JPH0264003A - Production of oxide superconductor thin film - Google Patents

Abstract

PURPOSE:To readily and surely obtain an oxide superconducting thin film having oriented a-axis by heating a substrate at a temperature within a specific range and sputtering the substrate with oxygen gas or a mixed gas thereof and an inert gas containing a specific amount or more of the oxygen gas. CONSTITUTION:A substrate, such as SrTiO3, is heated at 510-680 deg.C and oxygen gas or a mixed gas thereof and an inert gas, such as Ar, containing >=80vol.% oxygen gas is used as a sputtering gas to sputter metals or compounds thereof constituting a saperconductor. Thereby, an oxide superconductor thin film having the a-axis of crystals perpendicular to the substrate surface is obtained. The thickness of the thin film is preferably within the range of 200 to 2X10<3>nm for use in electronic devices, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a method for manufacturing an oxide superconductor thin film, and particularly to a method for manufacturing an oxide superconductor thin film having an a-axis orientation.

(Prior art) In 1986, La-
Since the Ba-Cu-0-based layered perovskite-type oxide superconductor was announced, oxide-based superconducting materials have attracted attention. Furthermore, in 1987, a defective perovskite type ((
LnBa Cu O type) (δ is oxygen defect Table 237
-δ is usually 1 or less, Ln is Y% La5SC% Nd
, 5IIls Eu5Gd, Dy, I(o, E
at least selected from r, Tl5Yb and Lu
It was confirmed that the critical temperature of the oxide superconductor of one element (Ba, in which part of it can be replaced with Sr, etc.) is higher than the liquid nitrogen temperature (-77K), which is 90°C or higher. This discovery has made it possible to apply superconductors using cheaper liquid nitrogen instead of expensive liquid helium as a refrigerant, and research is being actively conducted in various places. Furthermore, recently, the B1-8r-Ca-Cu-0 system with a critical temperature of about 105 and the Tl
-Ba-Ca-Cu-0 based oxide superconductor has been discovered.

When using these oxide superconductors as thin films, various attempts have been made to apply sputtering methods.

Formation of an oxide superconductor thin film using a sputtering method uses, for example, a sintered body of an oxide superconductor or a single substance or compound of each metal element constituting the oxide superconductor as a target, and oxygen is added at a volume ratio of 20%. Spackling is performed in a mixed gas of oxygen gas and inert gas containing approximately 70% to 70% without heating the substrate to which the film is to be deposited, or with the substrate heated to 510°C or higher. There is.

By the way, if a film is formed by sputtering without heating the substrate, the resulting thin film is in an amorphous state and cannot obtain superconducting properties as it is.

Therefore, the obtained thin film is heat-treated at high temperature for a long time in an oxygen atmosphere to crystallize it, thereby forming an oxide superconductor thin film.

However, the oxide superconductor thin films obtained in this way are generally polycrystalline, with almost no orientation, or in rare cases, C
This is to the extent that the axial orientation and C-axis orientation are strengthened.

On the other hand, when sputtering is performed to form a film while the substrate is heated to 510°C or higher, the resulting thin film crystallizes immediately after the film is formed, and has the advantage that superconducting properties can be obtained even as it is. .

It has also been reported that a C-axis oriented oxide superconductor thin film can be obtained by sputtering a heated MgO substrate using the (100) plane of MgO as the film deposition surface.

However, as an example of an oxide superconductor thin film with orientation so far, there is only the above-mentioned example of C-axis orientation, and an oxide superconductor thin film with a-axis orientation has not been obtained.

In an oxide superconductor, when a current is passed parallel to the 0 plane of the crystal, and when a current is passed perpendicular to the 0 plane, the 0
It is known that the critical current density can be greatly improved by passing current parallel to the plane, but when using oxide superconductor thin films as various superconductor devices, it is necessary to use not only C-axis oriented thin films. Naturally, it is thought that an oxide superconductor thin film with a-axis orientation will also be required.

(Problems to be Solved by the Invention) As mentioned above, in the conventional method for manufacturing oxide superconductor thin films using sputtering, only C-axis oriented thin films can be obtained with the same orientation and property. Therefore, no a-axis oriented oxide superconductor thin film was obtained.

The present invention was made in order to deal with the circumstances of the prior art, and provides a method for producing an oxide superconductor thin film that makes it possible to easily and reliably obtain an oxide superconductor thin film with a-axis orientation. is intended to provide.

[Structure of the Invention] (Means and Effects for Solving the Problems) In the method for producing an oxide superconductor thin film of the present invention, in forming an oxide superconductor thin film on a substrate by sputtering, the substrate is heated at 510°C. While heating in the range of ~680°C, sputtering is performed using oxygen gas or a mixed gas of oxygen gas and inert gas containing 80% or more of oxygen gas by volume as sputtering gas, so that the a-axis of the crystal is aligned with the substrate. It is characterized by forming an oxide superconductor thin film perpendicular to the surface.

Many oxide superconductors are known, but in the present invention, oxide superconductors having a perovskite structure containing rare earth elements, B1-8r-Ca-
Cu-0 based oxide superconductor, Tl-Ba-Ca-Cu-
A zero-based oxide superconductor or the like is applied.

The oxide superconductor containing a rare earth element and having a perovskite structure may be one that can realize a superconducting state, for example, LnM CuO system (L
n is Y, La, Sc, Nd, Sm.

237-δ Eu, Gd, Dy, llo, Er, Tl11%
At least one element selected from rare earth elements such as Yb5Lu, M is at least one element selected from Ba, S, and Ca, δ represents an oxygen defect, usually a number of 1 or less, and Cu Parts are Ti1V, Cr, Mn5Fe
, GoSNi, Zn, etc. can be substituted. ) and other oxides are exemplified. Rare earth elements are defined in a broad sense, and Sc
, Y and La systems. In addition to the Y-Ba-Cu-0 system, representative systems include Y for hu, Dys
Examples include systems substituted with rare earth elements such as 80% Er and Tms Ybs Lu.

As the sputter target used in this invention, a sintered body of the oxide superconductor as described above may be used, or a single substance or a combination of each metal element constituting the oxide superconductor may be used. good. For example, in the case of producing a Y-Ba-Cu-0 based oxide superconductor thin film, YBa2Cu307-δ sintered body, or metal y, y203, BaO, Ba2 Cu03
Examples include combinations of sintered bodies, metal Cu, CuO, and the like.

Examples of the substrate on which the film is deposited include an MgO substrate, a 5rT10x substrate, a Y-stabilized ZrO2 (hereinafter referred to as YSZ) substrate, or a thin film of these materials formed on a St substrate. It is preferable to use the (■0) plane.

In this invention, using these sputter targets and dilute film substrates, the base tlj temperature is set at 510°C to 680°C.
Sputtering is performed in oxygen gas or a mixed gas of oxygen gas and inert gas containing 8026 or more oxygen gas by volume to produce a thin film of the oxide superconductor.

If the substrate heating temperature during sputtering is less than 510°C, it will not crystallize during sputtering and will become polycrystalline during heat treatment for crystallization, and if it exceeds 680°C, a square product will appear.
Heat treatment is required to transform it into an orthorhombic system.

In addition, in the sputtering gas, the C-axis orientation disappears by setting the content of oxygen gas to 80% or more by volume in a mixed gas of at least oxygen gas and inert gas.
An axially oriented oxide superconductor thin film is obtained. This sputtering gas uses oxygen gas or a mixed gas of oxygen gas and inert gas. The inert gas is an inert gas belonging to Group 0 of the periodic table, and Ar gas is particularly preferable.

Note that sputtering conditions other than these, such as gas pressure during sputtering, may be appropriately set from general conditions in consideration of other conditions, and are not particularly limited.

The oxide superconductor thin film obtained in this way is crystallized in the deposited state and exhibits superconducting properties, but even if it is subsequently subjected to heat treatment in an oxygen-containing atmosphere to improve its superconducting properties. good.

Further, the thickness of the obtained oxide superconductor thin film is not particularly limited, but for example, when used as an electronic device, the film thickness is 10OnIIl-LX 10'no+, and a more preferable film thickness is 200tv. ~2
It is X103nI11.

(Example) Next, embodiments of the invention will be described.

Example 1 FIG. 1 is a diagram schematically showing a sputtering apparatus used in this example. In the figure, reference numeral 1 denotes a grasshopper chamber. In this sputtering chamber 1, a target 2.3.4 for magnetron sputtering and a substrate holder 5 are installed. Behind the substrate holder 5, a substrate heating A heater 6 is provided, and sputtering power supplies 7, 8, and 9 are connected to the targets 2, 3, and 4, respectively.

Further, two gas supply systems for introducing sputtering gas, namely a first gas supply system 10 and a second gas supply system 11, and an exhaust system 12 are connected to the sputtering chamber 1.

A Y-Ba-Cu-0 based oxide superconductor thin film was produced using the sputtering apparatus having such a configuration according to the following procedure.

First, a 5rTi03 (100) substrate was used as the film deposition substrate 13, set in the substrate holder 5, and heated to 510°C to 6110°C by the substrate heating heater 6.
Only oxygen gas with a purity of 99.999% was supplied from the first gas supply system 11, and the gas pressure in the sputtering chamber 1 was adjusted to 5×10' Torr. Target 2.3
．． 4 includes metal Y, Ba2 CuO3 sintered body,
Using metal Cu, RF power was supplied from the sputtering power supply 7.8 to the metal Y and Ba2 Cu03 sintered body, and DC power was supplied to the metal Cu from the sputtering power supply 9, and Y-Ba- A Cu-0 based oxide superconductor thin film was formed. In addition, three types of targets 2.3.
The input power ratio to 4 is determined when the composition of the thin film to be formed is Y
:Ba:Cu=1:2:3, and the film thickness was 500nw.

In order to evaluate the superconducting properties of the Y-Ba-Cu-0 based oxide superconductor thin film obtained in this manner immediately after film formation, 4
When the temperature dependence of electrical resistivity was measured using the terminal method, it was confirmed that the material exhibits a superconducting state.

Further, the crystallinity and orientation of this oxide superconductor thin film were evaluated by X-ray diffraction. The X-ray diffraction results are shown in FIG.

As is clear from FIG. 2, the oxide superconductor thin film produced in this example is oriented along the a-axis.

In addition, in order to improve the superconducting properties of this Y-Ba-Cu-0 based oxide superconductor thin film, heat treatment was performed at 8° 50°C for 1 hour in an oxygen gas atmosphere, and then X When line diffraction was performed, the orientation did not change.

Example 2 A 5rTi03 (100) substrate was set on the substrate holder 5 in the same manner as in Example 1, and oxygen gas with a purity of 99.999% was supplied from the first gas supply system 11 and the second gas supply system 12 as sputtering gases. A Y-Ba-Cu-0 based oxide superconductor thin film was produced under the same conditions as in Example 1, except that argon gas with a purity of 99.999% was supplied so that the volume ratio of oxygen gas was 80%. did.

In addition, for comparison with this invention, a mixed gas of oxygen and argon (comparative example 1) with a volume ratio of oxygen gas of 20% and a mixed gas of oxygen and argon with a volume ratio of oxygen gas of 50% were used as the sputtering gas. 5rTi03 (100) under the same conditions as Example 1 using a mixed gas of (Comparative Example 2).
A Y-Ba-Cu-0 based oxide superconductor thin film was produced on a W plate.

Note that the composition of the oxide superconductor thin film to be formed remains the same even if the mixing ratio of the sputtering gas is changed.
By adjusting the power ratio of Y:Ba:Cu-1:
The ratio was set to 2:3.

Each of the Y-Ba-Cu-0 based oxide superconductor thin films obtained in this manner exhibited a superconducting state immediately after the film was formed.

Further, when the orientation of each of these Y-Ba-Cu-0 based oxide superconductor thin films was evaluated by X-ray diffraction, the results shown in FIGS. 3 to 5 were obtained.

As is clear from Figure 3, the mixing ratio of oxygen gas is 80%.
The Y=Ba-Cu-0-based oxide superconductor thin film formed as a comparative example has an a-axis orientation, whereas the Y-Ba-Cu-0-based oxide superconductor thin film formed as a comparative example has oxygen The oxide superconductor thin film formed with a gas mixing ratio of 20% (Comparative Example 1) has C-axis orientation, and the oxide superconductor thin film formed with an oxygen gas mixing ratio of 50% (Comparative Example 2). )
had a mixture of a-axis orientation and c-axis orientation.

Further, Y-Ba-C
When u-0 type oxide superconductor thin films were produced, a-axis oriented thin films were obtained in all cases.

Also, even when using Mg0 (+00) substrate and YSZ (100) substrate, 5rT1(h (100)
A Y-Ba-Cu-0 based oxide superconductor thin film having the same a-axis orientation as the substrate was obtained.

The heating conditions for the film-coated substrate are 510°C to 68°C.
Similar results were obtained within the temperature range of 0°C.

As is clear from the results of these Examples and Comparative Examples, in the mixed gas of oxygen gas and inert gas used as the sputtering gas, the mixing ratio of oxygen gas should be 80% or more (including 100% oxygen gas). Thus, a C-axis oriented oxide superconductor thin film can be obtained.

[Effects of the Invention] As explained above, according to the method for manufacturing an oxide superconductor thin film of the present invention, an oxide superconductor thin film having a-axis orientation can be easily and reliably provided.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the sputtering apparatus used in the examples of this invention, and FIGS. 2 to 5 show Y-Ba-Cu-0 based oxides produced in the examples and comparative examples of this invention FIG. 3 is a diagram showing an X-ray diffraction pattern of a superconductor thin film. 1...Sputtering chamber, 5...Substrate holder, 6...Substrate heating heater, 10...
First gas supply system, 11... Second gas supply system, 13... Film-deposited substrate. Applicant Toshiba Corporation Patent Attorney Sasa Suyama - Figure 2 Figure 3

Claims (1)

[Claims] (1) When forming an oxide superconductor thin film on a substrate by sputtering, the substrate is heated in the range of 510°C to 680°C, and the sputtering gas contains oxygen gas or oxygen gas at a volume ratio of 80% or more. Production of an oxide superconductor thin film characterized by performing sputtering using a mixed gas of oxygen gas and inert gas to form an oxide superconductor thin film in which the a-axis of the crystal is perpendicular to the substrate surface. Method.