U.S. patent application number 13/119377 was filed with the patent office on 2011-07-07 for method for storing target comprising rare earth metal or oxide thereof.
This patent application is currently assigned to JX NIPPON MINING & METALS CORPORATION. Invention is credited to Yoshimasa Koido, Kazuyuki Satoh.
Application Number | 20110162322 13/119377 |
Document ID | / |
Family ID | 42128772 |
Filed Date | 2011-07-07 |
United States Patent
Application |
20110162322 |
Kind Code |
A1 |
Satoh; Kazuyuki ; et
al. |
July 7, 2011 |
Method for Storing Target Comprising Rare Earth Metal or Oxide
Thereof
Abstract
Provided is a method for storing a target comprising a rare
earth metal or oxide thereof, wherein oxide of the same rare earth
metal as the material of the rare earth metal or its oxide target
to be stored is introduced as a desiccant into a container or a
film-type seal for storing the target, and the target is stored by
sealing the storage container or the film-type seal. This invention
aims to provide technology for enabling the long-term storage of a
target by devising the method for storing a target comprising a
rare earth metal or oxide thereof, and thereby inhibiting the
pulverization of the target caused by the oxidation and
hydroxylation of such target due to the ingress of air.
Inventors: |
Satoh; Kazuyuki; (Ibaraki,
JP) ; Koido; Yoshimasa; (Ibaraki, JP) |
Assignee: |
JX NIPPON MINING & METALS
CORPORATION
Tokyo
JP
|
Family ID: |
42128772 |
Appl. No.: |
13/119377 |
Filed: |
October 23, 2009 |
PCT Filed: |
October 23, 2009 |
PCT NO: |
PCT/JP2009/068248 |
371 Date: |
March 16, 2011 |
Current U.S.
Class: |
53/403 ; 53/432;
53/467 |
Current CPC
Class: |
C23F 15/00 20130101;
C23C 14/3407 20130101 |
Class at
Publication: |
53/403 ; 53/467;
53/432 |
International
Class: |
B65B 31/02 20060101
B65B031/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 29, 2008 |
JP |
2008-277725 |
Claims
1. A method for storing a target comprising a rare earth metal or
oxide thereof, wherein oxide of the same rare earth metal as the
material of the target comprising the rare earth metal or oxide
thereof to be stored is introduced as a desiccant into a container
or a film-type seal for storing the target, and the target is
stored by sealing the container or the film-type seal.
2. A method for storing a target comprising a rare earth metal or
oxide thereof, wherein rare earth metal oxide having greater
hygroscopic property than the material of the target comprising the
rare earth metal or oxide thereof to be stored is introduced as a
desiccant into a container or a film-type seal for storing the
target, and the target is stored by sealing the container or the
film-type seal.
3. The method for storing a target comprising a rare earth metal or
oxide thereof according to claim 2, wherein the target comprises
two or more types of rare earth metals or their oxides, and wherein
an oxide of the rare earth metal with the greatest hygroscopic
property is used as the desiccant.
4. The method for storing a target comprising a rare earth metal or
oxide thereof according to claim 3, wherein the step of sealing is
vacuum sealing.
5. The method for storing a target comprising a rare earth metal or
oxide thereof according to claim 3, wherein the step of sealing is
vacuum sealing with a flexible film.
6. The method for storing a target comprising a rare earth metal or
oxide thereof according to claim 3, further comprising the step of
filling inert gas having a dew point of -80.degree. C. or less into
the container or film-type seal and encapsulating the target.
7. The method for storing a target comprising a rare earth metal or
oxide thereof according to claim 6, wherein the rare earth metal
oxide to be used as the desiccant is mounted on or filled in a
space created when the target is encapsulated.
8. The method for storing a target comprising a rare earth metal or
oxide thereof according to claim 2, wherein the rare earth metal
configuring the target is La or contains La.
9. The method for storing a target comprising a rare earth metal or
oxide thereof according to claim 8, wherein the rare earth metal
oxide to be used as the desiccant is La oxide.
10. The method for storing a target comprising a rare earth metal
or oxide thereof according to claim 9, wherein the amount of
moisture penetration through the flexible film to be used in
encapsulating and storing the target or the amount of moisture
ingress into the container from the outside is 0.1 g/m.sup.224 h or
less.
11. The method according to claim 2, further comprising the step of
filling inert gas having a dew point of -80.degree. C. or less into
the container or film-type seal and encapsulating the target.
12. The method according to claim 2, wherein the oxide to be used
as the desiccant is mounted on or filled in a space created when
the target is encapsulated by the container or film-type seal.
13. The method according to claim 2, wherein an amount of moisture
penetration through the flexible film to be used in encapsulating
and storing the target or the amount of moisture ingress into the
container from the outside is 0.1 g/m.sup.224 h or less.
14. The method according to claim 1, wherein the step of sealing is
vacuum sealing.
15. The method according to claim 1, wherein the step of sealing is
vacuum sealing with a flexible film.
16. The method according to claim 1, further comprising the step of
filling inert gas having a dew point of -80.degree. C. or less into
the container or film-type seal and encapsulating the target.
17. The method according to claim 1, wherein the oxide to be used
as the desiccant is mounted on or filled in a space created when
the target is encapsulated by the container or film-type seal.
18. The method according to claim 1, wherein the rare earth metal
configuring the target is La or contains La.
19. The method according to claim 19, wherein the oxide to be used
as the desiccant is La oxide.
20. The method according to claim 1, wherein an amount of moisture
penetration through the flexible film to be used in encapsulating
and storing the target or the amount of moisture ingress into the
container from the outside is 0.1 g/m.sup.224 h or less.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for storing a
target comprising a rare earth metal or oxide thereof that is
easily pulverized due to oxidation or hydroxylation.
BACKGROUND ART
[0002] Rare earth metals are contained in the earth's crust as a
mixed composite oxide. Rare-earth elements are so called because
they are separated from relatively rare minerals, but they are not
that rare in light of the overall earth's crust. In recent years,
rare earth metals are attracting attention as an electronic
material, and research and development for using rare earth metals
are being promoted.
[0003] Among the rare earth metals, lanthanum (La) is attracting
particular attention. To briefly introduce lanthanum, lanthanum is
a white metal having an atomic number of 57 and an atomic weight of
138.9, and comprises a double hexagonal close-packed structure at
normal temperature. Lanthanum has a melting point of 921.degree.
C., boiling point of 3500.degree. C., and density of 6.15
g/cm.sup.3, its surface is oxidized in the atmosphere, and it
gradually melts in water.
[0004] Lanthanum is soluble in hot water and acid. Although it is
not ductile, it is slightly malleable. Lanthanum's resistivity is
5.70.times.10.sup.-6 .OMEGA.cm, and it becomes oxide
(La.sub.2O.sub.3) when burned at 445.degree. C. or higher (refer to
Dictionary of Physics and Chemistry). With rare earth elements, it
is generally said that compounds with the oxidation number 3 are
stable, and lanthanum is also trivalent.
[0005] Lanthanum is a metal that is attracting attention as an
electronic material such as a metal gate material or a
high-dielectric constant (High-k) material. Rare earth elements
other than lanthanum also have attributes similar to lanthanum.
[0006] A rare earth metal such as lanthanum is a material in which
high purification is difficult to achieve since it is easily
oxidized during the refining process. In addition, if a rare earth
metal such as lanthanum is left in the atmosphere, there is a
problem in that the handling thereof is difficult since it will
become oxidized and tarnished in a short time.
[0007] In recent years, thinning of a gate insulator film is being
demanded in the next-generation MOSFET, but with the SiO.sub.2 that
has been conventionally used as the gate insulator film, the leak
current increases due to the tunnel effect, and normal operation is
becoming difficult.
[0008] Thus, as a substitute for the SiO.sub.2 described above,
HfO.sub.2, ZrO.sub.2, Al.sub.2O.sub.3 and La.sub.2O.sub.3 with high
dielectric constant, high thermal stability, and high energy
barrier against the holes and electrons in the silicon have been
proposed. in particular, among the foregoing materials,
La.sub.2O.sub.3 is valued highly, and a research on its electrical
properties and for its use as a gate insulator film in the
next-generation MOSFET has been reported (refer to Non Patent
Document 1). Nevertheless, with Non Patent Document 1, the subject
of research is a La.sub.2O.sub.3 film, and it does not make any
reference to the properties and behavior of La metal.
[0009] It could be said that rare earth metals such as lanthanum
and their oxides are still in the research phase. When studying the
properties of such rare earth metals and their oxides, if a rare
earth metal or oxide thereof itself exists as a sputtering target
material, it is possible to form a thin film of such rare earth
metal or oxide thereof on a substrate. It will be easy to study the
behavior at the interface with the silicon substrate, and the
properties of a high-dielectric gate insulator film or the like
after forming a rare earth metal compound. There is also a
significant advantage in that the freedom of the target as a
product will increase.
[0010] Nevertheless, even if a lanthanum sputtering target is
prepared, as described above, it becomes oxidized in a short time
in the atmosphere. Generally speaking, a stable oxide layer is
formed on a metal target surface, but since it is extremely thin,
it peels off during the initial stage of sputtering and does not
affect the sputtering characteristics significantly. However, with
a lanthanum sputtering target, the oxide layer becomes thick, and
deterioration of the electrical conductivity will occur and thereby
cause defective sputtering.
[0011] In addition, if the lanthanum sputtering target is left in
the atmosphere for a long time, it reacts with the moisture in the
air to become covered with white hydroxide powder and ultimately
become pulverized, and it may even cause a problem of not allowing
normal sputtering to be performed. Thus, after the target is
prepared, it is necessary to take measures for preventing oxidation
and hydroxylation such as by immediately vacuum-packing or coating
the target with fats and oils.
[0012] As a method for storing rare earth metals, the standard
method is to store the rare earth metals in mineral oil in order to
prevent such rare earth metals from being exposed to the air.
However, when using a rare earth metal for a sputtering target, it
is necessary to clean the target before its use in order to remove
the mineral oil. However, there is a problem in that the cleaning
of the target itself is difficult due to its reactivity with
oxygen, moisture and carbon dioxide.
[0013] Accordingly, under normal circumstances, it is necessary to
store and package the target based on vacuum packing. However, even
in a state where the target is vacuum packed, since pulverization
caused by oxidation or hydroxylation will progress even with a
small amount of moisture that penetrates the used film, it was
difficult to store the sputtering target in enabled condition for a
long time.
[0014] When reviewing the conventional background art, there are
the following methods; namely, a method of covering the
hollow-cathode-type sputtering target with a resin bag (refer to
Patent Document 1), a method of coating the target with a plastic
protective film (refer to Patent Document 2), a method of packaging
the target using a film having a surface that does not release
particles (refer to Patent Document 3), a method of preparing a
target storage container with a transparent lid of acrylic resin
and screwing shut the storage container (refer to Patent Document
4), and a method of encapsulating the sputtering target in a bag
(refer to Patent Document 5). Nevertheless, since the foregoing
Documents disclose that the target is encapsulated with a resin lid
or a resin film, they are insufficient as a method for storing a
target comprising a rare earth metal or oxide thereof.
[0015] [Non Patent Document 1] Written by Eisuke Tokumitsu and two
others, "Research on Oxide Material for High-k Gate Insulator Film"
The Institute of Electrical Engineers of Japan, Research Paper of
Electronic Materials, Vol. 6-13, Pages 37 to 41, Published on Sep.
21, 2001
[Patent Document 1] International Publication No. W02005/037649
[Patent Document 2] Japanese Laid-Open Patent Publication No.
2002-212718
[Patent Document 3] Japanese Laid-Open Patent Publication No.
2001-240959
[0016] [Patent Document 4] Japanese Laid-Open Patent Publication
No. H8-246135 [Patent Document 5] Japanese Laid-Open Patent
Publication No. H4-231461
DISCLOSURE OF THE INVENTION
Problems which the Invention Intends to Solve
[0017] An object of this invention is to provide technology for
allowing the long-term storage of a sputtering target in enabled
condition by devising the method for storing a target comprising a
rare earth metal or oxide thereof, and thereby inhibiting the
pulverization of the target caused by the oxidation and
hydroxylation of such target due to residual air or ingress of
air.
Means for Solving the Problems
[0018] The present invention provides: [0019] 1) A method for
storing a sputtering target comprising a rare earth metal or oxide
thereof, wherein oxide of the same rare earth metal as the material
of the target comprising the rare earth metal or oxide thereof to
be stored is introduced as a desiccant into a container or a
film-type seal for storing the target, and the sputtering target is
stored by sealing the container or the film-type seal; and [0020]
2) A method for storing a target comprising a rare earth metal or
oxide thereof, wherein rare earth metal oxide having greater
hygroscopic property than the material of the target comprising the
rare earth metal or oxide thereof to be stored is introduced as a
desiccant into a container or a film-type seal for storing the
target, and the target is stored by sealing the container or the
film-type seal.
[0021] The present invention additionally provides: [0022] 3) The
method for storing a target comprising a rare earth metal or oxide
thereof according to 2) above, wherein, if the target comprises two
or more types of rare earth metals or their oxides, an oxide of the
rare earth metal with the greatest hygroscopic property is used as
a desiccant; [0023] 4) The method for storing a target comprising a
rare earth metal or oxide thereof according to any one of 1) to 3)
above, wherein the encapsulating and storing method for the target
is based on vacuum sealing; and [0024] 5) The method for storing a
target comprising a rare earth metal or oxide thereof according to
any one of 1) to 4), wherein the encapsulating and storing means
for the target is a vacuum sealing with a flexible film.
[0025] The present invention further provides: [0026] 6) The method
for storing a target comprising a rare earth metal or oxide thereof
according to any one of 1) to 5) above, wherein the encapsulating
and storing method for the target is performed by filling inert gas
having a dew point of -80.degree. C. or less to encapsulate the
target; [0027] 7) The method for storing a target comprising a rare
earth metal or oxide thereof according to any one of 1) to 6)
above, wherein the rare earth metal oxide to be used as a desiccant
is mounted on or filled in a space created when the target is
encapsulated; [0028] 8) The method for storing a target comprising
a rare earth metal or oxide thereof according to any one of 1) to
7) above, wherein the rare earth metal configuring the target is La
or contains La; [0029] 9) The method for storing a target
comprising a rare earth metal or oxide thereof according to any one
of 1) to 8) above, wherein the rare earth metal oxide to be used as
a desiccant is La oxide; and [0030] 10) The method for storing a
target comprising a rare earth metal or oxide thereof according to
any one of 1) to 9) above, wherein the amount of moisture
penetration through the flexible film to be used in encapsulating
and storing the target or the amount of moisture ingress into the
container from the outside is 0.1 g/m.sup.224 h or less.
EFFECT OF THE INVENTION
[0031] When encapsulating and storing a conventional target
comprising a rare earth metal or oxide thereof in a hermetic
container or with a plastic film, if it goes unattended for a long
time, it will react with oxygen and moisture and become covered
with white hydroxide powder, and there is a problem in that normal
sputtering cannot be performed. Nevertheless, the target that is
stored in a storage container or a film-type seal according to the
present invention yields a significant effect of being able to
avoid the foregoing problems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 A diagram showing an example where the surface and
side face of the La target are thinly coated with La oxide powder
and vacuum packing is performed thereto.
[0033] FIG. 2 A diagram showing an example where La oxide powder is
placed in a space due to the unevenness (difference in level)
between the La target and BP (backing plate) and vacuum packing is
performed thereto.
[0034] FIG. 3 A diagram showing an example where a La target is
placed in a metallic container, La oxide powder is filled around
the periphery of the La target, ambient air is once replaced with
argon having a dew point of -80.degree. C. or less, and vacuum
sealing is subsequently performed thereto.
[0035] FIG. 4 A diagram showing an example where a metal alloy
target comprising La and Er is placed in a metallic container, a
sintered La oxide block is placed at the uneven part between the
target and BP, air in the container is replaced with argon gas, and
vacuuming is subsequently performed thereto.
[0036] FIG. 5 A diagram showing an example where the La target is
subject to vacuum sealing with a film.
[0037] FIG. 6 A diagram showing an example where the La target is
subject to vacuum sealing with a film, and silica gel is placed as
a desiccant.
[0038] FIG. 7 A diagram showing an example where the
La.sub.2O.sub.3 target is subject to vacuum sealing with a
film.
BEST MODE FOR CARRYING OUT THE INVENTION
[0039] Rare earths, in particular lanthanum and lanthanum oxide,
are known to have extremely strong hygroscopic properties
(reactivity with moisture). Thus, the challenge to date was how to
prevent lanthanum and lanthanum oxide from absorbing moisture as
much as possible, and how to store lanthanum and lanthanum oxide in
an environment with minimal moisture.
[0040] Nevertheless, as a result of taking advantage of the fact
that lanthanum oxide has a higher hygroscopic property than
lanthanum, the oxidation or hydroxylation of the lanthanum target
body can be prevented by coating, mounting or placing lanthanum
oxide (powder or sintered compact of a plate or block) on the
target surface upon storing the lanthanum target.
[0041] Moreover, when storing a lanthanum oxide target, moisture
can be absorbed and eliminated more effectively by enclosing the
powdered or granular lanthanum oxide of larger surface area and,
therefore, degradation of the target caused by hydroxylation can be
prevented.
[0042] Specifically, the method for storing a target comprising a
rare earth metal or oxide thereof according to the present
invention is to introduce, as a desiccant, oxide of the same rare
earth metal as the material of the rare earth metal or its oxide
target to be stored into a storage container or a film-type
seal.
[0043] Here, even if lanthanum oxide reacts with moisture to be
hydroxylated and pulverized and it adheres to the target surface,
since it is a compound of the identical metal in a powdered form,
the foregoing powder will not cause any contamination since it can
be eliminated easily. This is a significant advantage in comparison
to the case of using a desiccant made of other metals.
[0044] Moreover, in cases where the contamination by other rare
earth metals will not cause a problem: it is possible to introduce
oxide of rare earth metal having a greater hygroscopic property
than the material of the rare earth metal or its oxide target to be
stored, as a desiccant, into a storage container or a film-type
seal for the target, and store the target by sealing the storage
container or the film-type seal.
[0045] If the target is made of two or more types of rare earth
metals or their oxides, an oxide of the rare earth metal with the
greatest hygroscopic property can be used as a desiccant.
[0046] As an encapsulating and storing method for target, it is
preferable to prevent the ingress of outside air as much as
possible. Vacuum sealing can be performed as one such method.
Moreover, when vacuum sealing and storing the target, it is
preferable to once replace the inside of the container or the
film-type seal with inert gas having a dew point of -80.degree. C.
or less and thereafter perform vacuum sealing. As means for
encapsulating and storing the target, flexible film may be used in
the form of a hermetic bag and subject to vacuum sealing.
[0047] Although the case of performing vacuum sealing was explained
above, inert gas having a dew point of -80.degree. C. or less may
be filled and sealed as the method for storing a target. All of the
foregoing methods prevent the ingress of outside air.
[0048] As described above, contact with outside air is blocked and
the ingress of moisture in the outside air is inhibited as much as
possible. Nevertheless, even if there is slight ingress of outside
air, hydroxylation of the target body can be inhibited by mounting
or filling the foregoing rare earth oxide to be used as the
desiccant in the space created when the target is encapsulated.
[0049] A target is generally bonded to a backing plate. For
instance, when using a flexible film in the form of a hermetic bag
and performing vacuum sealing thereto, unevenness will inevitably
arise between the target and the backing plate, and a space is
likely to be formed. Outside air is easily accumulated in such
space. Pulverization of the target tends to advance from such
space. Thus, it is desirable to fill the rare earth oxide as the
desiccant at such uneven part or in such space.
[0050] In this respect, it should be easy to understand that the
rare earth oxide to be used as the desiccant is preferably in the
form of powder or granule of large surface area. Nevertheless, it
is effective to simply place a small piece of rare earth oxide at a
location where outside air is easily accumulated.
[0051] Moreover, although it is most effective to place the rare
earth oxide and the target to be in direct contact, adhesion of
powder to the target surface may cause the generation of particles
during sputtering. In the foregoing case, a sufficient effect can
be yielded even by enclosing the rare earth oxide packed with a
permeable film as with a general desiccant.
[0052] The method for storing a target according to the present
invention is particularly effective for a lanthanum target or a
target containing lanthanum as the rare earth metal configuring the
target. Moreover, the foregoing rare earth oxide to be used as the
desiccant is lanthanum oxide. This is ironic, but lanthanum oxide
that is most easily hydroxylated has the greatest inhibitory effect
on hydroxylation of a target comprising a rare earth metal or oxide
thereof in the method for storing a target comprising a rare earth
metal or oxide thereof.
[0053] It is also important, as the method for storing a target
comprising a rare earth metal or oxide thereof, to keep the amount
of moisture penetration through the flexible film to be used in
encapsulating and storing the target or the amount of moisture
ingress into the storage container from the outside to be 0.1
g/m.sup.224 h or less and to prevent the ingress of moisture as
much as possible.
[0054] Table 1 shows the favorable examples of the flexible film to
be used in encapsulating and storing the target, as well as the
non-favorable examples.
[0055] In Table 1, the examples having properties of GX Barrier
(product name) or higher are effective. As shown in Table 1, GX
Barrier (product name) and a bag containing Al foil are favorable.
Table 1 shows representative examples, and it goes without saying
that other flexible films may be used so as long as they satisfy
the foregoing conditions.
TABLE-US-00001 TABLE 1 Permeability Water vapor Oxygen (g/m.sup.2
24 h) (cm.sup.3/m.sup.2 24 h atm) Eval 4 3 NM Barrier 0.32 0.24 GX
Barrier <0.02 0.063 Bag containing Al Foil <0.02 0.047
[0056] Examples of implementing the present invention are now
explained.
[0057] Incidentally, these Examples are merely illustrative, and
the present invention shall in no way be limited thereby. In other
words, various modifications and other embodiments based on the
technical spirit claimed in the claims shall be covered by the
present invention as a matter of course.
Example 1
[0058] This is an example where the surface and side face of a La
target are thinly coated with La oxide powder and vacuum packing is
performed thereto. A specific example is shown in FIG. 1.
[0059] As shown in FIG. 1, as a result of a lanthanum oxide layer
existing between the vacuum-packing film and the La target, the
lanthanum oxide powder absorbs the moisture remaining inside the
vacuum package and the moisture that penetrates the film and is
fixed as lanthanum hydroxide. Thus, this is effective in preventing
the phenomenon where the La target surface reacts with moisture to
become hydroxide and be pulverized.
Example 2
[0060] This is an example where La oxide powder (as with a silica
gel bag) is placed in a space due to the unevenness with BP and
vacuum packing is performed thereto. A specific example is shown in
FIG. 2.
[0061] As shown in FIG. 2, since La oxide absorbs the moisture in
the slight space remaining in the vacuum package and is fixed as
lanthanum hydroxide. Thus, this is effective in preventing the
phenomenon where the La target reacts with moisture to become of
hydroxide and be pulverized.
Example 3
[0062] This is an example where a La oxide target is placed in a
metallic container, La oxide powder is filled around the periphery
of the La target, ambient air is once replaced with argon having a
dew point or -80.degree. C. or less, and vacuum sealing is
subsequently performed thereto. A specific example is shown in FIG.
3.
[0063] As shown in FIG. 3, lanthanum oxide absorbs the moisture
remaining after the vacuuming and is fixed as lanthanum hydroxide.
Thus, this is effective in preventing the phenomenon where La
reacts with moisture to become hydroxide and be pulverized.
Example 4
[0064] This is an example where a metal alloy target comprising La
and Er is placed in a metallic container, a sintered La oxide block
is placed at the uneven part between the target and BP, air in the
container is replaced with argon gas having a dew point of
-80.degree. C. or less, and vacuuming is subsequently performed
thereto.
[0065] As shown in FIG. 4, lanthanum oxide absorbs the moisture
remaining after the vacuuming and is fixed as lanthanum hydroxide.
Thus, this is effective in preventing the phenomenon where La
reacts with moisture to become hydroxide and be pulverized.
Comparative Example 1
[0066] This is an example where the La target was subject to vacuum
sealing with a film. A specific example is shown in FIG. 5. As
shown in FIG. 5, the small amount of moisture remaining in the
space created between the vacuum-packing film and the target
reacted with the La target, and La became lanthanum hydroxide. It
resulted in pulverization.
Comparative Example 2
[0067] This is an example where the La target was subject to vacuum
sealing with a film, and silica gel was placed as a desiccant. A
specific example is shown in FIG. 6.
[0068] When silica gel is placed as shown in FIG. 6, pulverization
progressed faster than the case of not placing silica gel. The
reason for this is considered to be that the moisture adsorbed by
the silica gel became desorbed and discharged inside the
vacuum-packing film, and the reaction of moisture and La was
promoted and resulted in lanthanum hydroxide. In light of the
above, it is evident that silica gel that is used as a general
desiccant is useless, or even undesirable, in preventing the
pulverization phenomenon of the rare earth metal or rare earth
metal oxide.
Comparative Example 3
[0069] This is an example where the La.sub.2O.sub.3 target was
subject to vacuum sealing with a film. A specific example is shown
in FIG. 7. As shown in FIG. 7, since La oxide (La.sub.2O.sub.3)
absorbs the moisture in the slight space remaining in the vacuum
package and is fixed as lanthanum hydroxide, the La.sub.2O.sub.3
target reacts with moisture, and La.sub.2O.sub.3 becomes hydroxide.
It results in pulverization.
[0070] As evident from the foregoing Examples and Comparative
[0071] Examples, upon storing a target comprising a rare earth
metal or oxide thereof, it is evident that the introduction of
oxide of the same rare earth metal as the material of the target
comprising the rare earth metal or oxide thereof to be stored as a
desiccant into a hermetic container or seal is extremely effective.
It is thereby possible to effectively inhibit the pulverization of
the target caused by the oxidation and hydroxylation of such target
due to residual air or ingress of air.
INDUSTRIAL APPLICABILITY
[0072] Conventionally, if a rare earth metal or a rare earth metal
oxide sputtering target is left in the atmosphere for a long time,
it reacts with the moisture in the air and becomes covered with
white hydroxide powder, and there is a problem in that normal
sputtering cannot be performed. Nevertheless, the method for
storing a target comprising a rare earth metal or oxide thereof
according to the present invention enables to avoid the foregoing
problems.
[0073] The method for storing a target comprising a rare earth
metal or oxide thereof according to the present invention is to
introduce, as a desiccant, oxide of the same rare earth metal as
the material of the target comprising the rare earth metal or oxide
thereof to be stored into a storage container or a film-type seal.
It is thereby possible to effectively inhibit the condition where
the target reacts with the moisture in the atmosphere and becomes
covered with white hydroxide powder.
[0074] Accordingly, targets can be stably supplied as an electronic
material such as a metal gate material or a high-dielectric
constant (High-k) material, and the present invention is extremely
useful industrially.
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