WO2014103983A1

WO2014103983A1 - Method for producing glass substrate for information recording medium

Info

Publication number: WO2014103983A1
Application number: PCT/JP2013/084417
Authority: WO
Inventors: 裕也高田; 直之福本
Original assignee: Hoya株式会社
Priority date: 2012-12-27
Filing date: 2013-12-24
Publication date: 2014-07-03

Abstract

The present invention is provided with a step of preparing a glass substrate group having a plurality of glass substrates, an evaluation step of evaluating surfaces of the glass substrates included in the glass substrate group, and a transition step of determining whether or not to transition a glass substrate group to a step of forming a magnetic thin film. The evaluation step includes: a step of forming, on the surface of a glass substrate for evaluation selected from among the glass substrate group, a reflective film for which reflectivity with respect to an inspection-use laser light is higher than reflectivity of the surface of the glass substrate; and a step of evaluating pass or fail of the surface state of the glass substrate using a glass surface evaluation device that radiates an inspection laser on the reflective film and uses scattering of the inspection laser. The transition step includes a step of transitioning, to the step which forms the magnetic thin film, only glass substrate groups to which, in the evaluation step, glass substrates that were evaluated as passing belong, excluding the glass substrate used for evaluation.

Description

Manufacturing method of glass substrate for information recording medium

The present invention relates to a method for producing a glass substrate for an information recording medium.

Conventionally, aluminum substrates or glass substrates (glass substrates for information recording media) have been used as information recording media (magnetic disk recording media) used in computers and the like. A magnetic thin film layer is formed on these substrates, and information is recorded on the magnetic thin film layer by magnetizing the magnetic thin film layer with a magnetic head.

In recent years, recording density has been increased in hard disk drive (HDD) devices. As the recording density is increased, the gap (flying height) between the information recording medium (medium) and the head that reads and writes the recording while floating on the information recording medium is reduced to about several nanometers.

As the flying height decreases, read / write errors when accessing data recorded on the information recording medium when the information recording medium is used in a hard disk drive, head crash where the magnetic head collides with the surface of the information recording medium It is easy for problems to occur. In order to suppress these problems, information recording media are required to have high detection accuracy of minute defects such as cleanliness and surface smoothness of the glass substrate surface.

A glass surface evaluation apparatus using laser scattering is used to detect minute defects on the surface of a glass substrate used for an information recording medium. In recent years, in order to improve the detection accuracy of minute defects, the detection accuracy of minute defects has been improved by improving the output of a laser used in a glass surface evaluation apparatus, making the laser spot diameter finer, and the like.

Japanese Patent Application Laid-Open No. 2003-50209 (Patent Document 1) discloses a glass for detecting defects with high accuracy without being affected by the directivity of scattered light due to scratches and chipping results on the glass substrate surface. A surface evaluation apparatus is disclosed.

JP 2003-50209 A

However, in recent years, as a result of evaluation using the glass surface evaluation apparatus as described above, even a glass substrate for an information recording medium using a glass substrate that has passed, a hard disk on which the glass substrate for information recording medium is mounted In the drive apparatus, the case where it fails is produced.

As a cause of this, when the detection accuracy of the glass surface evaluation apparatus is improved (laser output improvement / miniaturization of laser spot diameter, etc.), any glass substrate of amorphous material and crystallized glass material, There were the following problems.

When inspection is performed with the glass substrate surface exposed, the glass substrate noise signal (defect of the glass substrate itself) and the glass substrate internal defect signal (inclusion, bubble, This is because it is difficult to detect the actual defect signal and the substrate internal scattering signal separately from the glass substrate noise.

In particular, in the case of a glass substrate using a crystallized glass material, since there are microcrystalline particles on the surface of the glass substrate, the actual defect signal of the glass substrate and the substrate internal scattering signal are compared to the glass substrate using an amorphous material. Is more difficult to detect.

The present invention has been made in order to solve the above-mentioned problems, and includes an evaluation process that makes it possible to easily detect an actual defect signal and a substrate internal scattering signal of a glass substrate by reducing glass substrate noise. It is providing the manufacturing process of the glass substrate for information recording media provided.

The method for producing a glass substrate for information recording medium according to the present invention is a method for producing a glass substrate for information recording medium, which is used for an information recording medium in which a magnetic thin film is formed on the surface of the glass substrate. A step of preparing a glass substrate group having a glass substrate, an evaluation step of evaluating the surface of the glass substrate included in the glass substrate group, and a step of moving the glass substrate group to a step of forming the magnetic thin film. And a transition step for determining whether or not.

The evaluation step has a reflectance higher than the reflectance of the surface of the glass substrate on the surface of the glass substrate for evaluation selected from the glass substrate group. Using the glass surface evaluation apparatus that irradiates the inspection laser on the reflection film and uses the scattering of the inspection laser to evaluate the pass condition or rejection of the glass substrate. Process.

The transition step includes a step of transferring only the glass substrate group to which the glass substrate evaluated to be acceptable belongs to the step of forming the magnetic thin film except the glass substrate used in the evaluation in the evaluation step. Including.

In one embodiment, the reflective film is a film using a metal material.
In one embodiment, the metallic material consists of a material selected from the group of Cr, Al and Ag.

In one embodiment, the reflective film has a thickness of 10 nm to 50 nm.
In one embodiment, the glass substrate is a crystallized glass material.

According to the present invention, there is provided a manufacturing process of a glass substrate for an information recording medium, comprising an evaluation process that makes it possible to easily detect a glass substrate defect signal and a substrate internal scattering signal by reducing glass substrate noise. It is possible to provide.

It is a perspective view which shows an information recording device. It is a top view which shows the glass substrate manufactured by the manufacturing method of the glass substrate for information recording media based on this Embodiment. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. It is a top view which shows the information recording medium provided with the glass substrate as an information recording medium. FIG. 5 is a cross-sectional view taken along line VV in FIG. 4. It is a flowchart which shows the manufacturing method of a glass substrate. It is a schematic diagram which shows the evaluation process of the glass substrate surface using a defect inspection apparatus. It is a figure which shows the glass substrate noise in the evaluation process of the glass substrate using an amorphous material, and the intensity image of an actual defect signal, (A) is evaluation with respect to the conventional defect, (B) is evaluation with respect to the conventional minute defect, ( C) is a diagram showing an evaluation for a minute defect when a reflective film is provided. It is a figure which shows the intensity | strength image of the glass substrate noise in the evaluation process of the glass substrate using a crystallized glass material, and a real defect signal, (A) is evaluation with respect to the conventional defect, (B) is evaluation with respect to the conventional minute defect. (C) is a figure which shows the evaluation with respect to a micro defect at the time of providing a reflecting film. It is a figure which shows the intensity | strength image of the glass substrate noise and internal defect signal in the evaluation process of the glass substrate using an amorphous material, (A) is evaluation with respect to the conventional defect, (B) is a case where a reflecting film is provided. It is a figure which shows the evaluation with respect to a micro defect. It is a figure which shows the intensity | strength image of the glass substrate noise in the evaluation process of the glass substrate using a crystallized glass material, and an internal defect signal, (A) is evaluation with respect to the conventional defect, (B) provided the reflecting film. It is a figure which shows the evaluation with respect to the minute defect in a case. It is a figure which shows the flow of the evaluation process of the glass substrate in an Example. FIG. 6 is a diagram showing evaluation results in Examples 1-1 to 1-4 and Comparative Example 1. FIG. 6 is a diagram showing evaluation results in Examples 2-1 to 2-4 and Comparative Example 2.

Embodiments and examples based on the present invention will be described below with reference to the drawings. In the description of the embodiments and the examples, when the number, amount, and the like are referred to, the scope of the present invention is not necessarily limited to the number, amount, and the like unless otherwise specified. In the description of the embodiment and each example, the same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated.

[Embodiment]
(Information recording device 30)
The information recording device 30 will be described with reference to FIG. FIG. 1 is a perspective view showing the information recording apparatus 30. The information recording apparatus 30 includes the glass substrate 1 manufactured by the method for manufacturing a glass substrate for information recording medium (hereinafter also simply referred to as a glass substrate) in the embodiment as the information recording medium 10.

Specifically, the information recording device 30 includes an information recording medium 10, a housing 20, a head slider 21, a suspension 22, an arm 23, a vertical shaft 24, a voice coil 25, a voice coil motor 26, a clamp member 27, and a fixing screw. 28. A spindle motor (not shown) is installed on the upper surface of the housing 20.

An information recording medium 10 such as a magnetic disk is rotatably fixed to the spindle motor by a clamp member 27 and a fixing screw 28. The information recording medium 10 is rotationally driven by this spindle motor at, for example, several thousand rpm. Although details will be described later with reference to FIGS. 4 and 5, in the information recording medium 10, a compression stress layer 12 (see FIG. 5) and a magnetic recording layer 14 (see FIGS. 4 and 5) are formed on the glass substrate 1. To be manufactured.

The arm 23 is attached so as to be swingable around the vertical axis 24. A suspension 22 formed in a leaf spring (cantilever) shape is attached to the tip of the arm 23. A head slider 21 is attached to the tip of the suspension 22 so as to sandwich the information recording medium 10.

A voice coil 25 is attached to the opposite side of the arm 23 from the head slider 21. The voice coil 25 is clamped by a magnet (not shown) provided on the housing 20. A voice coil motor 26 is constituted by the voice coil 25 and the magnet.

A predetermined current is supplied to the voice coil 25. The arm 23 swings around the vertical axis 24 by the action of electromagnetic force generated by the current flowing through the voice coil 25 and the magnetic field of the magnet. As the arm 23 swings, the suspension 22 and the head slider 21 also swing in the direction of the arrow AR1. The head slider 21 reciprocates on the front and back surfaces of the information recording medium 10 in the radial direction of the information recording medium 10. A magnetic head (not shown) provided on the head slider 21 performs a seek operation.

While the seek operation is performed, the head slider 21 receives a levitation force due to the air flow generated as the information recording medium 10 rotates. Due to the balance between the levitation force and the elastic force (pressing force) of the suspension 22, the head slider 21 travels with a constant flying height with respect to the surface of the information recording medium 10. By the traveling, the magnetic head provided on the head slider 21 can record and reproduce information (data) on a predetermined track in the information recording medium 10. The information recording apparatus 30 on which the glass substrate 1 is mounted as a part of the members constituting the information recording medium 10 is configured as described above.

(Glass substrate 1)
FIG. 2 is a plan view showing glass substrate 1 manufactured by the method for manufacturing a glass substrate for information recording medium according to the present embodiment. 3 is a cross-sectional view taken along the line III-III in FIG.

As shown in FIGS. 2 and 3, the glass substrate 1 (glass substrate for information recording medium) used as a part of the information recording medium 10 (see FIGS. 4 and 5) has a main surface 2, a main surface 3, It has the inner peripheral end surface 4, the hole 5, and the outer peripheral end surface 6, and is formed in a disk shape as a whole. The hole 5 is provided so as to penetrate from one main surface 2 toward the other main surface 3. A chamfer 7 is formed between the main surface 2 and the inner peripheral end surface 4 and between the main surface 3 and the inner peripheral end surface 4. Between the main surface 2 and the outer peripheral end surface 6 and between the main surface 3 and the outer peripheral end surface 6, a chamfered portion 8 (chamfer portion) is formed.

The size of the glass substrate 1 is, for example, 0.8 inch, 1.0 inch, 1.8 inch, 2.5 inch, or 3.5 inch. The thickness of the glass substrate is, for example, 0.30 mm to 2.2 mm from the viewpoint of preventing breakage. In addition, the thickness of a glass substrate means the average value of the value measured in arbitrary arbitrary points which become point symmetry on a glass substrate. Moreover, it is preferable that the information recording medium in which the glass substrate for information recording medium in this Embodiment is employ | adopted is used for a portable use.

In the present embodiment, the glass substrate has an outer diameter of about 64 mm, an inner diameter of about 20 mm, and a thickness of about 0.8 mm. The thickness of the glass substrate is a value calculated by averaging the values measured at a plurality of arbitrary points to be pointed on the glass substrate. From the viewpoint of increasing the hardness of the glass substrate, the Vickers hardness of the glass substrate 1 is preferably 610 kg / mm ² or more.

(Information recording medium 10)
FIG. 4 is a plan view showing an information recording medium 10 provided with a glass substrate 1 as an information recording medium. FIG. 5 is a cross-sectional view taken along the line VV in FIG.

4 and 5, the information recording medium 10 includes a glass substrate 1, a compressive stress layer 12, and a magnetic recording layer 14. The compressive stress layer 12 is formed so as to cover the

main surfaces

2 and 3, the inner peripheral end face 4, and the outer peripheral end face 6 of the glass substrate 1. The magnetic recording layer 14 is formed so as to cover a predetermined region on the

main surfaces

2 and 3 of the compressive stress layer 12. By forming the compressive stress layer 12 on the inner peripheral end face 4 of the glass substrate 1, a hole 15 is formed inside the inner peripheral end face 4. The information recording medium 10 is fixed to a spindle motor provided on the housing 20 (see FIG. 1) using the holes 15.

In the information recording medium 10 shown in FIG. 5, the magnetic recording layer 14 is formed on both the compressive stress layer 12 formed on the main surface 2 and the compressive stress layer 12 formed on the main surface 3 (both sides). Is formed. The magnetic recording layer 14 may be provided only on the compression stress layer 12 (one side) formed on the main surface 2, or on the compression stress layer 12 (one side) formed on the main surface 3. It may be provided.

The magnetic recording layer 14 is formed by spin-coating a thermosetting resin in which magnetic particles are dispersed on the compressive stress layer 12 on the

main surfaces

2 and 3 of the glass substrate 1 (spin coating method). The magnetic recording layer 14 may be formed by a sputtering method or an electroless plating method performed on the compressive stress layer 12 on the

main surfaces

2 and 3 of the glass substrate 1.

The thickness of the magnetic recording layer 14 is about 0.3 μm to 1.2 μm for the spin coating method, about 0.04 μm to 0.08 μm for the sputtering method, and about 0.05 μm to about the electroless plating method. 0.1 μm. From the viewpoint of thinning and high density, the magnetic recording layer 14 is preferably formed by sputtering or electroless plating.

As a magnetic material used for the magnetic recording layer 14, a Co-based alloy or the like containing Ni or Cr as a main component is added for the purpose of adjusting the residual magnetic flux density. Is preferably used.

In order to improve the sliding of the magnetic head, the surface of the magnetic recording layer 14 may be thinly coated with a lubricant. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon.

The magnetic recording layer 14 may be provided with a base layer or a protective layer as necessary. The underlayer in the information recording medium 10 is selected according to the type of magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni.

The underlayer provided on the magnetic recording layer 14 is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

Examples of the protective layer for preventing wear and corrosion of the magnetic recording layer 14 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be formed continuously with an in-line type sputtering apparatus together with the underlayer and the magnetic film. These protective layers may be a single layer, or may have a multilayer structure composed of the same or different layers.

Other protective layers may be formed on the protective layer or instead of the protective layer. For example, instead of the protective layer, colloidal silica fine particles are dispersed and coated on a Cr layer with tetraalkoxylane diluted with an alcohol solvent, and then fired to form a silicon oxide (SiO2) layer. May be.

(Glass substrate manufacturing method)
Next, the manufacturing method of the glass substrate (glass substrate for information recording media) in this Embodiment is demonstrated using the flowchart figure shown in FIG.

First, in a “glass melting step” of step 10 (hereinafter abbreviated as “S10”, the same applies to step 11 and subsequent steps), the glass material constituting the glass substrate is melted.

In S11 “press molding process”, a glass substrate was produced by pressing the molten glass material using an upper mold and a lower mold. The glass composition used was a general aluminosilicate glass. The method for producing the glass substrate is not limited to molding, and may be cut out from plate glass, which is a known technique, and the glass composition is not limited thereto.

In the “first lapping step” of S12, both main surfaces of the glass substrate were lapped. This first lapping step was performed using a double-sided lapping device using a planetary gear mechanism. Specifically, the lapping platen was pressed on both surfaces of the glass substrate from above and below, the grinding liquid was supplied onto the main surface of the glass substrate, and these were moved relatively to perform lapping. By this lapping process, a glass substrate having a substantially flat main surface was obtained.

In the “coring step” of S13, a hole was formed in the center of the glass substrate using a cylindrical diamond drill to produce an annular glass substrate. The inner peripheral end surface and the outer peripheral end surface of the glass substrate were ground with a diamond grindstone, and a predetermined chamfering process was performed.

In the “second lapping step” of S14, lapping was performed on both main surfaces of the glass substrate in the same manner as in the first lapping step (S12). By performing the second lapping step, the fine uneven shape formed on the main surface in the coring and end face processing in the previous step can be removed in advance. As a result, the polishing time of the main surface in the subsequent process can be shortened.

In the “outer / inner periphery polishing step” of S15, the outer peripheral end surface and the inner peripheral end surface of the glass substrate were subjected to mirror polishing by brush polishing. At this time, as the abrasive grains, a slurry containing general cerium oxide abrasive grains was used.

In the “first polishing step” of S16, the main surface was polished. The first polishing step is mainly intended to correct scratches and warpage remaining on the main surface in the first and second lapping steps (S12, S14) described above. In the first polishing step, the main surface was polished by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, general cerium oxide abrasive grains were used.

In the “chemical strengthening step” of S17, a surface reinforcing layer was formed on the main surface of the glass substrate 1G. Specifically, chemical strengthening was performed by bringing the glass substrate 1G into contact with a mixed solution of potassium nitrate (70%) and sodium nitrate (30%) heated to 300 ° C. for about 30 minutes. As a result, the lithium ion and sodium ion on the inner peripheral end surface and outer peripheral end surface of the glass substrate are respectively replaced with sodium ions and potassium ions in the chemical strengthening solution, and a compressive stress layer is formed, thereby forming the main surface of the glass substrate and The end face was strengthened.

In addition, this chemical strengthening process is not an essential process, and when it is not necessary to strengthen the main surface and the end face of the glass substrate, the chemical strengthening process may not be performed.

The main surface polishing step was performed in the “second polishing step” of S18. This second polishing step aims to eliminate the fine defects on the main surface that have been generated and remain in the above-described steps and finish it in a mirror shape, to eliminate warpage and finish it to a desired flatness. In the second polishing step, polishing was performed by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, colloidal silica having an average particle diameter of about 20 nm was used to obtain a smooth surface.

Next, in the “final cleaning process” in S19, final cleaning of the main surface and the end surface of the glass substrate is performed. Thereby, the deposits remaining on the glass substrate are removed. The final cleaning process is a process performed at the end of the glass substrate manufacturing process, and includes a drying process as appropriate.

Next, in the “100% inspection process” of S20, the shape inspection and the surface quality inspection of the glass substrate were performed on all the glass substrates after the final cleaning process. Thereafter, a glass substrate group having a plurality of glass substrates was prepared. Usually, one glass substrate group includes 100 glass substrates.

Next, in the “reflection film forming step” of S30, the reflectance of the inspection laser light on the surface of the glass substrate for evaluation selected from the glass substrate group is higher than the reflectance of the surface. A reflective film was formed. In FIG. 3, the case where the reflective film 100 is formed on the glass substrate 1 is illustrated by a one-dot chain line.

When the inspection laser beam is directly incident on the surface of the glass substrate on which the reflective film is not formed, the laser beam is incident on the inside of the glass substrate, and the laser beam is irregularly reflected inside the glass substrate. As a result, the level of glass substrate noise detected by the glass surface evaluation apparatus increases.

On the other hand, when the inspection laser is irradiated from the air on the surface side where the reflective film is provided on the glass substrate on which the reflective film having a reflectance higher than the reflectance of the surface is reflected with respect to the inspection laser light The inspection laser is reflected according to the surface state (unevenness state) of the glass substrate, and the inspection laser incident inside the glass substrate is reflected by the reflection film, and the surface of the glass substrate on the side where the reflection film is formed Is not emitted to the outside.

As a result, the reflected light of the inspection laser detected by the glass surface evaluation apparatus is only the inspection laser reflected according to the surface state of the glass substrate, and the level of the glass substrate noise detected by the glass surface evaluation apparatus can be lowered. It becomes possible.

As described above, in order to suppress light scattering noise from the inside of the glass substrate, it is desirable to generate a reflective surface similar to a mirror surface, and a reflective film made of a metal material generally used as a reflective coat may be used.

In particular, a metal film made of a material selected from the group consisting of Cr, Al, and Ag can generate a reflective surface having good reflection characteristics for various measurement wavelengths, and thus it is preferable to use it as a reflective film in this embodiment. .

Next, with reference to FIG. 7, a glass surface evaluation step (S40) using a glass surface evaluation apparatus (for example, 7120 manufactured by KLA-Tencor Candela) will be described as an example of a defect inspection apparatus using laser scattering. To do. FIG. 7 is a schematic view showing an evaluation process of the glass substrate surface using the glass surface evaluation apparatus.

An inspection laser having a wavelength of, for example, 390 nm to 650 nm is incident on the glass substrate 1 from the irradiation optical system 110 at a different angle from the irradiation optical system 110, and each scattered signal is detected by the detection optical system 210. By setting a threshold value between a typical glass substrate noise and an actual defect signal, a defect on the glass substrate surface is quantitatively detected.

Note that the average reflectance of the glass substrate before the formation of the reflective film at the inspection laser wavelength of 390 nm to 650 nm with respect to the air is generally about 3% to 5%. It is desirable that the reflectance is 10% or more, which is twice or more the reflectance before coating.

8 to 11, the quantitative detection of defects when the reflective film is not provided and when the reflective film is provided will be described. FIG. 8 and FIG. 9 are diagrams showing strength images of glass substrate noise and actual defect signals in an evaluation process of a glass substrate using an amorphous material and a crystallized glass material, and FIG. (B) is an evaluation for a conventional minute defect, and (C) is a diagram showing an evaluation for a minute defect when a reflective film is provided.

FIG. 10 and FIG. 11 are diagrams showing strength images of glass substrate noise and internal defect signals in the evaluation process of a glass substrate using an amorphous material and a crystallized glass material, and FIG. Evaluation, (B) is a diagram showing evaluation for a minute defect when a reflective film is provided.

Referring to FIG. 8, when an amorphous material is used for the glass substrate, as shown in FIG. 8A, the level of the actual defect signal DS1 for the conventional relatively large actual defect is higher than the level of the glass substrate noise signal GLN1. Since there is a large level difference, it was possible to clearly distinguish both signals.

However, as shown in (B), when the size of the defect to be detected becomes small, the level of the actual defect signal DS2 becomes clear because the level difference becomes small with respect to the level of the glass substrate noise signal GLN1. It becomes difficult to distinguish both signals.

On the other hand, in the present embodiment, as shown in (C), a glass substrate on which a reflective film having a reflectance higher than that of the glass substrate surface is used for the inspection. Thus, as described above, the level of the glass substrate noise signal GLN1 generated due to the scattering factor inside the glass substrate detected by the glass surface evaluation apparatus can be lowered (in (C)). Arrow A1).

As a result, the level of the actual defect signal DS2 with respect to a small actual defect has a level difference with respect to the level of the glass substrate noise signal GLN1, and it is possible to clearly identify both signals.

Similarly, referring to FIG. 9, when a crystallized glass material is used for the glass substrate, since the microcrystals existing inside the glass substrate become a scattering factor, as shown in (A), the crystallized glass material is The level of the glass substrate noise signal GLN2 generated due to the scattering factor inside the glass substrate is higher than that of the amorphous material. Therefore, even with the conventional actual defect signal DS3 for a relatively large actual defect, it may be difficult to clearly distinguish both signals with respect to the level of the glass substrate noise signal GLN2.

As shown in (B), when the size of the actual defect to be detected is reduced, the level of the actual defect signal DS4 is buried in the level of the glass substrate noise signal GLN2, and the two signals are identified. Is extremely difficult.

On the other hand, in the present embodiment, as shown in (C), a glass substrate on which a reflective film having a reflectance higher than that of the glass substrate surface is used for the inspection. Thus, as described above, the level of the glass substrate noise signal GLN3 generated due to the scattering factor inside the glass substrate detected by the glass surface evaluation apparatus can be lowered (in (C)). Arrow A2).

As a result, the level of the actual defect signal DS4 with respect to a small actual defect has a level difference with respect to the level of the glass substrate noise signal GLN3, so that both signals can be clearly identified. Next, referring to FIG. 10, when an amorphous material is used for the glass substrate, the internal defect signal due to inclusion, bubbles, internal contamination, etc., as shown in FIG. It was difficult to distinguish from the defect signal DS6.

On the other hand, in the present embodiment, as shown in (B), a glass substrate on which a reflective film having a reflectance higher than the reflectance of the glass substrate surface is used for the inspection. Thus, as described above, the level of the glass substrate noise signal GLN3 generated due to the scattering factor inside the glass substrate detected by the glass surface evaluation apparatus can be lowered (in (B)). In addition to the arrow A3), even if there are relatively large internal defects such as internal inclusions, bubbles, and internal contamination, the reflection film provided on the surface can reduce the incidence of laser light on the internal defects.

Further, even if a laser is incident on an internal defect, the amount of emission from the inside of the glass substrate can be suppressed, so that the internal defect signal DS6 can be prevented from being generated, and only the actual defect signal DS5 can be detected with high accuracy. It becomes possible.

As a result, the glass substrate can be evaluated based only on the actual defect signal DS5.

Next, referring to FIG. 11, when a crystallized glass material is used for the glass substrate, the internal defect signal due to inclusion, bubbles, internal contamination, etc., as shown in FIG. And the internal defect signal DS8 are difficult to distinguish.

On the other hand, in the present embodiment, as shown in (B), a glass substrate on which a reflective film having a reflectance higher than the reflectance of the glass substrate surface is used for the inspection. Thus, as described above, the level of the glass substrate noise signal GLN4 generated due to the scattering factor inside the glass substrate detected by the glass surface evaluation apparatus can be lowered (in (B)). In addition to the arrow A4), the internal defect signal DS8 can be prevented from being generated for the same reason as described above, so that only the actual defect signal DS7 can be accurately detected.

The manufacturing method of the glass substrate in the present embodiment is configured as described above. By using this method for producing a glass substrate, a glass substrate 1G shown in FIG. 1 capable of forming a magnetic thin film on the surface of the glass substrate is obtained. Thereafter, the information recording medium 1 shown in FIG. 2 is obtained using the glass substrate 1G thus obtained.

Referring again to FIG. 6, in the glass surface evaluation step (S40), after the evaluation of the glass substrate for evaluation, the glass substrate used for the evaluation is excluded except for the glass substrate used for the evaluation. Only the group is shifted to the magnetic thin film forming step (S50) for forming the magnetic thin film.

As a magnetic thin film layer film forming step in the manufacture of an information recording medium, after cleaning the glass substrate 1G obtained through the above-described steps, both main surfaces of the glass substrate 1G are formed of an adhesion layer made of a Cr alloy and a CoFeZr alloy. An information recording medium of a perpendicular magnetic recording system is formed by sequentially forming a soft magnetic layer, an orientation control underlayer made of Ru, a perpendicular magnetic recording layer made of a CoCrPt alloy, a C-based protective layer, and an F-based lubricating layer. To manufacture. This configuration is an example of a configuration of a perpendicular magnetic recording system, and a magnetic layer or the like may be configured as an in-plane information recording medium. Thereafter, the information recording medium 1 is completed by performing a heat treatment step and the like.

As mentioned above, according to the manufacturing method of the glass substrate for information recording media in this Embodiment, evaluation which makes it possible to detect a glass substrate defect signal and a substrate internal scattering signal easily by reducing glass substrate noise. The manufacturing process of the glass substrate for information recording media provided with a process is made possible.

Specifically, by providing the above-mentioned reflective film on the glass substrate used for the surface evaluation of the glass substrate surface, the glass substrate noise on the glass substrate surface is reduced and the SN ratio of the defect signal is improved. It becomes possible to make it.

This improves the number of detections of micro-defects that are conventionally difficult to evaluate, and improves the sorting accuracy between glass substrate noise and other defect noises (actual defect signal, internal defect signal). As a result, minute defects can be evaluated, and the outflow of a defective glass substrate that causes a subsequent error can be effectively reduced. As a result, an information recording medium (magnetic disk) having a high recording density can be stably supplied.

In FIG. 12, the flow of the evaluation process of the glass substrate in an Example is shown.
The steps S10 to S20 described above were performed, and 1000 glass substrates that were determined to be non-defective (passed) in the step S20 were prepared. In 100% inspection in S20, defects of 1 μm or more such as scratches or chips on the surface of the glass substrate were determined as defective products (failed).

100 glass substrates subjected to the same S18 (second polishing step) on 1000 glass substrates were defined as one glass substrate group (1 batch). Therefore, 10 groups (batch) of glass substrate groups were prepared (S110).

Two glass substrates were selected from one glass substrate group as a glass substrate for evaluation using a glass surface evaluation apparatus (S120). A reflective film was provided on the surface of the glass substrate for evaluation by sputtering (S130). For the glass surface evaluation apparatus (OSA: Optical Surface Analyzer), 7120 manufactured by KLA-Tencor Candela was used.

The glass substrate for evaluation on which the reflective film was formed was evaluated using a glass surface evaluation apparatus (S140). In the evaluation, whether or not a non-defective product (pass) is acceptable is determined based on a determination line (in this embodiment, the number of defects of 1 μm or less is 15 counts or less).

The glass substrate group to which the glass substrate determined to be non-defective (pass) is evaluated as non-defective (OK product) (S150). On the other hand, the glass substrate group to which the glass substrate determined to be defective (failed) belongs is evaluated as defective (NG product) (S160), and the process of S18 (second polishing step) is performed again. Processing and reevaluation are performed (S170).

Note that the decision line is determined by the required quality of the glass substrate corresponding to the specifications of the hard disk drive in which the glass substrate is finally incorporated.

Example 1-1
A sputtering apparatus was used for the reflective film formed on the glass substrate using an amorphous material. A Cr film was formed to a thickness of about 5 nm by discharging for 10 s at a deposition target Cr, a discharge vacuum of 5 × 10 ⁻² Pa, and an RF power of 500 W.

When the surface reflectance of the glass substrate after film formation was measured, it increased from 2.5% before film formation to 10% (inspection laser wavelengths: 405 nm, 633 nm).

(Examples 1-2 to 1-4)
As in Example 1-1, a glass substrate with a reflective film thickness of 20 nm was prepared as Example 1-2, and a glass substrate with a reflective film thickness of 50 nm was prepared as Example 1-3. As Example 1-4, a glass substrate having a reflective film thickness of 90 nm was prepared.

The evaluation results of Examples 1-1 to 1-4 are shown in FIG. As Comparative Example 1, a glass substrate (amorphous material) on which no reflective film was formed was prepared. In each example, a magnetic thin film is formed on a glass substrate belonging to a glass substrate group evaluated as good (OK) and incorporated into a hard disk drive, and the rate of occurrence of subsequent errors such as read / write errors and head crashes is confirmed. did.

For comparison, the rate of occurrence of late errors such as read / write errors and head crashes by forming a magnetic thin film on a glass substrate belonging to a group of glass substrates evaluated as defective (NG) and incorporating it into a hard disk drive. It was confirmed.

In Example 1-1, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as non-defective (OK) was 8%. On the other hand, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as defective (NG) was 59%.

In Example 1-2, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as non-defective (OK) was 5%. On the other hand, the occurrence rate of subsequent errors using a glass substrate belonging to the glass substrate group evaluated as defective (NG) was 87%.

In Example 1-3, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as non-defective (OK) was 4%. On the other hand, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as defective (NG) was 92%.

In Example 1-4, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as non-defective (OK) was 10%. On the other hand, the occurrence rate of subsequent errors using a glass substrate belonging to the glass substrate group evaluated as defective (NG) was 93%.

In Comparative Example 1, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as non-defective (OK) was 13%. On the other hand, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as defective (NG) was 40%.

Example 2-1
A sputtering apparatus was used for the reflective film formed on the glass substrate using the crystallization material. A Cr film was formed to a thickness of about 5 nm by discharging for 10 s at a deposition target Cr, a discharge vacuum of 5 × 10 ⁻² Pa, and an RF power of 500 W.

(Examples 2-2 to 2-4)
As in Example 2-1, a glass substrate with a reflective film thickness of 20 nm was prepared as Example 1-2, and a glass substrate with a reflective film thickness of 50 nm was prepared as Example 1-3. As Example 1-4, a glass substrate having a reflective film thickness of 90 nm was prepared.

The evaluation results of Examples 2-1 to 2-4 are shown in FIG. As Comparative Example 2, a glass substrate (crystallization material) on which no reflective film was formed was prepared. In each example, a magnetic thin film is formed on a glass substrate belonging to a glass substrate group evaluated as good (OK) and incorporated into a hard disk drive, and the rate of occurrence of subsequent errors such as read / write errors and head crashes is confirmed. did.

In Example 2-1, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as non-defective (OK) was 11%. On the other hand, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as defective (NG) was 53%.

In Example 2-2, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as non-defective (OK) was 7%. On the other hand, the occurrence rate of subsequent errors using a glass substrate belonging to the glass substrate group evaluated as defective (NG) was 85%.

In Example 2-3, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as non-defective (OK) was 4%. On the other hand, the incidence of subsequent errors using a glass substrate belonging to the glass substrate group evaluated as defective (NG) was 91%.

In Example 2-4, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as non-defective (OK) was 14%. On the other hand, the occurrence rate of subsequent errors using a glass substrate belonging to the glass substrate group evaluated as defective (NG) was 94%.

In Comparative Example 2, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as non-defective (OK) was 18%. On the other hand, the rate of occurrence of subsequent errors using glass substrates belonging to the glass substrate group evaluated as defective (NG) was 38%.

From the above examples and comparative examples, in the glass surface evaluation apparatus using laser scattering, by forming a reflective film on the surface of the glass substrate, compared to a glass substrate on which no reflective film is formed, By providing the reflective film described above, the glass substrate noise on the glass substrate surface is reduced, and the SN ratio of the defect signal can be improved.

In particular, in the case of a glass substrate using a crystallized glass material, since there are microcrystalline particles on the surface of the glass substrate, the actual defect signal of the glass substrate and the substrate internal scattering signal are compared to the glass substrate using an amorphous material. It was difficult to detect.

However, from Examples 2-1 to 2-4, even in the case of a glass substrate using a crystallized glass material, it is possible to reduce the rate of occurrence of subsequent errors by improving the SN ratio of the defect signal. It was confirmed that it was possible.

Also, since the rate of occurrence of subsequent errors is 7% or less, the thickness of the reflective film is preferably 20 nm to 50 nm.

In addition, as shown in the said Example, both the glass substrate using an amorphous material and the glass substrate using a crystallized glass material can be used for a glass substrate. A glass substrate using an amorphous material is characterized in that scattered light noise in optical inspection is small because internal light scattering is small. Moreover, there is an advantage that the smoothness after polishing is excellent. On the other hand, a glass substrate using a crystallized glass material has an advantage of excellent strength.

As mentioned above, although embodiment and each Example based on this invention were described, embodiment and each Example disclosed this time are illustrations in all points, and are not restrictive. The technical scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Glass substrate, 2, 3 Main surface, 4 Inner peripheral end surface, 5,15 hole, 6, Outer peripheral end surface, 7,8 Chamfer part, 10 Information recording medium, 12 Compression stress layer, 14 Magnetic recording layer, 20 Housing 21 Head slider, 22 suspension, 23 arm, 24 vertical axis, 25 voice coil, 26 voice coil motor, 27 clamp member, 28 fixing screw, 30 information recording device, 100 reflective film.

Claims

A method for producing a glass substrate for an information recording medium used for an information recording medium in which a magnetic thin film is formed on the surface of a glass substrate,
Preparing a glass substrate group having a plurality of glass substrates;
An evaluation step for evaluating the surface of the glass substrate included in the glass substrate group;
A transition step of determining whether to shift the glass substrate group to a step of forming the magnetic thin film; and
The evaluation step includes
On the surface of the glass substrate for evaluation selected from the glass substrate group, a reflection film having a reflectance higher than that of the surface of the glass substrate is higher than the reflectance of the surface of the glass substrate. Process,
Irradiating the inspection laser to the reflective film and using a glass surface evaluation apparatus using scattering of the inspection laser, and evaluating the pass or fail of the surface state of the glass substrate, and
The transition process includes
In the evaluation step, except for the glass substrate used in the evaluation, including a step of transferring only the glass substrate group to which the glass substrate evaluated as acceptable belongs to the step of forming the magnetic thin film.
A method for producing a glass substrate for an information recording medium.
The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein the reflective film is a film using a metal material.
The method for producing a glass substrate for an information recording medium according to claim 1, wherein the metal material is made of a material selected from the group consisting of Cr, Al, and Ag.
3. The method for producing a glass substrate for an information recording medium according to claim 1, wherein the reflective film has a thickness of 10 nm to 50 nm.
The method for producing a glass substrate for an information recording medium according to any one of claims 1 to 3, wherein the glass substrate is a crystallized glass material.