JP2007102843A - Glass substrate for magnetic recording medium and magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for a magnetic recording medium capable of preventing generation of particles and enhancing substrate strength even when the glass substrate has an inner hole having a small diameter difficult to polish and to provide a magnetic disk. <P>SOLUTION: In the glass substrate 1 for the disk-like magnetic disk having the inner hole 2, chamfered parts 12b are formed at an inner peripheral edge surface 12 and then the inner peripheral edge surface 12 is subjected to chemical treatment, and chamfered parts 11b are formed at an outer peripheral edge surface 11 and then the outer peripheral edge surface is subjected to chemical treatment and mirror polishing treatment. Thereby, the glass substrate having extremely fewer particles and the magnetic disk having extremely fewer projecting parts can be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic disk used for a magnetic recording medium such as a hard disk, and a glass substrate serving as a substrate thereof.

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

  As the magnetic recording technology has been increased in density, the magnetic head has been changed from a thin film head to a magnetoresistive head (MR head) and a large magnetoresistive head (GMR head). The flying height from the center is narrowed to about 10 nm. A magnetic head equipped with such a magnetoresistive element may cause a thermal asperity failure as an inherent failure. Thermal asperity failure means that the magnetoresistive element is heated by adiabatic compression or contact of air when the magnetic head passes while flying over a minute convex or concave shape on the magnetic disk surface. This is a failure that causes a read error. Therefore, for a magnetic head equipped with a magnetoresistive element, the surface of the magnetic disk is required to have extremely high smoothness and flatness. Further, if the magnetic layer is formed with dust or foreign matter attached, a convex portion is formed. Therefore, the glass substrate is required to prevent dust generation by removing irregularities and to perform advanced cleaning to remove foreign matter.

  Furthermore, in recent years, there is a tendency for the size of a substrate to be reduced in order to mount a large-capacity magnetic recording medium in a portable device. For this reason, 1.8-inch substrates, 1-inch substrates, or even smaller substrates have been demanded from conventional 3.5-inch substrates and 2.5-inch substrates. The smaller the substrate, the smaller the allowable dimensional error, and there is a need for more precise outer shape processing.

  In the above situation, generation of particles (dust) is cited as one of the causes of the convex portion that causes thermal asperity. That is, a convex part is formed by forming a magnetic layer, with the generated particles adhering to the glass substrate. One cause of the generation of particles is the roughness of the edge of the glass substrate. When the edge of the glass substrate is rough, when the glass container is taken in or out and supported by a jig in each step, fine glass chipping occurs, the storage container is scraped, and particles are generated. Conceivable.

  On the other hand, JP 2003-228814 A (Patent Document 1) discloses a glass capable of preventing the generation of particles by mirror-polishing the inner peripheral end surface and the outer peripheral end surface of a glass substrate to a predetermined roughness. A substrate has been proposed.

  Further, as disclosed in Japanese Patent Application Laid-Open No. 7-230621 (Patent Document 2), it is known that scratches remaining on the end face of the glass substrate, particularly the inner peripheral end face, affect the strength of the glass substrate. In Patent Document 2, the strength of the glass substrate can be improved by etching or etching the end face of the glass substrate by chemical treatment to make the scratches shallow.

JP 2003-228814 A JP-A-7-230621

  However, in recent years, the size of the inner hole has been reduced due to the reduction in size of the glass substrate. For example, the diameter of the inner hole of the 2.5 inch substrate is 20 mm, but the diameter of the inner hole of the 1 inch substrate is 7 mm. It is difficult to polish the inner peripheral end face with such a small diameter. In general, mirror polishing of the substrate end surface is performed by laminating and supporting a large number of substrates and polishing them with a brush while applying slurry. Here, if the diameter of the inner hole is reduced, the brush must also be made thinner, so that the strength of the brush shaft cannot be ensured, resulting in an unstable state. Therefore, sufficient polishing cannot be performed.

  For this reason, conventionally, for a substrate of 1 inch or smaller, it is conceivable to perform only the forming process for forming the chamfered portion on the inner peripheral end face. However, in this case, the surface of the inner peripheral end surface becomes rough and it becomes easy to adsorb particles, and particles are generated when the spindle is mounted, which may cause thermal asperity. In addition, the substrate strength may be reduced.

  Therefore, the present invention is for a magnetic recording medium that prevents the generation of particles, eliminates convex portions that cause thermal asperity, and improves the substrate strength, even for a glass substrate having a small-diameter inner hole that is difficult to polish. An object is to provide a glass substrate and a magnetic disk.

  A typical configuration of the magnetic disk glass substrate according to the present invention is a disk-shaped magnetic disk glass substrate having an inner hole. The inner peripheral end surface is subjected to chemical treatment after forming a chamfered portion, and the outer peripheral end surface is A chemical treatment and a mirror polishing treatment are performed after forming a chamfered portion. Thereby, since the surface area of the inner peripheral end face is reduced, the adsorption of particles can be reduced. Moreover, since the fine protrusion has disappeared, generation of particles from the inner peripheral end face can be prevented. By performing mirror polishing on the outer peripheral end surface, generation and adsorption of particles can be further prevented. From these things, a glass substrate with very few particles can be obtained, and it can be prevented that particles move to the main surface and cause thermal asperity. In addition, since small scratches disappear and large scratches are smooth, a glass substrate with improved substrate strength can be obtained.

  The outer peripheral end face may be etched by chemical treatment after mirror polishing. Thereby, since the machining allowance in the mirror polishing process is secured, a glass substrate with high dimensional accuracy can be obtained.

  The glass substrate may be made of aluminosilicate glass. In such a case, an excellent glass substrate for a magnetic disk can be obtained.

  The glass substrate for a magnetic disk may be a glass substrate for a magnetic disk mounted on a 1-inch hard disk drive or a hard disk drive using a magnetic disk having a smaller diameter than the 1-inch hard disk drive. The present invention is particularly effective for a glass substrate having such a small-diameter inner hole.

  A typical structure of the magnetic disk according to the present invention is characterized in that at least a magnetic layer is provided on the surface of the glass substrate for magnetic disk. Thereby, a magnetic disk having extremely high smoothness and flatness can be obtained.

  According to the present invention, it is possible to obtain a glass substrate with very few particles that cause convex portions that cause thermal asperity, and a magnetic disk with extremely few convex portions. In addition, since small scratches disappear and large scratches are smooth, the substrate strength of the glass substrate and the magnetic disk can be improved.

  The glass substrate for magnetic recording media and the magnetic disk according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating the structure of a glass substrate. FIG. 1A shows a glass substrate for a magnetic recording medium that serves as a base of a magnetic disk used for a magnetic recording medium such as a hard disk drive. As shown in the figure, the glass substrate 1 is an annular glass in which an inner hole 2 is formed at the center of a disk-shaped glass substrate. A flat surface 11a and a chamfered portion 11b are formed on the outer peripheral end surface 11 by a forming process described later. Similarly, a flat surface 12 a and a chamfered portion 12 b are formed on the inner peripheral end surface 12. In addition, when mirror polishing is performed on the end surface with a brush, the angular portion that becomes the boundary between the flat surface and the chamfered portion becomes a curved surface, and has an overall curved cross-sectional shape.

  FIG. 1B shows the dimensions of the glass substrate. As shown in the drawing, for example, the diameter of the inner hole of the 2.5 inch substrate was 20 mm, but the diameter of the inner hole of the 1 inch substrate was 7 mm. Although not shown, if the substrate is a 0.85 inch substrate, the diameter of the inner hole is further reduced. Thus, it is difficult to brush the inner peripheral end surface of the inner hole 2 having a small diameter.

  Therefore, it is desired to etch the inner peripheral end face by chemical treatment, but it is necessary to select a suitable etching solution. Further, although the substrate strength can be improved by etching, the surface becomes rough if it is excessively etched, so that it is necessary to specify an optimum etching amount. Furthermore, since the main surface and the outer peripheral end face are also etched during the chemical treatment, it is necessary to consider at which stage in the glass substrate manufacturing process it is optimal to perform the etching.

[Select Etching Solution]
FIG. 2 is a diagram for explaining the etching solution. As shown in the figure, etching was performed with Shrek detergent, silica hydrofluoric acid, and hydrofluoric acid, respectively, and the surface properties of the inner peripheral end face and the outer peripheral end face were compared. The outer peripheral end face is mirror-polished before chemical treatment. As a result, the Shrek detergent and silicic acid were not etched to the extent that the scratches disappeared or became shallow. Therefore, it was judged that it is suitable to use hydrofluoric acid in order to achieve the object of the present invention.

[Examination of etching amount]
FIG. 3 is a diagram for explaining a state in which the etching amount is examined from the strength. The strength was measured using a bending strength tester (Shimadzu Autograph DDS-2000) shown in FIG. That is, the glass substrate 1 supports the outer peripheral portion by the substrate holder 20, puts the steel ball 21 in the inner hole 2, pressurizes it by the pressurizer 22, and records the load when it is broken and damaged. The reason why the load is applied to the central portion in this way is that the magnetic disk is supported only by the spindle (rotary shaft) attached to the inner hole 2 inside the magnetic recording medium (hard disk or the like). It is.

  FIG. 3B is a diagram showing the relationship between the etching amount and the strength. From the figure, it was found that the strength hardly increased when the etching amount was 2 μm, increased at about 7 μm, and thereafter the strength increased as the etching amount increased. Further detailed investigations revealed that an etching amount of at least 5 μm or more is necessary to improve the strength.

  On the other hand, as described above, the outer peripheral end face and the main surface are parts that do not want to be affected by chemical treatment as much as possible. In particular, the tolerance of the substrate thickness dimension is as strict as 8 to 15 μm, and the main surface needs to be polished until there is no trace of chemical treatment, so excessive etching imposes a burden on the subsequent main surface polishing step. It will be multiplied. Therefore, considering the balance between the improvement in strength and the burden on the post-process, it is optimal that the thickness be about 9 μm or less. From the above examination, it is desirable that the etching amount by chemical treatment is 5 to 9 μm.

[Examination of setup]
Although the manufacturing process of the glass substrate will be described later, the outline is as follows: (1) Shape processing process and first lapping process, (2) Cutting process (coring process for forming inner holes, and inner and outer peripheral end faces Forming step), (3) end surface polishing step (only outer peripheral end surface), (4) second lapping step, (5) main surface polishing step (first polishing, second polishing), (6) chemistry A strengthening step, and (7) a texture processing step. In addition, an end surface grinding | polishing process and a 2nd lapping process may be followed. In these steps, the chemical treatment needs to be at least after the cutting step. In addition, we examined at which stage the best results were obtained by chemical treatment.

  FIG. 4 is a diagram showing the relationship between the setup for etching and various properties of the completed glass substrate. As the setup, comparison was made without chemical treatment, after forming (after the cutting process), after mirror polishing of the outer peripheral end face, after the second lapping, after the first polishing of the main surface, and after the second polishing of the main surface. Further, as various properties, the main surface waviness, the main surface micro waviness, the main surface Rq (double average square root height), and the strength were compared. Moreover, even if it was a case where it chemical-processed in any step, it compared after completing a glass substrate (after a texture treatment process).

  As a result of the comparison, it was found that when the chemical treatment is performed after the main surface first polishing and after the main surface second polishing, the waviness and microwaviness of the main surface deteriorate. In addition, the strength was not changed after the main surface first polishing after the second lapping, but rather was weakened after the main surface second polishing. This is considered to be because if the chemical treatment is performed after the main surface first polishing, the influence of the chemical treatment remains on the main surface. Therefore, it is necessary to perform the chemical treatment before the main surface first polishing.

  FIG. 5 is a diagram showing a list of the setup for etching and the evaluation of the completed glass substrate. As described above, after the main surface first polishing, undulation and fine undulation are poor. It is also shown that the strength is insufficient without chemical treatment. For these reasons, the chemical treatment is optimally performed after the forming step for forming the chamfered portions on the outer peripheral end surface and the inner peripheral end surface and before the main surface polishing step for mirror polishing the main surface.

  However, when a chemical treatment is performed after forming, a deep dent will be formed if etching is performed with a chemical solution in an uneven shape. If the polishing is performed for the same time as when no chemical treatment is performed by end face polishing, the dents cannot be removed and remain on the surface. For this reason, it is evaluated that the machining allowance is insufficient (insufficient polishing) during the inspection. Here, the above problem can be avoided by forming the outer diameter larger by a predetermined amount in the cutting step and increasing the polishing amount of the outer peripheral end face mirror polishing. However, there is a problem that the working time is increased.

  In addition, when a chemical treatment is performed after mirror polishing of the outer peripheral end face, the outer peripheral end face is also etched and the surface thereof becomes rough. However, as described above, even if it is polished to a mirror surface, fine scratches are latent, and the chemical treatment improves the strength. In other words, the mirror surface state is advantageous in that it is difficult to adsorb particles, and the state in which the mirror surface state is chemically treated is advantageous in that the strength is improved, and by combining the above-described appropriate amount of chemical treatment, both advantages are combined. Can do. Therefore, it is preferable to perform the chemical treatment after the step of mirror polishing the outer peripheral end face.

  Further, the second lapping step is a step of greatly polishing the main surface, and it is considered that the influence of chemical treatment on the main surface can be more reliably eliminated. However, from the results of the above examination, the influence of the chemical treatment can be sufficiently eliminated by the main surface first polishing. Therefore, the effect of the present invention can also be obtained by performing chemical treatment after the second lapping step. Furthermore, as described above, the second lapping step may be performed prior to the outer peripheral end surface mirror polishing, and in that case, the second lapping step, the outer peripheral end surface mirror polishing, and the chemical treatment may be performed in this order.

  By configuring as described above, the glass substrate for a magnetic disk according to the present embodiment performs the chemical treatment after forming the chamfered portion on the inner peripheral end surface, and chemically treating the outer peripheral end surface after forming the chamfered portion. In addition, the mirror polishing process was performed. Thereby, since the surface area of the inner peripheral end face is reduced, the adsorption of particles can be reduced. Further, since the fine protrusions disappear, it is possible to prevent the generation of particles from the inner peripheral end face. In addition, since small scratches disappear and large scratches become smooth, the substrate strength can be improved. By performing mirror polishing on the outer peripheral end face, generation and adsorption of particles can be further prevented.

[Example 1]
In this example, a glass substrate for a magnetic disk and a magnetic disk were manufactured through the following steps.

(1) Shape processing step and first lapping step First, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper die, a lower die, and a barrel die to obtain an amorphous plate glass. In addition, the glass for chemical strengthening was used as aluminosilicate glass. The obtained disk-shaped plate-like glass had a diameter of 96 mm and a plate thickness of 1.8 mm. In this case, in addition to the direct press, a disk-shaped glass substrate for a magnetic disk may be obtained by cutting a sheet glass formed by a downdraw method or a float method with a grinding wheel. As the aluminosilicate _glass, SiO 2: 58 to 75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: 3 to 10 _wt%, Na 2 O: 4 to 13 principal component weight% Chemically strengthened glass contained as

  Next, both main surfaces of the plate glass were lapped to form a disk-shaped glass base material. This lapping process was performed using alumina free abrasive grains with a double-sided lapping apparatus using a planetary gear mechanism. Specifically, the lapping platen is pressed on both sides of the plate glass from above and below, the grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relative to each other for lapping. went. By this lapping process, a glass base material having a flat main surface was obtained. Moreover, the plate | board thickness of the glass base material was reduced rather than plate glass by this lapping process, and became 0.6 mm.

(2) Cutting process (coring, forming)
Next, the glass base material was cut using a diamond cutter, and a glass substrate having a diameter of 29 mm was cut out from the glass base material. The diameter of the glass base material was 96 mm, and six glass substrates could be collected from one glass base material.

  Next, using a cylindrical diamond drill, a circular hole was formed in the center of the glass substrate to obtain a donut-shaped glass substrate (coring). Then, the inner peripheral end face and the outer peripheral end face were ground with a diamond grindstone and subjected to predetermined chamfering (forming).

(3) End surface polishing process Next, the end surface of the glass substrate was mirror-polished by a brush polishing method. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used. Next, the inner peripheral side end face was mirror polished by a magnetic polishing method. And the glass substrate which finished the end surface grinding | polishing process was washed with water. By this end surface polishing step, the end surface of the glass substrate was processed into a mirror surface state capable of preventing generation of particles and the like. As a result, the diameter of the glass substrate becomes 27.4 mm, which can be used as a substrate for a 1-inch magnetic disk.

  In this end surface polishing step, the glass substrate is overlapped and the end surface is polished. In this case, in order to avoid scratches on the main surface of the glass substrate, before the first polishing step described later, Alternatively, it may be performed before and after the second polishing step.

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

(5) Chemical treatment step Next, etching by chemical treatment, which is a feature of the present invention, was performed. The glass substrate was immersed in hydrofluoric acid for about 4 minutes to obtain an etching amount of 6.9 μm.

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

  The glass substrate that has finished the first polishing step is sequentially immersed in cleaning baths of neutral detergent, pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam drying), and cleaned. did.

  Next, a second polishing step was performed as the main surface polishing step. The purpose of this second polishing step is to finish the main surface into a mirror surface. In the second polishing step, mirror polishing of the main surface was performed using a soft foamed resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains finer than the cerium oxide abrasive grains used in the first polishing step were used.

  After the second polishing process, the glass substrate is made of neutral detergent (1), neutral detergent (2), pure water (1), pure water (2), IPA (isopropyl alcohol), IPA (steam-dried). It was immersed in each washing tank in order and washed. Note that ultrasonic waves were applied to each cleaning tank.

(7) Chemical strengthening process Next, the glass substrate which finished the above-mentioned lapping process and polishing process was chemically strengthened. For chemical strengthening, a chemical strengthening solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared, and the chemically strengthened solution is heated to 400 ° C., and the cleaned glass substrate is heated to 300 ° C. The sample was preheated and immersed in a chemical strengthening solution for about 3 hours. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, it was carried out in a state of being accommodated in a holder so that a plurality of glass substrates were held at the end surfaces.

  Thus, by immersing in a chemical strengthening solution, the lithium ion and sodium ion of the surface layer of a glass substrate are each substituted by the sodium ion and potassium ion in a chemical strengthening solution, and a glass substrate is strengthened. The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 μm to 200 μm.

  The glass substrate that had been subjected to the chemical strengthening treatment was immersed in a water bath at 20 ° C. for rapid cooling and maintained for about 10 minutes. And the glass substrate which finished quenching was immersed in the concentrated sulfuric acid heated at about 40 degreeC, and was wash | cleaned. Further, the glass substrate after the sulfuric acid cleaning was cleaned by immersing in a cleaning bath of pure water (1), pure water (2), IPA (isopropyl alcohol) and IPA (steam drying) sequentially. In addition, ultrasonic waves were applied to each cleaning tank.

  As described above, by applying the first lapping step, the cutting step, the end surface polishing step, the second lapping step, the first and second polishing steps, the precision cleaning, and the chemical strengthening step, a flat and smooth, high rigidity A glass substrate for a magnetic disk was obtained.

(8) Texture processing step Polishing and circumferential texture processing were performed using a tape-type texture device. A woven fabric type tape was used as the tape, and a slurry in which polycrystalline diamond having an average particle size of 0.125 μm was dissolved in a dispersant / lubricant (glycerin) was used as the hard abrasive. After this texturing step, pre-cleaning with an ultrapure water shower was performed for 5 seconds in order to wash away the diamond slurry and dispersant (lubricant) of the abrasive.

(9) Precision cleaning process Next, the glass disk in which the texture was formed was precisely cleaned. This is to remove abrasive residues and foreign iron-based contaminants that cause head crush and thermal asperity failure, and to obtain a glass substrate with a smooth surface and a clean surface. This precision cleaning process includes the following series of cleaning processes.

  First, a cleaning process using a cleaning solution was performed. In this cleaning solution, a chemical solution in which KOH and NaOH were mixed at a ratio of 1: 1 was diluted with ultrapure water, and a nonionic surfactant was added to enhance the cleaning ability. The pH of the cleaning liquid was adjusted to 12.4 by diluting ultrapure water. The glass disk was immersed in this cleaning solution and then washed for 2 minutes while rocking. At this time, the temperature of the cleaning liquid was set to 50 ° C., and ultrasonic waves were applied to enhance the cleaning effect.

  Next, the water rinse washing | cleaning process was performed for 2 minutes. This is for removing the residue of the cleaning liquid used in the above-described cleaning. Then, the IPA washing process was performed for 2 minutes. This is for cleaning the glass disk and removing water on the substrate. Finally, the IPA vapor drying process was performed for 2 minutes. This is for drying while removing the liquid IPA adhering to the substrate with the IPA vapor.

(10) Magnetic disk manufacturing process A seed layer, Cr underlayer, CrMo underlayer, CoPtCrTa magnetic layer, hydrogenation on both surfaces of the glass substrate textured through the above-described steps, using a single-wafer sputtering apparatus. A carbon protective layer was formed, and a perfluoropolyether lubricating layer was formed by a dip method to produce a magnetic disk.

[Evaluation]
FIG. 6A is a diagram showing the state of the surface properties of the end face with and without chemical treatment, observed with an electron microscope (SEM), and FIG. 6B shows the strength with and without chemical treatment. FIG. The electron microscope was observed before the magnetic layer was formed.

  As shown in FIG. 6A, the inner peripheral end face when the chemical treatment is not performed is rough, and many scratches and irregularities are formed. Moreover, although the outer peripheral end surface is mirror-polished, it can be seen that fine scratches remain. When the chemical treatment is performed, the inner peripheral end face is widened and the sharpness is eased, and the unevenness is rounded. In addition, the outer peripheral end surface is spread with fine scratches remaining to reduce sharpness.

  Here, the decrease in strength due to scratches is considered to be due to the growth of cracks due to stress concentration at the sharply shaped tips of the scratches. Accordingly, by reducing the sharpness of the scratches by the chemical treatment in this way, it was possible to improve the strength as shown in FIG. 6B.

  FIG. 7 is a diagram comparing the roughness of the end face with and without chemical treatment. The measurement was performed using the surface roughness measuring device P-12 manufactured by KLA-Tencor under the conditions shown in FIG.

  As shown in FIG. 7B, the roughness of the outer peripheral end surface is increased, the maximum height (Rmax) is about 0.313 μm, the minimum height (Rmin) is about 0.240 μm, and the arithmetic average roughness (Ra) is about It is about 0.269 μm. This is thought to be due to the fact that the scratches on the mirror-polished surface are widened by chemical treatment to increase the roughness. Although the roughness of the inner peripheral end surface is slightly increased, the maximum height (Rmax), the minimum height (Rmin), and the arithmetic average roughness (Ra) are about 0.235 μm, and the width of variation is It is extremely small. This is presumably because the roughness of the rough inner peripheral end face is averaged by chemical treatment.

  According to the waveform diagram shown in FIG. 7 (c), when the outer peripheral end face is not subjected to chemical treatment, the surface roughness varies finely, but the scratches are widened and smoothened by the chemical treatment. . For this reason, it is considered that the roughness is increased numerically. As for the inner peripheral end face, a surface that is large and sharply fluctuates without chemical treatment is a surface that fluctuates gently by chemical treatment. In this case as well, the surface roughness is numerically increased, but it is considered that the large protrusions are averaged by being etched away. And generation | occurrence | production and adsorption | suction of a particle can be prevented by reducing a surface area in this way.

  FIG. 8 is a diagram for explaining the measurement of the amount of particles adhering to the glass substrate. The measurement was performed by a spray method using LPC (Laser Particle Counter: Model KL-26) manufactured by RION. Specifically, as shown in FIG. 8A, a clean 1000 ml beaker 30 is prepared, and the glass substrate 1 is supported by the support member 31 above the beaker 30. Then, ultrapure water (DL water) is sprayed from the nozzle 32 at an angle of 45 degrees at 350 ml / min for 30 seconds on the surface, for 30 seconds on the back surface, and for 10 seconds on the surface. And the water in a beaker is taken in into LPC not shown, and the number of particles is counted.

  FIG. 8B shows the measurement result of the particles thus measured. The value is the number of particles per ml, and the comparison was made without chemical treatment, with chemical treatment, and when the inner peripheral end face was also mirror-polished. As a result, it was 32.3 pieces / ml without chemical treatment, and 10.2 pieces / ml with chemical treatment. It was found that the generation and adsorption of particles could be greatly reduced, although it was less than 7.7 / ml when mirror polishing to the inner peripheral end face.

  From these, it can be seen that the substrate strength is improved and the generation and adsorption of particles are reduced as compared with the case where the inner peripheral end face is formed only.

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

  The present invention can be used as a magnetic disk used for a magnetic recording medium such as a hard disk and a glass substrate serving as a substrate thereof.

It is a figure explaining the structure of a glass substrate. It is a figure explaining examination of etching liquid. It is a figure explaining a mode that the etching amount was examined from strength. It is a figure which shows the relationship between the setup which etches, and various properties of a glass substrate. It is a figure which shows the list of the setup to etch and the evaluation of a glass substrate. It is the figure which compared the surface property and intensity | strength of the end surface when not carrying out with a chemical treatment. It is the figure which compared the roughness of the end surface when not carrying out with a chemical process. It is a figure explaining measurement of the amount of particles adhering to a glass substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Glass substrate 2 ... Inner hole 11 ... Outer peripheral end surface 11a ... Flat surface 11b ... Chamfering part 12 ... Inner peripheral end surface 12a ... Flat surface 12b ... Chamfering part 20 ... Substrate holder 21 ... Steel ball 22 ... Pressurizer 30 ... Beaker 31 ... Support member 32 ... Nozzle

Claims (5)

In a disk-shaped magnetic disk glass substrate having an inner hole,
The inner peripheral end surface is etched by chemical treatment after forming a chamfered portion,
A glass substrate for a magnetic disk, wherein a chamfered portion is formed on an outer peripheral end surface, and chemical etching and mirror polishing are performed. 2. The glass substrate for a magnetic disk according to claim 1, wherein the outer peripheral end surface is subjected to a mirror polishing process and then subjected to a chemical process etching. 2. The glass substrate for a magnetic disk according to claim 1, wherein the glass substrate is made of aluminosilicate glass. 2. The glass substrate for a magnetic disk according to claim 1, which is a glass substrate for a magnetic disk mounted on a 1-inch hard disk drive or a hard disk drive using a magnetic disk having a smaller diameter than that of the 1-inch hard disk drive. A magnetic disk comprising at least a magnetic layer on the surface of the glass substrate for a magnetic disk according to any one of claims 1 to 4.