JPH0714815B2 - Method for producing YBCO-based oxide high temperature superconducting thin film - Google Patents

Description

The present invention relates to a method for producing a YBCO-based oxide high temperature superconducting thin film. The thin film according to the present invention has an extremely wide range of application fields such as the electronics field, the power field, and the transportation field.

[Prior Art] Many methods for producing an oxide high-temperature superconducting thin film have been attempted. Particularly, in the case of producing from a gas phase, a single crystal can be obtained without heat treatment, and very excellent characteristics can be obtained. (For example, JP-A-62-236792 and JP-A-62-23679)
3). However, the characteristics of oxide high-temperature superconducting materials are greatly affected by the subtle differences in the stoichiometric composition of the constituent elements, so when trying to obtain a sample with good characteristics, the size of the sample is extremely limited. It has become a problem for industrialization now. Further, even if it is manufactured from a liquid phase, the local composition ratio is largely deviated and a single phase cannot be formed, so that a satisfactory critical current density is not obtained.

Recently, we have obtained a uniform high temperature superconducting thin film over a wide area.
As a simple method with a small initial investment of the equipment, a method of separately laminating the constituent elements and then heat treating them has been devised (for example, CXQui and I.Shih, Appl.Phys.Lett.52 (19
88), 587, Masaaki Futamoto and Yukio Honda, Jpn.JA
ppl.Phys.27 (1988), 173). This method is also a promising method for industrialization because it has a merit that it can be easily applied even when the number of constituent elements of superconductivity is further increased.

However, when considering the surface smoothness that is important in the application to electronic devices, this method requires a subsequent heat treatment to form a superconducting thin film, and there is a problem that the surface smoothness is easily lost at this stage. there were. In order to obtain a superconducting thin film while maintaining the surface smoothness, it is necessary to lower the heat treatment temperature and shorten the heat treatment time, and to supplement the superconducting thin film with high characteristics, it is necessary to supplement oxygen sufficiently.

[Problems to be Solved by the Invention] The present invention has the above-mentioned problems by stacking Ba, Y, and Cu and then performing oxygen plasma treatment, that is, lowering the heat treatment temperature, shortening the heat treatment time, and sufficiently reducing the heat treatment time. It is an object of the present invention to solve the problem of oxygen addition and provide a method for producing a superconducting thin film having high characteristics in a large area.

[Means for Solving the Problems] The present invention provides a method for producing a YBCO-based oxide high-temperature superconducting thin film by a dry process, in which Ba, Y, C are formed on the substrate.
The three layers are continuously laminated in the order of u so that the total film thickness is 100Å to 1000Å, and the three laminated films are continuously and repeatedly laminated so that the total film thickness is 1000Å to 2 μm.
In an atmosphere of 0.1 to 100 Torr, in a container in which oxygen plasma is generated with plasma power of 1 to 1000 W, at 1 to 700 to 850 ° C.
A method for producing a YBCO-based oxide high-temperature superconducting thin film using a Ba, Y, Cu laminated film, which enables the YBCO-based oxide high-temperature superconducting thin film to be obtained by performing oxygen plasma treatment for 60 minutes.

Structure of the laminated film disclosed in the present invention, that is, the stacking order,
The total film thickness and the total film thickness of the three layers were determined for the following reasons based on the results of intensive research.

Taking the affinity for oxygen into consideration, the stacking order uses copper, which has the lowest affinity for oxygen, as the outermost layer, and Ba, which has the highest affinity for oxygen, as the innermost layer, which gives stability when left in air after deposition. did. This is important when manufacturing a superconducting thin film with high stability of the film in air, and it was found from the results of various experiments that the stacking order was changed. This is because the stability of the film in air is low and the surface is roughened by the reaction with oxygen and moisture in the air before the post-treatment.

The total film thickness of the three layers, the so-called stacking period, must be in the range of 100 to 1000Å. Because 1 is less than 100Å
The layer thickness becomes too thin to form a film-like structure, and an island-like structure is laminated, so that compositional deviations occur locally and a heterogeneous phase occurs before the YBCO-based superconductor structure appears in the post-treatment. Is caused. Also, if it exceeds 1000Å, diffusion of each layer due to post-treatment will not be sufficient, higher processing temperature and longer processing time will be required, surface smoothness will be lost, diffusion from substrate to thin film and thin film This is because the supplement of oxygen into the inside is not carried out sufficiently, resulting in deterioration of superconducting properties.

The total film thickness must be in the range of 1000Å to 2 μm.
This is because if the thickness is less than 1000Å, the superconducting thin film will not be a uniform film over the entire area and island-shaped superconducting materials will be scattered. If it is thicker than 2 μm, the substrate and the superconducting thin film will be This is because the peeling of the film occurs due to the difference in the coefficient of thermal expansion between them.

It is desirable that the repetition cycle of these three layers is 5 to 100 cycles,
This cycle is automatically determined from the thickness of the unit three layers and the total film thickness, and is not particularly limited because the post-treatment conditions only change.

The substrate used in the present invention, MgO, SrTiO ₃ , ZrO ₂ , Si
O ₂ , yttria-stabilized zirconia, Al ₂ O ₃ , BaTiO ₃ , NdGaO ₃
Although the single crystal of is most suitable for the production of highly oriented superconducting thin films,
In fields where high critical current density is not required, such as when applied to electromagnetic shields or electromagnetic mirrors, non-oriented superconducting thin films can be produced on various substrates such as metals.

In order to form a superconducting thin film from the laminated film, it is necessary to diffuse the laminated film in a post-treatment to crystallize the superconducting structure and further add oxygen sufficiently. Moreover, it is necessary to perform the treatment at a sufficiently low temperature for a short time so as not to lose the surface smoothness. The inventors of the present invention have extensively studied various post-treatment methods, and have found that oxygen plasma treatment is the most effective and suitable.
Further, this oxygen plasma treatment, when compared to the sample before treatment having a superconducting crystal structure to some extent, or an amorphous structure which is completely mixed even if the crystal structure does not appear, We have found an interesting fact that oxygen is added more effectively to laminated films. It is considered that this is because Ba, which has a high oxygen affinity, is bound to oxygen on the surface when the laminated film diffuses and diffuses inside to cause a reaction, which serves as an oxygen absorbing driving hose. That is, the present invention is based on the discovery of the peculiarities of this oxygen plasma treatment, and in a method for producing a superconducting thin film by performing heat treatment after forming a laminated film to obtain a large-area superconducting thin film, It is disclosed that surface smoothness and superconducting properties can be dramatically improved by substituting the oxygen plasma treatment for the heat treatment.

Next, a method of oxygen plasma treatment will be described.

The oxygen partial pressure is preferably 0.1 to 100 Torr. Because 0.1T
This is because if it is less than orr, the absolute amount of oxygen is too small to effectively add oxygen, and if it exceeds 100 Torr, plasma cannot be stably maintained. More preferably, it is 1 to 10 Torr.

The plasma power is preferably 1 to 1000 W. Because, if it is less than 1 W, plasma is not generated,
On the other hand, if it exceeds 1000 W, the surface sputtered by the particles accelerated by the plasma sheath applied to the sample surface will precede, and the surface smoothness will be lost. More preferably, it is 2 to 50W.

In the case of the present invention, a high temperature is required to diffuse the laminated film to crystallize the superconducting crystal structure, and the temperature needs to be suppressed to the extent that the surface smoothness is not lost. Sample temperature is particularly important. That is, the sample temperature is preferably 700 to 850 ° C. If the temperature is lower than 700 ° C, the crystallization of the superconducting structure will be insufficient.
This is because when the temperature exceeds 850 ° C, the surface smoothness is lost. Further, it is necessary to consider the treatment time in order to maintain the surface smoothness. The treatment time is preferably in the range of 1-60 minutes. This is because if it is less than 1 minute, crystallization of the superconducting structure and oxygen uptake are insufficient, and if it exceeds 60 minutes, the degree to which plasma sputters the substrate surface cannot be ignored and the surface smoothness is lost. Is. In normal heat treatment, the temperature as described here,
It is difficult to crystallize a superconducting structure and to add oxygen in a sufficient time,
Further, it requires a high temperature and a long time, for example, 900 ° C. for about 1 hour.

The method of producing a superconducting thin film from the laminated film described in the present invention will be described below in detail with reference to the examples of the apparatus and the production procedure.

[Example] A schematic view of the apparatus used is shown in FIG. The apparatus used a single beam / triple hearth electron beam of a type that contained three evaporation sources so that it could be deposited continuously.
A crystal oscillation type film thickness meter is used as a film thickness monitor, and this monitor, electron beam gun, and shutter are connected to a personal computer to control the electron beam output so that the deposition rate of each evaporation source is constant, and the target film for each layer. The shutter opening / closing linked to the thickness and the switching of the beam irradiation position can all be performed automatically.

In the experiment, the deposition rate of each evaporation source was fixed at 1Å / s.
The electron beam output at this time was 20 to 25 mA for barium, 200 to 250 mA for yttrium, and 500 to 700 mA for copper. Evacuation was performed using an oil diffusion pump during the film formation, and the degree of vacuum was 1 × 10 ⁻⁵ Torr.

For the substrate, 1 cm ² square MgO (100) single crystal was used.
7 pieces are installed in the φ holder, and Ba326Å, Y85Å,
Cu89Å was deposited and laminated for 20 cycles. The film thickness of each layer in one cycle was previously determined by calculation so that the ratio of the numbers of Y, Ba, and Cu atoms was 1: 2: 3. In calculating the film pressure of each layer, it was assumed that the metal was deposited on the surface of the substrate and its density was equal to that of the bulk. The substrate was not heated during film formation.

FIG. 2 shows a schematic diagram of a plasma generator used for oxygen plasma treatment of the obtained thin film. In the apparatus, there is a pair of plasma generating electrode, reference electrode and substrate electrode in the plasma generating container. Place the sample of the laminated film obtained above on the substrate electrode, exhaust it to 10 ^-6 Torr with a turbo molecular pump, introduce oxygen at a flow rate of 2000 CC / min and helium 400 CC / min from the gas inlet, and pass it through the conductance valve. It was evacuated with a rotary pump (at this time, the oxygen partial pressure was 5 Torr and the helium partial pressure was 5 Torr). An alternating current of 50 Hz was applied to the plasma generating electrode at a power of 4 W to generate plasma, and a direct current voltage of +150 V was applied between the reference electrode and the substrate electrode. An infrared image furnace was used to heat the container, and while monitoring the substrate temperature, the temperature was raised to 800 ° C at a heating rate of 50 ° C / min.
After holding for 5 minutes, it was cooled at 50 ° C / minute.

The superconducting property of the obtained film is Tc = 83K (electrical resistance O), J
It was c = 5 × 10 ⁵ A / cm ² . When the surface smoothness was examined with a stylus-type surface roughness meter, Ra = 23Å. The composition by EDX analysis was Y: Ba: Cu = 1: 1.93: 3.10, and almost no composition deviation was observed. It was found from the X-ray diffraction profile that a clean C-axis alignment film was formed.
It was found that there was no change in the superconducting property of the thin film due to the difference in the mounting position of the substrate, and that the film had uniform properties over the entire area of 10 cmφ.

In the same experiment, the results obtained by changing the film thickness of one cycle and the maximum heating temperature in the oxygen plasma treatment are summarized in FIG.
Other experimental conditions are unchanged. It can be seen from FIG. 3 that the required temperature must be increased as the stacking period increases, but the temperature and time are sufficiently reduced.

[Comparative Example 1] Using a normal magnetron sputtering device, YBCO
A superconducting thin film was prepared. The substrate used was 1 cm ² square MgO (100), and the target had a stoichiometric composition of 1: 2: 3. In order to increase the oxygen concentration in the vicinity of the substrate, oxygen is supplied onto the surface of the substrate. The substrate was not heated. When the film formed was evaluated by X-ray diffraction, it was found that no superconducting structure was observed and the film had an amorphous structure as a whole. From the result of EDX composition analysis, 5% even in this narrow area
A slight compositional deviation was observed.

When this sample was subjected to oxygen plasma treatment under the above-mentioned conditions, a thin film showing a superconducting property of Tc = 53K (electrical resistance O) was obtained, but a thin film having a Tc higher than this was not obtained even if the conditions were changed. It was

From the above facts and examples, by using a laminated structure, Ba, which has the highest affinity with oxygen, combines with oxygen on the surface and carries oxygen to the inside by diffusion. The generation mechanism of being born can be considered.

Comparative Example 2 A thin film having a laminated structure produced by the method described in the example is
The heat treatment was performed in an atmosphere of oxygen at 1 atm. Heating rate 100
The maximum temperature was variously changed to
It was found that the highest heat treatment temperature was 900 ° C. and the heat treatment time was 2 hours. Although it was easily imagined under such heat treatment conditions, the smoothness of the surface was almost lost, and Ra was 304Å.

[Advantages of the Invention] According to the present invention, it becomes possible to obtain a superconducting thin film having high surface smoothness and excellent characteristics over a wide area with good reproducibility. This made it possible to apply to devices considered in the electronics field.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a vacuum vapor deposition apparatus used for carrying out the present invention. FIG. 2 is a schematic diagram of an oxygen plasma processing apparatus used to carry out the present invention. FIG. 3 shows the results of an experiment conducted by changing the stacking period and the maximum heating temperature in the oxygen plasma treatment.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H01B 13/00 565 D 7244-5G H01L 39/24 ZAA B 9276-4M

Claims (1)

[Claims] 1. A method for producing a Y-Ba-Cu-O (hereinafter referred to as YBCO) -based oxide high-temperature superconducting thin film by a dry process, in which three layers of Ba, Y, and Cu are sequentially formed on the substrate. Laminate continuously so that the total film thickness is 100Å ~ 1000Å,
Further, the three laminated films are continuously and repeatedly laminated to obtain a total film thickness of 1000.
Å ~ 2μm, then in an atmosphere of oxygen partial pressure 0.1 ~ 100 Torr, by oxygen plasma treatment at 700 ~ 850 ℃ 1 ~ 60 minutes in a container that generated oxygen plasma with plasma power 1 ~ 1000W A method for producing a YBCO-based high-temperature superconducting thin film using a Ba, Y, Cu laminated film, which is characterized in that a YBCO-based high-temperature oxide superconducting thin film is obtained.