JP2668532B2 - Preparation method of superconducting thin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a superconducting thin film. More specifically, the present invention relates to a method for producing a superconducting thin film which has excellent superconducting properties and can be formed at low temperature and has good crystallinity. 2. Description of the Related Art The superconducting phenomenon, which is said to be a phase transition of electrons, is a phenomenon in which the electrical resistance of a conductor becomes zero under specific conditions, indicating complete diamagnetism. That is, under the superconductivity, even if a current flows through the superconductor, there is no power loss, and a high-density current continues to flow forever. For example, if superconducting technology is applied to power transmission, a power transmission loss of about 7%, which is currently caused by power transmission, can be significantly reduced. In addition, for applications as electromagnets for generating high magnetic fields, for example, in the field of power generation technology, together with MHD power generation and electric conductors, technology that advantageously promotes the realization of nuclear fusion reactions, which are said to consume more power than the amount of power generated for development It is expected as. In addition, as a power for magnetic levitation trains, electromagnetic propulsion vessels, etc.
It is expected to be used for R, pion therapy, high-energy physics experiments, etc. Apart from the use in the large-sized apparatus as described above, the superconducting material is used for producing various other superconducting elements.
A typical example is an element using the Josephson effect in which a quantum effect macroscopically appears by an applied current when weakly joining superconducting materials. Since the energy gap of the superconducting material is small, the tunnel junction type Josephson device is expected as a switching device with extremely high speed and low power consumption. In addition, since the Josephson effect on electromagnetic waves and magnetic fields appears as an accurate quantum phenomenon, it is expected that the Josephson element is used as an ultrasensitive sensor for magnetic fields, microwaves, radiation, and the like. Furthermore, as the degree of integration of electronic circuits increases, the power consumption per unit area reaches the limit of the cooling capacity. Therefore, the development of superconducting elements has been demanded for ultra-high-speed computers. On the other hand, despite various efforts, the superconducting critical temperature Tc of the superconducting material could not exceed 23K of Nb ₃ Ge for a long time, but since the end of last year, (La, Ba) ₂ CuO ₄ or Sintered composite oxides such as [La, Sr] ₂ CuO ₄ have been discovered as superconducting materials having a high Tc, and the possibility of realizing non-low-temperature superconductivity has greatly increased. For these substances, 30-50K
A dramatically higher T _C is observed compared to the conventional one.
Further, the Y-Ba-Cu-O-based composite oxide superconducting couple is 90K to 1K.
It is expected to be a 00K class superconductor. Problems to be Solved by the Invention The production of the thin film of the composite oxide superconductor described above has conventionally been performed by high frequency sputtering, magnetron sputtering, molecular beam epitaxy, or the like. However, the composite oxide superconductor thin film produced by these methods has a significantly lower _{TC than} that of a sintered body having the same composition, and has a temperature and electric resistance at which superconductivity starts to show completely zero. The difference between the temperature and the temperature has become very large. Further, when a superconductor thin film is formed by the above method, it is difficult to apply the method to semiconductor wiring because the substrate is heated to about 600 ° C. or higher. Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a method for producing a composite oxide superconducting thin film having excellent superconducting properties at a low temperature. According to the present invention, at least one element α selected from Group IIa elements of the periodic table II, at least one element β selected from Group IIIa elements of the periodic table, Law table Ib, II
b, IIIb, IVa, and sputtering using an electron cyclotron resonance ion source as an oxide target containing at least one element γ selected from Group VIII elements to form a thin oxide film on a substrate. A method for producing a superconducting thin film is provided. The raw material target of the superconductor thin film is represented by the general formula: (α _1−x β _x ) γ _y O _z (where α, β, and γ are the elements defined above, and x is α
The atomic ratio of β to + β is 0.1 ≦ x ≦ 0.9, and y and z are 0.4 ≦ y ≦ 3 when (α _1−x β _x ) is 1.
It is preferable that the composite oxide has a composition represented by the following formula: 0, 1 ≦ z ≦ 5. The superconducting thin film produced by the method of the present invention is composed of a composite oxide superconductor, and the composite oxide is considered to be mainly composed of a perovskite-type or pseudo-perovskite-type oxide. As the element α in the periodic table IIa contained in the superconducting thin film produced by the method of the present invention, Ba, Sr, Ca, Mg, Be and the like are preferable, and for example, Ba and Sr can be mentioned. 10 to 80% of α is 1 or 2 selected from Mg, Ca and Sr
It can also be replaced by a seed element. The periodic table II
Group Ia elements β include Y, La, Sc, Ce, Gd, Ho, E
r, Tm, Yb, Lu, etc. are preferable, and can be, for example, Y, La. Of these elements β, 10 to 80% is one or two elements selected from lanthanoid elements other than Sc or La Can be replaced by The element γ is generally Cu, but may be partially replaced with another element selected from the periodic table Ib, IIb, IIIb, IVa, and VIII groups, for example, Ti, V, and the like. it can. The method for producing a superconducting thin film of the present invention comprises the steps of: preparing at least one element α selected from Group a elements of the periodic table II;
Targets an oxide containing at least one element β selected from Group Ia elements and at least one element γ selected from Group Ib, IIb, IIIb, IVa, and VIII elements The main feature is that sputtering using an electron cyclotron resonance ion source is performed to form an oxide thin film on a substrate. Conventionally, in order to produce the above composite oxide superconducting thin film,
High-frequency sputtering, magnetron sputtering, or MBE (Molecular Beam Epitaxy) has been used with a target oxide prepared by sintering or the like as a target. However, the composite oxide superconductor thin film produced by these methods had extremely reduced superconductivity when compared with a sintered body having a similar composition. In order to produce the above composite oxide superconductor thin film by the conventional method, it is necessary to heat the substrate temperature to about 600 ° C. or higher. If the substrate temperature is lower than that, the energy required for the reaction on the substrate surface is not supplied.If deposited at a low temperature, the above composite oxide does not form a thin film, or even if a thin film is formed, No. Therefore, in order to produce a composite oxide superconductor thin film by a conventional method, the substrate must be heated to the above-mentioned temperature. It is considered that oxygen deficiency or the like becomes inappropriate and superconductivity is deteriorated. Further, when the substrate is heated to the above-mentioned temperature, the semiconductor is destroyed by heat, so that it was impossible to apply the above-mentioned composite oxide superconductor thin film to wiring of a semiconductor element. In the method of the present invention, electron cyclotron resonance (ECR)
Since sputtering is performed using an ion source, the above-described composite oxide superconductor thin film can be formed without heating the substrate. The composite oxide superconductor thin film produced by the method of the present invention has good crystallinity, and the substrate temperature during film formation is about 200 to 300 ° C., so that oxygen defects in the crystal are also appropriate. Therefore, the composite oxide superconductor produced by the method of the present invention has excellent superconducting properties. Furthermore, when a composite oxide superconducting thin film is produced by a conventional method, the thin film has poor superconducting properties and may not exhibit superconductivity at all unless heat treatment is performed in an oxygen-containing atmosphere after film formation. However, the thin film obtained by the method of the present invention is
Since the crystallinity and oxygen deficiency are appropriate, it is not always necessary to perform the heat treatment that has been conventionally required. However, by performing the above-described heat treatment, the superconductivity is further improved. Next, the apparatus used to carry out the method of the present invention will be described. FIG. 1 is a schematic view of a sputtering apparatus having an electron cyclotron resonance ion source used for producing a composite oxide superconducting thin film by the method of the present invention. The apparatus shown in FIG. 1 is an electron cyclotron resonance (ECR) ion source comprising a chamber 1, a substrate 2 placed in the chamber 1, a target 3, a magnetic coil 5 mounted on the upper part of the chamber 1, and a rectangular waveguide 7. Be composed. The chamber 1 is provided with an exhaust hole 6 for evacuating the inside to a vacuum. Further, the ECR ion source is also provided with the introduction hole 4 for introducing the gas serving as the ion source, and the cooling water passage 9 is further provided.
And an ion extraction electrode 10 is provided. In the following, a procedure for realizing the method of the present invention using the apparatus of FIG. 1 will be described. However, the position of the target substrate can be set at another place, and is not limited to the arrangement of FIG. . The substrate 2 and the target 3 are mounted in the chamber 1, and the inside of the chamber 1 and the ECR ion source are evacuated to a vacuum. Desired atmospheric gas and ion source gas are introduced into the chamber 1 and the ECR ion source through the gas introduction hole 3 to a predetermined pressure. After flowing the cooling water, microwaves are introduced from the rectangular waveguide 7 and the magnetic coil 5 is energized to perform sputtering. Hereinafter, the present invention will be described in more detail with reference to examples. However, the following is an example of the present invention, and the technical scope of the present invention is not limited at all by the following disclosure. Example A composite oxide superconducting thin film was produced using the apparatus shown in FIG. Target 3, the La ₂ O _3, SrCO ₃ La, the molar ratio of Sr
LaSr ₂ Cu obtained by mixing at a ratio of 1: 2 and mixing CuO in a molar ratio of La: Sr: C of 10% by weight in excess of an amount of 1: 2: 3 and sintering at 925 ° C.
_{A 3} O ₇ sintered body block was used, and the (2) SrTiO ₃ single crystal was used as the film formation surface for the substrate 2. After attaching the target 3 and the substrate 2 described above, the inside of the chamber 1 is evacuated to a vacuum, and 5.0 × 10 ^-2 Torr of Ar gas is added.
1.0 × 10 ^-2 Torr O ₂ gas was introduced. Magnetic flux density 875 Gauss
The microwave frequency was 2.45 GHz. The substrate is heated to 300 ° C, the film formation rate is about 5Å / sec, and the film thickness is 1μ.
The film was formed until it reached m. For comparison, a composite oxide superconducting thin film was formed by magnetron sputtering under the same conditions using the same target and substrate, but no thin film was formed without heating the substrate. Then, a sample was prepared for measuring the resistance and current of the obtained thin film. In the sample for performing the resistance measurement, a pair of Al electrodes was further formed on both ends of the thin film formed on the substrate 2 by vacuum evaporation, and a lead wire was soldered to the Al electrode. The critical temperatures Tc and Tcf were measured by immersing the sample in liquid helium in a cryostat, cooling it to 8K, and then confirming that the sample showed superconductivity. And the temperature (Tc) at which the superconductivity of the sample disappears and exhibits the same electrical resistance as in the normal state was measured. The critical current density Jc was measured at 50K. Tc 69K Tcf 58K Jc 1.5 × 10 ⁵ A / cm ² As described above, according to the method of the present invention, excellent superconducting properties can be obtained without heating the substrate during film formation and without performing heat treatment after film formation. Can be produced. Therefore, the method of the present invention can also be applied to a case where a wiring of a semiconductor element or the like is formed of a superconductor. Effects of the Invention As described in detail above, according to the method of the present invention, a composite oxide superconducting thin film having excellent characteristics can be formed while keeping the substrate temperature lower than in the conventional method. This is possible for the first time by sputtering using an electron cyclotron resonance ion source unique to the method of the present invention. According to the present invention, it has become possible to use a complex oxide superconductor for wiring of a semiconductor element such as Si or GaAs. Further, the present invention is also applied to a field in which a superconductor is applied as a thin film element, for example, a switching element of Matisoo called Josephson element, a memory element of Anacker, and a superconducting quantum interferometer (SQUID). It is effective when used.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an example of a sputtering apparatus using an electron cyclotron resonance ion source used to carry out the method of the present invention. [Main reference numbers] 1... Chamber 2... Substrate 3... Target 4... Gas introduction hole 5... Magnetic coil 6. Exhaust hole 7. ... Plasma, 9 ... Cooling channel, 10 ... Ion extraction electrode

Continuation of front page    (56) References JP-A-60-50167 (JP, A)                 JP 62-83463 (JP, A)                 IEICE Technical Report SC               E87-2087 [137] (1987), pp49               −54, “Oxide ceramics superconducting film               Fabrication by puttering method "                 JAPANESE JOURNAL               OF APPLIED PHYSICS                 26 [4] (1987), pp L388-L               390, "Compositional               and Structural Ana               lyses for Optimizi               ng the Preparation                 Conditions of Sup               erconductor (La ▲ Lower 1               ▼ ▲ Lower- ▼ ▲ Lower x ▼ Sr ▲ Lower x ▼) ▲ Lower               y ▼ CuO ▲ 4 ▼ ▲ Lower- ▼ ▲ Lower δ ▼               Films by Sputterin               g "                 JAPANESE JOURNAL               OF APPLIED PHYSICS                 26 [4] (1987), pp L410-L               412 "High Tc Thin Fi               lms of (La ▲ lower 1 ▼ lower-▼               ▲ Lower x ▼ M ▲ Lower x ▼) ▲ Lower y ▼ CuO               ▲ Lower 4 ▼ ▲ Lower- ▼ ▲ Lower δ ▼ (M = S               r, Ba, Ca) Prepared b               y Sputtering "

Claims (1)

(57) [Claims] At least one element α selected from Group IIa elements of the periodic table, at least one element β selected from Group IIIa elements of the periodic table, Periodic Table 1b, IIb, IIIb, IVa, V
A target of an oxide containing at least one element γ selected from Group III elements is irradiated with ions generated by an electron cyclotron resonance ion source to perform sputtering, and the temperature is 200 ° C. or more and less than 600 ° C. A method for producing a superconducting thin film, comprising forming an oxide thin film on a substrate. 2. The raw material target of the superconducting thin film is represented by the following general formula: (α _1−x β _x ) γ _y O _z (where α, β, and γ are the elements defined above, and x is α
The atomic ratio of β to + β is 0.1 ≦ x ≦ 0.9, and y and z are 0.4 ≦ y ≦ 3 when (α _1−x β _x ) is 1.
2. The method for producing a superconducting thin film according to claim 1, wherein the oxide has a composition represented by the formula: 0, 1 ≦ z ≦ 5. 3. 3. The method according to claim 2, wherein the target is an oxide having a perovskite crystal structure. 4. 4. The target according to claim 1, wherein said target is obtained by mixing powders of oxides or carbonates of Ba, Y and Cu and sintering them at a temperature of 250 to 1200 ° C. Item 9. A method for producing a superconducting thin film according to any one of items. 5. The atomic ratio Y / (Y + Ba) of the above target is 0.06 to 0.94
The method for producing a superconducting thin film according to claim 4, characterized in that 6. The method for producing a superconducting thin film according to claim 5, wherein the atomic ratio Y / (Y + Ba) of the target is 0.1 to 0.4. 7. 4. The target according to claim 1, wherein the target is obtained by mixing powders of oxides or carbonates of Sr, La and Cu and sintering the mixture at a temperature of 234 to 1260 ° C. Item 9. A method for producing a superconducting thin film according to any one of items. 8. Atomic ratio Sr / (La + Sr) of the above target is 0.03 to 0.9
The method for producing a superconducting thin film according to claim 7, wherein the superconducting thin film is in the range of 5. 9. The atomic ratio Sr / (La + Sr) of the above target is 0.05-0.1
9. The method for producing a superconducting thin film according to claim 8, wherein: 10. The method for producing a superconducting thin film according to any one of claims 1 to 9, wherein the target is a powder of a sintered body. 11. The method for producing a superconducting thin film according to any one of claims 1 to 9, wherein the target is a block of a sintered body. 12. The method for producing a superconducting thin film according to any one of claims 1 to 11, wherein a plurality of targets are used. 13. 13. The method for producing a superconducting thin film according to claim 12, wherein one of the plurality of targets is made of Cu. 14． The one of the plurality of targets is made of an oxide of Cu.
A method for producing a superconducting thin film according to item. 15. The sputtering atmosphere, Ar, superconducting according to any one of the claims paragraph 1 - paragraph 14, which comprises a Kr or one or more inert gas and O ₂ of the Xe How to make a thin film.