JPH068502B2 - Method and device for producing oxide superconductor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an improved oxide superconductor thin film and an apparatus therefor.

(Prior Art) In recent years, oxide superconductors have been discovered, and the technical development thereof is proceeding at a rapid pace. It is generally known that the oxygen content of an oxide superconductor has a great influence on the characteristics of the superconductor, but it is extremely difficult to control the oxygen concentration in the superconductor.

For example, when forming a superconductor of BA ₂ YCu ₃ Ox (X may be zero), barium carbonate (BaCO ₃ ), yttrium oxide (Y ₂ O ₃ ), and copper oxide (CuO) are prescribed. The mixture was mixed at a ratio of 1, and then compression-molded to form a pellet, and the pellet was heated to 930 ° C. in an oxygen atmosphere furnace. This beret shows tetragonal crystals at this point. However, this sample, as it is, has a low oxygen content and does not exhibit superconducting properties. (Hereinafter, a tetragonal substance is referred to as a substance of this type).

In order to adjust the oxygen content to a proper value to obtain the best superconducting material, the furnace must be annealed in the oxygen atmosphere for a day from 930 ° C. By doing so, an orthorhombic crystal is formed and superconducting characteristics are exhibited at a temperature of around 90 K or less. (Hereinafter, the orthorhombic substance is referred to as this type of substance).

However, in order to obtain good superconducting properties, it is not possible to mass-produce industrially if it is necessary to cool the furnace in an oxygen atmosphere for one day as described above.

BG Bagley et al. (Appl / Phys. Lett. 51 (1987))
In P.622-P.624), it is shown that by subjecting a tetragonal substance that does not exhibit superconducting properties to an orthorhombic system and exhibiting superconducting properties, high-frequency discharge treatment in an oxygen atmosphere is performed. ing.

However, even in this case, 2 is required to obtain 90K-class superconducting properties.
The above-mentioned treatment for 85 hours is required, and this is not industrially usable as described above.

S. Minomo et al. (Jpn. J. Appl. Phys. 27 (1988) PL
411-P.L413), ECR discharge treatment, 60K
It is shown that the superconducting material of the class is improved to 90K class by the treatment at 400 ° C. for 30 minutes, but the superconducting characteristic was improved by treating the sample which originally had the superconducting characteristic. However, the superconducting property is not generated by changing the crystal structure of a tetragonal material that does not exhibit the superconducting property.

Slightly, 35th Applied Physics Lecture in 1985 29a-
At x-5, Jianglong et al. succeeded in locally changing the tetragonal material to the orthorhombic material by oxygen ion implantation and laser annealing. It was limited and could not be applied to mass production of an extremely large area.

An example of using a vapor deposition method for producing a superconductor is a paper by B. Oh (Appl. Phys. Lett. 51.852 (1987)).

This is yttrium, while introducing oxygen into the reaction chamber,
Three kinds of metals, barium and copper, are simultaneously deposited on the surface of the substrate by using an electron beam evaporation source to form a thin film. Then, this thin film is heated at 650 ° C. for 3 to 6 hours, and at 750 ° C. for 1 hour,
Alternatively, a superconducting thin film is obtained by annealing in an oxygen atmosphere at 850 ° C. for 1 hour and then gradually cooling in an annealing furnace. Therefore, in this case as well, there is no change in that it takes a long time to manufacture.

(Problems to be Solved by the Invention) As described above, in order to obtain an orthorhombic substance having a good superconducting property, a long-time treatment is required regardless of the manufacturing method. However, all the conventional methods have problems in mass productivity.

(Object of the invention) The present invention solves this problem, does not require annealing such as gradual cooling from high temperature, and is a novel manufacturing method capable of producing an oxide superconductor thin film having good superconducting properties in a short time. And its device.

(Means for Solving Problems) The present invention relates to an oxygen-based active species prepared by high-temperature non-equilibrium plasma or high-temperature equilibrium plasma on the surface of a substrate during the production of an oxide superconductor on the surface of the substrate by a vacuum deposition method. The above object is achieved by a manufacturing method of irradiating with.

Especially when the oxide superconductor has a composition of BA ₂ YCu ₃ O _x , the method of the present invention showed good results.

An apparatus for implementing the method of the present invention includes a substrate, a temperature adjusting mechanism for adjusting the temperature of the substrate, and an evaporation source for evaporating an element constituting the oxide superconductor or a compound containing the element. Chamber and a discharge chamber for producing a high temperature non-equilibrium plasma or a high temperature equilibrium plasma are connected so as to be communicable with each other through a valve, or a differential exhaust chamber provided with an orifice communicating with each of the two chambers. The adopted device is adopted.

(Function) The high temperature non-equilibrium plasma or the high temperature equilibrium plasma generates a large amount of atomic oxygen-based active species in the oxygen plasma.
This active species has a large diffusion coefficient during fixation and has a property of rapidly diffusing at low temperature. By irradiating the surface of the oxide superconductor or the raw material of the superconductor being produced with such an oxygen-based active species by the vapor deposition method, the oxide superconductor having excellent superconducting properties or the oxide superconducting raw material containing a large amount of oxygen Can be created on the spot.

The sample does not need to be annealed and slowly cooled, or at least the time can be significantly reduced.

(Examples) The present invention is the applicant of the present application, and Japanese Patent Application No. 61-0
No. 69646 "Surface treatment method and apparatus" is used for producing an oxide superconductor which was not generally known at the time of the application.

The “LTE plasma” in the specification of the above patent application corresponds to the “high temperature non-equilibrium plasma or high temperature equilibrium plasma” in the present specification.

FIG. 1 shows a schematic front sectional view of an apparatus according to an embodiment of the present invention. Reference numeral 10 is a deposition chamber made of stainless steel, and a valve 18 is connected to an exhaust device in the direction of arrow 16. The substrate holder 12 holding the substrate 15 is mounted on the
It is possible to raise the temperature above ° C. The temperature of the substrate holder 12 is measured by a thermocouple 82, and the electric power of the lamp 81 is adjusted by P, PI, PID control or ON / OFF control using a relay by using a temperature controller (not shown) and a thyristor unit together. When necessary, a cooling mechanism such as water cooling is also used. 83 is a vacuum gauge.

Reference numeral 21 denotes a discharge tube, which is a double tube of quartz glass, and has a structure in which water is flowed between the double tubes to be water-cooled. Reference numerals 26 and 26 'indicate the flow of cooling water.

Reference numeral 22 is a coil made of a copper pipe, and the inside of the pipe is water-cooled (not shown). One of the coils 22 is grounded and the other is connected to a high frequency power supply 24 through a matching circuit 23. The frequency of the high frequency power supply is 13.56 MH
z.

The differential exhaust chamber 30 made of stainless steel and the discharge tube 21 made of quartz glass are joined together by using a rubber O-ring (not shown). Reference numeral 17 denotes a pressure gauge, which measures the pressure in the differential exhaust chamber 30, and the adjustment to make the pressure constant is performed by adjusting the valve 19 and an exhaust device connected to the tip thereof.

As described in Japanese Patent Application No. 61-096646,
When power is injected from the high frequency power supply 24 into the coil 22,
At first, a high-frequency glow discharge that spreads widely in the discharge tube 21 occurs. When high power is injected, a high temperature non-equilibrium plasma or a high temperature equilibrium plasma 27 locally pinched inside the coil 22 is generated. (The high-temperature non-equilibrium plasma or the high-temperature non-equilibrium plasma is described in detail in Hideo Sannohe et al., "Vacuum," Vol. 31, No. 4, (1988) P271-P278, and the references cited therein.) Alternatively, the high-temperature equilibrium plasma has a very high emission intensity as compared with the high-frequency glow discharge, and therefore a large amount of active species is generated, but there are many atomic active species. In addition, it has a characteristic that the discharge impedance is significantly reduced electrically.

A glow discharge plasma is observed around the high temperature non-equilibrium plasma or the high temperature equilibrium plasma 27 depending on the pressure (on the side of a pressure lower than around 10 Torr), and in the active species 28 in the differential exhaust chamber 30, high temperature non-equilibrium plasma is observed. The active species produced by the equilibrium plasma or the high temperature equilibrium plasma 27 include the active species produced by the glow discharge.

Oxygen-based active species are passed through the differential exhaust chamber 30 and the deposition chamber 10
The lifetime of the active species when transported to
JM Cook's paper Solid State Technology / Japan version May (19
87) Details on P.28-P.33 and this reference. They are discussing the lifetime under the oxygen atom generated by microwave discharge, and show that the lifetime is 90% or more even 50 cm behind the plasma if the flow velocity is appropriate.

As described above, oxygen is supplied from a cylinder (not shown) to a pressure reducing valve,
It is introduced from the direction of arrow 25 through the flow rate controller and is exhausted in the direction of arrow 29 through the differential exhaust chamber 30 and the valve 19. The pressure reading of the differential exhaust chamber 30 is read by the pressure gauge 17.
The fine adjustment to make the pressure constant is made by adjusting the conductance of the valve 19. As an exhaust pump connected to the arrow 29,
It uses a roots pump and an oil rotary pump. Most of the active species 28 in the differential exhaust chamber 30 is exhausted through the valve 19 in the direction of the arrow 29, but a part of the active species 28 is ejected into the deposition chamber 10 through the orifice 50.

FIG. 2 is a view of the inside of the apparatus of FIG. 1 viewed from the arrow AA ′. The electron beam evaporation sources 41, 42, 43 are the second
As shown in the figure, they are arranged in rotational symmetry. Each is C
It is an evaporation source of u, Ba, and Y.

On the other hand, the structure of each electron beam evaporation source 41, 42, 43 is as shown in FIG. The electrons emitted from the filament (electron source) 63 heated by the current from the filament power source 65 are accelerated by the acceleration electrode 64 having a higher potential than the filament 63 to become the electron beam 67. Then, the electron beam 67 is deflected by the magnet 68 and the deflection magnetic field 69
Is deflected and the surface of the substance to be evaporated contained in the crucible 61 mounted on the base 62 cooled with water by a cooling pipe (not shown) is bombarded to heat and evaporate it. Copper, barium, and yttrium, which are evaporation targets, are put into the crucible 61.

FIG. 4 is a view of FIG. 1 viewed from the arrow BB ′. The cup-shaped film thickness monitors 71, 72, 73 are arranged corresponding to the respective evaporation sources. The film thickness monitor 71 shows only the evaporation amount from the electron beam evaporation source 41, and the film thickness monitor 72 shows the electron beam evaporation source 42. From the electron beam evaporation source 43, and the film thickness monitor 73 measures only the evaporation amount from the electron beam evaporation source 43.

The pressure in the deposition chamber 10 is controlled by the pressure gauge 83, and the adjustment for keeping the pressure constant is performed by adjusting the conductance of the valve 18.

With the apparatus of this example, first, a thin film was prepared in a state where no electric power was applied to the coil 22 from the high frequency power supply 24, that is, in a state where high temperature non-equilibrium plasma or high temperature equilibrium plasma was not generated.

Oxygen is introduced into the differential exhaust chamber 30 through the discharge tube 21 in the direction of arrow 25. The conductance of the valve 19 is adjusted so that the pressure of the differential exhaust chamber 30 becomes 1 Torr when the flow rate of oxygen is set to 200 sccm. Oxygen enters the deposition chamber 10 from the differential exhaust chamber 30 through the orifice 50. Then, the conductance of the valve 16 is adjusted so that the pressure in the deposition chamber 30 becomes 10 ⁻⁴ Torr. SrTiO ₃ was used as the material of the base 15. Then, the temperature of the base 15 is set to 60
The temperature was set to 0 ° C., and yttrium, barium, and copper were evaporated from the electron beam evaporation sources 41, 42, and 43 to form a thin film on the surface of the substrate 15.

The composition ratio of yttrium, barium, and copper in the thin film is 1:
It became 2: 3, and the thin film formation rate was 600Å / min.
The deposition rates of yttrium, barium, and copper were adjusted so that

Then, the vapor deposition was stopped when the thickness of the thin film reached about 10 μm, and the substrate 15 was taken out of the deposition chamber 10 and left in the atmosphere. The thin film in this case had a composition ratio of yttrium, barium, and copper of 1: 2: 3, but did not exhibit superconducting properties because oxygen was insufficient.

Next, electric power from the high frequency power supply 24 is applied to the coil 22 to generate high temperature non-equilibrium plasma or high temperature equilibrium plasma to generate oxygen-based active species 28, and a thin film is formed under the same conditions as described above. The thin film showed excellent superconducting properties of 90K class.

Next, not only Ba ₂ YCu ₃ O _x but also other Y and Ln-based elements are used as the raw material of the superconductor, that is, MBa ₂ Cu ₃ O _x, where M = Y, Ln (= La, Ce , Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, Lu) and other stoichiometric compounds having the same elemental composition or Bi-type Bi ₂ Ca ₂ Sr ₂ Cu ₃ O _x T system-T ₂ Ba ₂ Ca ₂ Cu ₃ O _x , other stoichiometric compounds having the same elemental composition,
Other compounds having various stoichiometry with various elemental constitutions were also tried, but in any case, the method of the present invention was effective.

The apparatus for generating high temperature non-equilibrium plasma or high temperature equilibrium plasma used in the method of the present invention is not limited to the structure shown in FIG. The apparatus of various structures described in the above-mentioned Japanese Patent Application No. 61-096646, a document written by the inventor of the present application, "Vacuum", Vol. 31, No. 4 (1988), P. 271-P. 278, and others. The present invention can obtain the same effect by using the device of each cited document.

In the present embodiment, the crucible 61 uses an element such as copper, barium, or yttrium as the substance to be evaporated, but a compound containing the element may be used. For example, oxides such as cupric oxide containing copper, barium carbonate containing barium, and yttrium oxide containing yttrium may be used.

FIG. 5 shows another embodiment. Instead of the differential exhaust chamber 30 of FIG. 1, a transport pipe 31 and a valve 32 for oxygen-based active species are used.
Is provided. In this configuration, the differential pumping system can be omitted as appropriate.

In the above description, oxygen was used as the oxidizing gas, but it was found that the same effect can be obtained by using a gas such as ozone or nitrous oxide.

Furthermore, it has been found that the deposition conditions are not limited to the above-mentioned pressure, oxygen flow rate, etc., and that a wide range of conditions can be selected. However, when there is a shortage of oxygen-based active species, it has not been possible to produce oxide superconductors (those exhibiting a certain level of superconducting properties), and superconductor raw materials (possibly a superconductor as a composition, but still not available) Those that do not show superconducting characteristics)
However, a superconducting property can be imparted to such a film in a relatively short time by subjecting such a film to a subsequent step of irradiating the film with the oxygen-based active species. .

(Effects of the Invention) As described above, according to the method and apparatus of the present invention, the active species of oxygen produced by the high-temperature non-equilibrium plasma or the high-temperature equilibrium plasma are used, so that the vapor deposition method can be performed for an extremely short time. In addition, the oxide superconductor or the superconductor raw material thereof can be produced.

[Brief description of drawings]

FIG. 1 is a schematic front sectional view of an apparatus of the present invention for carrying out the method of the present invention. FIG. 2 is a view of the interior of the deposition chamber taken along the line AA '. FIG. 4 is a view likewise seen from the arrow BB ′. FIG. 3 is a schematic front sectional view of an evaporation source. FIG. 5 is a view similar to FIG. 1 of another embodiment. 10 ... Deposition chamber, 12 ... Substrate holder, 15 ... Substrate, 21
... discharge tube, 27 ... high temperature non-equilibrium plasma or high temperature equilibrium plasma, 28 ... active species, 30 ... differential exhaust chamber.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication H01B 12/06 ZAA 8936-5G 13/00 HCU Z 7244-5G

Claims (4)

[Claims] 1. Oxidation characterized by irradiating an oxygen-based active species produced by high-temperature non-equilibrium plasma or high-temperature equilibrium plasma on the surface of a substrate during the production of an oxide superconductor by a vacuum deposition method. Method for manufacturing superconductors. 2. The oxide superconductor is Ba ₂ YCu ₃ O _x.
The method for producing an oxide superconductor according to claim 1, wherein the oxide superconductor has the following composition. 3. A substrate on the surface of which an oxide superconductor is to be deposited, a temperature adjusting mechanism for adjusting the temperature of the substrate, an element constituting the oxide superconductor or a compound containing the element, or Preparation of an oxide superconductor characterized in that a deposition chamber containing an evaporation source for evaporating a mixture, and a discharge chamber for producing high temperature non-equilibrium plasma or high temperature equilibrium plasma are connected so as to be communicable via a valve. apparatus. 4. A substrate on which an oxide superconductor is deposited, a temperature adjusting mechanism for adjusting the temperature of the substrate, an element constituting the oxide superconductor or a compound containing the element. A deposition chamber containing an evaporation source for evaporation and a discharge chamber for producing high-temperature non-equilibrium plasma or high-temperature equilibrium plasma are coupled via a differential exhaust chamber having an orifice communicating with both chambers. A device for producing an oxide superconductor.