JPH0416595A - Production of oxide superconducting film - Google Patents

Abstract

PURPOSE:To obtain a superconducting film with the conventional evaporating cell by heating metallic complexes contg. metallic elements as starting materials in a high vacuum, depositing evaporated molecules as beams on a substrate and forming a single crystal film on the substrate. CONSTITUTION:Metallic complexes or organometallic compds. contg. the constituent metallic elements of an oxide superconducting material are used as evaporating sources. These sources each having a lower evaporation temp. than the metal are evaporated by heating in a high vacuum. Evaporated molecules are deposited as beams on a substrate and a single crystal film of the oxide superconducting material is formed on the substrate to obtain a superconducting film.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an oxide-based superconducting film, and in particular,
This invention relates to improvements in the manufacturing method of oxide-based superconducting films using the BE method (molecular beam epitaxy method).

[Prior art] La-based (La-Ba-Cu-0), Y-based (Y-Ba-
Cu-0), Bi-based (Bi-8r-Ca-Cu
-0) and TN-based (Tj!-Ba-Ca-Cu-0
) and other oxides are conventional alloy-based and intermetallic compound-based materials, such as Nb-Ti-based and Nb-Ti-based
Compared to b5Sn-based superconducting materials, its critical temperature (T
c) is high, and is expected to be applied to various uses.

As a premise for such applications, in order to manufacture superconducting coils, superconducting elements, etc. using oxide-based superconducting materials,
It is necessary to establish wire rod and thin film technology,
Among these, for use in electronic materials such as Josephson devices, it has become important to establish a manufacturing technology for thin films that can easily create weak bonds between superconductors, can be easily microfabricated, and can be highly integrated. .

Conventionally, (a) sputtering method, (b) CVD method, and ()X) vapor deposition method are known as main methods for producing thin films.

Method (a) above applies a voltage between the target and the substrate in a gas atmosphere such as Ar, causes gas ions generated by electron collisions to collide with the target, and the ejected atoms adhere to the substrate. This method has the advantage that since the main mechanism is not a thermal process, it is easy to make a thin film of a high melting point material and a film with strong adhesion to the substrate can be obtained. Also above (
The method (b) is a method in which raw materials are supplied in the form of compounds such as halides and hydrides, and a thin film is grown by reaction on a high-temperature substrate, and has the advantage of extremely high growth rate and mass production. Furthermore, in the method (c) above, an evaporation source is set up for each component, and the evaporation rate is independently controlled while simultaneously evaporating and combining on the substrate, which makes it easy to control the composition and achieves high purity. It has the advantage that a thin film can be obtained.

However, in the methods (a) to (c) above, ■ controlling the growth film thickness at the atomic layer level, ■ obtaining a surface with smoothness on the atomic scale, and ■ controlling the effects of interdiffusion of atoms. It has the disadvantage that it is difficult to prevent deterioration of superconducting properties and (1) to accurately control the composition.

In recent years, as a method to overcome these difficulties, the MBE method (Molecular Beam Epitaxy:
The production of thin films using molecular beam epitaxy (molecular beam epitaxy) is being considered.

In this method, the material to be grown is heated in a high vacuum to form a beam of evaporated molecules of each element and evaporated toward the substrate, thereby depositing a single crystal on the substrate. Theoretically, the mean free path for molecular collisions in ultra-high vacuum is longer than at normal pressure, so vaporized molecules can reach the substrate without colliding with other molecules.

This MBE method overcomes all of the above-mentioned difficulties, and has the advantage that it is possible to observe the crystal by electron beam diffraction, etc. during crystal growth, and to perform selective growth using a vapor deposition mask. have

[Problems to be Solved by the Invention] As mentioned above, when manufacturing an oxide superconducting film by the MBE method, it is necessary to control the composition with high precision and form a monoatomic layer by controlling the raw material temperature, substrate temperature, use of a shutter, etc. It has the advantage of being able to control the film thickness and can be expected to grow epitaxially, but since the Y, Ba, etc. used as the evaporation source are high melting point metals, it is necessary to use a high melting point crucible or electron gun for melting and evaporating them.
The device structure becomes complicated, and the oxidizing species (02, 03, Oo) introduced to generate the oxide film oxidizes the raw metal and changes the deposition rate, which limits the oxygen partial pressure during growth. There are other problems. Changes in evaporation conditions can also cause bumping of the raw material due to increased power due to the feedback circuit.

An example of manufacturing an oxide-based superconducting film using the MBE method is (
d) Single-crystal YBCO thin film fabricated by reactive vapor deposition (J pn, J, App IPhys, 27.L
91-93.1988), (e) YBCO thin film fabricated in the molecular beam region using ECR plasma (Jp
n, J. Appl, Phys., 27. L2075-2
077゜1988) or (to) In order to avoid the problem of oxidation of raw materials, the evaporation source and the growth chamber are separated and a differential pumping system is used to evacuate them separately (Jpn.

J, Appl, Phys., 28. L635-638.
1989), etc.

However, in the method (d) above, the oxide is produced by increasing the oxygen partial pressure around the substrate, but the area around the substrate does not reach the molecular beam region, and the shutter control, which is an advantage of the MBE method, is Atomic layer control is difficult. In addition, in method (e) above, since a high-melting point metal such as Y is used as an evaporation source, there is a problem that the raw material oxidizes, and in method (f), the equipment is complicated and the oxygen It has the disadvantage that the partial pressure is limited.

The present invention has been made to solve the above-mentioned difficulties.
In other words, in the MBE method, it is possible to increase the oxygen partial pressure while maintaining the molecular beam region without requiring equipment such as a high melting point crucible or an electron gun, and to form an oxide-based superconducting film without causing the problem of oxidation of the raw material. Its purpose is to provide a method for manufacturing.

[Means for Solving the Problems] In order to achieve the above object, the method for producing an oxide-based superconducting film of the present invention provides a method for producing an oxide-based superconducting film using a metal complex or an organic metal complex containing a metal element constituting an oxide-based superconducting substance. The compound is deposited by heating each compound in a high vacuum and evaporating the evaporated molecules toward the substrate in the form of a beam, thereby producing a single crystal film of an oxide-based superconducting material on the substrate. be.

The oxide-based superconducting material in the present invention is not particularly limited, but typically Y-based, Bi-based, etc. superconducting materials can be used.

In addition, as substances containing metal elements constituting oxide-based superconducting materials, metal complexes or organometallic compounds whose evaporation temperature is significantly lower than that of metals are used, and in particular, β-diketone-based metals are Complexes are preferred.

β-diketone is a keto-enol tautomer, in which the enol is bound to many metals as bidentate ligands, and is a powdery solid at room temperature, but evaporates when heated. Since the evaporation temperature is much lower than that of metals, sufficient vapor pressure can be maintained even at low temperatures, and since it is more stable against oxygen than metals, there is no problem of oxidation of the raw material. Among β-diketone metals, D PM (dipivaloyl met
hane) and PPM (pentafluoroprop
Based on the deposition rate on the substrate and the results of thermogravimetric analysis (TGA) regarding Y(PPM) a
, B a (P P M) * and Cu (DPM)2
was found to be suitable as a raw material. The relationship between the Mg0 (100) substrate temperature and the amount of metal deposited when the evaporation temperature of these raw materials is 120° C. is shown in Table 1, and the structural diagram is shown in FIG. 4.

Table 1 Deposition rate of Y-based raw material In the method of the present invention, the deposition of evaporated molecules onto the substrate is performed under high vacuum in order to maintain the molecular beam region, but the degree of vacuum in this case is 5X10-' or less , especially preferably 10 −4 or less. When the degree of vacuum exceeds 5XIO-', the mean free path of the evaporated molecules becomes short, resulting in a decrease in controllability.

Further, the evaporated molecules deposited on the heated substrate decompose and grow into oxide crystals, but heat treatment can be performed in an oxidizing atmosphere if necessary. That is, when using 100% ozone or active oxygen, it is possible to produce a superconducting film without heat treatment after deposition, but when the oxygen partial pressure is low, heat treatment is required. In the case of a Y-string conductive membrane, a suitable temperature is 880-950°C. When the heat treatment temperature is less than 880°C, the crystal growth of YBCO is small, and 9
BaO can also be removed by heat treatment at temperatures exceeding 50℃ or for long periods of time.
decomposition products, such as decomposition products, resulting in deterioration of properties and failure to exhibit superconductivity.

In the case of the Y system described above, as the second invention of the present application, a β-diketone metal complex containing a metal element constituting a Y-Ba-Cu-0 system superconductor is prepared in a high vacuum. MgO
After being deposited on the substrate by evaporation toward the substrate, a single crystal film of the oxide-based superconducting material is deposited on the substrate by heat treatment at a temperature of 880 to 950°C in an oxidizing atmosphere. This is described as a method for producing an oxide-based superconducting film.

[Function] In the method of the present invention, a metal complex or an organometallic compound whose evaporation temperature is lower than that of the metal is used as the evaporation source, so a normal evaporation cell can be used, and the raw material is more resistant to oxidation than the metal. Because it is stable, the partial pressure of oxygen required to generate oxides can be increased. Furthermore, since the vacuum region allows shutter control, superconducting films can be manufactured while maintaining high precision controllability.

Furthermore, since the evaporated molecules react on the substrate surface, MOCV
Unlike method D, the raw materials do not react or decompose during the process.

That is, the method of the present invention can be said to be a crystal growth method that combines the advantages of the MBE method and the MOCVD method.

[Example] Examples of the present invention will be described below.

FIG. 3 is a schematic diagram showing an embodiment of the MBE apparatus 1 used in the method of the present invention. In the figure, 2 is a reaction chamber;
3 is a load lock chamber, and 4 is an evaporation cell.

The reaction chamber 2 and the load lock chamber 3 are evacuated by a turbo molecular pump 5 and a rotary pump 6, respectively, and can be evacuated to 10<-4> Torr or less without introducing gas. The raw materials 7 are each housed in a crucible 8 made of BN (boron nitride) and heated by a tantalum heater 10 controlled by a temperature controller 9.

The structure is such that the evaporated raw material moves straight toward the substrate, and the amount of evaporated molecules reaching the substrate can be adjusted by opening and closing the shutter 11.

Oxygen introduced into the reaction chamber 2 is controlled in the range of 0 to 5 ccm by a mass flow controller 12, and is blown onto the substrate 14 through a nozzle 13 to a position approximately 15 cm from the substrate. The substrate 14 is made of, for example, MgO (Zoo),
It is bonded with indium or the like to a holder 15 made of molybdenum, and the holder 15 is heated by a plate-shaped tantalum heater 17 controlled by a temperature controller 16. still,
18 is a gate valve, and 19 is a substrate transfer device.

Example 1 YBCO (Y-B
Multi-dimensional vapor deposition of superconducting materials (a-Cu-0 series) was performed. A β-diketone metal complex of Y, Ba and Cu was used as a raw material.

These raw materials were placed in a crucible of an evaporation cell equipped with a shutter and heated with a Ta heater to grow a thin film on the substrate. For the substrate, MgO was used, which has a coefficient of thermal expansion and a lattice constant almost similar to those of the above-mentioned superconducting material, and is chemically stable because it contains an alkaline earth metal.

The deposition conditions at this time are shown below.

Substrate・・・・・・・・・MgO (100) substrate temperature・
...800℃ Raw material temperature...Y (PPM)3...1
20'CB a (P P M) z"160℃Cu
(D P M) 2”...45℃ Oxygen amount...
・3cm"/min degree of vacuum...lXl0-
4 Torr Deposition rate: 2700 people/hr The metal composition ratio of the film thus obtained is Y:Ba:C
u=1: 2.39 24.54. Then,
The above film was annealed by heating in an oxygen stream (100 ml/ml) for 900'CX 1 hr using an infrared gold image furnace.

The XRD (X-ray diffraction) pattern of the obtained superconducting film is shown in FIG. 1, and the temperature dependence of its electrical resistance is shown in FIG. As is clear from both figures, this superconducting film exhibits almost C-axis orientation, and Tc (onset) = 80 KST.
It has a value of c (end)=74.

Example 2 A thin film was grown on the substrate using the same types of raw materials and substrates and the temperatures of the raw materials and substrates as in Example 1, the amount of oxygen at 1 cm"7 min, and the degree of vacuum at 10-4 Torr. Next, a thin film was grown on the substrate. , the above film was annealed in the same manner as in Example 1.

The properties of this superconducting film are shown in Table 2. The reason why the Tc value is lower than that in Example 1 is considered to be because the oxidizing power is weak.

In Table 2, ◯ indicates a good condition, × indicates a poor condition, and △ indicates an intermediate condition.

Comparative Example 1 The types of raw materials and substrate and the temperature of the raw materials and substrate were the same as in Example 1, the amount of oxygen was 5 cm"7 min, and the degree of vacuum was 10-" Torr, and a thin film was grown on the substrate. Ta. The above film was then annealed in the same manner as in Example 1.

The properties of the membrane thus obtained are shown in Table 2. In this case, shutter control was not possible and the obtained thin film did not exhibit Tc.

Comparative Example 2 A thin film was grown on a substrate by the same method as Comparative Example 1, except that an electron gun was used to evaporate Y and Ba, and a high melting point crucible was used to evaporate Cu.

The properties of the membrane thus obtained are shown in Table 2. In this case, the raw material was oxidized and film formation was impossible.

Comparative Example 3 The evaporation temperature of Cu was 1500°C, and the amount of oxygen was 3cm”/
A thin film was grown on the substrate in the same manner as in Comparative Example 2 except that the vacuum level was 10 −4 Torr.

The properties of the membrane thus obtained are shown in Table 2. In this case, controllability was poor due to oxidation of the raw material, and the obtained thin film did not exhibit Tc.

[Effects of the Invention] As described above, according to the method for producing an oxide-based superconducting film of the present invention, since a metal complex or an organometallic compound whose evaporation temperature is lower than that of a metal is used as an evaporation source, a high melting point crucible can be used. Superconducting films can be produced using a normal evaporation cell without the need for an electron gun or an electron gun.

Additionally, since the raw material is more stable against oxidation than metals, it is possible to increase the oxygen partial pressure required for oxide production without the need for equipment such as a differential pumping system, and shutter control is possible. Since it is a high vacuum region, superconducting films can be manufactured while maintaining high precision controllability.

[Brief explanation of drawings]

Figure 1 shows the superconducting film produced by the method of the present invention.
RD pattern, Fig. 2 is a graph showing the temperature dependence of its electrical resistance, Fig. 3 is a schematic diagram of the MBE apparatus used in the method of the present invention, and Fig. 4 is a structural diagram of the raw material used in the method of the present invention. It is. 2... Reaction tube 3... Load lock chamber 4... Evaporation self... Raw material 10.17... Tantalum heater 11...・・・
・Shutter 13... Nozzle 14... Board

Claims (4)

[Claims] (1) Deposit by heating the metal complexes or organometallic compounds containing metal elements constituting the oxide-based superconducting material in a high vacuum, and forming the evaporated molecules into a beam shape and evaporating them toward the substrate. A method for producing an oxide-based superconducting film, characterized in that a single crystal film of an oxide-based superconducting material is produced on the substrate. (2) β-diketone-based metal complexes containing metal elements constituting Y-Ba-Cu-O-based superconducting materials are heated in a high vacuum, and their evaporated molecules are formed into a beam to produce Mg.
After being deposited on the substrate by evaporation toward the O substrate, a single crystal film of the oxide-based superconducting material is deposited on the substrate by heat treatment at a temperature of 880 to 950°C in an oxidizing atmosphere. A method for producing an oxide-based superconducting film, the method comprising: producing an oxide-based superconducting film. (3) The method for producing an oxide-based superconducting film according to claim 1, wherein the metal complex is a β-diketone-based metal complex. (4) The method for producing an oxide-based superconducting film according to claim 1 or 2, wherein the degree of vacuum is a high vacuum of 5 x 10^-^4 Torr or less.