JPH0558640A - Production of oxide superconducting thin film - Google Patents

Abstract

PURPOSE:To obtain a Bi-Sr-Ca-Cu-O oxide superconducting thin film excellent in superconductive characteristics with excellent mass productivity and good reproducibility by the presence of an interlayer between the thin film and a substrate, and producing the oxide superconducting thin film according to a specific chemical vapor deposition method. CONSTITUTION:A beta-diketone metallic complex containing a Bi-containing organometallic compound and at least Sr, Ca and Cu is used as an evaporation source raw material and the objective Bi-Sr-Ca-Cu-0 oxide superconducting thin film is produced on a substrate by a chemical vapor deposition method. In the process, an interlayer is present between the substrate and the oxide superconducting thin film. The interlayer preferably has excellent lattice conformity with the superconducting thin film and a thermal expansion coefficient close to that of the superconducting thin film. If a thin film will not cause diffusion into the superconducting thin film or reaction with the thin film, it is more preferred as the interlayer. Furthermore, since the interlayer contains the same elements as those in the superconducting thin film, it is considered that the diffusion into the superconducting thin film or reaction with the thin film will not affect the deterioration in superconductive characteristics by using the above-mentioned oxides as the interlayer even if the diffusion or reaction occurs to some extent.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a chemical vapor deposition method (hereinafter,
Bi-Sr-Ca formed by CVD method)
And a method for manufacturing a Cu-O oxide superconducting thin film.

[0002]

2. Description of the Related Art A Bi-Sr-Ca-Cu-O-based oxide superconductor has a superconducting transition temperature (Tc) of about 10K.
24Å phase (Bi ₂ Sr ₂ CuO _x ) showing 30 ° C. (Bi ₂ Sr ₂ CaCu ₂ O _x ) showing a Tc of about 80 K and 37Å phase showing a Tc of about 110 K (Bi ₂ Sr ₂ C)
The existence of three kinds of superconducting phases of a ₂ Cu ₃ O _x ) has been clarified.

In order to apply this Bi-Sr-Ca-Cu-O-based oxide superconductor to a sensor, an element, a device, a wire or the like which operates at a liquid nitrogen temperature, a higher T
Development of a superconducting phase having c is desired. Bi-based superconductors, especially 37Å phase showing Tc of 110 K, are Y-Ba-
Tc is about 20 K higher than that of Cu-O system, and it is economically inexpensive because it does not contain expensive rare earth elements. Therefore, its synthesis is being actively studied.

However, while the 24Å phase and the 30Å phase are relatively easy to synthesize, the 37Å phase is difficult to synthesize and the Tc is high.
It is difficult to synthesize a superconductor having a temperature of 110K. In the sintering method, stable addition of Pb to 37Å
Phase synthesis is being considered.

Also, in a Bi-Sr-Ca-Cu-O-based oxide superconducting thin film using a physical deposition method (hereinafter abbreviated as PVD method) or a thin film forming technique typified by a CVD method. , 24Å phase and 30Å phase are easily synthesized, whereas 37Å phase is very difficult to synthesize. Therefore, let alone thin films with Tc exceeding 100K,
There are few reports of thin film synthesis that stably show Tc at a temperature of liquid nitrogen or higher. Also for thin films, P by CVD method
Although the effect of b addition has been studied, no improvement in superconducting properties is observed.

To generate the 37Å phase, the synthesized Bi-Sr is used.
A method of heat-treating a -Ca-Cu-O thin film in a Pb atmosphere has been attempted. A Bi-Sr-Ca-Cu-O-based oxide superconducting thin film and Pb or PbO powder were introduced into a crucible, and heat treatment in Pb vapor was achieved at 600 ° C to 900 ° C, and Tc (R = O) = 102K. Japanese Unexamined Patent Publication No. 2-170311 has been filed. Pb
In the case of a Bi-based superconducting thin film without addition of Tc = 97K, there is a report that Tc = 97K was obtained by performing long-time synthesis of 80 hours at a growth rate of 12Å / hr by using the CVD method.

Further, in manufacturing a thin film, a substrate (substrate) on which a superconducting thin film is deposited is required, but mutual diffusion between the substrate and the thin film, lattice mismatch, or generation of cracks due to difference in thermal expansion coefficient, etc. It seems that superconducting properties are deteriorated by this. In thin film synthesis, it is difficult to obtain a thin film with excellent superconducting properties unless these points are taken into consideration.

[0008]

In order to obtain a Bi-Sr-Ca-Cu-O oxide superconducting thin film having excellent superconducting properties, Pb is added by heat treatment or the growth rate is made very slow. It was said that the method of performing the synthesis for a long time was good. However, there are many disadvantages from the viewpoint of industrial mass productivity.

The present invention has been made by paying attention to the problems of these prior arts. It has no post-treatment such as heat treatment, synthesizes a thin film without reducing the film formation rate, and has a lattice mismatch with the substrate or By relaxing the difference in thermal expansion coefficient,
Bi-S with excellent mass productivity, good reproducibility, and excellent superconductivity
It is an object of the present invention to provide a method for producing an r-Ca-Cu-O oxide superconducting thin film.

[0010]

In order to solve the above-mentioned problems, the present invention provides phenyl bismuth, Sr, Ca, Cu.
In the production of a Bi-Sr-Ca-Cu-O oxide superconducting thin film by the CVD method using the β-diketone metal complex as described above as an evaporation source material, an intermediate layer is present between the substrate (substrate) and the superconducting thin film. Adopt the method of making.

On the surface of the substrate, the substrate and Bi-Sr-C are
A thin film (intermediate layer) which is less likely to diffuse and react with the a-Cu-O oxide superconducting thin film is formed, and a Bi-Sr-Ca-Cu-O oxide superconducting thin film is formed on the thin film. It is a composition.

The intermediate layer preferably has good lattice matching with the superconducting thin film and has a close thermal expansion coefficient, and more preferably a thin film that does not cause diffusion or reaction to the superconducting thin film. Furthermore, as an intermediate layer, at least Bi, S
By using an oxide containing one or more elements of r, Ca or Cu, even if some diffusion or reaction occurs in the superconducting thin film, it is the same element as the superconducting thin film, so It is considered that it does not affect the deterioration of characteristics.

Furthermore, at least B is used as the intermediate layer.
i ₂ Sr ₂ CuO _x phase or Bi ₂ Sr ₂ CaCu
_{It is considered} that the use of the ₂ O _X phase achieves good lattice matching and relaxation of the thermal expansion coefficient, and that deterioration of superconducting properties due to diffusion into the superconducting thin film or reaction is not considered.

In the manufacturing method, first, a thin film to be an intermediate layer is formed on a substrate by using a thin film forming technique such as a PVD method or a CVD method. The substrate having the intermediate layer is placed in a reaction furnace, and the substrate is further heated. The heating of the substrate is performed by placing a heater in the reaction furnace to heat the substrate, or by heating the substrate from outside the reaction furnace. Further, a method such as high frequency heating or a method such as microwave plasma or RF plasma may be used.

The heating temperature of the substrate is higher than the temperature at which the organic metal containing Bi and the β-diketone metal complex containing Sr, Ca, Cu are sufficiently decomposed and polymerized, and the diffusion of the substrate with the intermediate layer and the superconducting thin film is prevented. When a reaction is considered, it is preferably at least below the temperature at which diffusion or reaction occurs. An inert gas containing oxygen gas or a gas containing oxygen and a vapor containing each element is introduced onto the substrate heated by any method.

The composition ratio of the thin film can be adjusted by the heating temperature of the evaporation source raw material, the flow rate of the inert gas, or a combination of both. The pressure in the reaction furnace is a reduced pressure, and the pressure is related to the flow rates of the carrier gas and the oxidizing gas and the temperature gradient in the reaction furnace, but the vapor containing at least the introduced elements decomposes and polymerizes on the substrate. Any pressure may be used as long as it can maintain a sufficient flow rate.

By the above manufacturing method, mutual diffusion between the substrate and the thin film can be suppressed, and since it is an intermediate layer containing the same element as the thin film, the lattice mismatch between the substrate and the thin film or the thermal expansion coefficient. It seems that there is a function to alleviate the difference between.

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a diagram showing an example of a hot wall type thermal CVD apparatus applicable in the manufacturing method of the present invention. Triphenyl bismuth and Sr, Ca, and Cu of the β-diketone metal complex were used as the evaporation source material, and they were inserted into each boat of 1 to 4.

Each raw material is heated and evaporated by the heater 5 in the temperature range of 82 ° C. to 230 ° C.
The r gas 6 was introduced into the reaction furnace 7 at a flow rate of 50 ml / min. The oxygen gas 8 was introduced into the reaction furnace 7 at a flow rate of 720 ml / min separately from the carrier gas. The pressure inside the reaction furnace 7 is reduced by a vacuum pump 10 to a pressure of 10
It was set to 0 Torr. Further, Ar gas 9 was introduced into the reaction furnace 7 through a route different from the carrier gas for adjusting the oxygen concentration. When the flow rate of Ar gas 9 is 280 ml / min, the oxygen partial pressure is 60 Torr.

The substrate 11 has a mirror-finished MgO (10
0) A single crystal substrate was used. The film formation was performed at a deposition temperature of 800 ° C. by the heater 12, but the temperature was measured by the thermocouple 13 installed directly under the substrate. The deposition time was 2 hours. After the completion of precipitation, the gas flow rate at the time of synthesis was maintained at 760 Torr and the temperature was rapidly cooled to room temperature.

With respect to the film thus obtained, the film was identified by X-ray and the chemical composition was analyzed by fluorescent X-ray. The X-ray diffraction pattern of the obtained film is shown in FIG.

A substrate having at least a Bi ₂ Sr ₂ CaCu ₂ O _x phase deposited on the surface after completion of film identification and chemical composition analysis was again set at 11 in FIG. 1 and at least Bi ₂ Sr ₂ Ca ₂ heating each evaporation source material at material heating temperature thin film containing 37Å phase of Cu ₃ O _X is synthesized, at precipitation temperature 800 ° C., it was thin synthesized in the same manner as described above. The deposition time was 3 hours. After the deposition is completed, the temperature is raised from the deposition temperature to about 100 ° C. at 20 ° C. under 760 Torr of oxygen.
In-situ oxygen treatment of cooling at 1 / min was performed.

The X-ray diffraction pattern of the obtained film is shown in FIG. The c-axis oriented 30Å phase was remarkably observed, and a film in which a very small amount of c-axis oriented 37Å phase was mixed was formed. FIG. 4 shows the temperature dependence of the resistance of this film. The resistance decreased as the temperature decreased, and showed higher Tc above the liquid nitrogen temperature as compared with the thin film having no intermediate layer.

[0024]

EFFECT OF THE INVENTION Bi synthesized by the above manufacturing method
In the -Sr-Ca-Cu-O superconducting thin film, a film excellent in crystallinity, orientation and superconducting properties can be obtained by interposing an intermediate layer between the substrate and the superconducting thin film, and high heat treatment and the like can be obtained. T
No post-process for conversion to c is required, and the deposition rate is high, which is a simple manufacturing process.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an apparatus that can be used in the manufacturing method of the present invention.

FIG. 2 is an X-ray diffraction pattern of a film as an intermediate layer according to an example of the present invention.

FIG. 3 is an X-ray diffraction pattern of a film according to an example of the present invention.

FIG. 4 is a diagram of temperature dependence of resistance of a film according to an example of the present invention. a: Thin film having no intermediate layer b: Thin film having an intermediate layer

[Explanation of symbols]

 1-4 evaporation source raw material 5 raw material heating heater 6 carrier gas 7 reaction furnace 8 oxygen gas 9 Ar gas 10 vacuum pump 11 substrate 12 substrate heating heater 13 thermocouple

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Politics Hasei, 810 Kumagaya, Kumagaya, Saitama Prefecture, inside the Kumagaya Plant, Inc. (72) Hideyuki Kurosawa, 810, Kumagaya, Kumagaya, Saitama Prefecture, inside Kumagaya, Ltd. (72) Inventor Toshio Hirai, 3-4 Takamori, Izumi-ku, Sendai-shi, Miyagi 91 (72) Hisanori Yamane 21-3 Ninomori 21-3, Miyagino-ku, Sendai-shi, Miyagi Twin Hills A401

Claims (4)

[Claims] 1. An organic metal containing Bi and at least S
By a chemical vapor deposition method using a β-diketone metal complex containing r, Ca, Cu as an evaporation source material, Bi-Sr-
A method for producing an oxide superconducting thin film of Ca-Cu-O, characterized in that an intermediate layer is present between the substrate and the oxide superconducting thin film. 2. At least Bi, Sr, C as an intermediate layer
The method for producing a thin film according to claim 1, further comprising an oxide containing one or more elements of a or Cu. 3. At least Bi ₂ Sr ₂ C as an intermediate layer
The method for producing a thin film according to claim 1, having a uO _x phase. 4. At least Bi ₂ Sr ₂ C as an intermediate layer
The method for producing a thin film according to claim 1, having a phase of aCu ₂ O _x .