JP2948943B2 - Mold for oxide superconductor target - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a case where a target used for forming an oxide superconducting thin film containing copper such as Y--Ba--Cu--O by sputtering is formed by hot press firing. Regarding the type used.

[0002]

2. Description of the Related Art An oxide superconducting thin film is formed by a CVD method,
Laser beam evaporation, reactive evaporation, sputtering and the like are employed. Among them, the sputtering method is capable of increasing the area and the like, so that a method for forming the sputtering method is being established. In this sputtering method, ions or the like are irradiated to a target material to strike out atoms or molecules constituting the target material to form a thin film on a predetermined substrate.

On the other hand, as an oxide superconducting material, YB
a-Cu-O, Bi-Sr-Ca-Cu-O, Tl-C
Composite oxides such as a-Ba-Cu-O are known,
When obtaining a thin film composed of a plurality of oxides such as such an oxide superconductor, for example, a sintered body having the same composition as the thin film to be obtained is used as a target material, In general, a method is used in which a correction target is provided, or a plurality of targets are used to form while adjusting the amount of atoms or molecules generated from these targets.

Conventionally, this type of target material is manufactured by calcining and pulverizing a powder of an oxide-forming compound such as an oxide of a constituent element of an oxide superconductor or an oxide such as a carbonate or a nitrate, followed by hot press firing or the like. Usually, a method of firing is adopted.

[0005]

The characteristics required of such a target include a high density itself (relative density of about 60% or more with respect to the theoretical density) in order to increase the film formation rate, and a size. Since it is required that the same shape can be produced, hot press sintering is particularly adopted.

However, when baking at a high temperature in a hot press using a general carbon mold, if copper or a copper oxide is present in the sample, cracks are generated in the sample reduced by the presence of carbon, It may cause the sample to stick to the carbon mold. In addition, there is a fatal problem that barium in the sample changes to barium carbonate due to the reaction with the carbon dioxide generated at this time.
There was a problem that high-temperature sintering became impossible, and a high-density target material could not be obtained.

[0007]

Means for Solving the Problems The present inventors have studied methods for preventing the above-mentioned phenomenon from sticking to a hot press mold, and as a result, have found that silicon nitride or silicon nitride can be used instead of the carbon mold. By using a mold composed of a sintered body containing silicon carbide as a main component, it is possible to sinter in the air, effectively prevent sticking, and even when barium is contained in the sample, barium carbonate by carbon dioxide is used. It has been found that a high-density target material can be obtained by suppressing the occurrence of sintering and enabling high-temperature sintering.

The target for forming an oxide superconducting thin film formed according to the present invention is, specifically, REBa _x Cu _Y O _z
It consists (2 ≦ x ≦ 4,3 ≦ y ≦ 10) and BaCuO ₂ calcinated etc., mainly RE-Ba-Cu-O system (RE: rare earth element) is useful in the formation of the oxide superconducting thin film. In that case, the oxide superconductor forming element in the present invention refers to a rare earth element, an alkaline earth element, and a copper element.

The production method of the present invention will be described in detail. First, as a mixed powder for forming a target, an oxide powder of the element for forming an oxide superconducting thin film or a powder of a carbonate or a nitrate which forms an oxide by firing is obtained. It is mixed so as to have the same composition as the thin film to be formed, or copper oxide or a combination of copper and one or more oxides of other thin film constituent elements as an auxiliary target material when forming the thin film. And mix appropriately at a predetermined ratio.

Next, the mixed powder is directly hot-pressed, or hot-pressed once after molding by a known method such as press molding. Further, it is desirable that the mixed powder is calcined and pulverized before being subjected to sintering or before forming to produce a powder having the same composition as the composite oxide sintered body to be obtained.

Next, the hot press firing in the present invention will be described with reference to FIG. In the figure, 1 is a die, 2 is a press punch, 3 is a sample, and the die 1 and the press punch 2 are so-called molds. According to the present invention, it is important that the die 1 and the press punch 2 are made of a known sintered body containing silicon carbide or silicon nitride as a main component.

[0012] For example, Kibushi clay or the like
~ 8% by weight and molded to 1300-
A silicon carbide sintered body fired in a non-oxidizing atmosphere at 1500 ° C., or a product obtained by adding C, B, Al ₂ O _3, etc. to silicon carbide, is fired in an inert atmosphere at 1300 to 1500 ° C. Silicon carbide-based sintered body or a silicon nitride-silicon carbide-based composite obtained by adding silicon nitride to silicon carbide at a ratio of 22 to 25% by weight and firing in a nitrogen atmosphere at 1900 to 2100 ° C A sintered body is used.

An oxide of Group 3a of the periodic table, such as Y ₂ O ₃ , is added to silicon nitride at a ratio of 1 to 10% by weight, and the molded product is placed in a nitrogen atmosphere at 1600 to 2000 ° C. A fired silicon nitride sintered body is used.

[0014]

Further, in the present invention, it is preferable to perform firing by interposing a release material 4 made of a known powder such as boron nitride between the die 1 and the sample 3 and between the punch 2 and the sample 3 during firing. . Specifically, prior to firing, the above powder may be formed into a slurry and applied to the surface of each mold with a brush, a roller, or the like to a thickness of about 0.1 to 1 mm.

As a target, for example, Y-Ba-Cu-
When preparing an O composition or a Ba-Cu-O composition, the mold release material powder is used at 300 to 1000 ° C.
Hot press firing in the air at the temperature described above.

[0017]

According to the above method, the reduction of copper oxide due to the presence of carbon does not occur, there is almost no reaction between the sample and the mold material, and it can be fired in the air. Almost no production of barium carbonate is observed, and a high-density target can be produced. Even when the release material adheres to the surface of a part of the sintered body, it can be easily removed by light polishing.

[0018]

【Example】

Example 1 A CuO powder and a BaCO ₃ powder were weighed and mixed at a molar ratio of 1: 1 and then calcined in the air at 900 ° C. for 5 hours, pulverized, calcined again under the same conditions, and then BaCuO _2. A powder was obtained.

On the other hand, a BN slurry was slightly applied to a sample contact surface of a SiC type sample having a diameter of 105 mm with a thickness of 0.2 mm and dried. The SiC type material was prepared by mixing raw materials of 78% by weight of SiC and 22% by weight of Si ₃ N ₄ ,
It consists of a sintered body obtained by firing at 00 ° C. in a nitrogen atmosphere.

Next, the BaCuO prepared by the above method is used.
₂ of the calcined powder was filled in a SiC type described above, the pressure 110k
g / cm ² and the temperature was increased at a rate of 5 ° C./min.
After hot press calcination in air at 50 ° C. for 20 minutes, it was cooled to room temperature and a sintered body was taken out from the SiC mold. As a result, there was no adhesion between the SiC type and the sintered body and no cracks in the sintered body, and a BaCuO ₂ sintered body having a theoretical density ratio of 67% was obtained. In addition, BN as a release material adhered to the surface of the sintered body, but could be easily removed by lightly polishing the surface. When X-ray diffraction of the polishing powder was performed to examine the crystal structure of the produced sintered body, no peaks of other substances were observed.

Comparative Example 1 In Example 1, a carbon mold was used in place of the SiC mold, the pressure was raised while applying a pressure of 50 kg / cm ² , and firing was performed under the same conditions in an atmosphere of carbon dioxide. Was.

As a result, only a BaCuO ₂ sintered body having a density as low as 50% of the theoretical density was obtained, and sticking between the sample and the mold was recognized. X-ray diffraction of this sintered body showed peaks of barium carbonate as a decomposition product.

Example 2 Y ₂ O ₃ powder, BaCO ₃ powder and CuO powder were 0.5:
Weigh and mix so as to have a molar ratio of 2: 3.
In crushed after 10 hours calcined, repeated three times this YBa ₂
A Cu ₃ O _7- δ powder was obtained.

On the other hand, a SiC mold having a diameter of 105 mm prepared in the same manner as in Example 1 was prepared, and a BN slurry was slightly applied to the sample contact surface with a thickness of 0.2 mm and dried. The YBa ₂ Cu ₃ O _7- δ powder prepared above was mixed with the above S
After filling into an iC mold, the temperature was raised at a rate of 5 ° C./min, a pressure of 110 kg / cm ² was applied, and hot press firing was performed at 900 ° C. for 1 hour in air, then cooled to room temperature and sintered from a SiC mold. I took my body out. As a result, there was no adhesion between the SiC type and the sintered body and no cracks in the sintered body, and the theoretical density ratio was 80%.
YBa ₂ Cu ₃ O _7- δ sintered body was obtained.

Although BN powder as a release material adhered to the surface of the sintered body, it could be easily removed by lightly polishing the surface.

Comparative Example 2 In Example 2, a carbon mold was used and the pressure was 50 kg /
The temperature was raised and pressurized over cm ² , and the firing was performed in exactly the same manner thereafter. As a result, a sintered body having a theoretical density of 70% was obtained. However, when left in the air, cracks occurred.

Example 3 Y ₂ O ₃ powder, BaCO ₃ powder and CuO powder were 0.5:
Weigh and mix so as to have a molar ratio of 2.5: 6.
After calcination at 00 ° C. for 10 hours, pulverization is performed, and this is repeated three times.
Ba ₂ Cu ₃ O _7- δ1mol + BaCuO ₂ 0.5mo
A calcined powder of l + CuO 2.5 mol was obtained.

On the other hand, a BN slurry was slightly applied to a sample contact surface of a SiC type sample having a diameter of 105 mm and having a thickness of 0.2 mm and dried by a method similar to that of Example 1 and dried. The calcined powder of Y: Ba: Cu = 1: 2.5: 6 prepared above was filled in the SiC mold, heated at a rate of 5 ° C./min, and then subjected to a pressure of 40 kg / cm ² . It was baked by hot press at 900 ° C. for 10 hours, then cooled to room temperature, and a sintered body was taken out from the SiC mold. As a result, there was no adhesion between the SiC type and the sintered body and no cracks in the sintered body, and a sintered body having a theoretical density ratio of 83% was obtained. The BN powder of the release material adhered to the surface of the sintered body, but could be easily removed by lightly polishing the surface.

Comparative Example 3 In Example 3, a carbon mold was used and the pressure was 50 kg /
cm ² , and the temperature was increased and the pressure was increased. As a result, the sintered body was fixed to the carbon mold.

[0030]

[0031]

[0032]

Example 4 CuO powder and BaCO ₃ powder were weighed and mixed at a molar ratio of 1: 1 and then calcined at 900 ° C. for 5 hours in the air and pulverized. It was baked to obtain BaCuO ₂ powder.

On the other hand, a BN slurry was lightly applied to a sample contact surface of a Si ₃ N ₄ type having a diameter of 105 mm with a thickness of 0.2 mm and dried. The Si ₃ N ₄ type material was obtained by adding 5% by weight of Y ₂ O ₃ powder to silicon nitride, molding and firing at 1700 ° C. in a nitrogen atmosphere.

Next, the BaCuO prepared by the above method is used.
The calcined powder of No. ₂ was filled in the above-mentioned Si ₃ N ₄ type, and a pressure of 11
After applying 0 kg / cm ² , the temperature was raised at a rate of 5 ° C./min, baked in air at 650 ° C. for 20 minutes, cooled to room temperature, and a sintered body was taken out from the Si ₃ N ₄ type. As a result, there was no adhesion between the Si ₃ N ₄ type and the sintered body and no cracks in the sintered body, and a BaCuO ₂ sintered body having a theoretical density ratio of 65% was obtained. The surface of the sintered body has a release material BN
Was adhered, but could be easily removed by slightly polishing the surface. When X-ray diffraction of the polishing powder was performed to examine the crystal structure of the produced sintered body, no peaks of other substances were observed.

[0036]

As described in detail above, according to the present invention, when a target containing copper is produced by a hot press method as a target used for forming an oxide superconducting thin film, a hot press mold is used. By using a silicon carbide-based sintered body or a silicon nitride-based sintered body, cracks are not generated in the sample, the reaction between the sample and the mold is prevented, and the sample and the mold are not fixed. Further, when barium is contained in the sample, the production of barium carbonate is suppressed, and high-temperature sintering in air is possible, so that a high-density target can be manufactured. Accordingly, when the oxide superconducting thin film is formed by a sputtering method, a high-purity film can be formed while improving the film formation rate.

[Brief description of the drawings]

FIG. 1 is a schematic layout diagram for explaining hot press firing in a manufacturing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Die 2 Press punch 3 Sample 4 Release material

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C23C 14/00-14/58 C01G 1/00 C01G 3/00 ZAA

Claims (1)

(57) [Claims] 1. A mold for hot-press firing a sample comprising an oxide powder or an oxide-forming compound powder containing at least a copper element among metal elements constituting an oxide superconductor, the mold comprising silicon carbide Alternatively, a mold for an oxide superconductor target, comprising a sintered body containing silicon nitride as a main component.