a magnetic disk before the cleaning step, and according to the size of the foreign matter measured in the cleaning step. The sound pressure and frequency of the ultrasonic wave used for ultrasonic cleaning are adjusted. In this case, when the size of the foreign matter to be removed is mainly 1.0 μm or less, the ultrasonic frequency is set to 80 kHz to 120 kHz or more, and the ultrasonic sound pressure is set to 1.5 mV to 2.5 mV. Preferably, when the size of the foreign matter to be removed is mainly larger than 1.0 μm, the ultrasonic frequency is set to 40 kHz to 80 kHz, and the ultrasonic sound pressure is set to 1.0 mV to 2. It is preferably 0 mV.

In the cleaning process of the magnetic disk glass substrate, the binding energy between the remaining foreign matter that has passed through the cleaning process such as acid cleaning, alkali cleaning, and solvent cleaning increases. This point will be described in detail. When a certain foreign substance remaining on the glass substrate surface is considered, it is rare to exist in a pure state (for example, pure metal). Most of them exist in a mixed state (pure metal + organic matter / pure metal A + pure metal B, etc.). Such foreign matter is present on the surface of the glass substrate by polishing or strengthening, but in this state, it can be easily detached from the surface of the glass substrate. This is because the binding energy between the glass substrate and the foreign material is relatively low. However, when the glass substrate passes through acid cleaning, alkali cleaning, or is dried in the air, H ₂ O present at the interface between the foreign matter and the glass substrate surface is caused by a metal redox reaction. Organic substances and the like that are consumed and are present at the interface are locally condensed and shift from a simple binding state to a strong binding state by a complex molecule (high binding energy).

  In this way, it is not easy to remove the foreign matter from the glass substrate surface in a state where the binding energy is high. FIG. 1 shows the ratio of foreign matter remaining on the glass substrate surface when the glass substrate is subjected to ultrasonic cleaning after being left for a predetermined time with respect to foreign matter remaining on the glass substrate surface after polishing or chemical strengthening on the glass substrate. Is shown. As shown in FIG. 1, when the standing time after the processing with respect to the glass substrate elapses, the binding energy between the glass substrate and the foreign matter becomes high and is difficult to remove. Therefore, it is important to remove the foreign matter when the binding energy between the foreign matter and the glass substrate surface is relatively low. Specifically, it is preferable that the time from the process immediately before the cleaning process to the cleaning process is within one hour.

  A preferable example of the glass substrate material is aluminosilicate glass. The aluminosilicate glass can realize an excellent smooth mirror surface and can increase the breaking strength by, for example, chemical strengthening.

As the aluminosilicate glass, SiO ₂ : 62 wt% to 75 wt%, Al ₂ O ₃ : 5 wt% to 15 wt%, Li ₂ O: 4 wt% to 10 wt%, Na ₂ O: 4 wt% to 12% by weight, ZrO ₂ : 5.5% by weight to 15% by weight as a main component, and a weight ratio of Na ₂ O to ZrO ₂ is 0.5 to 2.0, Al ₂ O ₃ and ZrO ₂ The glass for chemical strengthening whose weight ratio is 0.4 to 2.5 is preferable.

  Further, the material forming the glass substrate for a magnetic disk manufactured in the present invention is not limited to the above-described materials. That is, as the material of the glass substrate, 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.

  The manufacturing process of the glass substrate for a magnetic disk includes a material processing process and a first lapping process; an edge shape process (a coring process for forming a hole, a chamfered surface at an outer edge and / or an inner edge) Chamfering step (chamfered surface forming step)); second lapping step; end surface polishing step (outer peripheral end and inner peripheral end); main surface polishing step (first and second polishing step); chemical strengthening step : Includes processes such as a cleaning process. The main surface polishing step (second polishing step) and the chemical strengthening step may be in reverse order.

Below, each process of the manufacturing process of the glass substrate for magnetic discs is demonstrated.
(1) Material processing step and first lapping step First, in the material processing step, the surface of the sheet glass is lapped (ground) to form a glass base material, and the glass base material is cut to cut out a glass disk. Various plate glasses can be used as the plate glass. This plate-like glass can be manufactured by using a known manufacturing method such as a press method, a float method, a downdraw method, a redraw method, or a fusion method using a molten glass as a material. Of these methods, if a press method is used, a sheet glass can be produced at a low cost.

  In the first lapping step, both main surfaces of the sheet glass are lapped to form a disk-shaped glass substrate. This lapping process can be performed using alumina free abrasive grains with a double-sided lapping apparatus using a planetary gear mechanism. Specifically, the lapping platen is pressed on both sides of the plate glass from above and below, the grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relative to each other for lapping. Do. By this lapping process, a glass substrate having a flat main surface can be obtained.

(2) End shape process (coring process for forming a hole, chamfering process for forming a chamfer on the end (outer peripheral end and inner peripheral end) (chamfered surface forming process))
In the coring step, for example, an inner hole is formed at the center of the glass substrate using a cylindrical diamond drill to obtain an annular glass substrate. In the chamfering step, the inner peripheral end surface and the outer peripheral end surface are ground with a diamond grindstone, and a predetermined chamfering process is performed.

(3) Second Lapping Step In the second lapping step, the second lapping process is performed on both main surfaces of the obtained glass substrate in the same manner as in the first lapping step. By performing this second lapping process, it is possible to remove in advance the fine irregularities formed on the main surface in the previous cutting process and end face polishing process, and shorten the subsequent polishing process on the main surface. Will be able to be completed in time.

(4) End surface polishing step In the end surface polishing step, the outer peripheral end surface and the inner peripheral end surface of the glass substrate are mirror-polished by a brush polishing method. At this time, as the abrasive grains, for example, a slurry containing cerium oxide abrasive grains (free abrasive grains) can be used. By this end face polishing step, the end face of the glass substrate is in a mirror state that can prevent the precipitation of sodium and potassium.

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

(6) Main surface polishing step (final polishing step)
Next, a second polishing process is performed as a final polishing process. The second polishing step is a step aimed at finishing the main surface into a mirror surface. In the second polishing step, mirror polishing of the main surface is performed using a soft foam resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the slurry, colloidal silica abrasive grains (average particle diameter of 0.5 μm or less) finer than the cerium oxide abrasive grains used in the first polishing step can be used.

(7) Chemical strengthening step In the chemical strengthening step, the glass substrate that has been subjected to the lapping step and polishing step described above is chemically strengthened. As a chemical strengthening solution used for chemical strengthening, for example, a mixed solution of potassium nitrate (60%) and sodium nitrate (40%) can be used. In the chemical strengthening, the chemical strengthening solution is heated to 300 ° C. to 400 ° C., the cleaned glass substrate is preheated to 200 ° C. to 300 ° C., and immersed in the chemical strengthening solution for 3 hours to 4 hours. In soaking, in order to chemically strengthen the entire surface of the glass substrate, the immersion is preferably performed in a state of being accommodated in a holder so that the plurality of glass substrates are held at the end surfaces.

  Thus, by immersing in the chemical strengthening solution, the lithium ions and sodium ions in the surface layer of the glass substrate are respectively replaced with sodium ions and potassium ions having a relatively large ion radius in the chemical strengthening solution. Will be strengthened.

(8) Foreign matter measuring step Immediately before the chemical strengthening step for chemically strengthening the glass substrate for magnetic disk, or when performing the second polishing after chemical strengthening, immediately before the main surface polishing step for polishing the main surface of the glass substrate for magnetic disk In addition, the size of the foreign matter remaining on the magnetic disk glass substrate is measured. Then, the size distribution of the foreign matter is obtained, and the sound pressure and frequency of the ultrasonic wave in the cleaning process are adjusted according to the size of the foreign matter contained at the highest rate. An SEM (electron microscope) or the like can be used as an apparatus for measuring the size and distribution of foreign matter.

(9) Cleaning Step In the cleaning step, the magnetic disk glass substrate D is ultrasonically cleaned using an ultrasonic cleaning apparatus as shown in FIG. The ultrasonic cleaning apparatus shown in FIG. 2 has a cleaning tank 1 that contains a cleaning liquid 2, an ultrasonic vibrator 3 that is immersed in the cleaning liquid and generates cavitation in the cleaning liquid, and an ultrasonic frequency in the cleaning liquid. It mainly comprises a frequency detector 4 to be detected, a carrier 5 that supports a plurality of magnetic disk glass substrates D, and a control unit 6 that controls the frequency and sound pressure of the ultrasonic transducer 3. In the control part 6, it sets to the frequency and sound pressure according to the magnitude | size of the foreign material measured at the foreign material measurement process. Thereby, ultrasonic cleaning is performed at the frequency and the sound pressure.

Next, examples performed for clarifying the effects of the present invention will be described.
Example 1
First, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper mold, a lower mold, and a barrel mold to obtain an amorphous plate glass material (blanks). At this point, the diameter of the blanks was 66 mm. Next, both main surfaces of the blanks were subjected to a first lapping process, and then a cylindrical core drill was used to form a hole in the center of the glass substrate to process it into an annular glass substrate (coring). . And the chamfering process (chamfering surface formation process) which forms a chamfering surface in the edge part (an outer peripheral edge part and an inner peripheral edge part) was given, and it was set as the glass substrate of diameter 2.5 inches. Thereafter, a second lapping process was performed on the glass substrate.

  Next, the outer peripheral end of the glass substrate was mirror polished by a brush polishing method. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used. And the glass substrate which finished the mirror polishing process was washed with water.

Next, as a main surface polishing step, a first polishing step was performed on both main surfaces of the glass substrate. In the first polishing step, a double-side polishing machine was used as the polishing apparatus. A urethane pad was used as a polishing pad in this polishing apparatus. A cerium abrasive was used as the abrasive. The polishing conditions were a processing surface pressure of 130 g / cm ² and a processing rotation speed of 22 rpm. As a result, the surface roughness Ra of the main surface of the glass substrate was about 1.0 nm.

Next, a second polishing step for finishing the main surface into a mirror surface was performed on both main surfaces of the glass substrate. In the second polishing step, a double-side polishing machine was used as the polishing apparatus. As a polishing pad in this polishing apparatus, a soft suede pad (Asker C hardness: 54, compression deformation amount: 476 μm, density: 0.53 g / cm ³ ) was used. Moreover, as an abrasive | polishing agent, the colloidal silica abrasive | polishing agent with an average particle diameter of 20 nm was used. The polishing conditions were a processing surface pressure of 60 g / cm ² and a processing rotation speed of 20 rpm.

  The glass substrate after the second polishing step is immersed in an alkali solution, cleaned by applying ultrasonic waves, scrubbed using an alkali cleaning solution, diluted with a very small amount of diluted sulfuric acid and the alkali cleaning solution. After washing, IPA (isopropyl alcohol) was vapor-dried.

  Next, chemical strengthening was applied to the glass substrate after the final polishing step described above. For chemical strengthening, a chemical strengthening solution in which potassium nitrate (60%) and sodium nitrate (40%) are mixed is prepared, this chemical strengthening solution is heated to 380 ° C., and the cleaned glass substrate is placed therein for about 4 hours. This was done by dipping. Then, acid cleaning, alkali cleaning, and pure water cleaning were sequentially performed on the glass substrate after the chemical strengthening.

  With respect to the glass substrate for magnetic disk thus obtained, the size and distribution of foreign matters were measured by SEM, and the size was mainly 0.1 μm to 0.7 μm. For this reason, the frequency of the ultrasonic wave was set to 80 kHz, and the sound pressure was set to 1.5 mV to 2.5 mV. Under such conditions, ultrasonic cleaning was performed using the ultrasonic cleaning apparatus shown in FIG. Moreover, the substrate leaving time from the chemical strengthening process to the cleaning process was within 1 hour. And when the main surface of the glass substrate for magnetic disks was test | inspected using the optical defect inspection apparatus for every batch, the US damage was 1 or less in any batch. Moreover, when the foreign material was observed with SEM, the foreign material was almost removed.

(Example 2)
A glass substrate for a magnetic disk was produced in the same manner as in Example 1 except that the order of the chemical strengthening step and the second polishing step was reversed. About the glass substrate for magnetic discs completed to the 2nd grinding | polishing process, when the magnitude | size and distribution of the foreign material were measured by SEM, the magnitude | size was 0.1 micrometer-0.5 micrometer mainly. For this reason, the frequency of the ultrasonic wave was set to 120 kHz, and the sound pressure was set to 1.5 mV to 2.5 mV. Under such conditions, ultrasonic cleaning was performed using the ultrasonic cleaning apparatus shown in FIG. Further, the substrate standing time from the second polishing step to the cleaning step was within 1 hour. And when the main surface of the glass substrate for magnetic disks was test | inspected using the optical defect inspection apparatus for every batch, the US damage was 1 or less in any batch. Moreover, when the foreign material was observed with SEM, the foreign material was almost removed.

Example 3
The glass substrate for magnetic disk, which was cleaned with RO water and pure water and subjected to IPA drying or spin dry drying on the glass substrate that had been chemically strengthened in the same manner as in Example 1, was analyzed by SEM. When the thickness and distribution were measured, the size was mainly 1.0 μm to 3.0 μm. For this reason, the frequency of the ultrasonic wave was set to 40 KHz, and the sound pressure was set to 1.0 mV to 2.0 mV. Under such conditions, ultrasonic cleaning was performed using the ultrasonic cleaning apparatus shown in FIG. Moreover, the substrate leaving time from the chemical strengthening process to the cleaning process was within 1 hour. And when the main surface of the glass substrate for magnetic disks was test | inspected using the optical defect inspection apparatus for every batch, the US damage was 1 or less in any batch. Moreover, when the foreign material was observed with SEM, the foreign material was almost removed.

(Comparative Example 1)
In the same manner as in Example 1, the chemical strengthening process was performed to obtain a glass substrate for magnetic disk. In the cleaning process, the glass substrate for magnetic disk was subjected to ultrasonic cleaning with an ultrasonic wave having a frequency of 160 kHz and an acoustic pressure of 1.5 mV to 2.5 mV using the ultrasonic cleaning apparatus shown in FIG. And when the main surface of the glass substrate for magnetic disks was inspected for each batch using an optical defect inspection apparatus, when a substrate having a large ratio of concave defects was investigated in a certain batch, several US damages were found. There were many. Moreover, when the foreign material was observed with SEM, the foreign material was almost removed. This is considered to be because the glass substrate for magnetic disks was damaged due to the high frequency of ultrasonic waves.

(Comparative Example 2)
In the same manner as in Example 1, the chemical strengthening process was performed to obtain a glass substrate for magnetic disk. In the cleaning step, the glass substrate for magnetic disk was subjected to ultrasonic cleaning with an ultrasonic wave having a frequency of 20 kHz and a sound pressure of 1.5 mV to 2.5 mV using the ultrasonic cleaning apparatus shown in FIG. Moreover, the substrate leaving time from the chemical strengthening process to the cleaning process was within 1 hour. And when the main surface of the glass substrate for magnetic disks was test | inspected using the optical defect inspection apparatus for every batch, the US damage was 1 or less in any batch. However, when the foreign matter was observed with SEM, the residual rate of the foreign matter was high. This is thought to be because the cleaning power against foreign matter is weak because the frequency of the ultrasonic waves is low.

(Comparative Example 3)
In the same manner as in Example 1, the chemical strengthening process was performed to obtain a glass substrate for magnetic disk. In the cleaning step, the glass substrate for magnetic disk was subjected to ultrasonic cleaning with ultrasonic waves having a frequency of 80 kHz and a sound pressure of 3.0 mV to 4.0 mV using the ultrasonic cleaning apparatus shown in FIG. And when the main surface of the glass substrate for magnetic disks was inspected for each batch using an optical defect inspection apparatus, when a substrate having a large ratio of concave defects was investigated in a certain batch, several US damages were found. There were many. Moreover, when the foreign material was observed with SEM, the foreign material was almost removed. This is presumably because the magnetic disk glass substrate was damaged due to the high sound pressure of the ultrasonic waves.

(Comparative Example 4)
In the same manner as in Example 1, the chemical strengthening process was performed to obtain a glass substrate for magnetic disk. In the cleaning step, this glass substrate for magnetic disk was subjected to ultrasonic cleaning with ultrasonic waves having a frequency of 80 kHz and a sound pressure of 0.5 mV to 1.0 mV using the ultrasonic cleaning apparatus shown in FIG. And when the main surface of the glass substrate for magnetic disks was test | inspected using the optical defect inspection apparatus for every batch, the US damage was 1 or less in any batch. However, when the foreign matter was observed with SEM, the residual rate of the foreign matter was high. This is thought to be because the cleaning power against foreign matters is weak because the sound pressure of the ultrasonic waves is low.

  The present invention is not limited to the above embodiment, and can be implemented with various modifications. For example, the material, the number, the size, the processing procedure, and the like in the above embodiment are merely examples, and various modifications can be made within the range where the effects of the present invention are exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

DESCRIPTION OF SYMBOLS 1 Cleaning tank 2 Cleaning liquid 3 Ultrasonic vibrator 4 Frequency detector 5 Carrier 6 Control part D Glass substrate for magnetic discs

Claims (6)

  A method of manufacturing a magnetic disk glass substrate including a cleaning step of ultrasonically cleaning the magnetic disk glass substrate, wherein the foreign material measures the size of the foreign material remaining on the magnetic disk glass substrate before the cleaning step. A method for producing a glass substrate for a magnetic disk, comprising a measurement step, wherein in the cleaning step, a sound pressure and a frequency of an ultrasonic wave used in the ultrasonic cleaning are adjusted according to a size of the foreign matter.   2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the step immediately before the cleaning step is a main surface polishing step for polishing the main surface of the glass substrate for magnetic disk.   2. The method of manufacturing a glass substrate for magnetic disk according to claim 1, wherein the step immediately before the cleaning step is a chemical strengthening step for chemically strengthening the glass substrate for magnetic disk.   4. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the time from the step immediately before the cleaning step to the cleaning step is within one hour.   When the size of the foreign matter to be removed is mainly 1.0 μm or less, the ultrasonic frequency is 80 kHz to 120 kHz, and the ultrasonic sound pressure is 1.5 mV to 2.5 mV. The manufacturing method of the glass substrate for magnetic discs in any one of Claim 1 to 4.   When the size of the foreign matter to be removed is mainly larger than 1.0 μm, the ultrasonic frequency is set to 40 kHz to 80 kHz, and the ultrasonic sound pressure is set to 1.0 mV to 2.0 mV. The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 4, wherein:

Images