JPH04219318A - Production of oxide superconductor film - Google Patents

Abstract

PURPOSE:To obtain an oxide thin fifth having a perovskite structure with little deviation from the target composition by evaporating and depositing a volatile substance containing Cu and/or Bi and a group II element on a substrate under a prescribed vacuum degree. CONSTITUTION:A volatile substance is evaporated in a vacuum of 10<-3> to 10<-5>Torr to deposit an oxide superconductor thin film having perovskite structure or pseudo-perovskite structure on a substrate. In the above process, the volatile substance composed of metal or its oxide containing Cu and/or Bi element is evaporated by electron beam evaporation process and the volatile substance composed of an oxide containing a group II element is evaporated by laser evaporation process.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxide superconducting film. More specifically, the present invention relates to a method for stably producing an oxide superconducting film with a small deviation from the intended composition.

0002

[Prior Art] Since the discovery of a Y-based oxide superconductor with a superconducting transition temperature higher than the boiling point of liquid nitrogen (77K), B
Efforts are being made to put into practical use oxide superconducting thin films having a perovskite structure or a pseudo-perovskite structure such as i-based and Tl-based structures.

However, the superconducting properties of these oxides strongly depend on the composition ratio of the constituent atoms, and the better the superconducting properties, the more stringent compositional control is required. For example, in the case of Bi-based oxide superconductors, Bi, Sr, Ca, Cu and O
(oxygen), and its superconducting properties improve as the composition ratio of Ca and Cu increases. However, Bi2Sr2Ca2Cu3Ox, which has the highest transition temperature,
Preparation requires strict adjustment of the composition ratio of the ingredients. Therefore, when producing an excellent superconducting film, it is essential to control the film composition ratio, which requires independent control of each element.

[0004]Currently, as a vapor deposition method that allows independent control, there is a multi-source vacuum vapor deposition method that uses a plurality of electron guns.
It is not easy to stably produce an oxide film having a predetermined composition. This is for the following reasons.

■ I, a constituent element of oxide superconductors
Group Ia elements have a temperature difference of 900° C. or less between their boiling point and melting point, which is small compared to other elements, so local heating with an electron gun tends to cause bumping (splash), making the deposition flow rate unstable.

■ Oxidizing gas (O2
.

For this reason, in the multi-source vacuum deposition method, in order to control the film composition, the same number of film thickness sensors as the number of deposition sources are prepared, and during film formation, the amount of irradiation energy is constantly monitored for each deposition source. It has been reported that adjustments need to be made (Jap
anese Journal of Appli
edPhysics, Vol. 27 (1988), p.
p. L1262-L1264).

However, with such a method, control becomes difficult, and the apparatus becomes complicated and expensive. In addition, even if a film thickness sensor is installed at each deposition source, each sensor is affected by the deposition flow from other deposition sources, especially the deposition flow from group IIa elements, so it is difficult to measure the composition ratio within the film. It is difficult to match the composition ratio.

On the other hand, recently, attempts have been made to fabricate a superconducting film by using a sintered material of an oxide superconductor as a target and irradiating it with laser light (J. Mater.
Res. Vol. 27 (1988), P258-26
4).

[0010] However, in general, the laser vapor deposition method has a problem in that the target composition and the film formation composition do not match, and in particular, there is a large discrepancy in the Cu element ratio. Therefore, in order to obtain a film with an arbitrary composition by laser vapor deposition, strict composition control of the target is required.

[0011]

[Problems to be Solved by the Invention] An object of the present invention is to stably produce an oxide superconducting film with a desired composition ratio of the constituent elements in the film with good reproducibility, that is, with a small deviation from the intended composition. Our goal is to provide a way to do so.

0012

[Means for Solving the Problems] The present inventors have made the following findings as a result of intensive study on a method for producing an oxide superconducting film without deviating from the target composition.

[0013] In the electron beam evaporation method, the amount of evaporation material deposited with respect to a constant heating output of the electron beam is unstable due to bumping in the evaporation material containing a group IIa element with a small temperature difference between the boiling point and the melting point. The amount decreases due to significant changes in the irradiated surface over time, but with deposited materials that have a relatively large temperature difference between the boiling point and melting point, the deposited surface will be in a uniform molten state, and there will be no rapid change in the amount of deposition due to bumping, and the amount will change over time. A stable evaporation rate can be obtained.

[0014] In the laser evaporation method, when a single target is used, the compositional deviation within the deposited film is significant for evaporated materials with a large temperature difference between the boiling point and the melting point. In terms of elements, it is approximately equal to the target composition ratio.

■ If a deposition material with a large temperature difference between the boiling point and the melting point is deposited using the electron beam evaporation method, and a deposition material with a small temperature difference between the boiling point and the melting point is deposited using the laser deposition method, the deviation of the composition from the target composition ratio can be reduced. Any small oxide film can be created.

[0016] The gist of the present invention is as follows.
Using a metal or an oxide thereof containing one or more elements of Cu and Bi, and an oxide containing one or more elements of group IIa elements, these vapor deposition materials are deposited under a vacuum degree of 10-
A method for producing a film of an oxide superconductor having a perovskite structure or a pseudo-perovskite structure on a substrate by vapor deposition in a vacuum atmosphere of 3 Torr to 10-5 Torr, the method comprising: one of the above-mentioned Cu and Bi; The vapor deposition material of a metal or its oxide containing the above elements is deposited by an electron beam evaporation method, and the vapor deposition material of an oxide containing one or more elements of Group IIa elements is deposited by a laser evaporation method. ``Method for manufacturing oxide superconducting film''.

[0017] The above-mentioned electron beam vapor deposition and laser vapor deposition may be performed simultaneously.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view showing an example of an apparatus for carrying out the method of the present invention.

In FIG. 1, 1 is a substrate, 2 is a film thickness monitor, 3 is a reaction gas nozzle, 4 is a deposition material, 5 is an electron gun,
6 is a target for laser deposition, 7 is a laser entrance port,
8 is a laser beam, and 9 is a reaction chamber.

The vapor deposition substance 4 is a metal or an oxide thereof containing one or more elements of Cu and Bi, and the target for laser vapor deposition is an oxide containing one or more elements of group IIa elements. made from things. The reason why a metal containing one or more elements of Cu and Bi or an oxide thereof was used as the vapor deposition material 4 is because a metal can supply a highly pure element, and an oxide This is because oxygen can be easily introduced into the film in this case.

This vapor deposition material 4 is melted by an electron beam irradiated from an electron gun 5 and is vapor deposited onto the substrate 1. On the other hand, the laser deposition target 6 is melted by the laser beam 8 irradiated through the laser entrance 7 and is deposited on the substrate 1 . Vapor deposition takes place inside the reaction chamber 9.
The vacuum level is maintained at −3 Torr to 10 −5 Torr. This means that at a vacuum level lower than 10-3 Torr, the mean free path distance of each evaporated particle (atom, molecule) is 1.
This is because the length is very short, less than 0 cm, which limits the size of the reaction chamber and makes it difficult to insert an electron gun, a target for laser deposition, and other equipment into the reaction chamber. This is because, if the temperature is too high, oxygen will not be sufficiently introduced into the film, making it difficult to form an oxide film.

FIG. 2 shows an investigation of the relationship between the number of evaporated atoms and the electron beam heating output when Cu metal and Bi oxide are used as vapor deposition materials and are heated and vapor deposited using an electron beam. FIG. 3 shows an investigation of the relationship between the number of evaporated atoms and the electron beam heating time when Cu metal and Bi oxide were similarly used as evaporation materials and were heated and evaporated with an electron beam. Figure 4 shows Ca element and Sr element selected from Group IIa elements, and their composition ratios as Ca:
The relationship between the Ca/Sr composition ratio and the laser energy density was investigated when oxides containing Sr=2:1, 1:1, and 1:2 were used as targets.

It can be seen from FIGS. 2 and 3 that the number of evaporated atoms is almost proportional to the electron beam heating output, and is constant with respect to time immediately after the start of beam irradiation. On the other hand, it can be seen from FIG. 4 that the evaporation ratio of any target is constant for any given laser output, and is the same as the target composition ratio.

[0025] Therefore, a vapor deposition material of a metal or an oxide thereof containing one or more elements of Cu and Bi is evaporated with an electron beam, and a vapor deposition material of an oxide containing one or more elements of group IIa elements is evaporated with an electron beam. By vapor depositing with laser,
It is possible to manufacture an oxide superconducting film with no composition deviation with respect to a target composition ratio. In addition, by arbitrarily selecting the electron beam output and target composition ratio and performing simultaneous vapor deposition, it is possible to manufacture oxide superconducting films with various composition ratios without deviation from the target composition ratio. .

[0026]

[Example] In the apparatus shown in Fig. 1, Bi, Sr, Ca, Cu
An oxide film having an atomic ratio of as shown in Table 1 was prepared,
The deviation of the composition from the target value of the atomic ratio was investigated.

In the example of the present invention, Bi2O3 and Cu pure metal are heated with an electron beam, and Sr and Ca elements are converted to Sr.
A solid solution bulk obtained by mixing a mixed powder of rCO3 and CaCO3 at a predetermined composition ratio and heating the mixture at a temperature of 1500° C. was used as a target for vapor deposition using a laser.

Conventional examples include a multiple electron beam evaporation method equipped with a plurality of electron guns and a laser evaporation method using a single target. In the multiple electron beam evaporation method, Bi, Sr, Ca In the laser evaporation method, Bi2O
After mixing the respective oxides of 3, SrCO3, CaCO3 and CuO in a predetermined ratio, 8
A solid solution bulk obtained by calcining at a temperature of 50°C for 15 hours, repeating pulverization and mixing, and sintering again at a temperature of 850°C for 15 hours was used as a target.

[0029] The degree of vacuum during film formation was 5 x 10-4 in all cases.
Torr, and the composition ratio of the produced oxide film was determined by IPC spectroscopy.

[0030]

[Table 1]

As is clear from Table 1, the oxide film produced by the method of the present invention has a small deviation in composition from the target composition ratio. On the other hand, oxide films produced by multiple electron beam evaporation and laser evaporation have large compositional deviations.

[0032]

As shown in the examples, according to the method of the present invention, an oxide superconducting film having a target composition can be stably produced.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of an apparatus for carrying out the method of the present invention, and FIG. 2 shows the number of evaporated atoms and electrons when Cu metal and Bi oxide are used as evaporation materials and electron beam evaporation is performed. A graph showing the relationship between the beam heating output and Fig. 3 is a graph showing the relationship between the number of evaporated atoms and the electron beam heating time when Cu metal and Bi oxide are used as evaporation materials and are subjected to electron beam evaporation. 4 shows the relationship between the Ca/Sr composition ratio and the laser energy density when laser evaporation is performed using oxides containing Ca:Sr=2:1, 1:1, and 1:2 as targets. This is a graph showing.

[Explanation of symbols]

1 is the substrate, 2 is the film thickness monitor, 3 is the reaction gas nozzle, 4
5 is an evaporation material, 5 is an electron gun, 6 is a target for laser evaporation, 7 is a laser entrance, 8 is a laser beam, and 9 is a reaction chamber.

Claims (2)

[Claims] Claim 1: A metal or an oxide thereof containing one or more elements of Cu and Bi, and I
Using oxides containing one or more elements of group Ia elements, these vapor deposition materials are heated at a vacuum level of 10-3 Torr to 10-
A method for producing an oxide superconductor film having a perovskite structure or pseudo-perovskite structure on a substrate by vapor deposition in a vacuum atmosphere of 5 Torr, the method comprising: depositing one or more elements of Cu and Bi on a substrate; An oxide superconductor characterized in that the vapor deposition material of a metal or its oxide is deposited by an electron beam evaporation method, and the vapor deposition material of an oxide containing one or more elements of group IIa elements is deposited by a laser vapor deposition method. Membrane manufacturing method. 2. The method for producing an oxide superconducting film according to claim 1, wherein the deposition by electron beam evaporation and the deposition by laser evaporation are performed simultaneously.