WO2014050507A1 - Method for producing glass substrate for information recording medium - Google Patents

Abstract

In this method for producing a glass substrate for an information recording medium, the first grinding step comprises a step for grinding the principal surfaces (2, 3) by blasting the principal surfaces (2, 3) with particles (200g) such that the arithmetic mean roughness Ra₁ of the respective principal surfaces (2, 3) is kept within the range of from 1 µm to 5 µm, and the arithmetic mean roughness Ra₂ in a case where the cutoff value is set between 2.5 µm and 80 µm falls within the range of from 0.1 µm to 1.0 µm.

Description

Manufacturing method of glass substrate for information recording medium

The present invention relates to a method for manufacturing a glass substrate for information recording media, and in particular, manufacturing a glass substrate for information recording media mounted as part of an information recording medium in an information recording device such as a hard disk drive (HDD). Regarding the method.

Information recording devices equipped with information recording media, such as hard disk drives, are expanding their usage and usage environment year by year. The demands on information recording devices for increasing capacity, impact resistance, heat resistance, and the like tend to increase year by year. Along with this tendency, various conditions are also required for a glass substrate for information recording medium (also simply referred to as a glass substrate) used for manufacturing an information recording medium.

For example, as the capacity of an information recording apparatus is increased (for example, a recording medium having a recording capacity of 500 GB (single side 250 GB) and a surface recording density of 600 Gbit / in 2 or more with one 2.5 inch recording medium), information recording is performed. The bit area of the medium is reduced. As a result, even a slight defect generated in the glass substrate causes a reading failure of the information recording medium. Defects include convex protrusions, inclusions, and concave crack defects (or pit defects). Convex protrusions are relatively easy to find by inspection, but crack defects are difficult to find by inspection.

In recent years, it has become the mainstream to use a diamond sheet in the grinding process for the purpose of countermeasures against crack defects (see Japanese Patent Application Laid-Open No. 2009-99249 (Patent Document 1)). This grinding process using a diamond sheet is advantageous for removing crack defects. However, there is also a problem that it is difficult to set conditions for grinding.

The glass substrate production methods are roughly classified into a sheet method for producing a glass substrate from a sheet material and a direct press method for producing a glass substrate by pressing molten glass into a disk shape with a molding machine or the like.

In the sheet method, when a glass substrate is manufactured from sheet glass called a sheet material, a grinding process using a diamond sheet is performed after a roughening process.

On the other hand, the direct press method requires time for manufacturing a glass substrate in a single wafer type, but has been attracting attention again in recent years because it can be manufactured with various glass compositions. Since the glass substrate manufactured by the direct press method is already rough, the grinding process using the diamond sheet is performed without performing the roughening process.

JP 2009-99249 A

The recent years have been affected by the increase in the storage capacity of information recording media, and even in the method of manufacturing a glass substrate for information recording media using the direct press method, a roughening step is required before performing the grinding step. It has become to. This is due to the need for a substrate with higher hardness as the storage capacity increases.

Specifically, if the hardness of the glass substrate is low, a minor scratch is made on the glass substrate due to a minor thing, which becomes a defect. Therefore, a glass substrate with high hardness is used. However, if a grinding process using a diamond sheet is performed on a glass substrate with high hardness without performing a roughening process, it is necessary to increase the pressure during grinding as compared to when the surface is roughened. New cracks are generated on the surface of the substrate. Therefore, even in the production of a glass substrate by the direct press method, a roughening step is required before performing the grinding step.

Examples of the roughening process performed by the conventional float process include a frost process using a chemical solution and a rough grinding process using loose abrasive grains with a flat surface polishing machine.

As described above, in the production of a glass substrate by the direct press method, a roughening step is required before performing the grinding step, but when the above roughening step is applied to the direct press method as it is. Causes the following problems.

When the frost process with chemicals is applied, the surface of the glass substrate is roughened by etching, but as a result, the chemical enters the scratches or cracks that originally existed, and the scratches or cracks become deeper. This leads to increased grinding amount and longer time.

When a rough grinding process using loose abrasive grains by a flat polishing machine is applied, new cracks are generated in the glass substrate due to pressurization from the polishing machine.

The present invention has been made to solve the above problems, and even when a glass substrate having a high hardness is used, it is possible to realize a roughening process suitable for the pre-process of the grinding process. It aims at providing the manufacturing method of the glass substrate for information recording media.

According to the present invention, there is provided a method for producing a glass substrate for an information recording medium, wherein the main surface of the glass substrate is ground by spraying a plurality of particles from a nozzle onto the main surface of the glass substrate obtained by a direct press method. The main surface of the glass substrate is ground with fixed abrasive grains mainly composed of diamond particles having an average particle diameter of 2 μm to 10 μm with respect to the glass substrate that has undergone the first grinding step and the first grinding step. 2 grinding processes.

In the first grinding step, the average arithmetic roughness Ra ₁ when the average arithmetic roughness Ra _{1 of the} main surface is maintained within the range of 1 μm to 5 μm and the cutoff value is set to 2.5 μm to 80 μm. ₂ includes the step of spraying the particles onto the main surface and grinding the main surface so that ₂ falls within the range of 0.1 μm to 1.0 μm.

In another embodiment, the main surface has a Vickers hardness of 610 kg / mm ² or more.
In another form, the maximum particle size of the particles is from 50 μm to 150 μm.

In another embodiment, the spray pressure of the particles is 0.1 MPa to 1 MPa.

According to the present invention, there is provided a method for manufacturing a glass substrate for an information recording medium capable of realizing a roughening process suitable for a pre-process of a grinding process even when a glass substrate having high hardness is used. It is possible to do.

It is a perspective view which shows an information recording device provided with the glass substrate manufactured by using the manufacturing method of the glass substrate for information recording media in embodiment. It is a top view which shows the glass substrate manufactured by the manufacturing method of the glass substrate for information recording media in 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 manufactured by the manufacturing method of the glass substrate for information recording media in embodiment as an information recording medium. FIG. 5 is a cross-sectional view taken along line VV in FIG. 4. It is a flowchart figure which shows each process of the manufacturing method of the glass substrate for information recording media in embodiment. It is a schematic diagram which shows the structure of the blasting apparatus used for the blasting process with respect to the glass substrate in embodiment. It is a schematic diagram which shows the implementation condition of the blasting process with respect to the glass substrate in embodiment. It is sectional drawing which shows the double-side polish machine used for the rough polishing process of the manufacturing method of the glass substrate for information recording media in embodiment. It is a figure which shows the evaluation result in Examples 1-4 and Comparative Examples 1 and 2. FIG.

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.

In the specification, cracks are minute scratches or dents that are present on the glass surface and are invisible to the eyes (or an optical microscope). Also called Griffiths flow.

The glass breakage occurs because when the tensile stress is applied to the glass surface, the stress concentrates on the tip of the crack and the crack progresses. The size of the crack is several tens of nm to several tens of μm. Cracks occur naturally when glass is handled, and cracks already exist even in the state of glass blanks.

Once this crack has entered the glass once, it will be difficult to remove completely because the crack will develop (grow) due to pressure during polishing even if the surface is later shaved by a polishing process. turn into. Therefore, in the grinding process, it is important how to suppress the generation of new cracks while removing existing cracks.

(Information recording device 30)
First, 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 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.

Another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, tetraalkoxylane is diluted with an alcohol-based solvent on a Cr layer, and then colloidal silica fine particles are dispersed and applied, followed by baking to form a silicon oxide (SiO ₂ ) layer. It may be formed.

(Glass substrate manufacturing method)
Next, the manufacturing method S100 of the glass substrate (glass substrate for information recording media) in this Embodiment is demonstrated using the flowchart figure shown in FIG. The glass substrate manufacturing method S100 in the present embodiment includes a plate-like glass forming step S10, a cut-out forming step S20, a blasting step S30, a lapping step S40, an end surface polishing step S50, a rough polishing step S60, a cleaning step S65, and a chemical strengthening step. S70, precision polishing process S80, and scrub cleaning process S90 are provided.

The magnetic thin film forming step S200 is performed on the glass substrate obtained through the scrub cleaning step S90. Through the magnetic thin film forming step S200, the information recording medium 10 (see FIGS. 4 and 5) is obtained. Hereinafter, the details of the steps S10 to S90 constituting the glass substrate manufacturing method S100 will be described in order.

(Plate-shaped glass forming step S10)
First, in the glass sheet forming step S10, a glass sheet is manufactured using a known glass forming method such as a direct press method, a float method, a down draw method, a redraw method, or a fusion method using a molten glass as a material. Among these, the direct press method can be directly molded from a melted glass into a target glass molded product, and thus is suitable for producing a large amount of plate-like glass having the same shape. In the direct press method, molten glass is supplied to a press mold and pressed with a press mold while the glass is in a softened state to form a sheet glass.

As the material of the glass substrate, for example, amorphous glass or crystallized glass can be used. When amorphous glass is used, chemical strengthening can be appropriately performed, and a glass substrate for an information recording medium excellent in flatness of the main surface and substrate strength can be provided.

(Cut-out molding step S20)
In the cut-out forming step S20, an inner hole is formed in the center of the glass substrate using a cylindrical diamond drill, and an annular glass substrate is formed (coring process). Thereafter, the inner peripheral end face and the outer peripheral end face are ground with a diamond grindstone and subjected to predetermined chamfering (forming, chamfering).

(Blasting process S30)
In the blasting step S30, the main surfaces 2 and 3 of the glass substrate 1 are ground by spraying 200 g of a plurality of particles (abrasive grains) onto the main surfaces 2 and 3 of the glass substrate 1 formed by the steps S10 and S20. Perform (first grinding step).

The blasting step S30 will be described with reference to FIGS. FIG. 7 is a schematic diagram illustrating a configuration of a blasting apparatus 100 used in a blasting process for the glass substrate 1, and FIG. 8 is a schematic diagram illustrating an implementation status of the blasting process for the glass substrate 1.

In FIG. 7, blasting is performed on the main surfaces 2 and 3 of the glass substrate 1 using a blasting apparatus 100. The blast apparatus 100 includes a support table 120 that supports the glass substrate 1 and a nozzle 110 that sprays 200 g of particles (abrasive grains) on the main surface of the glass substrate 1 supported by the support table 120. The blasting apparatus 100 performs a blasting process on the entire main surfaces 2 and 3 of the glass substrate 1 substantially evenly by moving the support 120 or the nozzle 110. When the blasting process for the main surface 2 is completed, the blasting apparatus 100 moves the glass substrate 1 to perform the blasting process for the main surface 3.

An ejection hole is formed at the tip of the nozzle 110, and 200 g of particles (abrasive grains) are ejected from the ejection hole. 200 g of particles (abrasive grains) ejected from the nozzle 110 are sprayed onto the glass substrate 1 while spreading in the range of the spray opening angle A ° around the center line CL. When blasting the glass substrate 1, the nozzle 110 is disposed so that the center line CL is substantially perpendicular to the main surfaces 2 and 3.

FIG. 8 is a schematic plan view showing the glass substrate (glass substrate precursor) 1 before being subjected to blasting by the blasting apparatus 100. R30 in FIG. 8 indicates an area (blast area) to be blasted (polished) by 200 g of particles (abrasive grains) ejected from the nozzle 110.

As shown in FIG. 8, the nozzle 110 moves so as to scan the surface of the glass substrate 1 in, for example, a zigzag pattern (line P in the figure). Thereby, 200 g of particles (abrasive grains) ejected from the nozzle 110 perform a blasting process on the entire surface of the glass substrate 1. The nozzle 110 may be fixed and the glass substrate 1 side may be moved.

The size of 200 g of particles (abrasive grains) affects the grinding speed and the grinding amount efficiency. If the diameter of 200 g of particles (abrasive grains) is too large, the glass substrate 1 is damaged, and if the diameter is too small, the glass substrate 1 cannot be ground. As the particles (abrasive grains) 200 g, those having sufficient hardness such as alumina particles, ceramic particles, SiC and the like are preferably used. As the particles (abrasive grains) 200 g, those having a maximum particle diameter of 50 μm to 150 μm are used.

When the spray pressure of 200 g of particles (abrasive grains) is low, the glass substrate 1 cannot be ground. If the spraying pressure is too high, the glass substrate 1 may be chipped. The machining allowance (grinding thickness) of the glass substrate 1 has a correlation with the diameter of 200 g of particles (abrasive grains). When the diameter of 200 g of particles (abrasive grains) is large, it is necessary to perform relatively large grinding. This is because cracks occur depending on the particle diameter at the initial stage of grinding. The spraying pressure of 200 g of particles (abrasive grains) is preferably 0.1 MPa to 1 MPa.

In the grinding in the blasting step S30, the glass substrate 1 may be sprayed with 200 g of a plurality of particles (abrasive grains) dispersed in water. By dispersing 200 g of particles in water, it is possible to remove glass waste generated by grinding at the same time. By this blasting step S30, the glass substrate 1 having a predetermined main surface roughness is obtained.

Here, in the blasting step S30 in the present embodiment, the average arithmetic roughness Ra ₁ of the main surfaces 2 and 3 is maintained within the range of 1 μm to 5 μm, and the cut-off value is set to 2.5 μm to 80 μm. The main surfaces 2 and 3 are ground by spraying 200 g of particles onto the main surfaces 2 and 3 so that the average arithmetic roughness Ra ₂ when set is within a range of 0.1 μm to 1.0 μm.

Here, the average arithmetic roughness Ra ₁ is an arithmetic average roughness measured based on “JIS B0601: 2001” and “JIS B0633: 2001” of Japanese Industrial Standards. The above-mentioned JIS B0601: 2001 "conforms to ISO 4287: 1997, and" JIS B0633: 2001 "conforms to ISO 4288: 1996.

The average arithmetic roughness Ra ₂ is different from the average arithmetic roughness Ra ₁ and means an arithmetic average roughness obtained from a roughness curve in which a cutoff value (wavelength) is set in an arbitrary range.

For measuring the roughness of the main surfaces 2 and 3 of the glass substrate 1, a contact type roughness measuring machine SURFCOM 1400D manufactured by Mitutoyo Corporation is used. The measurement is performed based on the above Japanese Industrial Standard.

In roughness measurement, the low-frequency cut-off depends on the tip shape of the touching palpation. The tip shape used this time was θ = 60 °, rtip = 2 μm, and the low-frequency cut-off (λ _S ) was 2.5 μm.

In the measurement of the average arithmetic roughness Ra ₁ , the high-frequency cut-off (λ _C ) is set to an appropriate value according to the measurement shape in accordance with the Japanese Industrial Standard. When Ra is 0.1 μm to 10 μm, it is set to 0.25 mm or 0.8 mm. Evaluation length was set to 5 times the length of the lambda _C.

When λ _C is forcibly set, the measurement does not conform to the JIS standard. In the present embodiment, it has been found that grinding with a fixed abrasive can be performed smoothly by changing (increasing) the roughness component in a wavelength region significantly shorter than a general cutoff value. Therefore, to set the forced lambda _c.

The high frequency cut-off (λ _C ) was a roughness curve at 80 μm. Measurement length, as well as the evaluation length was set to 5 times the length of the lambda _C.

The definition of roughness was based on JIS B00601: 2001 (based on ISO 4287: 1996).

“Arithmetic average roughness” indicates an amplitude average parameter in the height direction, “Roughness curve” indicates a band-pass filter having a cutoff value λ _s −λ _c , and “Filter” has an attenuation factor of 50%. The phase compensation type filter which makes the wavelength which becomes the cut-off value is shown.

Moreover, about the method of calculating | requiring roughness, a measurement cross-section curve is first obtained with a measuring machine. Next, a cross-sectional curve is obtained from the measured cross-sectional curve through a low-pass filter (λ _S ). Further, a “roughness curve” is obtained by passing a high-pass filter (λ _C ) through this cross-sectional curve.

The average of the absolute value of the height at each point from the average value of the “roughness curve” is the arithmetic average roughness. Λ _C of Ra ₁ was changed in accordance with JIS B0633: 01 to obtain a “roughness curve”. Λ _C of Ra2 was set to 80 μm to obtain a “roughness curve”.

(Lapping step S40)
In the lapping step S40, the main surfaces 2 and 3 of the glass substrate 1 are processed using a diamond-shaped sheet made of resin as abrasive grains (second grinding step).

The particle diameter of diamond can be appropriately changed depending on the purpose, but the average particle diameter is preferably 2 μm to 10 μm. When the diamond particle diameter is less than 2 μm, the processing does not proceed and the cracks generated on the main surfaces 2 and 3 of the glass substrate 1 cannot be removed. If the particle diameter of diamond exceeds 10 μm, the main surface 2 and 3 of the glass substrate 1 are cracked by diamond.

With the recent increase in density, the diamond particle diameter is becoming smaller, but 2 μm to 4 μm is more preferable because of the balance of workability. In this grinding process, the main surfaces 2 and 3 of the glass substrate 1 are ground to a thickness of about 50 μm to 250 μm.

(End face polishing step S50)
In the end surface polishing step S50, the inner peripheral end surface and the outer peripheral end surface of the glass substrate 1 are polished using a polishing brush having a spiral brush bristle material. While supplying the polishing slurry between the polishing brush and each end surface of the glass substrate 1, the polishing brush is rotated in contact with each end surface. With the glass substrate 1 immersed in the polishing liquid, the polishing brush may be rotated in contact with each end face.

(Rough polishing step S60)
The glass substrate 1 whose inner peripheral end face and outer peripheral end face are polished has its main surfaces 2 and 3 polished roughly in a plurality of times. For example, the main surfaces 2 and 3 are polished in two steps of the first and second rough polishing steps. By gradually increasing the finishing accuracy of the glass substrate 1, the glass substrate 1 having a highly smooth and flat surface can be obtained. When performing rough polishing in two steps, the first rough polishing step is mainly intended to remove scratches and distortions remaining on the main surfaces 2 and 3 in the lapping step, and the second rough polishing step The purpose is to finish the main surfaces 2 and 3 in a mirror shape.

In the rough polishing step S60, the polishing slurry is applied to the main surfaces 2 and 3 of the glass substrate 1 so that the surface roughness of the glass substrate 1 finally required in the subsequent precision polishing step S80 can be efficiently obtained. This is a step of performing rough polishing by using. It does not specifically limit as a grinding | polishing method employ | adopted at this process, It is possible to grind | polish using a double-side polisher.

In the present embodiment, a double-side polishing machine 40 shown in FIG. 9 was used. The double-side polishing machine 40 includes a lower surface plate 41 and an upper surface plate 42 that are provided opposite to each other in the vertical direction. Polishing pads 43 and 44 are fixed to opposing surfaces of the lower surface plate 41 and the upper surface plate 42, respectively.

The glass substrate 1 is held in the holding hole of the carrier 45 and is sandwiched between the lower surface plate 41 and the upper surface plate 42. The lower surface plate 41 and the upper surface plate 42 are rotated by a drive source (not shown). The rotation drive of the lower surface plate 41 and the upper surface plate 42 is controlled by the control device 48. With the glass substrate 1 held by the holding holes of the carrier 45, the main surfaces 2 and 3 of the glass substrate 1 are simultaneously polished by the upper and lower polishing pads 43 and 44. At the time of polishing, polishing slurry is supplied from the abrasive supply device 46. In FIG. 9, the abrasive supply device 46 is one place, but is not limited thereto, and the position and the number thereof can be arbitrarily configured.

In the rough polishing step S60, the polishing liquid (polishing slurry) used may contain cerium oxide, zirconium oxide, zirconium silicate or the like as abrasive grains. The concentration of cerium oxide in the polishing liquid is, for example, about 5% to 10%. The thickness of the machining allowance for the main surfaces 2 and 3 of the glass substrate 1 to be polished is, for example, 10 μm to 30 μm. By rough polishing, the undulation and roughness of the surface of the glass substrate 1 can be kept low. The shape of the inner peripheral end face and the outer peripheral end face of the glass substrate 1 can be adjusted by rough polishing. The surface Ra of the glass substrate 1 after rough polishing is, for example, about 3 to 10 mm. As described above, the main surfaces 2 and 3 of the glass substrate 1 are roughly polished. After the rough polishing, the glass substrate 1 is acid cleaned using sulfuric acid or hydrofluoric acid.

(Washing step S65)
Referring again to FIG. 6, after the rough polishing step S60, the glass substrate 1 is subjected to a cleaning process using an acidic cleaning liquid. The purpose of this cleaning treatment is to remove from the surface of the glass substrate 1 any of cerium oxide, zirconium oxide, or zirconium silicate used as a polishing slurry in the rough polishing step S60, which is the previous step.

Specifically, after removing the glass substrate 1 after the rough polishing from the polishing pad used in the rough polishing step S60, the surface of the glass substrate 1 is etched using a cleaning liquid containing sulfuric acid and / or hydrofluoric acid. Wash. The polishing slurry such as cerium oxide, zirconium oxide, or zirconium silicate adhering to the surface of the glass substrate 1 is appropriately removed by a strongly acidic cleaning liquid such as sulfuric acid and / or hydrofluoric acid. Thereafter, the glass substrate 1 is cleaned using an acidic cleaning solution.

The cleaning liquid used in the cleaning step S65 varies depending on the chemical resistance of the glass substrate 1, but a concentration of about 1% to 30% is preferable for sulfuric acid, and 0.2% to 5% for hydrofluoric acid. A concentration of about is preferred. Cleaning using these cleaning liquids may be performed while applying ultrasonic waves in a cleaning machine in which an aqueous solution is stored. The frequency of the ultrasonic wave used at this time is preferably 78 kHz or higher.

(Chemical strengthening step S70)
After the cleaning step S65, the glass substrate 1 is chemically strengthened. As the chemical strengthening liquid, for example, a mixed liquid of potassium nitrate (60%) and sodium sulfate (40%) can be used. The chemical strengthening liquid is heated to, for example, 300 ° C. to 400 ° C. The cleaned glass substrate 1 is preheated to 200 ° C. to 300 ° C., for example. The glass substrate 1 is immersed in the chemical strengthening solution for 3 hours to 4 hours, for example.

When dipping, the plurality of glass substrates 1 can be held in their respective holders so that the entire main surfaces 2 and 3 of the glass substrate 1 are chemically strengthened. preferable. By immersing the glass substrate 1 in the chemical strengthening solution, alkali metal ions (lithium ions and sodium ions) on the surface layer of the glass substrate 1 are chemically strengthened salts (sodium ions) having a relatively large ion radius in the chemical strengthening solution. And potassium ions). As a result, a compressive stress layer having a thickness of, for example, 50 μm to 200 μm is formed on the surface layer of the glass substrate 1.

The surface of the glass substrate 1 is strengthened by the formation of the compressive stress layer, and the glass substrate 1 has good impact resistance. The glass substrate 1 subjected to the chemical strengthening treatment is appropriately washed. For example, the glass substrate 1 is further cleaned using pure water or IPA (isopropyl alcohol) after being cleaned with sulfuric acid.

(Precision polishing step S80)
After the chemical strengthening step S70, a precision polishing process is performed on the glass substrate 1. The precision polishing step S80 is intended to finish the main surface of the glass substrate 1 in a mirror shape. In the precision polishing step S80, as in the above-described rough polishing step S60, the glass substrate 1 is precisely polished using a double-side polishing machine (see FIG. 9).

In the fine polishing step S80 and the rough polishing step S60, the composition of the polishing abrasive grains contained in the polishing liquid (slurry) used and the polishing pad used are different. In the precision polishing step S80, the grain size of the abrasive grains in the polishing liquid supplied to the main surfaces 2 and 3 of the glass substrate 1 on which the compressive stress layer is formed is made smaller than in the rough polishing step S60. Soften the hardness.

The polishing pad used in the precision polishing step S80 is, for example, a soft foam resin polisher. As the polishing liquid used in the precision polishing step S80, for example, colloidal silica having a finer particle size than the cerium oxide abrasive used in the rough polishing step S60 is used. The particle size (primary) of the colloidal silica used in the precision polishing step S80 is preferably 15 nm to 80 nm. The smoothness of the main surfaces 2 and 3 of the glass substrate 1 is increased by precision polishing using colloidal silica.

(Scrub cleaning step S90)
After the precision polishing step S80, a scrub cleaning process is performed on the glass substrate 1. Specifically, the glass substrate 1 after the precision polishing is removed from the polishing pad used in the precision polishing step S80, and then the cleaning liquid is supplied to the surface of the glass substrate 1 while the compression stress layer is formed. Scrub cleaning is performed on the surface using a scrub cleaning device.

The glass substrate 1 may be temporarily stored in water after being removed from the polishing pad of the double-side polishing machine. By storing in water, it is possible to reduce the amount of foreign matter such as polishing wrinkles or loose abrasive grains adhering to the glass substrate 1 after precision polishing while preventing the surface of the glass substrate 1 from drying after precision polishing. After the glass substrate 1 is stored in water for a predetermined time, the glass substrate 1 is set in a scrub cleaning device and scrub cleaning is performed on the glass substrate 1.

As the scrub cleaning, for example, a cleaning liquid such as a detergent or pure water is used. The pH of the cleaning solution used for scrub cleaning is preferably 9.0 or more and 12.2 or less. Within this range, the ζ potential can be easily adjusted and scrub cleaning can be performed efficiently. As scrub cleaning, both scrub cleaning with a detergent and scrub cleaning with pure water may be performed. By using a detergent and pure water, the glass substrate 1 can be more appropriately cleaned. The glass substrate 1 may be further rinsed with pure water between scrub cleaning with a detergent and scrub cleaning with pure water.

After the scrub cleaning, the glass substrate 1 may be further subjected to ultrasonic cleaning. After scrub cleaning with detergent and pure water, ultrasonic cleaning with chemical solution such as sulfuric acid aqueous solution, ultrasonic cleaning with pure water, ultrasonic cleaning with detergent, ultrasonic cleaning with IPA, and / or steam drying with IPA, etc. Further, it may be performed.

The manufacturing method S100 of the glass substrate 1 in the present embodiment is configured as described above. By using manufacturing method S100 of glass substrate 1, glass substrate 1 of this embodiment shown in Drawing 2 and Drawing 3 can be obtained.

(Magnetic thin film forming step S200)
A magnetic recording layer is formed on the main surfaces 2 and 3 (or one of the main surfaces 2 and 3) of the glass substrate 1 after the scrub cleaning process is completed. The magnetic recording layer includes, for example, an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoFeZr alloy, an orientation control underlayer made of Ru, a perpendicular magnetic recording layer made of a CoCrPt alloy, a protective layer made of a C system, and an F system. Are formed by sequentially forming the lubricating layer. By forming the magnetic recording layer, the information recording medium 10 shown in FIGS. 4 and 5 can be obtained.

(Example)
Next, with reference to FIG. 10, each Example of the manufacturing method of the said glass substrate 1 is demonstrated below with a comparative example. FIG. 10 is a diagram showing evaluation results in Examples 1 to 4 and Comparative Examples 1 and 2.

In Examples 1 to 4 and Comparative Example 2, the main surface of the glass substrate 1 was ground (roughened) using the above-described particles (abrasive grains) in the blasting step S30. Alumina particles were used as the particles (abrasive grains), the alumina particles were 110 μm, and the opening diameter of the nozzle 110 was 6.5 mm. The Vickers hardness of the glass substrate 1 is 610 kg / mm 2.

In order to control the roughness, the spraying pressure and the spraying time (grinding allowance) were changed to change to Ra1 and Ra2 shown in FIG. 10, respectively, and then the subsequent steps S30 to S90 were performed. Ra1 and Ra2 of the glass substrate were controlled by the abrasive grain size and machining allowance (grinding thickness). In Comparative Example 1, the post-processes S30 to S90 were performed without performing the blast process S30.

In the evaluation of each example and each comparative example, the number of defects was examined. The number of defects was evaluated by OSA (Optical Surface Analyzer). For OSA, Candala 6300 manufactured by KLA Tencor was used. In the evaluation, a case where the number of defects was 20 or less was accepted, and a case where the number of defects was 21 or more was rejected.

(Example 1)
The processing conditions of the blasting step S30 in Example 1 were an abrasive grain size of 67 μm and a machining allowance (grinding thickness) of 5 μm. As a result, Ra1 was 1 μm, Ra2 was 0.1 μm, the number of defects was 15, and the evaluation was “pass”.

(Example 2)
The processing conditions of the blasting step S30 in Example 2 were an abrasive grain size of 67 μm and a machining allowance (grinding thickness) of 10 μm. As a result, Ra1 was 2 μm, Ra2 was 0.2 μm, the number of defects was 5, and the evaluation was “pass”.

(Example 3)
The processing conditions of the blasting step S30 in Example 3 were an abrasive grain size of 90 μm and a machining allowance (grinding thickness) of 12 μm. As a result, Ra ₁ was 2 μm, Ra ₂ was 0.3 μm, the number of defects was 5, and the evaluation was “pass”.

Example 4
The processing conditions of the blasting step S30 in Example 4 were an abrasive grain size of 110 μm and a machining allowance (grinding thickness) of 12 μm. As a result, Ra ₁ was 5 μm, Ra ₂ was 1 μm, the number of defects was 13, and the evaluation was “pass”.

(Comparative Example 1)
In Comparative Example 1, the blasting step S30 was not performed. As a result, Ra ₁ was 2 μm, Ra ₂ was 0.01 μm, the number of defects was 23, and the evaluation was “fail”. Compared with Examples 1 to 3, since the value of Ra ₂ is small, cracks are likely to occur in the subsequent process, and the number of defects is considered to have increased.

(Comparative Example 2)
The processing conditions of the blasting step S30 in Comparative Example 2 were an abrasive grain size of 150 μm and a machining allowance (grinding thickness) of 30 μm. As a result, Ra ₁ was 6 μm, Ra ₂ was 1.5 μm, the number of defects was 32, and the evaluation was “fail”. Compared with Examples 1 to 3, it is considered that cracks occurred and the number of defects increased because an excessive blasting process was performed.

From the results of the above examples, in the blasting step S30, the average arithmetic roughness Ra ₁ of the main surfaces 2 and 3 is maintained within the range of 1 μm to 5 μm, and the cut-off value is set to 2.5 μm to 80 μm. By grinding the main surfaces 2 and 3 by spraying 200 g of particles onto the main surfaces 2 and 3 so that the average arithmetic roughness Ra ₂ when set is within the range of 0.1 μm to 1.0 μm. It was confirmed that the generation of cracks was effectively suppressed.

As described above, according to the method for manufacturing the glass substrate for information recording medium in the present embodiment, in the blasting process which is the first grinding process, the average arithmetic roughness Ra ₁ of the main surface is in the range of 1 μm to 5 μm as described above. In addition, particles are sprayed onto the main surface so that the average arithmetic roughness Ra ₂ when the cutoff value is set to 2.5 μm to 80 μm is within the range of 0.1 μm to 1.0 μm. Thus, by grinding the main surface, it is possible to realize a roughening step suitable for the previous step of the grinding step even when a glass substrate having high hardness is used.

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.

1 glass substrate (glass substrate for information recording medium), 2, 3 main surface, 4 inner peripheral end surface, 5,15 holes, 6 outer peripheral end surface, 7, 8 chamfer, 10 information recording medium, 12 compressive 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, 40 double-side polishing machine, 41 Lower surface plate, 42 Upper surface plate, 43, 44 polishing pad, 45 carrier, 46 abrasive supply device, 48 control device, 100 blast device, 110 nozzle, 120 support base, 200 g particles (abrasive grains).

Claims (4)

1. A first grinding step of grinding the main surface of the glass substrate by spraying a plurality of particles from a nozzle on the main surface of the glass substrate obtained by a direct press method;
   A second grinding step of grinding the main surface of the glass substrate with fixed abrasive grains mainly composed of diamond particles having an average particle diameter of 2 μm to 10 μm with respect to the glass substrate having undergone the first grinding step; With
   The first grinding step includes
   The average arithmetic roughness Ra _{1 of the} main surface is maintained within the range of 1 μm to 5 μm, and the average arithmetic roughness Ra ₂ when the cutoff value is set to 2.5 μm to 80 μm is 0.1 μm to The manufacturing method of the glass substrate for information recording media including the process of spraying the said particle | grain on the said main surface so that it may become in the range of 1.0 micrometer, and grinding the said main surface.
2. The manufacturing method of the glass substrate for information recording media of Claim 1 whose Vickers hardness of the said main surface is 610 kg / mm < ² > or more.
3. 3. The method for producing a glass substrate for an information recording medium according to claim 1, wherein the maximum particle diameter of the particles is 50 μm to 150 μm.
4. The method for producing a glass substrate for an information recording medium according to any one of claims 1 to 3, wherein a spraying pressure of the particles is 0.1 MPa to 1 MPa.

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