JP2791407B2 - Method for producing target material for forming oxide superconducting thin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a target material used for forming a Y-Ba-Cu-O-based oxide superconducting thin film by a sputtering method.

(Prior Art) For forming an oxide superconducting thin film, a CVD method, a laser beam evaporation method, a reactive evaporation method, a sputtering method or the like is employed. Of these, the sputtering method irradiates a target material with ions or the like to strike out atoms or molecules constituting the target and 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 a target material, or correction is performed in addition to the above-mentioned target. In general, a method is used in which a target is provided, and the target is formed while adjusting the atomic or molecular weight generated from the target.

Conventionally, this type of target material is manufactured by calcining a powder of an oxide or an oxide-forming compound (such as a carbonate or a nitrate) of an oxide superconductor constituent element, followed by hot press firing or normal firing (forming). A method of adding and mixing a binder for use and baking) is generally employed.

(Problems to be Solved by the Invention) By the way, as a characteristic required for the above-mentioned target material, the target material itself has a high density (a relative density with respect to a theoretical density is about 60% or more) so as to increase a film forming rate. It is desirable that the same shape can be produced in dimension. However, the above manufacturing method has the following problems. That is, in the case of the hot press firing method, in a hot press using a carbon mold, when hot pressing is performed at a high temperature to obtain a dense body, the oxide is reduced at the contact surface between the sample and the carbon mold, and the carbon mold is heated. May stick. If the firing temperature is lowered in order to avoid this sticking, the density decreases, and the strength at the time of bonding with the target support becomes insufficient. Further, when a mold of alumina or silicon carbide ceramic other than carbon is used, a foreign element diffuses from the mold into the sintered body, and when this is used as a target, the resulting thin film is adversely affected.

On the other hand, in the case of the ordinary firing method, the binder added at the time of molding is decomposed during firing, but cracks, warpage, and the like occur due to generation of the decomposition gas, and it is difficult to obtain a desired shape. In addition, since the dimensional shrinkage during firing is large and the degree of shrinkage varies depending on the composition and the density of the molded body, it is necessary to machine the shape after firing to the desired size. At this time, a problem of crack breakage due to machining is newly generated.

(Objects of the Invention) The present invention has been made in view of the above, and has been described in view of the fact that an oxide is not reduced by a carbon mold at the time of production, and a high density which does not cause cracking or warpage at the time of bonding to a target support. Another object of the present invention is to provide a method for producing a target material for forming an oxide superconducting thin film having excellent dimensional stability.

(Means for Solving the Problems) To achieve the above object, the present invention provides an oxide superconductor comprising an oxide powder or an oxide-forming compound (carbonate, nitrate, etc.) powder of an element (excluding oxygen). A target material for forming an oxide superconducting thin film, wherein after calcination of one or more kinds of mixed powders, several times of hot press sintering with a carbon mold set so that the sintering temperature is gradually increased. Manufacturing method.

The target material obtained by the method of the present invention is mainly RE-Ba
—Cu—O-based (RE; Y and rare earth element) oxide superconducting thin film is intended to be used when formed by a sputtering method. Therefore, in this case, the elements constituting the oxide superconductor are: Rare earth elements (including yttrium), alkaline earth elements (barium) and copper elements are referred to.

The sintering by hot pressing is performed in several stages as described above, and the sintering temperature starts from a low temperature, and is set to a high value after each stage. Is done. The normal firing temperature here varies depending on the target composition to be prepared. For example, YBa ₂ Cu ₃ O _{7- δ}
When forming a target, the temperature is preferably 750 to 850 ° C., and the temperature in the initial stage is preferably 450 ° C. or less. After completion of each firing step, the temperature is once cooled to room temperature and kept in the atmosphere, and then the process proceeds to the next firing step.

(Operation) In the above-mentioned production method, the raw material oxide is not reduced by carbon-type carbon even in a reducing atmosphere because the temperature is low in the initial stage of firing. In addition, since it is densified to some extent at this stage, even if the temperature is increased stepwise in the subsequent sintering step, the holding time at a high temperature can be shortened, so that it is less susceptible to the reducing action by the carbon, and after the final sintering step Can obtain a very dense sintered body without sticking to the carbon mold. Moreover, since it is fired in the mold,
If the dimensions of the mold match the specified target dimensions,
There is no need for machining after sintering, and since no binder is used, there is no occurrence of cracks or warpage. Furthermore,
Since the carbon mold is used, diffusion of foreign elements into the sintered body does not occur.

(Examples) Next, the present invention will be described in more detail with reference to Examples.

Example 1 (i) A mixed powder of Y ₂ O ₃ : BaCO ₃ : CuO = 0.5: 2: 3 (molar ratio) was calcined in the air at 900 ° C. for 5 hours and pulverized, and then again under the same conditions. It was calcined and jet milled to obtain a calcined powder having an average particle size of 3 μm.

(Ii) About 240 g of the above calcined powder is carbon type (101 mm in diameter)
, A pressure of 50 kg / cm ² was applied, the temperature was increased at a rate of 20 ° C./min by induction heating, and the temperature was maintained at 400 ° C. for 15 minutes. Then, it cooled to room temperature. It was hot-pressed again at the same pressure and at the same heating rate as above, and kept at 600 ° C. for 15 minutes. This was cooled to room temperature, and further hot-pressed at the same pressure and at the same temperature raising rate, and kept at 800 ° C. for 15 minutes. After the three-stage hot press firing, the temperature was cooled to room temperature, and the sintered body was taken out.

(Iii) The diameter of the obtained sintered body was 101 mm, the thickness was 6.5 mm, and the relative density to the theoretical density was 73%. Also,
No sticking or cracking with the carbon mold was observed. According to the X-ray diffraction, a peak indicating slight generation of BaCO ₃ was observed on the surface, but in the inner layer obtained by cutting the surface of the sintered body sample by 0.2 mm, only a clear peak of YBa ₂ Cu ₃ Oy was observed. Observed.

<Comparative Example 1-1> (i) The calcined powder of Example-1 (i) was filled in the same carbon mold as described above, and hot-pressed at the same pressure and at the same temperature raising rate as in Example 1; Hold for 15 minutes.

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

<Comparative Example 1-2> (i) The hot pressing condition in Comparative Example 1-1 was 900 ° C.
And hopless baking for 15 minutes.

(Ii) The obtained sintered body was strongly adhered to the carbon mold, and the interface thereof was colored red copper. When the surface was shaved and the inside was analyzed by X-ray diffraction, BaCO ₃ , Cu ₂ O, Y ₂ BaCuO
₅ , YBa ₂ Cu ₃ Oy and the like were detected, which suggested that there was a reductive decomposition reaction.

<Comparative Example 1-3> (i) The hot pressing condition in Comparative Example 1-1 was 800 ° C.
And hopless baking.

(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 ₃ : CuO = 1: 1 (molar ratio) was mixed with 90
The mixture was calcined and pulverized at 0 ° C. for 5 hours, and this calcining and pulverization was repeated three times to obtain a synthetic powder of BaCuO ₂ .

(Ii) Filling about 230 g of this synthetic powder into the same carbon mold as above, and holding at 400 ° C. for 15 minutes and holding at 660 ° C. for 15 minutes
Stage hot press firing, diameter 101mm, thickness 6.5
mm was obtained. In each case, the pressure was 50 kg / cm ² , and the heating rate was 20 ° C./min.

(Iii) The relative density of the obtained sintered body to the theoretical density is 7
It was 0%. According to X-ray diffraction, some B
Although aCO ₃ was produced, the inside was all BaCuO ₂ .

<Comparative Example 2-1> (i) The synthetic powder of Example 2 (i) was filled in a carbon mold and baked at 660 ° C. for 15 minutes.

(Ii) The relative density of the obtained sintered body to the theoretical density is 49
%, Which was extremely brittle and cracked during bonding. According to X-ray diffraction, it was observed that BaCO ₃ was also generated inside.

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

(Ii) The synthetic powder was fired by hot pressing in the same manner as in Example-2 (ii) to obtain a sintered body.

(Iii) The obtained sintered body did not adhere to the carbon mold and had a relative density of 75% with respect to the theoretical density, which was extremely dense.

(Example-4) (i) The raw material mixed powder in Example-2 (i) was
₃ : CuO = 2: 1 (molar ratio), and calcined under the same conditions as in Example 2 to obtain a calcined powder having a single phase of Ca ₂ CuO ₃ .

(Ii) The calcined powder was subjected to three-stage hot press firing at 400 ° C., 600 ° C., and 700 ° C. (the holding time was 15 minutes each) to obtain a sintered body.

(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
Table 1 summarizes the results of -1.

The target material obtained in Example-1 was Y-Ba
-Cu-O based superconducting thin film is used as a main target when it is formed by a sputtering method. Also,
The targets according to Examples-2 to 4 are, for example, Y-Ba-Cu
The -O-based target is arranged and used as a correction target for controlling the generated 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 step using a carbon mold is divided into several steps, and the firing temperature is set to be higher for each step. Thus, the object to be processed is densified to some extent in the initial stage of firing, and a very dense sintered target material which is not subjected to the reducing action of the carbon of the carbon even by the subsequent temperature increase and has no sticking to the carbon is obtained. . In addition, since the sintered body is sintered in the mold, the sintered body can be formed into a predetermined shape as it is, and no mechanical processing is required. Further, since no binder is used, there is no occurrence of cracks or warpage, and since the carbon type is used, there is no concern that foreign elements diffuse into the sintered body.

As described above, the target material obtained by the present invention exerts extremely excellent suitability when forming an oxide superconducting thin film by sputtering, and its useful value is extremely large.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C04B 35/00-35/22 C04B 35/447-35/457 C04B 35/622-35/65 C01G 1/00-57 / 00

Claims (3)

(57) [Claims] After calcination of a powder mixture of one or more oxide powders or oxide-forming compound powders of the elements constituting the oxide superconductor, the calcination temperature is set so as to increase stepwise. A method for producing a target material for forming an oxide superconducting thin film, comprising performing hot press firing several times with a carbon mold. 2. An element constituting the oxide superconductor is a rare earth element, an alkaline earth element, and a copper element.
The manufacturing method as described. 3. The method according to claim 2, wherein said rare earth element is yttrium.