JP2006221680A - Glass substrate for recording medium, manufacturing method of glass substrate for recording medium, information recording medium, and information recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for a recording medium having mechanical strength and chemical stability adaptive to a vertical magnetic recording system without performing reinforcement treatment such as chemical reinforcement treatment. <P>SOLUTION: Mechanical strength and chemical stability of the glass substrate for the recording medium are enhanced by forming a metal layer, a metal oxide layer or an organic material layer containing metal on an outer surface of a glass substrate and then forming a high hardness glass layer thereon. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a glass substrate, a method for producing a glass substrate, an information recording medium, and an information recording apparatus, and more specifically, a glass substrate for a recording medium suitable for a perpendicular magnetic recording system, a method for producing a glass substrate for a recording medium, The present invention relates to an information recording medium and an information recording apparatus using a glass substrate for recording medium.

  Conventionally, as a substrate for a magnetic disk, an aluminum alloy substrate is generally used for a stationary type such as a desktop computer or a server, while a glass substrate is generally used for a portable type such as a notebook computer or a mobile computer. Since the alloy is easily deformed and the hardness is insufficient, the smoothness of the substrate surface after polishing cannot be said to be sufficient. Further, when the head mechanically contacts the magnetic disk, there is a problem that the magnetic film is easily peeled off from the substrate. Therefore, it is predicted that glass substrates with little deformation, good smoothness and high mechanical strength will be widely used not only for portable devices but also for stationary devices and other household information devices in the future. Yes.

  On the other hand, in order to improve the recording density and recording stability of a magnetic disk, a perpendicular magnetic recording method has been developed as a method replacing the conventional horizontal magnetic recording method (see, for example, Patent Document 1). When the perpendicular magnetic recording system is put into practical use, a large-capacity disk can be realized with a smaller magnetic disk than before, so that it is more competitive than the conventional 1.8 inch type and 1 inch type as a semiconductor memory. A small 0.85-inch type ultra-small magnetic disk is planned, and it is expected that the magnetic disk will be mounted on a mobile phone or the like that has not been conventionally used. To achieve this, a smaller and higher performance glass substrate is indispensable.

  As a glass substrate, chemically tempered glass is known in which a compressive strain is generated by replacing an alkali element on the substrate surface with another alkali element and mechanical strength is improved (for example, see Patent Document 2). However, chemically tempered glass requires a complicated ion exchange step, and rework after ion exchange is impossible, so it is difficult to increase the production yield. In addition, in order to give the glass substrate ion exchange properties, it was made easy for alkali ions to move in the substrate, so that the alkali ions on the surface of the substrate were heated during the heating process when forming the magnetic film. There has been a problem in that the chemical reliability is lowered such as moving to the surface to elute, eroding the magnetic film, or deteriorating the adhesion strength of the magnetic film.

  On the other hand, as a general glass substrate not subjected to chemical strengthening treatment, there is a soda lime substrate, but mechanical strength and chemical durability are insufficient to use the soda lime substrate as an information recording substrate.

Furthermore, when a glass substrate is used for information recording, when the information recording film is formed on the glass substrate, the glass substrate is cracked by pressure, heating, or impact applied to the surface, and the product yield is increased. There was a decline. In addition, there has been a problem in yield reduction due to scratches and cracks caused by pressure and impact when the glass substrate is incorporated into the magnetic disk drive. This problem has become a major issue in terms of yield improvement and cost reduction as the size of the magnetic disk becomes smaller. It is an exaggeration to say that improving the mechanical strength of the glass substrate is the key to realizing a small magnetic disk. It is not a problem.
Japanese Patent Laid-Open No. 6-76202 JP-A-5-32431

  The present invention has been made in view of the above circumstances, and can achieve both improvement in mechanical strength and improvement in chemical reliability without performing complicated processing. An object is to provide a suitable glass substrate for an information recording medium.

  The object of the present invention can be achieved by the following constitution.

(Claim 1)
A glass substrate for a recording medium, comprising a high-hardness glass layer having a hardness higher than that of the glass substrate on an outer surface of the glass substrate.

(Claim 2)
The glass substrate for a recording medium according to claim 1, further comprising a metal-containing layer containing at least one of a metal, a metal oxide, or a metal-containing organic compound on an outer surface of the glass substrate.

(Claim 3)
The glass substrate for a recording medium according to claim 1 or 2, wherein the glass substrate for a recording medium is not subjected to a tempering treatment.

(Claim 4)
A method for producing a glass substrate for a recording medium, comprising: a high-hardness glass layer forming step of forming a high-hardness glass layer having a hardness higher than that of the glass substrate on an outer surface of the glass substrate.

(Claim 5)
5. The glass substrate for a recording medium according to claim 4, further comprising a step of forming a metal-containing layer containing at least one of a metal, a metal oxide, or a metal-containing organic compound on the outer surface of the glass substrate. Manufacturing method.

(Claim 6)
The method for manufacturing a glass substrate for a recording medium according to claim 5, wherein the metal-containing layer is formed by plating.

(Claim 7)
The method for producing a glass substrate for a recording medium according to claim 5, wherein the metal-containing layer is formed by a vapor phase growth method.

(Claim 8)
The method for manufacturing a glass substrate for a recording medium according to claim 5, wherein the metal-containing layer is formed by a coating process.

(Claim 9)
6. The recording medium according to claim 5, wherein the high-hardness glass layer forming step forms the high-hardness glass layer by mutually diffusing the components of the glass substrate and the metal-containing layer. Method for manufacturing glass substrate.

(Claim 10)
An information recording medium for a perpendicular magnetic recording system, comprising a recording layer on a main surface of the glass substrate for a recording medium according to claim 1.

(Claim 11)
An information recording apparatus comprising the information recording medium according to claim 10.

  According to the invention of claim 1 and claim 4, by forming a high-hardness glass layer on the outer surface of the glass substrate, it becomes possible to achieve both improvement in mechanical strength and chemical reliability, A glass substrate for a recording medium suitable for a small perpendicular magnetic recording type magnetic disk can be provided.

  According to the invention described in claim 2, by forming the metal-containing layer and the high-hardness glass layer on the outer surface of the glass substrate, both mechanical strength and chemical reliability can be improved. A glass substrate for a recording medium suitable for a perpendicular magnetic recording type magnetic disk can be provided.

  According to the invention described in claim 3, since the strength that can be used as the substrate for the recording medium can be obtained even if the glass substrate is not tempered, in addition to the effects obtained in claims 1 and 2, As a result, it is possible to improve the chemical reliability as well as increase the manufacturing yield. As a result, a glass substrate for a recording medium suitable for a small perpendicular magnetic recording type magnetic disk can be provided more efficiently.

  According to the invention described in claim 5, the recording in which both the mechanical strength and the chemical reliability are improved by the manufacturing method of forming the high-hardness glass layer after forming the metal-containing layer on the outer surface of the glass substrate. A glass substrate for a medium can be manufactured, and a glass substrate for an information recording medium suitable for a small-sized perpendicular magnetic recording type magnetic disk can be provided.

  According to the invention of any one of claims 6 to 8, the metal-containing layer can be easily formed on the outer surface of the glass substrate by a conventionally known method, and mechanical strength and A glass substrate for a recording medium that achieves both improved chemical reliability can be manufactured, and a glass substrate for an information recording medium suitable for a small-sized perpendicular magnetic recording type magnetic disk can be provided.

  According to the invention described in claim 9, a high-hardness glass layer can be easily formed by mutually diffusing the components of the glass substrate and the metal-containing layer, and the mechanical strength and the chemical reliability can be formed. In addition, a glass substrate for a recording medium that achieves both improved performance can be manufactured, and a glass substrate for an information recording medium suitable for a small-sized perpendicular magnetic recording type magnetic disk can be provided.

  According to the invention described in claim 10 or 11, mechanical strength and chemical reliability are improved by using the glass substrate for recording medium according to claim 1 or 2 for an information recording medium or an information recording apparatus. A small-sized perpendicular magnetic recording type information recording medium or information recording apparatus can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram showing a configuration of a glass substrate 10 for a recording medium according to the present invention.

  As shown in FIG. 1A, the glass substrate 10 for recording medium has a disk shape having a hole 4 in the center and having an outer diameter φ1 and an inner diameter φ2. As shown in FIG. 1B, the glass substrate 10 for recording medium has a high-hardness glass layer 3 formed so as to surround the glass substrate 1, and the metal-containing layer 2 is formed so as to surround the high-hardness glass layer 3. Is formed.

  The glass substrate 1 is not particularly limited in material, and various conventionally known glasses or glass ceramics can be used. Table 1 shows various glasses grouped. For example, 1) there are aluminosilicate glass, soda lime glass, soda silicate glass, borosilicate glass, quartz glass, Vycor glass, etc. as silicate glass, and 2) borate glass, lead glass as non-silicate glass, Examples thereof include phosphate glass, tellurite glass, fluoride glass, fluorophosphate glass, and 3) glass ceramics such as crystallized glass and composite glass. These may be glass that has not been tempered. Further, the glass substrate surface may be a glass substrate subjected to tempering treatment such as ion exchange, air cooling tempering, dealkalizing treatment or the like.

  Table 2 shows the components constituting the metal-containing layer 2 in groups. The metal elements constituting the metal-containing layer 2 are 1) alkaline earth metal, 2) first transition metal element group, 3) second transition metal element group, 4) third transition metal element group, 5) lanthanoid metal, The metal layer, the metal oxide layer, and the metal-containing organic material layer that are classified into 6) aluminum group and 7) carbon group and include one or more metal elements in Table 2 may be used.

  The high-hardness glass layer 3 contains both components of the glass layer 1 and the metal-containing layer 2, has a higher hardness than the glass layer 1, and has a very thin thickness t of about several tens of nanometers. It is. The hardness of the high-hardness glass layer 3 can be calculated by a density measurement method using X-rays, short-wave electromagnetic waves, or the like. In addition, the cross section can be directly measured using a micro hardness meter (nanoindentation).

  Next, the manufacturing method of the glass substrate 10 for recording media shown in FIG. 1 is demonstrated using FIG. FIG. 2 is a schematic diagram showing a manufacturing process of the glass substrate 10 for recording media according to the present invention. In the figure, the same parts as those in FIG.

  FIG. 2A is a cross-sectional view of the glass substrate 1 having a hole 4 at the center, which is the basis of the glass substrate 10 for recording medium. The upper surface, the lower surface, the outer peripheral end surface, and the inner peripheral end surface of the glass substrate 1 are collectively referred to as an outer surface 5.

  In the case of a metal layer or metal oxide layer on the outer surface 5 of the glass substrate 1 in the metal-containing layer forming step 6, plating treatment, vapor phase growth method (sputtering, CVD, etc.), or coating treatment (spin coating, In the case of a metal-containing organic material layer, the metal-containing layer 2 is formed in a stacked manner by a method such as a coating process (FIG. 2B).

  Next, in the high-hardness glass layer forming step 7, the glass substrate 1 on which the metal-containing layer 2 shown in FIG. 2B is laminated is heated at a predetermined temperature and a predetermined time in a heating furnace in an air atmosphere. As a result, both components of the glass substrate 1 and the metal-containing layer 2 diffuse to each other, and a high-hardness glass layer 3 is formed in the middle region (FIG. 2 (c)). However, due to the difference in concentration and diffusion rate of the components of both the glass substrate 1 and the metal-containing layer 2, the high-hardness glass layer 3 is mainly on the glass substrate 1 side as shown by the arrows in FIG. It is formed.

  The high-hardness glass layer can be formed by a method such as heating in a heating furnace in an air atmosphere, heating in a heating atmosphere in a nitrogen atmosphere or high vacuum, ultraviolet irradiation, infrared irradiation, or the like.

  Next, the characteristic evaluation of the glass substrate 10 for recording media manufactured by the manufacturing method shown in FIG. 2 will be described with reference to FIG. FIG. 3 is a schematic diagram showing a method for evaluating the glass substrate 10 for recording media according to the present invention. In the figure, the same parts as those in FIGS.

  FIG. 3A is a schematic diagram showing the shape of a sample for evaluation of the glass substrate 10 for recording medium. The sample is a disk-shaped glass substrate having an outer diameter φ1 = 65 mm, an inner diameter φ2 = 20 mm, and a plate thickness d = 0.635 mm, and is the same size as a glass substrate used for a normal 2.5-inch hard disk.

  FIG. 3B is a schematic diagram of an annular bending test machine 20 used in a test called an annular bending strength test for measuring the breaking strength of the glass substrate 10 for recording medium shown in FIG. is there.

  The annular bending test machine 20 places an evaluation sample of the recording medium glass substrate 10 on a support base 23 to support the outer periphery 8 in an annular shape, and supports the iron ball 22 in the hole 4 of the recording medium glass substrate 10. A pressure-destructive test is performed by placing a force on the inner periphery 9 of the recording medium glass substrate 10 with the load 21 through the iron ball 22 through the inner periphery 9. In this example described later in Table 1, the breaking load at the time of breaking the recording medium glass substrate 10 is defined as the breaking strength. This method is the same as a method generally used in the industry as a strength test of a recording medium for hard disk.

  The support base 23 has a cylindrical shape with an outer diameter φ5 = 70 mm, an inner diameter φ6 = 63 mm, and a height h = 50 mm. The sample for evaluation of the glass substrate 10 for recording medium is placed on the upper part of the cylinder, and the outer periphery 8 is supported in an annular shape. To do.

  The iron ball 22 is an iron ball having a diameter of φ4 = 28.57 mm, and has a mass of about 100 grams, which is negligible compared to the pressure applied by the load 21. The iron ball 22 abuts on the inner periphery 9 of the sample for evaluation of the glass substrate for recording medium 10 and applies pressure, so that it becomes a sample for evaluation of the glass substrate for recording medium 10 supported on the outer periphery 8 by the support base 23. Apply bending stress.

  The load 21 has a cylindrical shape with an outer diameter φ3 = 30 mm, and the breaking strength can be measured by applying a bending stress to the inner periphery 9 of the sample for evaluation of the glass substrate 10 for recording medium via the iron ball 22. . The pressing speed of the load 21 is about 0.5 mm / min.

  Next, an example using the test method shown in FIG. 3 will be described. In this example, six types of samples in which the high-hardness glass layer 3 was formed and three types of samples in which the high-hardness glass layer 3 was not formed were evaluated for comparison. The results are summarized in Table 3.

  The types of glass substrate 1 are: 1) aluminoborosilicate glass and aluminosilicate glass as representative of silicate glass, 2) borate glass as representative of non-silicate glass, and 3) crystallization as representative of glass ceramics. Glass was selected.

  The types of the metal-containing layer 2 are 1) Mg as a representative of alkaline earth metal, 2) Cr, Co, Ni as a representative of the first transition metal element group, and 3) As a representative of the second transition metal element group. Ag, 4) Au as the representative of the third transition metal element group, 5) Al as the representative of the aluminum group, and 6) Sn as the representative of the carbon group were selected.

  In this way, by conducting experiments using representative examples of each group for both glass types and metal elements, it is possible to determine the types of glass in each group without having to exhaustively experiment with all glass types and metal elements. It is possible to analogize the performance when metal elements are used.

  In the table, “sputtering” in the manufacturing method means “RF magnetron sputtering”. The thickness of the metal-containing layer can be measured by observing the cross-sectional shape of the sample optically or electronically.

As can be seen from the results in Table 3, when the high-hardness glass layer 3 is formed on the aluminoborosilicate glass substrate, a strength improvement of 1.32 times to 1.59 times is achieved compared to the case where it is not formed. In addition, the strength of the crystallized glass substrate is improved by 1.23 times, and the aluminosilicate glass substrate is improved by 1.55 times to 1.68 times, and in any case including borate glass, 100N (Newton). Breaking strength exceeding is achieved. According to conventional experience, it has been found that the yield of the glass substrate for recording medium 10 is greatly changed at a breaking strength of 100 N, which has a great influence on productivity improvement. Therefore, the present invention can greatly contribute to the productivity improvement of the glass substrate 10 for recording media.
In addition, as shown in Table 3, all the glass substrates on which the high-hardness glass layer 3 is formed have a fracture strength exceeding 100 N, even though no strengthening treatment such as chemical strengthening is performed. From this, it can be seen that even when a glass substrate that has not been tempered is formed, a strength that can be used as a substrate for a recording medium can be obtained by forming the high hardness glass layer 3. Therefore, since a complicated strengthening process is not required, it is possible to increase the manufacturing yield, and to provide a recording medium glass substrate suitable for a small-sized perpendicular magnetic recording type magnetic disk more efficiently and inexpensively. Can do.

  Further, Table 3 also shows the measurement results of the alkali elution amount as a measure of the chemical stability described above. Regarding the alkali elution amount, the sample glass was immersed in 50 ml of pure water at 80 ° C. for 24 hours, and then the elution amount was analyzed with an ICP emission spectroscopic analyzer. The sample glass was a 2.5-inch disk substrate, the sample surface was polished with cerium oxide to prepare a smooth surface with an Ra value of 2 nm or less, and then the surface was washed to be a clean sample. The alkali elution amount was the total of Li, Na, and K elution amounts.

  As can be seen from the results in Table 3, with respect to the alkali elution amount, all the samples with the high hardness glass layer 3 formed showed an order of magnitude less elution amount than the samples without the high hardness glass layer. The formation of 3 indicates that the chemical stability has been remarkably improved. In addition, it is thought that the presence of the metal-containing layer 2 is also effective in suppressing the alkali elution amount.

  As described above, by forming the high-hardness glass layer 3 and the metal-containing layer 2 on the outer surface of the normal glass substrate 1, it was possible to achieve an improvement in mechanical strength and chemical stability. .

  Next, the structure of the information recording medium 11 using the glass substrate 10 for recording media shown in FIG. 1 is demonstrated using FIG. FIG. 4 is a schematic diagram showing a configuration of an information recording medium 11 using the recording medium glass substrate 10 according to the present invention. In the figure, the same parts as those in FIGS.

  In FIG. 4A, a glass substrate 10 for recording medium has a high-hardness glass layer 3 formed on an outer surface 5 of a glass substrate 1 and a metal-containing layer 2 formed thereon. The information recording medium 11 is configured by laminating a recording layer 13 made of a magnetic material or the like on the main surface 12 that is the upper surface of the metal-containing layer 2 of the glass substrate 10 for recording medium. In this example, recording layers 13 are formed on both surfaces of the glass substrate for recording medium 10. Since the information recording medium 11 of this configuration is excellent in mechanical strength and chemical stability, it has a large capacity or ultra-small magnetic recording such as a perpendicular magnetic recording method that requires the recording magnetic head to be closer to the information recording medium. Ideal as a medium.

  FIG. 4B schematically shows the configuration of the recording layer 13 used in the perpendicular magnetic recording method. The recording layer 13 includes a magnetic recording layer 13a responsible for actual recording, a backing soft magnetic layer 13c forming part of a magnetic circuit of a recording / reproducing head (not shown), improvement in crystallinity and magnetic characteristics of the magnetic recording layer 13a, and magnetic recording. The intermediate layer 13b is responsible for controlling the temporal interaction between the layer 13a and the backing soft magnetic layer 13c.

  The glass substrate 10 for a recording medium of the present invention has a feature that the backing soft magnetic layer 13c can be easily formed by having the metal-containing layer 2 immediately below the main surface 12 thereof. Moreover, if the material (for example, Ni, Fe, etc.) used for a backing soft magnetic layer is used as a metal containing layer, it is also possible to use a metal containing layer as a backing soft magnetic layer. Of course, depending on the configuration of the recording layer 13, the recording layer 13 may be formed on the high hardness layer 3 by removing the metal-containing layer 2 by polishing, etching, or the like.

  Next, an information recording apparatus equipped with the information recording medium 11 according to the present invention will be described with reference to FIG. FIG. 5 is a schematic perspective view showing a load / unload type hard disk device 50 which is an information recording device equipped with the information recording medium 11 according to the present invention. In the figure, the same parts as those in FIGS.

  The hard disk device 50 includes a head actuator 59 including an information recording medium 11, a recording / reproducing head 52, a suspension 54 that supports the recording / reproducing head 52, and an arm 56 that fixes the suspension 54.

  The head actuator 59 is attached so that the arm 56 can rotate with respect to the casing 51 about the pivot 57. The head actuator 59 is driven to rotate by a voice coil motor 58 provided on the opposite side of the suspension 54 with the pivot 57 interposed therebetween. Furthermore, power is supplied to the head actuator 59 and signals are exchanged with the recording / reproducing head 52 via a flexible printed board 55 fixed to the arm 56.

  In the hard disk device 50, a lift tab 53 is provided at the tip of the suspension 54, and the lift tab 53 is guided to a position regulation lamp 60 attached to the housing 51 so as to overlap the end of the information recording medium 11, thereby recording and reproducing. Unloading is performed for retracting the head 52 from the surface of the information recording medium 11 to the outside, and loading is performed for landing the head 52 from the outside of the information recording medium 11 to the surface.

  The lift tab 53 is a protrusion provided at the tip of the suspension 54 and is located on the tip side of the head 52. The position restricting ramp 60 has a slope with which the lift tab 53 comes into contact. While the lift tab 53 is in contact with the slope of the ramp 60, the distance between the two suspensions 54 is restricted, and the head 52 contacts with each other. Contact with the information recording medium 11 is prevented.

  The head 52 floats from the surface of the information recording medium 11 by the air flow generated by the rotation of the information recording medium 11 mounted on the rotating spindle. For this reason, when the head 52 is loaded onto the surface of the information recording medium 11, the lift tab 53 is supported by the position restriction lamp 60 until the head 52 reaches the surface of the information recording medium 11. When the head 52 is unloaded to the outside of the information recording medium 11, the lift tab 53 is supported by the position restricting lamp 60 before the head 52 comes out of the information recording medium 11.

  By using the information recording medium 11 of the present invention as the recording medium of the hard disk device 50, it becomes possible to perform high-performance and high-density recording. It becomes possible.

  In addition, the detailed configuration and detailed operation of each component constituting the recording medium glass substrate, the recording medium glass substrate manufacturing method, the information recording medium, and the information recording apparatus according to the present invention also depart from the spirit of the present invention. It can be changed as appropriate within the range where there is no.

It is a schematic diagram which shows the structure of the glass substrate for recording media which concerns on this invention. It is a schematic diagram which shows the manufacturing method of the glass substrate for recording media which concerns on this invention. It is a schematic diagram which shows the evaluation method of the glass substrate for recording media which concerns on this invention. It is a schematic diagram which shows the structure of the information recording medium using the glass substrate for recording media which concerns on this invention. 1 is a schematic perspective view of an information recording apparatus equipped with an information recording medium according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Metal-containing layer 3 High-hardness glass layer 4 Hole part 5 Outer surface 6 Metal-containing layer formation process 7 High-hardness glass layer formation process 8 Outer periphery 9 Inner periphery 10 Glass substrate for recording media 11 Information recording medium 12 Main surface 13 Recording layer 13a Magnetic recording layer 13b Intermediate layer 13c Backing soft magnetic layer 20 Ring bending tester 21 Load 22 Iron ball 23 Support base 50 Hard disk device 51 Housing 52 Recording / reproducing head 53 Lift tab 54 Suspension 55 Flexible printed circuit board 56 Arm 57 Pivot 58 Voice coil motor 59 Head actuator 60 Position restriction lamp

Claims (11)

A glass substrate for a recording medium, comprising a high-hardness glass layer having a hardness higher than that of the glass substrate on an outer surface of the glass substrate. The glass substrate for a recording medium according to claim 1, further comprising a metal-containing layer containing at least one of a metal, a metal oxide, or a metal-containing organic compound on an outer surface of the glass substrate. The glass substrate for a recording medium according to claim 1 or 2, wherein the glass substrate for a recording medium is not subjected to a tempering treatment. A method for producing a glass substrate for a recording medium, comprising: a high-hardness glass layer forming step of forming a high-hardness glass layer having a hardness higher than that of the glass substrate on an outer surface of the glass substrate. 5. The glass substrate for a recording medium according to claim 4, further comprising a step of forming a metal-containing layer containing at least one of a metal, a metal oxide, or a metal-containing organic compound on the outer surface of the glass substrate. Manufacturing method. The method for manufacturing a glass substrate for a recording medium according to claim 5, wherein the metal-containing layer is formed by plating. The method for producing a glass substrate for a recording medium according to claim 5, wherein the metal-containing layer is formed by a vapor phase growth method. The method for manufacturing a glass substrate for a recording medium according to claim 5, wherein the metal-containing layer is formed by a coating process. 6. The recording medium according to claim 5, wherein the high-hardness glass layer forming step forms the high-hardness glass layer by mutually diffusing the components of the glass substrate and the metal-containing layer. Method for manufacturing glass substrate. An information recording medium for a perpendicular magnetic recording system, comprising a recording layer on a main surface of the glass substrate for a recording medium according to claim 1. An information recording apparatus comprising the information recording medium according to claim 10.

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