U.S. patent application number 17/319375 was filed with the patent office on 2021-09-02 for sputtering target.
The applicant listed for this patent is TANAKA KIKINZOKU KOGYO K.K., TOHOKU UNIVERSITY. Invention is credited to Shintaro Hinata, Ryousuke Kushibiki, Shin Saito, Kim Kong Tham, Toshiya Yamamoto.
Application Number | 20210269911 17/319375 |
Document ID | / |
Family ID | 1000005599383 |
Filed Date | 2021-09-02 |
United States Patent
Application |
20210269911 |
Kind Code |
A1 |
Tham; Kim Kong ; et
al. |
September 2, 2021 |
SPUTTERING TARGET
Abstract
Provided is a sputtering target with which it is possible to
form a magnetic thin film having a high coercive force Hc. The
sputtering target is a sputtering target that contains metallic Co,
metallic Pt, and an oxide, wherein the sputtering target contains
no metallic Cr except inevitable impurities, the oxide is
B.sub.2O.sub.3 and the sputtering target comprises 10 to 50 vol %
of the oxide.
Inventors: |
Tham; Kim Kong;
(Tsukuba-shi, JP) ; Kushibiki; Ryousuke;
(Tsukuba-shi, JP) ; Yamamoto; Toshiya;
(Tsukuba-shi, JP) ; Saito; Shin; (Sendai-shi,
JP) ; Hinata; Shintaro; (Sendai-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TANAKA KIKINZOKU KOGYO K.K.
TOHOKU UNIVERSITY |
Tokyo
Sendai-shi |
|
JP
JP |
|
|
Family ID: |
1000005599383 |
Appl. No.: |
17/319375 |
Filed: |
May 13, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15779012 |
May 24, 2018 |
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PCT/JP2016/083777 |
Nov 15, 2016 |
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17319375 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 2998/10 20130101;
C04B 2235/405 20130101; C04B 2235/408 20130101; C22C 19/07
20130101; C04B 35/01 20130101; H01J 37/3429 20130101; C22C 1/0466
20130101; C22C 1/05 20130101; H01J 37/3491 20130101; C22C 5/04
20130101; C23C 14/3414 20130101; C22C 1/0441 20130101; C23C 14/18
20130101; C23C 14/0688 20130101; G11B 5/851 20130101; C04B
2235/3409 20130101; C22C 2202/02 20130101; C22C 1/1084
20130101 |
International
Class: |
C23C 14/34 20060101
C23C014/34; C22C 19/07 20060101 C22C019/07; G11B 5/851 20060101
G11B005/851; C22C 5/04 20060101 C22C005/04; C22C 1/10 20060101
C22C001/10; C23C 14/06 20060101 C23C014/06; H01J 37/34 20060101
H01J037/34; C04B 35/01 20060101 C04B035/01; C23C 14/18 20060101
C23C014/18 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 2015 |
JP |
2015-232446 |
Claims
1. A sputtering target comprising metallic Co, metallic Pt, and an
oxide, wherein the sputtering target contains no metallic Cr except
inevitable impurities, the oxide is B.sub.2O.sub.3, and the
sputtering target comprises 10 to 50 vol % of B.sub.2O.sub.3.
2. (canceled)
3. (canceled)
4. (canceled)
5. The sputtering target according to claim 1, wherein the
sputtering target comprises 20 to 40 vol % of B.sub.2O.sub.3.
6. The sputtering target according to claim 1, wherein the
sputtering target comprises 25 to 35 vol % of B.sub.2O.sub.3.
7. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates to sputtering targets, and in
particular, to a sputtering target that contains metallic Co,
metallic Pt, and an oxide, and with which a magnetic thin film
having a high coercive force can be fabricated.
[0002] In the present description, the sputtering target that
contains metallic Co, metallic Pt, and an oxide may be described as
a CoPt-oxide based target. Further, a magnetic thin film that
contains metallic Co, metallic Pt, and an oxide may be described as
a CoPt alloy-oxide based magnetic thin film.
BACKGROUND ART
[0003] A magnetic disk for a hard disk drive utilizes a magnetic
thin film having a granular structure of a CoPt-based alloy-oxide
as one example of magnetic recording films that serve to record
information signals (see, for example, Non-Patent Literature 1).
The granular structure is composed of columnar CoPt-based alloy
crystal grains and crystal grain boundaries formed from an oxide
that surrounds the columnar CoPt-based alloy crystal grains. In
order to further improve the recording density of the magnetic thin
film having the granular structure of the CoPt-based alloy-oxide,
there is a need to micronize the CoPt-based alloy crystal grains
contained in the magnetic recording layer (magnetic thin film).
[0004] However, the progress of micronization of the CoPt-based
alloy crystal grains has resulted in occurrence of the so-called
thermal fluctuation phenomenon, in which the superparamagnetic
phenomenon impairs the thermal stability of recorded signals and
leads to loss of the recorded signals. This thermal fluctuation
phenomenon has contributed a major obstacle to increasing the
recording density of magnetic disks.
[0005] In order to surmount this obstacle, the magnetic energy of
respective CoPt-based alloy crystal grains needs to be increased
such that the magnetic energy exceeds the thermal energy. The
magnetic energy of respective CoPt-based alloy crystal grains is
obtained by v.times.K.sub.u, which is a product of the volume v of
the CoPt-based alloy crystal grains and the magnetocrystalline
anisotropy constant K.sub.u. Therefore, the magnetocrystalline
anisotropy constant K.sub.u of the CoPt-based alloy crystal grains
needs to be increased in order to increase the magnetic energy
(see, for example, Non-Patent Literature 2).
[0006] Examples of the measures for increasing K.sub.u of the
CoPt-based alloy crystal grains may include one in which stacking
faults in respective CoPt-based alloy crystal grains are decreased,
and one in which the periodicity of the stacking structure of Co
atoms and Pt atoms is improved (see, for example, Non-Patent
Literatures 3 and 4).
[0007] On the other hand, in order to grow the CoPt-based alloy
crystal grains having large K.sub.u in a columnar shape, phase
separation between the CoPt-based alloy crystal grains and grain
boundary material must be achieved. If the phase separation between
the CoPt-based alloy crystal grains and the grain boundary material
is insufficient to increase the grain interaction between the
CoPt-based alloy crystal grains, the magnetic thin film having the
granular structure of the CoPt-based alloy-oxide has had reduced
coercive force Hc. As a result, the thermal stability is impaired,
and the thermal fluctuation phenomenon may occur with ease. Thus,
it is important to reduce the grain interaction between the
CoPt-based alloy crystal grains.
[0008] In order to satisfy the foregoing requirements, various
oxides have been investigated for use as grain boundary materials
for the CoPt-based alloy crystal grains (see, for example,
Non-Patent Literatures 5 and 6). However, there is no clear
guideline for selecting materials, and even today, the
investigation for searching oxides used as grain boundary materials
for the CoPt-based alloy crystal grains is being continued.
CITATION LIST
Non-Patent Literature
[0009] Non-Patent Literature 1: T. Oikawa et al., IEEE TRANSACTIONS
ON MAGNETICS, September 2002, VOL. 38, NO. 5, p. 1976-1978 [0010]
Non-Patent Literature 2: S. N. Piramanayagam, JOURNAL OF APPLIED
PHYSICS, 2007, 102, 011301 [0011] Non-Patent Literature 3: A.
Ishikawa and R. Sinclair, IEEE TRANSACTIONS ON MAGNETICS, September
1996, VOL. 32, NO. 5, p. 3605-3607 [0012] Non-Patent Literature 4:
S. Saito, S. Hinata, and M. Takahashi, IEEE TRANSACTIONS ON
MAGNETICS, March 2014, VOL. 50, NO. 3, 3201205 [0013] Non-Patent
Literature 5: J. Ariake, T. Chiba, and N. Honda, IEEE TRANSACTIONS
ON MAGNETICS, October 2005, VOL. 41, NO. 10, p. 3142-3144 [0014]
Non-Patent Literature 6: V. Sokalski, J. Zhu., and D. E. Laughlin,
IEEE TRANSACTIONS ON MAGNETICS, June 2010, VOL. 46, NO. 6, p.
2260-2263
SUMMARY OF INVENTION
Technical Problem
[0015] In light of such circumstances, an object of the present
invention is to provide a sputtering target with which it is
possible to form a magnetic thin film having a high coercive force
Hc.
Solution to Problem
[0016] The inventors of the present invention have diligently
carried out studies to solve the above-mentioned problems. As a
result, the inventors have found that the oxide suitable for
increasing the coercive force Hc of the magnetic thin film is an
oxide having a melting point of 600.degree. C. or lower and a
standard Gibbs free energy of formation .DELTA.Gf with respect to 1
mol O.sub.2 being -1,000 kJ/mol O.sub.2 or more and -500 kJ/mol
O.sub.2 or less.
[0017] The present invention has been made on the basis of this new
findings.
[0018] Namely, an aspect of a sputtering target according to the
present invention is a sputtering target comprising metallic Co,
metallic Pt, and an oxide, wherein the sputtering target contains
no metallic Cr except inevitable impurities, and the oxide has a
melting point of 600.degree. C. or lower and a standard Gibbs free
energy of formation .DELTA.Gf of the oxide with respect to 1 mol
O.sub.2 being -1,000 kJ/mol O.sub.2 or more and -500 kJ/mol O.sub.2
or less.
[0019] It is preferable that the oxide has B.sub.2O.sub.3.
[0020] It is preferable that the oxide is B.sub.2O.sub.3.
[0021] It is preferable that the sputtering target comprises 10 to
50 vol % of the oxide, it is more preferable that the sputtering
target comprises 20 to 40 vol % of the oxide, and it is still more
preferable that the sputtering target comprises 25 to 35 vol % of
the oxide.
[0022] The sputtering target can be preferably used for forming a
magnetic thin film.
Advantageous Effects of Invention
[0023] The present invention can provide a sputtering target with
which it is possible to form a magnetic thin film having a high
coercive force Hc.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 is a set of graphs showing hysteresis loops of
magnetic thin films (CoPt alloy-oxide based magnetic thin
films).
[0025] FIG. 2 is a graph showing a relationship between a melting
point Tm of oxide and a coercive force Hc of magnetic thin film
(CoPt alloy-oxide based magnetic thin films).
[0026] FIG. 3 is a graph showing a relationship between a standard
Gibbs free energy of formation .DELTA.Gf of oxide with respect to 1
mol O.sub.2 and a coercive force Hc of magnetic thin film (CoPt
alloy-oxide).
[0027] FIG. 4 is a metallurgical microscope photograph of the cross
section in the thickness direction of a sintered test piece
according to Example 1.
[0028] FIG. 5 is a metallurgical microscope photograph of the cross
section in the thickness direction of a sintered test piece
according to Example 1.
DESCRIPTION OF EMBODIMENTS
[0029] A sputtering target according to an embodiment of the
present invention contains metallic Co, metallic Pt, and an oxide,
and is characterized in containing no metallic Cr except inevitable
impurities, and in that the oxide contains B.sub.2O.sub.3. In the
present description, the metallic Co may be simply described as Co
and the metallic Pt may be simply described as Pt.
1. Components of Target
[0030] The sputtering target according to this embodiment contains
Co and Pt as metallic components and may further contain other
metals (for example, Au, Ag, Ru, Rh, Pd, Ir, W, Ta, Cu, B, Mo,
etc.) unless these metals interfere with formation of the magnetic
thin film. As demonstrated in the earlier application of the
inventors of the present invention (Japanese Patent Application No.
2014-95566 and PCT/JP2015/061409), the sputtering target cannot
contain metallic Cr except inevitable impurities because the
presence of metallic Cr has an adverse effect on the
magnetocrystalline anisotropy constant K.sub.u of the resulting
magnetic thin film.
[0031] Metallic Co and metallic Pt are components of magnetic
crystal grains (fine magnet) in the granular structure of the
magnetic thin film formed by sputtering.
[0032] Co is a ferromagnetic metal element and plays a central role
in the formation of the magnetic crystal grains (fine magnet) in
the granular structure of the magnetic thin film. In order to
increase the magnetocrystalline anisotropy constant K.sub.u of the
CoPt alloy particles (magnetic crystal grains) in the magnetic thin
film obtained by sputtering and to maintain the magnetism of the
CoPt alloy particles in the obtained magnetic thin film, the
content percentage of Co in the sputtering target according to this
embodiment is preferably 20 to 90 at % and more preferably 25 to 85
at % relative to the total metallic components (the total of Co and
Pt).
[0033] Platinum, when alloying with Co in a predetermined
composition range, has the function of reducing the magnetic moment
of the alloy and thus has a role of adjusting the magnetic strength
of the magnetic crystal grains. In order to increase the
magnetocrystalline anisotropy constant K.sub.u of the CoPt alloy
particles (magnetic crystal grains) in the magnetic thin film
obtained by sputtering and to adjust the magnetism of the CoPt
alloy particles (magnetic crystal grains) in the obtained magnetic
thin film, the content percentage of Pt in the sputtering target
according to this embodiment is preferably 10 to 80 at % and more
preferably 15 to 75 at % relative to the total metallic
components.
[0034] The sputtering target according to this embodiment contains
B.sub.2O.sub.3 as an oxide component. The oxide component serves as
a non-magnetic matrix that separates the magnetic crystal grains
(fine magnet) from each other in the granular structure of the
magnetic thin film.
[0035] The sputtering target according to this embodiment contains
B.sub.2O.sub.3 as an oxide and may further contain other oxides
(for example, SaO.sub.2, TiO.sub.2, Ti.sub.2O.sub.3,
Ta.sub.2O.sub.5, Cr.sub.2O.sub.3, CoO, Co.sub.3O.sub.4, MnO,
Mn.sub.3O.sub.4, Fe.sub.2O.sub.3, CuO, Y.sub.2O.sub.3, MgO,
Al.sub.2O.sub.3, ZrO.sub.2, Nb.sub.2O.sub.5, MoO.sub.3, CeO.sub.2,
Sm.sub.2O.sub.3, Gd.sub.2O.sub.3, WO.sub.2, WO.sub.3, HfO.sub.2,
NiO.sub.2, etc.) unless these oxides interfere with formation of
the magnetic thin film. As demonstrated in Examples described
below, using only B.sub.2O.sub.3 as an oxide is preferred because
using only B.sub.2O.sub.3 as an oxide can significantly increase
the coercive force Hc of the magnetic thin film deposited at room
temperature.
[0036] The content percentage of metallic components and the
content percentage of oxide components in the entire sputtering
target depend on the composition of a desired magnetic thin film.
Although not limited, the content percentage of metallic components
in the entire sputtering target may be, for example, 88 to 94 mol
%, and the content percentage of oxide components in the entire
sputtering target may be, for example, 6 to 12 mol %.
[0037] As described above, the oxide component serves as a
non-magnetic matrix that separates the magnetic crystal grains
(fine magnet) from each other in the granular structure of the
magnetic thin film. Thus, a large oxide content in the magnetic
thin film is preferred because it is easy to assuredly separate the
magnetic crystal grains from each other and to make the magnetic
crystal grains independent from each other. The oxide content in
the sputtering target according to this embodiment is preferably 10
vol % or larger, and more preferably 20 vol % or larger, and still
more preferably 25 vol % or larger.
[0038] However, an excessively large oxide content in the magnetic
thin film has an adverse effect on the crystallinity of the CoPt
alloy particles (magnetic crystal grains) because the CoPt alloy
particles (magnetic crystal grains) are contaminated with the
oxide, which may increase the proportion of structures other than
the hcp structure in the CoPt alloy particles (magnetic crystal
grains). In addition, an excessively large oxide content in the
magnetic thin film reduces the number of the magnetic crystal
grains per unit area of the magnetic thin film and thus makes it
difficult to increase the recording density. In light of such
views, the oxide content in the sputtering target according to this
embodiment is preferably 50 vol % or less, more preferably 40 vol %
or less, and still more preferably 35 vol % or less.
[0039] Therefore, the oxide content in the sputtering target
according to this embodiment relative to the entire sputtering
target is preferably 10 to 50 vol %, more preferably 20 to 40 vol
%, and still more preferably 25 to 35 vol %.
2. Microstructure of Sputtering Target
[0040] The microstructure of the sputtering target according to
this embodiment is not particularly limited, but is preferably a
microstructure in which a metal phase and an oxide phase are finely
dispersed in each other. Such a microstructure makes it difficult
to generate defects such as nodules and particles during
sputtering.
3. Process for Production of Spattering Target
[0041] The sputtering target according to this embodiment can be
produced, for example, in the following manner.
[0042] (1) Preparation of CoPt Alloy-Atomized Powder
[0043] Co and Pt are weighed so as to obtain a prescribed
composition (the atomic ratio of metallic Co to the total of the
metallic Co and metallic Pt is 20 to 90 at %), and a molten CoPt
alloy is produced. Subsequently, the molten CoPt alloy is
gas-atomized to prepare a CoPt alloy-atomized powder having a
prescribed composition (the atomic ratio of metallic Co to the
total of the metallic Co and metallic Pt is preferably 20 to 90 at
%). The produced CoPt alloy-atomized powder is classified so that
the particle size becomes not larger than a predetermined particle
size (for example, 106 .mu.m or smaller).
[0044] In order to increase the magnetism of the CoPt
alloy-atomized powder, the atomic ratio of metallic Co to the total
of the metallic Co and metallic Pt contained in the power is
preferably 25 at % or larger and more preferably 30 at % or
larger.
[0045] (2) Preparation of Powder Mixture for Pressure Sintering
[0046] A B.sub.2O.sub.3 powder is added to the CoPt alloy-atomized
powder prepared in (1). The mixture is dispersedly mixed with a
ball mill to prepare a powder mixture for pressure sintering. By
dispersedly mixing the CoPt alloy-atomized powder and the
B.sub.2O.sub.3 powder with the ball mill, a powder mixture for
pressure sintering in which the CoPt alloy-atomized powder and the
B.sub.2O.sub.3 powder are finely dispersed in each other can be
prepared.
[0047] In the magnetic thin film formed by using the obtained
sputtering target, the volume fraction of the B.sub.2O.sub.3 powder
in the entire powder mixture for pressure sintering is preferably
10 to 50 vol %, more preferably 20 to 40 vol %, and still more
preferably 25 to 35 vol % in order to easily make the magnetic
crystal grains independent from each other by assuredly separating
the magnetic crystal grains from each other by B.sub.2O.sub.3, to
makes it easy for the CoPt alloy particles (magnetic crystal
grains) to have the hcp structure, and to increase the recording
density.
[0048] (3) Molding
[0049] The powder mixture for pressure sintering prepared in (2) is
pressure-sintered and molded using, for example, a vacuum hot
pressing method to produce a spattering target. Since the powder
mixture for pressure sintering prepared in (2) has been dispersedly
mixed with a ball mill and the CoPt alloy-atomized powder and the
B.sub.2O.sub.3 powder are finely dispersed in each other, defects
such as generation of nodules and particles are unlikely to occur
during sputtering using the spattering target obtained by this
production process.
[0050] The method for pressure-sintering the powder mixture for
pressure sintering is not limited. The method may be a method other
than a vacuum hot pressing method and may be, for example, a HIP
method.
[0051] (4) Modification
[0052] The example production process described in (1) to (3)
involves preparing the CoPt alloy-atomized powder by an atomizing
method, adding the B.sub.2O.sub.3 powder to the prepared CoPt
alloy-atomized powder, and dispersedly mixing the mixture with the
ball mill to prepare the powder mixture for pressure sintering. A
Co single powder and a Pt single powder may be used instead of
using the CoPt alloy-atomized powder. In such a case, three types
of powder, which are a Co single powder, a Pt single powder, and a
B.sub.2O.sub.3 powder, are dispersedly mixed with a ball mill to
prepare a powder mixture for pressure sintering.
EXAMPLES
[0053] As demonstrated in the earlier application of the inventors
of the present invention (Japanese Patent Application No.
2014-95566 and PCT/JP2015/061409), since the presence of metallic
Cr has an adverse effect on the magnetocrystalline anisotropy
constant K.sub.u of the resulting magnetic thin film, sputtering
targets for use in formation of magnetic thin films are free of
metallic Cr except inevitable impurities in the present
invention.
[0054] In Examples and Comparative Examples descried below, studies
were carried out using 13 types of oxides in total, provided that
the sputtering targets for use in formation of the magnetic thin
films were free of metallic Cr except inevitable impurities (the
magnetic crystal grains in the magnetic thin film were formed from
a CoPt alloy that did not contain metallic Cr except inevitable
impurities).
Example 1
[0055] A magnetic recording film was formed by sputtering with a DC
sputtering apparatus. The magnetic recording film was formed on a
glass substrate. The stacked structure of the formed magnetic
recording film includes, in order of increasing distance from the
glass substrate, Ta (5 nm, 0.6 Pa)/Pt (6 nm, 0.6 Pa)/Ru (10 nm, 0.6
Pa)/Ru (10 nm, 8 Pa)/Co.sub.60Cr.sub.40-26 vol % SiO.sub.2 (2 nm, 4
Pa)/CoPt alloy-B.sub.2O.sub.3 (16 nm, 8 Pa)/C (7 nm, 0.6 Pa). The
number on the left side in parenthesis indicates the film
thickness, and the number on the right side indicates the pressure
of an Ar atmosphere during sputtering. CoPt alloy-B.sub.2O.sub.3 is
a magnetic thin film that serves as the recording layer of a
perpendicular magnetic recording medium.
[0056] The composition of the entire target prepared as Example 1
is 91.4 (80Co-20Pt)-7.5B.sub.2O.sub.3 in terms of molar ratio. The
target was prepared and evaluated in the following manner. The
composition of the entire target prepared in Example 1, when the
content percentage of the oxide (B.sub.2O.sub.3) is expressed as
the volume fraction in the entire target, is (80Co-20Pt)-30 vol %
B.sub.2O.sub.3.
[0057] To prepare the target according to Example 1, an 80Co-20Pt
alloy-atomized powder was prepared first. Specifically, metals were
weighed so as to obtain an alloy composition of Co: 80 at % and Pt:
20 at % and heated to 1500.degree. C. or higher to prepare a molten
alloy. The molten alloy was gas-atomized to prepare an 80Co-20Pt
alloy-atomized powder.
[0058] The prepared 80Co-20Pt alloy-atomized powder was separately
classified through 150 mesh sieves to obtain 80Co-20Pt
alloy-atomized powder having a particle diameter of 106 .mu.m or
smaller.
[0059] To 1150 g of the classified 80Co-20Pt alloy-atomized powder,
74.78 g of a B.sub.2O.sub.3 powder was added. Then, the mixture was
mixed and dispersed by a ball mill to obtain a powder mixture for
pressure sintering. The cumulative rotation number of a ball mill
was 2,805,840.
[0060] The obtained powder mixture (30 g) for pressure sintering
was subjected to hot pressing under the conditions of sintering
temperature: 720.degree. C., pressure: 24.5 MPa, time: 30 min, and
atmosphere: 5.times.10.sup.-2 Pa or lower to prepare a sintered
test piece (.phi. 30 mm). The relative density of the prepared
sintered test piece was 99.009%. The calculated density is 9.04
g/cm.sup.3.
[0061] FIG. 4 and FIG. 5 are metallurgical microscope photograph of
the cross section in the thickness direction of the obtained
sintered test piece. FIG. 4 is a photograph at a photographing
magnification of 100 times (a bar scale in the photograph
represents 500 .mu.m), and FIG. 5 is a photograph at a
photographing magnification of 500 times (a bar scale in the
photograph represents 100 .mu.m).
[0062] As can be seen from FIG. 4 and FIG. 5, the 80Co-20Pt-alloy
phase and the B.sub.2O.sub.3 phase were finely dispersed in and
mixed with each other.
[0063] Next, the prepared powder mixture for pressure sintering was
subjected to hot pressing under the conditions of sintering
temperature: 720.degree. C., pressure: 24.5 MPa, time: 60 min, and
atmosphere: 5.times.10.sup.-2 Pa or lower to prepare a target with
.phi.153.0.times.1.0 mm+.phi.161.0.times.4.0 mm. The relative
density of the prepared target was 101.0%.
[0064] The prepared target was evaluated for leakage flux on the
basis of ASTM F2086-01. As a result, the average magnetic leakage
flux rate was 30.9%. This average magnetic leakage flux rate is
sufficient for favorable magnetron sputtering.
[0065] Next, a magnetic thin film made of (80Co-20Pt)-30 vol %
B.sub.2O.sub.3 was deposited on a substrate by magnetron sputtering
using the prepared target to produce a sample for determining
magnetic properties. The stacked structure of this sample for
determining magnetic properties includes, as was described earlier,
in order of increasing distance from the glass substrate, glass/Ta
(5 nm, 0.6 Pa)/Pt (6 nm, 0.6 Pa)/Ru(10 nm, 0.6 Pa)/Ru(10 nm, 8
Pa)/Co.sub.60Cr.sub.40-26 vol % SiO.sub.2 (2 nm, 4 Pa)/CoPt
alloy-B.sub.2O.sub.3 (16 nm, 8 Pa)/C (7 nm, 0.6 Pa). The number on
the left side in parenthesis indicates the film thickness, and the
number on the right side indicates the pressure of an Ar atmosphere
during sputtering.
[0066] CoPt alloy-B.sub.2O.sub.3 is a magnetic thin film deposited
by using the target prepared in present Example. This magnetic thin
film was deposited at room temperature without heating the
substrate during film deposition.
[0067] The hysteresis loop was measured using a magneto-optical
Kerr effect apparatus for the resulting sample for determining
magnetic properties thereof. The coercive force Hc was read from
the hysteresis loop. As a result, the read value of the coercive
force Hc was 8.8 kOe. It should be noted that the coercive forces
Hc of magnetic thin films available on the basis of the current
technology are about 6 to 7 kOe.
[0068] The hysteresis loop of Example 1 is shown in FIG. 1 together
with the results of other Comparative Examples. The horizontal axis
of FIG. 1 represents the strength of the magnetic field applied.
The vertical axis of FIG. 1 represents the value normalized by
dividing the rotation angle (Kerr rotation angle) of the
polarization axis of incident light by the saturation Kerr rotation
angle.
[0069] FIGS. 2 and 3 show the measured result of the coercive force
Hc together with the results of Comparative Examples. The vertical
axis of FIGS. 2 and 3 represents the coercive force Hc while the
horizontal axis of FIG. 2 represents a melting point Tm (.degree.
C.) of oxide and the horizontal axis of FIG. 3 represents a
standard Gibbs free energy of formation .DELTA.Gf (kJ/mol O.sub.2)
with respect to 1 mol O.sub.2 when oxide is formed.
Comparative Example 1
[0070] The composition of the entire target prepared as Comparative
Example 1 is (80Co-20Pt)-30 vol % WO.sub.3. A target was prepared
in the same manner as in Example 1 except that WO.sub.3 was used as
an oxide. Samples for determining magnetic properties were also
prepared in the same manner as in Example 1 by using the prepared
target.
[0071] The hysteresis loop was measured, using a magneto-optical
Kerr effect apparatus, for the sample for determining magnetic
properties in the same manner as in Example 1. Then, the coercive
force Hc was read from the hysteresis loop. As a result, the read
value of the coercive force Hc was 7.1 kOe. The hysteresis loop of
Comparative Example 1 is shown in FIG. 1 together with the results
of other Examples and Comparative Examples. FIGS. 2 and 3 also show
the measured result of the coercive force Hc together with the
results of other Examples and Comparative Examples.
Comparative Example 2
[0072] The composition of the entire target prepared as Comparative
Example 2 is (80Co-20Pt)-30 vol % TiO.sub.2. A target was prepared
in the same manner as in Example 1 except that TiO.sub.2 was used
as an oxide. Samples for determining magnetic properties were also
prepared in the same manner as in Example 1 by using the prepared
target.
[0073] The hysteresis loop was measured, using a magneto-optical
Kerr effect apparatus, for the sample for determining magnetic
properties in the same manner as in Example 1. Then, the coercive
force Hc was read from the hysteresis loop. As a result, the read
value of the coercive force Hc was 5.8 kOe. The hysteresis loop of
Comparative Example 2 is shown in FIG. 1 together with the results
of other Examples and Comparative Examples. FIGS. 2 and 3 also show
the measured result of the coercive force Hc together with the
results of other Examples and Comparative Examples.
Comparative Example 3
[0074] The composition of the entire target prepared as Comparative
Example 3 is (80Co-20Pt)-30 vol % SiO.sub.2. A target was prepared
in the same manner as in Example 1 except that SiO.sub.2 was used
as an oxide. Samples for determining magnetic properties were also
prepared in the same manner as in Example 1 by using the prepared
target.
[0075] The hysteresis loop was measured, using a magneto-optical
Kerr effect apparatus, for the sample for determining magnetic
properties in the same manner as in Example 1. Then, the coercive
force Hc was read from the hysteresis loop. As a result, the read
value of the coercive force Hc was 5.2 kOe. The hysteresis loop of
Comparative Example 3 is shown in FIG. 1 together with the results
of other Examples and Comparative Examples. FIGS. 2 and 3 also show
the measured result of the coercive force Hc together with the
results of other Examples and Comparative Examples.
Comparative Example 4
[0076] The composition of the entire target prepared as Comparative
Example 4 is (80Co-20Pt)-30 vol % Al.sub.2O.sub.3. A target was
prepared in the same manner as in Example 1 except that
Al.sub.2O.sub.3 was used as an oxide. Samples for determining
magnetic properties were also prepared in the same manner as in
Example 1 by using the prepared target.
[0077] The hysteresis loop was measured, using a magneto-optical
Kerr effect apparatus, for the sample for determining magnetic
properties in the same manner as in Example 1. Then, the coercive
force Hc was read from the hysteresis loop. As a result, the read
value of the coercive force Hc was 0.8 kOe. The hysteresis loop of
Comparative Example 4 is shown in FIG. 1 together with the results
of other Examples and Comparative Examples. FIGS. 2 and 3 also show
the measured result of the coercive force Hc together with the
results of other Examples and Comparative Examples.
Comparative Example 5
[0078] The composition of the entire target prepared as Comparative
Example 5 is (80Co-20Pt)-30 vol % MoO.sub.3. A target was prepared
in the same manner as in Example 1 except that MoO.sub.3 was used
as an oxide. Samples for determining magnetic properties were also
prepared in the same manner as in Example 1 by using the prepared
target.
[0079] The hysteresis loop was measured, using a magneto-optical
Kerr effect apparatus, for the sample for determining magnetic
properties in the same manner as in Example 1. Then, the coercive
force Hc was read from the hysteresis loop. As a result, the read
value of the coercive force Hc was 5.1 kOe. The hysteresis loop of
Comparative Example 5 is shown in FIG. 1 together with the results
of other Examples and Comparative Examples. FIGS. 2 and 3 also show
the measured result of the coercive force Hc together with the
results of other Examples and Comparative Examples.
Comparative Example 6
[0080] The composition of the entire target prepared as Comparative
Example 6 is (80Co-20Pt)-30 vol % ZrO.sub.2. A target was prepared
in the same manner as in Example 1 except that ZrO.sub.2 was used
as an oxide. Samples for determining magnetic properties were also
prepared in the same manner as in Example 1 by using the prepared
target.
[0081] The hysteresis loop was measured, using a magneto-optical
Kerr effect apparatus, for the sample for determining magnetic
properties in the same manner as in Example 1. Then, the coercive
force Hc was read from the hysteresis loop. As a result, the read
value of the coercive force Hc was 1.6 kOe. The hysteresis loop of
Comparative Example 6 is shown in FIG. 1 together with the results
of other Examples and Comparative Examples. FIGS. 2 and 3 also show
the measured result of the coercive force Hc together with the
results of other Examples and Comparative Examples.
Comparative Example 7
[0082] The composition of the entire target prepared as Comparative
Example 7 is (80Co-20Pt)-30 vol % Co.sub.3O.sub.4. A target was
prepared in the same manner as in Example 1 except that
Co.sub.3O.sub.4 was used as an oxide. Samples for determining
magnetic properties were also prepared in the same manner as in
Example 1 by using the prepared target.
[0083] The hysteresis loop was measured, using a magneto-optical
Kerr effect apparatus, for the sample for determining magnetic
properties in the same manner as in Example 1. Then, the coercive
force Hc was read from the hysteresis loop. As a result, the read
value of the coercive force Hc was 4.7 kOe. The hysteresis loop of
Comparative Example 7 is shown in FIG. 1 together with the results
of other Examples and Comparative Examples. FIGS. 2 and 3 also show
the measured result of the coercive force Hc together with the
results of other Examples and Comparative Examples.
Comparative Example 8
[0084] The composition of the entire target prepared as Comparative
Example 8 is (80Co-20Pt)-30 vol % MnO. A target was prepared in the
same manner as in Example 1 except that MnO was used as an oxide.
Samples for determining magnetic properties were also prepared in
the same manner as in Example 1 by using the prepared target.
[0085] The hysteresis loop was measured, using a magneto-optical
Kerr effect apparatus, for the sample for determining magnetic
properties in the same manner as in Example 1. Then, the coercive
force Hc was read from the hysteresis loop. As a result, the read
value of the coercive force Hc was 5.6 kOe. The hysteresis loop of
Comparative Example 8 is shown in FIG. 1 together with the results
of other Examples and Comparative Examples. FIGS. 2 and 3 also show
the measured result of the coercive force Hc together with the
results of other Examples and Comparative Examples.
Comparative Example 9
[0086] The composition of the entire target prepared as Comparative
Example 9 is (80Co-20Pt)-30 vol % Cr.sub.2O.sub.3. A target was
prepared in the same manner as in Example 1 except that
Cr.sub.2O.sub.3 was used as an oxide. Samples for determining
magnetic properties were also prepared in the same manner as in
Example 1 by using the prepared target.
[0087] The hysteresis loop was measured, using a magneto-optical
Kerr effect apparatus, for the sample for determining magnetic
properties in the same manner as in Example 1. Then, the coercive
force Hc was read from the hysteresis loop. As a result, the read
value of the coercive force Hc was 3.3 kOe. The hysteresis loop of
Comparative Example 9 is shown in FIG. 1 together with the results
of other Examples and Comparative Examples. FIGS. 2 and 3 also show
the measured result of the coercive force Hc together with the
results of other Examples and Comparative Examples.
Comparative Example 10
[0088] The composition of the entire target prepared as Comparative
Example 10 is (80Co-20Pt)-30 vol % Y.sub.2O.sub.3. A target was
prepared in the same manner as in Example 1 except that
Y.sub.2O.sub.3 was used as an oxide. Samples for determining
magnetic properties were also prepared in the same manner as in
Example 1 by using the prepared target.
[0089] The hysteresis loop was measured, using a magneto-optical
Kerr effect apparatus, for the sample for determining magnetic
properties in the same manner as in Example 1. Then, the coercive
force Hc was read from the hysteresis loop. As a result, the read
value of the coercive force Hc was 1.2 kOe. The hysteresis loop of
Comparative Example 10 is shown in FIG. 1 together with the results
of other Examples and Comparative Examples. FIGS. 2 and 3 also show
the measured result of the coercive force Hc together with the
results of other Examples and Comparative Examples.
Comparative Example 11
[0090] The composition of the entire target prepared as Comparative
Example 11 is (80Co-20Pt)-30 vol % WO.sub.2. A target was prepared
in the same manner as in Example 1 except that WO.sub.2 was used as
an oxide. Samples for determining magnetic properties were also
prepared in the same manner as in Example 1 by using the prepared
target.
[0091] The hysteresis loop was measured, using a magneto-optical
Kerr effect apparatus, for the sample for determining magnetic
properties in the same manner as in Example 1. Then, the coercive
force Hc was read from the hysteresis loop. As a result, the read
value of the coercive force Hc was 3.3 kOe. The hysteresis loop of
Comparative Example 11 is shown in FIG. 1 together with the results
of other Examples and Comparative Examples. FIGS. 2 and 3 also show
the measured result of the coercive force Hc together with the
results of other Examples and Comparative Examples.
Comparative Example 12
[0092] The composition of the entire target prepared as Comparative
Example 12 is (80Co-20Pt)-30 vol % Mn.sub.3O.sub.4. A target was
prepared in the same manner as in Example 1 except that
Mn.sub.3O.sub.4 was used as an oxide. Samples for determining
magnetic properties were also prepared in the same manner as in
Example 1 by using the prepared target.
[0093] The hysteresis loop was measured, using a magneto-optical
Kerr effect apparatus, for the sample for determining magnetic
properties in the same manner as in Example 1. Then, the coercive
force Hc was read from the hysteresis loop. As a result, the read
value of the coercive force Hc was 5.3 kOe. The hysteresis loop of
Comparative Example 12 is shown in FIG. 1 together with the results
of other Examples and Comparative Examples. FIGS. 2 and 3 also show
the measured result of the coercive force Hc together with the
results of other Examples and Comparative Examples.
--Discussion about Types of Oxides (Example 1 and Comparative
Examples 1 to 12)--
[0094] The following table 1 lists the melting points and the
standard Gibbs free energies .DELTA.Gf of formation with respect to
1 mol O.sub.2 of the oxides used in Example 1 and Comparative
Examples 1 to 12, and the values of the coercive forces Hc of the
magnetic thin films obtained as the samples for determining
magnetic properties of Example 1 and Comparative Examples 1 to 12.
Note that the content of each of the oxides used in Example 1 and
Comparative Examples 1 to 12 is 30 vol % relative to the entire
target.
TABLE-US-00001 TABLE 1 oxide melting Coercive content point Tm
.DELTA.Gf force Hc oxide (vol %) (.degree. C.) (kJ/mol O.sub.2)
(kOe) B.sub.2O.sub.3 30 450 -795.8 8.8 (Example 1) WO.sub.3 30 2473
-509.4 7.1 (Comparative Example 1) TiO.sub.2 30 1843 -885.0 5.8
(Comparative Example 2) SiO.sub.2 30 1600 -856.7 5.2 (Comparative
Example 3) Al.sub.2O.sub.3 30 2072 -1054.6 0.8 (Comparative Example
4) MoO.sub.3 30 795 -445.3 5.1 (Comparative Example 5) ZrO.sub.2 30
2700 -1042.8 1.6 (Comparative Example 6) Co.sub.3O.sub.4 30 895
-397.1 4.7 (Comparative Example 7) MnO 30 1945 -725.8 5.6
(Comparative Example 8) Cr.sub.2O.sub.3 30 2435 -7 05.3 3.3
(Comparative Example 9) Y.sub.2O.sub.3 30 2425 -1151.3 1.2
(Comparative Example 10) WO.sub.2 30 1700 -533.9 3.3 (Comparative
Example 11) Mn.sub.3O.sub.4 30 1564 -641.5 5.3 (Comparative Example
12)
[0095] As can be seen from Table 1 and FIGS. 2 and 3, the value of
the coercive force Hc of the magnetic thin film tends to increase
as the melting point Tm of the used oxide becomes lower, and the
value is remarkably large when the melting point is 600.degree. C.
or lower. On the other hand, when the standard Gibbs free energy of
formation .DELTA.Gf of the oxide with respect to 1 mol O.sub.2 is
considered, the value of the coercive force Hc of the magnetic thin
film tends to increase if the standard Gibbs free energy of
formation .DELTA.Gf of the oxide falls within the range of -1,000
kJ/mol O.sub.2 or more and -500 kJ/mol O.sub.2 or less.
[0096] Thus, the oxide suitable for increasing the coercive force
Hc of the magnetic thin film is considered to have a melting point
of 600.degree. C. or lower and a standard Gibbs free energy of
formation .DELTA.Gf with respect to 1 mol O.sub.2 being -1,000
kJ/mol O.sub.2 or more and -500 kJ/mol O.sub.2 or less.
[0097] At present it is uncertain why the oxide suitable for
increasing the coercive force Hc of the magnetic thin film has a
melting point of 600.degree. C. or lower and a standard Gibbs free
energy of formation .DELTA.Gf with respect to 1 mol O.sub.2 being
-1,000 kJ/mol O.sub.2 or more and -500 kJ/mol O.sub.2 or less.
However, why the value of the coercive force Hc of the magnetic
thin film tends to increase as the melting point Tm of the used
oxide becomes lower can be explained as follows. Specifically, the
Ru layer located at the lower layer than the magnetic thin film
(closer to the substrate) has a surface with irregularities. During
the cooling process after sputtering, the CoPt alloy, which has a
relatively high melting point of 1460.degree. C., is first
selectively deposited on the projected portions of the Ru layer
(Co.sub.60Cr.sub.40-26 vol % SiO.sub.2 layer on the surface of the
projected portion of the Ru layer) to grow in a columnar shape
while the oxide having the low melting point is still in a liquid
state. Thus, it is assumed that the oxide in the liquid state is
present between the CoPt alloy particles growing in a columnar
shape. As the cooling progresses further, the liquid oxide present
between the CoPt alloy particles is solidified, and the oxide
becomes wall body to separate between the CoPt alloy particles
having grown in a columnar shape and form a granular structure.
[0098] Thus, the use of an oxide having a low melting point
assuredly separates the CoPt alloy particles by the wall body of
the oxide. As the result, the interaction between the CoPt alloy
particles becomes small. Thus, it is assumed that the magnetic thin
film using the oxide having a low melting point has a larger
coercive force Hc.
[0099] Note that the smaller the standard Gibbs free energy of
formation .DELTA.Gf of an oxide with respect to 1 mol O.sub.2 is
(larger minus value), the more stable the oxide is as an oxide.
From the viewpoint of this, it is assumed that the smaller standard
Gibbs free energy of formation .DELTA.Gf of an oxide (.DELTA.Gf of
larger minus value) with respect to 1 mol O.sub.2 is preferred.
[0100] Further, as can be seen from Table 1, the oxide
B.sub.2O.sub.3 used for the sputtering target of Example 1 has a
melting point Tm of 450.degree. C., which is equal to or lower than
600.degree. C., and the standard Gibbs free energy of formation
.DELTA.Gf with respect to 1 mol O.sub.2 of -795.8 kJ/mol O.sub.2,
which is -1,000 kJ/mol O.sub.2 or more and -500 kJ/mol O.sub.2 or
less. Thus, the sputtering target of Example 1 is encompassed by
the present invention. The coercive force Hc of the sample for
determining magnetic properties produced in Example 1 is 8.8 kOe,
which is remarkably larger than those of Comparative Examples 1 to
12 using other oxides, and the sample produced in Example 1 is the
only sample that has the coercive force Hc exceeding 8 kOe.
[0101] Therefore, it is assumed that the most appropriate means to
increase the coercive force Hc of the CoPt alloy-oxide based
magnetic thin film is to use the CoPt alloy-oxide based target
using B.sub.2O.sub.3 as in Example 1.
--Additional Studies about Content of Oxide (Examples 2 to 8)--
[0102] As discussed above, the previous studies suggest that the
most appropriate means to increase the coercive force Hc of the
CoPt alloy-oxide based magnetic thin film is to use the CoPt
alloy-oxide based target using B.sub.2O.sub.3 as in Example 1.
[0103] However, the B.sub.2O.sub.3 content in the sputtering
targets used in Example 1 was 30 vol %, only one type of
content.
[0104] Therefore, additional studies were carried out by producing
a plurality of targets (the composition of Co and Pt was 80Co-20Pt)
in the same manner as in Example 1 except that the content of
B.sub.2O.sub.3 was changed. The B.sub.2O.sub.3 contents in the
sputtering targets in additional studies (Examples 2 to 8) were 10
vol % in Example 2, 15 vol % in Example 3, 20 vol % in Example 4,
25 vol % in Example 5, 35 vol % in Example 6, 40 vol % in Example
7, and 50 vol % in Example 8. Samples for determining magnetic
properties were prepared in the same manner as in Example 1 by
using the prepared target.
[0105] The hysteresis loop was measured, using a magneto-optical
Kerr effect apparatus, for the sample for determining magnetic
properties in the same manner as in Example 1. Then, the coercive
force Hc was read from the hysteresis loop.
[0106] The following table 2 lists these measurement results
together with the measurement results of Example 1.
TABLE-US-00002 TABLE 2 oxide content Coercive force Hc oxide (vol
%) (kOe) B.sub.2O.sub.3 10 5.5 (Example 2) B.sub.2O.sub.3 15 7.1
(Example 3) B.sub.2O.sub.3 20 7.6 (Example 4) B.sub.2O.sub.3 25 8.2
(Example 5) B.sub.2O.sub.3 30 8.8 (Example 1) B.sub.2O.sub.3 35 8.5
(Example 6) B.sub.2O.sub.3 40 8.1 (Example 7) B.sub.2O.sub.3 50 6.2
(Example 8)
[0107] As can be seen from Table 2, all the coercive forces Hc in
Examples 1 to 8 exceed 5 kOe, showing favorable results. Thus, when
the CoPt-oxide target using B.sub.2O.sub.3 as the oxide is used and
the content of B.sub.2O.sub.3 relative to the entire target is 10
vol % or more and 50 vol % or less, it is assumed that the
favorable magnetic thin film having a coercive force Hc exceeding 5
kOe can be obtained.
[0108] Furthermore, as can be seen from Table 2, when the content
of B.sub.2O.sub.3 relative to the entire target is 20 vol % or more
and 40 vol % or less, the favorable magnetic thin films having a
coercive force Hc of 7.6 kOe or larger are obtained. Thus, it is
assumed that the content of B.sub.2O.sub.3 relative to the entire
target should more preferably be 20 vol % or more and 40 vol % or
less.
[0109] Furthermore, as can be seen from Table 2, when the content
of B.sub.2O.sub.3 relative to the entire target is 25 vol % or more
and 35 vol % or less, the favorable magnetic thin films having a
coercive force Hc of 8.2 kOe or larger are obtained. Thus, it is
assumed that the content of B.sub.2O.sub.3 relative to the entire
target should particularly preferably be 25 vol % or more and 35
vol % or less.
INDUSTRIAL APPLICABILITY
[0110] The sputtering target according to the present invention is
a sputtering target with which a magnetic thin film having a high
coercive force can be fabricated, and thus has industrial
applicability.
* * * * *