JP2003242627A - Glass substrate for information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for an information recording medium capable of expanding a recording area by improving the flatness of a slope of a ski jump. <P>SOLUTION: The ski jump 22 is determined as follows. That is to say, a position away by 1.5% of a radius from the outer circumferential end edge of a substrate surface 10 along a radial direction is defined as a reference point, and a first measurement point 24a is determined on the slope 23 of the ski jump 22 at a position on the substrate surface 10, being on an inner side from the reference point. A second measurement point 24b is determined on the slope 23 away only by 0.5 to 3.0 mm to the inner side of the glass substrate from the first measurement point 24a along a radial direction. A straight line is connected between the first measurement point 24a and the second measurement point 24b, and by using the straight line as a reference straight line 25, the distance from the reference straight line to the surface of an actual slope 23 is defined as a radial curvature (RC). The RC represents the shape of the ski jump 22, and the RC is defined to be 50 nm or less. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording medium glass substrate for use in an information recording medium such as a magnetic disk, a magneto-optical disk, an optical disk, etc., which is a magnetic recording medium of an information recording apparatus such as a hard disk. The present invention relates to a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, as one of the above information recording media, a magnetic disk incorporated in a hard disk device is known. The magnetic disk is manufactured by laminating a magnetic layer or the like on the surface of a glass substrate for information recording medium (hereinafter, also simply referred to as a glass substrate). Further, a magnetic head (hereinafter, also simply referred to as a head) for reading the magnetic recording information recorded on the magnetic disk is configured to move in a state of floating above the surface of the magnetic disk. If there are irregularities on the surface of the magnetic disk when the head moves, the irregularities and the head may collide with each other, causing problems such as damage to the head and scratches on the magnetic disk.
In order to suppress the occurrence of such defects, the glass substrate is subjected to a polishing treatment at the time of manufacture so that the substrate surface becomes a smooth surface.

[0003]

By the way, in recent magnetic disks, the recording area is being expanded in order to increase the recording capacity thereof. However, when the glass substrate is subjected to polishing treatment, slight distortion, bending, warpage of the glass substrate,
Due to polishing stress and the like during the polishing process, mountain-shaped protrusions called ski jumps are formed at the outer peripheral edge of the substrate surface with high probability. This ski jump has various shapes depending on the polishing conditions, and there are one in which the slope is flat and continues in a straight line, one in which the slope of the slope greatly changes in the middle, and one in which large and small irregularities are formed on the slope.

When the slope of the ski jump is flat, the head can move on the slope.
However, if the slope of the ski jump has a small radius of curvature and becomes steep or has unevenness, the head cannot move on the slope of the ski jump and collides with the slope. Therefore, in order to expand the recording area, it is necessary to improve the flatness of the slope of the ski jump so that the head can move on the slope.

The surface condition of the glass substrate is generally determined by JI such as center line average roughness (Ra) and maximum height (Rmax).
It is evaluated by the magnitude of the surface roughness defined by S B0601. However, the surface roughness is calculated by taking an average value of the surface states of the entire substrate surface into consideration, and it is not possible to consider only the slope of the ski jump.

The present invention has been made by paying attention to the problems existing in the prior art. An object of the invention is to provide a glass substrate for an information recording medium, which can increase the recording area by improving the flatness of the slope of the ski jump.

[0007]

In order to achieve the above object, the invention of a glass substrate for an information recording medium according to claim 1 is such that a disk-shaped glass substrate is protruded from an outer peripheral edge portion on the substrate surface. An apex of the mountain-shaped ski jump is formed between the outer peripheral edge of the substrate surface and a position spaced radially inward from the outer peripheral edge by 1.5% of the radius. From the first measurement point on the slope of the ski jump extending inward from the substrate surface to a predetermined distance W (m
m) defines a second measurement point on a slope that is separated by a distance, and a straight line connecting the first measurement point and the second measurement point is used as a reference straight line, and the reference straight line is located closer to the substrate surface side than the reference straight line. When the distance to the surface of the slope located is a radial curve (RC), RC is 50 nm or less.

The invention of the glass substrate for an information recording medium described in claim 2 is characterized in that, in the invention described in claim 1, the predetermined distance W is 0.5 to 3.0 mm. .

The invention of the glass substrate for an information recording medium described in claim 3 is the invention of claim 1 or 2, wherein the height from the substrate surface to the top of the ski jump is 0.5 μm or less. It is characterized by being.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. The glass substrate for an information recording medium has a disk shape having a circular hole at the center, and is used as a substrate for an information recording medium such as a magnetic disk, a magneto-optical disk, an optical disk. Examples of the material for forming this glass substrate include soda lime glass, aluminosilicate glass, borosilicate glass, and crystallized glass produced by the float method, downdraw method, redraw method or press method. An information recording medium is constructed by laminating a magnetic film or the like on the surface of the glass substrate, and the substrate surface with the magnetic film or the like laminated serves as an information recording portion of the information recording medium. Of the information recording portion of this information recording medium, for example, a portion excluding a region in contact with the head (landing zone), chamfered portions (chamfer portion) formed on the outer peripheral edge and the inner peripheral edge, stores information on the information recording medium. It is used as a data area for recording.

The above information recording medium can be increased in recording capacity by achieving high density recording or by expanding the data area. Among these, as a method for achieving high-density recording, there is a method of narrowing the distance between the information recording portion, that is, the surface of the information recording medium and the head for reading the information recorded on the information recording medium. As a method of expanding the data area, there is a method of using the entire information recording unit as the data area.

Regardless of which of these methods is adopted, if there is unevenness on the surface of the glass substrate, unevenness is also formed on the information recording portion. Then, the head that is moving in the data area contacts or interferes with the unevenness, so that the recorded information cannot be read accurately, the head is damaged, the information recording section is damaged, and the like. It may occur. Therefore, in the glass substrate used for the information recording medium, an attempt has been made to suppress the occurrence of unevenness by subjecting the surface of the substrate, which becomes the information recording portion, to highly precise polishing.

These irregularities are specifically measured by an atomic force microscope (AFM). Then, based on the measurement result, the arithmetic mean roughness (Ra), the maximum height (Rmax), and the maximum peak height (Rp), which represent the surface roughness, are obtained in accordance with the regulations of JIS B0601. It should be noted that Rmax represents the height difference between the highest peak and the deepest valley in the unevenness, and Rp represents the height of the highest one from the center line in each convex portion.

In the glass substrate, Ra is preferably 0.8 nm or less, more preferably 0.3 nm or less. If Ra is larger than 0.8 nm, a large number of irregularities are generated and the surface of the substrate is roughened, so that the movement of the head becomes unstable and the above-mentioned problems may occur. Further, Rmax is preferably 2 to 5 nm. It is difficult to set Rmax to less than 2 nm, and there is a risk that the manufacturing efficiency will be decreased. On the other hand, when Rmax is greater than 5 nm, at least a portion of the substrate surface may be greatly roughened, making it difficult to increase recording capacity. In addition, R
It is preferable that p is 3 nm or less. If Rp is larger than 3 nm, large protrusions may be formed on at least a part of the substrate surface, and the head may collide with such protrusions, causing the above-mentioned problems.

When the state of the substrate surface of the glass substrate after the polishing treatment is actually measured, distortion, bending, warpage of the glass substrate,
There may be a case where a mountain-shaped raised portion called a ski jump is formed on the outer peripheral edge portion due to mechanical strain, polishing stress, or the like during polishing. The ski jump causes large irregularities on the outer peripheral edge of the substrate surface. For this reason, there are obstacles both when the distance between the information recording section and the head is reduced to achieve high density recording and when the data area is expanded. Therefore, in order to increase the recording capacity, it is an important issue to suppress the obstacle by making the shape of the ski jump proper.

There is a possibility that ski jumps may also be formed on the inner peripheral edge of the substrate surface. However, since a supporting jig or the like is attached to the circular hole of the glass substrate when it is incorporated in a hard disk device or the like, it is unlikely that the data area is expanded to the inner peripheral edge. Therefore, the present invention focuses on the ski jump formed on the outer peripheral edge and considers it.

The ski jump is specifically defined as follows. That is, as shown in FIG. 1, when the outer peripheral edge portion of the substrate surface 10 of the glass substrate is raised above the reference line 21, this raised portion serves as a ski jump 22. The reference line 21 has a radius of 15 to 19 along the radial direction from the outer peripheral edge on the substrate surface 10.
It is obtained by approximating the line along the substrate surface 10 between the measurement points separated by% and the measurement points separated by 27 to 31% of the radius to be a straight line. Note that, hereinafter, the left direction in FIG. 1 is the inside of the substrate surface 10, and the right direction in FIG. 1 is the outside of the substrate surface 10.

The formation position of the ski jump 22 can be adjusted by changing the polishing conditions. The apex 22a of the ski jump 22 has a radius of 1. from the outer peripheral edge of the substrate surface 10 along the radial direction.
It is formed so as to be arranged within a range up to a position separated by 5%. If the height of the ski jump 22 is SJ, SJ is represented by the length from the reference line 21 to the apex 22a. This SJ is preferably 0.5 μm or less. When SJ is higher than 0.5 μm, the probability of the head colliding with the ski jump 22 increases, and it becomes difficult to expand the data area.

When expanding the data area, if the head can move on the slope 23 extending from the apex 22a of the ski jump 22 toward the inside of the substrate surface 10, expand the data area to the apex 22a. Is possible. Therefore, the present inventors have concluded that the data area can be expanded by improving the flatness of the slope 23.

As a method of defining the flatness of the slope 23, when the surface of the slope 23 is assumed to be a flat surface, there is a method of expressing it by the distance from this flat surface to the actual surface of the slope 23. The distance from the flat surface to the actual surface of the slope 23 (hereinafter referred to as radial curver, abbreviated as RC) is specifically determined by the following method.

That is, first, a position separated from the outer peripheral edge of the substrate surface 10 along the radial direction by 1.5% of the radius is set as a reference point, and the slope 23 at a position located inside the substrate surface 10 from the reference point. The first measurement point 24a is defined above. Next, the second measurement point 2 is formed on the slope 23 that is separated from the first measurement point 24a in the radial direction by a distance W (mm) inward of the glass substrate.
Define 4b. After that, the first measurement point 24a and the second measurement point 24b are connected by a straight line, and the straight line is used as a reference straight line 25 representing a flat surface when the surface of the slope 23 is assumed to be a flat surface. Then, RC is determined by the distance from the reference straight line 25 to the actual surface of the slope 23.

When determining RC, the reference point is set to a radius of 1.5.
When it is set outside the substrate surface 10 rather than the position separated by%, the apex 22a of the ski jump 22 may be present between the first measurement point 24a and the second measurement point 24b. It may not be possible to accurately request the information. The distance W from the first measurement point 24a to the second measurement point 24b is preferably 0.5 to 3.0 mm. If the distance W is less than 0.5 mm, it may not be possible to accurately obtain the reference straight line 25. If the length is longer than 3.0 mm, the second measurement point 2
4b may not be able to be set on the slope 23 of the ski jump 22.

Other than the one shown in FIG. 1, there are ski jumps having the following shapes. That is, FIG.
As shown in FIG. 4A, the apex 22a is not clear as compared with that in FIG. 1, and the slope of the slope 23 greatly changes in the middle. As shown in FIG. The slope is located below the reference line 21, and the surface sags (rolls off).
And the like. These FIGS. 4 (a) and 4 (b)
The RC indicated by can also determine the RC as described above.

The RC determined as described above is 50n.
m or less, and more preferably 25 nm or less. R
When C is longer than 50 nm, the head comes into contact with the surface of the slope 23 and cannot move on the slope 23. Then, by setting RC to 50 nm or less, the flatness of the slope 23 can be favorably maintained, and since the slope 23 can be included in the data area, the data area can be expanded. . Although the lower limit of RC is not particularly specified, the smaller the RC, the more preferable, and therefore it is 0 nm or more.

Next, a method for manufacturing the glass substrate will be described. As shown in FIG. 3, the glass substrate 37 is formed into a disk shape having a circular hole at the center by cutting the sheet-shaped glass base plate 31 in the disk processing 32 step. Further, in the process of the same disk processing 32, the glass base plate 31 is ground and processed so that the outer and inner diameters thereof have predetermined lengths, and the corners of the inner and outer peripheral end surfaces are ground. Be chamfered.

A glass base plate 31 on which a disk processing 32 is applied
Is subjected to rough polishing 33 in the primary polishing step, and its surface is roughly polished. This rough polishing 33 sets the thickness of the glass base plate 31 to a predetermined value, removes large undulations and large defects such as chipping (crapping) and cracks (cracks), and makes RC a certain good value. To be done.

Now, the structure of the polishing apparatus for performing the rough polishing process 33 will be described. As shown in FIGS. 2A and 2B, the polishing apparatus 41 includes a disc-shaped upper plate 42b and a lower plate 4 which are vertically arranged so as to be parallel to each other.
2a, and an internal gear 43 having an annular shape arranged so as to surround the upper surface plate 42b and the lower surface plate 42a inside. A rotary shaft 44 is provided so as to project from the center of the lower turn table 42a, and a sun gear 45 is provided on the outer peripheral surface of the lower end of the rotary shaft 44. Upper surface plate 42
An insertion hole 46 is transparently provided at the center of b.
A rotary shaft 44 is inserted through the shaft 6. And upper surface plate 4
2b, the lower surface plate 42a, the internal gear 43, and the sun gear 45 are driven by a motor or the like so that they can rotate independently of each other.

A plurality of carriers 47 are arranged between the lower turn table 42a and the upper turn table 42b so as to be sandwiched therebetween. The carrier 47 is provided with a plurality of circular holes 48, and the glass base plate 31 is housed in each circular hole 48. A gear 49 is provided on the outer peripheral edge of each carrier 47, and the gear 49 of each carrier 47 is meshed with the internal gear 43 and the sun gear 45, respectively.

During the polishing process, the polishing device 41 concerned.
The carrier 47 is sandwiched between the lower surface plate 42a and the upper surface plate 42b in a state where a plurality of glass base plates 31 are accommodated in each carrier 47. Then, the lower surface plate 42a and the upper surface plate 4
The upper surface plate 42b, the lower surface plate 42a, the internal gear 43, and the sun gear 45 are rotated while supplying an abrasive between the 2b and the glass base plate 31. Then, lower surface plate 4
2a and the upper surface plate 42b, each carrier 47 is revolved around the rotation shaft 44 while rotating while rotating the glass element plate 31 in contact with the lower surface plate 42a and the upper surface plate 42b. The substrate surface of the plate 31 is polished.

In the primary polishing step, a hard polisher is attached to the contact surface of each surface plate 42 of the polishing apparatus 41 with the glass base plate 31, and rough polishing 33 is performed. The hard polisher has a hardness (JIS A) of 65 to 85 and a compression elastic modulus of 6
It is made of a foamed resin of 0 to 65% and is used so that the compression rate is 2 to 4%. If the hardness is less than 65 and the compression modulus is higher than 65% or the compression rate is higher than 4%, the hard polisher may be deformed during polishing and a large roll-off may be formed. If the hardness is greater than 85, the compression modulus is less than 60% or the compression rate is less than 2%, the surface of the base plate is scratched by the hard polisher, and the surface condition is rather roughened or RC is increased. There is a risk that

The abrasive used in the primary polishing step has an average particle size of 1.
A slurry in which an abrasive having a diameter of about 2 μm is dispersed in water as a solvent is used. Examples of the abrasive include alumina abrasive grains, rare earth oxides such as cerium oxide and lanthanum oxide, zirconium oxide, manganese dioxide, aluminum oxide and colloidal silica. Of these, rare earth oxides are preferable because they have excellent polishing efficiency, and cerium oxide is more preferable among the rare earth oxides. The polishing amount in the primary polishing step is preferably 15-
It is 40 μm. If the polishing amount is less than 15 μm, large defects cannot be sufficiently removed. On the other hand, even if the polishing exceeds 40 μm, the RC does not decrease further, but rather the polishing time becomes longer, resulting in a decrease in production efficiency.

Then, the glass base plate 31 is subjected to the primary polishing process.
Preferably has an RC of 25 to 70 nm. R
Although it is not impossible to set C to be less than 25 nm, it is not realistic because the polishing time becomes very long and the production efficiency may be lowered. Further, if RC is higher than 70 nm, the time required for the subsequent steps may be long, which may lead to a decrease in production efficiency, and when the glass substrate 37 is used, RC may not be 50 nm or less.

Following the above primary polishing step, the glass base plate 3
1 is subjected to precision polishing processing 34 in the secondary polishing process,
The surface is precision polished. This precision polishing process 34
In addition to undulations and defects that could not be removed in the primary polishing step, polishing stress remaining on the surface of the glass base plate 31 after the primary polishing step, polishing marks formed, etc. are removed. Further, in the second polishing step, the glass base plate 31 is
Precision polishing process 3 until the surface roughness after polishing becomes almost the same as the surface roughness required for the substrate of the information recording medium.
4 and RC is set to 50 nm or less.

In the secondary polishing step, the polishing apparatus 41 used in the primary polishing step is not used as it is, but
The precision polishing process 34 is performed by using another polishing apparatus 41 having the same configuration but prepared only for the secondary polishing step. This is because if the polishing apparatus 41 used in the primary polishing step is used as it is, the polishing accuracy in the secondary polishing step may be reduced due to the polishing agent remaining in the primary polishing step, and the polishing conditions may be reset. This is because complicated work is required and the production efficiency may decrease.

As the polishing device 41 used in the secondary polishing step, one having a soft polisher attached to each surface plate 42 is used. The soft polisher has a hardness (Asker C) of 5
The pad is made of suede having a compression modulus of 8 to 78 and a compression modulus of 58 to 78%, and is used so that the compression rate is 1 to 5%. When the hardness is less than 58 and the compression elastic modulus is higher than 78% or the compression ratio is higher than 5%, the soft polisher may be deformed during polishing and the roll-off may be increased. When the hardness is higher than 78, the compression modulus is less than 58% or the compression rate is less than 1%, the surface of the base plate is scratched by the soft polisher, and the surface condition is rather roughened or RC is increased to 5%.
There is a possibility that the thickness may not be 0 nm or less.

The abrasive used in the secondary polishing step has an average particle size of 0.
A slurry in which an abrasive having a diameter of about 8 μm is dispersed in water as a solvent is used. Examples of the abrasive include rare earth oxides such as cerium oxide and lanthanum oxide, zirconium oxide, manganese dioxide, aluminum oxide, colloidal silica and the like. Of these, rare earth oxides are preferable because they have excellent polishing efficiency, and cerium oxide is more preferable among the rare earth oxides.

The polishing amount in the secondary polishing step is preferably 2 to 10 μm. If the polishing amount is less than 2 μm, RC may be greater than 50 nm, and the surface roughness may not be reduced to a desired value or less. On the other hand, even if polishing is performed to exceed 10 μm, the surface roughness and RC are less likely to be good values, and the polishing time is rather prolonged, which may lead to a decrease in production efficiency.

The glass base plate 31 is preferably chemically strengthened in order to improve impact resistance, vibration resistance, heat resistance and the like required as an information recording medium. Therefore, in this embodiment, the chemical strengthening treatment 35 is performed on the glass base plate 31 that has been subjected to the precision polishing process 34.

The chemical strengthening treatment 35 means the glass base plate 3
Ion exchange of monovalent metal ions such as lithium ions and sodium ions contained in the composition of 1 to monovalent metal ions such as sodium ions and potassium ions having a larger ionic radius compared to this. . And
In this method, a compressive stress is applied to the surface of the glass base plate 31 to chemically strengthen it. The chemical strengthening treatment 35 is performed by immersing the glass base plate 31 in a chemical strengthening treatment liquid obtained by heating and melting a chemical strengthening salt for a predetermined time. Specific examples of the chemically strengthened salt include potassium nitrate, sodium nitrate, silver nitrate, etc., each alone or as a mixture of at least two kinds.

The temperature of the chemical strengthening treatment liquid is the glass base plate 31.
The temperature is preferably about 50 to 150 ° C. lower than the strain point of the material used for, and more preferably the temperature of the chemical strengthening treatment liquid itself is about 350 to 400 ° C. Glass base plate 31
If the temperature is lower than the strain point of the above material by about 150 ° C., the glass base plate 31 cannot be sufficiently chemically strengthened. On the other hand, when the temperature exceeds the strain point of the material of the glass base plate 31 by about 50 ° C., the glass base plate 31 is likely to be distorted when the glass base plate 31 is subjected to the chemical strengthening treatment 35.

When the glass base plate 31 is subjected to the chemical strengthening treatment 35 as described above, the compressive stress acts,
A reinforcing layer is formed on the surface of the base plate. However, when the chemical strengthening treatment 35 is performed, the surface of the glass base plate 31 may be roughened due to the action of compressive stress, and the surface roughness may be deteriorated. Therefore, the glass base plate 31 has Ra of 0.3 to 1.0 nm and Rmax of 3 in the step prior to the chemical strengthening treatment 35.
-10 nm and Rp are preferably 3 to 7 nm. When Ra is less than 0.3 nm, Rmax is less than 3 nm, or Rp is less than 3 nm, the time required in the step prior to the chemical strengthening treatment 35 becomes long, which may lead to a decrease in production efficiency. Ra greater than 1.0 nm, Rmax
Is larger than 10 nm or Rp is larger than 7 nm, Ra, Rmax in a step after the chemical strengthening treatment 35
Since each of Rp and Rp is set to a desired value or less, the time required in each process becomes long, which may lead to a decrease in production efficiency.

The glass base plate 31 which has been subjected to the chemical strengthening treatment 35 as described above is subjected to ultra-precision polishing processing 36 in the third polishing step, and the surface thereof is subjected to ultra-precision polishing. This ultra-precision polishing process 36 has a depth of 0.1 to 1 from the surface of the blank plate.
This is for smoothing the part of μm, and it is performed to remove minute defects such as minute roughness, undulation, and traces and defects formed in the process before the third polishing process that have occurred on the surface of the base plate. Be seen.

Also in the third polishing step, the polishing apparatus 41 used in the primary polishing step and the secondary polishing step is not used as it is, but another polishing apparatus 41 having the same structure but prepared exclusively for the same step. Ultra-precision polishing process using
I do. This is because the third polishing step requires higher polishing accuracy than the previous polishing steps. Therefore, if the polishing apparatus 41 used in each polishing step is used as it is, the polishing agent remaining in each polishing step may cause This is because the polishing accuracy may decrease.

As the polishing apparatus 41 used in the third polishing step, one having a soft polisher attached to each surface plate 42 is used. The soft polisher has a hardness (Asker C) of 5
The pad is made of suede having a compression modulus of 8 to 78 and a compression modulus of 58 to 85%, and is used so that the compression rate is 1 to 5%. If the hardness is less than 58 and the compression modulus is higher than 85% or the compression rate is higher than 5%, the soft polisher may be deformed during polishing and the roll-off may be increased. When the hardness is higher than 78, the compression modulus is less than 58% or the compression rate is less than 1%, the surface of the base plate is scratched by the soft polisher, and the surface condition is rather roughened or RC is increased to 5%.
There is a possibility that the thickness may not be 0 nm or less.

The average particle size (D
An abrasive having a ₅₀ ) of 10 to 150 nm is dispersed in water as a solvent to form a slurry. If the average particle size of the abrasive is less than 10 nm, the polishing efficiency may be reduced and minute defects may not be sufficiently removed. If the average particle size exceeds 150 nm, a polishing mark may be formed on the surface of the base plate by the polishing material, and minute waviness or minute unevenness may occur due to the polishing mark.

Colloidal silica is preferred as the abrasive because it has a small particle size and can suppress excessive polishing of the surface of the base plate. The concentration of the abrasive in the abrasive is preferably 5-40% by weight. If the concentration of the abrasive is less than 5% by weight, polishing efficiency may be reduced and minute waviness may not be sufficiently removed. If it exceeds 40% by weight, polishing marks may be formed on the surface of the raw plate by the polishing material, and minute waviness or minute unevenness may occur due to the polishing marks.

The polishing amount in the third polishing step is preferably 100 to 1000 nm. If the polishing amount is less than 100 nm, minute undulations may not be sufficiently removed. On the other hand, even if polishing exceeds 1000 nm, fine defects cannot be removed any more, and rather the polishing time becomes longer, resulting in a decrease in production efficiency.

When one polishing operation is regarded as one batch in the third polishing step, the ultra-precision polishing process 36 is applied to the plurality of glass base plates 31 in each batch. At this time, the difference in the thickness of the glass base plate 31 in each batch is preferably 4 μm or less, and more preferably 2 μm or less. If the difference in thickness exceeds 4 μm, the glass base plate 31
It becomes difficult to maintain the polishing amount in the range of 100 to 1000 nm, which may lead to deterioration of the production quality of the glass substrate 37. The lower limit of the thickness difference is not particularly limited, but is preferably 0 μm or more.

In this third polishing process, RC of the glass base plate 31
It is possible to reduce the surface roughness as compared with the steps up to the secondary polishing step. RC at this time is preferably 25 nm or less. In addition, Ra is preferably 0.8 nm or less, Rmax is preferably 2 to 5 nm, R
p is preferably 3 nm or less.

After the third polishing step, the glass base plate 31
Are cleaned, and the adhered substances such as abrasive powder, abrasives, and dust adhering to the surface are removed to form the glass substrate 37. Examples of the cleaning liquid for cleaning the glass base plate 31 include organic solutions, acidic solutions, alkaline solutions, water, and hot water. As this organic solution, isopropyl alcohol (I
PA), methanol, ethanol, butanol and the like. Examples of the acidic solution include hydrofluoric acid, sulfuric acid, sulfamic acid, hydrochloric acid, nitric acid, phosphoric acid and the like. Examples of the alkaline solution include potassium hydroxide, sodium hydroxide, ammonia, tetramethyl hydroxide and the like. Further, a cleaning auxiliary agent (builder) generally used for this type of cleaning such as a cationic, anionic or nonionic surfactant and a chelating agent may be added to these cleaning solutions.

In addition, when colloidal silica is used as an abrasive in the third polishing step, at least one selected from water, hot water and an alkaline aqueous solution having a pH of 12 or less can be removed efficiently without causing the agglomeration of the colloidal silica. It is preferred to wash with seeds. Further, in order to further enhance the cleaning degree, cleaning may be performed using a strong alkaline aqueous solution, an acidic aqueous solution or an organic solution having a pH of more than 12 after the cleaning.

The effects exerted by the above embodiment will be described below. In the glass substrate of the embodiment, the flatness of the slope 23 of the ski jump 22 is assumed to be a flat surface, and the distance from the flat surface to the actual surface of the slope 23, that is, the radial curve. (RC). Therefore, the shape of the slope 23 can be accurately expressed by considering only the ski jump 22 instead of the entire substrate surface. Therefore, the ski jump 22 can be formed by forming the glass substrate so that the RC has an appropriate value.
The flatness of the slope 23 can be improved. Since the RC is set to 50 nm or less, the flatness of the slope 23 can be made good and can be included in the data area, so that the recording area can be expanded.

When defining RC, the distance W from the first measurement point 24a defined on the slope 23 of the ski jump 22 to the second measurement point 24b is 0.5 to 3.0 m.
It is supposed to be m. Therefore, from the first measurement point 24a to the second measurement point
The top 2 of the ski jump 22 in the area up to the measurement point 24b
2a is prevented from being included, the shape of the slope 23 can be expressed more accurately, and the flatness thereof can be reliably improved.

In addition, by setting the height from the substrate surface 10 to the apex 22a of the ski jump 22 to be 0.5 μm or less, it is possible to suppress the formation of a large ski jump 22 and effectively expand the recording area. Can be achieved.

The embodiment can be modified and embodied as follows. -For example, the glass base plate 31 may be subjected to the ultra-precision polishing process 36 and then subjected to the chemical strengthening process 35. With such a configuration, since the hard reinforcing layer is not formed on the surface of the base plate when performing the ultraprecision polishing process 36, the ultraprecision polishing can be performed easily and in a short time.

Further, the glass base plate 31 is processed into a disc 32.
After the above, the chemical strengthening treatment 35 may be performed, and thereafter, the rough polishing process 33, the precision polishing process 34, and the ultra-precision polishing process 36 may be sequentially performed. In the case of such a configuration, as compared with the case where the ultra-precision polishing process 36 is performed after the chemical strengthening treatment 35 is performed, the surface of the raw plate is more easily polished, and the surface of the raw plate after the polishing is chemically strengthened 35. Roughness can also be suppressed. Therefore, it is possible to obtain a high-quality glass substrate while improving the production efficiency.

In addition, a chemical strengthening process 35 may be performed between the rough polishing process 33 and the precision polishing process 34. If the impact resistance, vibration resistance, heat resistance, etc. required of the information recording medium can be satisfied, the glass substrate may be manufactured by omitting the chemical strengthening treatment 35. When omitting the chemical strengthening treatment 35 in this way, the glass base plate 31
It is preferable to maintain the strength of the glass substrate by melting, shaving, etc., filling and removing defects such as chipping and cracks that occur when processing by cutting, grinding, polishing, etc. .

When the waviness, distortion, warpage, bending, etc. generated in the glass base plate 31 are very large, the glass base plate 31 may be subjected to the lapping process in a step prior to the rough polishing process 33. . This lapping process is performed by using the polishing device 41 having the same structure as that used in the primary to tertiary polishing steps. In the lapping process, a hard or soft polisher is not used, and the surface of each platen 42 is covered with the glass base plate 3
Lapping is performed by directly contacting the surface of 1. In addition, in the lapping process, an abrasive having a larger particle size than that used in the primary to tertiary polishing steps is used. The lapping amount in the lapping process is preferably 70 to 300 μm. With this configuration, it is possible to remove very large undulations, distortions, warps, flexures, etc. that are difficult to remove in the primary polishing process.

R in each step up to the secondary polishing step
The third polishing step may be omitted if C can be made sufficiently small. With this configuration, the manufacturing process can be simplified and the production amount can be increased.

The glass base plate 31 may be washed by using the cleaning liquid mentioned above between the first to third polishing steps. With this configuration, the quality of the glass substrate manufactured can be improved.

In the embodiment, the first measurement point 24a and the second measurement point 24a
The entire slope 23 existing between the measurement point 24b and the measurement point 24b is located closer to the substrate surface 10 side than the reference straight line 25. In the case of defining RC, the shape of the slope 23 is not limited to this, and a part of the slope is a shape that is raised above the reference straight line 25, and the entire slope is a shape that is raised above the reference straight line 25. May be. In the slope having such a shape, for example, the curvature of the slope changes between the first measurement point 24a and the second measurement point 24b, and the slope swells toward the substrate surface 10 side on the inner side of the substrate surface 10. An example is a circular arc shape, and an inclined surface on the outer side of the substrate surface 10 has an arc shape that bulges toward the upper side of the substrate surface 10. Even on such slopes,
The slope 23 can be included in the data region by setting the RC having the larger numerical value out of the RC swelling toward the substrate surface 10 side and the RC swelling toward the upper side of the substrate surface 10 to 50 nm or less. is there. In addition, as the shape of the slope 23, it is preferable that the slope 23 swells toward the substrate surface 10 side rather than swells toward the upper side of the substrate surface 10. This is because the area from the substrate surface 10 to the start end of the slope 23 is substantially flat, and the head can easily climb on the slope 23.

Further, the technical idea which can be understood from the above embodiment will be described below. On the substrate surface, the arithmetic mean roughness (Ra), the maximum height (Rmax) and the maximum peak height (Rp) defined in JIS B0601 are Ra 0.8 nm or less, Rmax 2-5 nm and Rp, respectively. Is 3 nm or less, The glass substrate for information recording media according to any one of claims 1 to 3. With such a configuration, it is possible to more effectively suppress the occurrence of defects when the information recording medium is used.

The glass substrate for an information recording medium according to any one of claims 1 to 3, wherein the RC is 25 nm or less. With such a configuration, the flatness of the slope of the ski jump can be made better, and a wider recording area can be secured while coping with higher recording density.

A method of manufacturing a glass substrate for an information recording medium according to claim 1, wherein a primary polishing step for performing a rough polishing process for roughly polishing the substrate surface of the glass substrate using a hard polisher, A glass for information recording medium, comprising: a secondary polishing step for performing a precision polishing process in which a substrate surface after rough polishing is precisely polished using a soft polisher having a hardness (Asker C) of 58 to 78. Substrate manufacturing method. With this structure, it is possible to improve the flatness of the slope of the ski jump and to produce a glass substrate that can expand the recording area.

The glass substrate for an information recording medium according to any one of claims 1 to 3, wherein the inclined surface is formed in an arc shape which bulges toward the substrate surface side. With this configuration, the head can easily climb on the slope.

[0066]

As described in detail above, the present invention has the following effects. According to the glass substrate for an information recording medium of the first aspect, the recording area can be expanded by improving the flatness of the slope of the ski jump.

According to the glass substrate for an information recording medium of the invention described in claim 2, in addition to the effect of the invention described in claim 1, in addition to the effect of the invention described in claim 1, the ski jump is formed in the area from the first measurement point to the second measurement point. It is possible to prevent the apex from being included, more accurately express the shape of the slope, and surely improve the flatness.

According to the glass substrate for an information recording medium of the invention described in claim 3, in addition to the effect of the invention described in claim 1 or 2, the formation of a large ski jump is suppressed, The recording area can be effectively expanded.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a ski jump formed on a substrate surface.

FIG. 2 is a perspective view showing a polishing device.

FIG. 3 is a flowchart showing a manufacturing process of a glass substrate.

4A and 4B are conceptual diagrams showing another form of ski jump.

[Explanation of symbols]

Reference numeral 10 ... Substrate surface, 22 ... Ski jump, 22a ... Apex, 23 ... Slope, 24a ... First measurement point, 24b ... Second measurement point, 25 ... Reference straight line, 37 ... Glass substrate.

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Claims (3)

[Claims] 1. An apex of a ski jump having a mountain shape raised from the outer peripheral edge on a substrate surface of a disk-shaped glass substrate has an outer peripheral edge on the substrate surface and a radius extending from the outer peripheral edge along a radial direction. The first measurement point is defined on the slope of the ski jump that is formed between a position spaced inward by 1.5% and extends inward of the substrate surface from the apex.
A predetermined distance W from the measurement point inward of the substrate surface along the radial direction
A second measurement point is defined on a slope that is separated by (mm), and a straight line connecting the first measurement point and the second measurement point is set as a reference straight line. The reference straight line is closer to the substrate surface side than the reference straight line. A glass substrate for an information recording medium, wherein RC is 50 nm or less when a distance to the surface of the slope located at is a radial curve (RC). 2. The glass substrate for an information recording medium according to claim 1, wherein the predetermined distance W is 0.5 to 3.0 mm. 3. The glass substrate for an information recording medium according to claim 1, wherein the height from the substrate surface to the top of the ski jump is 0.5 μm or less.