JP2002092867A - Method of manufacturing glass substrate for information recording medium and method of manufacturing information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a glass substrate for an information recording medium which allows the exact control of the microwaving of its surface and is usable as a substrate for the information recording medium (low glide height and low modulation) dealing with high-density recording and the glass substrate for the information recording medium as well as a method of manufacturing the information recording medium and the information recording medium. SOLUTION: When the glass substrate 4 for the information recording medium is set between upper and lower surface plates 53 and 54 stuck with polishing pads 53a and 54a of a soft polisher and both main surfaces are polished, the surface roughness of a polishing pad surface 4 to be used in a polishing process step is selected by utilizing the phenomenon that the value of the microwaving of the main surface of the glass substrate 4 for the information recording medium after the polishing process step depends on the value of the surface roughness on the surface of the polishing pad 4 used in the polishing process step, by which the microwaving of the main surface 4 of the glass substrate for the information recording medium after the polishing process step is made to attain the prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a glass substrate for an information recording medium used as a recording medium of an information processing device and a method of manufacturing an information recording medium.

[0002]

2. Description of the Related Art A magnetic disk is known as one of information recording media. A magnetic disk is formed by forming a thin film such as a magnetic layer on a substrate, and an aluminum substrate or a glass substrate has been used as the substrate. However, recently, in response to a demand for higher recording density, the ratio of a glass substrate capable of making the distance between a magnetic head and a magnetic disk narrower than that of an aluminum substrate has been gradually increasing.

[0003] Such a glass substrate is chemically strengthened to produce a chemically strengthened glass so that it can withstand an impact when mounted on a magnetic disk drive. In addition, a crystallized glass substrate whose strength is improved by heat treatment and crystallization of the glass substrate surface is manufactured. In addition, the surface of the glass substrate can reduce the flying height of the magnetic head as much as possible,
Polishing with high precision realizes high recording density.

However, even if the surface roughness (Rmax (maximum height), Ra (center line average roughness)) is reduced by polishing with high precision, the flying height of the magnetic head cannot be reduced. A problem arose. It has been found that the cause is microwaves existing on the substrate surface, and an information recording medium substrate in which the microwaves on the substrate surface are set to a predetermined value has already been filed (Japanese Patent Application No. 20-210).
00-99720).

[0005]

Generally, a glass substrate for an information recording medium is manufactured through a grinding process and a polishing process. Among various parameters in the manufacturing process, a factor which determines a minute waviness is grasped. Therefore, it was difficult to control minute undulations on the substrate surface.

[0006] The present invention provides a glass substrate for an information recording medium, which is capable of accurately controlling minute waviness on the surface and which can be used as a substrate of an information recording medium (low glide height, low modulation) corresponding to high density recording. It is an object of the present invention to provide a method of manufacturing a glass substrate for an information recording medium, a method of manufacturing an information recording medium, and an information recording medium.

[0007]

In order to solve the above-mentioned problems, the first means is to set a glass substrate for an information recording medium between an upper and lower platen on which a polishing pad of a soft polisher is stuck. In the method for manufacturing a glass substrate for an information recording medium having a polishing step of polishing the surface, the value of the minute waviness of the main surface of the glass substrate for an information recording medium after the polishing step is such that the surface roughness of the polishing pad surface used in the polishing step is reduced. Utilizing the phenomenon that depends on the value of the polishing pad, by selecting the surface roughness of the polishing pad surface used in the polishing step, the fine waviness of the information recording medium glass substrate main surface after the polishing step is a predetermined value. A method for manufacturing a glass substrate for an information recording medium, characterized in that: However, the value of the minute undulation Ra ′ is such that the period of the minute undulation is 2 μm to 4 m.
m, which is represented by the following equation.

(Equation 2) A second means is the method for manufacturing a glass substrate for an information recording medium according to the first means, wherein the surface roughness Rz of the polishing pad surface is 20 μm or less. Here, Rz is a ten-point average roughness. Third means, wherein the polishing pad has a substrate and a nap layer from the side of the platen, and the thickness of the nap layer is set to a predetermined range, any of the first and second, A method for producing a glass substrate for an information recording medium according to the above means. A fourth means is the method for manufacturing a glass substrate for an information recording medium according to the third means, wherein the thickness of the nap layer is 430 to 620 µm. A fifth means is a method for manufacturing a glass substrate for an information recording medium according to any one of the first to fourth means, wherein the surface of the nap layer is corrected by a pad dresser of diamond abrasive grains. A sixth means is the method for manufacturing a glass substrate for an information recording medium according to any one of the first to fifth means, wherein the glass substrate for an information recording medium is a glass substrate for a magnetic disk.
A seventh means is a method for manufacturing an information recording medium, wherein at least a recording layer is formed on a main surface of a glass substrate for an information recording medium according to any one of the first to sixth means. Eighth means is the method for manufacturing an information recording medium according to the seventh means, wherein the recording layer is a magnetic layer.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of a main part of a polishing apparatus having upper and lower platens, FIG. 2 is an explanatory view of a driving mechanism of the polishing apparatus, FIG. 3 is a partial sectional view of a polishing pad, and FIG. 4 is a graph showing a relationship between a fine waviness on a main surface of a glass substrate for a recording medium and a surface roughness of a polishing pad. Hereinafter, a method for manufacturing a glass substrate for an information recording medium, a glass substrate for an information recording medium, a method for manufacturing an information recording medium, and an information recording medium according to an embodiment of the present invention will be described with reference to these drawings.

In the method of manufacturing a glass substrate for an information recording medium according to the embodiment, a glass substrate for an information recording medium is set between upper and lower platens to which a polishing pad of a soft polisher is attached, and both main surfaces are polished. In the method of manufacturing a glass substrate for an information recording medium having a polishing step, the value of the fine undulation of the main surface of the glass substrate for the information recording medium after the polishing step, the value of the surface roughness of the polishing pad surface used in the polishing step Utilizing the phenomenon of dependence, by selecting the surface roughness of the polishing pad surface used in the polishing step, so that the micro-undulation of the glass substrate main surface for the information recording medium after the polishing step becomes a predetermined value. It is characterized by having done.

In the above-described configuration, the polishing apparatus for performing the "polishing step of setting the glass substrate for the information recording medium between the upper and lower platens to which the polishing pad of the soft polisher is attached and polishing the two main surfaces" is as follows. It has the following configuration. That is,
1 and 2, a polishing apparatus 5 includes a polishing carrier mounting portion having an internal gear 51 and a sun gear 52 that are driven to rotate at a predetermined rotation ratio, respectively, and the polishing device 5 is driven to rotate in opposite directions with respect to the polishing carrier mounting portion. An upper surface plate 53 and a lower surface plate 54 are provided.

When a plurality of polishing carriers 1 are set in the polishing carrier mounting portion, the gears of these polishing carriers 1 mesh with the internal gear 51 and the sun gear 52. When the information recording medium glass substrate 4 which is the object to be polished is set in the object holding holes 2a to 2g of each of the polishing carriers 1 and polishing is started, the polishing carrier 1 rotates with the internal gear 51 and the sun gear 52. The planetary motion is performed by the number difference. At the same time, the upper platen 53 and the lower platen 54 rotate in opposite directions, and the front and back surfaces of the glass substrate 4 for information recording medium are polished by the polishing pads 53a and 54a provided on them.

In the present embodiment, the surface roughness of the polishing pad surface used in the polishing step is set so that the value of the minute waviness on the main surface of the glass substrate for the information recording medium after the polishing step by the polishing apparatus is set to a predetermined value. To a predetermined value. That is, the polishing pad 53a (the same applies to the polishing pad 53b)
As shown in FIG. 3, a base material 531a is formed on a base material 530a, and a NAP (nap) layer 53 is formed thereon.
2a is formed. The surface roughness of the surface 533a of the NAP layer 532a is set to a predetermined value. Thereby, the value of the minute waviness on the main surface of the glass substrate for the information recording medium after the polishing step by the polishing apparatus can be set to a predetermined value.

The inventors of the present invention discovered for the first time that the fine waviness value of the main surface of the glass substrate for an information recording medium after the polishing step depends on the value of the surface roughness of the polishing pad surface used in the polishing step. It was done. That is, as shown in FIG. 4, the horizontal axis represents the surface roughness of the polishing pad (Rz = ten-point average roughness; unit: μm), and the vertical axis represents the value of minute waviness on the substrate main surface (95% PV). Value; unit μm)
And both are represented by a straight line having a substantially predetermined gradient.

The minute undulation of the glass substrate for an information recording medium according to the present embodiment is defined by a value measured by a multifunctional surface analyzer (MicroXAM) manufactured by Face Shift Technology. Unlike a conventional stylus-type surface roughness meter, white light is scanned over a predetermined area of the substrate surface using light (wavelength: 552.8 nm) obtained by using a coherent filter or the like, and the white light is scanned from the substrate surface. The reflected light and the reflected light from the reference plane are combined, and from the interference fringe generated at the combined point,
It can be obtained by calculating minute undulations. FIG. 5 is a diagram illustrating the measurement principle of the multifunctional surface analysis apparatus. As shown in FIG.
According to the principle of the interferometer, light waves are divided into two and then synthesized, and interference fringes appear due to an optical path difference between an optical path of A → B and an optical path of C → D. The light used for the measurement can be changed without departing from the principle of the measurement.

The measurement of minute waviness by the multifunctional surface analysis apparatus is performed by measuring 50 μm in an arbitrary area (recording / reproducing area) of the substrate, preferably in an area separated from the center or an end by a predetermined distance.
A rectangular area is appropriately selected from the range of m □ to 4 mm □. For example, the area is smaller than the area of the slider surface of the head slider, and is about 500 μm × about 600 μm
Is selected (approximately 250,000 pixels).
The swell period (distance between peaks and valleys or valleys and valleys) measured by this device is about 2 μm to 4 mm,
The fine undulation is obtained by the following equation.

[0016]

(Equation 3) Here, Ra ′ is the difference between the averages of the absolute values of the deviations from the center line to the measurement curve, xi is the measurement point value at the measurement point (the height from a certain reference line to the measurement curve at the measurement point), and x is , Average value n of the above measurement point values
Is the number of measurement points.

The maximum height wa of the minute undulation is a value of the difference between the heights of the highest point and the lowest point of the measurement curve at all the measurement points in the measurement area. However, the substrate surface may include abnormal protrusions such as particles that are not directly related to the surface state of the substrate itself. In some cases, if the maximum height wa is used, a large error occurs.

As a method for excluding the measured value of the abnormal projection, the measured value is plotted on all the measuring points on the horizontal axis.
When a histogram (a distribution diagram showing the relationship between the measured values and the corresponding number, which is usually a normal distribution curve) is displayed on the vertical axis of the measured number at which the measured value is obtained, the distribution curve is obtained. In the above, when the number of measurements corresponding to each measured value is accumulated while gradually increasing the measured value from the minimum value, the measured value when the accumulated number becomes 95% of the total number is effective. Use the method that sets the maximum value of the measured values. The maximum value obtained by this method is defined as “95% PV value”, the “95% PV value” is defined as the maximum height wa, and the maximum height wa can be expressed as a minute undulation. It is also known that there is a correlation between the above-mentioned Ra ′ and the 95% PV value (for details, refer to Japanese Patent Application No. 2000-99720).

In the present invention, the fine waviness on the substrate surface, which is correlated with the surface roughness of the polishing pad surface, is the above-mentioned R
Either a 'or the 95% PV value may be adopted. The polishing pad of the soft polisher used in the present invention is not particularly limited. Polishing pads made of a soft polisher are roughly classified into an independent foaming system and a continuous foaming system according to a foaming structure. In the independent foaming system, since the polishing slurry does not penetrate into the inside of the polishing cloth from the foaming form and exists only between the workpiece and the polishing cloth or only at the contact interface, the flow rate of the slurry is generally reduced under the same processing pressure. It is said that it can be. As the independent foaming system, there are a bubble-mixing type and a bubble-free type.

In the continuous foaming system, a nonwoven fabric is generally used as a base material, and various resins impregnated in the transition entangled body serve as a binder between fibers, and the resin phase itself has a continuous foamed structure. In the continuous foaming system, unlike the closed foaming system, penetration of the slurry into the polishing cloth occurs. As the independent foam type, there are a suede type and a polishing cloth (coagulated polymer type, coagulated / light type) based on a nonwoven fabric.

Among them, a suede type polishing pad is used as a polishing pad for precision polishing of a glass substrate. Suede type polishing cloth, for example, natural fibers,
A polyurethane elastomer solution is applied to a base material obtained by filling a woven or nonwoven fabric made of recycled fibers or synthetic fibers, or a rubber-based substance such as styrene-butadiene rubber or nitrile-butadiene rubber, or a resin such as polyurethane elastomer. This is treated with a coagulating liquid, and wet coagulation is performed to form a porous silver surface layer. After washing with water and drying, the surface of the silver surface layer is polished with a sanding machine or the like to obtain a uniform surface pore shape. Thus, a suede-type polishing pad having uniform spindle-shaped pores having a uniform cross-sectional hole shape perpendicular to the substrate surface is manufactured.

The materials of the substrate and the nap layer are not particularly limited. Polyurethane is generally used as the nap layer.
In addition, any measurement method can be used as long as it can quantify the surface roughness of the polishing pad surface. For example, there are a method using a stylus-type measuring instrument, an atomic force microscope, and a method for measuring a cross section of a polishing pad by taking a photograph with an optical microscope.

In the examples of the present invention, since the surface roughness of the polishing pad surface was larger than the surface roughness of the glass substrate surface, the surface roughness was measured using a stylus type surface roughness meter. As a parameter of the surface roughness, Rz (ten-point average roughness) was adopted. This is because it has the best correlation with the 95% PV value.

Rz is a value defined as follows. That is, when the evaluation length is extracted from the cross-sectional curve in the direction of the average line and measured in the direction of the longitudinal magnification from a straight line parallel to the average line and not crossing the cross-sectional curve, the highest to fifth peaks of the cross-sectional curve are obtained. Let Rz be the difference between the average value of the altitude of the peak and the average value of the altitude of the bottom of the cross-sectional curve from the deepest to the fifth.

However, the peak of the cross-sectional curve means a portion of the cross-sectional curve connecting two points adjacent to each other at the intersection where the substance protrudes from the average line when the cross-sectional curve is cut along the average line. The peak is the highest point in the peak of the sectional curve. Further, the valley of the cross-sectional curve means a portion of the cross-sectional curve connecting two adjacent points of the intersection where the substance is depressed with respect to the average line when the cross-sectional curve is cut by the average line. The valley bottom is the lowest point in the valley of the sectional curve.

When Rz is adopted as a parameter indicating the surface roughness, the surface roughness of the polishing pad surface is 20
μm or less, preferably 15 μm or less, more preferably 10 μm or less. Rz is 20μ
If it exceeds m, the fine waviness on the surface of the glass substrate obtained after polishing is undesirably large. The surface roughness of the polishing pad surface can be reduced by buffing with a fine-grained sandpaper or the like.

When the polishing pad has a structure having a base material and a nap layer from the side of the surface plate, the thickness of the nap layer is also one factor that determines the minute waviness on the surface of the glass substrate after polishing. The preferable thickness of the nap layer is 430 to 6
20 μm, more preferably 480-530 μm.

Since the polishing pad wears as the polishing process is repeated, the surface condition of the polishing pad is preferably the same as that before the polishing pad is used, depending on the purpose of securing the polishing rate and the smoothness of the obtained substrate surface. Modifications are made to make it so. As a correction method, there are a pad dresser in which diamond abrasive grains are embedded, a diamond pellet, a ring dresser, and the like. Among them, it is preferable to modify the surface of the nap layer with a pad dresser made of diamond and grains because the adhesion to the surface plate is likely to be good. The number of times of correction, the time, and the like are not particularly limited.

The glass substrate of the present invention can be used for various purposes such as a glass substrate for a magnetic disk, a glass substrate for an optical disk, and a glass substrate for a magneto-optical disk. The glass type, size, and the like of the glass substrate are not particularly limited. Examples of glass types include aluminosilicate glass, soda lime glass, sodaaluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, crystallized glass, and the like. In terms of smoothness, amorphous glass is generally better than crystallized glass.
Chemically strengthened glass such as aluminosilicate glass is preferred from the viewpoint of mechanical strength, impact resistance, vibration resistance and the like.

As the aluminosilicate glass, Si
O2: fifty-eight to seventy-five wt%, Al2 O3: 5 to 23 wt%, Li ₂ O: 3~10 wt%, Na ₂ O: 4~13 like chemically tempered glass containing by weight% as a main component is preferable.

In recent years, since a substrate having high smoothness has been required, a crystallized glass substrate having a crystal grain diameter of 100 nm or less has been developed. Crystallized glass has higher mechanical strength than amorphous glass, and has excellent flatness due to the advantage of grinding using diamond pellets in the manufacturing process.
In addition, a substrate with high smoothness can be obtained, which is preferable.

By forming at least a recording layer on the seed surface of the glass substrate for an information recording medium, an information recording medium compatible with high-density recording can be obtained. In particular, in the case of a magnetic disk in which the recording layer is a magnetic layer, a magnetic disk with small undulations can be obtained, so that low glide height and low modulation can be achieved.

For example, in the case of a magnetic disk, the surface roughness of the substrate is adjusted according to the recording / reproducing method (CSS type, load / unload type) and the magnetic head to be used under polishing conditions (type of abrasive grains, particle size, processing conditions, etc.). ) And the chemical treatment conditions after polishing are controlled to obtain the desired surface roughness (Rm
ax, Ra, Rp, etc.). The surface roughness of the glass substrate for CSS type magnetic disks is Rma
x = 5 to 12 nm, Ra = 0.5 to 1.2 nm, Rp =
2.5 to 6 nm, the surface roughness of the glass substrate for a magnetic disk of a load / unload type is Rmax = 8 nm or less;
Ra = 0.8 nm or less and Rp = 4 nm or less.

The material of the magnetic layer formed on the glass substrate is not particularly limited. As the magnetic layer, for example, Co
, CoPt, CoCr, CoNi, CoN containing
iCr, CoCrTa, CoPtCr, CoNiPt,
CoNiCrPt, CoNiCrTa, CoCrPtT
a, CoCrPtB, CoCrPtTaB and the like. The magnetic layer is formed by converting the magnetic film to a non-magnetic film (for example,
(Cr, CrMo, CrV, CrMnC, etc.) to reduce noise. If necessary, a seed layer or an underlayer may be provided between the glass substrate and the magnetic layer, and a protective layer or a lubricating layer may be provided on the magnetic layer.

The seed layer has a role of controlling the crystal grain size of the underlayer and the magnetic layer formed thereon, and examples thereof include materials such as NiAl, CrNi, and CrTi. The underlayer is provided for the purpose of improving the magnetic characteristics, and is, for example, Cr, Mo, V, Ta, Ti, W,
A non-magnetic film made of at least one or more materials selected from non-magnetic metals such as B, Al, and Ni. The underlayer may be a single layer or a plurality of layers.

The protective layer is provided for mechanical durability, corrosion resistance, and the like. For example, Cr, Cr alloy, carbon, hydrogenated carbon, carbon nitride, zirconia, Si
O2 and the like. The lubricating layer is provided for preventing adsorption to the magnetic head and reducing the coefficient of friction, and a perfluoropolyether lubricant or the like is generally used.

Next, the present invention will be described more specifically with reference to examples of the present invention. Example 1 In this example, (1) a rough lapping step, (2) a shaping step, (3) an end face polishing step, (4) a fine lapping step,
(5) a first polishing step, (6) a second polishing step, (7) a cleaning step, (8) a chemical strengthening step, (9) a cleaning step, and (10) a magnetic disk manufacturing step. Hereinafter, each step will be described in detail.

(1) Rough lapping step First, the molten glass is directly pressed using an upper mold, a lower mold, and a body mold, and a glass substrate made of a disk-shaped aluminosilicate glass having a diameter of 66 mm and a thickness of 1.2 mm. I got In this case, in addition to the direct press, a disk-shaped glass substrate may be obtained by cutting out a sheet glass formed by a down-draw method or a float method with a grinding wheel. In addition,
As aluminosilicate glass, SiO2: 58-
75% by weight, Al2O3: 5 to 23% by weight, Li2O:
A chemically strengthened glass containing 3 to 10% by weight and Na2O: 4 to 13% by weight as a main component was used.

Next, a lapping step was performed on the glass substrate. This lapping process aims at improving the dimensional accuracy and the shape accuracy. The lapping process was performed using a double-sided lapping apparatus, and the grain size of the abrasive grains was performed at # 400. Specifically, by using alumina abrasive grains having a grain size of # 400, setting the load L to about 100 kg, and rotating the internal rotation gear and the external rotation gear, both surfaces of the glass substrate housed in the carrier can have a surface accuracy of 0 to 0. Finished to about 1 μm and surface roughness Rmax of about 6 μm.

(2) Shape processing step Next, a hole is made in the center of the glass substrate using a cylindrical grindstone, and the outer peripheral end surface is also ground to a diameter of 65 mmφ. Chamfered. At this time, the surface roughness of the glass substrate end face (inner circumference, outer circumference) was about 4 μm in Rmax.

(3) End Face Polishing Step Next, the surface roughness of the end face (inner circumference, outer circumference) of the glass substrate is adjusted to Rma by rotating the glass substrate by brush polishing.
Polishing was performed to about 1 μm with x and about 0.3 μm with Ra. The surface of the glass substrate after the end face polishing step was washed with water.

(4) Fine Lapping Step Next, the grain size of the abrasive grains is changed to # 1000, and the glass substrate surface is wrapped, so that the flatness is 3 μm, the surface roughness Rmax is about 2 μm, and Ra is about 0.2 μm. did.
Note that Rmax and Ra are measured by an atomic force microscope (AFM), and the flatness is measured by a flatness measuring device, and the vertical direction (vertical to the surface) of the highest portion and the lowest portion of the substrate surface is measured. Direction) (distance). The glass substrate after the above-described fine lapping step was washed by sequentially immersing it in a washing tank of a neutral detergent and water.

(5) First Polishing Step Next, a polishing step was performed. This polishing step is for the purpose of removing scratches and distortions remaining in the above-described lapping step, and was performed using a double-side polishing apparatus.
Specifically, a hard polisher was used as a polisher, and the polishing was performed under the following polishing conditions. Polishing liquid: cerium oxide (average particle size: 1.3 μm) + water Load: 80-100 g / cm 2 Polishing time: 30-50 minutes Removal amount: 35-45 μm

The glass substrate after the polishing step was washed by sequentially immersing it in a washing bath of a neutral detergent, pure water, pure water, IPA, and IPA (steam drying). In addition, ultrasonic waves were applied to each cleaning tank. This cleaning step can be omitted when the polishing liquid used in the next second polishing step is the same. Further, the hard polisher used in the first polishing step is not particularly limited, and can be appropriately selected depending on a target surface roughness, an end shape of the substrate, and the like.

(6) Second Polishing Step (Final Polishing) Next, using the double-side polishing apparatus used in the first polishing step, a second polishing step was performed by changing the polisher from a hard polisher to a soft polisher. The surface roughness Rz of the used soft polisher was measured by a small surface roughness measuring device (Surftest SJ-401: manufactured by Mitutoyo Corporation) as a stylus type surface roughness meter, and it was 12.2 μm.
The nap layer used was 480 μm. The polishing conditions were as follows: polishing liquid: cerium oxide (average particle diameter 0.8 μm) + water load: 80 to 100 g / cm 2 polishing time: 10 to 15 minutes removal amount: 3 to 5 μm

(7) Cleaning Step After the glass substrate after the second polishing step has been immersed in sulfuric acid having a concentration of 50 wt% (temperature: 70 ° C. × 3 minutes), citric hydrofluoric acid (concentration: 6.5 mS (wt%) ),temperature:
(38 ° C. × 100 seconds) for washing. In addition, ultrasonic waves were applied to each cleaning tank. Further, it was washed by sequentially immersing it in a washing tank of a neutral detergent, pure water, pure water, IPA, and IPA (steam drying).

(8) Chemical Strengthening Step Next, the glass substrate after the lapping, polishing and cleaning steps was chemically strengthened. For the chemical strengthening, a chemically strengthened salt prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared, and the chemically strengthened salt is heated to 375 ° C., and the cleaned glass substrate preheated to 300 ° C. The immersion was performed for about 3 hours. At the time of this immersion, a plurality of glass substrates were housed in a holder so as to be held at the end faces so that the entire surface of the glass substrate was chemically strengthened.

As described above, by performing the immersion treatment in the chemically strengthened salt, lithium ions and sodium ions in the surface layer of the glass substrate are replaced by sodium ions and potassium ions in the chemically strengthened salt, and the glass substrate is strengthened. The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 to 200 μm. The glass substrate that has been chemically strengthened is immersed in a water bath at 20 ° C. and rapidly cooled.
Maintained 0 minutes.

(9) Washing Step The glass substrate that had been quenched was immersed in sulfuric acid heated to about 40 ° C., and washed while applying ultrasonic waves. When the surface roughness of the surface of the glass substrate thus obtained was measured by AFM, Rmax = 6.12 nm and Ra = 0.
The average roughness Ra ′ of the fine undulation is 0.5 nm.
Good results were obtained at 58 nm and 95% PV value of 2.79 nm.

(10) Manufacturing Process of Magnetic Disk The glass substrate for a magnetic disk obtained through the above-described process is subjected to NiA by an in-line sputtering apparatus.
A 1-layer seed layer, a CrV underlayer, a CoPtCrB magnetic layer, and a hydrogenated carbon protective layer were formed, and a perfluoropolyether lubricating layer was formed by a dipping method to produce a magnetic disk.

For the obtained magnetic disk, the glide height using an AE sensor, a CSS test (100,000 times),
When a load / unload test (400,000 times) was performed, it was confirmed that contact did not occur between the head and the medium until the head flying height reached 17 nm (that is, the glide height of this magnetic disk was 7 to 8 nm). .). In the CSS test and the load / unload test, good results were obtained in both tests without crash.

Examples 2 to 4 (pad surface roughness Rz and 95
% PV value) Next, in Example 1 described above, as the soft pad used in the second polishing step, the surface roughness of the pad was Rz.
22 μm (Example 2), 16.5 μm (Example 3),
A glass substrate for a magnetic disk and a magnetic disk were produced in the same manner as in Example 1 except that a substrate having a thickness of 9.8 μm (Example 4) was used (buffering conditions were appropriately adjusted).

9 of minute undulation on the surface of the obtained glass substrate
FIG. 6 shows the relationship between the 5% PV value and the surface roughness Rz of the pad surface. As shown in FIG. 6, it can be seen that there is a correlation between the roughness Rz of the polishing pad surface (NAP layer surface) used in the final polishing step and the fine waviness of the glass substrate surface obtained after polishing. Therefore, as can be seen from this result, in order to achieve a small undulation on the predetermined substrate surface,
By selecting a polishing pad having a good surface roughness of the polishing pad surface, fine waviness can be accurately controlled. In addition, the surface roughness of the obtained substrate surface was equivalent to that of Example 1.

Further, regarding the obtained magnetic disk, A
Glide height, CSS test (100,000 times), and load / unload test (400,000 times) were performed using the E sensor. As a result, it was confirmed that contact between the head and the medium did not occur up to the head flying height of 17 nm. (That is, the glide height of this magnetic disk was 7 to 8 nm.) Also, C
Also in the SS test and the load / unload test, no crash occurred and good results were obtained in both tests.

Example 5 (Modification of Pad) After the manufacturing process of the glass substrate for a magnetic disk described in Example 1 was completed, the polishing pad used in the second polishing process was modified. To correct the polishing pad, first, the carrier for setting the glass substrate is changed to a carrier for pad dresser, and several tens of μm diamond abrasive grains are fixed to the stainless steel disk-shaped substrate surface in the holding holes of this carrier. Set the pad dresser.

Thereafter, while applying a load to the pad dresser in the same manner as for polishing a glass substrate, the upper and lower platens, the inner gear, and the outer gear are rotated to correct the polishing pad. At this time, water is supplied to the polishing liquid reservoir. After a predetermined period of time has passed and the polishing pad has been repaired, the glass substrate is replaced again with the carrier to be shy.
In the same manner as in the above, a glass substrate for a magnetic disk was produced.

As a result, even when the manufacturing process of the glass substrate for a magnetic disk was repeatedly performed, the surface roughness (Rmax, Ra), the average height Ra 'of the minute undulations were almost the same as those of the first embodiment,
A 95% PV value was obtained. Since the polishing pad is periodically repaired as described above, the surface roughness of the polishing pad surface is maintained, so that a magnetic disk glass substrate having substantially the same substrate surface can be obtained stably.

Example 6 (Change of Glass Substrate) Next, the same procedure as in Example 1 was repeated except that the aluminosilicate glass in Example 1 was changed to crystallized glass (Example 6). Glass substrate,
And a magnetic disk was produced. As a result, the surface roughness of the obtained substrate was the same as that of Example 1, but the 95% PV value of the fine waviness was 2.23 nm (Example 6).
It is better than the case of the chemically strengthened glass substrate.

Further, regarding the obtained magnetic disk, A
The glide height, CSS test (100,000 times), and load / unload test (400,000 times) using the E sensor were performed. As a result, it was confirmed that there was no contact between the head and the medium up to the head flying height of 15 nm. Was. (That is, the glide height of this magnetic disk was 5 to 6 nm.)
Also in the SS test and the load / unload test, no crash occurred and good results were obtained in both tests.

In the above Examples 1 to 4, the surface roughness Rz of the polishing pad surface was determined by a stylus type roughness meter. You can ask for it. Draw a straight line so that it passes near the surface of the nap layer. Determine any 10 points. Measure the distance between the straight line and the surface of the nap layer. Find the average value of

FIG. 7 is a graph showing the relationship between Rz and micro undulations of the glass substrate obtained from a pad cross-sectional photograph by an optical microscope. As shown in FIG. 7, it can be seen that there is also a correlation between the result obtained from the pad cross-sectional photograph by the optical microscope and the minute waviness on the substrate surface. However, it is better to determine the surface roughness of the pad surface with a stylus roughness meter from the measurement accuracy, measurement time, and the like.

[0062]

As described above in detail, the present invention provides a polishing step of setting a glass substrate for an information recording medium between upper and lower platens to which a polishing pad of a soft polisher is attached and polishing both main surfaces. In the method for manufacturing a glass substrate for an information recording medium having the above, a phenomenon that the value of minute waviness on the main surface of the glass substrate for an information recording medium after the polishing step depends on the value of the surface roughness of the polishing pad surface used in the polishing step. By using, the surface roughness of the polishing pad surface used in the polishing step is selected, so that the micro waviness of the glass substrate main surface for the information recording medium after the polishing step is set to a predetermined value. This allows precise control of minute waviness on the surface and can be used as a substrate for information recording media (low glide height, low modulation) compatible with high-density recording. To obtain a manufacturing method and information recording medium can recording method of manufacturing a glass substrate for a medium and an information recording medium glass substrate and the information recording medium.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a polishing apparatus having upper and lower stools.

FIG. 2 is an explanatory diagram of a driving mechanism of the polishing apparatus.

FIG. 3 is a partial cross-sectional view of a polishing pad.

FIG. 4 is a graph showing the relationship between the fine waviness on the main surface of the glass substrate for an information recording medium and the surface roughness of the polishing pad surface (NAP layer surface).

FIG. 5 is a diagram illustrating the measurement principle of the multifunctional surface analysis apparatus.

FIG. 6 is a graph showing the relationship between 95% PV value of minute waviness on the substrate surface and surface roughness Rz of the polishing pad surface (NAP layer surface) for Examples 2 to 4.

FIG. 7 shows R determined from a photograph of a cross section of a pad by an optical microscope
5 is a graph showing a relationship between z and minute waviness of a glass substrate.

[Explanation of symbols]

4 glass substrate for information recording medium, 5 polishing machine, 53
Upper surface plate, 53a: polishing pad, 54: lower surface plate, 54a ...
Polishing pad.

Claims (8)

[Claims] 1. A method for manufacturing a glass substrate for an information recording medium, comprising: a polishing step of setting a glass substrate for an information recording medium between an upper and lower platen to which a polishing pad of a soft polisher is attached and polishing both main surfaces. Utilizing the phenomenon that the value of minute waviness on the main surface of the glass substrate for an information recording medium after the polishing step depends on the value of the surface roughness of the polishing pad surface used in the polishing step; Manufacturing a glass substrate for an information recording medium, wherein the fine waviness on the main surface of the glass substrate for an information recording medium after the polishing step is set to a predetermined value by selecting the surface roughness of the pad surface. Method. However, the value of the minute undulation Ra 'has a period of the minute undulation of 2 μm to 4 mm, and is represented by the following equation. (Equation 1) 2. A polishing pad having a surface roughness Rz of 2
2. The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein the thickness is 0 μm or less. Here, Rz is a ten-point average roughness. 3. The information according to claim 1, wherein the polishing pad has a base material and a nap layer from a surface plate side, and the thickness of the nap layer is set to a predetermined range. A method for manufacturing a glass substrate for a recording medium. 4. The nap layer has a thickness of 430 to 620.
4. The method for manufacturing a glass substrate for an information recording medium according to claim 3, wherein the glass substrate has a thickness of μm. 5. The method for manufacturing a glass substrate for an information recording medium according to claim 1, wherein the surface of the nap layer is modified by a pad dresser of diamond abrasive grains. 6. The method for producing a glass substrate for an information recording medium according to claim 1, wherein the glass substrate for an information recording medium is a glass substrate for a magnetic disk. 7. A method for manufacturing an information recording medium, comprising forming at least a recording layer on the main surface of the glass substrate for an information recording medium according to claim 1. 8. The method according to claim 7, wherein the recording layer is a magnetic layer.