JPH01614A - Method for producing oxide superconducting 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 a method for producing a superconducting thin film used in a superconducting device.

[Conventional technology]

Superconducting thin films are formed on substrates such as oxides, metals, and semiconductors. Superconducting properties depend on the composition, crystallinity, and impurity concentration, which in turn depends on the conditions during the deposition of the thin film.

Recently < (La14Baz)zcu04 and (Y+-xB
ax) The layered structure oxide represented by tcuo4 is 30~
It has been found to exhibit Tc as high as 100 (e.g. Z.

Phys, B64 (1986) 189. Phys.
Rev, Lett, 5B (1986) 408)
. When forming a thin film of such a high Tc oxide superconductor, important parameters in forming the thin film are the realization of an optimum composition in the thin film state and the substrate temperature, which influences crystallinity. In forming a thin film of such an oxide superconductor, the substrate temperature generally needs to be 500'C or higher. Conventional.

The superconducting thin film is ^1z(h, 5rTiO+, TiCh
A thermally oxidized substrate such as Si is used.

[Problem that the invention seeks to solve]

On these substrates, the above-mentioned high Tc oxide superconductor was deposited at several hundred degrees.
Even if deposited at a substrate temperature above C.

It was not easy to deposit thin films with good superconducting properties. There are two reasons for this.

(2) The oxide superconductor with high Tc is a multi-component system consisting of oxides of metals of group (2) and (2) and oxide of Cu, and it is not easy to achieve an optimum ratio (composition) of all elements.

■The constituent oxides are determined by sputtering efficiency, adhesion rate to the substrate,
Since the vapor pressure and the like are different, there is a difference in the deposition efficiency on the substrate, and the composition of the formed thin film is different from the target composition. ) ■What is the Cu oxide that makes up the oxide superconductor?

It has a property that it becomes difficult to adhere to the substrate as the substrate temperature rises.

For the above reasons, thin films of oxide superconductors.

When deposited on a substrate, it is difficult to obtain a thin film with good properties.

An object of the present invention is to overcome the drawbacks of the conventional techniques of thin film deposition of oxide superconductors and to provide a high quality superconducting oxide thin film with a high Tc that can be applied to superconducting devices.

[Means for solving problems]

The present invention forms a thin film of an oxide superconductor with a high Tc by depositing a thin film with an optimal composition by placing metal elements that are insufficient due to thinning on a target in the form of metal or oxide. It is characterized by: In particular, in the present invention, as a compensation method for missing elements, Ml and M
Two elements.

After thinning the film, prepare a target with an optimal ratio, and add Cu oxide on the target to compensate for the lack of Cu element.
Alternatively, it is based on compensation by arranging a metal, and in this case, the target may or may not contain CuO.

Under predetermined deposition conditions, it is better to include component amounts close to the optimal composition.
If fine adjustment of the atomic ratio of Ml and M2 is required to easily realize a thin film with an optimal composition, it is also possible to compensate by placing the missing element on the target, similar to Cu.

Conventionally, thin films of superconductors made of nine alloys/compounds were made using thermally oxidized S.
It is deposited on a T substrate, a sapphire substrate, etc. For A15 type compounds, etc., high quality thin films have been produced at substrate temperatures of 600° C. or higher.

For Nb3Ge, Nb3Ga, etc., there is almost no difference between the target composition and the thin film composition, and it does not change much depending on the substrate temperature. However, in Nb and AI, Nb and ^l
Although the difference in vapor pressure is relatively large and changes as the substrate temperature rises, the difference in composition is only a few percent at most. However, in oxide systems, a compositional deviation of 20 to 30x easily occurs. For this reason, we take into account the compositional deviation between the target and the thin film.

A target is produced by compensating the composition by the amount of deviation, and a thin film is produced using the target. However, the oxide material discovered this time is a multi-component system, and it is not easy to adjust the composition deviation due to thinning.Furthermore, the deposition efficiency largely depends on the substrate temperature, and it is difficult to adjust the composition deviation due to thinning. It is difficult to form thin films with good conductivity at arbitrary substrate temperatures.

When a high Tc oxide superconductor is made into a thin film by sputtering etc. 2
It was found that it has the following characteristics:

(2) When M1 metal and M2 metal are made into thin films, their compositions do not vary much depending on the deposition conditions, although they differ from the target composition.

(2) The deposition efficiency of CuO is affected by the substrate temperature and decreases significantly as the temperature rises.

Based on this result9, in the present invention, we focused on the atomic ratio of Ml and M2, created a target with a composition that took into account the compositional deviation during thinning, and the elements to be compensated on the target were:
The Cu element is mainly affected by the substrate temperature.

[Example 1] Targets of Y+BazCu+OX and Y, Ba6Cu, and Ox were prepared. The superconducting critical temperature (Tc) of Y, BazCu30x target is Tce(endpaint)
It was 90.

Y, Ba, Cu, and Ox targets did not exhibit superconductivity even at 4.2. Using these targets, Ar+
By RF sputtering in lOx02 gas, gas pressure: 3
A thin film of 3000 A was formed at a substrate temperature of 600° C. and an electric crab pressure of 30° C. as a substrate.

A sapphire substrate was used. Y1BazCu exhibiting high Tc
Thin films obtained from lOx targets did not exhibit superconducting properties. A compositional analysis of this thin film revealed that Y:Ba
:Cu atomic ratio was 1:0.3:0.09. On the other hand, the thin film obtained from the Y+BaaCu+*O target also did not exhibit superconducting properties, but the Y:B
The atomic ratio of a:Cu was h2:1. Ys of this thin film
The Ba ratio is a high Tc composition ratio.

There was a lack of Cu.

Therefore, we used a target of YJa6Cu+40X.

Place a CuO pellet on top of it, Y:Ba:
A thin film in which the atomic ratio of Cu was close to 1:2:3 was fabricated. The substrate temperature during fabrication was 600°C. This thin film.

It exhibited superconducting properties, with Tce=80.

In addition, Y1M2zCu30x thin film (M2: Be, Mg
, Ca, Sr+ Zn+Cd, Hg, Cf), Y, M, yCu, Ox targets were also produced. Although the value of y varied from 1 to 8 depending on the metal of M2, the atomic ratio of Y:M2 in IM was close to 1:2. Using these targets, a thin film with a Y:M2:Cu atomic ratio close to 1=2:3 with a high Tc composition was obtained by placing a Cu metal piece on the target. The Tc of these thin films was 30-75.

[Example 2] In Example 1, a Si substrate was used instead of the sapphire substrate, ^r gas was used as the sputtering gas, and Y
+BazCusOx and Y1BabCu+aOx targets were 600°C. The composition of the thin film obtained from Y, BagCu+Ox target is: Y:Ba:Cu =
The ratio was 1:0.1:0.1.

On the other hand, the composition of the thin film obtained from the target of Y, Ba, Cu+40x is: Y:Ba:Cu =1:1.6:
It was 1.5.

Neither film showed superconducting properties. By placing a Ha,Cu piece on the latter target.

A thin film with a high Tc composition of Y:Ba:Cu=1:2:3 was obtained. When the Tc of this thin film was measured, it was found that Tce・
It was on 10th. This is due to the lack of oxygen. Therefore, it was annealed in oxygen at 600°C for 10 hours. The Tc of this thin film was 85K.

Similarly, M1, Ba, Cu5Ox (Ml:
Sc, Ce.

Pr, Nd, Pm, Yb, Lu, B+AI, Ga, I
n, T1. A thin film of Es) was produced under the above conditions. As a target.

Ml + BayCu, , Ox were produced. The value of y varied from 0.8 to 1.5 depending on the type of metal of Ml. Using these targets, a Cu piece was placed on the target and sputtered. When the ratio of Ml and Ha deviated significantly from 2, the missing element was placed simultaneously with the Cu piece and sputtered to produce a thin film with a composition close to a high Tc. Although the Tc of the obtained thin film was low.

By annealing in oxygen, Tc increases to 40~
It became a thin film of 85 mm.

〔Effect of the invention〕

As explained above, according to the present invention, when thinning a multi-component oxide, a target prepared in advance with an elemental system with little variation by one composition shift is used, and the deposition efficiency significantly changes depending on the substrate temperature. Since the affected Cu is placed on the target and compensated for, there is an advantage that a thin film composition with high Tc can be realized at any substrate temperature.

Claims (3)

[Claims] (1) (M1_1_−_XM2_X)_YCuO_Z(
0<X<1, 1≦Y≦2, 2≦Z<5, M1 is a group III metal (Sc, Y, La, Ce, Pr, Nd, Pm, Yb,
one or more metals selected from the group consisting of Lu, B, Al, Ga, In, Tl, Es), M2 is a group II metal (
Be, Mg, Ca, Br, Ba, Zn, Cd, Hg, C
f) A method of depositing a thin film of an oxide superconductor consisting of one or more metals selected from the group consisting of A method for producing an oxide superconducting thin film, which comprises disposing it in a metal or oxide state and performing sputtering. (2) The method for producing an oxide superconducting thin film according to claim 1, wherein the sputtering method is any one of sputtering, reactive sputtering, ion beam sputtering, and reactive ion beam sputtering. . (3) Sputtering is performed by using a target in which the composition of M1 and M2 has an optimal atomic ratio after thinning, and by arranging the Cu element on the target. Or the method for producing an oxide superconducting thin film according to item 2.