JPH0442895A - Production of thin film superconductor - Google Patents

Abstract

PURPOSE:To obtain a multiple compound thin film superconductor with excellent superconducting characteristics through such a process that, when a multiple compound film is to be irradiated with oxygen ion or oxygen plasma, the direct current voltage to apply to said ion or plasma is either intermittently or continu ously varied with time. CONSTITUTION:When a multiple compound film 12 (11: substrate; 13: surface) is to be irradiated with oxygen ion or oxygen plasma (31: ionic source), the direct current voltage (electric source 37) to apply on said ion or plasma is either intermittently or continuously varied with time. Heating with a heater 36 of the film 12 under the irradiation with the oxygen ion or plasma will improve the superconducting characteristics. The heating temperature is pref. room temperature to <=500 deg.C, and the ion-accelerating voltage is pref. <=2kv.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of Application The present invention relates to thin film superconductors, and in particular to a method for producing composite compound thin film superconductors.

Conventional technologyBa-La- exhibiting a superconducting transition temperature Tc of 30 to 40K
Cu-0-based high-temperature superconductor [J, G,
Bednorz) and K, A, Muller (Mal
ler), Zeitshrift ff1r physik
B) Condensed Matter 64.189
-193 (1986)] was discovered, ITc was 90
Y-Ba7Cu-0 material exceeding K Maf, TC is 1
B1-3r-Ca-Cu-〇 series materials and Tl-Ba-Ca-Cu-0 series materials have been discovered one after another.The details of the superconducting mechanism of these materials are not clear. There is a possibility that the amount of energy will increase even further, and promising applications such as the realization of new devices are expected.

When applying such oxide superconducting materials to devices and the like, it is strongly desired to make them thinner. Thin film formation methods include sputtering storm, reactive vapor deposition (mcVD) (chemical vapor deposition), and laser ablation. However, even if the composite compound film formed into a long plate has good orientation, its superconducting properties change depending on the content of oxygen, which is a constituent element in the film. In other words, when the oxygen content is low, superconducting properties are not exhibited or are not good. This is because not enough oxygen is taken in during film formation. Heat treatment of the resulting composite compound coating in an oxygen atmosphere at a high temperature of 800°C or higher is required.Plasma treatment in oxygen plasma [H, Tamura].

A. Yoshida, S. MoCIA
Morohashi and S, A Suo (
Hasuo), Applied Physics Letter (
Appi, Phys, Lett,) 53.
618 (1988) or S, Minomo (M
inomo), M, Taniguchi (Taniguchi)
i), Y, Ishida, Muki'yo, T, Takahashi
), M,) Tonouchi, S,
Kita and T, Kohe'yashi (Ko)
bayashi).

Japanese Journal of Applied Physics (Jpn, J, Appl, Phys,)
27. L411 (1988)] to compensate for the oxygen content in the coating.9 Problems to be Solved by the Invention As mentioned above, when a composite compound coating is heat treated in an oxygen atmosphere in a furnace or the like, it is possible to obtain good superconductivity. There are still problems in that it is difficult to set the conditions, it takes a long time, and it requires a high temperature process of 800℃ or more. (The plasma itself has a voltage of at most 50 to 100 eV.)
Only the surface layer of the film can be treated using the energy of ℃. Superconducting properties are realized and formed by temporally changing the direct current voltage applied to oxygen ions or oxygen plasma.

In addition, other thin film superconductor manufacturing methods (i.e., superconducting properties are achieved by continuously changing the DC voltage applied to the oxygen ions or oxygen plasma over time when irradiating the composite compound film with oxygen ions or oxygen plasma) It is said that it is formed by

The inventors believe that this type of material is an oxide, and that its superconducting properties can be controlled by precisely controlling the amount of oxygen atoms.
Research on the irradiation effects of oxygen ions and oxygen plasma, and based on this research, invent a new method for manufacturing thin film superconductors of composite compounds.
When irradiating a composite compound film with oxygen ions or oxygen plasma, in order to change the direct current voltage applied to the oxygen ions or oxygen plasma intermittently over time, it is necessary to irradiate the composite compound film at a depth corresponding to the amount of energy, with the center at that position. Oxygen is injected in a form close to the Gaussian distribution, making it possible to oxidize the film almost uniformly in the depth direction.Also, the amount of oxygen atoms in the film can be controlled by adjusting the irradiation time.
As a result, it is possible to control the superconducting properties of the film, and it is also possible to form a thin film superconductor in a short time using a low temperature process of 500°C or less. When a composite compound film is irradiated with oxygen ions or oxygen plasma, the direct current voltage applied to the oxygen ions or oxygen plasma is continuously changed over time, so that the oxidation treatment is performed uniformly in the depth direction of the film. In addition, similar to the above invention, the amount of oxygen atoms in the film can be controlled by changing the irradiation time, and as a result, the superconducting properties of the film can be controlled. Although it is possible to form a thin film superconductor by processing, an embodiment of the present invention will be described with reference to the drawings. The surface 13 of the coating 12 is irradiated with oxygen ions or oxygen plasma while intermittently changing the DC voltage for ion acceleration.
In another manufacturing method of the present invention, the surface 13 of the coating 12 is irradiated with oxygen ions or oxygen plasma while continuously changing the DC voltage for ion acceleration. Plasma is generated by discharging a gas containing at least oxygen in a vacuum chamber, and the generated oxygen ions or plasma and coating 1
In the first invention, a direct current accelerating voltage of 2 kV or less is applied intermittently in the first invention, and in the second invention, a direct current accelerating voltage is applied between the specimen stage and the sample stage on which the specimen is installed. It was confirmed that the film 12 exhibits good superconducting properties through two different processes.This is thought to be due to the metal atoms in the film being oxidized by the action of oxygen ions or plasma in each method. It will be done. However, the energy of the irradiated oxygen ions changes intermittently or continuously, depending on the magnitude of the energy. Although it is thought that oxygen is injected to a depth that is uniformly oxidized in the depth direction, the inventors have also confirmed that the superconducting properties can be controlled by the concentration of the irradiated oxygen ions or oxygen plasma When processing with oxygen plasma,
It was found that the superconducting properties were improved by heating the substrate 13.The optimum heating temperature was between room temperature and 500°C.At temperatures above this point, the amount of oxygen coming in from the inside of the film was greater than the amount of oxygen coming in due to irradiation. The amount of oxygen released due to thermal desorption exceeds the amount of oxygen, and the oxygen content in the film decreases.
As the resistivity increases, the properties of the film become unstable and do not exhibit steep superconducting properties.

Oxygen is a relatively light element and can be treated with fairly good uniformity even when irradiated with acceleration at a low accelerating voltage of 2 kV or less, so the present invention has the advantage of not causing major damage to the thin film. In order to further deepen the understanding of the contents of the present invention, specific examples will be shown below.

(Specific Example) Using a magnesium oxide (100) surface as the substrate 11 1.
X, Gd+BatCu4. sintered by high-frequency Brenner magnetron scattering. sQx target with Ar and 0
A thin film was formed by sputtering deposition in a mixed gas atmosphere of 2. In this case, the substrate temperature was 600°C, the total gas pressure was 3X10-'Torr, and the sputtering power was 160W, and sputtering deposition was performed for about 1 hour. A thin film with a thickness of 0.6 μm was obtained.The composition of the formed film was investigated.The ratio of metal elements was Gd:B a :Cu = 1:1.98:
3.07, which was a stoichiometric ratio of approximately 1:2:3.Also, the crystal structure of the thin film was found to be a crystal structure in which the C-axis was oriented perpendicular to the substrate by X-ray diffraction.
However, the formed film ζ had an onset temperature of 94, which indicates a sign of superconductivity, and a zero resistance temperature of 62, which is a low value although it indicates superconductivity.Therefore, the formed Gd-Ba-Cu- The 0 compound film 12 was heated to 300°C and subjected to oxygen ion plasma treatment.
The acceleration voltage applied to the plasma is 1.5.1.2.0.9
．． 0.6.0.3 kV and 50V were intermittently varied, each for 5 journeys and a total irradiation time of 30 minutes.The superconducting transition temperature of the film thus obtained was an onset temperature of 94K and a zero resistance temperature. Figure 2 shows the temperature dependence of resistivity before and after oxygen ion plasma treatment.

Next I will show a specific example of another manufacturing method of the present invention.

With C-axis orientation obtained in the same manner as above, Gd-BaCu-0 at onset temperature of 94 and zero resistance temperature of 62.
The thin film was heated to 300°C and subjected to oxygen ion plasma treatment.
The acceleration voltage applied to oxygen ions/plasma was continuously varied from 1.5 kV to 50 V in 30 minutes in a vacuum chamber of RR.The superconducting transition temperature of the film thus obtained was on-set. Temperature is 94 to 1 Zero resistance temperature is 85 to 9 Zero resistance temperature is 23 compared to before treatment
However, even if the oxygen ion or plasma irradiation method described above is improved, the method of irradiation with oxygen ions or plasma may be performed by a third doctor. First, a gas containing at least oxygen is introduced into the ion source 31 of FIG. Electrodes 32.3 facing each other with this gas in between
Plasma is generated by applying a high frequency signal to 3. A magnetic field generation source 34 is arranged to form a magnetic field in this plasma, and the efficiently generated oxygen ions and plasma are transferred to the substrate 11 on which a composite compound film is formed. By applying an electric field from the DC voltage source 37 between the placed substrate table 35 and the plasma of the ion source, oxygen ions are extracted from the ion source and irradiated onto the coating 12. In this case, in either invention, if the applied voltage is 2 kV or less, the surface 13 of the coating 12 It was confirmed that the constituent metal atoms could be oxidized effectively inside the film and uniformly in the depth direction.The heater 36 heats the substrate during the oxygen treatment.

FIG. 4 shows that at least acid is present in the plasma generation chamber 41.

Oxygen plasma is generated by introducing a gas containing an element and introducing microwaves generated by a microwave power source 42 into this gas through a waveguide 43 to cause a discharge. The ion source used was one in which a magnetic field was applied to increase the ionization efficiency of oxygen ions. In this case, if a 2.45 GHz microwave is normally used for the microwave source 42 and the magnetic field strength is set to about 875 Gauss, electron cyclotron resonance will occur, thereby increasing oxygen ionization efficiency.

By applying a DC voltage between the plasma generation chamber 4I and the sample chamber 44 via the insulating section 45, oxygen ions can be easily controlled to the composite compound coating 12 installed on the substrate stand 35 in the sample chamber 44. In this case, even if the applied DC voltage tL is changed intermittently in the first invention and continuously in the second invention, in either case, if the applied DC voltage tL is 2 kV or less, Regarding the processing equipment that has been confirmed to be able to oxidize the constituent metal atoms effectively and uniformly in the depth direction inside the film (in addition to this, we introduced a gas containing at least oxygen into the vacuum chamber). A high frequency is applied to this gas to parallel electrodes to cause a discharge, a compound film is placed in this discharge plasma, and a DC electric field is applied between the plasma and the sample stage on which the compound film is placed, and the applied voltage is changed intermittently to C. , - or it is possible to perform oxygen treatment while changing the oxygen continuously.It is also possible to combine these devices as a source of oxygen ions and plasma, and in this case, there is an advantage of further improving controllability. &mi As a gas containing oxygen, ozone (0
3) and nitrous oxide (N2O) are used, but 03 uses 02 generated at a concentration of 5% by an ozonizer.903 Differences between N2O and oxygen alone When a microwave plasma source that utilizes electron cyclotron resonance is used as a plasma generation source, it is possible to generate oxygen plasma with high ionization efficiency at lower power. However, when N2O is used, the effects of physical damage due to active nitrogen plasma and ions may be seen at microwave powers of 400 W or more, and at relatively low powers of 150 to 300 W, the results of plasma spectroscopy show that It was confirmed that the two methods of the present invention are effective in improving the superconducting properties. The irradiation effect with oxygen ions or oxygen plasma, which has made it possible to obtain the body with good reproducibility, is well controllable, and the low energy does not cause major damage to the membrane, and the treatment can be performed at temperatures below 500℃. However, even though oxidation treatment can be carried out easily and evenly in the depth direction of the film, thin film superconductors with little damage can be realized very easily and at low temperatures.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the basic concept of a thin film superconductor according to an embodiment of the present invention. Figure 2 is a characteristic diagram of the temperature dependence of electrical resistance of a thin film superconductor realized by the present invention. Figure 3 is a diagram of the present invention. 11 is a cross-sectional view showing a schematic configuration of an oxygen treatment apparatus used in carrying out the method for producing a thin film superconductor; and FIG.
... Table sleep 31 ... Ion nails 32.33 ... Electric machine
34... Magnetic field generating claw 35... Substrate stand 36... Heater 37... DC voltage switch 41... Plasma generation chamber 42... Microwave generator 43... Waveguide, 44・
...Sample room 45...Name of insulating agent Patent attorney
Shigetaka Awano 1 person Figure 1 Figure 2 Eyebrow rv (K)

Claims (11)

[Claims] (1) A thin film superconductor characterized in that when a composite compound film is irradiated with oxygen ions or oxygen plasma, the DC voltage applied to the oxygen ions or oxygen plasma is intermittently changed over time. Production method. (2) A thin film superconductor characterized in that when a composite compound film is irradiated with oxygen ions or oxygen plasma, the DC voltage applied to the oxygen ions or oxygen plasma is continuously changed over time. Production method. (3) The method for producing a thin film superconductor according to claim 1 or claim 2, characterized in that the composite compound film is heated during irradiation with oxygen ions or oxygen plasma. (4) The method for producing a thin film superconductor according to claim 1 or 2, wherein plasma generated by discharging a gas containing at least oxygen in a vacuum chamber is used as the oxygen ion or oxygen plasma source. (5) As an oxygen ion or oxygen plasma source device,
5. The method for manufacturing a thin film superconductor according to claim 4, characterized in that a plasma processing apparatus for plasma decomposition using microwaves is used. (6) As an oxygen ion or oxygen plasma source device,
6. The method of manufacturing a thin film superconductor according to claim 5, further comprising applying a magnetic field so as to satisfy an electron cyclotron resonance absorption condition. (7) The method for manufacturing a thin film superconductor according to claim 3, characterized in that the composite compound film upon irradiation with oxygen ions or oxygen plasma is heated while being maintained at a predetermined temperature of 500° C. or less. (8) Oxygen ions are irradiated by installing an electrode that can arbitrarily set the potential between the plasma generated by applying a high-frequency voltage to a gas containing at least oxygen and the sample stage on which the composite compound coating is installed. 5. The method for producing a thin film superconductor according to claim 4. (9) The method for manufacturing a thin film superconductor according to claim 1 or 2, characterized in that a DC variable voltage of 2 kV or less is applied as the ion accelerating voltage. (10) The method for manufacturing a thin film superconductor according to claim 4, characterized in that the composite compound film is placed in plasma generated by applying a high frequency voltage to a gas containing at least oxygen. (11) The method for manufacturing a thin film superconductor according to claim 4, characterized in that at least one type of gas selected from oxygen, ozone (O_3), and nitrous oxide (N_2O) gas is used as the gas containing at least oxygen.