U.S. patent application number 09/892854 was filed with the patent office on 2002-02-07 for method of producing a substrate for an information recording medium and method of producing an information recording medium.
This patent application is currently assigned to HOYA CORPORATION. Invention is credited to Isono, Hideki, Kawai, Hisao, Takeda, Hiroshi.
Application Number | 20020016132 09/892854 |
Document ID | / |
Family ID | 27343896 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020016132 |
Kind Code |
A1 |
Isono, Hideki ; et
al. |
February 7, 2002 |
Method of producing a substrate for an information recording medium
and method of producing an information recording medium
Abstract
In a method of producing a substrate for an information
recording medium, the method including a washing/drying step of
washing and drying said substrate subjected to precision polishing,
a correlation is preliminarily obtained between a contact angle of
water on a surface of the substrate before the washing/drying step
and a size (height) of protrusions attached to the surface of the
substrate during the washing/drying step. The contact angle of
water on the surface of the substrate before the washing/drying
step is controlled so that the protrusions have the size so as not
to cause a hit when at least a recording layer is formed on the
surface of the substrate to produce the information recording
medium and when a slider provided with a recording device and/or a
reproducing device is made to run on a surface of the information
recording medium. The contact angle of water on the surface of the
substrate before the washing/drying step may be controlled so that
the protrusions have the size so as not to cause the hit and so as
not to cause an error upon recording and/or reproducing the
information recording medium which is produced by forming at least
the recording layer on the surface of the substrate.
Inventors: |
Isono, Hideki; (Tokyo,
JP) ; Takeda, Hiroshi; (Tokyo, JP) ; Kawai,
Hisao; (Tokyo, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3213
US
|
Assignee: |
HOYA CORPORATION
|
Family ID: |
27343896 |
Appl. No.: |
09/892854 |
Filed: |
June 28, 2001 |
Current U.S.
Class: |
451/8 ; 451/11;
451/41; G9B/5.299 |
Current CPC
Class: |
Y10S 977/888 20130101;
G11B 5/8404 20130101; G11B 23/502 20130101; G11B 5/82 20130101 |
Class at
Publication: |
451/8 ; 451/11;
451/41 |
International
Class: |
B24B 049/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 29, 2000 |
JP |
196212/2000 |
Jun 29, 2000 |
JP |
196377/2000 |
Jun 29, 2000 |
JP |
196516/2000 |
Claims
What is claimed is:
1. A method of producing a substrate for an information recording
medium, said method including a washing/drying step of washing and
drying said substrate subjected to precision polishing, said method
comprising the steps of: obtaining a correlation between a contact
angle of water on a surface of said substrate before said
washing/drying step and a size of protrusions attached to the
surface of said substrate during said washing/drying step; and
controlling the contact angle of water on the surface of said
substrate before said washing/drying step so that said protrusions
have the size so as not to cause a hit when at least a recording
layer is formed on the surface of said substrate to produce said
information recording medium and when a slider provided with a
recording device and/or a reproducing device is made to run on a
surface of said information recording medium.
2. A method as claimed in claim 1, wherein said controlling step is
for controlling the contact angle of water on the surface of said
substrate before said washing/drying step so that said protrusions
have the size so as not to cause said hit and so as not to cause an
error upon recording and/or reproducing the information recording
medium which is produced by forming at least said recording layer
on the surface of said substrate.
3. A method of producing a substrate for an information recording
medium, said method including a washing/drying step of washing and
drying said substrate subjected to precision polishing, wherein: a
correlation is established between a contact angle of water on a
surface of said substrate before said washing/drying step and a
glide test fail rate in a glide test carried out by forming at
least a recording layer on the surface of said substrate to produce
said information recording medium and by causing a slider provided
with a recording device and/or a reproducing device to run on a
surface of said information recording medium; the contact angle of
water on the surface of said substrate having a value such that the
glide test does not result in failure.
4. A method as claimed in claim 3, wherein: an additional
correlation is also established between the contact angle of water
on the surface of said substrate before said washing/drying step
and an error rate where recording and/or reproducing are carried
out for the information recording medium produced by forming at
least said recording layer on the surface of said substrate; the
contact angle of water on the surface of said substrate having a
value such that the glide test does not result in failure and that
a recording error and/or a reproducing error are not caused when
the recording and/or the reproducing are carried out for the
information recording medium produced by forming at least said
recording layer on the surface of said substrate.
5. A method of producing a substrate for an information recording
medium, said method including the step of packaging said substrate
obtained through a washing/drying step, wherein: a contact angle of
water on a surface of said substrate is kept at 20.degree. or less
at least immediately before pre-washing and drying step which is
for pre-washing and drying said substrate prior to deposition of a
film on said substrate after it is unpacked.
6. A method of producing an information recording medium, said
method including the steps of preparing a substrate subjected to
precision polishing, washing and drying said substrate before
depositing a film thereon, and forming at least a recording layer
on said substrate after said washing and drying step, said method
comprising the steps of: obtaining a correlation between a contact
angle of water on a surface of said substrate before said washing
and drying step and a size of protrusions attached to the surface
of said substrate during said washing and drying step; and
controlling the contact angle of water on the surface of said
substrate before said washing and drying step so that said
protrusions have the size so as not to cause a hit when at least
said recording layer is formed on the surface of said substrate to
produce said information recording medium and when a slider
provided with a recording device and/or a reproducing device is
made to run on a surface of said information recording medium.
7. A method as claimed in claim 6, wherein said controlling step is
for controlling the contact angle of water on the surface of said
substrate before said washing and drying step so that said
protrusions have the size so as not to cause said hit and so as not
to cause an error upon recording and/or reproducing the information
recording medium which is produced by forming at least said
recording layer on the surface of said substrate.
8. A method of producing an information recording medium, said
method including the steps of preparing a substrate subjected to
precision polishing, washing and drying said substrate before
depositing a film thereon, and forming at least a recording layer
on said substrate after said washing and drying step, wherein: a
correlation is established between a contact angle of water on a
surface of said substrate before said washing and drying step and a
glide test fail rate in a glide test carried out by forming at
least said recording layer on the surface of said substrate to
produce said information recording medium and by causing a slider
provided with a recording device and/or a reproducing device to run
on a surface of said information recording medium; the contact
angle of water on the surface of said substrate having a value such
that the glide test does not result in failure.
9. A method as claimed in claim 8, wherein: an additional
correlation is also established between the contact angle of water
on the surface of said substrate before said washing and drying
step and an error rate where recording and/or reproducing are
carried out for the information recording medium produced by
forming at least said recording layer on the surface of said
substrate; the contact angle of water on the surface of said
substrate having a value such that the glide test does not result
in failure and that a recording error and/or a reproducing error
are not caused when the recording and/or the reproducing are
carried out for the information recording medium produced by
forming at least said recording layer on the surface of said
substrate.
10. A method of producing a substrate for an information recording
medium, said method including a washing/drying step of washing and
drying said substrate subjected to precision polishing, said method
comprising the steps of: preliminarily obtaining a correlation
between a content of at least one element of C, Al, Si, Fe, Cu, Zn,
and Zr contained in water used in said washing/drying step and a
size of protrusions attached to a surface of said substrate during
said washing/dying step; and determining the content of said at
least one element contained in the water used in said
washing/drying step so that said protrusions have the size so as
not to cause a hit when at least a recording layer is formed on the
surface of said substrate to produce said information recording
medium and when a slider provided with a recording device and/or a
reproducing device is made to run on a surface of said information
recording medium.
11. A method as claimed in claim 10 wherein said determining step
is for determining the content of said at least one element
contained in the water used in said washing/drying step so that
said protrusions have the size so as not to cause said hit and so
as not to cause an error upon recording and/or reproducing the
information recording medium which is produced by forming at least
said recording layer on the surface of said substrate.
12. A method of producing a substrate for an information recording
medium, said method including a washing/drying step of washing and
drying said substrate subjected to precision polishing, wherein:
the content of said at least one element of C, Al, Si, Fe, Cu, Zn,
and Zr contained in water used in said washing/drying step is equal
to 20 ppb (parts per billion) or less.
13. A method of producing an information recording medium, said
method including the steps of preparing a substrate subjected to
precision polishing, washing and drying said substrate before
depositing a film thereon, and forming at least a recording layer
on said substrate after said washing and drying step, said method
comprising the steps of: preliminarily obtaining a correlation
between a content of at least one element of C, Al, Si, Fe, Cu, Zn,
and Zr contained in water used in said washing and drying step and
a size of protrusions attached to a surface of said substrate
during said washing and drying step; and determining the content of
said at least one element contained in the water used in said
washing and drying step so that said protrusions have the size so
as not to cause a hit when at least a recording layer is formed on
the surface of said substrate to produce said information recording
medium and when a slider provided with a recording device and/or a
reproducing device is made to run on a surface of said information
recording medium.
14. A method as claimed in claim 13, wherein said determining step
is for determining the content of said at least one element
contained in the water used in said washing/drying step so that
said protrusions have the size so as not to cause said hit and so
as not to cause an error upon recording and/or reproducing the
information recording medium which is produced by forming at least
said recording layer on the surface of said substrate.
15. A method of producing an information recording medium, said
method including the steps of preparing a substrate subjected to
precision polishing, washing and drying said substrate before
depositing a film thereon, and forming at least a recording layer
on said substrate after said washing and drying step, wherein: the
content of said at least one element of C, Al, Si, Fe, Cu, Zn, and
Zr contained in water used in said washing and drying step is equal
to 20 ppb (parts per billion) or less.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a method of producing an
information recording medium for use as a recording medium for an
information processing apparatus and to a method of producing a
substrate for the information recording medium. This invention also
relates to the information recording medium for use as the
recording medium and to the substrate for the information recording
medium.
[0002] A magnetic disk is known as one of information recording
media for use as a recording medium for an information processing
apparatus. The magnetic disk comprises a substrate and a thin film
such as a magnetic layer formed thereon. With a recent demand for
an increase in recording density, a flying height which is a
distance between the magnetic disk and a magnetic head has a very
small value, for example, equal to 30 nm or less. As a consequence,
it is desired to provide a substrate having a surface high in
flatness and smoothness. The substrate having a surface high in
flatness and smoothness can be obtained by appropriately selecting
a polishing pad used in a polishing step or by reducing a particle
size of abrasive grains used in the polishing step.
[0003] In addition to the improvement in flatness and smoothness of
the surface of the substrate, the magnetic head is improved from a
thin film head to a magnetoresistive head (MR head) and a giant
magnetoresistive head (GMR head) utilizing an anisotropic
magnetoresistance in order to meet the increase in recording
density.
[0004] As described above, the high flatness of the surface of the
magnetic disk is essential and indispensable in order to achieve a
low flying height required to increase the recording density. In
case where the MR head is used, the surface of the magnetic disk is
required to be high in flatness and smoothness in view of thermal
asperity also. The thermal asperity is a phenomenon such that, if a
protrusion is present on the surface of the magnetic disk, the MR
hiead is affected by the protrusion to generate heat and, as a
consequence, the MR head becomes unstable in resistance value to
cause malfunction in electromagnetic conversion.
[0005] Thus, in order to reduce the flying height of the magnetic
head and to prevent occurrence of the thermal asperity, the demand
for the high flatness and the high smoothness of the surface of the
magnetic disk is more and more increasing day by day.
[0006] However, at the present stage, the increase in recording
density of the magnetic disk can not be achieved only by polishing
the surface of the substrate with high precision. Even if
high-precision polishing is performed, protrusions may thereafter
be formed on the substrate due to presence of foreign matters. In
this event, the high flatness and the high smoothness of the
magnetic disk can not be achieved. In fact, the removal of the
protrusions due to presence of the foreign matters is already
performed. However, the protrusions on the substrate, which are
very small and need not be removed in the past, cause a serious
problem at a present level of the increase in recording
density.
[0007] If the thin film such as the magnetic layer is deposited on
the substrate with the protrusions of the type attached to the
surface of the substrate, protrusions are formed on the surface of
the magnetic disk to become a factor inhibiting the reduction in
flying height of the magnetic head and the prevention of occurrence
of the thermal asperity (prevention of occurrence of a recording or
a reproducing error).
[0008] Likewise, if the thin film such as a recording layer is
deposited on the substrate with the protrusions of the type
attached to the surface of the substrate, protrusions are formed on
the surface of the information recording medium to become a factor
causing a defect such as the recording or the reproducing
error.
SUMMARY OF THE INVENTION
[0009] It is an object of this invention to provide a method of
producing a substrate for an information recording medium, which is
capable of suppressing and preventing a protrusion from being
formed on a substrate to act as a factor inhibiting a reduction in
flying height of a magnetic head and a prevention of occurrence of
thermal asperity and/or as a factor causing a defect in an
information recording medium,
[0010] It is another object of this invention to provide a method
of producing an information recording medium using the
above-mentioned substrate.
[0011] It is still another object of this invention to provide a
substrate for an information recording medium which is capable of
suppressing the influence of protrusions acting as a factor
inhibiting a reduction in flying height of a magnetic disk and a
prevention of occurrence of thermal asperity and/or as a factor
causing a defect in the information recording medium.
[0012] It is a further object of this invention to provide an
information recording medium using the above-mentioned
substrate.
[0013] The present inventors found out that, even if a substrate is
washed and dried in a washing/drying step, some protrusions may be
left without being diminished and that, if a thin film such as a
magnetic layer is deposited on the substrate with the protrusions
attached to the surface of the substrate, protrusions are formed on
the surface of a magnetic disk to become a factor inhibiting a
reduction in flying height of a magnetic head and a prevention of
occurrence of thermal asperity.
[0014] It has also been found out that the protrusions contain at
least one of C, O, Al, Si, Fe, Cu, Zn, and Zr present in a cleaning
liquid or an atmosphere.
[0015] The present inventors have investigated the reason why the
protrusions containing the above-mentioned element or elements are
attached to the substrate. As a consequence, it has been found out
that, if the surface of the substrate is washed or rinsed with
water and thereafter dried, the protrusions are left on the
substrate at local spots where the water is deposited and then
dried. It has also been found out that some of the protrusions
containing the above-mentioned element or elements can not be
removed by various washing techniques and can only be removed by
polishing the substrate again.
[0016] As the water used in the washing/drying step, use is
generally made of filtered water, DI water (deionized water), and
the like. The washing/drying step is carried out in a clean
atmosphere within a clean room or in an atmospheric air. The water
or the atmosphere mentioned above contains C, Al, Si, Fe, Cu, Zn,
Zr, and the like. It has been found out that the water containing
such element or elements, in combination with the surface condition
(hydrophobic nature) of the substrate, is left in particular
regions to form the protrusions. Even if the water containing such
element or elements has a very small amount on the order of ppb,
the protrusions are formed on the surface of the substrate.
[0017] It has been found out that the product defects due to
presence of the protrusions containing at least one of C, O, Al,
Si, Fe, Cu, Zn, and Zr can be avoided by determining and
controlling the content of such element or elements contained in
the water used in the washing/drying step and causing the
protrusions so that the product defects are avoided. This leads to
the completion of this invention.
[0018] Furthermore, investigation has been made about how the
protrusions are formed. As a result, it has been found out that the
size (height) of the protrusions is closely related to the
wettability of the surface of the substrate before washing.
Specifically, if the surface of the substrate before washing is
inferior in wettability (i.e., hydrophobic), water droplets of the
cleaning liquid locally stay on the surface of the substrate and
are dried. In this event, those elements contained in the water or
the atmosphere concentrate to the particular regions to form the
protrusions. On the other hand, if the surface of the substrate
before washing is superior in wettability (i.e., hydrophilic), the
water droplets of the cleaning liquid spread over the surface of
the substrate and are dried. In this event, those elements
contained in the water or the atmosphere do not concentrate to the
particular regions but are dispersed throughout the surface of the
substrate. Therefore, no protrusions are formed or, even if the
protrusions are formed, the height of the protrusions is too small
to cause occurrence of head crash or the thermal asperity.
[0019] As an index representative of the surface condition
(wettability) of the substrate, use is generally made of a contact
angle of water. The contact angle of water is an angle formed
between a surface of an object and a water droplet sifting on the
surface. It has been found out that the protrusions tend to be
produced in case where the contact angle of water on the surface of
the substrate before the washing/drying step exceeds
20.degree..
[0020] It has been found out that, in a production process of a
substrate for an information recording medium, product defects can
be avoided by the use of a correlation between the contact angle of
water and the size (height) of the protrusions. Specifically,
measurement is made of the contact angle of water on the surface of
the substrate before the washing/drying step. Measurement is also
made of the size (height) of the protrusions attached to the
surface of the substrate after the washing/drying step and
containing at least one of C, O, Al, Si, Fe, Cu, Zn, and Zr as a
main component. Then, the correlation between the contact angle of
water and the size (height) of the protrusions is obtained. Based
on the correlation, the contact angle of water on the surface of
the substrate before the washing/drying step is controlled so that
the protrusions will have such a size (height) that no product
defects are caused.
[0021] The wettability of the surface of the substrate is related
to the surface condition of the surface of the substrate and is
generally represented by the contact angle of water. The contact
angle of water is typically measured by a method called a sessile
drop method.
[0022] The surface condition (the wettability or the contact angle
of water) of the surface of the substrate depends upon treatment
techniques (such as in the washing/drying step) upon production of
the substrate, the environment upon production and inspection of
the substrate, the environment during storage of the substrate,
such as a packaging condition of the substrate and the type of a
bag packaging the substrate (the amount of a gas released from the
bag, the number of particles produced from the bag, and so on), the
storage period of the substrate, the surface roughness of the
substrate, the material of the substrate, the surface treatment
(for example, hydrophilic treatment) of the substrate, and the
like. A combination of those factors determines the wettability of
the surface of the substrate. It has been found out that not only
the washing/drying step but also those factors must be controlled
to control the contact angle of water on the surface of the
substrate before the washing/drying step. Based on these findings,
this invention has been made.
[0023] Thus, it has been found out that the product defects can be
avoided by defining the height of the protrusions formed on the
surface of the substrate and containing at least one of C, O, Al,
Si, Fe, Cu, Zn, and Zr to a predetermined value or less. This leads
to the completion of this invention.
[0024] This invention includes the following structures.
[0025] Structure 1-1
[0026] A method of producing a substrate for an information
recording medium, the method including a washing/drying step of
washing and drying the substrate subjected to precision polishing,
the method comprising:
[0027] obtaining a correlation between a contact angle of water on
a surface of the substrate before the washing/drying step and a
size (height) of protrusions attached to the surface of the
substrate after the washing/drying step; and
[0028] controlling (setting) the contact angle of water on the
surface of the substrate before the washing/drying step so that the
protrusions will have such a size (height) that no hit is caused
when at least a recording layer is formed on the substrate to
produce the information recording medium and a slider provided with
a recording device and/or a reproducing device is made to run on a
surface of the information recording medium and/or that no error is
caused upon carrying out a recording operation and/or a reproducing
operation.
[0029] Structure 1-2
[0030] A method of producing a substrate for an information
recording medium, the method including a washing/drying step of
washing and drying the substrate subjected to precision polishing,
wherein:
[0031] a correlation is established between a contact angle of
water on a surface of the substrate before the washing/drying step
and a glide test fail rate in a glide test carried out by forming
at least a recording layer on the surface of the substrate to
produce the information recording medium and by causing a slider
provided with a recording device and/or a reproducing device to run
on a surface of the information recording medium;
[0032] an additional correlation being also established between the
contact angle of water on the surface of said substrate before said
washing/drying step and an error rate where recording and/or
reproducing are carried out for the information recording medium
produced by forming at least said recording layer on the surface of
said substrate;
[0033] the contact angle of water on the surface of said substrate
having a value such that the glide test does not result in failure
and that a recording error and/or a reproducing error are not
caused when the recording and/or the reproducing are carried out
for the information recording medium produced by forming at least
said recording layer on the surface of said substrate.
[0034] Structure 1-3
[0035] A method as described in the structure 1-1 or 1-2, wherein
the contact angle of water on the surface of the substrate before
the washing/drying step is equal to 20.degree. or less.
[0036] Structure 1-4
[0037] A method of producing a substrate for an information
recording medium, the method including the step of packaging the
substrate obtained through a washing/drying step, wherein:
[0038] the contact angle of water on a surface of the substrate is
kept at 20.degree. or less at least immediately before pre-washing
and drying the substrate prior to deposition of a film on the
substrate after it is unpacked.
[0039] Structure 1-5
[0040] A method as described in the structure 1-4, wherein:
[0041] the contact angle of water on a surface of the substrate at
is kept at 20.degree. or less for a period immediately after the
washing/drying step and immediately before a pre-washing and drying
step performed before a film is deposited on the substrate which is
unpacked.
[0042] Structure 1-6
[0043] A method as described in any one of the structures 1-1
through 1-5, wherein the substrate is a glass substrate.
[0044] Structure 1-7
[0045] A method as described in any one of the structures 1-1
through 1-6, wherein the substrate is a substrate for a magnetic
disk.
[0046] Structure 1-8
[0047] A method of producing an information recording medium, the
method including the steps of preparing a substrate subjected to
precision polishing, washing and drying the substrate before
depositing a film thereon, and forming at least a recording layer
on the substrate after the washing and drying step, the method
comprising:
[0048] obtaining a correlation between a contact angle of water on
a surface of the substrate prior to washing in the washing and
drying step and a size (height) of protrusions attached to the
surface of the substrate after the washing and drying step; and
[0049] controlling (setting) the contact angle of water on the
surface of the substrate prior to washing in the washing and drying
step so that the protrusions will have such a size (height) that no
hit is caused when at least a recording layer is formed on the
substrate to produce the information recording medium and a slider
having a recording device and/or a reproducing device is made to
run on a surface of the information recording medium and/or that no
error is caused upon carrying out a recording operation and/or a
reproducing operation.
[0050] Structure 1-9
[0051] A method of producing an information recording medium, the
method including the steps of preparing a substrate subjected to
precision polishing, washing and drying the substrate before
depositing a film thereon, and forming at least a recording layer
on the substrate after the washing and drying step, wherein:
[0052] a correlation is established between a contact angle of
water on a surface of the substrate before the washing and drying
step and a glide test fail rate in a glide test carried out by
forming at least the recording layer on the surface of the
substrate to produce the information recording medium and by
causing a slider provided with a recording device and/or a
reproducing device to run on a surface of the information recording
medium;
[0053] an additional correlation being also established between the
contact angle of water on the surface of said substrate before said
washing and drying step and an error rate where recording and/or
reproducing are carried out for the information recording medium
produced by forming at least said recording layer on the surface of
said substrate;
[0054] the contact angle of water on the surface of said substrate
having a value such that the glide test does not result in failure
and that a recording error and/or a reproducing error are not
caused when the recording and/or the reproducing are carried out
for the information recording medium produced by forming at least
said recording layer on the surface of said substrate.
[0055] Structure 1-10
[0056] A method as described in the structure 1-8 or 1-9, wherein
the contact angle of water on the surface of the substrate prior to
washing in the washing and drying step is equal to 20.degree. or
less.
[0057] Structure 1-11
[0058] A method as described in any one of the structures 1-8
through 1-10, wherein the washing and drying step uses spin
dry.
[0059] Structure 1-1 2
[0060] A method as described in any one of the structures 1-8
through 1-11, wherein the substrate is a glass substrate.
[0061] Structure 1-13
[0062] A method as described in any one of the structures 1-8
through 1-11 wherein the substrate is a substrate for a magnetic
disk.
[0063] According to the structure 1-1, the contact angle of water
on the surface of the substrate before the washing/drying step
(particularly before drying) as a factor causing protrusions
containing at least one of C, O, Al, Si, Fe, Cu, Zn, and Zr is set
(determined, preferably, controlled) so that product defects can be
avoided. Thus, it is possible to avoid product defects.
[0064] Specifically, the contact angle of water on the surface of
the substrate before the washing/drying step is set that, when at
least the recording layer is formed on the substrate to produce the
information recording medium, protrusions will have a size (height)
too small to hit the slider provided with the recording and/or the
reproducing device and/or that no error is caused upon carrying out
the recording operation and/or the reproducing operation.
Therefore, it is possible to prevent occurrence of head crash and
thermal asperity and to eliminate negative factors causing a defect
such as an error in the recording operation and/or the reproducing
operation of the information recording medium.
[0065] In this invention, the washing/drying step involves a
washing operation immediately after precision polishing (final
polishing), a washing operation after chemical reinforcement, a
washing operation before shipment, a washing operation immediately
before deposition, or any other washing operation carried out after
the precision polishing and before the deposition. Once the
protrusions including at least one of C, O, Al, Si, Fe, Cu, Zn and
Zr are formed in any one of the washing/drying steps corresponding
to the above-mentioned washing operations, such protrusions may not
be removed by the subsequent washing step or steps. Therefore, it
is preferable that the contact angle of water on the surface of the
substrate before each of these washing/drying steps is determined
and controlled so as to avoid product defects.
[0066] In the structure 1-1, it is sufficient that the contact
angle has a value such that the product defects are avoided.
Therefore, the contact angle need not be so small as to require an
excessively high cost. In other words, the contact angle can be
determined taking the cost into consideration.
[0067] The size (height) of the protrusions may be a value obtained
by directly measuring only the protrusions containing at least one
of C, O, Al, Si, Fe, Cr, Zn, and Zr or may be a value obtained by
measuring the surface roughness of the substrate before and after
the washing/drying step.
[0068] With the structure 1-2, the contact angle of water on the
surface of the substrate has a value such that the glide test does
not result in failure and that a recording error and/or a
reproducing error are not caused. Thus, it is possible to produce
the substrate for the information recording medium capable of
avoiding the defect and the error mentioned above.
[0069] In the structure 1-3, the contact angle of water on the
surface of the substrate for the information recording medium
before the washing/drying step (particularly before drying) of the
substrate is controlled to be equal to 20.degree. or less so that
the height of the protrusions formed on the substrate and
containing at least one of C, O, Al, Si, Fe, Cu, Zn, and Zr is
reduced so as to avoid the product defects when the information
recording medium is produced.
[0070] As the contact angle of water on the surface of the
substrate for the information recording medium before the
washing/drying step of the substrate is smaller, the height of the
protrusions containing at least one of C, O, Al, Si, Fe, Cu, Zn,
and Zr is reduced. Specifically, the contact angle of water on the
surface of the substrate before the washing/drying step is
preferably equal to 5.degree. or less, more preferably, 10.degree.
or less.
[0071] With the structure 1-4, in the method of producing the
substrate for an information recording medium including the step of
packaging the substrate obtained after the washing/drying step, the
contact angle of water on the surface of the substrate is kept at
20.degree. or less (preferably, 10.degree. or less) at least
immediately before pre-washing and drying the substrate prior to
deposition of a film on the substrate after it is unpacked With the
structure 1-5, the contact angle of water on the surface of the
substrate is kept at 20.degree. or less (preferably, 10.degree. or
less) for the period immediately after the washing/drying step and
immediately before a pre-washing and drying step performed before
the film is deposited on the substrate which is unpacked. Thus,
even if spin dry is performed after the substrate is washed by DI
water alone, the protrusions containing at least one of C, O, Al,
Si, Fe, Cu, Zn, and Zr and having a height causing the product
defects are not formed. Therefore, it is possible to shorten the
production process and to lower the cost.
[0072] For example, the contact angle of water on the surface of
the substrate is kept at 20.degree. or less (preferably, 10.degree.
or less) during the above-mentioned period by (1) shortening a time
period required to wash, inspect, and package the substrate, (2)
using, as a case or a bag for packaging the substrate, a packaging
material which produces a less amount of a release gas or a less
number of particles, and (3) packaging the substrate in the case or
the bag with a desiccant contained therein.
[0073] The structure 1-6 is defined because this invention is
particularly effective in case where the substrate is the glass
substrate.
[0074] The structure 1-7 is defined because the above-mentioned
protrusions cause a serious problem particularly in the substrate
for the magnetic disk intended to reduce the flying height of a
magnetic head.
[0075] The substrate for an information recording medium according
to this invention is adapted to the substrate for the magnetic disk
subjected to recording/reproducing operations with an extremely
small distance kept between a slider and the surface of the
magnetic disk.
[0076] Furthermore, the above-mentioned protrusions cause a serious
problem particularly in the substrate for the magnetic disk to be
used with the magnetoresistive head (MR head) intended to prevent
the thermal asperity, more particularly in the substrate for the
magnetic disk to be used with the giant magnetoresistive head (GMR
head). Therefore, the above-mentioned substrate for a magnetic disk
is particularly effective for use with the magnetoresistive head or
the giant magnetoresistive head.
[0077] In the structure 1-8, in the method of producing an
information recording medium, the step of washing ad drying the
substrate for the information recording medium prior to deposition
of the film on the substrate (particularly, the step of pre-washing
and drying the substrate immediately before deposition) has the
content similar to that of the structure 1-1. This is because the
spin dry is carried out in the step of washing and drying the
substrate for the information recording medium prior to deposition
of the film on the substrate and because, even if the
above-mentioned protrusions are not formed on the substrate,
product defects can not be avoided in case where the protrusions
are formed during the step of washing and drying the substrate
prior to deposition.
[0078] The structure 1-9 is effective as mentioned in conjunction
with the structure 1-2.
[0079] With the structure 1-10, the contact angle of water on the
surface of the substrate before washing prior to deposition
(particularly, pre-washing immediately before deposition) of a film
on the substrate is equal to 20.degree. or less. Thus, the height
of the protrusions formed on the substrate and containing at least
one of C, O, Al, Si, Fe, Cu, Zn, and Zr as a main component is
reduced to a level such that the product defects are not caused
when the information recording medium is made.
[0080] For example, the contact angle of water on the surface of
the substrate before washing prior to deposition is controlled to
be equal to 20.degree. or less by the method described in
conjunction with the structure 1-4 or by treating the substrate in
a washing bath (acid, alkali, neutral detergent, and the like) or a
hydrophilic treatment bath (silicofluoric acid) prior to
deposition.
[0081] This invention is particularly effective in the
washing/drying step using a drying technique which does not require
a chemical solution. For example, such drying method may be the
spin dry, air knife (drying by blowing compressed air), and heat
drying. The structure 1-11 is defined because the protrusions are
produced particularly in the washing/drying step using the spin
dry.
[0082] Typically, the spin dry performs dehydration alone by
high-speed rotation. The spin dry is applicable to both of cassette
type (batch type) processing and sheet-feed type processing. In the
spin dry, a clean gas such as nitrogen can be made to flow in a
desiccator or can be blown to the surface of the substrate. The
spin dry includes a method of spraying a pure water shower onto the
surface of the substrate to wash or rinse the substrate and to
prevent the substrate from being dried, then stopping the pure
water shower, and drying the substrate by high speed rotation, a
method of directing a jet of high-pressure water (pure water) onto
the surface of the substrate being rotated at a high speed to wash
the substrate, then stopping the jet of the high-pressure water,
and drying the substrate by high speed rotation, and so on.
[0083] The washing/drying step using the spin dry includes the spin
dry after the washing by the DI water alone, the spin dry after
rinsing with the DI water, or the like.
[0084] The structure 1-12 is defined because this invention is
effective in case where the substrate is the glass substrate
excellent in flatness and smoothness.
[0085] The structure 1-13 is defined because the above-mentioned
protrusions cause a serious problem particularly in the magnetic
disk intended to reduce the flying height of the magnetic head.
[0086] This invention is particularly effective in case where the
magnetic disk is to be mounted in an information recording
apparatus using a magnetoresistive head or a giant magnetoresistive
head as a recording/reproducing head.
[0087] Structure 2-1
[0088] A method of producing a substrate for an information
recording medium, the method including a washing/drying step of
washing and drying the substrate subjected to precision polishing,
the method comprising:
[0089] preliminarily calculating a correlation between a content of
at least one element of C, Al, Si, Fe, Cu, Zn, and Zr contained in
water used in the washing/drying step and a size (height) of
protrusions attached to the surface of the substrate after the
washing/drying step; and
[0090] determining the content of the element contained in the
water used in the washing/drying step so that the protrusions will
have such a size (height) that no hit is caused when at least a
recording layer is formed on the substrate to produce the
information recording medium and a slider provided with a recording
device and/or a reproducing device is made to run afloat on a
surface of the information recording medium and/or that no error is
caused upon carrying out a recording operation and/or a reproducing
operation.
[0091] Structure 2-2
[0092] A method of producing a substrate for an information
recording medium, the method including a washing/drying step of
washing and drying the substrate subjected to precision polishing,
wherein:
[0093] the content of at least one element of C, Al, Si, Fe, Cu,
Zn, and Zr contained in water used in the washing/drying step is
equal to 20 ppb or less.
[0094] Structure 2-3
[0095] A method as described in the structure 2-1 or 2-2, wherein
drying in the washing/drying step is spin dry.
[0096] Structure 2-4
[0097] A method as described in any one of the structures 2-1
through 2-3, wherein the substrate is a substrate for a magnetic
disk.
[0098] Structure 2-5
[0099] A method as described in the structure 2-4, wherein the
substrate is a substrate for a magnetic disk to be used with a
magnetoresistive head or a giant magnetoresistive head.
[0100] Structure 2-6
[0101] A method of producing an information recording medium, the
method including the steps of preparing a substrate subjected to
precision polishing, pre-washing and drying the substrate before
depositing a film thereon, and forming at least a recording layer
on the substrate after the pre-washing and drying step, the method
comprising:
[0102] preliminarily calculating a correlation between a content of
at least one element of C, Al, Si, Fe, Cu, Zn, and Zr contained in
water used in pre-washing in the pre-washing and drying step and a
size (height) of protrusions attached to the surface of the
substrate after the pre-washing and drying step; and
[0103] determining the content of the element contained in the
water used in the pre-washing and drying step so that the
protrusions will have such a size (height) that no hit is caused
when at least a recording layer is formed on the substrate to
produce the information recording medium and a slider having a
recording device and/or a reproducing device is made to run afloat
on a surface of the information recording medium and/or that no
error is caused upon carrying out a recording operation and/or a
reproducing operation.
[0104] Structure 2-7
[0105] A method of producing a substrate for an information
recording medium, the method including the steps of preparing a
substrate subjected to precision polishing, pre-washing and drying
the substrate before depositing a film thereon, and forming at
least a recording layer on the substrate after the pre-washing and
drying step, wherein:
[0106] the content of at least one element of C, Al, Si, Fe, Cu,
Zn, and Zr contained in water used in the pre-washing and drying
step is equal to 20 ppb or less.
[0107] Structure 2-8
[0108] A method as described in the structure 2-6 or 2-7, wherein
drying in the pre-washing and drying step is spin dry.
[0109] Structure 2-9
[0110] A method as described in any one of the structures 2-6
through 2-8, wherein the substrate is a substrate for a magnetic
disk.
[0111] Structure 2-10
[0112] A method as described in the structure 2-9, wherein the
substrate is a substrate for a magnetic disk to be used with a
magnetoresistive head or a giant magnetoresistive head.
[0113] According to the structure 2-1, the content of at least one
element of C, Al, Si, Fe, Cu, Zn, and Zr contained in the water
used in the washing/drying step and causing protrusions containing
at least one of C, O, Al, Si, Fe, Cu, Zn, and Zr is determined and
controlled so that product defects can be avoided. Thus, it is
possible to avoid product defects.
[0114] Specifically, the content of at least one element of C, Al,
Si, Fe, Cu, Zn, and Zr contained in the water used in the
washing/drying step is determined and controlled so that, when at
least the recording layer is formed on the substrate to produce the
information recording medium, protrusions will have a size (height)
too small to hit the slider provided with the recording and/or the
reproducing device and/or that no error is caused upon carrying out
the recording operation and/or the reproducing operation.
Therefore, it is possible to prevent occurrence of head crash and
thermal asperity and to eliminate negative factors causing a defect
such as an error in the recording operation and/or the reproducing
operation of the information recording medium. The height of the
protrusions is represented by Rp or the like and is preferably
equal to 0 nm (i.e., no protrusion is formed). The height of the
protrusions may be a value obtained by directly measuring only the
protrusions or may be a value obtained by measuring the surface
roughness of the substrate before and after the washing/drying
step.
[0115] In this invention, the washing/drying step involves a
washing operation immediately after precision polishing (final
polishing), a washing operation after chemical reinforcement, a
washing operation before shipment, a washing operation immediately
before deposition, or any other washing operation carried out after
the precision polishing and before the deposition. Once the
protrusions including at least one of C, O, Al, Si, Fe, Cu, Zn and
Zr are formed in any one of the washing/drying steps corresponding
to the above-mentioned washing operations, such protrusions may not
be removed by the subsequent various washing steps. Therefore, it
is preferable that the content of at least one element of C, Al,
Si, Fe, Cu, Zn, and Zr contained in the water used in each of these
washing/drying steps is determined and controlled so as to avoid
product defects.
[0116] The washing/drying step generally comprises (1) a washing
step using acid, alkali, a neutral detergent, and any other
appropriate cleaning agent, (2) a rinsing step using pure water or
a solvent, and (3) a drying step. However, the washing/drying step
may be a simple process comprising dipping into DI water followed
by spin dry.
[0117] In the structure 2-2, the content of at least one element of
C, Al, Si, Fe, Cu, Zn, and Zr contained in the water used in the
washing/drying step of the substrate for an information recording
medium is equal to 20 ppb or less so that the size (height) of the
protrusions formed on the substrate and containing at least one
element of C, O, Al, Si, Fe, Cu, Zn, and Zr is reduced so as to
avoid the product defects when the information recording medium is
produced.
[0118] As the content of at least one element of C, Al, Si, Fe, Cu,
Zn, and Zr contained in the water used in the washing/drying step
of the substrate is smaller, the size (height) of the protrusions
containing at least one of C, O, Al, Si, Fe, Cu, Zn, and Zr is
reduced (lowered). Specifically, the content is preferably equal to
15 ppb or less, more preferably, 10 ppb or less.
[0119] The content of the element or elements contained in the
water can be obtained, for example, by the absorptionmetric
analysis or the ICP (Inductively Coupled Plasma) atomic emission
spectroscopy. The content of the above-mentioned element contained
in the water can be appropriately adjusted, for example, by
repetition of filtering or ion exchange. The height of the
protrusions is represented by Rp or the like and is preferably
equal to 0 nm (i.e., no protrusion is formed).
[0120] The protrusions are formed particularly when a drying
technique without using a chemical solution is performed. For
example, the drying technique without using the chemical solution
may be the spin dry, air knife (drying by blowing compressed air),
and heat drying, The structure 2-3 is defined because the
protrusions are formed particularly in the washing/drying step
using the spin dry.
[0121] The structure 2-4 is defined because the above-mentioned
protrusions cause a serious problem particularly in the substrate
for the magnetic disk intended to reduce the flying height of a
magnetic head.
[0122] The substrate for an information recording medium according
to this invention is adapted to the substrate for the magnetic disk
subjected to recording/reproducing operations with an extremely
small distance kept between a slider and the surface of the
magnetic disk.
[0123] The structure 2-5 is defined because the above-mentioned
protrusions cause a serious problem particularly in the substrate
for the magnetic disk to be used with the magnetoresistive head (MR
head) intended to prevent the thermal asperity, more particularly
in the substrate for the magnetic disk to be used with the giant
magnetoresistive head (GMR head).
[0124] The structure 2-6 defines the method of producing an
information recording medium, in which the content similar to that
of the structure 2-1 is applied to the step of washing and drying
the substrate for the information recording medium prior to
deposition of the film on the substrate (particularly, the step of
pre-washing and drying the substrate immediately before
deposition). This is because the spin dry is often carried out in
the step of washing and drying the substrate for the information
recording medium prior to deposition of the film on the substrate
and because, even if the above-mentioned protrusions are not formed
on the substrate, product defects can not be avoided in case where
the protrusions are formed during the step of washing and drying
the substrate prior to deposition.
[0125] With the structure 2-7, the content of at least one element
of C, Al, Si, Fe, Cu, Zn, and Zr contained in the water used in the
step of washing (particularly, pre-washing immediately before
deposition) and drying the substrate prior to deposition of a film
on the substrate is controlled to be equal to 20 ppb or less. Thus,
the size (height) of the protrusions formed on the substrate and
containing at least one of C, O, Al, Si, Fe, Cu, Zn, and Zr is
reduced to a level such that the product defects are not caused
when the information recording medium is made.
[0126] As the content of the above-mentioned element contained in
the water used in the pre-washing and drying step is smaller, the
size (height) of the protrusions containing at least one of C, O,
Al, Si, Fe, CU, Zn, and Zr is reduced (lowered). Specifically, the
content is preferably equal to 15 ppb or less, more preferably, 10
ppb or less. The height of the protrusions is represented by Rp or
the like and is preferably equal to 0 nm (i.e., no protrusion is
formed).
[0127] The protrusions are formed particularly when a drying
technique without using a chemical solution is performed. For
example, the drying technique without using the chemical solution
may be the spin dry, air knife (drying by blowing compressed air),
and heat drying. The structure 2-8 is defined because the
protrusions are formed particularly in the washing/drying step
using the spin dry.
[0128] Typically, the spin dry performs dehydration alone by
high-speed rotation. The spin dry is applicable to both of cassette
type (batch type) processing and sheet-feed type processing. In the
spin dry, a clean gas such as a nitrogen gas can be made to flow in
a desiccator or can be blown to the surface of the substrate. The
spin dry includes a method of spraying a pure water shower onto the
surface of the substrate to wash or rinse the substrate and to
prevent the substrate from being dried, then stopping the pure
water shower, and drying the substrate by high speed rotation, a
method of directing a jet of high-pressure water (pure water) onto
the surface of the substrate being rotated at a high speed to wash
the substrate, then stopping the jet of the high-pressure water,
and drying the substrate by high speed rotation, and so on.
[0129] The washing/drying step using the spin dry includes the spin
dry after the washing by the DI water alone, the spin dry after
rinsing with the DI water, or the like.
[0130] The structure 2-9 is defined because the above-mentioned
protrusions cause a serious problem particularly in the magnetic
disk intended to reduce the flying height of the magnetic head.
[0131] With the structure 2-9, the magnetic disk capable of
carrying out high-density recording/reproducing operations can be
obtained.
[0132] The structure 2-10 is defined because the above-mentioned
protrusions cause a serious problem particularly in the substrate
for the magnetic disk to be used with the magnetoresistive head (MR
head) intended to prevent the thermal asperity, more particularly
in the substrate for the magnetic disk to be used with the giant
magnetoresistive head (GMR head).
[0133] With the structure 2-10, the magnetic disk capable of
carrying out higher-density recording/reproducing operations can be
obtained.
[0134] The height of the protrusions containing at least one of C,
O, Al, Si, Fe, Cu, Zn, and Zr depends upon the surface condition
(wettability) of the surface of the substrate. If the wettability
of the surface of the substrate is improved (i.e., the contact
angle of water becomes small), water droplets of the cleaning water
spread over the surface of the substrate and are dried. In this
event, C, O, Al, Si, Fe, Cu, Zn, and/or Zr forming the protrusions
do not concentrate to particular regions but are dispersed
throughout the surface of the substrate.
[0135] As described above, if the content of at least one element
of C, Al, Si, Fe, Cu, Zn, and Zr contained in the water used in the
washing/drying step is equal to 20 ppb or less, the protrusions
containing at least one of C, O, Al, Si, Fe, Cu, Zn, and Zr and
having the size (height) causing the product defects are not formed
in general. Furthermore, it the content of at least one element of
C, Al, Si, Fe, Cu, Zn, and Zr contained in the water is controlled
to 20 ppb or less and simultaneously if the wettability of the
surface of the substrate is improved, the protrusions are more
hardly produced.
[0136] The contact angle of water on the surface of the substrate
is preferably equal to 20.degree. or less, more preferably, equal
to 10.degree. or less. The contact angle of water is measured by
the sessile drop method.
[0137] The contact angle of water (wettability) depends upon the
amount of organic substances attached to the surface of the
substrate, the surface roughness of the substrate, the material of
the substrate, and the like. Among others, the amount of the
organic substances attached to the surface of the substrate greatly
affects the contact angle. Therefore, it is desirable to store the
substrates under an environment capable of keeping the contact
angle at a small value, i.e., an environment in which a less amount
of the organic substances are produced from a substrate case or a
bag and attached to the surface of the substrate.
[0138] Structure 3-1
[0139] A substrate for an information recording medium, wherein
protrusions attached and formed on a surface of the substrate and
containing at least one of C, O, Al, Si, Fe, Cu, Zn, and Zr have a
height (Rp) such that no hit is caused when at least a recording
layer is formed on the substrate to produce the information
recording medium and a slider provided with a recording device
and/or a reproducing device is made to run afloat on a surface of
the information recording medium and/or that no error is caused
upon carrying out a recording operation and/or a reproducing
operation.
[0140] Structure 3-2
[0141] A substrate as described in the structure 3-1, wherein the
height (Rp) of the protrusions is such that no hit is caused when
the slider is made to run afloat with respect to the surface of the
information recording medium at a flying height of 30 nm or less
and/or that no error is caused upon carrying out a recording
operation and/or a reproducing operation.
[0142] Structure 3-3
[0143] A substrate as described in the structure 3-1 or 3-2,
wherein the height of the protrusions attached and formed on the
surface of the substrate falls between 0 and 30 nm in terms of
Rp.
[0144] Structure 3-4
[0145] A substrate as described in any one of the structures 3-1
through 3-3, wherein the protrusions have a ratio Rp/Rv which is
not smaller than 10.
[0146] Structure 3-5
[0147] A substrate as described in any one of the structures 3-1
through 3-4, wherein an interface indicative of attachment of
foreign matters is present between the protrusions and the surface
of the substrate.
[0148] Structure 3-
[0149] A substrate as described in any one of the structures 3-1
through 3-5, wherein the protrusions are formed by an impurity
element contained in water used in a washing/drying step of washing
and drying the substrate.
[0150] Structure 3-7
[0151] A substrate as described in the structure 3-6, wherein a
contact angle of water on the surface of the substrate before the
washing/drying step is equal to 20.degree. or less.
[0152] Structure 3-8
[0153] A substrate as described in any one of the structures 3-1
through 3-7, wherein the substrate is a substrate for a magnetic
disk.
[0154] Structure 3-9
[0155] An information recording medium comprising a substrate
described in any one of the structures 3-1 through 3-8 and at least
a recording layer formed thereon.
[0156] Structure 3-10
[0157] An information recording medium as described in the
structure 3-9, wherein the recording layer is a magnetic layer.
[0158] Structure 3-11
[0159] An information recording medium as described in the
structure 3-10, wherein the information recording medium is a
magnetic disk for use with a magnetoresistive head or a giant
magnetoresistive head.
[0160] According to the structure 3-1, the protrusion attached and
formed on the surface of the substrate and containing at least one
of C, O, Al, Si, Fe, Cu, Zn, and Zr has a height (Rp) such that the
product defects can be avoided. Thus, the product defects can be
avoided.
[0161] Specifically, the protrusion attached and formed on the
surface of the substrate and containing at least one of C, O, Al,
Si, Fe, Cu, Zn, and Zr has a height (Rp) such that no hit is caused
when at least a recording layer is formed on the substrate to
produce the information recording medium and a slider provided with
a recording device and/or a reproducing device is made to run
afloat on a surface of the information recording medium and/or that
no error is caused upon carrying out a recording operation and/or a
reproducing operation. Thus, it is possible to prevent occurrence
of head crash and thermal asperity and to eliminate negative
factors causing a defeat such as an error in the recording
operation and/or the reproducing operation of the information
recording medium. Herein, the height of the protrusions may be a
value obtained by directly measuring only the protrusions or may be
a value obtained by measuring the surface roughness of the
substrate before and after the washing/drying step.
[0162] As described in the structure 3-2, the slider has a flying
height which is preferably equal to 30 nm or less, more preferably
20 nm or less, in order to enable recording and reproducing
operations at a high density. Depending upon a
recording/reproducing system, the slider may be brought into pseudo
contact with the surface of the recording medium or the slider may
run in contact therewith. In such events, the flying height of the
slider may be equal to 0 nm. Therefore, this invention includes the
case where the flying height of the slider is equal to 0 nm.
[0163] In the structure 3-3, the height of the protrusions attached
and formed on the surface of the substrate is controlled to fall
between 0 and 30 nm in terms of Rp. With this structure, it is
possible to avoid the hit of the slider when the slider has a
flying height of 30 nm. Furthermore, in case where the slider has a
flying height smaller than 30 nm and 20 nm, the height of the
protrusions are controlled to fall between 0 and 20 nm and between
0 and 10 nm in terms of Rp, respectively. Thus, it is possible to
obtain the information recording medium capable of carrying out the
recording and the reproducing operations at a high density without
causing a hit of the slider and a recording or a reproducing
error.
[0164] Herein, Rp represents a distance from a mean line to a
highest peak. Rp can be measured by the atomic force microscope or
a probe-type surface roughness meter such as Talystep
(Taylor-Hobson). In this invention, it is necessary to obtain
accurate and strict information about the surface condition of the
substrate (medium) in order to achieve high-density recording and
reproducing operations. Therefore, the value measured by the atomic
force microscope is used as Rp.
[0165] It is noted here that the value of Rp never exceeds the
maximum roughness Rmax. Rmax has a correlation with the flying
height of the slider afloat on the surface of the medium. Unless
Rmax is sufficiently smaller than the flying height of the slider,
the head inevitably collides with the protrusions. In case of a
hard disk of the CSS (Contact Start Stop) system in which the
flying height of the slider is 30 nm or less, it is practically
desired that Rmax is equal to about 10 nm. In case of a hard disk
of the CSS system in which the flying height of the slider is 20 nm
or less, Rmax is required to have a further small value. In case
where the recording or the reproducing operation is carried out
while the slider is kept In contact with the surface of the medium,
it is necessary to keep the surface condition such that the slider
is not attracted and attached to the surface of the medium.
[0166] In the structure 3-4, Rv represents the height from the
center line to the bottom. Rv is produced by polishing and has a
value between 2 and 3 nm irrespective of presence or absence of the
protrusions. If the surface roughness is small, Rv has a smaller
value. The surface of the substrate obtained by typical grinding
and polishing has a ratio Rp/Rv smaller than 10. On the other hand,
the protrusions causing the product defects are indicated by the
ratio Rp/Rv not smaller than 10 and are produced due to the
presence of impurity elements contained in the cleaning water. In
the substrate for the magnetic disk to be used with the slider
having a flying height of 30 nm or less, the protrusions causing
the product defects have a height not smaller than 20 to 30 nm.
Therefore, if the ratio Rp/Rv of the surface of the substrate is
great, this means that the protrusions causing the product defects
are formed. If the ratio Rp/Rv of the surface of the substrate is
smaller than 10, the protrusions are very low in height and do not
cause the product defects even if the protrusions are formed.
[0167] As described in the structure 3-5, the protrusions can be
judged as the foreign matters attached to the substrate in case
where the interface is present between the protrusions and the
surface of the substrate.
[0168] Thus, since the protrusions are substances attached to the
substrate, the protrusions are similarly produced in any substrate
other than the glass substrate.
[0169] As described in the structure 3-6, the protrusions are
formed by the impurity elements (C, O, Al, Si, Fe, Cu, Zn, or Zr)
contained in the water used in the washing/drying step. From the
experimental results which will later be described, it has been
confirmed that the protrusions depend upon the surface condition
(wettability) of the surface of the substrate. If the wettability
of the surface of the substrate is improved (i.e., the contact
angle of water becomes small), water droplets of the cleaning water
containing the impurity elements spread over the surface of the
substrate and are dried. In this event, the impurity elements
forming the protrusions do not concentrate to particular regions
but are dispersed throughout the surface of the substrate so that
the protrusions are not formed or, even formed, are extremely small
in size. On the contrary, if the contact angle of water on the
surface of the substrate is increased, each water droplet of the
cleaning water containing the impurity elements concentrates to a
single spot and is then dried. Therefore, the above-mentioned
problems are caused and the protrusions are formed.
[0170] The protrusions are formed particularly when a drying
technique without using a chemical solution is performed. For
example, the drying technique without using the chemical solution
may be the spin dry, air knife (drying by blowing compressed air),
and heat drying. In these drying techniques, a small amount of the
DI water is left on the surface as a thin film so that the
protrusions are readily formed, unlike the washing/drying technique
using IPA.
[0171] Accordingly, as described in the structure 3-7, it is
preferable that the contact angle of water on the surface of the
substrate is reduced in case where the substrate is washed and
dried as described in the structure 3-6. Specifically, the contact
angle is preferably equal to 20.degree. or less, more preferably,
10.degree. or less. The contact angle of water is measured by the
sessile drop method.
[0172] The structure 3-8 is defined because the above-mentioned
protrusions cause a serious problem particularly in the substrate
for the magnetic disk intended to reduce the flying height of a
magnetic head.
[0173] The substrate for an information recording medium according
to this invention is adapted to the substrate for the magnetic disk
subjected to recording/reproducing operations with an extremely
small distance kept between the slider and the surface of the
magnetic disk.
[0174] As described in the structure 3-9, the magnetic disk capable
of carrying out high-density recording and reproducing operations
can be obtained by forming the magnetic layer on the substrate
described in any one of the structures 3-1 and 3-8.
[0175] As described in the structure 3-10, the information
recording medium suppressed in occurrence of defects can be
obtained by forming a recording layer on the substrate described in
any one of the structures 3-1 through 3-8.
[0176] The structure 3-11 is defined because the above-mentioned
protrusions cause a serious problem particularly in the magnetic
disk to be used with the magnetoresistive head (MR head), more
particularly in the magnetic disk to be used with the giant
magnetoresistive head (GMR head).
[0177] With the structure 3-11, the magnetic disk capable of
carrying out higher-density recording/reproducing operations can be
obtained.
BRIEF DESCRIPTION OF THE DRAWING
[0178] FIG. 1 shows the relationship between the contact angle of
water and glide test pass rate; and
[0179] FIG. 2 is a front view for describing a test for
investigating the relationship between a package material and the
contact angle of water on the surface of the substrate.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
EXAMPLE 1-1
[0180] In Example 1-1, investigation has been made about the
relationship between a contact angle and a protrusion height and
the relationship between the contact angle and a glide defect
(namely, a glide test fail or a glide fail).
[0181] Several thousands of disk-shaped glass substrates were
prepared. A pair of principal surfaces of each glass substrate were
subjected to precision-polishing to obtain the surface roughness
represented by 5.3 nm<Rmax<9.3 nm, 0.6 nm<Ra<1.0 nm,
and 2.8 nm<Rp<5.5 nm. Each of these glass substrates was
dipped successively into washing baths of a neutral detergent, DI
water, IPA (isopropylatcohol) with an ultrasonic wave applied to
the washing baths. Thereafter, the glass substrates were dried in
IPA (steam dry tank) and put in disk cases (manufactured by EMPAK,
Inc.) each of which contains 25 substrates. These disk cases were
packaged in a bag made of polyethylene (PE) commercially available.
The interior of the bag was forcedly evacuated. The bag was sealed
by hot sealing and thereafter held in a clean room environment for
several days. Each of the disk cases comprises an outer container
made of polypropylene (PP) and an inner substrate holder made of
polyethylene (PE) and releases a less amount of an organic gas or a
less number of particles.
[0182] Next, the substrates were taken out from the disk cases and
measurement was made of the contact angle of water on the surface
of each substrate. Thereafter, each substrate was dipped into the
DI water and dried by tho spin dry to obtain a glass substrate for
a magnetic disk. The contact angle of water was measured by a
sessile drop method (in the following description, the contact
angle was measured in the same method).
[0183] The surface of the glass substrate for the magnetic disk
obtained as mentioned above was observed by a microscope and an
electron microscope. As a result, it has been confirmed that
semispherical protrusions having a size between about 1 .mu.m and
several .mu.m were formed on some glass substrates.
[0184] Investigation was made about the relationship between the
contact angle of water on the surface of the substrate and the
surface roughness (height of protrusions) of the substrate. As a
result, it has been confirmed that the surface roughness (height of
protrusions) of the substrate become greater as the contact angle
of water before dipping into the DI water and the spin dry was
increased, as will be understood from Table 1-1.
1TABLE 1-1 Contact Angle 5.degree. 10.degree. 15.degree. 20.degree.
30.degree. Surface Roughness 2.8- 4.5- 5.8- 7.3- 15.1- of Substrate
3.9 nm 5.5 nm 10.2 nm 19.6 nm 31.3 nm (Height of Protrusions)
(Rp)
[0185] The protrusions were analyzed by EDS (Energy Dispersive
X-ray Spectroscopy) to confirm that the protrusions mainly
contained Si and O.
[0186] The protrusions were analyzed by TOF-SIMS (Time of Flight
Secondary Ion Mass Spectrometry) to confirm that the protrusions
contained SiOH as a main component.
[0187] On each of opposite surfaces of the glass substrate after
the spin dry, an NiAl seed layer, a CrV underlying layer, a CoCrPtB
magnetic layer, a carbon protection layer, and a perfluoropolyether
lubricant layer were formed to obtain a magnetic disk for use with
a MR head.
[0188] Each of the magnetic disks obtained as mentioned above was
subjected to a glide test. In the glide test, a minimum flying
height of the magnetic head was varied from 18 nm to 10 nm assuming
the case where the recording/reproducing operations were carried
out with the MR head kept at the flying height of 20 nm. The result
is shown in FIG. 1. In FIG. 1, a left ordinate represents a glide
test pass rate and a right ordinate represents the contact angle of
water on the surface of the substrate before dipping into the DI
water and the spin dry. An abscissa represents the substrates
having the contact angles represented by the right ordinate. In
FIG. 1, the glide test pass rate is given by a bar and the contact
angle is given by a symbol ".smallcircle.".
[0189] As is obvious from FIG. 1, when the contact angle of water
on the surface of the substrate is great and exceeds 20.degree.,
the glide test pass rate is low (that is, a glide test fail rate is
high). The glide test is to detect, throughout an entire
circumference of the substrate, the protrusions having a
predetermined height or more by the use of a head running at the
predetermined flying height. The fact that the glide test pass rate
is low represents that the probability of production of the
protrusions is high. A glide test fail or a glide fail is
equivalent in meaning to a glide defect.
[0190] Thus, the relationship between the contact angle of water on
the surface of the substrate before the washing/drying step and the
height of the protrusions (surface roughness of the substrate)
attached to the surface of the substrate obtained through the
washing/drying step is preliminarily grasped or detected.
Furthermore, the contact angle of water on the surface of the
substrate is suppressed to a predetermined value or less (for
example, 20.degree. or less) so that the height of the protrusions
(surface roughness) is not greater than an allowable height of the
protrusions causing no hit or no recording/reproducing error when
the slider is made to run afloat. In this manner, it is possible to
reliably prevent the glide defect or the degradation in
recording/reproducing function due to the thermal asperity when the
magnetic disk is formed by the use of the substrate. In an actual
production process of the glass substrate or the magnetic disk, the
correlation between the contact angle of water on the surface of
the substrate before the washing/drying step and each of the glide
yield and the error rate upon the recording or the reproducing
operation is sometimes known in advance. In this event, by simply
setting the contact angle to a value such that no glide defect
and/or no recording/reproducing error is caused, the glide defect
or the degradation in recording/reproducing function due to the
thermal asperity can be avoided.
[0191] Examples 1-2 through 1-6 given below provide methods (means)
for suppressing the increase in contact angle of water
(specifically, suppressing the contact angle of water to 20.degree.
or less) in order to prevent the glide defect or the occurrence of
thermal asperity in the method of producing the substrate for an
information recording medium comprising the step of packaging the
substrate obtained through the washing/drying step. In each
Example, a factor related to the contact angle of water is
mentioned as well as means for dealing with such factor to suppress
the increase in contact angle and the effect achieved thereby.
EXAMPLE 1-2
[0192] In Example 1-1, it has been found out that the contact angle
of water on the surface of the substrate before dipping into the DI
water and the spin dry is related to the production of the
protrusions. In Example 1-2, the relationship between the type of
the bag (the release of the gas) and the contact angle of water on
the surface of the substrate was examined.
[0193] Referring to FIG. 2, description will be made of a test for
investigating the relationship between the material of the bag and
the contact angle of water. Preparation was made of PE bags and
PE/AI/PE laminate bags each of which has a thickness of 0.08 mm. As
illustrated in FIG. 2, a piece of each of the PE and the PE/AI/PE
bags, having a predetermined size, was put in the disk case
containing 25 substrates and was spread at the bottom. The disk
cases were put in a PE bag. The bag was forcedly evacuated, seated
by hot sealing, and held in an environment of 50.degree. C. and 90%
RH (Relative Humidity) for 24 hours.
[0194] Measurement was made of the contact angle of water on the
surface of each substrate held in the above-mentioned environment.
As a result, the substrates held together with the PE bag had an
average contact angle of water of 50.4.degree. which is high as
compared with those substrates held with the PE/AI/PE laminate bag.
The contact angle on the substrate was measured for each of
different parts of the substrate, i.e., an upper part, a bottom
part, intermediate parts (left and right) upon storage in the case.
As a result, the contact angle was highest at the bottom part of
the substrate which is nearest to the piece of the bag. It is
believed that the gas released from the bag is contacted and
attached to the surface of the substrate to increase the contact
angle.
[0195] Therefore, by the use of the bag which does not release the
gas increasing the contact angle of water, it is possible to
suppress the contact angle of water of the substrate stored in the
disk case. Actually, the magnetic disk was prepared in the manner
similar to Example 1-1 by the use of the bag releasing a less
amount of the gas. After measuring the contact angle, the glide
test was performed. As a result, the contact angle of water was
smaller than 10.degree. in all substrates and no glide defect was
caused.
EXAMPLE 1-3
[0196] In Example 1-3, investigation was made of the relationship
between the amount of particles contained in the bag and the
contact angle of water of the substrate.
[0197] Preparation of made of three kinds of bags. A predetermined
amount of pure water was poured into each bag so as to contact with
a preselected area of the bag. Thus, the particles were extracted.
By the use of an LPC (Liquid Particle Counter), the amount of
particles contained in each bag and greater in diameter than 0.5
.mu.m was measured.
[0198] Measurement was made of the contact angle of water for the
substrates contained in each bag. As a result, the substrates
packaged in the bag containing a greatest amount of particles
(2387.5 count/cm.sup.3) had the contact angle of water of
32.6.degree.. On the other hand, the contact angles were
6.5.degree. and 5.2.degree. for those substrates packaged in the
relatively clean bags containing particle amounts of 569.6
count/cm.sup.3 and 20.8 count/cm.sup.3, respectively. Thus, for the
substrates packaged in the former bag, the contact angle was high
as compared with those in the latter bags and the glide defect was
caused. It is understood that, if organic particles which are
hydrophobic are attached to the substrate, the contact angle will
be increased. On the other hand, preparation was made of magnetic
disks in the manner similar to Example 1-1 by the use of substrates
packaged in two other types of relatively clean bags. These
substrates were subjected to the glide test. As a result, no glide
defect was caused.
[0199] From the above-mentioned result, the amount of particles
present in the bag is desired to be small. Specifically, those
particles exceeding 0.5 .mu.m are contained preferably in an amount
of 1000 count/cm.sup.3 or less, more preferably, 500 count/cm.sup.3
or less, further preferably, 250 count/cm.sup.3 or less.
EXAMPLE 1-4
[0200] In Example 1-4, investigation was made about the
relationship between the temperature and the humidity (moisture
transmittance) in the bag and the contact angle of water on the
surface of the substrate.
[0201] The substrates in the disk cases were packaged and sealed in
the PE bags with and without the desiccant contained therein. After
a holding period of three months, the contact angle of water on the
surface of the substrate was measured. As a result, the contact
angle was as low as 10.degree. or less on the surface of each
substrate held in the bag with the desiccant On the other hand, for
those substrates held in the bag without the desiccant for three
months, weathering or a stain was locally formed on the glass
surface and the contact angle of water on the surface of the
substrate exceeds 20.degree. to reach about 45.degree.. This is
presumably because water molecules attached to the glass surface
repeatedly adsorb the particles and evaporate. The glide test was
carried out in the manner similar to Example 1-1. As a result, the
protrusions described in conjunction with Example 1-1 were high and
the glide defect was caused in the magnetic disks comprising the
substrates having such a large contact angle. On the other hand,
magnetic disks were prepared in the manner similar to Example 1-1
by the use of substrates held in an environment with a desiccant
contained therein to adjust the humidity. These magnetic disks were
subjected to the glide test. As a result, no glide defect was
caused.
[0202] Therefore, by putting the desiccant in the bag, it is
possible to suppress the increase in contact angle of the substrate
during long-term storage such as three months and to prevent the
glide defect due to the protrusions.
EXAMPLE 1-5
[0203] In Example 1-5, investigation was made of the relationship
between a holding time of holding the substrate in the clean room
after washing the substrate and the contact angle of water on the
surface of the substrate.
[0204] In the production process of the substrate, the substrate
after precision polishing is subjected to final washing
(pre-shipment washing) directly after the precision polishing or
via another step. Then, the substrate was subjected to a testing
step, stored in a shipping container such as a disk case, and put
in the bag to be shipped. In the above-mentioned process, the
substrate is held in the clean room for a relatively long holding
time after washing the substrate and before packaging the substrate
following the testing step. The influence of the holding time was
examined in Example 1-5.
[0205] Preparation was made of 200 substrates after the final
washing (preshipment washing). The 100 substrates were put in a
washing basket and held in the clean room. The remaining 100
substrates were put in the disk cases each of which contained 25
substrates. The disk cases were respectively packaged in the PE
bags which were sealed and held. For those substrates which were
not put in the bag, the contact angle was increased with the lapse
of the holding time starting from the time instant immediately
after the washing step. In particular, the contact angle of water
on the surface of the substrate exceeded 20.degree. when the
holding time exceeds about 70 hours. On the other hand, for those
substrates put and sealed in the bag immediately after the
washing/drying step, no substantial increase in contact angle was
observed even after the lapse of the holding time. Therefore, it
will be understood that, by shortening the holding time of the
substrate after completion of a series of production steps (after
the washing/drying step) and before packaging following the testing
step, the increase in contact angle of the substrate can be
suppressed. In the manner similar to Example 1-1, magnetic disks
were prepared by the use of substrates which were put and sealed in
a bag immediately after washed and dried and substrates which were
held for the holding time of 60 hours. These substrates were
subjected to the glide test. As a result, no glide defect was
caused.
[0206] The time from the completion of the washing/drying step to
the packaging of the substrate following the testing step is
preferably not longer than 70 hours, more preferably not longer
than 30 hours, further preferably not longer than 10 hours.
EXAMPLE 1-6
[0207] In Example 1-6, each of the substrates put in the washing
basket and left in the clean room in Example 1-5 was successively
dipped in the washing bath (acid, alkali, neutral detergent, or the
like) or the hydrophilic treating bath (silicofluoric acid or the
like), the pure water bath, and the DI water bath, and then
dehydrated by the spin dry. As a result, the protrusions of the
height causing the product defects were not formed.
[0208] In this case, the contact angle of water on the surface of
the substrate before pre-washing is great. However, the contact
angle of water on the surface of the substrate before the spin dry
is lowered by the treatment in the washing bath or the hydrophilic
treating bath. Therefore, no protrusion is formed. However, the
above-mentioned dipping step increases the number of steps and the
cost.
EXAMPLE 2-1
[0209] A plurality of disk-shaped glass substrates were prepared. A
pair of principal surfaces of each glass substrate were subjected
to precision-polishing to obtain the surface roughness represented
by 5.3 nm<Rmax<9.3 nm, 0.6 nm<Ra<1.0 nm, and 2.8
nm<Rp<5.5 nm. Each of these glass substrates was dipped
successively into washing baths of a neutral detergent and pure
water with an ultrasonic wave applied to the washing baths. On the
other hand, DI water was prepared by multiple repetition of ion
exchange so that the content of Si is adjusted to 5 ppb, 10 ppb, 20
ppb, and 30 ppb. Thereafter, each glass substrate was dipped into
the DI water and dried by the spin dry. Thus, glass substrates for
magnetic disks were obtained as substrates after the spin dry. The
content of Si in the DI water was measured by the absorptionmetric
analysis (in the following description, the content of Si was
measured in the same method).
[0210] The surface of the glass substrate for the magnetic disk
obtained as mentioned above was observed by a microscope and an
electron microscope. As a result, it has been confirmed that
semispherical protrusions having a size between about 1 .mu.m and
several .mu.m were formed on some glass substrates.
[0211] The protrusions were analyzed by EDS (Energy Dispersive
X-ray Spectroscopy) to confirm that the protrusions mainly
contained Si and O. The protrusions were analyzed by TOF-SIMS (Time
of Flight Secondary Ion Mass Spectrometry) to confirm that the
protrusions contained SiOH as a main component.
[0212] Furthermore, the surface roughness (height of protrusions)
of the substrate after the above-mentioned spin dry was measured by
an atomic force microscope (AFM). The result is shown in Table
2-1.
[0213] Prior to deposition of a thin film such as a magnetic layer
on each substrate after the spin dry, pre-washing was carried out
by successively dipping the substrate into washing baths of a
neutral detergent, DI water (the content of Si being 20 ppb), and
IPA (isopropylalcohol) with an ultrasonic wave applied to the
washing baths. Thereafter, the glass substrate was dried in IPA
(steam dry tank). Thus, a plurality of glass substrates for
magnetic disks were obtained as substrates after the IPA dry.
[0214] The surface roughness (height of protrusions) of the
substrate after the IPA dry was measured by the atomic force
microscope (AFM). The result is shown in Table 2-1.
2TABLE 2-1 Content of Si 5 ppb 10 ppb 20 ppb 30 ppb Surface After
2.7-5.6 nm 2.8-5.8 nm 5.8-9.2 nm 9.3- Rough- Spin Dry 23.1 nm ness
After 2.9-5.7 nm 3.0-5.9 nm 6.0-9.5 nm 10.5- (Rp) IPA Dry 24.2
nm
[0215] As is obvious from Table 2-1, the surface toughness (height
of protrusions) (Rp) of the substrate after the spin dry is greater
with the increase in content of Si in the DI water in which the
substrate was dipped before the spin dry. When the content of Si in
the DI water is not greater than 20 ppb, the surface roughness
(height of protrusions) (Rp) of the substrate is smaller than 10
nm. When the content of Si exceeds 20 ppb, the surface roughness
(height of protrusions) (Rp) of the substrate is dramatically
increased.
[0216] Since the IPA dry is used in the pre-washing step, the
surface roughness (height of protrusions) (Rp) of the substrate is
not increased. Specifically, even if the content of Si in the DI
water used in the pre-washing step is equal to 20 ppb, the surface
roughness (height of protrusions) (Rp) of the substrate is not
increased in case of the IPA dry.
[0217] When the content of Si was equal to 5 ppb and 10 ppb, no
protrusion was observed on the surface of the substrate. When the
content of Si was equal to 20 ppb, the protrusions were formed but
had a maximum height of 4 nm which did not cause any problem.
[0218] Next, on each of opposite surfaces of the glass substrate
after the pre-washing, an NiAl seed layer, a CrV underlying layer,
a CoCrPtB magnetic layer, a carbon protection layer, and a
perfluoropolyether lubricant layer were formed to obtain a magnetic
disk for use with an MR head.
[0219] Each of the magnetic disks obtained as mentioned above was
subjected to a glide test. In the glide test, a minimum flying
height of the magnetic head was varied from 18 nm to 10 nm assuming
the case where the recording/reproducing operations would be
carried out with the MR head kept at the flying height of 20 nm. As
a result, glide defects were caused in a part of the glass
substrates which were washed by the DI water with the content of Si
being 30 ppb and then dried by the spin dry. The remaining glass
substrates, which were washed by the DI water with the content of
Si being 30 ppb and then dried by the spin dry, passed the glide
test but later suffered malfunction in the reproducing operation
due to the thermal asperity. On the other hand, for those glass
substrates washed by the DI water with the content of Si being 20
ppb or less and dried by the spin dry, neither glide defects nor
malfunction in the reproducing operation due to the thermal
asperity was caused.
EXAMPLE 2-2
[0220] A plurality of disk-shaped glass substrates were prepared. A
pair of principal surfaces of each glass substrate were subjected
to precision-polishing to obtain the surface roughness represented
by 5.3 nm<Rmax<9.3 nm, 0.6 nm<Ra<1.0 nm, and 2.8
nm<Rp<5.5 nm. Each of these glass substrates was dipped
successively into washing baths of a neutral detergent, DI water,
DI water (content of Si being 30 ppb), and IPA (isopropylalcohol)
with an ultrasonic wave applied to the washing baths. Thereafter,
each glass substrate was dried by IPA (steam dry tank). Thus, a
plurality of glass substrates for magnetic disks were obtained as
substrates after the IPA dry.
[0221] The surface roughness (height of protrusions) of the
substrate obtained as mentioned above was measured by the atomic
force microscope. The result of measurement is shown in Table 2-2.
Furthermore, evaluation was made of the wettability of the
substrate obtained as mentioned above to reveal that the contact
angle of water was 6 to 10.degree.. The contact angle of water was
measured by the sessile drop method (in the following description,
the contact angle was measured in the same method).
[0222] Prior to deposition of a thin film such as a magnetic layer
on each glass substrate, the glass substrate after the IPA steam
dry was dipped into the DI water (the content of Si being 5 ppb, 10
ppb, 20 ppb, 30 ppb) and dried by the spin dry. Thus, a plurality
of glass substrates for magnetic disks after the spin dry were
obtained.
[0223] The surface roughness (height of protrusions) of the
substrate after the spin dry was measured by the atomic force
microscope. The result of measurement is shown in Table 2-2.
3TABLE 2-2 Content of Si 5 ppb 10 ppb 20 ppb 30 ppb Surface After
2.8-6.2 nm 2.7-6.3 nm 2.5-6.2 nm 2.7- Rough- IPA Dry 6.1 nm ness
After 2.7-6.1 nm 2.9-6.5 nm 6.1-8.9 nm 10.3- (Rp) Spin Dry 32.0
nm
[0224] As is obvious from Table 2-2, the surface roughness (height
of protrusions) (Rp) of the substrate is small since the washing
after precision polishing uses the IPA dry. Even if the DI water
used in this washing step contains Si at the content of 30 ppb, the
surface roughness (height of protrusions) (Rp) of the substrate is
suppressed or small by the use of the IPA dry.
[0225] The surface roughness (height of protrusions) (Rp) of the
substrate after the spin dry in the pre-washing step is greater
with the increase in content of Si in the DI water in which the
substrate is dipped before the spin dry. When the content of Si in
the DI water is not greater than 20 ppb, the surface roughness
(height of protrusions) (Rp) of the substrate is smaller than 10
nm. When the content of Si exceeds 20 ppb, the surface roughness
(height of protrusions) (Rp) of the substrate is dramatically
increased.
[0226] When the content of Si was equal to 5 ppb and 10 ppb, no
protrusion was observed on the surface of the substrate. When the
content of Si was equal to 20 ppb, the protrusions were formed but
had a maximum height of 3 nm which did not cause any problem.
[0227] The protrusions were observed by EDS and TOF-SIMS. As a
result, it has been confirmed that the protrusions were similar to
those in Example 2-1.
[0228] Next, on each of opposite surfaces of the glass substrate
after the pre-washing, an NiAl seed layer, a CrV underlying layer,
a CoCrPtB magnetic layer, a carbon protection layer, and a
perfluoropolyether lubricant layer were formed to obtain a magnetic
disk for use with a MR head.
[0229] Each of the magnetic disks obtained as mentioned above was
subjected to a glide test. In the glide test, a minimum flying
height of the magnetic head was varied from 18 nm to 10 nm assuming
the case where the recording/reproducing operations would be
carried out with the MR head kept at the flying height of 20 nm. As
a result, glide defects were caused in a part of the glass
substrates which were washed by the DI water with the content of Si
being 30 ppb and then dried by the spin dry. The remaining glass
substrates, which were washed by the DI water with the content of
Si being 30 ppb and then dried by the spin dry, passed the glide
test but later suffered malfunction in the reproducing operation
due to the thermal asperity. On the other hand, for those glass
substrates washed by the DI water with the content of Si being 20
ppb or less and dried by the spin dry, neither glide defects nor
malfunction in the reproducing operation due to the thermal
asperity were caused.
[0230] As described above, it is understood that, for those glass
substrates to be used as the magnetic disks such that the recording
and reproducing operations are carded out with the MR head kept at
the flying height of 20 nm, the content of Si contained in the
water used in the washing/drying step of the glass substrate is
desired to be equal to 20 ppb or less. In this event, it is
possible to obtain the glass substrate for a magnetic disk and the
magnetic disk capable of reducing the flying height of the magnetic
head and preventing the thermal asperity.
EXAMPLE 2-3
[0231] In the manner similar to Example 2-2 except that the surface
of the glass substrate was subjected to hydrophilic treatment
(specifically, silicofluoric acid treatment) before the
pre-washing, a plurality of glass substrates were obtained.
Evaluation was made of tho wettability of the surface of each
substrate after the hydrophilic treatment. As a result, the contact
angle was 4 to 8.degree..
[0232] The surface roughness (height of protrusions) of the
substrate after the pre-washing was measured by the atomic force
microscope. As a result, the surface roughness (height of
protrusions) was reduced by about 5 to 10% as compared with Example
2-2. This is because, as a result of improvement in wettability of
the surface of the substrate, water droplets of the DI water were
spread and then dried so that the components forming the
protrusions are dispersed.
[0233] The surface roughness (height of protrusions) of the
substrate after the pre-washing was measured by the atomic force
microscope. The result of measurement was shown in Table 2-3.
4TABLE 2-3 Content of Si 5 ppb 10 ppb 20 ppb 30 ppb Surface Rough-
2.4-5.7 nm 2.6-6.0 nm 5.5-9.6 nm 9.6-28.2 nm ness after Hydrophilic
Treatment (Rp)
[0234] On each of opposite surfaces of the glass substrate, an NiAl
seed layer, a CrV underlying layer, a CoCrPtB magnetic layer, a
carbon protection layer, and a perfluoropolyether lubricant layer
were formed to obtain a magnetic disk for use with a MR head.
[0235] Each of the magnetic disks obtained as mentioned above was
subjected to a glide test. In the glide test, a minimum flying
height of the magnetic head was varied from 18 nm to 10 nm assuming
the case where the recording/reproducing operations would be
carried out with the MR head kept at the flying height of 20 nm. As
a result, glide defects were caused in a part of the glass
substrates which were subjected to the washing/drying step using
the DI water with the content of Si being 30 ppb, The remaining
glass substrates, which were subjected to the washing/drying step
using the DI water with the content of Si being 30 ppb, passed the
glide test but later suffered malfunction in the reproducing
operation due to the thermal asperity.
[0236] As described in Examples 2-1 through 2-3, the relationship
between the content of Si contained in the water used in the
washing/drying step and the height of the protrusions formed on the
substrate is detected or grasped. Then, the allowable content of Si
contained in the water is determined in accordance with the
allowable height of the protrusions which will cause no hit or no
recording/reproducing error when the slider is made to run afloat.
In this manner, it is possible to reliably prevent the glide defect
or the recording/reproducing error due to the thermal asperity. In
these Examples, attention is directed to Si. Alternatively,
consideration may be made of other elements such as C, Al, Fe, Cu,
Zn, and Zr.
EXAMPLE 3-1
[0237] A plurality of disk-shaped glass substrates were prepared.
Like in Example 2-1, a pair of principal surfaces of each glass
substrate were subjected to precision-polishing to obtain the
surface roughness represented by 5.3 nm<Rmax<9.3 nm, 0.6
nm<Ra<1.0 nm, and 2.8 nm<Rp<5.5 nm. Each of these glass
substrates was dipped successively into washing baths of a neutral
detergent and pure water with an ultrasonic wave applied to the
washing baths. On the other hand, DI water was prepared by multiple
repetition of ion exchange so that the content of Si is adjusted to
5 ppb, 10 ppb, 20 ppb, and 30 ppb. Thereafter, each glass substrate
was dipped into the DI water and dried by the spin dry. Thus, glass
substrates for magnetic disks were obtained as substrates after the
spin dry. The content of Si in the DI water was measured by the
absorption metric analysis (in the following description, the
content of Si was measured in the same method).
[0238] In this example, Rmax, Ra, Rp, and Rv were measured by the
atomic force microscope (AFM) and defined in JIS B0601 (Japanese
Industrial Standard). In the following description, these values
were measured in the same method. Rmax represents a maximum
roughness height which is a distance from a highest peak of a
roughness profile to a lowest valley in the vertical direction. Ra
represents an average roughness which is an average of absolute
values of deviations from a center line to the roughness profile.
Rp represents the height of a highest peak, i.e., a distance from a
mean line to the highest peak. Rv represents a height from the
center line to a valley.
[0239] The surface of the glass substrate for the magnetic disk
obtained as mentioned above was observed by a microscope and an
electron microscope. As a result, it has been confirmed that
semispherical protrusions having a size between about 1 .mu.m and
several .mu.m were formed on those glass substrates which were
washed using the DI water with the content of Si being 2- ppb and
30 ppb and then dried.
[0240] The protrusions were analyzed by EDS (Energy Dispersive
X-ray Spectroscopy) to confirm that the protrusions mainly
contained Si and O.
[0241] The protrusions were analyzed by TOF-SIMS (Time of Flight
Secondary Ion Mass Spectrometry) to confirm that the protrusions
contained SiOH as a main component.
[0242] Next, the protrusions were machined by FIB (Focus Ion Beam)
to observe their sections with TEM (Transmission Electron
Microscope). As a result, substances forming the protrusions were
bright or dark as compared with the glass forming the substrate and
were therefore assumed to have a low density. Thus, it has been
confirmed that an interface was formed between the protrusions and
the surface of the substrate.
[0243] Furthermore, the surface roughness (height of protrusions)
of the substrate after the spin dry was measured by the atomic
force microscope (AFM). The result is shown in Table 3-1.
[0244] The ratio Rp/Rv of the semispherical protrusions were
measured by the atomic force microscope (AFM). The results are as
follows.
5 Content of Si in DI water Rp/Rv 5 ppb 1.0-3.0 10 ppb 2.1-3.5 20
ppb 4.5-10 30 ppb 10-55
[0245] From the above, it is understood that, if the ratio Rp/Rv is
not smaller than 10, the protrusions due to the cleaning water
containing Si may possibly be formed to cause the product
defects.
[0246] Prior to deposition of a thin film such as a magnetic layer
on each substrate after the spin dry, pre-washing was carried out
by successively dipping the substrate into washing baths of a
neutral detergent, DI water (the content of Si being 20 ppb), and
IPA (isopropylalcohol) with an ultrasonic wave applied to the
washing baths. Thereafter, the glass substrate was dried in IPA
(steam dry tank). Thus, a plurality of glass substrates for
magnetic disks were obtained as substrates after the IPA dry.
[0247] The surface roughness (height of protrusions) of the
substrate after the IPA dry was measured by the atomic force
microscope (AFM). The result is shown in Table 3-1.
6TABLE 3-1 Content of Si 5 ppb 10 ppb 20 ppb 30 ppb Surface After
2.7-5.6 nm 2.8-5.8 nm 5.8-9.2 nm 9.3- Rough- Spin Dry 23.1 nm ness
After 2.9-5.7 nm 3.0-5.9 nm 6.0-9.5 nm 10.5- (Rp) IPA Dry 24.2
nm
[0248] As is obvious from Table 3-1, the surface roughness (height
of protrusions) (Rp) of the substrate after the spin dry is greater
with the increase in content of Si in the DI water in which the
substrate was dipped before the spin dry. When the content of Si in
the DI water is not greater than 20 ppb, the surface roughness
(height of protrusions) (Rp) of the substrate is smaller than 10
nm. When the content of Si exceeds 20 ppb, the surface roughness
(height of protrusions) (Rp) of the substrate is dramatically
increased.
[0249] Since the IPA dry is used in the pre-washing step, the
surface roughness (height of protrusions) (Rp) of the substrate is
not increased. Specifically, even if the content of Si in the DI
water used in the pre-washing step is equal to 20 ppb, the surface
roughness (height of protrusions) (Rp) of the substrate is not
increased in case of the IPA dry.
[0250] When the content of Si was equal to 5 ppb and 10 ppb, no
protrusion was observed on the surface of the substrate. When the
content of Si was equal to 20 ppb, the protrusions were formed but
had a maximum height of 4 nm which did not cause any problem.
Herein, the height of the protrusions is a true or net height
exclusive of the surface roughness of the substrate itself. The
total surface roughness including the net height of the protrusions
and the surface roughness of the substrate itself is on the order
of 9 nm as shown in Table 1.
[0251] Next, on each of opposite surfaces of the glass substrate
after the pre-washing, an NiAl seed layer, a CrV underlying layer,
a CoCrPtB magnetic layer, a carbon protection layer, and a
perfluoropolyether lubricant layer were formed to obtain a magnetic
disk for use with an MR head.
[0252] Each of the magnetic disks obtained as mentioned above was
subjected to a glide test. In the glide test, a minimum flying
height of the magnetic head was varied from 18 nm to 10 nm assuming
the case where the recording/reproducing operations would be
carried out with the MR head kept at the flying height of 20 nm. As
a result glide defects were caused in a part of the glass
substrates which were washed by the DI water with the content of Si
being 30 ppb and then dried by the spin dry and which had Rp
greater than 20 nm. The remaining glass substrates, which were
washed by the DI water with the content of Si being 30 ppb and then
dried by the spin dry, passed the glide test but later suffered
malfunction in the reproducing operation due to the thermal
asperity. On the other hand, for those glass substrates washed by
the DI water with the content of Si being 20 ppb or less and dried
by the spin dry and which had Rp smaller than 10 nm, neither glide
defects nor malfunction in the reproducing operation due to the
thermal asperity was caused.
[0253] As described above, for the glass substrate for use as the
magnetic disk subjected to the recording and the reproducing
operations with the MR head kept at the flying height of 20 nm, the
height (Rp) of the protrusions formed on the glass substrate due to
the presence of the impurities (C, Al, Si, Fe, Cu, Zn, Zr, and the
like) contained in the water used in the washing/drying step is
preferably smaller than 10 nm. In this event, it is possible to
obtain the glass substrate for the magnetic disk as well as the
magnetic disk which allow the reduction in flying height of the
magnetic head and which prevent occurrence of the thermal
asperity.
[0254] If the flying height of the head is reduced further, the
height (Rp) of the protrusions formed on the glass substrate must
be reduced further. As described above or as will later be
described, the height of the protrusions can be controlled by
controlling the content of Si in the DI water used as the cleaning
water or the contact angle of water on the surface of the
substrate.
EXAMPLE 3-2
[0255] A plurality of disk-shaped glass substrates were prepared. A
pair of principal surfaces of each glass substrate were subjected
to precision-polishing to obtain the surface roughness represented
by 5.3 nm<Rmax<9.3 nm and 0.6 nm<Ra<1.0 nm. Each of
these glass substrates was dipped successively into washing baths
of a neutral detergent, DI water, DI water (content of Si being 30
ppb), and IPA (isopropylalcohol) with an ultrasonic wave applied to
the washing baths. Thereafter, each glass substrate was dried by
IPA (steam dry tank). Thus, a plurality of (25) glass substrates
for magnetic disks were obtained as substrates after the IPA
dry.
[0256] Although the content of Si in the DI water used in the
washing step is equal to 30 ppb, no protrusions were formed because
the IPA dry was used.
[0257] Thereafter, the glass substrates were put in a substrate
case. The substrate case was packaged in a bag made of polyethylene
(PE). After the interior of the bag was forcedly evacuated, the bag
was seated by hot sealing. The glass substrates thus packaged were
held for several days. The substrate case comprises an outer
container made of polypropylene (PP) and an inner substrate holder
made of polyethylene (PE) and releases a less amount of an organic
gas or a less number of particles.
[0258] Thereafter, evaluation was made of the wettability of the
substrates. As a result, the contact angle of water fell between 6
and 42.degree.. The contact angle was highest for those substrates
located at both sides of the substrate case and was decreased in
the inner substrates. The contact angle of water was measured by
the sessile drop method (in the following description, the contact
angle of water was measured in the same method).
[0259] Prior to deposition of a thin film such as a magnetic layer
on each glass substrate, the glass substrate was dipped into the DI
water as pre-washing and dried by the spin dry, Thereafter, on each
of opposite surfaces of the glass substrate, an NiAl seed layer, a
CrV underlying layer, a CoCrPtB magnetic layer, a carbon protection
layer, and a perfluoropolyether lubricant layer were formed to
obtain a magnetic disk for use with a MR head.
[0260] As a result, the glide defects were high when the contact
angle of water on the surface of the substrate exceeds 20.degree.,
as illustrated in FIG. 1. Those samples in which the contact angle
of water on the surface of the substrate is about 10.degree. or
less are omitted from FIG. 1 because the glide test pass rate was
equal to 100%. In FIG. 1, the abscissa represents the substrates
having the contact angles of water represented by the right
ordinate. The left ordinate represents the glide test pass rate
while the right ordinate represents the contact angle of water on
the surface of the substrate before dipping into the DI water and
the spin dry. In FIG. 1, the glide test pass rate is given by a bar
and the contact angle is given by a symbol ".smallcircle.".
[0261] Each of the magnetic disks obtained as mentioned above was
subjected to a glide test. In the glide test, a minimum flying
height of the magnetic head was varied from 18 nm to 10 nm assuming
the case where the recording/reproducing operations would be
carried out with the MR head kept at the flying height of 20 nm. As
a result, glide failures were caused for those glass substrates
having Rp greater than 20 nm. Even the glass substrates having
passed the glide test later suffered malfunction in the reproducing
operation due to the thermal asperity.
[0262] The protrusions were analyzed by EDS and TOF-SIMS. As a
result, it has been confirmed that the protrusions contained SiOH
as a main component, like in Example 3-1.
EXAMPLE 3-3
[0263] A plurality of disk-shaped glass substrates were prepared. A
pair of principal surfaces of each glass substrate were subjected
to precision-polishing to obtain the surface roughness represented
by 5.3 nm<Rmax<9.3 nm, 0.6 nm<Ra<1.0 nm, and 2.8
nm<Rp<5.5 nm. Each of these glass substrates was dipped
successively into washing baths of a neutral detergent and pure
water with an ultrasonic wave applied to the washing baths.
Thereafter, each glass substrate was dipped into the DI water with
the content of Si adjusted to 30 ppb and dried by the spin dry.
Thus, glass substrates for magnetic disks were obtained.
[0264] The semispherical protrusions formed on the surface of the
glass substrate were measured by the atomic force microscope. As a
result, Rp fell within the range between 15.1 and 24.6 nm.
[0265] The above-mentioned glass substrate was subjected to
pre-washing by successively dipping the substrate into washing
baths of a neutral detergent, DI water (the content of Si being 20
ppb), and IPA with an ultrasonic wave applied to the washing baths.
Thereafter, the glass substrate was dried by IPA steam dry. Then,
on each of opposite surfaces of the glass substrate, an NiAl seed
layer, a CrV underlying layer, a CoCrPtB magnetic layer, a carbon
protection layer, and a perfluoropolyether lubricant layer were
formed to obtain a magnetic disk for use with an MR head.
[0266] Each of the magnetic disks obtained as mentioned above was
subjected to a glide test at the minimum flying height of 30 nm. As
a result, no glide defect was caused. Furthermore, the magnetic
disks were subjected to the recording and reproducing operations
with the MR head kept at the flying height of 40 nm. As a result,
neither head crash nor malfunction in the reproducing operation due
to the thermal asperity was caused.
[0267] From the above-mentioned results, it is understood that a
desired content of Si in the DI water is changed if the flying
height of the MR head from the surface of the magnetic disk is
varied. It has been confirmed that a particular content of Si in
the DI water did not cause any problem if the flying height of the
MR head was 40 nm but was unacceptable if the flying height of the
MR head was 20 nm.
[0268] This invention is not restricted to the above-mentioned
Examples.
[0269] For example, the test condition of the glide test is not
restricted to that mentioned above. Assuming that the recording and
the reproducing operations are performed with the MR head running
at the flying height less than 10 nm, the glide test may be
performed while the minimum flying height of the magnetic head is
varied from 0 nm to 10 nm.
[0270] The substrate may be made of a material other than the
glass. For example, use may be made of aluminum, silicon, carbon,
ceramics, titanium, and other various materials. The glass is not
restricted in species and includes as chemically reinforced glass
and a crystallized glass.
[0271] This invention is applicable not only to the substrate for
the magnetic disk but also to a substrate for an optical disk or a
magnetooptical disk.
[0272] The hydrophilic treatment may be carried out by alkali
treatment using KOH, NaOH, or the like, acid treatment using
diluted sulfuric acid, nitric acid, or the like, ozone oxidation by
ultraviolet irradiation, and the like in addition to the
above-mentioned technique.
[0273] The washing/drying step in this invention is not restricted
to those described in conjunction with the Examples.
[0274] In this invention, the protrusions containing at least one
of C, O, Al, Si, Fe, Cu, Zn, and Zr are not restricted to the
protrusions produced through the washing/drying techniques and
steps described in conjunction with Examples.
[0275] As described above, according to this invention, the contact
angle of water on the surface of the substrate before the
washing/drying step is the factor closely related to production of
the protrusions containing at least one of C, O, Al, Si, Fe, Cu,
Zn, and Zr and can be determined and controlled so that the product
defects are avoided. Thus, the product defects can be avoided.
[0276] According to this invention, the content of at least one
element of C, Al, Si, Fe, Cu, Zn, and Zr contained in the water
used in the washing/drying step and causing the protrusions
containing at least one of C, O, Al, Si, Fe, Cu, Zn, and Zr can be
determined and controlled so that the product defects are avoided.
Thus, the product defects can be avoided.
[0277] According to this invention, the height of the protrusions
which are attached and formed on the surface of the substrate due
to presence of the impurity elements (C, O, Al, Si, Fe, Cu, Zn, Zr,
and the like) contained in the water used in the washing/drying
step and which contain at least one of C, O, Al, Si, Fe, Cu, Zn,
and Zr is controlled so that the products defects are avoided.
Thus, the product defects can be avoided.
[0278] Specifically, the protrusions containing at least one of C,
O, Al, Si, Fe, Cu, Zn, and Zr and/or the protrusions having a
height causing a hit in the glide test or an error in the recording
or the reproducing operation are not formed on the surface of the
substrate even through the washing/drying step. Thus, it is
possible to provide a substrate for a magnetic recording medium and
a magnetic recording medium, which are capable of preventing the
deterioration in recording/reproducing functions due to the thermal
asperity. Similarly, it is possible to eliminate the negative
factor causing a defect such as a recording or a reproducing error
of an information recording medium.
* * * * *