JPH03193605A - Production of target material for forming oxide superconducting thin film - Google Patents

Abstract

PURPOSE:To prevent the reduction of an oxide in production and to obtain a target material for forming a high density superconducting thin film excellent in dimensional stability by calcining the powder of the oxides of the elements constituting an oxide superconductor, hot-pressing and then sintering the powder in a carbon die several times os that the sintering temp. is increased in stages. CONSTITUTION:An oxide superconducting thin film based essentially on RE- Ba-Cu-O (RE is Y and rare-earth elements) is formed from a target material by sputtering. In this case, the mixed powder of the oxide, carbonate, nitrate, etc., of the component elements is calcined. The calcination product is placed in a carbon die, hot-pressed and then sintered with the sintering temp. increased from a low temp. to the regular temp. of the desired sintered body in stages to obtain the target material. The regular sintering temp. is preferably controlled to 750-850 deg.C when a YBa2Cu3O7-delta target material is formed, and the initial temp. is preferably adjusted to <=450 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing a target material used when forming an oxide superconducting thin film such as Y-B a -Cu-0 based by a sputtering method.

(Prior Art) A CVD method, a laser beam evaporation method, a reactive evaporation method, a sputtering method, etc. are employed to form an oxide superconducting thin film. Among these methods, the sputtering method is a method in which a target material is irradiated with ions or the like to knock out atoms or molecules constituting the target to form a thin film on a predetermined substrate. When obtaining a thin film made of a composite oxide like the above-mentioned superconductor, for example, a bulk body (sintered body) having the same composition as the thin film to be obtained is used as the target material, or a correction material is used in addition to the above-mentioned target. Generally, a method is used in which targets are set up and the atomic or molecular weight generated from these targets is adjusted.

Conventionally, methods for manufacturing this type of target material include calcining powder of oxides or oxide-forming compounds (carbonates, nitrates, etc.) of oxide superconductor constituent elements, followed by hot press firing or ordinary firing (molding). A method is generally adopted in which a binder is added, mixed, and then fired).

(Problem to be Solved by the Invention) By the way, the characteristics required of the above-mentioned target material are that it itself has a high density (relative density to the theoretical density is about 60% or more) so that the film formation rate can be increased. This is desirable, and it is also required that products of the same size can be produced. However, the above manufacturing method included the following problems. That is, in the case of the hot press firing method, when hot pressing using a carbon mold is performed at high temperature to obtain a dense body, oxides are reduced at the contact surface between the sample and the carbon mold, and the carbon mold is heated. It may get stuck. If the firing temperature is lowered to avoid this sticking, the density will decrease and the strength during bonding with the target support will be insufficient. Further, when a mold made of alumina or silicon carbide ceramic other than carbon is used, foreign elements diffuse from the mold into the sintered body, and when this is used as a target, it has an adverse effect on the thin film obtained.

On the other hand, in the case of the normal firing method, the binder added during molding decomposes during firing, and the generation of decomposed gas causes cracks, warping, etc., making it difficult to obtain the desired shape. Also,
Since the dimensional shrinkage during firing is large and the degree of shrinkage varies depending on the composition and density of the molded body, it is necessary to machine the shaped body after firing to adjust it to the desired dimensions. At this time, a new problem of crack breakage due to machining occurs.

(Objective of the Invention) The present invention has been made in view of the above, and is a high-density product that does not reduce oxides due to carbon mold during manufacturing and does not cause cracking or warping during bonding with a target support. Moreover, it is an object of the present invention to provide a method for manufacturing a target material for forming an oxide superconducting thin film that has excellent dimensional stability.

(Means for Solving the Problems) The present invention, which achieves the above-mentioned object, is a method of using oxide powders or oxide-forming compound (carbonate, nitrate, etc.) powders of elements (excluding oxygen) constituting an oxide superconductor. After calcining the seed or mixed powder consisting of multiple seeds.

The present invention provides a method for producing a target material for forming an oxide superconducting thin film, which is characterized by carrying out hot press firing several times using a carbon mold in which the firing temperature is set to increase stepwise.

The target material obtained by the method of the present invention is mainly RE-B
The target is those used when forming a-Cu-0 series (RELY and rare earth element) oxide superconducting thin films by sputtering. Therefore, in this case, the elements constituting the oxide superconductor are rare earth Commonly refers to elements (including yttrium), alkaline earth elements (barium), and copper elements.

Firing by hot press is carried out in several stages as described above, but the firing temperature starts from a low temperature and is set higher with each stage, until the final stage reaches the regular firing temperature of the target sintered body. It is said that The regular firing temperature here varies depending on the composition of the target to be created, but for example, YB a 2
75 when creating a Cu 307-a target
The temperature is preferably 0 to 850°C, and the initial temperature is 450°C.
Desirably below ℃.

Further, after each firing stage is completed, the product is once cooled to room temperature and held in the atmosphere, and then the firing stage is started.

(Function) In the above manufacturing method, since the temperature is low in the initial stage of firing, the raw material oxide is not reduced by carbon-type carbon even in a reducing atmosphere. In addition, since it is densified to some extent at this stage, even if the temperature is increased stepwise in the subsequent firing stage, the holding time at high temperature can be shortened, making it less susceptible to the reducing action of the carbon mentioned above, and after passing through the final firing stage. An extremely dense sintered body can be obtained without sticking to the carbon mold. Moreover, since the sintering is done in the mold, if the mold dimensions match the predetermined target dimensions, there is no need for machining after sintering, and since no binder is used, there is no need for cracking or warping. Nor. Furthermore, since a carbon type is used, diffusion of foreign elements into the sintered body does not occur.

(Example) Next, the present invention will be explained in further detail with reference to Examples.

(Example-1) (i) Y, O,: BaC:O,: Cu0=0.5
: A mixed powder of 2:3 (mole ratio) was calcined in the air at 900°C for 5 hours and crushed, then calcined again under the same conditions and crushed by a jet mill to obtain a calcined powder with an average particle size of 3 μm. .

(...) 240g of the above calcined powder was put into a carbon mold (diameter 1o)
III+) and applied a pressure of 50 kg/a#.

The temperature was raised by induction heating at a temperature increase rate of 20°C/min and held at 400°C for 15 minutes. It was then cooled to room temperature. Hot pressing was performed again at the same pressure and temperature increase rate as above and held at 600° C. for 15 minutes. This was cooled to room temperature, and then hot pressed at the same pressure and temperature increase rate to 800
It was held at ℃ for 15 minutes.

After the three-step hot press firing, the sintered body was cooled to room temperature and taken out.

(City) The diameter of the obtained sintered body was 101 m, the thickness was 6°, and the relative density was 73% of the theoretical density.

Furthermore, no adhesion or cracks with the carbon mold were observed. According to Xls diffraction, a peak indicating the formation of some BaCO3 was observed on the surface;
In the inner layer shaved 2m++, only clear peaks of YBa and Cu30y were observed.

<Comparative Example 1-1> (i) The calcined powder of Example-1(i) was filled into the same carbon mold as above, hot pressed at the same pressure and temperature increase rate as in Example 1, and heated to 800°C. Hold for 15 minutes.

(ii) The obtained sintered body had partial adhesion to the carbon mold, and the relative density to the theoretical density was 52%.

Comparative Example 1-2> (i) The hot press conditions in Comparative Example 1-1 were changed to 900
Hopless firing was performed by holding at ℃ for 15 minutes.

(ii) The obtained sintered body was strongly adhered to the carbon mold, and the interface had a coppery color. When the surface was scraped and the interior was analyzed by X-ray diffraction, it was found that BaCO3, Cu, O
lY 2 B a Cu Os, Y B a2Cu.

0y etc. were detected, which suggested that a reductive decomposition reaction had occurred.

Comparative Example 1-3> (i) The hot press conditions in Comparative Example 1-1 were changed to 800
Hopless firing was performed by holding at ℃ for 30 minutes.

(ii) The obtained sintered body was strongly adhered to the carbon mold, and the internal relative density was 65%.

(Example-2) (i) A mixed powder of BaCO,:Cu○=1:1 (molar ratio) was calcined and crushed in the air at 900°C for 5 hours, and this calcined and crushed process was repeated three times to produce BaCuO, A synthetic powder was obtained.

(■) Fill 230g of this synthetic powder into the same carbon mold as above, hold at 400℃ for 15 minutes, and hold at 660℃ for 1
Two-step hot press firing was performed for 5 minutes to obtain a sintered body with a diameter of 101 m and a thickness of 6.5 I. In both cases, the pressure is 50 kg/cd, and the temperature increase rate is 20°C/mi.
It was set as n.

(iii) The relative density of the obtained sintered body to the theoretical density was 70%. Also, according to X-ray diffraction.

Although some generation of B a COz was observed on the surface, the inside was entirely B a Cu O□.

Comparative Example 2-1> (i) The synthetic powder of Example 2(i) was filled into a carbon mold and hot press fired at 660°C for 15 minutes.

(n) The relative density of the obtained sintered body to the theoretical density is 4
It was 9%, extremely brittle, and cracks occurred during bonding. Moreover, according to X-ray diffraction, it was observed that BaC0 was also generated inside.

(Example-3) (i) The raw material mixed powder in Example-2(i) was
C0,:Cu0=2:3 (molar ratio), Example-2
The powder was calcined under the same conditions as above to obtain a synthetic powder whose crystal phase was a mixed phase of BaCuO□ and CuO.

(ii) This synthetic powder was hot press fired in the same manner as in Example 2 (it) to obtain a sintered body.

(■) The obtained sintered body does not stick to the carbon mold,
The relative density to the theoretical density was 75%, which was extremely dense.

(Example-4) (i) The raw material mixed powder in Example-2(i) was
Co3:Cu◯=2:1 (molar ratio) and calcined under the same conditions as in Example 2 to obtain a calcined powder with a single crystal phase of Ca and CuO3.

(ii) Calcined powder at 400℃, 600℃ and 700℃
A sintered body was obtained by three-step hot press firing at 15°C (holding time: 15 minutes).

(iii) The obtained sintered body did not adhere to the carbon mold and had a relative density of 63% with respect to the theoretical density.

Examples 1 to 4, Comparative Examples 1-1 to 3 and Comparative Example 2-
The results of 1 are summarized in Table 1.

(Left below) The target material obtained in Example-1 was Y-Ba
It is used as the main target when creating a -Cu-Q based superconducting thin film by sputtering. Further, the targets according to Examples 2 to 4 are, for example, Y-Ba
The -Cu-0 system target is also placed and used as a correction target for controlling the produced thin film to have a predetermined composition.

(Effects of the Invention) As described above, in the method for manufacturing a target material of the present invention, the hot press firing process using a carbon mold is divided into several stages, and the firing temperature is set to be higher in each stage. Therefore, the target material is densified to some extent in the initial stage of firing, and even when the temperature is raised thereafter, it is not affected by the reducing effect of carbon in the carbon type, and an extremely dense sintering target material that does not stick to the carbon type can be obtained. . Moreover, since sintering is performed in a mold, the sintered body can be formed into a predetermined shape as it is, eliminating the need for mechanical processing. Furthermore, since no binder is used, no cracking or warping occurs, and since a carbon mold is used, there is no concern that foreign elements will diffuse into the sintered body.

As described above, the target material obtained according to the present invention exhibits extremely excellent suitability when forming an oxide superconducting thin film by sputtering.

Its useful value is enormous.

one or more one

Claims (3)

[Claims] 1. After calcining a mixed powder consisting of one or more types of oxide powder or oxide-forming compound powder of the elements constituting the oxide superconductor, the number of carbon molds set so that the firing temperature is increased stepwise. A method for producing a target material for forming an oxide superconducting thin film, the method comprising performing hot press firing twice. 2. 2. The manufacturing method according to claim 1, wherein the elements constituting the oxide superconductor are rare earth elements, alkaline earth elements, and copper elements. 3. 3. The manufacturing method according to claim 2, wherein the rare earth element is yttrium.