JPH02267105A - Formation of oxide superconductor thin film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to oxide superconductors used in magnet wires, power cables, power storage links, magnetic shields, Meissner effect application devices, Josephson devices, 5QUID devices, etc. This invention relates to a method for forming a thin film.

[Conventional technology and its issues]

In recent years, oxide superconductors made of rare earth elements, alkaline earth metals, Cu, etc., which exhibit superconductivity above the liquid N2 temperature, have been discovered.

These oxide superconductors are much more economical than conventional metal superconductors that exhibit superconductivity at liquid He temperatures, and their use in various fields is being considered.

By the way, the above-mentioned oxide superconductors are brittle and cannot be plastically worked like metal materials, and in order to process them into wires, strips, etc., SUS or A method has been adopted in which an oxide superconductor is directly deposited in a thin film on a substrate such as a Hastelloy alloy tape.

However, the above thin film cannot obtain the desired superconducting properties because the arrangement and defect state of oxygen atoms in the crystal do not exhibit superconductivity at temperatures higher than the liquid nitrogen temperature, and the thin film cannot be obtained separately after the film has been formed. However, it is necessary to perform a predetermined heat treatment in an oxygen-containing atmosphere to replenish oxygen into the crystal and adjust the crystal structure, resulting in a problem of poor productivity.

For this reason, it is necessary to use liquid N2 while the thin film is being deposited.
Various methods have been studied to form a superconductor at a temperature of /IA degrees or higher; for example, a method has been proposed in which a film is formed while heating the substrate to a high temperature exceeding 7000 degrees Celsius, but according to this method, the constituent elements of the substrate There was a problem in that the superconducting properties of the obtained oxide superconductor thin film deteriorated due to diffusion of the oxide superconductor into the oxide superconductor.

Another method has been proposed that uses a combination of vapor phase growth and oxygen plasma generated by DC or RF discharge to increase reactivity and make the film a superconductor even if the substrate temperature is lowered. However, this method has the problem that plasma damage occurs in the obtained film-formed body, resulting in deterioration of superconducting properties, and that a heat treatment step is also required in the post-process.

[Means to solve the problem]

In view of this situation, the present invention has conducted extensive research, and by incorporating ozone into the atmosphere during film formation and/or cooling in the vapor phase growth method, T .

It was discovered that a thin film body with excellent superconducting properties could be obtained, and through further research, the present invention was completed.

That is, the present invention uses a sintered body of an oxide superconductor, a substance or a compound containing constituent elements of the oxide superconductor as a target, and coats the substrate to a desired thickness by vapor phase growth, and then coats the substrate with a desired thickness. In the method of forming an oxide superconductor thin film on a substrate by cooling, the substrate temperature is set at 400 to 70°C.
This is a method for forming an oxide superconductor thin film, characterized in that the coating step and/or cooling step are performed at 00° C. in an ozone-containing atmosphere.

In the method of the present invention, when forming an oxide superconductor thin film by a vapor phase growth method and then cooling it, active ozone having strong oxidizing power is contained in the atmosphere during film formation and/or cooling. By accelerating the reaction, the substrate temperature is kept at a relatively low temperature of 400 to 7000°C,
The obtained thin film body is formed into a crystal structure that exhibits superconducting performance at a temperature higher than the liquid N2 temperature in the thin film state, and is heated in an oxygen-containing atmosphere to prevent diffusion of the base constituent elements into the superconductor thin film. This is to omit the processing.

The reason why the substrate temperature is limited to 400 to 7000°C in the method of the present invention is that if it is less than 400°C, the oxygen atoms in the obtained thin film crystal will not be properly arranged, and if it exceeds 7000°C, the constituent elements of the substrate will be This is because it diffuses into the oxide superconductor thin film, resulting in low superconducting properties in either case.

In the method of the present invention, film formation by the vapor phase growth method and cooling of the thin film body are performed in the same chamber of a vapor phase growth apparatus, and the inside of the chamber is a reduced pressure atmosphere containing ozone. In addition to ozone, He, Ne,
There is no problem even if inert gases such as , Ar, and Xe, and gases such as Nx and F are mixed.

In the above, it is preferable that the ozone content is 10% by volume or more based on the total amount of gas because the reaction is activated and high superconducting properties are obtained.

In the method of the present invention, the vapor phase growth method includes sputtering method, vacuum evaporation method, laser evaporation method, ion beam sputtering method, molecular beam epitaxy method, ion blating method, MOCVD method, etc., and the target material includes: The same substance as the superconductor substance, the metal/element constituting the above substance, or a substance containing the above element, such as oxides, acetates, nitrates, halides, organometallic compounds, etc., are used.

In the method of the present invention, the oxide superconductor to be formed by vapor phase growth is, for example, YBazcu30. +δ(δζ0
, 1 to 0.5), and its crystal structure is a layered perovskite-type oxygen-deficient orthorhombic crystal structure exhibiting superconductivity.

[Effect]

In the method of the present invention, ozone is contained in the atmosphere during film formation of the oxide superconductor by vapor phase growth and/or cooling of the formed thin film, and the temperature of the substrate at which the oxide superconductor is deposited is adjusted. Since the temperature is maintained at 400 to 7000°C, during film formation, evaporated elements from the target actively react with ozone atoms to form an oxide superconductor, which creates superconductivity with properly arranged oxygen atoms on the substrate. A thin film having the crystal structure shown is formed, and constituent elements of the substrate do not diffuse into the obtained thin film during film formation.

During cooling, the thin film body actively reacts with ozone in the atmosphere, and a predetermined amount of oxygen is supplied, so that the thin film body is adjusted to have a crystal structure exhibiting superconductivity.

〔Example〕

The present invention will be explained in detail below using examples.

Embodiment 1 FIG. 1 is an explanatory view of the main parts of a vacuum evaporation apparatus showing an example of an apparatus for carrying out the method of the present invention. In times 1 is the chamber,
2 is a block heater for heating the substrate, 3.4 is an e-gun and a resistance heater for vaporizing the target, and 5 is an ozone generator with a mass flow controller (M
FC) 6 and is airtightly connected to the chamber 1 by a SUS pipe 7.

A MgO single crystal substrate 8 is placed in the block heater 2 in the chamber 1 so that the (100) plane is the evaporation surface.
Ba and Y were attached to the base e-gun, and Cu was attached as a single metal to the resistance heating element 4, and then 503 CCM of ozone was supplied from the ozone generator 5 into the chamber 1 with the flow rate controlled by the MFC 6. 0.5 m by suction
A reduced pressure atmosphere of Torr is created, and then the block heater 2 is heated to maintain the substrate 8 at 650°C, and the e-gu
A Y-Ba-Cu-0 based oxide is formed on the substrate 8 by evaporating Y, Cu, and Ba at an atomic ratio of Y:Cu:Ba of 1.2:3 using the n3 or the resistance heater 4. 1000 superconductors (hereinafter abbreviated as Y-based oxide superconductors)
Formed to the thickness of a person.

In the above, the composition and film thickness were controlled using a crystal resonator film thickness meter 9 and a shank.

Then, while maintaining the inside of the chamber 1 in the above atmosphere, the temperature of the block heater 2 is lowered, and the thin film body on the base 8 is heated at 2° (
The mixture was cooled to room temperature at a rate of :/min.

Example 2 The same method as in Example 1 was used except that the atmosphere in the chamber was a reduced pressure atmosphere of 0.5 mTorr of a mixed gas of ozone IO% and Ar during film formation and during cooling of the formed thin film. A Y-based oxide superconductor thin film was formed on a MgO single crystal substrate.

Example 3 A Y-based oxide superconductor was deposited on an MgO single crystal substrate in the same manner as in Example 1, except that the atmosphere in the chamber during film formation was a reduced pressure atmosphere of 0.5 mTorr of oxygen gas. A thin film was formed.

Example 4 A Y-based oxide superconductor thin film was formed on an MgO single crystal substrate by the same method as in Example 1 except that the substrate temperature was changed to 450°C.

Example 5 In Example 1, the atmosphere in the chamber during film formation was ozone Q and a reduced pressure atmosphere of 5 mTorr, and the atmosphere during cooling of the formed thin film was a reduced pressure atmosphere of oxygen 0.5 mTorr. A Y-based oxide superconductor thin film was formed on an MgO single crystal substrate by the same method as in Example 1.

Example 6 Using RF magnetron sputtering equipment, thickness 5
A Y-based oxide superconductor thin film of 0.00000000000000000000000000000000000000000000000000000000000000000000000000001 to 1000000000000000000000000000000 to type form to glory, a Y-based oxide superconductor thin film was formed on the (100) plane of MgO single crystal substrate.

In the above film formation, the target is Y, Ba2Cu30
Using a sintered body of X pre-sintered powder, the substrate was heated at 650° in a reduced pressure atmosphere of 100 mTorr mixed gas of 50% 0° → -Ar.
The sample was heated to 40°C and an RF output of 100 W was applied.

After film formation, the surrounding atmosphere was changed to ozone at 100 mTorr, and the formed thin film body was cooled to room temperature at a rate of 2°C/min.

Comparative Example 1 An MgO single crystal substrate was prepared in the same manner as in Example 1, except that the atmosphere in the chamber was a reduced pressure atmosphere of 0.5 mTorr of oxygen both during film formation and during cooling of the formed thin film. Second, a Y-based oxide superconductor thin film was formed.

Comparative Example 2 A film was deposited on an MgO single crystal substrate by the same method as in Example 4, except that the atmosphere in the chamber was a reduced pressure atmosphere of 0.5 mTorr of oxygen during film formation and during cooling of the formed thin film. A Y-based oxide superconductor thin film was formed.

Comparative Example 3 A Y-based oxide superconductor thin film was formed on an MgO single crystal substrate by the same method as in Example 6, except that a reduced pressure atmosphere of 100 mTorr of oxygen was used when cooling the thin film formed inside the chamber. did.

Comparative Example 4 A Y-based oxide superconductor thin film was formed on an MgO single crystal substrate by the same method as in Example 1 except that the substrate temperature was changed to 350°C.

Comparative Example 5 A Y-based oxide superconductor thin film was formed on an MgO single crystal substrate by the same method as in Example 1 except that the substrate temperature was changed to 750°C.

Comparative Example 6 The Y-based oxide superconductor thin film obtained in Comparative Example 3 was further heat-treated at 900°C2H in the atmosphere.

Tc was measured for each oxide superconductor thin film thus obtained. The results are shown in Table 1.

As is clear from Table 1, the method of the present invention (Examples 1 to 6)
) had a high Tc value of 79 or more.

On the other hand, in Comparative Examples 1 to 3, ozone was not contained in the atmosphere during film formation and cooling of the formed thin film, and in Comparative Examples 4 and 5, the substrate temperature was outside the limit value of the present invention. All of the thin films obtained for this purpose were T.

However, the value was as low as 67. In order to make T of the above-mentioned comparison method product equal to or higher than the liquid nitrogen temperature (77K), for example, as shown in Comparative Example 6. It was necessary to further heat-treat the obtained thin film body in an oxygen-containing atmosphere.

In the above embodiments, the Y-based oxide superconductor was explained, but the method of the present invention can also be applied to other oxide superconductors such as the B1-3r-Ca-Cu-0 system or the Tl-Ba-Ca-Cu-0 system. It is applicable.

〔effect〕

As described above, according to the method of the present invention, it is possible to efficiently form an oxide superconductor thin film on a substrate with a temperature of T equal to or higher than the temperature of liquid nitrogen, so that it has a significant industrial effect.

[Brief explanation of drawings]

FIG. 1 is an explanatory view of the main parts of a vacuum evaporation apparatus showing an example of an apparatus for carrying out the method of the present invention. l...Chamber 2...Block heater 3.
...e gun, 4...resistance heater, 5...
Ozone generator, 8...substrate.

Claims (1)

[Claims] A sintered body of an oxide superconductor, a substance or a compound containing the constituent elements of an oxide superconductor, etc. is used as a target to coat a substrate to a desired thickness by vapor phase growth, and then it is cooled and coated on the substrate. A method for forming an oxide superconductor thin film, characterized in that the substrate temperature is 400 to 7000°C, and the coating step and/or cooling step are performed in an ozone-containing atmosphere.