U.S. patent application number 15/969958 was filed with the patent office on 2018-09-06 for sintered compact magnesium oxide target for sputtering, and method for producing same.
The applicant listed for this patent is JX Nippon Mining & Metals Corporation. Invention is credited to Akira Hisano, Yuichiro Nakamura.
Application Number | 20180251889 15/969958 |
Document ID | / |
Family ID | 48697317 |
Filed Date | 2018-09-06 |
United States Patent
Application |
20180251889 |
Kind Code |
A1 |
Hisano; Akira ; et
al. |
September 6, 2018 |
SINTERED COMPACT MAGNESIUM OXIDE TARGET FOR SPUTTERING, AND METHOD
FOR PRODUCING SAME
Abstract
A sintered compact magnesium oxide target for sputtering has a
purity of 99.99 wt % or higher excluding C, a density of 3.57
g/cm.sup.3 or higher, and a whiteness of 60% or less. To uniformly
deposit a magnesium oxide film, a magnesium oxide target having a
higher purity and a higher density is demanded. An object is to
provide a target capable of realizing the above and a method for
producing such a target. While a magnesium oxide sintered compact
sputtering target is produced by hot-pressing a raw material
powder, there is a problem in that color shading occurs in roughly
.phi.60 (within a circle having a diameter of 60 mm) at the center
part of the target. Conventionally, no particularly attention was
given to this problem. However, in recent years, it has become
necessary to investigate and resolve this problem in order to
improve the deposition quality.
Inventors: |
Hisano; Akira; (Ibaraki,
JP) ; Nakamura; Yuichiro; (Ibaraki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JX Nippon Mining & Metals Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
48697317 |
Appl. No.: |
15/969958 |
Filed: |
May 3, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14356395 |
May 6, 2014 |
9988709 |
|
|
PCT/JP2012/083391 |
Dec 25, 2012 |
|
|
|
15969958 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 14/3414 20130101;
C04B 35/053 20130101; C04B 2235/9661 20130101; C04B 35/645
20130101; C04B 2235/81 20130101; C04B 2235/77 20130101; C23C
14/3407 20130101; C04B 2235/5445 20130101; C04B 2235/721 20130101;
C23C 14/081 20130101; C04B 2235/9646 20130101; C04B 2235/442
20130101 |
International
Class: |
C23C 14/34 20060101
C23C014/34; C04B 35/645 20060101 C04B035/645; C04B 35/053 20060101
C04B035/053; C23C 14/08 20060101 C23C014/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2011 |
JP |
2011-285757 |
Claims
1. A method for producing a sputtering target comprising a sintered
compact of magnesium oxide, comprising the steps of: adding raw
material powder of MgCO.sub.3 in an amount of 5 wt % or more and
less than 30 wt % to raw material powder of magnesium oxide (MgO),
the raw material powders of magnesium oxide (MgO) and MgCO.sub.3
having a purity of 99.99 wt % or higher excluding C and an average
grain size of 0.5 .mu.m or less; mixing the raw material powder of
MgCO.sub.3 with the raw material powder of magnesium oxide (MgO) to
produce a mixture; and hot pressing the mixture at a temperature of
1500.degree. C. or less and an applied pressure of 300 kgf/cm.sup.2
or more to obtain a sintered compact of magnesium oxide having a
purity of 99.99 wt % or higher excluding C, a density of 3.57
g/cm.sup.3 or higher, and a whiteness of 60% or less.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of co-pending U.S.
application Ser. No. 14/356,395 which is a 371 National Stage of
International Application No. PCT/JP2012/083391, filed Dec. 25,
2012, which claims the benefit under 35 USC 119 of Japanese
Application No. 2011-285757, filed Dec. 27, 2011.
BACKGROUND
[0002] The present invention relates to a magnesium oxide target
for use in forming a magnesium oxide layer for magnetic recording
mediums of magnetic disk devices or tunneling magnetoresistance
(TMR) elements and other electronic devices, and to the method of
producing such a magnesium oxide target; and particularly relates
to a sintered compact magnesium oxide target for sputtering of high
purity and high density and which is free of color shading that
occurs at the center of the target, and to the method of producing
such a sintered compact magnesium oxide target for sputtering.
[0003] In recent years, pursuant to the downsizing and higher
recording density of magnetic disks, research and development of
magnetic recording mediums are being conducted, and in particular
Co-based magnetic layers and under-layers have been improved
variously. Meanwhile, the recording density of hard disks has been
increasing rapidly year by year, and it is considered that current
surface density of 600 Gbit/in.sup.2 will reach 1 Tbit/in.sup.2 in
the future. When the recording density reaches 1 Tbit/in.sup.2, the
recording bit size will be less than 10 nm and, in such a case, it
is anticipated that the superparamagnetism caused by thermal
fluctuation will become a problem. The currently used magnetic
recording medium structure such as a structure with increased
magnetic crystalline anisotropy obtained by adding Pt to a
Co--Cr-based alloy will become insufficient. This is because
magnetic particles that behave with stable ferromagnetism at a size
of 10 nm or less require even greater magnetic crystalline
anisotropy.
[0004] Due to the foregoing reason, a Fe--Pt phase having an
L1.sub.0 structure is attracting attention as a structure for use
in an ultra-high density recording medium. Since the Fe--Pt phase
having an L1.sub.0 structure possesses high magnetic crystalline
anisotropy in addition to yielding superior corrosion resistance
and oxidation resistance, it is expected to be a structure that can
be suitably applied to a magnetic recording medium.
[0005] When using a Fe--Pt layer as a structure for use in an
ultra-high density recording medium, it is demanded to develop a
technology of dispersing ordered Fe--Pt magnetic particles
regulated in the same direction with a density as high as possible
in a magnetically isolated state. While it is necessary to control
the crystal orientation to provide magnetic anisotropy to the
Fe--Pt thin film, this can be easily performed by selecting a
single crystal substrate. In order to vertically align an easy
axis, it has been reported that a magnesium oxide film is suitable
as the under-layer of the Fe--Pt layer.
[0006] In addition, it is also known that a magnesium oxide film
can be suitably used as the insulating layer, i.e., tunnel barrier
of a TMR element that is used in a magnetic head (for hard disks)
or an MRAM. While the foregoing magnesium oxide film has been
conventionally formed via the vacuum deposition method, in recent
years the sputtering method is being used to produce magnesium
oxide films from the perspective of simplification of the
production process and facilitation of the production of large
screens.
[0007] There are the following publications as conventional
technology.
[0008] JP-A-H10-130827 describes a magnesium oxide target made from
a magnesium oxide sintered compact having a magnesium oxide purity
of 99.9% or higher than a relative density of 99% or higher,
wherein the magnesium oxide target has a fine structure in which
the average grain size is 60 .mu.m or less and round pores having
an average grain size of 2 .mu.m or less exist in the crystal
grains, and is compatible up to a sputter deposition rate of 1000
.ANG./min or more. This technique is based on a method of adding
fine magnesium oxide powder having an average grain size of 100 nm
or less to high purity magnesium oxide powder and mixing and
compacting the powders and subjecting the obtained compact to
primary sintering and secondary sintering.
[0009] JP-A-H10-130828 relates to a magnesium oxide target made
from a magnesium oxide sintered compact having a relative density
of 99% or higher and capable of achieving a deposition rate of 500
.ANG./min or higher in sputter deposition performed in an Ar
atmosphere or Ar-O.sub.2 mixed atmosphere, and proposes compacting
high purity magnesium oxide powder having an average grain size of
0.1 to 2 .mu.m based on CIP at a pressure of 3 t/cm.sup.2 or
higher, and sintering the obtained compact.
[0010] JP-A-H10-158826 describes a magnesium oxide target made from
a magnesium oxide sintered compact having a magnesium oxide purity
of 99.9% or higher and a relative density of 99.0% or higher, and
compatible up to a sputter deposition rate of 600 .ANG./min or
more. This technique is based on a method of adding electromelted
magnesium oxide powder and fine magnesium oxide powder having an
average grain size of 100 nm or less to high purity magnesium oxide
powder and mixing and compacting the powders and subjecting the
obtained compact to primary sintering and secondary sintering.
JP-A-H10-158826 describes that a magnesium oxide film having
favorable orientation, crystallinity and film properties can be
deposited via the sputtering method at a high deposition rate.
[0011] JP-A-H10-237636 describes a target having MgO as its main
component, as well as a method for producing such a target, and
proposes dispersing La particles, Y particles and Sc particles in a
target having MgO as its main component for use as a protective
film of a dielectric layer of an Ac-type PDP in order to achieve a
low discharge voltage, sputtering resistance during discharge,
quick responsiveness to discharge, and insulation properties.
[0012] JP-A-H11-6058 proposes, in a target having MgO as its main
component, dispersing LaB.sub.6 particles in the MgO matrix,
performing reduction treatment in a reduced gas atmosphere prior to
sintering, and perfoiiiiing primary sintering and secondary
sintering at a predetermined temperature in order to improve the
strength, fracture toughness value, and resistance to thermal
shock.
[0013] JP-A-H11-335824 prescribes the relative density and the
average crystal grain size to be 0.5 to 100 .mu.m in a target
having MgO as its main component, and dispersing the rare earth
elements of Sc, Y, La, Ce, Gd, Yb, and Nd in the MgO matrix.
[0014] JP-A-H11-139862 proposes sintering a MgO green compact based
on the spark plasma sintering method in order to produce a high
density sintered compact.
[0015] JP-A-2009-173502 and WO2009/096384 describe methods of
obtaining a MgO sintered compact with numerous (111) planes aligned
based on uniaxial pressure sintering and having an ultimate density
of 3.568 g/cm.sup.3 so as to achieve favorable mechanical property
and theinial conductivity, and reduction in contamination of the
atmosphere caused by the generation of gas, and propose subjecting
MgO raw material powder having a grain size of 1 .mu.m or less to
uniaxial pressure sintering, and subsequently performing heat
treatment in an oxygen atmosphere at a temperature of 1273 K or
higher. In the foregoing case, MgO is used as the raw material
powder, and the method of increasing the density is limited to the
sintering conditions.
[0016] JP-A-2000-169956 proposes a target for depositing a MgO film
in a large size and uniform manner. In addition to prescribing the
average crystal grain size, the density, the deflective strength,
and the center line average roughness of the target surface,
JP-A-2000-169956 proposes causing the grain size of the raw
material powder to be 1 .mu.m or less, subjecting the raw material
powder to granulation, sintering the granulated raw material powder
at a predetermined load and temperature, and finishing the surface
of the target to achieve a center line average roughness Ra of 1
.mu.m or less. Incidentally, while not directly related to the
present invention, aforementioned JP-A-H10-130827, JP-A-H10-130828,
JP-A-H10-158826, JP-A-H10-237636, JP-A-H11-6058, JP-A-H11-335824,
JP-A-2009-173502 , and WO2009/096384 describe the evaluation of the
"bending strength" of a target, and JP-A-2000-169956 describes the
evaluation of the "deflective strength" of a target.
SUMMARY
[0017] In recent years, the use of a magnesium oxide film in
recording mediums of magnetic disk devices (hard disks) or
tunneling magnetoresistance (TMR) elements and other electronic
devices is being considered, but a magnesium oxide target having a
higher purity and a higher density is being demanded in order to
uniformly deposit a magnesium oxide film. Nevertheless, since
expectations for higher purification and densification are
extremely high, it was conventionally difficult to produce a
magnesium oxide target capable of meeting the foregoing demands.
Thus, an object of this invention is to provide a target capable of
realizing the above, and a method for producing such a target.
[0018] Moreover, while a magnesium oxide sintered compact
sputtering target is produced by hot-pressing a raw material
powder, there is a problem in that color shading occurs in roughly
.phi.60 (within a circle having a diameter of 60 mm) at the center
part of the target. Conventionally, no particularly attention was
given to this problem. However, in recent years, it has become
necessary to investigate and resolve this problem to improve the
deposition quality.
[0019] In order to achieve the foregoing object, as a result of
intense study, the present inventors discovered that a magnesium
oxide target having a higher purity and a higher density can be
obtained with inexpensive processing conditions in comparison to
conventional methods based on the selection of raw material powders
and the optimal setting of sintering conditions. In addition, with
respect to the occurrence of color shading, the present inventors
additionally discovered that it is possible to produce a uniformly
gray magnesium oxide target that is free of color shading, and
which comprises a moderate oxygen defect.
[0020] Based on the foregoing discovery, the following invention is
provided, namely, a sintered compact magnesium oxide target for
sputtering having a purity of 99.99 wt % or higher excluding C, a
density of 3.57 g/cm.sup.3 or higher, and a whiteness of 60% or
less. The sintered compact magnesium oxide target may be produced
by using a raw material obtained by adding MgCO.sub.3 in an amount
of 5 wt % or more and less than 30 wt % to magnesium oxide (MgO).
The sintered compact magnesium oxide target may have a whiteness of
55% or higher and 60% or less and/or a variation in the whiteness
may be within 5%.
[0021] The invention also provides a method for producing a
sintered compact magnesium oxide target. The method uses a raw
material obtained by adding MgCO.sub.3 in an amount of 5 wt % or
more and less than 30 wt % to magnesium oxide (MgO), wherein raw
material powders made of magnesium oxide (MgO) and MgCO.sub.3
having a purity of 99.99 wt % or higher excluding C and an average
grain size of 0.5 .mu.m or less are mixed, and the mixed powders
are hot pressed at a temperature of 1500.degree. C. or less and an
applied pressure of 300 kgf/cm.sup.2 or more to obtain a sintered
compact magnesium oxide target for sputtering having a purity of
99.99 wt % or higher excluding C, and a density of 3.57 g/cm.sup.3
or higher.
[0022] The invention also provides a method for producing any of
the sintered compact magnesium oxide targets described above which
uses a raw material obtained by adding MgCO.sub.3 in an amount of 5
wt % or more and less than 30 wt % to magnesium oxide (MgO),
wherein raw material powders made of magnesium oxide (MgO) and
MgCO.sub.3 having a purity of 99.99 wt % or higher excluding C and
an average grain size of 0.5 .mu.m or less are mixed, and the mixed
powders are hot pressed at a temperature of 1500.degree. C. or less
and an applied pressure of 300 kgf/cm.sup.2 or more to obtain a
sintered compact magnesium oxide target for sputtering having a
purity of 99.99 wt % or higher excluding C, and a density of 3.57
g/cm.sup.3 or higher.
[0023] The present invention is effective in unifoimly depositing a
magnesium oxide film, and specifically provides a high purity, high
density sintered compact magnesium oxide target that is free of
color shading and can be produced at a low cost by selecting the
appropriate raw material powders. It is also possible to obtain a
high- density target having a uniform composition. Moreover, the
generation of particles during sputtering can be consequently
inhibited. In addition, since it is possible to produce a sintered
compact magnesium oxide target comprising a moderate oxygen defect,
excessive oxygen is not generated during sputtering, and an effect
of inhibiting oxidation of the adjacent deposition layer (metal
layer) is exhibited.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a diagram showing the correlation of the additive
amount of magnesium carbonate (MgCO.sub.3) and the relative density
of the sintered compact magnesium oxide target.
[0025] FIG. 2 is a diagram showing the correlation of the additive
amount of magnesium carbonate (MgCO.sub.3) and the whiteness of the
sintered compact magnesium oxide target.
DETAILED DESCRIPTION
[0026] The sintered compact magnesium oxide target for sputtering
of the present invention has a purity of 99.99 wt % or higher
excluding C, a density of 3.57 g/cm.sup.3 or higher, and a
whiteness of 60% or less, and a major feature of the present
invention is that the sintered compact magnesium oxide target for
sputtering has a whiteness of 55% or higher and 60% or less.
[0027] This target can be realized by producing the target using a
raw material obtained by adding MgCO.sub.3 in an amount of 5 wt %
or more and less than 30 wt % to magnesium oxide (MgO). Note that
the whiteness was measured using the micro surface spectral color
difference meter VSS400 (JIS Z 8722, ASTM E 308) manufactured by
Nippon Denshoku Industries. This Hunter-type color difference meter
was used to measure L: luminosity and ab (huechroma), and the
whiteness was obtained from the following formula: W
(whiteness)=100-((100-L).sup.2+(a.sup.2+b.sup.2)).sup.1/2.
[0028] Conventionally, magnesium oxide (MgO) was sintered, but
sufficient density could not be obtained unless the sintering
temperature was set high. The present invention can achieve a
density of 3.57 g/cm.sup.3 or more with a sintering temperature of
1500.degree. C. or less as described below. This is a low
temperature compared to conventional methods, and thus it is
possible to reduce the production cost. In addition, the present
invention can obtain a sintered compact magnesium oxide target for
sputtering having a purity of 99.99% or higher excluding C.
[0029] As described above, it is even more advantageous to have an
effect of reducing the nodules and particles because reduction of
the variation in whiteness causes improvement in the uniformity of
the sintered compact. Here, the variation in whiteness is
preferably adjusted to be within 5%.
[0030] Upon producing the sintered compact magnesium oxide target
for sputtering of the present invention, a MgCO.sub.3 raw material
in an amount of 5 wt % or more and less than 30 wt % is used. This
raw material has a purity of 99.99 wt % or higher excluding C, and,
after mixing the MgCO.sub.3 raw material powders having an average
grain size of 0.5 .mu.m or less, the mixed powders are hot pressed
at a temperature of 1500.degree. C. or less and an applied pressure
of 300 kgf/cm.sup.2 or more to obtain a target having a purity of
99.99 wt % or higher excluding C, and a density of 3.57 g/cm.sup.3
or higher. Note that magnesium carbonate (MgCO.sub.3) is decomposed
during sintering (MgCO.sub.3.fwdarw.MgO+CO.sub.2).
EXAMPLES
[0031] The Examples are now explained. Note that these Examples
merely illustrate preferred representative examples, and it should
be easy to understand that the present invention should not be
limited to these Examples. The technical concept of the present
invention shall be interpreted based on the overall descriptions of
this specification and particularly based on the scope of
claims.
Example 1
[0032] The sintered compact magnesium oxide target for sputtering
was produced according to the following method. A raw material
powder containing MgCO.sub.3 in an amount of 6.0 wt % and remainder
being magnesium oxide (MgO) having a purity of 99.99 wt % or higher
excluding C and an average grain size of 0.5 .mu.m or less was
mixed. Note that the C content in this raw material powder was 0.86
wt %.
[0033] Subsequently, this mixed powder was hot pressed for 2 hours
at a temperature of 1500.degree. C. and an applied pressure of 300
kgf/cm.sup.2 to produce a magnesium oxide target having a purity of
99.99 wt % or higher excluding C. Note that, since magnesium
carbonate (MgCO.sub.3) is decomposed during sintering
(MgCO.sub.3.fwdarw.MgO+CO.sub.2), magnesium carbonate (MgCO.sub.3)
does not exist in the sintered target. The density of the obtained
MgO sintered compact was measured with the Archimedes method.
Consequently, a density of 3.576 g/cm.sup.3 (relative density
99.74%) was obtained.
[0034] The sintered compact produced as described above was subject
to grinding and polishing to obtain a sintered compact magnesium
oxide target for sputtering. Upon visually observing the target,
the color was gray, and the target possessed optical transparency.
Moreover, upon examining the whiteness of the target, the whiteness
was 58.6%. In addition, the variation in whiteness was 3.9%. For
this whiteness, the whiteness by Hunter (Lab) was obtained by using
the "micro surface spectral color difference meter VSS400"
manufactured by Nippon Denshoku Industries. The measuring range
diameter in the foregoing case was 0.2 mm.phi.. Three points were
randomly measured to obtain the average value and variation
(.sigma.) thereof. In the following Examples and Comparative
Examples, the whiteness was measured, and the variation thereof was
measured in a similar manner.
TABLE-US-00001 TABLE 1 Additive Sinter- Variation C Amount of ing
Sintered in Content MgCO.sub.3 Temper- Hold Pressing Compact
Relative Optical White- White- in Raw Raw Material ature Time
Pressure Density Density Trans- ness ness Material (wt. %)
(.degree. C.) (Hours) (kgf/cm.sup.2) (g/cm.sup.3) (%) Color parency
(%) (%) (wt. %) Comparative 0.0 1500 2 300 3.280 91.49 White No
91.3 1.4 0.00 Example 1 Comparative 1.8 1500 2 300 3.482 97.11
White No 81.5 1.6 0.26 Example 2 Comparative 3.0 1500 2 300 3.540
98.74 Light Yes 72.2 10.5 0.43 Example 3 gray, spots Comparative
4.2 1500 2 300 3.568 99.53 Light Yes 63.5 0.3 0.60 Example 4 gray
Example 1 6.0 1500 2 300 3.576 99.74 Gray Yes 58.6 3.9 0.86 Example
2 9.0 1500 2 300 3.576 99.75 Gray Yes 57.6 0.6 1.28 Example 3 12.0
1500 2 300 3.572 99.64 Gray Yes 55.6 3.2 1.71 Example 4 15.0 1500 2
300 3.577 99.79 Gray Yes 56.6 1.1 2.14 Example 5 18.0 1500 2 300
3.571 99.62 Gray Yes 56.1 3.4 2.57 Comparative 30.0 1500 2 300
3.572 99.62 Gray, Yes 56.5 5.2 4.28 Example 5 spots Comparative
48.0 1500 2 300 3.577 99.78 Gray, Yes 56.4 6.8 6.84 Example 6 spots
Comparative 60.0 1500 2 300 3.573 99.65 Gray, Yes 56.6 8.1 8.55
Example 7 spots, cracks
Example 2
[0035] The sintered compact magnesium oxide target for sputtering
was produced according to the following method. A raw material
powder containing MgCO.sub.3 in an amount of 9.0 wt % and remainder
being magnesium oxide (MgO) having a purity of 99.99 wt % or higher
excluding C and an average grain size of 0.5 .mu.m or less was
mixed. Note that the C content in this raw material powder was 1.28
wt %.
[0036] Subsequently, this mixed powder was hot pressed for 2 hours
at a temperature of 1500.degree. C. and an applied pressure of 300
kgf/cm.sup.2 to produce a magnesium oxide target having a purity of
99.99 wt % or higher excluding C. Note that, since magnesium
carbonate (MgCO.sub.3) is decomposed during sintering
(MgCO.sub.3.fwdarw.MgO+CO.sub.2), magnesium carbonate (MgCO.sub.3)
does not exist in the sintered target. The density of the obtained
MgO sintered compact was measured with the Archimedes method.
Consequently, a density of 3.576 g/cm.sup.3 (relative density
99.75%) was obtained.
[0037] The sintered compact produced as described above was subject
to grinding and polishing to obtain a sintered compact magnesium
oxide target for sputtering. Upon visually observing the target,
the color was gray, and the target possessed optical transparency.
Moreover, upon examining the whiteness of the target, the whiteness
was 57.6%. In addition, the variation in whiteness was 0.6%.
Example 3
[0038] The sintered compact magnesium oxide target for sputtering
was produced according to the following method. A raw material
powder containing MgCO.sub.3 in an amount of 12.0 wt % and
remainder being magnesium oxide (MgO) having a purity of 99.99 wt %
or higher excluding C and an average grain size of 0.5 .mu.m or
less was mixed. Note that the C content in this raw material powder
was 1.71 wt %.
[0039] Subsequently, this mixed powder was hot pressed for 2 hours
at a temperature of 1500.degree. C. and an applied pressure of 300
kgf/cm.sup.2 to produce a magnesium oxide target having a purity of
99.99 wt % or higher excluding C. Note that, since magnesium
carbonate (MgCO.sub.3) is decomposed during sintering
(MgCO.sub.3.fwdarw.MgO+CO.sub.2), magnesium carbonate (MgCO.sub.3)
does not exist in the sintered target. The density of the obtained
MgO sintered compact was measured with the Archimedes method.
Consequently, a density of 3.572 g/cm.sup.3 (relative density
99.64%) was obtained.
[0040] The sintered compact produced as described above was subject
to grinding and polishing to obtain a sintered compact magnesium
oxide target for sputtering. Upon visually observing the target,
the color was gray, and the target possessed optical transparency.
Moreover, upon examining the whiteness of the target, the whiteness
was 55.6%. In addition, the variation in whiteness was 3.2%.
Example 4
[0041] The sintered compact magnesium oxide target for sputtering
was produced according to the following method. A raw material
powder containing MgCO.sub.3 in an amount of 15.0 wt % and
remainder being magnesium oxide (MgO) having a purity of 99.99 wt %
or higher excluding C and an average grain size of 0.5 .mu.m or
less was mixed. Note that the C content in this raw material powder
was 2.14 wt %.
[0042] Subsequently, this mixed powder was hot pressed for 2 hours
at a temperature of 1500.degree. C. and an applied pressure of 300
kgf/cm.sup.2 to produce a magnesium oxide target having a purity of
99.99 wt % or higher excluding C. Note that, since magnesium
carbonate (MgCO.sub.3) is decomposed during sintering
(MgCO.sub.3.fwdarw.MgO+CO.sub.2), magnesium carbonate (MgCO.sub.3)
does not exist in the sintered target. The density of the obtained
MgO sintered compact was measured with the Archimedes method.
Consequently, a density of 3.577 g/cm.sup.3 (relative density
99.79%) was obtained.
[0043] The sintered compact produced as described above was subject
to grinding and polishing to obtain a sintered compact magnesium
oxide target for sputtering. Upon visually observing the target,
the color was gray, and the target possessed optical transparency.
Moreover, upon examining the whiteness of the target, the whiteness
was 56.6%. In addition, the variation in whiteness was 1.1%.
Example 5
[0044] The sintered compact magnesium oxide target for sputtering
was produced according to the following method. A raw material
powder containing MgCO.sub.3 in an amount of 18.0 wt % and
remainder being magnesium oxide (MgO) having a purity of 99.99 wt %
or higher excluding C and an average grain size of 0.5 .mu.m or
less was mixed. Note that the C content in this raw material powder
was 2.57 wt %.
[0045] Subsequently, this mixed powder was hot pressed for 2 hours
at a temperature of 1500.degree. C. and an applied pressure of 300
kgf/cm.sup.2 to produce a magnesium oxide target having a purity of
99.99 wt % or higher excluding C. Note that, since magnesium
carbonate (MgCO.sub.3) is decomposed during sintering
(MgCO.sub.3.fwdarw.MgO+CO.sub.2), magnesium carbonate (MgCO.sub.3)
does not exist in the sintered target. The density of the obtained
MgO sintered compact was measured with the Archimedes method.
Consequently, a density of 3.571 g/cm.sup.3 (relative density
99.62%) was obtained.
[0046] The sintered compact produced as described above was subject
to grinding and polishing to obtain a sintered compact magnesium
oxide target for sputtering. Upon visually observing the target,
the color was gray, and the target possessed optical transparency.
Moreover, upon examining the whiteness of the target, the whiteness
was 56.1%. In addition, the variation in whiteness was 3.4%.
[0047] Comparative Example 1
[0048] The sintered compact magnesium oxide target for sputtering
was produced according to the following method. A raw material
powder containing magnesium oxide (MgO) having a purity of 99.99 wt
% or higher and an average grain size of 0.5 .mu.m or less was
used. Note that magnesium carbonate (MgCO.sub.3) was not added to
this raw material powder. C content was <10 ppm.
[0049] Subsequently, this raw material powder was hot pressed for 2
hours at a temperature of 1500.degree. C. and an applied pressure
of 300 kgf/cm.sup.2 to produce a magnesium oxide target having a
purity of 99.99 wt % or higher excluding C. The density of the
obtained MgO sintered compact was measured with the Archimedes
method. Consequently, a density of 3.280 g/cm.sup.3 (relative
density 91.49%) was obtained. In comparison to the Examples, the
density decreased significantly.
[0050] The sintered compact produced as described above was subject
to grinding and polishing to obtain a sintered compact magnesium
oxide target for sputtering. Upon visually observing the target,
the color was white, and the target did not possess optical
transparency. Moreover, upon examining the whiteness of the target,
the whiteness was 91.3%. In addition, the variation in whiteness
was 1.4%.
Comparative Example 2
[0051] The sintered compact magnesium oxide target for sputtering
was produced according to the following method. A raw material
powder containing magnesium oxide (MgO) and magnesium carbonate
(MgCO.sub.3) in an amount of 0.18 wt % having a purity of 99.99 wt
% or higher excluding C and an average grain size of 0.5 .mu.m or
less was mixed. C content was 0.26 wt %. In the foregoing case, the
amount of magnesium carbonate (MgCO.sub.3) did not satisfy the
amount of the present invention.
[0052] Subsequently, this mixed powder was hot pressed for 2 hours
at a temperature of 1500.degree. C. and an applied pressure of 300
kgf/cm.sup.2 to produce a magnesium oxide target having a purity of
99.99 wt % or higher excluding C. Note that, since magnesium
carbonate (MgCO.sub.3) is decomposed during sintering
(MgCO.sub.3.fwdarw.MgO+CO.sub.2), magnesium carbonate (MgCO.sub.3)
does not exist in the sintered target. The density of the obtained
MgO sintered compact was measured with the Archimedes method.
Consequently, a density of 3.482 g/cm.sup.3 (relative density
97.11%) was obtained. In comparison to the Examples, the density
decreased significantly.
[0053] The sintered compact produced as described above was subject
to grinding and polishing to obtain a sintered compact magnesium
oxide target for sputtering. Upon visually observing the target,
the color was white, and the target did not possess optical
transparency. Moreover, upon examining the whiteness of the target,
the whiteness was 81.5%. In addition, the variation in whiteness
was 1.6%.
Comparative Example 3
[0054] The sintered compact magnesium oxide target for sputtering
was produced according to the following method. A raw material
powder containing magnesium oxide (MgO) and magnesium carbonate
(MgCO.sub.3) in an amount of 3.0 wt % having a purity of 99.99 wt %
or higher excluding C and an average grain size of 0.5 .mu.m or
less was mixed. C content was 0.43 wt %. In the foregoing case, the
amount of magnesium carbonate (MgCO.sub.3) did not satisfy the
amount of the present invention.
[0055] Subsequently, this mixed powder was hot pressed for 2 hours
at a temperature of 1500.degree. C. and an applied pressure of 300
kgf/cm.sup.2 to produce a magnesium oxide target having a purity of
99.99 wt % or higher excluding C. Note that, since magnesium
carbonate (MgCO.sub.3) is decomposed during sintering
(MgCO.sub.3.fwdarw.MgO+CO.sub.2), magnesium carbonate (MgCO.sub.3)
does not exist in the sintered target. The density of the obtained
MgO sintered compact was measured with the Archimedes method.
Consequently, a density of 3.540 g/cm.sup.3 (relative density
98.74%) was obtained. In comparison to the Examples, the density
decreased.
[0056] The sintered compact produced as described above was subject
to grinding and polishing to obtain a sintered compact magnesium
oxide target for sputtering. Upon visually observing the target,
the color was light gray but "spots" appeared on the surface. The
target possessed optical transparency.
[0057] Moreover, upon examining the whiteness of the target, the
whiteness was 72.2%. In addition, the variation in whiteness was
10.5%.
Comparative Example 4
[0058] The sintered compact magnesium oxide target for sputtering
was produced according to the following method. A raw material
powder containing magnesium oxide (MgO) and magnesium carbonate
(MgCO.sub.3) in an amount of 4.2 wt % having a purity of 99.99 wt %
or higher excluding C and an average grain size of 0.5 .mu.m or
less was mixed. C content was 0.60 wt %. In the foregoing case, the
amount of magnesium carbonate (MgCO.sub.3) did not satisfy the
amount of the present invention.
[0059] Subsequently, this mixed powder was hot pressed for 2 hours
at a temperature of 1500.degree. C. and an applied pressure of 300
kgf/cm.sup.2 to produce a magnesium oxide target having a purity of
99.99 wt % or higher excluding C. Note that, since magnesium
carbonate (MgCO.sub.3) is decomposed during sintering
(MgCO.sub.3.fwdarw.MgO+CO.sub.2), magnesium carbonate (MgCO.sub.3)
does not exist in the sintered target. The density of the obtained
MgO sintered compact was measured with the Archimedes method.
Consequently, a density of 3.568 g/cm.sup.3 (relative density
99.53%) was obtained. In comparison to the Examples, the density
decreased.
[0060] The sintered compact produced as described above was subject
to grinding and polishing to obtain a sintered compact magnesium
oxide target for sputtering. Upon visually observing the target,
the color was light gray, and the target possessed optical
transparency. Moreover, upon examining the whiteness of the target,
the whiteness was 63.5%. In addition, the variation in whiteness
was 0.3%.
Comparative Example 5
[0061] The sintered compact magnesium oxide target for sputtering
was produced according to the following method. A raw material
powder containing magnesium oxide (MgO) and magnesium carbonate
(MgCO.sub.3) in an amount of 30.0 wt % having a purity of 99.99 wt
% or higher excluding C and an average grain size of 0.5 .mu.m or
less was mixed. C content was 4.3 wt %. In the foregoing case, the
amount of magnesium carbonate (MgCO.sub.3) exceeds the amount of
the present invention.
[0062] Subsequently, this mixed powder was hot pressed for 2 hours
at a temperature of 1500.degree. C. and an applied pressure of 300
kgf/cm.sup.2 to produce a magnesium oxide target having a purity of
99.99 wt % or higher excluding C. Note that, since magnesium
carbonate (MgCO.sub.3) is decomposed during sintering
(MgCO.sub.3.fwdarw.MgO+CO.sub.2), magnesium carbonate (MgCO.sub.3)
does not exist in the sintered target. The density of the obtained
MgO sintered compact was measured with the Archimedes method.
Consequently, a density of 3.572 g/cm.sup.3 (relative density
99.62%) was obtained, and the density was equivalent to the
Examples.
[0063] The sintered compact produced as described above was subject
to grinding and polishing to obtain a sintered compact magnesium
oxide target for sputtering. Upon visually observing the target,
the color was gray but "spots" appeared on the surface. This is
considered to be a result of an increase in the amount of magnesium
carbonate (MgCO.sub.3). Moreover, upon examining the whiteness of
the target, the whiteness was 56.5%. In addition, the variation in
whiteness was 5.2%.
Comparative Example 6
[0064] The sintered compact magnesium oxide target for sputtering
was produced according to the following method. A raw material
powder containing magnesium oxide (MgO) and magnesium carbonate
(MgCO.sub.3) in an amount of 48.0 wt % having a purity of 99.99 wt
% or higher excluding C and an average grain size of 0.5 .mu.m or
less was mixed. C content was 6.8 wt %. In the foregoing case, the
amount of magnesium carbonate (MgCO.sub.3) exceeds the amount of
the present invention.
[0065] Subsequently, this mixed powder was hot pressed for 2 hours
at a temperature of 1500.degree. C. and an applied pressure of 300
kgf/cm.sup.2 to produce a magnesium oxide target having a purity of
99.99 wt % or higher excluding C. Note that, since magnesium
carbonate (MgCO.sub.3) is decomposed during sintering
(MgCO.sub.3.fwdarw.MgO+CO.sub.2), magnesium carbonate (MgCO.sub.3)
does not exist in the sintered target. The density of the obtained
MgO sintered compact was measured with the Archimedes method.
Consequently, a density of 3.577 g/cm.sup.3 (relative density
99.78%) was obtained, and the density was equivalent to the
Examples.
[0066] The sintered compact produced as described above was subject
to grinding and polishing to obtain a sintered compact magnesium
oxide target for sputtering. Upon visually observing the target,
the color was gray but "spots" appeared on the surface. This is
considered to be a result of an increase in the amount of magnesium
carbonate (MgCO.sub.3). Moreover, upon examining the whiteness of
the target, the whiteness was 56.4%. In addition, the variation in
whiteness was 6.8%.
Comparative Example 7
[0067] The sintered compact magnesium oxide target for sputtering
was produced according to the following method. A raw material
powder containing magnesium oxide (MgO) and magnesium carbonate
(MgCO.sub.3) in an amount of 60.0 wt % having a purity of 99.99 wt
% or higher excluding C and an average grain size of 0.5 .mu.m or
less was mixed. C content was 8.55 wt %. In the foregoing case, the
amount of magnesium carbonate (MgCO.sub.3) considerably exceeds the
amount of the present invention.
[0068] Subsequently, this mixed powder was hot pressed for 2 hours
at a temperature of 1500.degree. C. and an applied pressure of 300
kgf/cm.sup.2 to produce a magnesium oxide target having a purity of
99.99 wt % or higher excluding C. Note that, since magnesium
carbonate (MgCO.sub.3) is decomposed during sintering
(MgCO.sub.3.fwdarw.MgO+CO.sub.2), magnesium carbonate (MgCO.sub.3)
does not exist in the sintered target. The density of the obtained
MgO sintered compact was measured with the Archimedes method.
Consequently, a density of 3.573 g/cm.sup.3 (relative density
99.65%) was obtained, and the density was equivalent to the
Examples.
[0069] The sintered compact produced as described above was subject
to grinding and polishing to obtain a sintered compact magnesium
oxide target for sputtering. Upon visually observing the target,
the color was gray but "spots" appeared on the surface. Moreover,
cracks were generated in addition to the "spots". This is
considered to be a result of an increase in the amount of magnesium
carbonate (MgCO.sub.3).
[0070] Moreover, upon examining the whiteness of the target, the
whiteness was 56.6%. In addition, the variation in whiteness was
8.1%.
[0071] As evident from the foregoing Examples and Comparative
Examples, the relative density of the sintered compact magnesium
oxide target of the present invention is affected by the additive
amount of the magnesium carbonate (MgCO.sub.3). A density of 3.57
g/cm.sup.3 (relative density of 99.5%) can be achieved by adding
MgCO.sub.3 in an amount of 5 wt % or more and less than 30 wt %.
This is shown in FIG. 1.
[0072] Moreover, the whiteness of the sintered compact magnesium
oxide target of the present invention is affected by the additive
amount of the magnesium carbonate (MgCO.sub.3). The whiteness
becomes 60% or less by adding MgCO.sub.3 in an amount of 5 wt % or
more and less than 30 wt %. This is shown in FIG. 2.
[0073] Accordingly, a target produced by using a raw material
obtained by adding MgCO.sub.3 in an amount of 5 wt % or more and
less than 30 wt % to the magnesium oxide (MgO) has a high density,
and is effective as a sintered compact magnesium oxide target for
sputtering.
[0074] Moreover, as evident from the foregoing Examples and
Comparative Examples, it is more effective to adjust the variation
in whiteness to be within 5% since an effect of decreasing the
cracks and nodules of the sintered compact can be obtained.
[0075] The present invention yields a superior effect of being able
to obtain a high purity, high density sintered compact magnesium
oxide target that is free of color shading and can be produced at a
low cost by selecting the appropriate raw material powder. It is
also possible to improve the characteristics of the deposition of
magnesium oxide. Further, the generation of particles during
sputtering can be consequently inhibited. In addition, since it is
possible to produce a sintered compact magnesium oxide target
comprising a moderate oxygen defect, excessive oxygen is not
generated during sputtering, and an effect of inhibiting oxidation
of the adjacent deposition layer (metal layer) is exhibited.
[0076] Accordingly, the magnesium oxide sintered compact sputtering
target of the present invention is useful as a magnesium oxide
sputtering target for use in forming a magnesium oxide layer for
magnetic recording mediums of magnetic disk devices or tunneling
magnetoresistance (TMR) elements and other electronic devices.
* * * * *