JPH06287100A - Method for forming superconducting oxide thin film containing rare earth element - Google Patents

Abstract

(57) [Summary] (Modified) [Objective] To provide a method capable of forming a (Ln) ₂ CuO ₄ type superconducting oxide thin film having high orientation, uniformity, small porosity and high critical current density. To do. [Structure] Using a three-pole DC magnetron sputtering device 1, a rare earth element or an alloy between them is targeted, and a copper element is targeted.
A metal multilayer film is formed on the substrate by spattering, and then an oxidative heat treatment is performed in an oxidizing atmosphere. The rare earth element or the alloy between them and the copper element may be sputtered at the same time.
Further, by using the three-pole type DC magnetron sputtering apparatus 1, a rare earth element or an alloy between them is used as a target, and a copper element is used as a target to simultaneously sputter them, and at the same time, an oxygen gas or neutral oxygen beam source is used. It is also possible to supply activated oxygen gas onto the substrate 4 to oxidize the metal particles to form a superconducting oxide thin film on the substrate 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a superconducting oxide thin film containing a rare earth element, and more specifically to a superconducting oxide thin film containing a rare earth element, which has high orientation, is smooth, and has excellent superconducting properties. The present invention relates to a forming method.

[0002]

2. Description of the Related Art Conventionally, superconducting materials have been limited to elements such as Nb and Ge, and metals such as Nb-Ge alloys. These are high density and rich in stretchability, but have a critical temperature Tc
Since it is as low as 23K or less, a large amount of expensive liquid helium must be used as a coolant when using it. Therefore, the superconducting machine and the sensor using them are large and expensive, and there is a problem in economic efficiency.

In recent years, Tc has been higher than the temperature of liquid nitrogen, Y-Ba-
The oxide superconducting ceramics such as Cu-O type and Bi-Pb-Sr-Ca-Cu-O type have been discovered, and the development of superconducting application technology has been activated.

However, since these systems are only hole-doped type (P-type superconductor), there are restrictions in constructing an electronic device. Further, the oxide superconducting ceramics have a problem that it is difficult to reproduce predetermined superconducting properties because the superconducting properties are greatly affected by the oxygen content and the water content.

[0005]

On the other hand, the so-called (Ln) ₂ CuO ₄ type oxide containing rare earths (Ln: rare earth element) has the following characteristics and is an application technique in the field of weak electric power. Is expected to be developed.

Among the high Tc superconducting oxides containing copper, (Ln)
_{The 2} CuO ₄ type is a general formula of (Ln ₁ , Ln ₂ , A) ₂ CuO _{4 —} z (where Ln ₁ and Ln ₂ are rare earth elements, and A is an alkali or alkaline earth metal element). It is represented by. The crystal structure has the simplest structure in which one unit of Cu-O is contained in the unit cell. Tc is 20 to 40K, which is lower than that of Y-based and Bi-based superconducting oxides, but is superior to that of metallic superconductors.

There are three kinds of compounds represented by this general formula. One is a K ₂ NiF ₄ type (T type) having a Cu coordination number of 6, and (La, Ba) ₂ CuO ₄ belongs to this, and is a superconductor having holes as carriers. . The second is a T'type, which has a Cu coordination number of 4, which is also called an electron-doped type, and is a superconductor having electrons as carriers. The third one is called T "type, and it has C
The coordination number of u is 5, which is a superconductor having holes as carriers.

As described above, (Ln) ₂ CuO ₄ type crystals are higher than the Tc of a metal or alloy superconductor, and there are two types: electron-doped type (n-type) and hole-doped type (p-type). The combination of the two has the advantage of doubling the types of electronic devices. Therefore, it is expected that the (Ln) ₂ CuO ₄ type oxide superconductor will be applied to weak electric fields such as magnetic sensors, infrared detectors, electromagnetic wave detectors, and ultra-high speed computer devices.

However, the (Ln) ₂ CuO ₄ type oxide is
Unlike the metal-based superconducting material, the flow direction of the superconducting conductor has a specific relationship with the crystal plane, and it is necessary to orient it with respect to the substrate.

Further, when forming a thin film, it is difficult to obtain a thin film having a desired composition by a conventional thin film synthesizing technique. Furthermore,
The oxide thin film is generally an insulator, and charge-up occurs during film formation, making it difficult to obtain a smooth thin film.

Under the circumstances as described above, it has been earnestly desired to develop a method for obtaining a thin film which is smooth, highly oriented and has a high current density.

[0012]

In view of the above-mentioned circumstances, the present invention has a high orientation and uniformity, and therefore has a low porosity and a high critical current density (Ln) ₂ CuO ₄ type superconducting oxidation. It is an object of the present invention to provide a method capable of forming an object thin film.

[0013]

As a result of earnest studies on the measures for solving the above-mentioned problems, the present inventor has formed a metal multilayer film by using the triode type DC sputtering method and has been used in various atmospheres. Contains rare earths by heat treatment (L
It has been found that a thin film of n) ₂ CuO ₄ type superconducting oxide can be formed.

That is, according to the present invention, a rare earth element or an alloy between them is used as a target and a copper element is used as a target by using a three-pole type DC magnetron sputtering apparatus, and these are sequentially sputtered to form a metal on a substrate. The gist is a method for forming a superconducting oxide thin film containing a rare earth element, which is characterized in that a multilayer film is formed and then an oxidative heat treatment is performed in an oxidizing atmosphere.

Further, according to another aspect of the present invention, a rare earth element or an alloy between them is used as a target and a copper element is used as a target to simultaneously sputter them by using a three-pole type DC magnetron sputtering apparatus, and to mix them. The gist is a method for forming a superconducting oxide thin film containing a rare earth element, which comprises forming a metal film on a substrate and then performing an oxidative heat treatment in an oxidizing atmosphere.

Another embodiment of the present invention uses a three-pole type DC magnetron sputtering apparatus, a rare earth element or an alloy between them is a target, and a copper element is a target to sputter them at the same time, and at the same time, oxygen is used. Formation of a superconducting thin film containing a rare earth element characterized by forming a superconducting oxide thin film on a substrate by supplying activated oxygen gas from a gas or a neutral oxygen beam source onto a substrate to oxidize metal particles The method is the gist.

The present invention will be described in more detail below.

[Action]

The characteristics of the triode DC sputtering method used in the forming method of the present invention are as follows.

First, unlike the conventional sputter particle source, most of the particles sputtered by Ar ions in the triode DC sputter particle source are neutral particles, and the charge-up during film formation occurs. Since it is basically absent, a smooth thin film can be obtained.

Next, in the conventional sputtering apparatus, since the voltage is applied between the target and the substrate, the amount of sputtered particles cannot be arbitrarily controlled for each composition. On the other hand, since a plurality of triode DC sputter particle sources are installed in the synthesizer, a plasma voltage for each particle source,
Since the current, the target voltage, and the current can be controlled independently, there is an advantage that a thin film having a desired composition can be formed.

As the target used in the method of the present invention, a rare earth element, an alloy composed of two or more kinds thereof, and a copper element can be generally used. Since the rare earth element is easily oxidized by itself, it is preferable to use an alloy in which two or more kinds of elements are melted. This makes it possible to increase the chemical durability and make it a good target for DC sputtering. For example, when Nd element and Ce element are mixed to form an Nd-Ce alloy in a non-oxidizing atmosphere and it is used as a target, it becomes a stable sputter particle source.

The substrate used in the present invention is not particularly limited. Quartz glass, alumina, zirconia, stabilized zirconia, magnesia (MgO), strontium titanate (SrTiO ₃ ) and the like are suitable, but in order to obtain an oriented or single crystal thin film, a specific crystal plane was cut out. A single crystal of MgO and SrTiO ₃ is preferable.

As a procedure of sputtering, first, direct current sputtering is performed by using argon ions as a target of a rare earth element alone or an alloy between rare earth elements. Then
Similarly, direct current sputtering with copper element as the target,
A metal multilayer film is formed on the substrate. Alternatively, the copper element may be sputtered first, and then the rare earth element or an alloy between the rare earth elements may be sputtered.

As another method, the rare earth element (or alloy thereof) and the copper element may be simultaneously sputtered from two or more sputter particle sources.

Further, a neutral oxygen beam source is installed in the synthesizer by the triode direct current sputtering method, and the metal particles deposited on the substrate by being knocked out from the triode type DC magnetron sputtered particle source are atomized. Can be oxidized at the level. Since the electrically neutral oxygen that has been activated is supplied from the oxygen beam source, the oxidation efficiency during film formation is high and charge-up obstacles are avoided, so a thin film with a smooth and small porosity is obtained. Can be obtained. Alternatively, as a simple method, a metal pipe with holes may be installed around the substrate, and ordinary oxygen may be blown out from the holes to oxidize the metal film.

The sputtering conditions are not particularly limited, the degree of vacuum is generally 10 ⁻⁷ to 10 ⁻⁴ Torr, and the substrate temperature is from room temperature to 1000 ° C.

The thin film produced under the above conditions is subjected to oxidative heat treatment in an electric furnace in an oxidizing atmosphere such as air. If the heat treatment is performed at a high temperature from the beginning, for example, 900 to 1100 ° C., the metal film evaporates and disappears. That is, first, after oxidizing at a relatively low temperature of 600 to 850 ° C. for 5 to 20 hours to form a metal film as an oxide,
A high-quality superconductor can be obtained by performing heat treatment in a higher temperature range of 900 to 1200 ° C. for 1 to 3 hours in the same atmosphere to improve crystallinity and orientation. However, if excessive oxidation progresses in the above-mentioned oxidation process, it becomes a semiconductor, and in that case, after the oxidation treatment, heat treatment is performed in a reducing atmosphere such as hydrogen gas or in a vacuum (10 ⁻⁷ to 10 ⁻³ Torr).

Since the produced thin film is formed by a three-pole type DC magnetron sputtered particle source having good controllability, the porosity is small, the deviation from the desired composition is small, and the desired film thickness is obtained. The surface is smooth, and the degree of orientation is good and good. Therefore, it is suitable for use in high-sensitivity magnetic, infrared, and microwave sensors, and high-speed computer devices.

Next, examples of the present invention will be described.

[0030]

【Example】

Using the synthesizer shown in FIGS. 1 and 2, 3
With-pole DC magnetron sputtering method (Nd _{0. 925}
Ce _{0. 075)} was prepared in the superconducting oxide thin film ₂ CuO ₄ composition.

The thin film production conditions were a vacuum degree of 10 ^-6 Torr, an emitter current of 40 A, a plasma current of 4.0 A, and a target voltage of 100 to 200V. Nd for target
-Ce alloys and copper metal, the substrate was used SrTiO ₃ (100 plane).

First, from one sputter particle source, Nd
A —Ce alloy was sputtered to form a metal film on the substrate, and then Cu was sputtered thereon to form a metal multilayer film. Then, the film was subjected to a two-step oxidation treatment. As a first step, the above membrane was exposed to 1 ° C in air at 800 ° C.
After being oxidized for 5 hours, as a second step, in order to improve the crystallinity of the film crystal, it was heat-treated in air at 1100 ° C. for 1 hour to obtain a C-axis oriented film (FIG. 3). It can be seen from this figure that it has a high C-axis orientation.

Then, this film was vacuumed at 10 ^-6 Torr, 9
Heat treatment was carried out at 00 ° C. for 5 hours to develop superconductivity. From the measurement of the temperature dependence of the electrical resistance, the critical temperature Tc of this film
(Zero) = 16K (Fig. 4).

[0035]

As described above, according to the present invention,
Since high-purity (99.99 to 99.9999%) metals and alloys can be used as targets, superconducting oxide thin films containing high-purity rare earth elements can be prepared, and reproducible electromagnetic properties are realized. be able to.

Further, the three-pole DC magnetron sputtering apparatus is equipped with a multi-source particle beam source, and the target is independent for each composition of the superconducting oxide containing a rare earth element, so that a thin film having a desired composition can be formed. Can be made.

Further, in the three-pole type DC magnetron particle source used, since electrically neutral particles are emitted from the target, charge-up at the time of forming a thin film on the substrate can be avoided, and it is smooth and has pores. A good quality thin film with a small rate can be produced. Such a thin film is suitable as an element for electronic devices.

Further, according to the present invention, a highly oriented thin film of a superconducting oxide containing a rare earth element can be easily produced, and it is suitable for producing a high performance electronic device element by utilizing this.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a three-pole type DC magnetron sputtering thin film synthesizing apparatus suitable for carrying out the method of the present invention.

FIG. 2 is a cross-sectional view of a three-pole type DC magnetron sputtered particle source which is a central part of the apparatus of FIG.

[Figure 3] formed in Example of the present invention _{(Nd 0. 925 Ce 0.} 075)
FIG. 3 is an X-ray diffraction pattern of a thin film having a composition of ₂ CuO ₄ —z.

[4] was formed in the embodiment of the present invention _{(Nd 0. 925 Ce 0.} 075)
FIG. 3 is a correlation diagram showing temperature dependence of electric resistance of a thin film of ₂ CuO ₄ _z composition.

[Explanation of symbols]

 1 3-pole DC magnetron sputter particle source 2 Same as above Shutter mechanism 3 Activated neutral oxygen beam source 4 Substrate 5 Substrate shutter 6 Substrate heating mechanism 7 Optical thermometer 8 Vacuum container 9 Vacuum gauge 10 Quadrupole gas mass spectrometer 11 Peep Window 21 Target 22 Magnet 23 Anode 24 Filament 25 Gas Insert 26 Target Control Mechanism 27 Automatic Ignition Mechanism 28 Plasma Discharge Mechanism 29 Filament Control Mechanism 30 Argon Gas Cylinder 31 Anode Protective Frame

Claims (4)

[Claims] 1. A metallic multi-layer film is formed on a substrate by sequentially sputtering a rare earth element or an alloy between them as a target and a copper element as a target using a three-pole DC magnetron sputtering apparatus. Then, a method for forming a superconducting oxide thin film containing a rare earth element, characterized by performing an oxidative heat treatment in an oxidizing atmosphere. 2. A three-pole type DC magnetron sputtering apparatus is used to target a rare earth element or an alloy between them as a target, and also a copper element as a target, and simultaneously sputter them to form a mixed metal film of both on a substrate. Make,
Next, a method for forming a superconducting oxide thin film containing a rare earth element, characterized by performing an oxidative heat treatment in an oxidizing atmosphere. 3. A rare earth element or an alloy between them is used as a target, and a copper element is used as a target to sputter them at the same time by using a three-pole type DC magnetron sputtering apparatus, and at the same time, oxygen gas or neutral oxygen is used. A method of forming a superconducting thin film containing a rare earth element, comprising supplying activated oxygen gas from a beam source onto a substrate to oxidize metal particles to form a superconducting oxide thin film on the substrate. 4. The composition of the superconducting oxide thin film containing a rare earth is represented by the general formula (Ln ₁ , Ln ₂ , A) ₂ CuO _{4 —} z (where the composition of each component is Ln ₁ : (1-xy)). , Ln ₂ :
x, A: y, Cu: 1.00, oxygen: (4-z). Here, Ln ₁ and Ln ₂ are rare earth elements, and Sc, Y and L
a, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, E
Represents r, Tm and Lu, A is an alkaline earth element and represents Mg, Ca, Sr and Ba. The composition ranges of x, y and z are 0 <x ≦ 0.5, 0 ≦ y ≦ 0.5, 0 <x + y ≦ 0.
5, 0 ≦ z ≦ 0.1. The method according to claim 1, 2 or 3, wherein the method comprises