U.S. patent application number 10/443849 was filed with the patent office on 2003-10-16 for glass substrate for magnetic recording medium, magnetic recording medium, and method of manufacturing the same.
This patent application is currently assigned to HOYA CORPORATION. Invention is credited to Miyamoto, Takemi.
Application Number | 20030194583 10/443849 |
Document ID | / |
Family ID | 14108663 |
Filed Date | 2003-10-16 |
United States Patent
Application |
20030194583 |
Kind Code |
A1 |
Miyamoto, Takemi |
October 16, 2003 |
Glass substrate for magnetic recording medium, magnetic recording
medium, and method of manufacturing the same
Abstract
In a method of manufacturing a glass substrate for a magnetic
recording medium for forming a predetermined roughness, a principal
surface of the glass substrate is precisely polished by the use of
polishing material containing free abrasive grain. Remaining stress
distribution for a portion of a polishing trace due to the free
abrasive grain is generated on the surface of the glass substrate.
A surface process is performed for at least the principal surface
of the glass substrate by the use of hydrosilicofluoric acid. A
portion having relatively high remaining distortion in the
generated remaining stress distribution is decided as an island
portion. The glass substrate is heated after precisely polishing
before performing the surface process by the use of the
hydrosilicofluoric acid.
Inventors: |
Miyamoto, Takemi; (Tokyo,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 Pennsylvania Avenue, NW
Washington
DC
20037-3213
US
|
Assignee: |
HOYA CORPORATION
|
Family ID: |
14108663 |
Appl. No.: |
10/443849 |
Filed: |
May 23, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10443849 |
May 23, 2003 |
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10122195 |
Apr 16, 2002 |
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10122195 |
Apr 16, 2002 |
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09540888 |
Mar 31, 2000 |
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6395634 |
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Current U.S.
Class: |
428/846.9 ;
G9B/5.288; G9B/5.299 |
Current CPC
Class: |
G11B 5/73921 20190501;
C03C 2204/08 20130101; C03C 15/00 20130101; C03C 19/00 20130101;
C03C 3/083 20130101; G11B 5/8404 20130101; G11B 5/7379
20190501 |
Class at
Publication: |
428/694.0SG ;
428/65.3 |
International
Class: |
B32B 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 1999 |
JP |
94378/1999 |
Claims
What is claimed is:
1. A method of manufacturing a glass substrate for a magnetic
recording medium for forming a predetermined roughness, comprising
the steps of: precisely polishing a principal surface of the glass
substrate by the use of polishing material containing free abrasive
grain, generating remaining stress distribution for a portion of a
polishing trace due to the free abrasive grain on the surface of
the glass substrate, performing a surface process for at least the
principal surface of the glass substrate by the use of
hydrosilicofluoric acid, and deciding a portion having relatively
high remaining distortion in the generated remaining stress
distribution as an island portion, the glass substrate being heated
after precisely polishing before performing the surface process by
the use of the hydrosilicofluoric acid.
2. A method of manufacturing a glass substrate for a magnetic
recording medium for forming a predetermined roughness, comprising
the steps of: precisely polishing a principal surface of the glass
substrate by the use of polishing material containing free abrasive
grain, generating remaining stress distribution for a portion of a
polishing trace due to the free abrasive grain on the surface of
the glass substrate, chemically strengthening at least the
principal surface of the glass substrate, and deciding a portion
having relatively high remaining distortion in the generated
remaining stress distribution as an island portion, the glass
substrate being heated by dipping the glass substrate in heated
solvent after precisely polishing before chemically strengthening
the surface.
3. A method as claimed in claim 2, wherein: the chemical surface
process comprises either one of an etching process by the use of
solution containing hydrofluoric acid, solution containing
hydrosilicofluoric acid, and alkali solution.
4. A method as claimed in any one of the claims 1 through 3,
wherein: heating temperature in the heating process step falls
within the range between 30.degree. C. and 180.degree. C.
5. A method as claimed in any one of the claims 1 through 4,
wherein: the heating process is carried out by the use of at least
one selected from the group consisting of hot water, heated
sulfuric acid, heated glycerin, and heated phosphoric acid.
6. A method as claimed in any one of the claims 1 through 5,
wherein: the glass substrate contains at least alkali metal oxide
and alkali earth oxide, and content of the alkali earth oxide is
not exceeding 3 mol %.
7. A method as claimed in claim 6, wherein: the glass constituting
the glass substrate contains SiO.sub.2 between 58 and 75 weight %,
Al.sub.2O.sub.3 between 5 and 23 weight %, Li.sub.2O between 3 and
10 weight %, and Na.sub.2O between 4 and 13 weight % as main
components.
8. A method as claimed in claim 7, wherein: the glass contains
SiO.sub.2 between 62 and 75 weight %, Al.sub.2O.sub.3 between 5 and
15 weight %, Li.sub.2O between 4 and 10 weight %, Na.sub.2O between
4 and 12 weight %, and ZrO.sub.2 between 5.5 and 15 weight % as
main components, and weight ratio of Na.sub.2O/ZrO.sub.2 falls
within the range between 0.5 and 2.0 while weight ratio of
Al.sub.2O.sub.3/ZrO.sub.2 falls within the range between 0.4 and
2.5.
9. A method as claimed in any one of claims 1 through 7, wherein:
the chemical strengthening process is carried out after the surface
process due to the hydrosilicofluoric acid.
10. A method of manufacturing a magnetic recording medium, wherein:
at least a magnetic layer is formed on the principal surface of the
glass substrate manufactured by the method claimed in any one of
claims 1 through 9.
11. A glass substrate for a magnetic recording medium for use in a
load/unload system, wherein: the glass substrate has a principal
surface, and surface roughness of the principal surface is
specified by Rmax=3-15 nm, Ra=0.2-2.5 nm, and Rmax/Ra=3-15, where
Ra is representative of a center-line mean roughness, and Rmax is
defined as a maximum height representative of a difference between
a highest point and a lowest point.
12. A glass substrate for a magnetic recording medium for use in a
load/unload system, wherein: the glass substrate has a principal
surface, and surface roughness of the principal surface is
specified by Rp=1-7 nm, Ra=0.2-2.5 nm, and Rp/Ra=1-15, where Ra is
representative of a center-line mean roughness, and Rp is
representative of a maximum height of a highest point.
13. A magnetic recording medium having at least a magnetic layer on
a glass substrate for use in a load/unload system, wherein: the
glass substrate has a principal surface, and surface roughness of
the principal surface is specified by Rmax=3-15 nm, Ra=0.2-2.5 nm,
and Rmax/Ra=3-15, where Ra is representative of a center-line mean
roughness, and Rmax is defined as a maximum height representative
of a difference between a highest point and a lowest point.
14. A magnetic recording medium having at least a magnetic layer on
a glass substrate for use in a load/unload system, wherein: the
glass substrate has a principal surface, and surface roughness of
the principal surface is specified by Rp=1-7 nm, Ra=0.2-2.5 nm, and
Rp/Ra=1-15, where Ra is representative of a center-line mean
roughness, and Rp is representative of a maximum height of a
highest point.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a glass substrate for use in a
magnetic recording medium, such as, a hard disk, a magnetic
recording medium having the glass substrate, and a method of
manufacturing the magnetic recording medium and the glass
substrate.
[0002] An interface between a magnetic head and a magnetic disk has
become a key technology for improving recording capacity in a
technical field for magnetically recording (writing) and
reproducing (reading).
[0003] It is necessary to excessively reduce a flying height of the
magnetic head which is float over a surface of the magnetic disk to
improve recording density.
[0004] However, when the record/reproduce (write/read) operation is
carried out in the known CSS (Contact Start Stop) method, the
magnetic head often sticks to the magnetic disk with a low flying
height of the magnetic head. Herein, it is to be noted that this
phenomenon is generally called "head stiction".
[0005] Suggestions conventionally have been made about a variety of
texture techniques to prevent such stiction of the magnetic head. A
representative suggestion has been made about a method of forming a
surface of an Al/NiP plating substrate into a rough surface by
mechanically polishing (mechanically texturing) the surface in
Japanese Unexamined Patent Publication (JP-A) No. S62-273619.
Further, another suggestion has been made about a method of
depositing a thin-film having the rough surface on a glass
substrate by the use of the known sputtering process in Japanese
Examined Patent Publication (JP-B) No. H04-62413 or a method of
forming the rough surface by the use of the chemical etching
process in Japanese Examined Patent Publication (JP-B) No.
H07-101507, Japanese Examined Patent Publication (JP-B) No.
H07-153059 when the glass substrate is superior in flatness in
comparison with an aluminum substrate.
[0006] In particular, an etching process is carried out by the use
of etching liquid after performing a moisture and heat insulation
process for a glass substrate in Japanese Examined Patent
Publication (JP-B) No. H07-153059. Thereby, repeatability of
formation of projections and uniformity of a projection height,
which conventionally have caused problems in the texturing
technique due to the chemical etching method, have been
improved.
[0007] Meanwhile, a glide height recently has reached 1.2.mu. inch
or less to improve the recording capacity.
[0008] However, the method of forming the texture, which has been
conventionally suggested and described above, is the texture
technique on the condition that the glide height is equal to about
8.mu. inch.
[0009] Therefore, even when the conventional texture forming method
is applied for the recent magnetic disk which records (writes) and
reproduces (reads) with the low flying height, it is difficult to
obtain the magnetic disk which simultaneously satisfies sufficient
electro-magnetic conversion characteristic and stiction preventing
effect of the magnetic head.
[0010] In this case, the conventional glide height was equal to
about 8.mu. inch. Therefore, the surface state (the surface
morphology) of the magnetic disk (the substrate) could be
sufficiently evaluated by the known thally step. Herein, the
surface roughness is measured by scanning a contact needle having
radius of several .mu.m (for example, 2.5 .mu.m) along the
surface.
[0011] However, when the flying height becomes 1.2.mu. inch or less
(1 inch=25.4 mm) which is recently required, it is difficult to
judge whether or not the surface state of the glass substrate can
realize prevention of the stiction of the magnetic head by the use
of the conventional thally step.
[0012] In the meantime, attention recently has been paid for a
magnetic disk apparatus of a load/unload system (a ramp load
system) in stead of the CSS system. In such a load/unload system, a
magnetic head travels on a data area of the magnetic disk via an
arm after the magnetic disk is rotated and is driven different from
the CSS system.
[0013] Consequently, it is unnecessary to provide the texture for
preventing the stiction when the magnetic head halts. Further, the
surface roughness of the disk surface becomes small, and the flying
height of the magnetic head for the magnetic disk also becomes
small. As a result, it is possible to reproduce with high recording
density.
[0014] Thus, it is required that the medium surface is flat ,the
projection height is low, and variation of the projection heights
is small (values of Rmax/Ra and Rp/Ra are small) in the load/unload
system (ramp load system) in comparison with the CSS system.
[0015] Specifically, it is necessary that Rmax falls within the
range between 3 and 15 nm, Ra falls within the range between 0.2
and 2.5 nm, Rmax/Ra falls within the range between 3 and 15, or Rp
falls within the range between 1 and 7 nm, Ra falls within the
range between 0.2 and 2.5 nm, and Rp/Ra falls within the range
between 1 and 15.
[0016] In this case, the surface preferably has projections within
the above-mentioned range, and is not completely flat in the
load/unload system. In particular, Ra preferably falls within the
range between 0.6 and 1.3 nm.
[0017] In the meantime, the surface roughness required for the CSS
system is specified by Rmax=6-18 nm, Ra=0.7-1.5 nm, and
Rmax/Ra=10-20. Further, the surface roughness is specified by
Rp=3-15 nm, Ra=0.7-1.5 nm ,and Rp/Ra=3-15 when the surface
roughness is controlled by Rp.
SUMMARY OF THE INVENTION
[0018] It is therefore an object of this invention to provide a
magnetic recording medium and a glass substrate for the magnetic
recording medium which is capable of realizing a glide height of
1.2.mu. inch or less and which is capable of realizing high
electromagnetic characteristic.
[0019] It is another object of this invention to provide a magnetic
recording medium and a glass substrate for the magnetic recording
medium which is suitable for a load/unload system by controlling a
projection height, projection density, variation of projection
heights, and variation of projections and which has high CSS
durability characteristic suitable for a CSS system .
[0020] Inventors have paid attention to specify the surface state
of the glass substrate by the use of the interatomic force
microscope (AFM) in order to evaluate the surface state of the
glass substrate. This is because it is impossible to identify
whether or not the surface state of the glass substrate is
suitable, since the resolution is low in the conventional measuring
method using the contact needle method.
[0021] Based upon the above-mentioned evaluation method, it has
been confirmed that height and distribution (namely, variation of
the height) of each projection of fine roughness, which are formed
on a principle surface of the glass substrate, are important
factors to achieve the above purpose.
[0022] Further, as a result of various experiments, it has been
found out that the glass substrate surface as a target or a goal
can not be obtained unless specific polishing condition and surface
process condition are properly combined. This invention is
performed based upon this analyzed result.
[0023] Specifically, inventors have discovered that the trace,
along which the abrasive grain passes, tends to be formed as the
island (peak) when the surface is processed by the
hydrosilicofluoric acid (which may be referred to as hydrofluosilic
acid or hexafluorosilicic acid) after polishing by the polishing
material containing the free abrasive grain.
[0024] Although this mechanism is not clear, the load in the
polishing step by the free abrasive grain is applied to the surface
of the glass substrate. Consequently, the network of Si--O is
(systematically and) structurally changed, and nonuniformity occurs
in the remaining stress distribution by the structural change.
[0025] As a result, the etching rate due to the hydrosilicofluoric
acid becomes slow in the portion having relatively high remaining
distortion (namely, a trace portion along which the free agrasive
grain passes). This is assumed to be the above-mentioned
mechanism.
[0026] An application is previously filed on the basis of this
analyzed result in Japanese Patent Application No. H10-233261.
[0027] It has been found out that the projection height can be
reduced, and the projection density can be reduced by heating the
glass substrate before processing the surface by the
hydrosilicofluoric acid in addition to the above-mentioned analyzed
result. Thereby, this invention has been completed.
[0028] (First Invention)
[0029] In a method of manufacturing a glass substrate for a
magnetic recording medium for forming a predetermined roughness
according the first invention, a principal surface of the glass
substrate is precisely polished by the use of polishing material
containing free abrasive grain.
[0030] Thereby, remaining stress distribution for a portion of a
polishing trace due to the free abrasive grain is generated on the
surface of the glass substrate.
[0031] Subsequently, a surface process is performed for at least
the principal surface of the glass substrate by the use of
hydrosilicofluoric acid.
[0032] Thereby, a portion having relatively high remaining
distortion in the generated remaining stress distribution is
decided as an island portion.
[0033] In this case, the glass substrate is heated after precisely
polishing before performing the surface process by the use of the
hydrosilicofluoric acid.
[0034] (Second Invention)
[0035] In a method of manufacturing a glass substrate for a
magnetic recording medium for forming a predetermined roughness
according the second invention, a principal surface of the glass
substrate is precisely polished by the use of polishing material
containing free abrasive grain.
[0036] Thereby, remaining stress distribution for a portion of a
polishing trace due to the free abrasive grain is generated on the
surface of the glass substrate.
[0037] Subsequently, a chemical strengthening (which may be
referred to as chemical reinforcement process is performed for at
least the principal surface of the glass substrate by the use of
hydrosilicofluoric acid.
[0038] Thereby, a portion having relatively high remaining
distortion In the generated remaining stress distribution is
decided as an island portion.
[0039] In this case, the glass substrate is heated by dipping the
glass substrate in heated solvent after precisely polishing before
chemically strengthening or reinforcing the surface.
[0040] (Third Invention)
[0041] The chemical surface process comprises either one of an
etching process by the use of solution containing hydrofluoric
acid, solution containing hydrosilicofluoric acid, and alkali
solution in the second invention.
[0042] (Fourth Invention)
[0043] Heating temperature in the heating process step falls within
the range between 30.degree. C. and 180.degree. C. in any one the
first invention through the third invention.
[0044] (Fifth Invention)
[0045] The heating process is carried out by the use of at least
one selected the group consisting of hot water, heated sulfuric
acid, heated glycerin, and heated phosphoric acid in any one of the
first invention through the fourth invention.
[0046] (Sixth Invention)
[0047] The glass substrate contains at least alkali metal oxide and
alkali earth oxide, and the content of the alkali earth oxide is
not exceeding 3 mol % in any one of the first invention through the
fifth invention.
[0048] (Seventh Invention)
[0049] The glass constituting the glass substrate contains
SiO.sub.2 between 58 and 75 weight %, Al.sub.2O.sub.3 between 5 and
23 weight %, Li.sub.2O between 3 and 10 weight %, and Na.sub.2O
between 4 and 13 weight % as main components in the sixth
invention.
[0050] (Eighth Invention)
[0051] The glass contains SiO.sub.2 between 62 and 75 weight %,
Al.sub.2O.sub.3 between 5 and 15 weight %, Li.sub.2O between 4 and
10 weight %, Na.sub.2O between 4 and 12 weight %, and ZrO.sub.2
between 5.5 and 15 weight % as main components, and the weight
ratio of Na.sub.2O/ZrO.sub.2 falls within the range between 0.5 and
2.0 while weight ratio of Al.sub.2O.sub.3/ZrO.sub.2 falls within
the range between 0.4 and 2.5 in the seventh invention.
[0052] (Ninth Invention)
[0053] The chemical strengthening process is carried out after the
surface process due to the hydrosilicofluoric acid in any one of
the first invention through the eighth invention.
[0054] (Tenth Invention)
[0055] In a method of manufacturing a magnetic recording medium, at
least a magnetic layer is formed on the principal surface of the
glass substrate manufactured by the method claimed in any one of
the first invention through the ninth invention.
[0056] (Eleventh Invention)
[0057] In a glass substrate for a magnetic recording medium for use
in a load/unload system, the glass substrate has a principal
surface, and surface roughness of the principal surface is
specified by Rmax=3-15 nm, Ra=0.2-2.5 nm, and Rmax/Ra=3-15.
[0058] In this event, Ra is representative of a center-line mean
roughness, and Rmax is defined as a maximum height representative
of a difference between a highest point and a lowest point.
[0059] (Twelfth Invention)
[0060] In a glass substrate for a magnetic recording medium for use
in a load/unload system, the glass substrate has a principal
surface, and surface roughness of the principal surface is
specified by Rp=1-7 nm, Ra=0.2-2.5 nm, and Rp/Ra=1-15.
[0061] In this case, Ra is representative of a center-line mean
roughness, and Rp is representative of a maximum height of a
highest point.
[0062] (Thirteenth Invention)
[0063] In a magnetic recording medium having at least a magnetic
layer on a glass substrate for use in a load/unload system, the
glass substrate has a principal surface, and surface roughness of
the principal surface is specified by Rmax=3-15 nm, Ra=0.2-2.5 nm,
and Rmax/Ra=3-15.
[0064] In this event, Ra is representative of a center-line mean
roughness, and Rmax is defined as a maximum height representative
of a difference between a highest point and a lowest point.
[0065] (Fourteenth Invention)
[0066] In a magnetic recording medium having at least a magnetic
layer on a glass substrate for use in a load/unload system, the
glass substrate has a principal surface, and surface roughness of
the principal surface is specified by Rp=1-7 nm, Ra=0.2-2.5 nm, and
Rp/Ra=1-15.
[0067] In this event, Ra is representative of a center-line mean
roughness, and Rp is representative of a maximum height of a
highest point.
[0068] According to the first invention, the glass substrate is
heated after the polishing process due to the free abrasive grain
before performing the surface process by the use of the
hydrosilicofluoric acid.
[0069] Thereby, the remaining distortion, which is generated on the
surface of the glass substrate by the polishing process due to the
free abrasive grain, is relieved.
[0070] Consequently, the projection height can be reduced in
comparison with such a case that the heating process is not carried
out. Further, the projection density, the variation of the
projection heights, and the variation of the projections can be
reduced.
[0071] Therefore, the magnetic recording medium, which is suitable
for the load/unload system, can be stably manufactured by
controlling the projection height and the projection density, and
the variation of the projection heights. In such a load/unload
system, the projection height and the projection density, and the
variation of the projection heights fall within the predetermined
range.
[0072] Further, the magnetic recording medium, which satisfies the
high CSS durability characteristic and which is suitable for the
CSS system, can be stably manufactured.
[0073] As mentioned above, inventors have discovered that the
trace, along which the abrasive grain passes, tends to be formed as
the island (peak) when the surface is processed by the
hydrosilicofluoric acid after polishing by the polishing material
containing the free abrasive grain.
[0074] Although this mechanism is not clear, the load in the
polishing step by the free abrasive grain is applied to the surface
of the glass substrate. Consequently, the network of Si--O is
(systematically and) structurally changed, and nonuniformity occurs
in the remaining stress distribution by the structural change.
Herein, the nonuniformity means that the remaining distortion of
the portion of the trace, along which the free abrasive grain
passes, becomes large in comparison with the remaining distortion
of the peripheral portion of the trace.
[0075] As a result, the etching rate due to the hydrosilicofluoric
acid becomes slow in the portion having relatively high remaining
distortion (namely, a trace portion along which the free agrasive
grain passes). This is assumed to be the above-mentioned
mechanism.
[0076] Moreover, the heating process is carried out before
performing the surface process by the use of the hydrosilicofluoric
acid. Thereby, the remaining distortion is relieved, and the
difference of the etching rate caused by the remaining distortion
becomes small.
[0077] Consequently, the projection density and the variation of
the projection heights, which give an affect for flying travel of
the magnetic head, are reduced in comparison with such a case (see
FIG. 1) that the heating process is not carried out, and further, a
fine projection having a low projection height is formed, as
illustrated in FIG. 2.
[0078] In this case, when process conditions (concentration,
temperature, dipping time) due to the hydrosilicofluoric acid are
changed, the projection height can be controlled to a certain
degree. However, the projection density can not be controlled.
[0079] Therefore, it is preferable to perform the heating process
before the process due to the hydrosilicofluoric acid like this
invention compared to this method because the projection height and
density can stably and accurately controlled for the low flying
travel of the magnetic head.
[0080] Namely, the remaining distortion due to the free abrasive
grain formed on the surface of the glass substrate is relieved by
the heating process before the process due to the
hydrosilicofluoric acid.
[0081] Consequently, the projection is not formed in the region
having a relatively small remaining distortion due to the polishing
step.
[0082] On the other hand, the remaining distortion becomes small,
and the height of the formed projection becomes small in the region
having a relatively high remaining distortion. The projection
density can be changed by controlling the condition of the heating
process.
[0083] The method of the heating process in the first invention is
not particularly restricted. There are exemplified a method in
which the glass substrate is dipped in the heated solvent, a method
in which the glass substrate is subjected in atmosphere (air,
vacuum) heated by an oven and a method in which a light ray (for
example, wavelength (infrared rays and ultraviolet rays) which
absorbs for the glass substrate) is irradiated for the glass
substrate as the heating process.
[0084] Among them, the method, in which the glass substrate is
dipped in the heated solvent, and particles for the glass substrate
can be removed at the same time with the heating process, is
superior from the viewpoint of quality and stability.
[0085] This is because when the particles exist on the surface of
the glass substrate during the process due to the
hydrosilicofluoric acid, only the portion of the particles is left
without the etching to form the projection, and the surface
roughness is not reduced on the whole.
[0086] Further, the remaining polishing material causes to form the
projection. Therefore, it is desirable that the remaining polishing
material can be simultanousely removed by the solvent. Such solvent
includes sulfuric acid and organic acid (phosphoric acid, formic
acid, acetic acid, propionic acid, acrylic acid, oxalic acid,
glycolic acid, glyceric acid, lactic acid, gluconic acid, succinic
acid, adipic acid, and the like).
[0087] Further, the hydrosilicofluoric acid used during processing
the surface of the glass substrate of this invention has weak
etching force (slow etching rate) as compared to hydrofluoric acid
solution which contains hydrofluoric acid or potassium fluoride and
which is conventionally used as the etching liquid.
[0088] Consequently, it is possible to precisely control the
surface roughness. Silicofluoric acid (H.sub.2SiF.sub.6) is
typically used as the hydrosilicofluoric acid.
[0089] The hydrosilicofluoric acid process may contain the other
acid (hydrofluoric acid, sulfuric acid, hydrochloric acid, nitric
acid) and commercially available washing materiel (natural washing
material, surfactant, alkali washing material) with fine quantity
in order to enhance the etching (washing) effect.
[0090] Further, the process condition of the hydrosilicofluoric
acid is mainly determined in dependency upon concentration of the
hydrosilicofluoric acid, immersing time into the hydrosilicofluoric
acid, temperature of the hydrosilicofluoric acid.
[0091] The hydrosilicofluoric acid is formed by dissolving the
silicofluoric acid into water. The concentration of the
hydrosilicofluoric acid indicates the concentration in which the
silicofluoric acid is dissolved in the water.
[0092] The concentration and the temperature of the
hydrosilicofluoric acid relate with the etching rate (the specific
range will be explained later) while the immersing time into the
hydrosilicofluoric acid relates with the obtained roughness and the
process time of the step.
[0093] The process condition of the above-mentioned
hydrosilicofluoric acid is suitably adjusted based upon the
roughness of the formed surface roughness. However, it is
preferable from controllability of the surface roughness that the
immersing time into the hydrosilicofluoric acid falls within the
range between 50 and 600 sec and the temperature of the
hydrosilicofluoric acid falls within the range between 15.degree.
C. and 60.degree. C.
[0094] The concentration of the hydrosilicofluoric acid preferably
falls within the range between 0.15 and 3.0 weight %.
[0095] When the concentration of the hydrosilicofluoric acid is not
exceeding 0.15 weight %, the etching effect or the washing effect
for the glass substrate is lowered. Consequently, the desired
surface roughness can not be obtained.
[0096] When the concentration exceeds 3.0 weight %, it is difficult
to control the surface roughness with high accuracy because the
etching rate became quick. Consequently, the glass substrate for
the magnetic recording medium having stable quality can not be
obtained. This is not preferable.
[0097] Inventors have found out that the surface roughness of the
glass substrate before the surface process gives large effect for
the height distribution (variation) of the islands (peaks) on the
substrate surface which is finally obtained to stably manufacture
the glass substrate for the magnetic disk of this invention which
is required to be controlled the surface roughness with high
accuracy.
[0098] Inventors have enthusiastically researched this case. As a
result, it is preferable that the surface of the glass substrate
before the surface process is in the mirror state. Specifically, it
is found out that Ra falls within the range between 0.1 and 1.0 nm,
more preferably, that Ra falls within the range between 0.1 and 1.0
nm, and Rmax falls within the range between 1 and 20 nm.
[0099] According to the second invention, the glass substrate is
heated by dipping the glass substrate in heated solvent after
precisely polishing before chemically strengthening the
surface.
[0100] Thereby, the magnetic recording medium, which can realize
the glide height of the 1.2.mu. inch or less and realize the high
electro-magnetic conversion characteristic, can be stably
manufactured from the same reason as the first invention.
[0101] In this case, the etching material used for the chemical
surface process is not particularly restricted. There are
exemplified a method (dipping, spraying and the like) which
utilizes etching liquid, such as, hydrofluoric acid,
hydrosilicofluoric acid, hydrofluoric acid-fluoride mixed solution,
hydrofluoric acid-inorganic acid mixed solution, and hydrofluoric
acid-organic mixed solution, and a method in which the etching
process is performed by contacting vapor of the hydrofluoric acid
with the surface of the glass substrate.
[0102] As mentioned before, the chemical surface process or the
surface process due to the hydrosilicofluoric acid is carried out
such that the portion having relatively high remaining distortion
in the remaining stress distribution generated for the portion of
the trace due to the free abrasive grain in the polishing process
of the glass substrate is decided as the island portion.
[0103] This invention positively utilizes such phenomenon, and
thereby, the predetermined surface roughness can be obtained.
Further, the predetermined surface roughness can be realized by
performing the heating process. Although this mechanism has been
described before, the other mechanism, which may occur this
phenomenon, is naturally within the scope of this invention.
[0104] According to the third invention, the glass substrate is
dipped in the heated solvent of the solution containing
hydrofluoric acid, the solution containing hydrosilicofluoric acid,
and the alkali solution in the second invention. This method can
remove the particles for the glass substrate at the same time with
the heating process, and is superior in the quality and stability
from the same reason as the above.
[0105] In this case, cerium oxide (CeO.sub.2), alumina
(Al.sub.2O.sub.3), colloidal silica (SiO.sub.2), iron oxide
(Fe.sub.2O.sub.3), chromium oxide (Cr.sub.2O.sub.3), zirconium
oxide (ZrO.sub.2), titanium oxide (TiO.sub.2) are exemplified as
the free abrasive grain use in this invention.
[0106] A particle diameter (size) of the free abrasive grain can be
suitably adjusted in dependency upon a desired surface roughness.
An average particle diameter preferably falls within the range
between 0.02 .mu.m and 3.0 .mu.m.
[0107] Preferred density of the island portions and a tip shape of
the island portion, which contacts with the magnetic recording
medium, can be obtained by selecting such a range of the particle
diameter. Consequently, higher CSS durability can be obtained in
the substrate for the magnetic recording medium.
[0108] When the particle diameter is not exceeding 0.02 .mu.m,
aggregation of the polishing material readily occurs, and the
number of the remaining substances after the washing step becomes
high. This is not preferable. On the other hand, when the particle
diameter exceeds 3.0 .mu.m, the roughness after the etching process
becomes excessively large. This is not also desirable.
[0109] According to the fourth invention, the heating temperature
in the heating process step preferably falls within the range
between 30.degree. C. and 180.degree. C.
[0110] When the heating temperature is not exceeding 30.degree. C.,
the heating process time becomes long, and production tact is
extended. This is not preferable. On the other hand, when the
heating temperature exceeds 180.degree. C., the solvent, which
endures the heating process of long time, is limited, and a large
equipment is necessary to perform the process. This is not also
desirable.
[0111] Further preferred range of the heating temperature falls
within the range between 60.degree. C. and 120.degree. C. For
example, the heating process time may be suitably adjusted in
accordance with the kinds of used solvent in the case of the
solvent. Specifically, the heating process time may fall within the
range between 30 and 600 sec.
[0112] According to the fifth invention, the heating process is
preferably carried out by the use of at least one selected from the
group consisting of hot water, heated sulfuric acid, heated
glycerin, and heated phosphoric acid. Among them, the heated
sulfuric acid is desirable because the variation of the surface
roughness becomes small. Namely, contaminants attached to the glass
substrate can simultaneously removed during the process due to the
heated sulfuric acid.
[0113] The concentration falls within the range between 5 wt % and
99 wt %, the heating temperature falls within the range between
30.degree. C. and 180.degree. C., and the process time falls within
the range between 30 sec and 600 sec as the conditions processed by
the heated sulfuric acid.
[0114] In this event, the concentration of the used sulfuric acid
is preferably higher, and dense sulfuric acid having 75 volume % or
more, and more preferably, 95 volume % or more, is desirable.
[0115] Further, the contaminants attached to the glass substrate
can be also removed by the heated phosphoric acid.
[0116] The heating temperature falls within the range between
30.degree. C. and 90.degree. C., the process time falls within the
range between 60 sec and 600 sec, and the concentration falls
within the range between 0.1% and 50% as the conditions processed
by the heated phosphoric acid.
[0117] Alternatively, organic acid other than the phosphoric acid
may be used. The phosphoric acid is superior in operability in
comparison with the sulfuric acid. Further, the sulfuric acid is
superior in an effect for reducing the roughness in comparison with
the phosphoric acid.
[0118] According to the sixth invention, the glass substrate
preferably contains at least alkali metal oxide and alkali earth
oxide, and the content of the alkali earth oxide is not exceeding 3
mol %.
[0119] Namely, it is assumed that an exchange reaction occurs
between H.sup.+ contained in the water and alkali ion (Na.sup.+,
Li.sup.+) contained in the glass in the polishing step due to the
free abrasive grain of the glass substrate surface.
[0120] By this exchange reaction, a hydration layer, which is
readily etched, is formed. In the hydration layer, OH was attached
to Si or Al which forms a network of the glass by the exchange
reaction. It is assumed that the stress distribution was formed for
the hydration layer in accordance with the stress distribution
applied by the free abrasive grain, and the roughness was formed in
dependency upon the etching rate.
[0121] Herein, it is to be noted that the etching rate is small at
a portion having large stress while the etching rate is large at a
portion having a small stress.
[0122] From such a mechanism, at least the alkali metal oxide is
necessary to form the hydration layer in the glass substrate.
Further, it is required that the content of the alkali earth oxide,
which prevents the exchange reaction of the alkali ions for forming
the hydration layer, is not exceeding 3 mol % (not exceeding 2.4
weight %), as disclosed in Japanese Patent Application No.
H11-233209.
[0123] The glass substrate of the sixth invention preferably
contains SiO.sub.2 between 58 and 75 weight %, Al.sub.2O.sub.3
between 5 and 23 weight %, Li.sub.2O between 3 and 10 weight %, and
Na.sub.2O between 4 and 13 weight % as main components like the
seventh invention.
[0124] Further, it is desirable that the glass does not contain
alkali earth metal oxide, such as, CaO or MgO to remarkably form
the island (peak) by the mechanism mentioned above.
[0125] In particular, it is preferable in the eighth invention that
the glass substrate is an aluminosilicate glass which contains
62-75 weight % of SiO.sub.2, 5-15 weight % of Al.sub.2 O.sub.3,
4-10 weight % of Li.sub.2O, 4-12 weight % of Na.sub.2O, and 5.5-15
weight % of ZrO.sub.2 as the main components, the weight ratio of
Na.sub.2O /ZrO2 falls within the range between 0.5 and 2.0, and the
weight ratio of Al.sub.2O.sub.3/ZrO.sub.2 falls within the range
between 0.4 and 2.5.
[0126] The transverse bending strength is increased, the
compressive stress layer becomes deep, the Knoop hardness is
excellent, and the controllability of the etching in the surface
process due to the hydrosilicofluoric acid is excessively superior
by chemically chemically strengthening the aluminosilicate
glass.
[0127] Therefore, such an aluminosilicate glass is desirable.
Herein, it is to be noted that N5 manufactured by HOYA CORPORATION
is representative of the above-mentioned aluminosilicate glass.
[0128] Further, the surface process due to the above
hydrosilicofluoric acid is performed twice. Moreover, the different
hydrosilicofluoric acid concentrations are used in the respective
steps. Thereby, the fine surface roughness on the substrate surface
can be controlled.
[0129] It is preferable that the chemical strengthening process is
carried out after chemical surface process or the surface process
due to the hydrosilicofluoric acid (the ninth invention). Herein,
the known chemical strengthening methods are used as the above
chemical strengthening method without limitation.
[0130] For example, the low-temperature ion exchange method, in
which the ion exchange is performed in the region which does not
exceed the transition point temperature from the viewpoint of the
glass transition point, is preferable. A fused salt used for the
chemical strengthening includes potassium nitrate, sodium nitrate,
nitrate mixed with them.
[0131] When the above surface process due to the hydrosilicofluoric
acid is performed immediately after the glass substrate surface is
chemically strengthened, the remaining distortion formed by the
free abrasive grains on the glass substrate surface is buried in
the stress of the chemical strengthening by chemically
strengthening. This is undesirable because the surface roughness
can not be controlled.
[0132] However, the same result as the above-mentioned case can be
obtained by interposing the polishing processing step due to the
free abrasive grains between (immediately after the surface process
due to the hydrosilicofluoric acid) the chemical strengthening
process step and the surface process due to the hydrosilicofluoric
acid as the chemical strengthening step .fwdarw. the polishing step
due to the free abrasive grains .fwdarw. the surface process due to
the hydrosilicofluoric acid.
[0133] According to the tenth invention, at least the magnetic
layer is formed on the principal surface of the glass substrate
manufactured by the method of manufacturing the glass substrate for
the magnetic recording medium, such as, the above-mentioned
magnetic disk.
[0134] Thereby, the magnetic recording medium, such as, the
magnetic disk satisfies the high electromagnetic conversion
characteristic and the high CSS durability characteristic.
[0135] Rmax, Ra, Rp and Rq are measured by the use of the
interatomic force microscope (AMF), and are defined by JIS standard
(JIS B 0601).
[0136] In this case, Rmax is defined as a maximum height
representative of a difference between a highest point and a lowest
point. Ra is representative of a center-line mean roughness (an
average of an absolute value of deviation between a center line and
a measuring line).
[0137] Rp is representative of a maximum height of a highest point
(a distance between an average line and a highest point). Rq is
representative of a root mean square roughness (a root of an
average square value of deviation between a center line and a
measuring line).
[0138] Herein, this roughness can be determined by suitably setting
a measuring region. Meanwhile, it is to be noted that a roughness
data of the following examples corresponds to a data of a region of
5 .mu.m.quadrature..
[0139] When the roughness exceeds an upper value of Rmax and Rp,
the head flying height becomes high. This is not preferable from
the viewpoint of the high recording/reproducing density.
[0140] When the roughness exceeds an upper value of Rmax/Ra and
Rp/Ra, the head crush or the thermal asperity readily takes place.
This is not desirable. When the roughness is not exceeding a lower
value of Rmax, Rp, Rmax/Ra, and Rp/Ra, the head stiction may occur
and, it is impossible to manufacture the glass substrate. This is
not preferable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0141] FIG. 1 is a schematic cross sectional view showing
projections in a conventional glass substrate for a magnetic
disk;
[0142] FIG. 2 is a schematic cross sectional view showing
projections in a glass substrate for a magnetic disk according to
an embodiment of this invention; and
[0143] FIG. 3 is a schematic view showing a magnetic disk according
to an embodiment of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
EXAMPLE 1
[0144] As illustrated in FIG. 1, a seed layer 2, an underlying
layer 3, a magnetic layer 4, a protection (protective) layer 5 and
a lubricant layer 6 are successively formed on a glass substrate 1
in a magnetic disk according to this embodiment.
[0145] The glass substrate 1 is an aluminosilicate glass which has
composition of 63.5 weight % of SiO.sub.2, 14.2 weight % of
Al.sub.2O.sub.3, 10.4 weight % of Na.sub.2O, 5.4 weight % of
Li.sub.2O and 6.0 weight % of ZrO.sub.2 ,0.4 weight % of
Sb.sub.2O.sub.3, and 0.1 weight % of As.sub.2O.sub.3, and is
processed to the disk shape having outer diameter (65 mm
.phi.),hole diameter(20 mm .phi.) of a central portion and a
thickness of 0.635 nm.
[0146] After the both principle surfaces, end surfaces and
chamfered portions are precisely polished, are thermally processed
by dipping into heated solvent (specifically, sulfuric acid), and
are processed the surfaces by the use of hydrosilicofluoric
acid.
[0147] Consequently, the surface roughness of the both principle
surfaces was specified by Ra=0.44 nm, Rmax=4.43 nm, Rp=2.75 nm,
Rmax/Ra=10.1, Rp/Ra=6.25, Rq=0.55 nm.
[0148] The seed layer 2 is a NiAl (Ni: 50 at %, Al: 50 at %) film
having the thickness of 40 nm. The seed layer 2 has small crystal
grain diameter and is superior in uniformity. In consequence, each
of the underlying layer 3 and the magnetic layer 4 formed thereon
has fine crystal grain diameter. Thereby, the seed layer 2 serves
to reduce noise.
[0149] As the seed layer 2, NiAlRu, NiAlNd, NiAlW, NiAlTa, NiAlHf,
NiAlMo,NiAlCr, NiAlZr, NiAlNb, CrTi, FeAl, and FeCo, in which the
other elements are added in addition to the NiAl other than the
above-mentioned NiAl, are exemplified.
[0150] The underlying layer 3 is a CrMo (Cr: 94 at %, Mo: 6 at %)
film having the film thickness of 25 nm. In the underlying film 3,
it is desirable that difference of crystal lattice distance of the
magnetic layer 4 formed thereon is reduced as possible, and the
underlying layer 3 serves to improve coercive force.
[0151] Cr and CrV are exemplified other than the above-mentioned
CrMo as the underlying layer 3. It is preferable to match with the
lattice distance of the seed layer 2 because the crystal growth
becomes excellent and the electromagnetic conversion characteristic
also becomes superior.
[0152] In this event, the underlying layer 3 is not restricted to a
single layer, and may be a multi-structure in which the same or the
different layers are laminated. For example, a multi-layer
underlying layer, such as, Cr/CrMo, Cr/CrV, and CrV/CrV are
exemplified.
[0153] The magnetic layer is a CoPtCrTa (Co: 75 at %, Cr: 16 at %,
Pt: 5 at %, Ta: 3 at %) film. Herein, it is to be noted that
material of the magnetic layer of the magnetic disk of this
invention is not particularly restricted. Specifically, a magnetic
thin-film, such as, CoPt, CoCr, CoNiCr, CoCrTa, CoPtCr, CoNiPt,
CoNiCrPt, CoNiCrTa, and CoCrTaPtNb, which contains Co as a main
component, is exemplified as the magnetic layer 4.
[0154] Alternatively, a multi-structure (for example,
CoCrPtTa/CrMo/CoCrPtTa), which is formed by dividing the magnetic
layer with a non-magnetic film (for example, Cr, CrMo, CrV) to
reduce the noise, may be used as the magnetic layer 4.
[0155] Further, the magnetic layer 4 may be granular having such a
structure that magnetic particles, such as, Fe, Co, FeCo, and
CoNiPt, are dispersed in a non-magnetic film consisting of
material, such as, ferrite based material, iron-rare earth-based
material or SiO.sub.2, BN other than the above-mentioned Co based
material.
[0156] Moreover, the magnetic layer 4 may be a recording form of an
in-plane type or a vertical type. The protection layer 5 is a
hydrogenation carbon (H: 30 at %) film having the film thickness of
10 nm. The protection film 5 achieves corrosion resistance and
resistance to abrasion of the magnetic layer 4.
[0157] As the protection layer 5, carbon, nitrogen carbon, hydrogen
nitrogen carbon, fluorine carbon, Cr, and SiO.sub.2 are exemplified
other than the above-mentioned hydrogenation carbon.
[0158] The lubricant layer 6 is a liquid lubricant film consisting
of perfluoropolyether having the film thickness of 1 nm. The
lubricant layer 6 achieves resistance to abrasion.
[0159] In addition, fluorocarbon based liquid lubricant material or
a lubricant material consisting of alkali metal salt of sulfonic
acid may be used as the material of the lubricant layer 6 other
than the above-mentioned perfluoropolyether.
[0160] In this event, if the protection layer 5 has function as a
solid lubricant material, the lubricant layer 6 can be omitted.
[0161] Hereinafter, description will be made about a method of
manufacturing the above-mentioned magnetic disk and glass substrate
for use in the magnetic disk.
Step of Producing Glass Substrate for Magnetic Disk
[0162] (1) Roughing Step:
[0163] First, a glass substrate of an aluminosilicate glass was cut
into a disc-shape having a diameter of 66 mm and a thickness of 3
mm by a grinding stone from a sheet glass formed by the down draw
method. The glass substrate was ground by a relatively rough
diamond grindstone to obtain the glass substrate having the
diameter of 66 mm and the thickness of 1.5 mm.
[0164] In this event, the glass substrate may be cut into the
disc-shape in the same manner as the above from the sheet glass
formed by the float method instead of the above-mentioned down draw
method.
[0165] A chemically strengthened glass was used as the
above-mentioned aluminosilicate glass. The chemically strengthened
glass contains 63.5 weight % of SiO.sub.2, 14.2 weight % of
Al.sub.2O.sub.3, 10.4 weight % of Na.sub.2O, 5.4 weight % of
Li.sub.2O and 6.0 weight % of ZrO.sub.2, 0.4 weight % of
Sb.sub.2O.sub.3, and 0.1 weight % of As.sub.2O.sub.3.
[0166] Subsequently, the both principal surfaces of the glass
substrate were ground by a diamond grindstone having grains smaller
than those of the above-mentioned grindstone at every one
surface.
[0167] In this case, a load was set to the extent of 100 Kg.
Thereby, the both principal surfaces of the glass substrate were
ground into a surface roughness Rmax of about 10 .mu.m.
[0168] Next, an opening was formed at a center portion of the glass
substrate by using a cylindrical grindstone. Further, the outer
side end surface was ground to a diameter of 65 mm.
[0169] Thereafter, the outer and the inner end surfaces were
chamfered. In this case, the end surface (the side surface and the
chamfered portion) of the glass substrate had a surface roughness
Rmax of about 4 .mu.m.
[0170] (2) Mirror Finishing Step of the End Surface:
[0171] Subsequently, the glass substrate was polished by the use of
a brush polishing by rotating the glass substrate so that the
surface roughness of the end surface portion (the angular portion,
the side surface and the chamfered portion) of the glass substrate
is set to about 1 .mu.m by Rmax and to about 0.3 .mu.m by Ra. The
mirror finishing step is effective for preventing a film defect
which is caused by dusts which are attached to the principal
surface of the glass substrate.
[0172] In this event, the dusts are generally generated from the
end surface of the glass substrate when the glass substrate is
transferred or when the glass substrate is cleaned. The glass
substrate was washed with water after the above-mentioned mirror
finishing step.
[0173] (3) Lapping Step:
[0174] The lapping step was performed for the glass substrate to
improve dimension and shape accuracy. The lapping step was carried
out by using the known lapping apparatus. In this case, the lapping
step was conducted two times by changing grain degree from #400 to
#1000.
[0175] Specifically, the lapping was performed for the both
principal surfaces of the glass substrates which were contained in
a carrier so that the principal surfaces had a surface accuracy of
0-1 .mu.m and the surface roughness (Rmax) of about 6 .mu.m.
[0176] In this event, the lapping was carried out by rotating an
inner gear and an outer gear by the use of alumina grains having a
grain degree of #400 in the condition that the load L was kept at
about 100 Kg.
[0177] Next, the lapping was performed by changing the grain degree
of the alumina grain into #1000. In this case, the surface
roughness (Rmax) was set to about 2 .mu.m. Subsequently, the glass
substrate was successively immersed in washing units of natural
detergent and water to be washed after the lapping step was
completed.
[0178] (4) First Polishing Step:
[0179] Next, a first polishing step was performed by the use of a
polishing apparatus to remove a defect and a distortion remaining
in the above-mentioned lapping process. Specifically, a hard
polisher (which may be a cerium pad LP66 made by Lodes) was used as
polisher. In this case, the first polishing was performed under the
following polishing condition.
[0180] Polishing liquid: oxide cerium (grain size of 1.3 .mu.m)
(free abrasive grain)+water
[0181] Load: 80-100 g/cm.sup.2
[0182] Polishing time: 30-50 minutes
[0183] Removing amount: 35-45 .mu.m
[0184] Revolution of lower surface plate: 40 rpm
[0185] Revolution of upper surface plate: 35 rpm
[0186] Revolution of inner gear: 14 rpm
[0187] Revolution of outer gear: 29 rpm
[0188] The glass substrate was washed by being successively dipped
in washing units of natural detergent, pure water, pure water, IPA
(isopropyl alcohol), IPA (vapor drying) after the above polishing
step. Herein, supersonic wave was applied to each washing unit.
[0189] In this event, the washing step may be omitted if a
polishing liquid in the subsequent second polishing step is the
same as the above case.
[0190] Further, the hard polisher used in the first polishing step
is not particularly restricted, and may be suitably selected in
dependency upon the surface roughness and end portion shape of the
substrate as the target (or the goal)
[0191] (5) Second Polishing Step (Final Polishing Step):
[0192] Next, a second polishing was conducted by changing the
above-mentioned hard polisher into a soft polisher (Kanebou N7519)
by using the polishing apparatus used in the first polishing
step.
[0193] The polishing condition is similar to the first polishing
step except for polishing liquid of oxide cerium (grain size of 0.8
.mu.m) (free abrasive grain)+water, the load of 80-100 g/cm.sup.2,
the polishing time of 9-15 minutes and the removing amount of 3-5
.mu.m.
[0194] The surface roughness of the glass substrate obtained in
this second polishing step was measured by the use of the
interatomic force microscope (AFM). Consequently, Ra was equal to
0.4 nm while Rmax was equal to 9.3 nm. Herein, it is to be noted
that the soft polisher used in the second polishing step is not
particularly restricted.
[0195] In this event, it is desirable to use polisher having
relatively small hardness to form a projection formed via the
subsequent surface processing step to an island shape. Herein, the
hardness (Asker C) of the polisher may preferably be 60 or less,
and more preferably, 55 or less.
[0196] (6) Heat Processing Step:
[0197] A heating process was carried out by dipping the glass
substrate after the second polishing step into sulfuric acid
(temperature: 100.degree. C..times.5 min) having concentration of
96 weight % or more.
[0198] (7) Surface Processing Step Due to Hydrosilicofluoric Acid
(Washing Step)
[0199] The glass substrate was successively immersed in each
processing (washing) unit of hydrosilicofluoric acid
(concentration: 0.35%, temperature: 45.degree. C., immersing time:
150 sec), hydrosilicofluoric acid (concentration: 0.28%,
temperature: 45.degree. C., immersing time: 200 sec) to be
processed (washed) the surface therein after the second polishing
step. In this case, a supersonic wave was applied to each of the
processing (washing) units.
[0200] The glass substrate was washed by being successively dipped
in each washing unit of natural detergent, pure water, pure water,
IPA (isopropyl alcohol), IPA (vapor drying) after the above surface
processing step. Herein, supersonic wave was applied to each
washing unit except for an IPA vapor unit used in the IPA (vapor
drying) step.
[0201] (7) Chemical Strengthening Step:
[0202] Next, a chemical strengthening step was performed for the
glass substrate after the grinding, the surface polishing
processing (washing) and the washing step were completed.
[0203] First, a chemical strengthening salt was prepared by mixing
potassium nitrate (60%) with sodium nitrate (40%). The chemical
strengthening salt was heated up to 400.degree. C. The glass
substrate which was washed and preheated to 300.degree. C. was
dipped in the chemical strengthening salt for 3 hours.
[0204] The chemical strengthening step was carried out in a holder
so that the entire surface of the glass substrate was chemically
strengthened with a plurality of glass substrates retained at the
end surface in the holder.
[0205] Under this circumstances, lithium ions and sodium ions on a
surface layer of the glass substrate were replaced by sodium ions
and potassium ions in the chemical strengthening salt by dipping
each glass substrate in the chemical strengthening salt. Thus, the
glass substrate was chemically strengthened.
[0206] A compressive stress layer formed in the surface layer of
the glass substrate had a thickness of about 100 to 200 .mu.m.
Next, the chemically strengthened glass substrate was dipped in a
water tank of 20.degree. C., quickly cooled and retained for 10
minutes.
[0207] (8) Washing Step:
[0208] Subsequently, the cooled glass substrate was dipped in a
sulfuric acid heated up to 40.degree. C., and was washed in the
condition that the supersonic wave was applied. The surface of the
glass substrate obtained thus was inspected. As a result, no
contaminant was detected.
[0209] In this event, the surface roughness of the principal
surface of the glass substrate after the above-mentioned washing
step was measured by the use of the interatomic force microscope
(AFM).
[0210] As a result, the surface roughness was specified by Ra=0.44
nm, Rmax4.43 nm, Rp=2.75 nm, Rmax/Ra=10.1, Rp/Ra=6.25, and Rq=0.55
nm.
[0211] In this case, Ra is representative of the center-line mean
roughness (defined in Japanese Industrial Standard JIS B0601) while
Rmax is defined as a maximum height representative of a difference
between a highest point and a lowest point (defined in Japanese
Industrial Standard JIS B0601).
[0212] Further, observation was made about the surface state of the
principal surface of the glass substrate after the final polishing
step and the surface state of the principal surface of the glass
substrate after the washing step by the AFM.
[0213] Consequently, it was confirmed that islands (peaks) were
formed at a portion of a trace of free abrasive grain in the final
polishing step.
[0214] Particularly, it is assumed that a portion having a
relatively high remaining distortion forms the islands (peaks) in
remaining stress distribution formed on the glass principal surface
by the free abrasive grain.
[0215] Step of Producing Magnetic Disk
[0216] Subsequently, a heat treatment of the glass substrate 1,
deposition of a seed layer 2, deposition of an the underlying layer
3, deposition of a magnetic layer 4 and deposition of the
protection layer 5 were successively carried out for the
above-mentioned glass substrate 1 for the magnetic disk by the use
of the known in-line sputtering apparatus.
[0217] The in-line type sputtering apparatus (not shown) has a
first chamber in which a substrate heater is arranged, a second
chamber in which a NiAl target (Ni: 50 at %, Al: 50 at %), a CrMo
target (Cr: 94 at %, Mo: 6 at %) and a CoCrPtTa target (Co: 75 at
%, Cr: 17 at %, Pt: 5 at %, Ta: 3 at %) are successively arranged,
a third chamber in which a carbon target is arranged, along the
moving direction.
[0218] With such a structure, the glass substrate 1 was introduced
into the first chamber via a load lock chamber. The glass substrate
was successively transferred into the respective chambers by a
desired carrier apparatus at a constant rate to deposit and process
in the following conditions.
[0219] Namely, the substrate was heated to 350.degree. C. for 2
minutes in the first chamber. The NiAl film having the film
thickness of 40 nm as the seed layer 2, the CrMo film having the
film thickness of 25 nm as the underlying layer 3, the CoCrPtTa
film having the film thickness of 27 nm as the magnetic layer 4 are
successively deposited in the second chamber. The hydrogenation
carbon film having the film thickness of 10 nm as the protection
layer 5 is deposited in the third chamber.
[0220] In this case, the sputtering conditions in the second and
third chambers were as follows.
[0221] Namely, the sputtering pressure was 2 mTorr in the second
chamber while the sputtering pressure was 3 mTorr in the third
chamber. An inactive gas of argon was used as the sputtering
atmosphere in the second chamber. A mixed gas in which 8% of
hydrogen is mixed into the inactive gas of argon was used as the
sputtering atmosphere in the third chamber.
[0222] In this event, the sputtering power was 2 kW in the second
chamber while the sputtering power was 3 kW in the third
chamber.
[0223] Subsequently, the substrate having the protection layer 5
was taken out from the in-line sputtering apparatus.
Perfluoropolyether is applied to the surface of the protection
layer 5 by the dipping process. Thereafter, the lubricant layer 6
having the film thickness of 1 nm was formed to obtain the magnetic
disk of the CSS system according to an example 1.
[0224] Evaluation results of the electromagnetic conversion
characteristic and the CSS durability characteristic of the
obtained magnetic disk is represented as follows. In this event,
the magnetic characteristic and the record/reproduce characteristic
were measured, and as a result, an excellent result was obtained.
Specifically, the coercive force was 2300 Oe and the S/N ratio was
20 dB.
[0225] In this case, the coercive force was measured by the use of
the known vibration sample type magnetometer at a maximum external
applying magnetic field of 10 KOe by cutting a sample of 8 mm .phi.
from the manufactured magnetic disk and applying the magnetic field
in the film surface direction.
[0226] Moreover, the record/reproduce characteristic (S/N ratio)
was measured as follows.
[0227] Namely, the obtained magnetic disk and the MR
(magneto-resistive type) head having the flying height of 0.055
.mu.m were used. In this event, the record/reproduce characteristic
in a line recording density of 163 kfcl (line recording density of
163,000 bits per 1 inch) was measured in the condition that a
relative rate between the MR head and the magnetic disk was set to
9.6 m/s.
[0228] Further, medium noise during recording/reproducing signals
was measured by the use of the known spectrum analyzer to calculate
the S/N ratio in the condition that carrier frequency was set to 23
MHz and measuring bandwidth was set to 26 MHz. The MR head, which
was used in the above-mentioned measurement, had a track width of
3.1/2.4 .mu.m and a magnetic head gap length of 0.35/0.28 .mu.m at
write/read sides.
[0229] Further, stiction between the magnetic disk and the magnetic
head did not occur in the CSS durability test of 10 tens thousand
with the rotating rate of the magnetic disk of 4000 rpm using 30%
slider of 3 g load in atmosphere of the room temperature and the
room moisture.
[0230] Moreover, the head crush did not occur. As a result, the
magnetic disk having the high CSS durability characteristic was
obtained.
[0231] Further, the static coefficient of friction between the
magnetic disk and the magnetic head was measured by the use of the
strain gage, and it was 0.6.
[0232] Subsequently, the glide height test was carried out by the
use of the AE sensor. It has been confirmed that no contact was
generated between the head and the medium up to the head flying
quantity of 1.0.mu. inch. That is, the glide height of this disk
was 1.0.mu. inch.
EXAMPLES 2-3
[0233] The glass substrate was manufactured in the same manner as
the example 1 except that hot water (90.degree. C..times.3 min)
(example 2) and heated glycerin (90.degree. C..times.3 min)
(example 2) were used as the solvent in the above-mentioned heating
process step.
[0234] When the surface roughness of the obtained glass substrate
for the magnetic recording medium was measured by the use of the
interatomic force microscope (AFM), the surface roughness was
specified by Ra=0.35 nm, Rmax=4.72 nm, Rp=3.10 nm, Rmax/Ra=13.5,
Rp/Ra=8.86, Rq=0.52 nm (example 2), and, Ra=0.39 nm, Rmax=5.22 nm,
Rp=3.75 nm, Rmax/Ra=13.4, Rp/Ra=9.62, and Rq=0.55 nm (example
3).
[0235] Further, the magnetic recording medium of the CSS system was
fabricated as the same manner as the example 1, and the CSS
durability test, the glide test, and the measurement of the
coefficient of friction were performed. As a result, an excellent
result was obtained.
Comparative Example 1
[0236] Subsequently, the glass substrate for the magnetic recording
medium of the CSS system was manufactured in the same manner as the
example 1 except that the heating process step was not
conducted.
[0237] When the surface roughness of the obtained glass substrate
for the magnetic recording medium was measured by the use of the
interatomic force microscope (AFM), the surface roughness was
specified by Ra=1.00 nm, Rmax=6.73 nm, Rp=4.2 nm, Rmax/Ra=6.73,
Rp/Ra=4.2, Rq=1.18 nm. In comparison with the above-mentioned
example, the surface roughness became rougher, and the projection
density was increased.
[0238] Further, the magnetic recording medium of the CSS system was
fabricated as the same manner as the example 1, and the CSS
durability test, the glide test, and the measurement of the
coefficient of friction were performed. As a result, the glide
height was high (1.2.mu. inch ) compared to the example 1.
EXAMPLES 4-7
Comparative Examples 2-3
[0239] Next, the glass substrate for the magnetic recording medium
of the CSS system was manufactured in the same manner as the
example 1 (sulfuric acid) except that the heating condition
(temperature) in the heating process were changed into 30.degree.
C. (example 4), 60.degree. C. (example 5), 120.degree. C. (example
6), 180.degree. C. (example 7), 28.degree. C. (comparative example
2), and 190.degree. C. (comparative example 3), and the process
time was suitably adjusted.
[0240] In consequence, an effect of the heating process is low, the
projections are formed in the same manner as the comparative
example 1, and the low flying height of the magnetic head is not be
achieved in the case of 28.degree. C. (comparative example 2). This
is not preferable.
[0241] The solvent, which endures the heating process of long time
is and usable, is limited, a large equipment is necessary to
perform the process, and operability is degraded in the case of
190.degree. C. (comparative example 3). This is not desirable.
[0242] Namely, it is found out that from the above results that the
heating temperature in the heating process preferably falls within
the range between 30.degree. C. and 180.degree. C.
EXAMPLE 8
Comparative Examples 4-5
[0243] The magnetic disk was manufactured in the same manner as the
example 1 except that the glass substrate was changed into an
aluminosilicate glass (example 8), a quartz glass (comparative
example 4) and a soldalime glass (comparative example 5), and the
polishing condition for setting the surfaces of these glass
substrates to desired surface roughness and the surface processing
condition due to the hydrosilicofluoric acid were suitably
changed.
[0244] In this case, the aluminisilicate glass used in the
above-mentioned example 8 had composition of 64.0 weight % of
SiO.sub.2, 16.0 weight % of Al.sub.2O.sub.3, 9.0 weight % of
Na.sub.2O, 7.0 weight % of Li.sub.2O and 4.0 weight % of
ZrO.sub.2.
[0245] On the other hand, the solalime glass used in the
above-mentioned comparative example 5 had composition of 72.5
weight % of SiO.sub.2, 15.0 weight % of Na.sub.2O, 1.0 weight % of
Al.sub.2O.sub.3, 9.0 weight % of CaO, and 2.5 weight % of MgO.
[0246] As a result, the surface roughness was specified by Ra=0.49
nm, Rmax=5.68 nm, Rp=3.23 nm, Rmax/Ra=11.6, Rp/Ra=6.59, and Rq=0.52
nm in the example 8. Further, the coefficient of friction was 1.9
and the CSS durability was also excellent.
[0247] However, the surface roughness of the comparative examples 4
and 5 was largely different in comparison with the above examples.
Specifically, the static coefficient of friction was 3 or more and
the superior result could not be obtained in the CSS durability
characteristic.
[0248] Herein, examination has been made about a reason regarding
differences between ways, in which the projection is formed, in
dependency upon the kind of the glass (glass type, glass
composition) from the results of the above-mentioned example and
the comparative examples 4 and 5.
[0249] It is assumed that an exchange reaction occurs between
H.sup.+ contained in the water and alkali ion (Na.sup.+, Li.sup.+)
contained in the glass in the polishing step due to the free
abrasive grain of the glass substrate surface.
[0250] By this exchange reaction, a hydration layer was formed. In
the hydration layer, OH was attached to Si or Al which forms a
network of the glass by the exchange reaction. It is assumed that
the distribution of the thickness of the hydration layer was formed
in accordance with the stress distribution applied by the free
abrasive grain in the hydration, and the roughness was formed in
dependency upon the etching rate.
[0251] Herein, it is to be noted that the etching rate is small at
a portion having large stress while the etching rate is large at a
portion having a small stress.
[0252] The formation of the hydration layer relates with the
roughness (projections) and depends upon the difference of the kind
of the glass (glass type, glass composition).
[0253] Therefore, it is confirmed that the glass used in the
manufacturing method according to this invention satisfies the
above-mentioned condition and may contain 58-75 weight % of
SiO.sub.2, 5-23 weight % of Al.sub.2O.sub.3, 3-10 weight % of
Li.sub.2O, and 4-13 weight % of Na.sub.2O as main components in the
composition ratio and preferably does not contains alkali earth
metal (oxide).
[0254] In particular, the aluminosilicate glass specified in the
invention 7 is desirable in the above-mentioned polishing condition
and the surface processing condition due to the hydrosilicofluoric
acid.
EXAMPLE 9
[0255] The glass substrate for the magnetic recording medium for
use in the ramp road system and the magnetic recording medium for
use in the ramp load system were manufactured in the same manner as
the example 1 (sulfuric acid) except that the heating condition in
the above-mentioned heating process was set to 90.degree. C., 6
min.
[0256] When the surface roughness of the obtained glass substrate
for the magnetic recording medium was measured by the use of the
interatomic force microscope (AFM), the surface roughness was
specified by Ra=0.65 nm, Rmax=6.02 nm, Rp=2.83 nm, Rmax/Ra=9.26,
Rp/Ra=4.35, Rq=0.76 nm. Further, an excellent result was obtained
in the glide test.
EXAMPLES 10-11
[0257] The glass substrate for the magnetic recording medium for
use in the ramp road system and the magnetic recording medium for
use in the ramp load system were manufactured in the same manner as
the example 1 (sulfuric acid) except that the heating condition in
the above-mentioned heating process was set to 90.degree. C., 10
min (example 10),and 80.degree. C., 5 min (example 11).
[0258] When the surface roughness of the obtained glass substrate
for the magnetic recording medium was measured by the use of the
interatomic force microscope (AFM), the surface roughness was
specified by Ra=0.54 nm, Rmax=4.31 nm, Rp=2.53 nm, Rmax/Ra=7.98,
Rp/Ra=4.69, Rq=0.65 nm (example 10), Ra=0.85 nm, Rmax=6.43 nm,
Rp=3.21 nm, Rmax/Ra=7.56, Rp/Ra=3.78, Rq=1.17 nm (example 11).
[0259] Further, an excellent result was obtained in the glide
test.
EXAMPLE 12
[0260] The glass substrate for the magnetic recording medium for
use in the ramp road system and the magnetic recording medium for
use in the ramp load system were manufactured in the same manner as
the example 1 (sulfuric acid) except that the solvent used in the
heating process was changed from sulfuric acid into phosphoric acid
(made by OHTOMO CHEMICAL INS., CORP.: SCHRECK #205
(1-hydroxy-ethane-1,1-diphosphoric acid)) 0.3%, 40.degree. C., 90
seconds.
[0261] When the surface roughness of the obtained glass substrate
for the magnetic recording medium was measured by the use of the
interatomic force microscope (AFM), the surface roughness was
specified by Ra=0.79 nm, Rmax=6.43 nm, Rp=4.12 nm, Rmax/Ra=8.14,
Rp/Ra=5.22, Rq=0.97 nm. Further, an excellent result was obtained
in the glide test.
[0262] As mentioned above, it is found out that variation of the
projection height is reduced in the examples 9-12 of the ramp load
system in comparison with the examples 1-8 of the CSS system by
suitably selecting the conditions of the heating process.
Specifically, the value of Rmax/Ra and the value of Rp/Ra become
low.
[0263] Although the invention has been so far explained with the
preferred embodiments, this invention is not always restricted to
the above-mentioned embodiments. For example, although the surface
process due to the hydrosilicofluoric acid was performed twice, the
surface process step may be performed once, and alternatively, may
be performed three times or more.
[0264] The same effect as the above-mentioned case was obtained in
an etching process due to solution containing hydrofluoric acid or
an etching process, in which, the glass substrate is subjected to
hydrofluoric acid vapor, instead of the hydrosilicofluoric
acid.
[0265] Further, although the chemically strengthened glass
substrate was used as the glass substrate of this invention, and
the chemically strengthened step was performed after the surface
process due to the hydrosilicofluoric acid, the surface process due
to the hydrosilicofluoric acid may be carried out after the
chemically strengthened process.
[0266] When the glass substrate is polished by the use of the free
abrasive grain and the above surface process due to the
hydrosilicofluoric acid is performed immediately after the glass
substrate surface is chemically strengthened, the remaining
distortion formed by the free abrasive grain on the glass substrate
surface is buried in the stress of the chemical strengthening. This
is undesirable because the surface roughness can not be
controlled.
[0267] However, the same result as the above-mentioned case can be
obtained by interposing the polishing processing step due to the
free abrasive grain between (immediately after the surface process
due to the hydrosilicofluoric acid) the chemical strengthening
process step and the surface process due to the hydrosilicofluoric
acid as the chemical strengthening step .fwdarw. the polishing step
due to the free abrasive grain .fwdarw. the surface process due to
the hydrosilicofluoric acid.
[0268] Further, the disk manufactured by this invention is not
restricted to the CSS system, and may be usable in the load/unload
system (the ramp load system), and in particular, can be suitably
used in the load/unload system (the ramp load system).
[0269] As mentioned before, according to this invention, the
project height can be reduced in comparison with such a case that
the heating process is not carried out. Further, the projection
density, the variation of the projection heights, and the variation
of the projections can be reduced. Consequently, the glide height
of 1.2.mu. inch and the high electromagnetic conversion
characteristic can be realized.
[0270] Moreover, the magnetic recording medium, which is suitable
for the load/unload system, can be manufactured by controlling the
projection height and the projection density according to this
invention. In such a load/unload system, the projection height and
the projection density fall within the predetermined range and the
head is positioned outside of the disk when the disk is not
rotated.
[0271] In addition, the magnetic recording medium, which satisfies
the sufficient electromagnetic conversion characteristic and the
stiction preventing effect of the magnetic head at the same time
and which is suitable for the CSS system superior in the high CSS
durability, can be manufactured according to this invention.
* * * * *