Title: Oxide sintered body and manufacturing method thereof
Abstract: The present invention relates to an oxide sintered body having a perovskite structure represented with a chemical formula of MRuO.sub.3 (M: one or more types among Ca, Sr, Ba), characterized in that the total content of alkali metals such as Na, K, and Fe, Ni, Co, Cr, Cu, Al is 100 ppm or less, the content of respective elements U, Th is 10 ppb or less, and the relative density is 90% or more, and provides an oxide sintered body and the manufacturing method thereof having a pervoskite structure represented with the chemical formula MRuO.sub.3 (M: one or more types among Ca, Sr, Ba) by using a MRuO.sub.3 sintered body raw material refined to a high density of 4N or more, which enables sintering at low temperatures, and which is capable of obtaining a high-density sintered body.
Patent Number: 6,843,975 Issued on 01/18/2005 to Suzuki
| Inventors:
|
Suzuki; Ryo (Ibaraki, JP)
|
| Assignee:
|
Nikko Materials Company, Limited (Tokyo, JP)
|
| Appl. No.:
|
130238 |
| Filed:
|
May 15, 2002 |
| PCT Filed:
|
September 17, 2001
|
| PCT NO:
|
PCT/JP01/08044
|
| 371 Date:
|
May 15, 2002
|
| 102(e) Date:
|
May 15, 2002
|
| PCT PUB.NO.:
|
WO02/05176 |
| PCT PUB. Date:
|
July 4, 2002 |
Foreign Application Priority Data
| Dec 26, 2000[JP] | 2000-394263 |
| Current U.S. Class: |
423/594.16; 264/125 |
| Intern'l Class: |
C01G 055/00; C01F011/00; B29C067/00 |
| Field of Search: |
423/594.16
264/125
|
References Cited [Referenced By]
U.S. Patent Documents
| 5624542 | Apr., 1997 | Shen et al. | 204/283.
|
| 5995359 | Nov., 1999 | Klee et al. | 361/305.
|
| 6555864 | Apr., 2003 | Cross et al. | 257/310.
|
| Foreign Patent Documents |
| 10-330924 | Dec., 1998 | JP.
| |
| 2000-001774 | Jan., 2000 | JP.
| |
| 2000-128638 | May., 2000 | JP.
| |
Other References
Machine translation of the specification of Japan 2000-128638, May 2000.*
Patent Abstracts of Japan, one page English language Abstract for JP
2000-128638, May 2000.
Patent Abstracts of Japan, one page English language Abstract for JP
2000-001774, Jan. 2000.
Patent Abstracts of Japan, one page English language Abstract for JP
10-330924, Dec. 1998.
|
Primary Examiner: Bos; Steven
Attorney, Agent or Firm: Howson and Howson
Claims
What is claimed is:
1. A method of manufacturing an oxide sintered body, comprising the steps
of:
covering a die with oxide ceramic, Al.sub.2 O.sub.3, ZrO.sub.2, Si.sub.3
N.sub.4, Ru, Pt, Ir, Co or Ni; and
pressure sintering an oxide powder in said die at a sintering temperature
of 1200.degree. C. to 1400.degree. C. to form an oxide sintered body
having a perovskite structure represented with a chemical formula of
MRuO.sub.3, wherein M represents at least one of Ca, Sr and Ba, and
wherein a total content of alkali metals including Na, X, and Fe, Ni, Co,
Cr, Cu, Al is 100 ppm or less, and a content of elements U and Th is 10
ppb or less, and wherein said oxide sintered body is has a relative
density of 90% or more.
2. A method according to claim 1, wherein said pressure sintering step is
conducted with a hot press at a pressurization of 200 kg/cm.sup.2 or more.
3. A mod according to claim 1, wherein said relative density is 95% or
more.
4. A method according to claim 3, wherein said pressure sintering step is
conducted with a hot press at a pressurization of 200 kg/cm.sup.2 or more.
Description
TECHNICAL FIELD
The present invention relates to a high-purity and high-density Ru oxide
sintered body and the manufacturing method thereof suitable for sputtering
targets having a purity of 4 N or more and a relative density of 90% or
more, and particularly to a Ru oxide sintered body and the manufacturing
method thereof extremely superior in forming a thin film excellent in
uniformity and having minimal formation of particles as the sputtering
target upon forming an electrode material for a high dielectric or
ferroelectric thin film memory.
BACKGROUND OF THE INVENTION
Today, ferroelectric thin films of BST and PZT as memory material of DRAMs,
FRAMs and so on are being actively developed, and major concerns in such
dielectric thin films are the fatigue characteristics and data-retention
characteristics of the film.
Generally, with respect to a dielectric memory material, a platinum
electrode is used as the electrode material of the ferroelectric thin film
provided on the SiO.sub.2 on the substrate. Nevertheless, with this
platinum electrode, due to its own catalytic effect, there are problems of
hydrogen deterioration of ferroelectric thin films caused by hydrogen
processing during the device process and fatigue deterioration resulting
from the localization of oxygen deficiency toward the electrode side, and
there is a problem in that the aforementioned characteristics cannot be
sufficiently acquired.
Thus, as a substitute for such platinum electrode, there is growing
interest in a Ru oxide sintered body. Electrode material obtainable from
such Ru oxide sintered body (e.g., SrRuO.sub.3) has the potential of
becoming a superior electrode material with bulk resistivity of
10.sup.-5.OMEGA..multidot.m or less.
However, the Ru oxide sintered body; that is, an oxide having a perovskite
structure represented with a chemical formula of MRuO.sub.3 (M: one or
more types among Ca, Sr, Ba), is difficult to sinter, and the density
obtainable with an ordinary pressureless sintering method is 70% or less.
Generally, sputtering is performed to a Ru oxide sintered body target to
form a thin film. Nevertheless, when machine processing this type of
low-density MRuO.sub.3 sintered body into a target, the yield becomes
extremely inferior and the formation of particles upon sputtering with
this target increases considerably. Thus, the formation of favorable thin
films cannot be realized.
Therefore, even if the characteristics as an electrode material are
superior, there is a major problem in that the uniformity and surface
morphology of the film will become inferior when used as a thin film
electrode.
Thus, although the sintering conditions are being devised with the
perspective of high densification of the MRuO.sub.3, the current status is
that a sufficient density is yet to be achieved. For example, although the
pressure sintering method is effective in high densification, when using a
graphite die generally employed in hot pressing, the intended MRuO.sub.3
sintered body cannot be obtained due to the reduction of MRuO.sub.3 caused
by the reaction between the die and MRuO.sub.3. Moreover, there is another
problem in that the consumption of the die is severe.
Meanwhile, in order to guarantee the operational performance as a reliable
semiconductor, it is important to reduce as much as possible the
impurities, which are detrimental to the semiconductor devices, in the
aforementioned materials formed after sputtering.
In other words,
(1) Alkali metals such as Na, K;
(2) Radioactive elements such as U, Th; and
(3) Class elements of transition metals such as Fe, Ni, Co, Cr, Cu, Al
should be reduced as much as possible, and it is desirable that the purity
be 4 N; that is, 99.99% (mass) or more. As used herein, every %, ppm and
ppb represents mass %, mass ppm and mass ppb, respectively.
Alkali metals such as Na, K, which are the aforementioned impurities, cause
the deterioration of MOS-LSI surface characteristics since they easily
move within the gate insulation film, radioactive elements such as U. Th
cause the soft error of devices with the a ray emitted by such elements,
and class elements of transition metals such as Fe, Ni, Co, Cr, Cu, Al
contained as impurities are known to cause trouble in interface bonding.
OBJECTS OF THE INVENTION
The present invention seeks to reduce as much as possible harmful
substances and to improve the sintering method, and to provide an oxide
sintered body and the manufacturing method thereof having a perovskite
structure represented with the chemical formula MRuO.sub.3 (M: one or more
types among Ca, Sr, Ba) by using a MRuO.sub.3 sintered body raw material
refined to a high density of 4 N or more, which enables sintering at low
temperatures, and which is capable of obtaining a high-density sintered
body.
SUMMARY OF THE INVENTION
The present invention provides:
1. An oxide sintered body having a perovskite structure represented with a
chemical formula of MRuO.sub.3 (M: one or more types among Ca, Sr, Ba),
characterized in that the total content of alkali metals such as Na, K,
and Fe, Ni, Co, Cr, Cu, Al is 100 ppm or less, the content of respective
elements U, Th is 10 ppb or less, and the relative density is 90% or more;
2. An oxide sintered body according to paragraph 1 above, characterized in
that the relative density is 95% or more;
3. A manufacturing method of an oxide sintered body characterized in
conducting pressure sintering using a die covered with Si.sub.3 N.sub.4,
Ru, Pt, Ir, Co, Ni, or an oxide ceramic such as Al.sub.2 O.sub.3 or
ZrO.sub.2 upon pressure sintering oxide powder having a perovskite
structure represented with a chemical formula of MRuO.sub.3 (M: one or
more types among Ca, Sr, Ba), characterized in that the total content of
alkali metals such as Na, K, and Fe, Ni, Co, Cr, Cu, Al is 100 ppm or
less, the content of respective elements U, Th is 10 ppb or less, and the
relative density is 90% or more;
4. A manufacturing method of an oxide sintered body according to paragraph
3 above, characterized in that the relative density is 95% or more;
5. A manufacturing method of an oxide sintered body according to paragraph
3 or paragraph 4 above, characterized in that the sintering is conducted
at a sintering temperature of 1200 to 1400.degree. C.; and
6. A manufacturing method of an oxide sintered body according to each of
paragraphs 3 to 5 above, characterized in that the pressure sintering is
conducted with a hot press at a pressurization of 200 kg/cm.sup.2 or more.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In order to manufacture oxide powder having a perovskite structure
represented with a chemical formula of MRuO.sub.3 (M: one or more types
among Ca, Sr, Ba), SrCO.sub.3 powder, CaCO.sub.3 powder, BaCO.sub.3 powder
and RuO.sub.2 powder refined to a high purity of 4 N or more are used.
For the high purification of these powders, for example, a
recrystallization method from a nitric saline solution in the case of
SrCO.sub.3 powder, CaCO.sub.3 powder and BaCO.sub.3 powder, and a vapor
phase refining method in the case of RuO.sub.2 powder are employed.
Pursuant to this high purification, it is possible to achieve a state
where the total content of alkali metals such as Na, K, and Fe, Ni, Co,
Cr, Cu, Al is 100 ppm or less, and the content of each element of the
radioactive elements such as U, Th is 10 ppb or less.
Upon sintering, it is desirable to use a hot press and to conduct sintering
at a sintering temperature of 1200 to 1400.degree. C. Here, larger the
specific surface area of the oxide powder, lower the temperature may be
for sintering, and it is possible to obtain a high-density sintered body
equivalent to a case of conducting sintering at a high temperature upon
suppressing the reaction with die.
Further, in order to suppress the reaction between the graphite die used in
sintering at high temperatures and the MRuO.sub.3, sintering is conducted
by using a die covered with Si.sub.3 N.sub.4, Ru, Pt, Ir, Co, Ni, or an
oxide ceramic such as Al.sub.2 O.sub.3, or ZrO.sub.2.
This sintering condition is important. Conventionally, there was no choice
but to conduct sintering at a temperature of 1000.degree. C. or less in
order to suppress the reaction between the aforementioned graphite die and
MRuO.sub.3. Therefore, there were cases where the target would crack
during the mechanical processing or sputtering thereof since sufficient
density could not be achieved, and the yield was significantly decreased
thereby. With the improvement of the aforementioned sintering process,
however, it was possible to achieve a relative density of 90% or more, and
even 95% or more, and the transverse rupture strength was significantly
increased thereby.
As a result, cracks are not generated during the mechanical processing of
the target or during the handling thereof, and the yield is improved
considerably. In addition, the thin film after sputtering is superior in
uniformity, and it was possible to obtain a thin film having extremely
superior characteristics as an electrode material for a dielectric thin
film memory.
EXAMPLES AND COMPARATIVE EXAMPLES
Next, the present invention is described based on the Examples. The
Examples are for facilitating the understanding of the invention, and the
present invention is not in any way limited thereby. In other words, the
present invention covers other Examples and modifications based on the
technical spirit of the invention.
Example 1
SrRuO.sub.3 single-phase powder was obtained by using SrCO.sub.3 powder and
RuO.sub.2 powder refined to a high purity of 4 N or more and
check-weighing and wet blending such powders to achieve Sr:Ru=1:1 (molar
ratio), and thereafter conducting thermal synthesis at 900.degree. C. for
10 hours in the atmosphere.
Next, using graphite die in which the obtained SrRuO.sub.3 single-phase
powder was covered with partially stabilized zirconia, hot press sintering
was conducted at 300 kg/cm.sup.2 and retained for 2 hours in an argon gas
atmosphere at the respective temperatures of 1200.degree. C., 1300.degree.
C. and 1400.degree. C.
As a result, although a slight reduction layer could be acknowledged in the
vicinity of the surface of the obtained sintered body, obtained was a
sintered body free from the generation of fractures and cracks. The
relative densities of the above, as shown in the following Table 1, are
all 90% or more, and the strength nearly quadrupled in comparison to the
transverse rupture strength of 76 kg/cm.sup.2 of a sintered body having a
relative density of 58% prepared with pressureless sintering at
1400.degree. C.
Further, the bulk resistivity measured with the four probe method was 300
.mu..OMEGA.cm or less, and was more than 100 .mu..OMEGA.cm less than the
one prepared with the pressureless sintering method.
Example 2
The characteristics of the sintered body prepared under the same conditions
as Example 1 other than that the hot press condition was set to
1400.degree. C., 200 kg/cm.sup.2 were such that, as also shown in Table 1,
the relative density was 91% and the resistivity was 277 kg/cm.sup.2,
whereby obtained was a favorable sintered body.
Example 3
CaRuO.sub.3 single-phase powder was obtained by using CaCO.sub.3 powder and
RuO.sub.2 powder refined to a high purity of 4 N or more and
check-weighing and wet blending such powders to achieve Ca:Ru=1:1 (molar
ratio), and thereafter conducting thermal synthesis at 800.degree. C. for
10 hours in the atmosphere.
Next, using graphite die in which the obtained CaRuO.sub.3 single-phase
powder was covered with partially stabilized zirconia, hot press sintering
was conducted at 300 kg/cm.sup.2 and retained for 2 hours in an argon gas
atmosphere at a temperature of 1400.degree. C.
Also as shown in Table 1, the relative density of the obtained sintered
body was 97%, and the transverse rupture strength and the resistivity were
both favorable.
Example 4
BaRuO.sub.3 single-phase powder was obtained by using BaCO.sub.3 powder and
RuO.sub.2 powder refined to a high purity of 4 N or more and
check-weighing and wet blending such powders to achieve Ba:Ru=1:1 (molar
ratio), and thereafter conducting thermal synthesis at 1050.degree. C. for
10 hours in the atmosphere.
Next, using graphite die in which the obtained BaRuO.sub.3 single-phase
powder was covered with partially stabilized zirconia, hot press sintering
was conducted at 300 kg/cm.sup.2 and retained for 2 hours in an argon gas
atmosphere at a temperature of 1400.degree. C.
Also as shown in Table 1, the relative density of the obtained sintered
body was 93%, and the transverse rupture strength and the resistivity were
both favorable.
Comparative Example 1
After forming the SrCO.sub.3 powder synthesized under the same conditions
as Example 1 at 1500 kg/cm.sup.2, pressureless sintering was conducted at
1400.degree. C. for 10 hours in the atmosphere. This is outside the scope
of the sintering pressure of the present invention.
The relative density of the obtained sintered body was 58%, and the
sintering hardly progressed. Moreover, as shown in Table 1, the transverse
rupture strength was also low at 76 kg/cm.sup.2, and was insufficient in
enduring the target processing.
Comparative Example 2
Hot press sintering was conducted to the SrRuO.sub.3 powder synthesized
under the same conditions as Example 1 at 300 kg/cm.sup.2 and retained for
2 hours in an argon gas atmosphere at temperatures of 1000.degree. C. and
1100.degree. C. These sintering temperatures are outside the scope of the
sintering temperature of the present invention.
As shown in Table 1, the relative density of the obtained sintered body was
less than 80%, and the transverse rupture strength was less than 1/2 of
the sintered body obtained in Example 1.
Comparative Example 3
Hot press sintering was conducted to the SrRuO.sub.3 powder synthesized
under the same conditions as Example 1 at 100 kg/Cm.sup.2 and retained for
2 hours in an argon gas atmosphere at a temperature of 1400.degree. C.
This sintering pressure is outside the scope of the present invention. As
shown in Table 1, the relative density of the obtained sintered body was
80%, and the transverse rupture strength was approximately 1/2 of the
sintered body obtained in Example 1.
TABLE 1
List of Sintering Conditions and Sintered Body Characteristics
of Examples and Comparative Examples
Trans-
verse
Sintering Rupture
Tem- Sintering Strength Resist-
perature Pressure Relative (kg/ ivity Judg-
(.degree. C.) (kg/cm.sup.2) Density cm.sup.2) (.mu..OMEGA.cm)
ment
Example 1 1200 300 92 300 300 .largecircle.
1300 300 94 305 255 .largecircle.
1400 300 96 300 260 .largecircle.
Example 2 1400 200 91 277 310 .largecircle.
Example 3 1400 300 97 350 330 .largecircle.
Example 4 1400 300 93 290 260 .largecircle.
Comparative 1400 0 58 76 460 X
Example 1
Comparative 1000 300 62 80 420 X
Example 2 1100 300 78 150 380 X
Comparative 1400 100 80 155 330 X
Example 3
The symbol .largecircle. represents a sintered body having favorable
relative density, transverse rupture strength and resistivity, whereas X
represents a sintered body in which the aforementioned items are
unfavorable.
The high-purity and high-density Ru oxide sintered body of the present
invention has significant characteristics in that it has a purity of 4 N
or more, a relative density of 90% or more, and a high transverse rupture
strength. The present invention has a superior effect in that it is able
to obtain a Ru oxide sintered body which does not generate cracks or the
like during machine processing to the sputtering target, which improves
the yield, and which is suitable in manufacturing such target.
*
