JPH0710759B2 - Method for manufacturing oxide-based superconducting film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a method for producing an oxide-based superconducting film, and particularly to MB.
The present invention relates to improvement of a method for producing an oxide-based superconducting film by the E method (molecular beam epitaxy method).

[Prior Art] La series (La-Ba-Cu-O), Y series (Y-Ba-Cu-O), Bi series (Bi-Sr)
-Ca-Cu-O) and Tl-based (Tl-Ba-Ca-Cu-O) and other oxide-based superconducting materials are conventional alloy-based or intermetallic compound-based, that is, Its critical temperature (Tc) is higher than that of Nb-Ti-based and Nb ₃ Sn-based superconducting materials, and its application to various applications is expected.

As a premise of such application, in order to manufacture a superconducting coil or a superconducting element using an oxide-based superconducting material,
It is necessary to establish wire rod and thin film technology,
Among them, for use in electronic materials such as Josephson devices, it has become important to establish thin film manufacturing technology that facilitates weak coupling between superconducting materials, facilitates fine processing, and enables high integration. .

Heretofore, (a) sputtering method, (b) CVD method, and (c) vapor deposition method have been known as main methods for manufacturing a thin film.

In the method (a) above, a voltage is applied between the target and the substrate in a gas atmosphere such as Ar, and gas ions generated by the collision of electrons are made to collide with the target, and the knocked-out atoms are attached to the substrate. Since the main mechanism is not a thermal process, it is easy to form a thin film of a high-melting point material, and there is an advantage that a film having a strong adhesion to a substrate can be obtained. The method (b) is a method in which a raw material is supplied in the form of a compound such as a halide or a hydride, and a thin film is grown by a reaction on a high temperature substrate. In addition, the above method (c) is a method in which an evaporation source is provided for each component to simultaneously evaporate while independently controlling the evaporation rate and to combine on the substrate, and the composition can be easily controlled. It has an advantage that a thin film with high purity can be obtained.

However, in the above methods (a) to (c), controlling the growth film thickness at the atomic layer level, obtaining a surface having atomic scale smoothness, and superconducting properties due to the effect of interdiffusion of atoms. It is difficult to prevent decrease in the composition and to accurately control the composition.

In recent years, the MBE method (M
The production of thin films by olecular beam epitaxy is being studied. In this method, a substance to be grown is heated in a high vacuum, and vaporized molecules of each element are made into a beam to be vaporized toward a substrate to deposit a single crystal on the substrate. Theoretically, the mean free path for collision of molecules in ultrahigh vacuum is longer than that under normal pressure, so that evaporated molecules reach the substrate without colliding with other molecules.

The MBE method overcomes all of the above-mentioned problems (1) to (3) and has the advantage that it can be observed by electron beam diffraction or the like during crystal growth and that selective growth can be performed using a vapor deposition mask.

[Problems to be Solved by the Invention] As described above, in the case of producing an oxide superconducting film by the MBE method, it is possible to control the composition with high accuracy by using a raw material temperature, a substrate temperature, the use of a shutter, or the like, and a monoatomic layer. The film thickness can be controlled,
Although it has the advantage that epitaxy growth can be expected, since Y, Ba, etc. used as evaporation sources are high melting point metals, it is necessary to use high melting point crucibles and electron guns for melting and vaporizing them, and the device structure becomes complicated. Oxidizing species (O ₂ , O ₃ , O ^* ) introduced to form an oxide film oxidize the metal of the raw material and change the deposition rate, which causes problems such as limiting the oxygen partial pressure during growth. is there. The change in the evaporation condition also causes the bumping of the raw material due to the power increase by the feedback circuit.

As an example of producing an oxide-based superconducting film by the MBE method,
(D) A single crystal YBCO thin film prepared by reactive evaporation (Jpn.J.Appl.Phys., 27, L91-93,1988), (e) YBCO in the molecular beam region using ECR plasma. A thin film (Jpn.J.Appl.Phys., 27, L2075-2077,1988) or (f) In order to avoid the problem of raw material oxidation, the evaporation source and the growth chamber are separated and exhausted separately. Those using a differential pumping system (Jpn.J.Appl.Phys., 28, L635-638, 1989) can be used.

However, in the method of (d) above, the oxide is produced by increasing the oxygen partial pressure around the substrate, but the periphery of the substrate does not reach the molecular beam region, and shutter control, which is an advantage of the MBE method, is achieved. It is difficult to control the atomic layer by. In the method (e), since a refractory metal such as Y is used as the evaporation source, there is a problem that the raw material is oxidized,
The method (f) has a drawback that the apparatus becomes complicated and the oxygen partial pressure during growth is limited.

The present invention has been made to solve the above problems,
That is, the MBE method does not require a device such as a high melting point crucible or an electron gun, increases the oxygen partial pressure while maintaining the molecular beam region, and produces an oxide-based superconducting film without causing the problem of raw material oxidation. The purpose is to provide a method of doing.

[Means for Solving the Problems] In order to achieve the above object, a method for producing an oxide-based superconducting film according to the present invention is a metal complex or an organometallic complex containing a metal element constituting an oxide-based superconducting substance. Compounds are heated in a high vacuum, and the vaporized molecules are deposited in the form of beams to evaporate toward a substrate to form a single crystal film of an oxide superconducting substance on the substrate. Is.

The oxide superconducting material in the present invention is not particularly limited, but it is typically applicable to Y-based, Bi-based superconducting materials and the like.

Further, as the substance containing a metal element constituting the oxide-based superconducting substance, a metal complex or an organometallic compound having an evaporation temperature significantly lower than that of the metal is used, and in particular, a β-diketone-based metal is used because of its deposition rate on the substrate. Complexes are preferred.

β-diketone is a keto-enol tautomer, which is an enol bound to many metals as a bidentate ligand, is a powdery solid at room temperature, and evaporates when heated. Since the evaporation temperature is much lower than that of metal, the vapor pressure can be sufficiently taken even at low temperature, and it is more stable to oxygen than metal, so that there is no problem of raw material oxidation. Among β-diketone-based metals, DPM (dipivaloyl methane) and PPM (pentaf
From the results of deposition rate on substrate and thermogravimetric analysis (TGA) of luoropropanoyl pivaloyl methane), Y (PPM) ₃ , Ba (PPM) ₂ and Cu (DP
It was found that M) ₂ is suitable as a raw material. Table 1 shows the relationship between the MgO (100) substrate temperature and the metal deposition amount when the evaporation temperature of these raw materials was 120 ° C., and its structural diagram is shown in FIG.

In the method of the present invention, the evaporation molecules are deposited on the substrate under a high vacuum in order to maintain the molecular beam region. In this case, the degree of vacuum is 5 × 10 ⁻⁴ or less, particularly 10 ⁻⁴ or less. Preferably. When the degree of vacuum exceeds 5 × 10 ^-4 , the mean free path of the vaporized molecules becomes short, which lowers the controllability.

Further, the vaporized molecules deposited on the heated substrate are decomposed and grow into oxide crystals, but if necessary, heat treatment can be performed in an oxidizing atmosphere. That is, when 100% ozone or active oxygen is used, it is possible to form a superconducting film without heat treatment after deposition, but when oxygen partial pressure is low, heat treatment is required. In the case of Y-based superconducting film,
A suitable temperature is 880 to 950 ° C. If the heat treatment temperature is lower than 880 ° C, YBCO crystal growth is small, and decomposition products such as BaO are generated even if the heat treatment is performed at a temperature higher than 950 ° C or for a long time, and the characteristics are deteriorated or superconductivity is not exhibited.

In the case of the Y-based case described above, as a second invention of the present application, a β-diketone-based metal complex containing a metal element constituting a Y-Ba-Cu-O-based superconducting material is placed in a high vacuum. By heating each, and after depositing on the substrate by evaporating the vaporized molecules toward the MgO substrate in the form of a beam, by applying a heat treatment at a temperature of 880 to 950 ° C. in an oxidizing atmosphere, It is described as a method of manufacturing an oxide-based superconducting film in which a single crystal film of an oxide-based superconducting material is formed on the substrate.

[Operation] In the method of the present invention, since a metal complex or an organometallic compound having an evaporation temperature lower than that of a metal is used as an evaporation source, an ordinary evaporation cell can be used, and the raw material is more resistant to oxidation than the metal. Since it is stable, the partial pressure of oxygen required for oxide formation can be increased. Further, since it is a vacuum region in which shutter control is possible, it is possible to manufacture a superconducting film while maintaining high precision controllability.

Further, since the vaporized molecules react on the surface of the substrate, the raw material does not react or decompose in the middle unlike the MOCVD method. That is, it can be said that the method of the present invention is a crystal growth method having the advantages of the MBE method and the MOCVD method.

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

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

The reaction chamber 2 and the load lock chamber 3 are exhausted by a turbo molecular pump 5 and a rotary pump 6, respectively, and can be evacuated to 10 ^-6 Torr or less without introducing gas. Each raw material 7 is housed in a crucible 8 made of BN (boron nitride) and heated by a tantalum heater 10 controlled by a temperature controller 9. The vaporized raw material goes straight toward the substrate, and the amount of vaporized molecules reaching the substrate can be adjusted by opening and closing the shutter 11.

Oxygen introduced into the reaction chamber 2 is controlled by the mass flow controller 12 within a range of 0 to 5 ccm, and is blown onto the substrate 14 through the nozzle 13 up to about 15 cm from the substrate. Board 14
Is made of, for example, MgO (100) and is bonded to a holder 15 made of molybdenum with indium or the like. The holder 15 is heated by a plate-shaped tantalum heater 17 controlled by a temperature controller 16. Reference numeral 18 is a gate valve, and 19 is a substrate carrier.

Example 1 Using the MBE device 1 shown in FIG. 3, YBCO (Y-Ba-Cu-O system)
Multi-element deposition of superconducting material was performed. As a raw material, a β-diketone-based metal complex of Y, Ba and Cu was used.

These raw materials were placed in a crucible of an evaporation cell equipped with a shutter and heated by a Ta heater to grow a thin film on the substrate. The substrate was made of MgO that is scientifically stable because it has a thermal expansion coefficient and a lattice constant close to those of the above-mentioned superconducting substance and contains an alkaline earth metal.

The deposition conditions at this time are shown below.

Substrate ……… MgO (100) Substrate temperature ……… 600 ℃ Raw material temperature ……… Y (PPM) ₃ ……… 120 ℃ Ba (PPM) ₂ … 160 ℃ Cu (DPM) ₂ … 45 ℃ Oxygen amount ………… 3cm ³ / min Vacuum degree ………… 1 × 10 ^-4 Torr Deposition rate ………… 2700Å / hr The metal composition ratio of the film thus obtained is Y: Ba: Cu = 1 :
It was 2.39: 4.54. Then, the above film was heated to 900 ° C in an oxygen stream (100 ml / min) using an ultraviolet gold image furnace.
It was annealed by heating for × 1 hr.

The XRO (X-ray diffraction) pattern of the obtained superconducting film is shown in FIG. 1, and the temperature dependence of its electric resistance is shown in FIG. As is clear from both figures, this superconducting film shows almost C-axis orientation, and Tc (on set) = 80K, Tc (end) = 74K.
Has a value of.

Example 2 The raw material and substrate type, the raw material and substrate temperature were the same as in Example 1, the oxygen amount was 1 cm ³ / min, and the vacuum degree was 10 ⁻⁵ Torr.
As a thin film was grown on the substrate. Then, the above film was annealed in the same manner as in Example 1.

The characteristics of this superconducting film are shown in Table 2. The decrease in the Tc value compared to Example 1 is considered to be due to the weak oxidizing power.

In Table 2, ◯ means good, × means bad, and Δ means intermediate state.

Comparative Example 1 The types of raw materials and substrates, the temperatures of raw materials and substrates were the same as in Example 1, the amount of oxygen was 5 cm ³ / min, and the degree of vacuum was 10 ⁻³ Torr.
As a thin film was grown on the substrate. Then, the above film was annealed in the same manner as in Example 1.

The characteristics of the film thus obtained are shown in Table 2. In this case, the shutter control was impossible, and the obtained thin film did not show Tc.

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

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

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

The characteristics of the film thus obtained are shown in Table 2. In this case, the controllability was poor due to the oxidation of the raw material, and the obtained thin film did not show 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 having an evaporation temperature lower than that of a metal is used as an evaporation source, the high melting point crucible is used. A superconducting film can be manufactured by using an evaporation cell in general, without the need for an electron gun or the like.

In addition, since the raw material is more stable against oxidation than metal, the oxygen partial pressure required for oxide generation can be increased and shutter control is possible without the need for a device such as a differential exhaust system. Since it is in the high vacuum region, the superconducting film can be manufactured while maintaining the controllability with high accuracy.

[Brief description of drawings]

FIG. 1 shows the XR of the superconducting film manufactured by the method of the present invention.
D pattern, FIG. 2 is a graph showing the temperature dependence of its electric resistance, FIG. 3 is a schematic diagram of an MBE apparatus used in the method of the present invention, and FIG. 4 is a structural diagram of raw materials used in the method of the present invention. Is. 2 ... Reaction tube 3 ... Load lock chamber 4 ... Evaporation cell 7 ... Raw material 10, 17 ... Tantalum heater 11 ... Shutter 13 ... Nozzle 14 ... Substrate

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location H01B 13/00 565 D 7244-5G H01L 39/24 ZAA C 9276-4M (72) Inventor Sada Yoshida History 1-4 Umezono, Tsukuba-shi, Ibaraki Electronic Technology Research Institute, Industrial Technology Institute (72) Yozo Ikedo 2-1-1 Oda Sakae, Kawasaki-ku, Kawasaki-shi, Kanagawa Showa Electric Wire & Cable Co., Ltd. Examiner Sanada Tadahiro

Claims (4)

[Claims] 1. A metal complex or an organometallic compound containing a metal element that constitutes an oxide-based superconducting substance is heated in a high vacuum to vaporize vaporized molecules of the vaporized molecules toward a substrate. And a single crystal film of an oxide-based superconducting material is formed on the substrate, to produce an oxide-based superconducting film. 2. A β-diketone-based metal complex containing a metal element constituting a Y-Ba-Cu-O-based superconducting substance is heated in a high vacuum to form vaporized molecules thereof into a beam. After being deposited on the substrate by evaporating toward the MgO substrate, a heat treatment is performed at a temperature of 880 to 950 ° C. in an oxidizing atmosphere to form a single crystal film of an oxide-based superconducting material on the substrate. A method for producing an oxide-based superconducting film, which comprises: 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 superconducting film according to claim 1, wherein the degree of vacuum is a high vacuum of 5 × 10 ⁻⁴ Torr or less.