JPH0288426A - Production of superconducting thin film - Google Patents

Abstract

PURPOSE:To obtain a superconducting thin film rich in a phase having higher Tc, hardly contg. impurities and having stable superconducting characteristics by depositing evaporated starting material contg. Bi, Sr, Ca and Cu on a substrate set at a temp. below the m.p. of a superconductor to be formed. CONSTITUTION:Starting material consisting of org. compds. or org. complexes of Bi, Sr, Ca and Cu is heated to a temp. at which vapors of them are obtd. and an inert gas such as Ar as a carrier gas is introduced into a reactor. Gaseous O2 or an O2-contg. gas is also introduced into the reactor separately from the inert gas, the internal pressure of the reactor is preferably regulated to <=50Torr and a thin film is formed on a substrate set at a temp. below the m.p. of the film to be formed on the substrate. A Bi-Sr-Ca-Cu-O superconducting thin film having superior superconducting characteristics because of the absence of a phase having <=10 Tc and impurities can be deposited on a large-sized substrate having a large area and a complex shape.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides B1-5r-Ca-Cu by chemical vapor deposition method.
The present invention relates to a method for manufacturing a superconducting thin film consisting of -0.

(Prior art) As a raw material for superconductors, B1-5r-Ca-Cu-0
The system has attracted attention because it exhibits better superconducting properties than other oxide-based superconductors, does not contain expensive rare earth elements, and is an economical and highly stable superconductor.

In the superconductor consisting of B1-5r-Ca-Cu-0, there is one Cu-0 layer between the B1-01 layers, and Big(SrCa)zcu exhibits a critical temperature (Tc) of 7 to 8 k.
Ox; Old tcsr-Ca with two Cu-0 layers and Tc of 80k) 3CL120X (low Tc phase)
Bi with three ICU-0 layers and Tc of 1)0k
Three types of superconductors have been revealed: gSrzCazCtl:+OX (high Tc phase). In addition, by observation using an electron microscope, some have been found to have four or five Cu-0 layers, but their superconducting properties have not yet been confirmed.

Sensors, elements, etc. that operate this superconductor at liquid nitrogen temperature,
In order to apply it to devices and wire materials, higher Tc and critical current are required.
) It is necessary to form a superconductor with low Tc such as zcuOx or a superconductor without an impurity initial layer.

It is also desirable to form a single-phase high-Tc superconductor. However, in this superconductor, the range of synthesis conditions for the high Tc phase is narrow, and it is difficult to obtain a single high Tc phase by controlling the composition and synthesis conditions.
By increasing the proportion of high Tc phase in the superconductor and further increasing Bit(
A superconductor free of Sr-Ca)zcuOx and impurities must be formed.

For this purpose, in the sintering method, a superconductor that is almost single-phase with a high Tc phase is synthesized by adding PB, but the Tc cannot necessarily be said to be sufficient for practical use. Moreover, this superconductor is made of ceramics, and is not suitable for forming a complex-shaped superconductor.

Further, in the sputtering method or the vacuum evaporation method, a film having a Tc of about 100 is formed, although it is a mixed phase of a low Tc phase and a high Tc phase. However, these methods involve forming a thin film in the plane facing the evaporation source and require high vacuum, making it difficult to form a superconductor film on a substrate with a complex shape, and making the equipment larger. difficult.

Furthermore, chemical vapor deposition method (C
In VD), a film with a Tc of about 100 is also formed, but at low temperatures below 1000°C, the decomposition of halides is incomplete, and the formed film often contains halogen, which affects the properties of the film. decreases. Further, the generated halogen gas may damage the substrate, the formed film, and the CVD furnace. Further, when the halide is in a solid state, the temperature at which it is gasified is high, and therefore, the halide is not preferred as a raw material in semiconductor-related fields where low temperatures are required.

The present invention has been made in order to solve the above-mentioned problems, and in the chemical vapor deposition method using an organometallic compound as an evaporation source material, superconducting properties containing many phases with higher Tc and fewer impurities can be achieved. The present invention provides a method for producing a superconducting thin film that can deposit a stable superconducting thin film onto a large-sized, large-area, long, and complex-shaped object at a faster deposition rate.

(Means for Solving the Problems and Their Effects) In order to solve the above-mentioned problems, the present invention uses a chemical vapor deposition method using an evaporation source material containing at least bismuth, strontium, calcium, and copper. A method is employed to form a superconducting film containing high Tc and few impurities on a substrate at a temperature below the melting point temperature of the film to be formed.

More specifically, the production method of the present invention uses organometallic or organometallic complexes of bismuth, strontium, calcium, and copper as raw materials. These four raw materials are heated to a temperature at which their vapor pressures are obtained, and an inert gas such as argon gas is introduced into the reaction vessel as a carrier gas. The carrier gas may be nitrogen helium or the like. Oxygen gas or a gas containing oxygen gas is introduced into the reaction vessel through a route different from the above gas. A substrate for depositing a film is placed in a reaction vessel, and this substrate is further heated. The substrate can be heated by placing a heater inside the reaction vessel and heating the substrate, or by heating the substrate from outside the reaction vessel. Furthermore, methods such as high frequency heating may be used. An inert gas containing oxygen gas or a gas containing oxygen gas and vapor of an organometallic or organometallic complex containing each constituent element is introduced onto the substrate heated by any of the methods. The pressure inside the reaction vessel is reduced, preferably 50 Torr or less. The heating temperature of the substrate is at least below the melting point temperature of the film formed on the substrate,
The temperature is preferably just below the melting point within a range where Bit(Sr-Ca)zcuOx is not formed. The melting point of the film varies depending on the pressure inside the reaction vessel and the raw material gas composition, but the melting point of the membrane varies depending on the pressure inside the reaction vessel I
Torr is in the range of 770 to 780°C. In addition, the composition of the superconductor can be controlled by the heating temperature of each raw material and the raw material supply amount by the carrier gas flow rate, and the ratio of the raw material supply amounts of bismuth, strontium, calcium, and copper is 2:2:2:
3 is preferred.

The film thickness can be arbitrarily controlled by the deposition time and the amount of raw material supplied. A film thickness of 4 to 8 microns can be achieved by one hour of treatment. Furthermore, if heat treatment is required, a gas such as air or oxygen is introduced into the reaction vessel following the forming of the film.
The heat treatment can be performed with the pressure inside the reaction vessel set to 1 atm. Further, similar to other film syntheses, heat treatment may be performed again after forming the superconducting film. As for the heat treatment conditions, it is desirable to maintain the temperature at or above the melting point of the film for a short time, and then maintain it at a temperature just below the melting point for 3 to 5 hours and slowly cool it.

(Example) The present invention will be described in detail with reference to FIGS. 1 to 5.

FIG. 1 shows an example of the manufacturing method according to the present invention. Organometallic or organometallic complexes of bismuth, strontium, calcium, copper, such as Bi(OCzlls)2 or Bi(Cbls)z, 5r(Czll+, 0z)z,
Ca(C++H+, Og)z, Cu(Czll+qO
z) Place z into raw material containers of 1 and 2.3.4, respectively, and heat with the heater 5. 13 for bismuth alkoxide
5℃, phenyl bismuth: 1) 0℃, strontium β-diketone complex: 230℃, calcium β-diketone complex: 175℃, copper β-diketone complex: 120℃
Heat to. Each raw material container l, 2.3.4 is supplied with 50n of argon gas as a carrier gas from the inert gas inlet 6.
1/min 4 people. Further, 100 al/a+in of oxygen gas is introduced into the reaction vessel from the oxygen gas introduction lower. Carrier gas containing vapor of raw materials containing each compositional element and oxygen gas are mixed in a reaction vessel 8,
m is introduced into the substrate 9.

The inside of the reaction vessel is under reduced pressure, and the pressure is I Torr.

As described above, precipitation was performed on a magnesia single crystal substrate at substrate temperatures of 750°C, 770°C, 780°C, and 800°C for 1 hour. The thickness of the membrane obtained was 1-2 μm. Second
Figure 3 shows the X-ray diffraction patterns and temperature dependence of resistivity of the films deposited at each temperature. Substrate temperature 800℃,
At 780°C, in addition to the peaks of the low Tc phase and high Tc phase, Bi
(SrCa) A peak of zcuox is seen. 770
At ℃, two phases are formed: a low Tc phase and a high Tc phase. 7
At 50°C, it is close to a single low Tc phase. Furthermore, the resistance change of the films deposited at 770°C and 780°C becomes zero at temperatures above the liquid nitrogen temperature, and the resistance of the films deposited at 800°C becomes zero at temperatures as low as 50°C or lower.

Furthermore, from the observation of the structure of the film, the melting point in this example was 770.
~780°C.

Further, in this example, results were shown using bismuth alkoxide as a raw material, but similar results were shown in the case of phenyl bismuth.

In the second example, the film obtained in the first example was heat-treated in oxygen. The heat treatment conditions were held at 890°C for 20 minutes, then held at 870°C for 5 hours, and then slowly cooled. The X-ray diffraction patterns and resistivity temperature dependence of the films deposited at each substrate temperature after heat treatment are shown in FIGS. 4 and 5. Substrate temperature 800
The film formed at ℃ becomes Bit(Sr-Ca) by heat treatment.
The proportion of zcuOx increased, and the resistance change was semiconductor-like and did not show zero resistance. Substrate temperature 780℃, 77
Although there is no major change in the X-ray diffraction pattern at 0°C, the peak of the high Tc phase becomes clear due to the heat treatment, which suggests that the crystallinity has improved. ) It rapidly decreases from around 0, and shows zero resistance above the liquid nitrogen temperature.

At a substrate temperature of 750° C., no change is observed in the X-ray diffraction pattern, but a slight change in resistance is observed near 1) 0, indicating that a high Tc phase is formed. Since a high Tc phase is formed even at 750°C, by controlling the composition, a high Tc phase can be obtained even at this temperature.
It is possible to form superconducting thin films that exhibit .

(Effect) In a chemical vapor deposition method using an organometallic or organometallic complex containing at least bismuth, strontium, calcium, and S as an evaporation source material, precipitation occurs at a temperature below the melting point of the superconductor formed on the substrate. The method of the present invention, which further performs heat treatment, can stably form a superconductor having a structure exhibiting a higher Tc.
Since it does not contain any of the following phases or impurity phases, thin films with excellent superconducting properties can be deposited on large, large-area, and complex-shaped substrates.

Furthermore, according to the present invention, a superconducting thin film exhibiting zero resistance above liquid nitrogen temperature is synthesized, and an even higher proportion of T
It is also possible to form a thin film having a Tc of 100 or more by stably forming a high Tc phase having a c of 1)0k and changing the heat treatment conditions.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an example of an apparatus related to the manufacturing method of the present invention, FIGS. 2 and 4 are X-ray diffraction diagrams of a film on a magnesia substrate, and FIGS. 3 and 5 are films according to an example. FIG. 2 is a diagram of the resistivity temperature dependence of In the figure: l, 2.3.4... Raw material container, 5... Original c [
Power. Thermal heater, 6... Inert gas inlet, 7... Oxygen gas inlet, 8... Inside reaction vessel, 9... Substrate, 10
...Substrate heater.

Claims (4)

[Claims] (1) Using a raw material as an evaporation source containing at least bismuth, strontium, calcium, and copper, the raw material heating temperature is 300.
A method for producing a superconducting thin film, characterized in that the superconducting thin film is formed on a substrate at a temperature below the melting point of the superconductor in a chemical vapor deposition method in which the superconducting thin film is formed on a substrate at a temperature below °C and under reduced pressure. (2) The method for producing a thin film according to claim (1), wherein a heat treatment is performed after forming the superconducting thin film. (3) The method for producing a thin film according to claim 1, wherein the heat treatment after forming the superconducting thin film is performed continuously in the same reaction chamber. (4) The method for producing a thin film according to claim (1), wherein the raw material for each compositional element constituting the thin film is an organic metal or a β-diketone complex.