WO2010050409A1

WO2010050409A1 - Method for storing target comprising rare earth metal or oxide thereof

Info

Publication number: WO2010050409A1
Application number: PCT/JP2009/068248
Authority: WO
Inventors: 和幸佐藤; 由将小井土
Original assignee: 日鉱金属株式会社
Priority date: 2008-10-29
Filing date: 2009-10-23
Publication date: 2010-05-06
Also published as: JPWO2010050409A1; KR20110047235A; JP5032662B2; US20110162322A1; CN102203314A; KR101290941B1; TW201016551A; CN102203314B; TWI472458B

Abstract

Disclosed is a method for storing a target comprising a rare earth metal or an oxide thereof. The method is characterized in that an oxide of the same rare earth metal as one contained in the target to be stored is introduced, as a desiccant, into a storage container or a film-like sealing material for storing the target therein, the storage container or the film-like sealing material is sealed, and the sealed storage container or the sealed film-like sealing material is stored. It becomes possible to provide a technique which enables the storage of a target comprising a rare earth metal or an oxide thereof for a long period by devising a method for storing the target so as to prevent the oxidation of the target upon the penetration of air or the dusting of the target caused by the hydroxylation of the target.

Description

Storage method of target comprising rare earth metal or oxide thereof

The present invention relates to a method for storing a target comprising a rare earth metal that is easily powdered by oxidation or hydroxylation, or an oxide thereof.

The rare earth metal is contained in the earth's crust as a mixed composite oxide. Since rare earth metals were separated from relatively rare (rare) minerals, they were named as such, but they are not rare when viewed from the entire crust. Recently, rare earth metals have attracted attention as electronic materials, and are being researched and developed.
Among these rare earth metals, lanthanum (La) is particularly attracting attention. Briefly introducing this lanthanum, the lanthanum has an atomic number of 57 and an atomic weight of 138.9, and is a white metal with a double hexagonal close-packed structure at room temperature. The melting point is 921 ° C., the boiling point is 3500 ° C., and the density is 6.15 g / cm ^{3. The} surface is oxidized in the air and gradually dissolved in water.
Soluble in hot water and acid. There is no ductility, but there is slight malleability. The resistivity is 5.70 × 10 ⁻⁶ Ωcm. It burns at 445 ° C or higher to become oxide (La ₂ O ₃ ) (see Physics and Chemistry Dictionary). As for rare earth metals, compounds having an oxidation number of 3 are generally stable, but lanthanum is also trivalent.
This lanthanum is a metal attracting attention as an electronic material, such as a metal gate material and a high dielectric constant material (High-k). Rare earth metals other than lanthanum have attributes similar to this lanthanum.

Since rare earth metals such as lanthanum have a problem that they are easily oxidized during purification, they are difficult materials to be highly purified. Further, when a rare earth metal such as lanthanum is left in the air, it is oxidized and discolored in a short time, so that there is a problem that handling is not easy.
Recently, thinning is required as a gate insulating film in next-generation MOSFETs, but in SiO ₂ that has been used as a gate insulating film so far, leakage current due to a tunnel effect increases and normal operation has become difficult. .
For this reason, HfO ₂ , ZrO ₂ , Al ₂ O ₃ , La ₂ O ₃ having a high dielectric constant, high thermal stability, and a high energy barrier against holes and electrons in silicon are proposed. Has been. In particular, among these materials, La ₂ O ₃ is highly evaluated, electrical characteristics have been investigated, and research reports as a gate insulating film in next-generation MOSFETs have been made (see Non-Patent Document 1). However, in the case of this patent document, the object of research is the La ₂ O ₃ film, and the characteristics and behavior of La metal are not particularly mentioned.

Thus, it can be said that the rare earth metals such as lanthanum and their oxides are still in the research stage, but when investigating the characteristics of such rare earth metals and their oxides, the rare earth metals and their oxides themselves are sputtered. If it exists as a target material, it is possible to form a thin film of rare earth metal and its oxide on the substrate, and also the behavior of the interface with the silicon substrate, and further the formation of a rare earth metal compound to form a high dielectric constant gate. It is easy to examine the characteristics of an insulating film and the like, and has a great advantage that the degree of freedom as a product is increased.

However, even if a lanthanum sputtering target is produced, it is oxidized in the air in a short time as described above. In general, a stable oxide film is formed on the surface of a metal target. However, since it is usually very thin, it peels off at the initial stage of sputtering and does not significantly affect the sputtering characteristics. However, in the lanthanum sputtering target, the oxide film becomes thick, the electric conductivity is lowered, and the sputtering is defective.
Also, if left in the air for a long time, it reacts with the moisture in the air and is covered with a white powder of hydroxide, eventually resulting in a powdered state, and normal sputtering is not possible Even it happens. For this reason, it is necessary to vacuum-pack or cover with oils and fats immediately after producing the target, and to take measures to prevent oxidation and hydroxylation.
As a rare earth metal storage method, it is common to store in mineral oil in order to avoid contact with the atmosphere, but when used as a sputtering target, it is necessary to clean the mineral oil before use. . However, there is a problem that cleaning itself is difficult due to the reactivity with oxygen, moisture, and carbon dioxide as described above.
Therefore, it is usually necessary to store and pack with a vacuum pack. However, even in a vacuum-packed state, even with a slight amount of moisture that permeates the film to be used, pulverization due to oxidation and hydroxylation proceeds, making it difficult to store for a long time in a usable state as a sputtering target. It was.

Looking at conventional known techniques, a method of covering a hollow cathode sputtering target with a resin bag (see Patent Document 1), a method of attaching a protective film of a plastic film to a target (see Patent Document 2), A method of packing a target using a nonexistent surface film (see Patent Document 3), a method of producing a target storage container using a transparent acrylic resin top cover and screwing (see Patent Document 4), a sputtering target There is a method (see Patent Document 5) that encloses a bag-like material. However, these enclose the target using a resin lid or a resinous film, and are not sufficient as a method for storing a target made of a rare earth metal or its oxide.
Eisuke Tokumitsu and 2 other authors, "Studies on oxide materials for high-k gate insulating films", Electrochemical Society of Japan, Materials for Electronic Materials, Vol. 6-13, Page. 37-41, issued on September 21, 2001 International Publication WO2005 / 037649 Japanese Patent Laid-Open No. 2002-212718 JP 2001-240959 A JP-A-8-246135 JP-A-4-231461

The present invention devised a method for storing a target made of a rare earth metal or its oxide, and suppresses oxidization of the target due to residual and intrusion of air and pulverization due to hydroxylation, so that it can be used as a sputtering target. It is an object of the present invention to provide a technique capable of storing a period.

The present invention
1) A method for storing a sputtering target comprising a rare earth metal or an oxide thereof, and a target comprising a rare earth metal or an oxide thereof stored in a container or film seal for storage of the target The same rare earth metal oxide is introduced as a desiccant, and the storage container or the film-like seal is sealed and stored. A method for storing a target comprising a metal or an oxide thereof, wherein the hygroscopic property is higher than that of a rare earth metal or an oxide target material stored in a container or film-like seal for storing the target. A large rare earth metal oxide is introduced as a desiccant, and the container for storage or the film-like seal is sealed and stored. Target storage method of a rare earth metal or an oxide thereof, characterized in, provides.

The present invention also provides:
3) In the case of a target composed of two or more kinds of rare earth metals or oxides thereof, the rare earth metal oxide having the highest hygroscopicity is used as a desiccant, or the rare earth metals or oxides thereof according to 2) above 4. A method for storing a target comprising 4) A method for carrying out sealing storage is vacuum sealing, wherein the target comprising a rare earth metal or oxide thereof according to any one of 1) to 3) above is characterized. 5. Storage method 5) The rare earth metal or oxide thereof according to any one of 1) to 4) above, wherein the sealed storage means is a vacuum seal using a flexible film. A method for storing a target.

Furthermore, the present invention provides
6) The rare earth metal according to any one of 1) to 5) above, wherein these are sealed by sealing with an inert gas having a dew point of −80 ° C. or lower. 7. Method for storing a target made of oxide 7) Any one of 1) to 6) above, wherein the rare earth metal oxide used as a desiccant is placed or filled in a space generated during sealing. 8. A method for storing a target comprising the rare earth metal or oxide thereof according to any one of 8) to 8), wherein the rare earth metal constituting the target contains La or La. 9. A method for storing a target comprising a rare earth metal or an oxide thereof according to 9), wherein the rare earth metal oxide used as a desiccant is a La oxide. Noble earth described in Metal or moisture intrusion of external moisture permeation or container flexible film storage method 10) used to seal storage target made of these oxides is the following 0.1g / m 2 · ^24h A method for storing a target comprising the rare earth metal or oxide thereof according to any one of 1) to 9) above is provided.

When storing a target made of a rare earth metal or an oxide thereof in a hermetically sealed container or a plastic film and storing it for a long time, it reacts with oxygen and moisture to form a hydroxide. It becomes a state of being covered with white powder, and there is a problem that normal sputtering cannot be performed, but the target stored in the storage container or the film-like seal of the present invention does not cause such a problem. It has a great effect.

It is a figure which shows the example at the time of carrying out thin filling with the La oxide powder on the surface and side surface of a La target, and vacuum-packing this. It is a figure which shows the example which put La oxide powder in the space of the level | step difference of La target and BP, and was vacuum-packed. An example is shown in which a La target is placed in a metal container, a La oxide powder is filled around the La target, the surrounding air is once replaced with argon having a dew point of −80 ° C. or lower, and then vacuum sealed. FIG. After placing a metal alloy target composed of La and Er in a metal container, and then placing a block of sintered La oxide on the step between the target and BP, and replacing the air in the container with argon gas It is a figure which shows the example evacuated. It is a figure which shows the example at the time of vacuum-sealing a La target with a film. It is a figure which shows the example at the time of vacuum-sealing a La target with a film and putting (silica gel) as a desiccant. The la ₂ O ₃ target in a film is a diagram illustrating an example of a case where vacuum sealing.

It is known that rare earths, particularly lanthanum and lanthanum oxides, are extremely hygroscopic (reactive with moisture). Therefore, until now, it has been a problem to prevent lanthanum and lanthanum oxide from absorbing moisture below or to store them in an environment with little moisture.
However, lanthanum oxide is more hygroscopic than lanthanum, and when storing lanthanum targets, lanthanum oxide (sintered powder, plates, blocks, etc.) It is intended to prevent oxidation and hydroxylation of the lanthanum target body by applying, placing, or placing on the lantern.
In addition, when storing a lanthanum oxide target, it is possible to absorb and remove moisture more effectively by encapsulating a powder with a larger surface area and granular lanthanum oxide. It is possible to prevent deterioration due to.

That is, the method for storing a target comprising a rare earth metal or an oxide thereof according to the present invention is the same as the rare earth metal stored in a storage container or a film-like seal. An oxide is introduced as a desiccant.
At this time, even if the lanthanum oxide reacts with water to be hydroxylated and powdered and adheres to the target surface, it is a compound of the same metal and is a powder, so it can be easily removed, causing contamination. Not. This is a significant advantage over the use of desiccants made of other metals.

In addition, when contamination with other rare earth metals is not particularly problematic, a rare earth metal oxide that has higher hygroscopicity than the stored rare earth metal or its oxide target material is used as a desiccant for target storage. It can be introduced into a container or film-like seal, and the storage container or film-like seal can be sealed and stored.
In the case of a target composed of two or more kinds of rare earth metals or oxides thereof, a rare earth metal oxide having the highest hygroscopicity can also be used as a desiccant.

About the method of sealing and storing, it is more preferable to prevent outside air from entering as much as possible, and as one of the methods, vacuum sealing can be used. Further, when vacuum-sealing and storing, it is desirable to replace the inside of the container or film-like seal once with an inert gas having a dew point of −80 ° C. or lower and then vacuum-seal. As a means for sealing and storing, a flexible film can be used, and this can be vacuum-sealed as a sealed bag.
In the above description, vacuum sealing has been described. However, as a storage method, an inert gas having a dew point of −80 ° C. or lower can be sealed and sealed. Both prevent outside air from entering.

In this way, it shuts off from the outside air and suppresses the entry of moisture in the outside air as much as possible, but even if there is a slight intrusion, the rare earth oxide used as a desiccant is placed in the space generated when sealed or By filling, it becomes possible to suppress hydroxylation of the target body.
In general, the target is bonded to the backing plate. For example, when using a flexible film and vacuum-sealing it as a sealed bag, the target inevitably has a step between the backing plate, and the gap Is likely to occur. In such a gap, the outside air is easily stored. And it becomes easy to advance powdering of the target from there. It is desirable to fill such a step or void with a rare earth oxide serving as a desiccant.
It will be understood that the rare earth oxide serving as the desiccant is preferably a powder or granule having a large surface area in this sense. However, simply placing a rare earth oxide blob in a place where the outside air can easily be stored is effective.
Moreover, it is most effective to place the rare earth oxide and the target in direct contact with each other, but the adhesion of the powder to the surface of the target may cause generation of particles during sputtering. In such a case, as with a general desiccant, even if sealed in a moisture-permeable film, it is sufficiently effective.

In the method for storing a target of the present invention target, the rare earth metal constituting the target is particularly effective for a lanthanum target or a target containing lanthanum. The rare earth oxide used as the desiccant is lanthanum oxide. Although this is an irony story, as a method of storing a target made of rare earth metal or its oxide, lanthanum oxide, which is most easily hydroxylated, is the most effective in suppressing the hydroxylation of a target made of rare earth metal or its oxide. It is expensive.
The moisture permeation amount of the flexible film used for sealed storage or the moisture intrusion amount from the outside of the container should be 0.1 g / m ² · 24 h or less to prevent moisture from entering as much as possible. It is important as a method for storing targets made of objects.
Table 1 shows preferable examples of the flexible film used for sealed storage and other examples. From Table 1, those having characteristics more than GX barrier (trade name) are effective. As shown in Table 1, a GX barrier (trade name) and a bag containing Al foil are suitable. Table 1 shows typical examples, and it goes without saying that other flexible films can be used as long as the above conditions are satisfied.

Next, an example when the present invention is implemented will be described. Note that this example is for easy understanding, and does not limit the present invention. That is, other examples and modifications within the scope of the technical idea of the present invention are included in the present invention.

Example 1
In this example, the La target is vacuum-packed, and La oxide powder is thinly filled on the surface and side surfaces. A specific example is shown in FIG.
As shown in FIG. 1, the presence of the lanthanum oxide layer between the vacuum pack film and the La target allows moisture remaining inside the vacuum pack and moisture passing through the film to be lanthanum oxide powder. And is fixed as lanthanum hydroxide, which is effective in preventing the phenomenon that the surface of the La target reacts with moisture and becomes hydroxide to be pulverized.

(Example 2)
This is an example in which a La target is vacuum-packed and La oxide powder is placed in a stepped space from BP (like a silica gel bag). A specific example is shown in FIG.
As shown in FIG. 2, in the vacuum pack, La oxide absorbs moisture remaining in the slightly remaining space and fixes it as lanthanum hydroxide, so that the La target reacts with moisture to become hydroxide and powder. This is effective in preventing the phenomenon that occurs.

(Example 3)
A La oxide target is placed in a metal container, and the target is filled with La oxide powder. Then, the surrounding air is temporarily replaced with argon having a dew point of −80 ° C. or lower, and then vacuum sealed. A specific example of the stopped example is shown in FIG.
As shown in FIG. 3, since lanthanum oxide absorbs moisture remaining after being evacuated and fixes it as lanthanum hydroxide, it is effective in preventing the phenomenon that La reacts with moisture to become hydroxide and powder. It is.

Example 4
A metal alloy target composed of La and Er is placed in a metal container, and then a sintered La oxide block is placed on the step between the target and BP, and the air in the container has a dew point of -80 ° C or less. This is an example of evacuation after replacement with argon gas.
As shown in FIG. 4, lanthanum oxide absorbs moisture remaining after being evacuated and is fixed as lanthanum hydroxide, which is effective in preventing the phenomenon that La reacts with moisture to form hydroxide and powder. It is.

(Comparative Example 1)
This is a case where the La target is vacuum-sealed with a film. A specific example is shown in FIG. As shown in FIG. 5, the La target reacted with the water slightly remaining in the space formed between the vacuum pack film and the target to become lanthanum hydroxide and powdered.

(Comparative Example 2)
This is a case where the La target is vacuum-sealed with a film and (silica gel) is placed as a desiccant. A specific example is shown in FIG.
As shown in FIG. 6, when silica gel was placed, it was pulverized faster than when no silica gel was present. This is presumably because the moisture adsorbed by the silica gel was desorbed and released into the vacuum pack film, so that the reaction between moisture and La was promoted to lanthanum hydroxide. This indicates that silica gel generally used as a desiccant is not useful for preventing the rare earth metal or rare earth metal oxide powdering phenomenon, and is rather undesirable.

(Comparative Example 3)
In this example, the La ₂ O ₃ target is vacuum-sealed with a film. A specific example is shown in FIG. As shown in FIG. 7, La oxide (La ₂ O ₃ ) absorbs moisture remaining in the slightly remaining space in the vacuum pack and fixes it as lanthanum hydroxide, so that the La ₂ O ₃ target reacts with moisture. It becomes a hydroxide and is pulverized.

As is clear from the above examples and comparative examples, when storing a target made of rare earth metal or an oxide thereof, the same rare earth as the target made of the rare earth metal or an oxide stored in a sealed container or seal is stored. It can be seen that introducing a metal oxide as a desiccant is extremely effective. As a result, it is possible to effectively suppress oxidization and pulverization of the target due to air remaining and intrusion.

Conventionally, if a rare earth metal and rare earth metal oxide sputtering target is left in the air for a long time, it will react with moisture in the air and will be covered with white hydroxide powder. However, the method for storing a target comprising a rare earth metal or its oxide according to the present invention does not cause such a problem.
In the method for storing a target comprising a rare earth metal or oxide thereof according to the present invention, the same rare earth metal oxide as the target comprising a rare earth metal or oxide stored therein is placed in a storage container or a film-like seal. Introduced as a desiccant. This effectively suppresses the state of reacting with moisture in the air and being covered with hydroxide white powder.
This makes it possible to stably supply a target as an electronic material such as a metal gate material and a high dielectric constant material (High-k), which is extremely useful industrially.

Claims

A method for storing a target comprising a rare earth metal or an oxide thereof, wherein the rare earth metal is the same as the target comprising a rare earth metal or an oxide stored in a container or film seal for storing the target. A storage method of a target comprising a rare earth metal or an oxide thereof, wherein the oxide is introduced as a desiccant and the container for storage or the film-like seal is sealed and stored.
A method for storing a target comprising a rare earth metal or an oxide thereof, wherein the target is stored in a container or a film-like seal, and is more hygroscopic than a rare earth metal or an oxide target material stored therein. A method for storing a target comprising a rare earth metal or an oxide thereof, wherein a rare earth metal oxide having a large particle size is introduced as a desiccant and the container or film-like seal for storage is sealed and stored.
3. The rare earth metal or oxide target according to claim 2, wherein a rare earth metal oxide having the highest hygroscopicity is used as a desiccant in the case of a target composed of two or more rare earth metals or oxides thereof. Storage method.
The method for storing a target comprising a rare earth metal or an oxide thereof according to any one of claims 1 to 3, wherein the sealed storage method is vacuum sealing.
The method for storing a target comprising a rare earth metal or an oxide thereof according to any one of claims 1 to 4, wherein the means for sealing and storing is a vacuum seal using a flexible film.
The rare earth metal or oxide thereof according to any one of claims 1 to 5, wherein the sealed storage is performed by sealing with an inert gas having a dew point of -80 ° C or lower. The target storage method.
7. The rare earth metal or oxide thereof according to any one of claims 1 to 6, wherein the rare earth metal oxide used as a desiccant is placed or filled in a space generated when sealed. A target storage method consisting of:
The method for storing a target comprising a rare earth metal or an oxide thereof according to any one of claims 1 to 7, wherein the rare earth metal constituting the target contains La or La.
The method for storing a target comprising a rare earth metal or an oxide thereof according to any one of claims 1 to 8, wherein the rare earth metal oxide used as a desiccant is La oxide.
The moisture permeation amount of the flexible film used for sealed storage or the moisture penetration amount from the outside of the container is 0.1 g / m 2 · 24 h or less, characterized in that it is not more than one. A method for storing a target comprising the rare earth metal or the oxide thereof according to item 2.