U.S. patent application number 10/256447 was filed with the patent office on 2003-06-19 for magnetic hard disk having concentric magnetic tracks with flat surface and fabrication method thereof.
This patent application is currently assigned to Fujitsu Limited. Invention is credited to Mukai, Ryoichi, Takeshita, Hiroto, Yamagishi, Wataru.
Application Number | 20030112560 10/256447 |
Document ID | / |
Family ID | 18504104 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030112560 |
Kind Code |
A1 |
Takeshita, Hiroto ; et
al. |
June 19, 2003 |
Magnetic hard disk having concentric magnetic tracks with flat
surface and fabrication method thereof
Abstract
A magnetic hard disk having magnetic tracks for storing data
which is read or written by a magnetic head floating immediately
above the magnetic track while the magnetic hard disk is rotating,
and the magnetic head rests on the magnetic hard disk while the
magnetic hard disk is not rotating. One aspect of the present
invention is that the magnetic hard disk comprises a non-magnetic
substrate having a plurality of banks and grooves alternately and
concentrically arranged thereon, a magnetic film formed on each of
the banks, and non-magnetic material formed on an entire surface of
the substrate all over the banks and grooves such that roughness of
the upper surface of the non-magnetic material is in a range
between 0.5 nm and 3 nm.
Inventors: |
Takeshita, Hiroto;
(Isehara-shi, JP) ; Mukai, Ryoichi; (Kawasaki-shi,
JP) ; Yamagishi, Wataru; (Ebina-shi, JP) |
Correspondence
Address: |
Patrick G. Burns
Suite 2500
300 South Wacker Drive
Chicago
IL
60606
US
|
Assignee: |
Fujitsu Limited
Kawasaki-shi
JP
|
Family ID: |
18504104 |
Appl. No.: |
10/256447 |
Filed: |
September 27, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10256447 |
Sep 27, 2002 |
|
|
|
09468962 |
Dec 22, 1999 |
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Current U.S.
Class: |
360/135 ;
428/848.3; 428/848.5; G9B/5.28; G9B/5.293; G9B/5.3; G9B/5.306 |
Current CPC
Class: |
G11B 5/855 20130101;
G11B 5/8408 20130101; G11B 5/72 20130101; G11B 5/82 20130101 |
Class at
Publication: |
360/135 ;
428/694.0TR; 428/694.0SG |
International
Class: |
G11B 005/82 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 1998 |
JP |
10-374594 |
Claims
What is claimed is:
1. A magnetic hard disk rotatable around a center of the disk
having a plurality of magnetic tracks concentrically disposed
around the center of the disk and spaced to each other, the
magnetic hard disk comprising: a substrate made of non-magnetic or
antiferro-magnetic material having an upper surface; a magnetic
film patterned concentrically around the center of said substrate
on the upper surface to form the magnetic tracks having a space
between each pair of the magnetic tracks adjacent to each other;
and a non-magnetic film continuously formed on both said magnetic
film and the space such that an upper surface of said non-magnetic
film is substantially in a plane parallel to a plane of rotation of
the magnetic hard disk, wherein the roughness of the upper surface
of said non-magnetic film is in a range between 0.5 nm and 3
nm.
2. A magnetic hard disk according to claim 1, further comprising: a
first non-magnetic film underlies at least said magnetic film.
3. A magnetic hard disk according to claim 1, wherein said
non-magnetic film comprises a second, third and fourth non-magnetic
films, the second non-magnetic film disposed on said magnetic film,
the third non-magnetic film filling the space such that both upper
surfaces of the second and third non-magnetic films are continuous
with each other and substantially in a plane parallel to the plane
of rotation of the magnetic hard disk, and the fourth non-magnetic
film continuously formed on both upper surfaces of the second and
third non-magnetic films, wherein the roughness of the upper
surface of said fourth non-magnetic film is in a range between 0.5
nm and 3 nm.
4. A magnetic hard disk according to claim 3, wherein said second
and third non-magnetic films are selected such that removing rate
of said second non-magnetic film is lower in simultaneous chemical
mechanical polishing or etching process than the removing rate of
said third non-magnetic film.
5. A magnetic hard disk according to claim 3, wherein said second
non-magnetic film is selected from the group consisting of
amorphous carbon, diamond-like carbon, silicon nitride and
chromium.
6. A magnetic hard disk according to claim 3, wherein said third
non-magnetic film is made of glass containing silicon oxide.
7. A magnetic hard disk according to claim 3, wherein said fourth
non-magnetic film is selected from the group consisting of
amorphous carbon, diamond-like carbon and silicon nitride.
8. A magnetic hard disk according to claim 1, wherein said
substrate is selected from the group consisting of glass, ceramics,
aluminum, aluminum alloy and plastics such as ploy-carbonate,
amorphous ploy-olefin and ploy-ethylmetacrylate.
9. A magnetic hard disk according to claim 1, wherein the space is
depressed from a lower surface of said magnetic film.
10. A magnetic hard disk according to claim 1, wherein width of the
space is selected such that a magnetic field from said magnetic
film on one of a pair of the magnetic tracks adjacent to the space
is negligible at said magnetic film on an opposite one of said
magnetic tracks across the space.
11. A magnetic hard disk according to claim 9, further comprising a
magnetic film patterned on a bottom surface of the depressed
space.
12. A magnetic hard disk according to claim 11, wherein depth of
the depressed space is selected such that a magnetic field from
said magnetic film on the bottom surface of the depressed space is
negligible at said magnetic film on said magnetic tracks adjacent
to the depressed space.
13. A magnetic hard disk according to claim 3, wherein a
coefficient of statical friction of the fourth non-magnetic film is
smaller than 0.75.
14. A magnetic hard disk according to claim 1, wherein the magnetic
hard disk has a data area and servo area thereon, the data area
including a plurality of concentric magnetic tracks spaced to each
other, the servo area extending in a radial direction crossing the
concentric magnetic tracks, and upper surfaces of the magnetic hard
disk in both data and servo areas have surface roughness between
0.5 nm and 3 nm.
15. A magnetic hard disk according to claim 1, wherein the upper
surface of said non-magnetic film has texture-like patterns.
16. A method for fabricating a magnetic hard disk rotatable around
a center of the disk having a plurality of magnetic tracks
concentrically disposed around the center of the disk and spaced to
each other, comprising the steps of: forming a first non-magnetic
film on an upper surface of a substrate made of non-magnetic or
antiferro-magnetic material; forming a magnetic film concentrically
patterned around the center of said substrate on an upper surface
of said first non-magnetic film to form the magnetic tracks;
forming a second non-magnetic film on said magnetic film; forming a
third non-magnetic film continuously on said second non-magnetic
film and a space between each pair of said magnetic tracks adjacent
to each other such that an upper surface of said third non-magnetic
film exceeds a plane of the upper surface of said second
non-magnetic film; removing an upper part of said third
non-magnetic film such that both upper surfaces of said second and
third non-magnetic films are in a plane parallel to a plane of
rotation of the magnetic hard disk; forming a fourth non-magnetic
film continuously on both said second and third non-magnetic films;
and roughening an upper surface of said fourth non-magnetic film
such that the upper surface has surface roughness greater than 0.5
nm maintaining a maximum surface roughness smaller than 3 nm.
17. A method for fabricating a magnetic hard disk according to
claim 16, further comprising the step of: forming a plurality of
grooves-concentrically disposed around the center of said substrate
leaving a bank between each pair of the grooves adjacent to each
other on the upper surface of said substrate such that each of the
magnetic tracks coincides with the bank in position.
18. A method for fabricating a magnetic hard disk according to
claim 16, wherein the step of removing the upper part of said third
non-magnetic film is carried out by chemical mechanical polishing
method until the upper surface of said second non-magnetic film is
fully exposed.
19. A method for fabricating a magnetic hard disk according to
claim 16, wherein the step of roughening an upper surface of said
fourth non-magnetic film is carried out by mechanical polishing
method using polishing powder.
20. A method for fabricating a magnetic hard disk rotatable around
a center of the disk having a plurality of magnetic tracks
concentrically disposed around the center of the disk and spaced to
each other, comprising the steps of: forming photoresist patterns
concentrically arranged around a center of a substrate disk on a
flat upper surface of a disk substrate such that width and space of
the photoresist patterns corresponds to space and width of the
magnetic tracks, respectively; depositing a first non-magnetic
film, a magnetic film, a second non-magnetic film successively on
the disk substrate having the photoresist patterns in the
perpendicular direction to the substrate by sputtering method;
removing the photoresist patterns together with deposited films
thereon by lift-off method such that deposited films on the flat
upper surface of the disk substrate are left; depositing a third
non-magnetic film isotropically over the disk substrate such that a
lowermost portion of an upper surface of the third non-magnetic
film exceeds an uppermost portion of an upper surface of the second
non-magnetic film; planarizing the third non-magnetic film by
chemical mechanical polishing method until the upper surface of the
second non-magnetic film is exposed such that the planarized
surface has surface roughness smaller than 3 nm; depositing a
fourth non-magnetic film all over the planarized surface; and
roughening an upper surface of the fourth non-magnetic film by
another polishing method such that the upper surface has roughness
greater than 0.5 nm maintaining the surface roughness smaller than
3 nm inherited from the surface roughness of the planarized
surface.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims priority of
Japanese Patent Application No. Hei 10-374594, filed the contents
being incorporated herein by reference.
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
[0002] The present invention relates to a magnetic hard disk
capable of writing and reading magnetic data thereon, and more
particularly, to a magnetic hard disk having concentric magnetic
tracks spaced to each other on a non-magnetic substrate, and a
fabrication method thereof.
DESCRIPTION OF THE RELATED ART
[0003] As the infrastructure of information and communication in
the society is progressed, a magnetic hard disk driver (or HDD) as
an external memory of computers rises in importance increasingly,
and its storage density increases rapidly year by year. Tendency
for seeking smaller size and larger volume in the memory demands
narrower magnetic tracks and higher storage density for the
magnetic hard disk.
[0004] Since storage density of the magnetic hard disk depends upon
both of linear density along a track and track density in the
radial direction, improvement of either one or both results in
higher storage density of the magnetic hard disk. The present
invention is directed to an improvement of a technology related to
the track density.
[0005] In general, auxiliary data is initially recorded on a
magnetic hard disk, which is information necessary for writing or
reading data on the magnetic hard disk, such as servo data (or
tracking servo data) for positioning a magnetic head on a track,
address data for registering a position of written data and PLL
lock data for reading out address data. To increase the track
density, simply narrowing a space between tracks results in a
serious problem under a circumstance that a track is generated by
writing data by a magnetic head as in conventional manner. FIG. 1A
is a partial cross-sectional view of a typical conventional
magnetic hard disk having a continuous magnetic film, in which the
magnetic disk consists of a flat substrate 1 and successively
laminated three thin films of chromium 2,
cobalt-chromium-platinum-tantalum alloy 3, and amorphous carbon 4.
When narrow-pitched magnetic tracks are written on a continuous
magnetic film by simply narrowing a spacing between magnetic head
trajectories of the nearest neighbors, a stray magnetic field
coming out laterally from both sides of the magnetic head
magnetizes a guard band between tracks which resultantly causes
magnetic noises. Narrowing track width also gives rise to decrease
of a signal to noise ratio (or S/N) problem at reading out a
written data. The similar problem occurs in recording of tracking
servo data for controlling a position of a magnetic head. As
narrowing the track width, it becomes increasingly difficult to
obtain a highly accurate servo data. To maintain the S/N ratio for
narrower track width, it has been proposed to form various physical
features such as bumps or grooves on a surface of a disk substrate
by which servo signal or position of a track is determined. ( for
instance, a Japanese Laid Open Patent Application H3-252922).
According to this technique, a servo mark is formed on the magnetic
disk for tracking a magnetic head by which the magnetic head can be
controlled to follow a magnetic track with high accuracy. The servo
mark is written by servo writer. Narrowing track width for higher
track density requires higher accuracy in positioning the servo
mark, which further needs higher positioning accuracy between a
servo writer and a HDD. Therefore, a drawback of this approach is
requirement for higher technical accuracy to the positioning device
which incurs extra cost. To overcome this drawback, it has been
proposed to pre-form the servo mark by which accuracy in
positioning the servo mark can be increased. Several methods for
pre-forming the servo mark are disclosed, for instance, by etching
a magnetic film as in Japanese Laid Open Patent Applications
S62-256225 and H1-23418, or by forming bumps and grooves on a disk
substrate as in H8-17155. FIG. 1B is a partial cross-sectional view
of another typical conventional magnetic hard disk having a
partially refilled groove between magnetic tracks neighboring to
each other, in which the magnetic disk consists of a flat substrate
1 and successively laminated three thin films of chromium 2,
cobalt-chromium-platinum-tantal- um alloy 3, and amorphous carbon
4, as same as FIG. 1A except that there are partially refilled
grooves 7 between pre-determined tracks 8.
[0006] However, a drawback of these methods is to leave surface
roughness from several tens nanometers to several hundreds
nanometers in overall height on the magnetic disk. Since floating
stability of a magnetic head, which means how stably a magnetic
head can maintain a predetermined distance from the rotating
magnetic disk, for a magnetic disk of high track density in a
conventional HDD can be attained by flattening and smoothing the
surface of a magnetic disk, and since decrease of the distance
between a floating magnetic head and a magnetic disk is also needed
to operate a magnetic disk having higher density maintaining the
appropriate S/N ratio, the both approaches clearly conflicts with
these technical requirements.
SUMMARY OF THE INVENTION
[0007] An object of the present invention is to provide a magnetic
hard disk having a plurality of concentrically disposed magnetic
tracks with high radial density, which maintains sufficiently long
durability of a non-contact magnetic head floating immediately
above the magnetic tracks, the magnetic hard disk comprising a
non-magnetic substrate having an upper surface with a
concentrically patterned magnetic film thereon, and a non-magnetic
protecting film on the entire upper surface of the magnetic hard
disk, wherein roughness of the upper surface of the non-magnetic
protecting film is in a range between 0.5 nm and 3 nm.
[0008] Another object of the present invention is to provide a
magnetic hard disk having high radial density of magnetic tracks
without degrading signal to noise ratio. According to one aspect of
the invention, a magnetic hard disk comprises a non-magnetic
substrate having alternately disposed concentric banks and grooves
on the upper surface, a magnetic film on each of the concentric
banks, and a non-magnetic film covering the magnetic film and
refilling the grooves such that the upper surface of the
non-magnetic film has the same surface roughness and continuity
across the banks and grooves.
[0009] Further object of the present invention is to provide a
reliable method for fabricating the magnetic hard disk having high
radial density of magnetic tracks, the method comprise the steps of
forming alternately disposed concentric banks and grooves on a
non-magnetic substrate, forming a magnetic film and a first
non-magnetic film on each of the concentric banks, successively
forming a second non-magnetic film on an entire surface of the
magnetic hard disk so as to cover the first non-magnetic film and
refill the grooves therewith, removing the second non-magnetic film
from the upper surface of the first non-magnetic film by Damascene
method until the first non-magnetic film is exposed, and
subsequently forming a third non- magnetic film on an entire
surface of the magnetic hard disk and finally roughening the upper
surface of the third non-magnetic film such that roughness of the
upper surface of the third non-magnetic film falls in a range
between 0.5 nm and 3 nm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention will be more apparent from the
following description, when taken to conjunction with the
accompanying drawings, in which:
[0011] FIG. 1A is a partial cross-sectional view of a prior art
magnetic hard disk having a continuous magnetic film.
[0012] FIG. 1B is a partial cross-sectional view of a prior art
magnetic hard disk having a groove between concentric tracks.
[0013] FIG. 2 is an instrument for the acoustic emission
measurement.
[0014] FIG. 3 is a partial cross-sectional view of a magnetic hard
disk having a continuous magnetic film for magnetic head stability
test.
[0015] FIG. 4 is a graph of relationship between an output voltage
of the acoustic emission (or AE) sensor and duration time on the
magnetic hard disk shown in FIG. 3.
[0016] FIG. 5 is a partial cross-sectional view of a magnetic hard
disk having a groove between concentric tracks for magnetic head
stability test.
[0017] FIG. 6 is a graph of relationship between an output voltage
of the AE sensor and duration time on the magnetic hard disks with
various groove depths.
[0018] FIG. 7 is a graph of relationship between static friction
and surface roughness of magnetic hard disks by CSS durability
test.
[0019] FIG. 8 is a graph of relationship between an AE sensor
output and surface roughness of magnetic hard disks by floating
durability test.
[0020] FIGS. 9A through 9C are partial cross-sectional views of a
magnetic hard disk in various fabrication processing steps for the
first embodiment according to the present invention.
[0021] FIG. 10 is a graph of relationship between output voltages
of an AE sensor and duration time on magnetic hard disks having
protective films of a-carbon and DLC.
[0022] FIG. 11 is a graph of relationship between output voltages
of an AE sensor and duration time on magnetic hard disks having
protective films of Al2O3 and SiO2.
[0023] FIGS. 12A and 12B are partial cross-sectional views of a
magnetic hard disk before and after planarization processes,
respectively, for the second through fourth embodiments according
to the present invention.
[0024] FIGS. 13A through 13D are partial cross-sectional views of a
magnetic hard disk in various fabrication processing steps for the
fifth embodiment according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] Thus, the inventors investigated the floating stability of a
magnetic head in terms of surface roughness of a magnetic hard disk
in more detail. The floating stability of a magnetic head can be
evaluated by an output voltage of an acoustic emission sensor
installed on the magnetic head which detects a dynamic contact of
the magnetic head against the surface of the magnetic hard disk
during rotating the magnetic disk. FIG. 2 shows an instrument for
the acoustic emission measurement, which mainly consists of a stage
11, air-spindle rotator 12, a magnetic hard disk 13, a magnetic
head 14, an acoustic emission sensor 15, amplifier/band-path filter
circuit 16 and output terminal 17. When the magnetic hard disk 13
is rotated at a constant track-speed of 12 meters per second for
measurements, the magnetic head 14 is lifted off by 25 nm above the
disk surface. FIG. 3 shows a cross-sectional view of a magnetic
hard disk having a flat surface with no grooves as a control, in
which the magnetic hard disk consists of a flat substrate 1 and
successively laminated three thin films of 20 nm-thick chromium 2,
20 nm-thick cobalt-chromium-platinum-tantalum alloy 3, and 20
nm-thick amorphous carbon 4. FIG. 4 shows an experimental result of
the magnetic hard disk having a flat surface with no grooves. The
result indicates that the output voltage of the acoustic emission
sensor versus time is unchanged for more than 1000 hours. It was
also confirmed that the floating stability was maintained for more
than 1000 hours during continuous operation with a currently
commercially available magnetic hard disk having grooves as far as
the floating distances of the magnetic head are 50 nm and 100 nm.
On the other hand, when the floating distances of the magnetic head
were changed to be 30, 25 and 20 nm, the crashes occurred within
50, 5 and 3 hours, respectively. FIG. 5 shows a cross-sectional
view of magnetic hard disks having concentric grooves of 30 nm, 60
nm, and 90 nm in depth with 0.3 nm in width and 3.0 nm in pitch.
FIG. 6 shows an experimental result of the magnetic disks having
different groove depths. Although there was some difference in
durability between the magnetic hard disks having different depths
of the groove, all of them started increasing in an output of the
acoustic emission ( or AE) sensor within 4 hours and that crashed
to the disk within about 30 minutes after the respective steep
increases of the output. The result of all durability tests of the
floating magnetic head by continuous operation are tabulated in
Table 1, together with the conventional magnetic hard disks.
1TABLE 1 Groove Depth Floating No. (nm) Distance (nm) Life (hour)
Notes 1 30 20 less than 3 2 30 25 less than 3 3 60 25 less than 4 4
90 25 less than 4.5 5 30 25 less than 5 6 0 25 more than 1000 7 30
30 less than 50 8 0 50 more than 1000 Prior Art 9 30 50 more than
1000 Prior Art 10 30 100 more than 1000
[0026] It can be concluded from these experiments that it becomes
more difficult to maintain sufficient stability of the floating
head as a distance between the floating head and the surface of the
grooved magnetic hard disks becomes smaller.
[0027] On the other hand, a magnetic head is usually rested on the
surface of a magnetic disk when the device is not operated. As the
disk starts rotating, the magnetic head is lifted off from the
surface of a magnetic disk by air-flow. This type of operating
method is called a "contact start and stop" (or CSS) method. It is
known that in the CSS method, a magnetic head often does not leave
promptly from the contact surface of the disk when the disk starts
rotating because the head clings to the contact surface. This
effect results in instability of the magnetic head or even
permanent damage of the magnetic head. Thus, another series of
experiments were carried out to study an effect of surface
roughness of protective films on the instability due to the CSS
method. Protective films having various surface roughness and
materials were prepared to measure the coefficient of static
friction and an AE sensor output for floating stabilities of static
and dynamic states, respectively. Samples for the measurements have
substantially the same structure as that shown in FIG. 3. Various
textured surfaces were provided by polishing the surface with
polishing powder having different sizes. FIG. 7 shows a
relationship between the coefficient of static friction and surface
roughness obtained by the CSS method. The graph indicates that the
coefficient of static friction increased rapidly as the surface
roughness decreased below 0.5 nm, in which the surface roughness is
measured by a height from an averaged center line as defined by
Japanese Industrial Standard (or JIS) B 0601-1982, unless otherwise
referred to. Further, the crash occurred after roughly 500
time-repetition of stop and start operation under contact condition
at an average surface roughness of 0.2 nm. In contrast, no crash
occurred after more than 1000 time-repetition test at an average
surface roughness of greater than 0.5 nm. FIG. 8 shows a
relationship between an output voltage of an AE sensor and surface
roughness. The graph in FIG. 8 indicates that the output voltage of
an AE sensor increased rapidly beyond an average surface roughness
of greater than 3 nm. The crash occurred within 50 hours at an
average surface roughness of 4.7 nm. While no crash occurred for
more than 1000 hours for dynamic floating durability test at an
average surface roughness of smaller than 3 nm.
[0028] Thus, flatness and roughness of the surface of a magnetic
hard disk should be precisely selected to fulfill the foregoing
technical requirements for an advanced magnetic hard disk having
high density magnetic tracks.
EMBODIMENT 1
[0029] FIGS. 9A through 9C are partial cross-sectional views of a
magnetic disk in various fabrication processing steps for the first
embodiment of the present invention.
[0030] A disk substrate 1 is made of non-magnetic material such as
aluminum, aluminum alloy, ceramics, glass or plastics, or
antiferro-magnetic material such as MnO, Cr.sub.2O.sub.3, FeS,
FeCl.sub.2 or MnAs. Further, a surface of the disk substrate 1 may
be coated by an aluminum oxide film, electroplating metal films or
alike to obtain better flatness and anti-corrosion. Concentric
grooves 7 are formed on the surface of the disk substrate 1 leaving
concentric banks 8 alternately to each other by photolithography
and anisotropic etching. FIG. 9A is a partial radial
cross-sectional view of a disk substrate 1. A magnetic film 3 is
formed on the surface of the banks by depositing magnetic material
in a normal direction to the surface of the disk substrate by which
the magnetic film may be deposited on the bottom of the grooves but
not on the side wall. Each of the magnetic films on the surface of
the banks must be separated from the nearest magnetic film on the
surface of the banks and bottoms so as to neglect magnetic
interference between them. A non-magnetic film 4 is successively
deposited over the entire surface of the disk substrate such that
the non-magnetic film 4 is thick enough to refill the grooves as
shown in FIG. 9B. Subsequently, the non-magnetic film 4 is polished
precisely until a thin protective film, such as 20 nm thick, on the
magnetic film 3 on each of the banks 8 is left and surface
roughness is in a range of 0.5 nm to 3 nm as shown in FIG. 9C. The
magnetic disk of this structure simultaneously satisfies both
requirements for surface roughness of the upper surface for the
stabilities of static and dynamic states and complete separation
between neighboring magnetic tracks.
EMBODIMENT 2
[0031] FIG. 12A is a partial cross-sectional view of a magnetic
hard disk before planarization for the second embodiment according
to the present invention.
[0032] Concentric grooves were formed on the surface of a glass
substrate 1 of 3.5 inch diameter. Width of a track was 2.7 .mu.m
wide. Width and depth of the groove were 0.3 .mu.m wide and 50 nm
deep, respectively. A 20 nm thick underlay of Chromium film 2, a 20
nm thick magnetic film 3 of Cobalt-Chromium-Platinum-Tantalum
alloy, a 20 nm thick Chromium film 4 of the first non-magnetic film
were successively deposited on the grooved substrate by sputtering
method, and subsequently a 80 nm thick SiO2 film 5 of the second
non-magnetic film was deposited by either sputtering or CVD method
until the groove was completely refilled as shown in FIG. 12A.
[0033] FIG. 12B is a partial cross-sectional view of a magnetic
hard disk after planarization for the second embodiment according
to the present invention.
[0034] The SiO2 film 5 was planarized by chemical mechanical
polishing (or CMP) method until the Chromium film 4 was exposed.
Detailed condition of the CMP method was as follows:
[0035] Polishing agent was KOH solution added colloidal silica
slurry (about 20 .mu.m in diameter ) diluted with water until the
volume reached ten times larger than that of the slurry. Polisher
was polyurethane cloth. Load was 2.6 kgf. Revolution speed of a
stage was 50 rpm. The planarization process is not only limited to
the CMP method but also an etch-back method widely used in
semiconductor wafer fabrication is feasible.
[0036] After planarization, a 10 nm thick amorphous carbon (or
a-carbon) film 6 as the third non-magnetic film was deposited all
over the polished surface. The a-carbon film acts as a protective
film for an anti-corrosion and anti-wearing purposes. This a-carbon
film had surface roughness of 0.83 nm. In the Embodiment 1, the
disk substrate can be replaced by poly-carbonate (PC), amorphous
poly-olefin (a-PO), or poly-methyl-metacrylate (PMMA) substrate.
The other conditions being equal, the third non-magnetic films for
these replaced disk substrates had the surface roughness of 0.91
nm, 0.88 nm, and 0.90 nm, respectively.
EMBODIMENT 3
[0037] Two different samples were prepared, wherein one of the disk
substrate was glass and another was poly-carbonate. The first and
second non-magnetic films of both cases were selected to be a 10 nm
thick a-carbon and a 10 nm thick Chromium film, and the other
conditions were equal to those in the Embodiment 2. All cases of
Embodiments 2 and 3 with surface roughness from 0.5 nm to 3 nm
satisfied the both requirements for dynamic and CSS durability
tests.
EMBODIMENT 4
[0038] To know the effect of materials of the protective film, the
third non-magnetic film in Embodiment 2, on the floating
characteristics of the magnetic head, two groups of samples having
different materials for the protective non-magnetic film 4 were
formed directly on disk substrates having a flat and smooth
surface, the disk substrates are made of glass and PC. The
protective non-magnetic films of the first and second groups were
a-carbon and diamond-like carbon (DLC), and AL2O3 and SiO2,
respectively. Both samples of the first group showed stable
operations for more than 1000 hours as shown in FIG. 10, while both
samples of the second group crashed within 100 to 200 hours as
shown in FIG. 11. These results suggest that hardness of the
protective (or third) non-magnetic film must be higher than that of
Al2O3 or SiO2 film. Silicon nitride (Si3N4) is another prospective
material for the protective (or third) non-magnetic film. All
experimental results on floating durability are summarized in Table
2.
2TABLE 2 1'st non- 2'nd non- surface Floating magnetic magnetic
Protective roughness durability No. substrate film film film (nm)
(hours) 1 glass Cr SiO2 a-carbon 0.83 more than 1000 2 PC Cr SiO2
a-carbon 0.91 more than 1000 3 a-PO Cr SiO2 a-carbon 0.88 more than
1000 4 PMMA Cr SiO2 a-carbon 0.90 more than 1000 5 glass a-carbon
Cr a-carbon 0.94 more than 1000 6 PC a-carbon Cr a-carbon 0.98 more
than 1000 7 glass -- -- a-carbon 0.90 more than 1000 or PC 8 glass
-- -- DLC 0.92 more than 1000 or PC 9 glass a-carbon -- -- 60 less
than 3 (groove depth) 10 PC a-carbon -- -- 60 less than 4 (groove
depth) 11 glass -- -- Al2O3 1.05 less than 100 or PC 12 glass -- --
SiO2 1.01 less than 200 or PC
[0039] As described above, to ensure stable continuous operation
for more than 1000 hours, the surface roughness of the magnetic
hard disk should be greater than 0.5 nm for the CSS type operation
and smaller than 3.0 nm for a floating head with a floating
distance lower than 30 nm. Although it is important that magnetic
tracks are magnetically isolated from each other on writing or
reading operation, a groove between concentric magnetic tracks is
not essential to the present invention.
EMBODIMENT 5
[0040] FIGS. 13A through 13D are partial cross-sectional views of a
magnetic hard disk in various fabrication processing steps for the
fifth embodiment according to the present invention.
[0041] Photoresist patterns 9 concentrically arranged around a
center of a substrate disk is formed on a flat upper surface of a
glass substrate 1, as shown in FIG. 13A. Width and space of the
patterns are 0.3 .mu.m wide and 2.7 .mu.m wide, respectively. A 20
nm thick underlay of Chromium film 2, a 20 nm thick magnetic film 3
of Cobalt-Chromium-Platinum-Tantalum alloy, a 20 nm thick Chromium
film 4 of the first non-magnetic film are successively deposited on
the patterned substrate from the perpendicular direction to the
substrate by sputtering method as shown in FIG. 13B. The
photoresist patterns 9 are removed together with the unnecessary
films deposited thereon by lift-off method to leave concentric
magnetic tracks on the substrate. Subsequently, a 80 nm thick SiO2
film 5 is deposited uniformly by either sputtering or CVD method
until the magnetic tracks and the space therebetween are completely
buried as shown in FIG. 13C. The SiO2 film 5 is planarized by CMP
method until the Chromium film 4 as a stopper film is exposed so
that the planarized surface have surface roughness smaller than 3
nm. A 10 nm thick a-carbon film 6 is deposited all over the
polished surface as shown in FIG. 13D. Finally, the surface is
roughened by another polishing so that the final surface has
roughness greater than 0.5 nm maintaining the surface roughness
smaller than 3 nm inherited from the surface roughness of the
underlaid SiO2 film.
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