JPH03197322A - Manufacturing method of thin film superconductor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a thin film superconductor, particularly a composite compound thin film superconductor having an N d2Cuo a type crystal structure.

Conventional technology Ba-L a whose superconducting transition temperature Tc is 30 to 40K
-Cu-0-based high-temperature superconductor [CIE, Hetornorf? [J, G, Bedno]
rz and ni, A, Mul 1er), Zeitsch
rift fur physikB)-Conde
nsed Matter 64, 189-193 (1
986)] was discovered, Y with Tc exceeding 90K
-Ba-Cu-0 system, and Tc exceeds 100K
B i-5r-Ca-Cu-0 based material, and T I
-Ba-Ca-Cu-0 based materials have been discovered one after another.

By the way, recently, Nd-Ce-Cu-
A new superconductor with the N d2CuOa type crystal structure represented by 04'm was discovered [V, Tokura, H
, Takagi and 5-tlchida),
Nature +- (Nature) vol, 337.
345-347 (1989)].

Although the details of the superconducting mechanism of this type of material are not clear, the transition temperature may be even higher, and promising applications such as the realization of new devices are awaited.

Problems to be Solved by the Invention N d-Ce-Cu-0 based materials can be formed as a thin film superconductor by using a thin film forming method such as sputtering. However, the superconducting properties of the formed film change depending on the amount of Ce11 or oxygen in the film. For example, replacing Nd atoms in Nd2CuOn with Ce atoms (
Good superconducting properties can be obtained by substituting x=0-07 or so) and further removing oxygen by heat treatment in a reducing atmosphere. This is because N in the film
d3ゝ is replaced with Ce” and the subsequent 800~
This is because the valence of Cu changes from +2 to +1 due to thermal desorption of oxygen bonded to Cu due to high temperature treatment at approximately 900° C., and electrons serving as a conductive medium are injected into the film. Further, as a method of injecting electrons, a method of replacing part of oxygen with fluorine in a high temperature atmosphere of 900° C. or higher has been used. In either case, heat treatment at a high temperature of 800° C. or higher was required.

An object of the present invention is to solve the problems of such conventional thin film superconductor manufacturing methods.

Means for Solving the Problems The method for manufacturing a thin film superconductor according to the present invention as set forth in claim 1 is characterized in that the main component is (A+
-xB) A composite compound coating represented by 2 cuOa is irradiated with fluorine ions or fluorine plasma (where A is at least one of Nd, Sm, and Pr, and B is at least one of Ce and Th). Indicates an element. Also, X is a numerical value in the range of 0≦X≦0.2.

) is a method for producing a thin film superconductor.

The present invention according to claim 2 is a method for manufacturing a thin film superconductor according to claim 1, characterized in that the composite compound film is heated during irradiation with fluorine ions or fluorine plasma.

The present invention according to claim 3 is the method according to claim 2, wherein the composite compound film is heated at 500°C during irradiation with fluorine ions or fluorine plasma.
This is a method for manufacturing a thin film superconductor, which is characterized by heating while maintaining the temperature at the following predetermined temperature.

Claim 40 The present invention provides a method for producing a thin film superconductor according to Claim 1, characterized in that plasma generated by discharging a gas containing at least fluorine in a vacuum chamber is used as the fluorine ion or fluorine plasma source. be.

Claim 50 The present invention is a method for producing a thin film superconductor according to claim 4, characterized in that a plasma processing apparatus by plasma decomposition using microwaves is used as the fluorine ion or fluorine plasma source apparatus.

The present invention according to claim 6 is a method for manufacturing a thin film superconductor according to claim 5, characterized in that a method of applying a magnetic field so as to satisfy an electron cyclotron resonance absorption condition as a fluorine ion or fluorine plasma source device is used. be.

The present invention according to claim 7 is the method according to claim 4, in which fluorine ions generated by electric discharge in the vacuum chamber are accelerated by applying a voltage between the plasma in the vacuum chamber and the sample stage on which the composite compound coating is installed. This is a method for manufacturing a thin film superconductor, which is characterized by irradiating the thin film superconductor.

The present invention according to claim 8 is the method according to claim 7, wherein an electrode set to a predetermined potential is installed between the plasma generated by applying a high frequency voltage to a gas containing at least fluorine and the sample stage to irradiate fluorine ions. This is a method for manufacturing a thin film superconductor, characterized by:

Claim 90 The present invention is a method for manufacturing a thin film superconductor according to Claim 7, characterized in that a DC voltage of 2 KV or less is applied between the plasma and the sample stage.

The present invention in claim 1O is a method for manufacturing a thin film superconductor according to claim 7, characterized in that a composite compound coating is placed in plasma generated by applying a high frequency voltage to a gas containing at least fluorine.

Claim 110 In claim 4, the present invention provides that the gas containing at least fluorine is F2, SFs, SF4, CF4,
This is a method for manufacturing a thin film superconductor characterized by using BF3.

Function: The method for producing a thin film superconductor according to the present invention allows the electron concentration in the film to be controlled by irradiating fluorine ions or fluorine plasma onto a composite compound film typified by Nd-Ce-Cu-0. As a result, the superconducting properties of the film can be controlled. Moreover, it is possible to form a thin film superconductor using a different charge transport carrier in a normal conductive state from that of the conventional thin film superconductor using a low-temperature process of 500° C. or lower.

Example Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, a composite compound coating 12 whose main component is (.A 1- t B In this case, the substrate 11 is intended to hold the composite compound coating 12. Further, by irradiating the surface 13 of the coating 12 with fluorine ions or fluorine plasma, the coating 12 exhibits good superconducting properties. This is thought to be due to the action of fluorine ions or plasma replacing some of the oxygen in the film with fluorine, reducing some of the copper, and injecting electrons to serve as a conductive medium. The present inventors also confirmed that superconducting properties can be controlled by the concentration of irradiated fluorine ions or fluorine plasma.

The present inventors have proposed that this type of composite compound coating be heat treated at a high temperature of 800°C or higher in a vacuum or reducing gas atmosphere, or treated with fluorine ions or fluorine plasma generated by discharge of a gas containing at least fluorine. We discovered that superconducting properties can be achieved by doing so. It has been found that when treated with fluorine ions or fluorine plasma, superconducting properties can be improved by heating the substrate. The optimal heating temperature range is room temperature to 500℃
Met. When the temperature exceeds this temperature, thermal desorption of oxygen occurs in addition to the oxygen substitution effect of fluorine, making it difficult to control the superconducting properties of the film by fluorine treatment.

Since fluorine ions or fluorine plasma are irradiated while being accelerated at a low accelerating voltage of 2 KV or less, the present invention has the advantage of not causing major damage to the thin film.

More specific examples will be shown below in order to provide a deeper understanding of the content of the present invention.

Strontium titanate 2. Using the (100) plane as the substrate ll, by high-frequency Brenner magnetron fluttering,
Sintered Nd+, esCew, +5Cu20x re-gets were deposited by sputtering in an Ar atmosphere to form a thin film. In this case, the substrate temperature was 650°C, the total gas pressure was 5 x 10-3 Torr, the sputtering power was 160W, and the film thickness was about 0.8 μm. was gotten. When the composition of the formed film was investigated, the ratio of metal elements was Nd:Ce:Cu=1.84:0.1
6:1.0, which was a nearly stoichiometric ratio. Also,
The crystal structure of the thin film was found to be an Nd2Cu04 type crystal structure in which the C axis is oriented perpendicular to the substrate by X-ray diffraction. However, the formed film did not exhibit superconductivity, and the temperature dependence of its electrical resistance exhibited semiconductor-like characteristics. Therefore, the formed compound film 12 was heated to 300° C. and subjected to fluorine ion plasma treatment. The processing conditions are
Using CFa gas, the processing time was 10 minutes at an accelerating voltage of 50 V in a vacuum chamber of 2 x 10-'Torr. The coating 12 thus obtained exhibited superconductivity, with a transition temperature of 27 K at onset and 20 at zero resistance. This situation is shown in FIG.

As a method for irradiating fluorine ions or plasma as described above, an apparatus having a configuration as shown in FIGS. 3 and 4 was used.

First, a fluorine-containing gas such as CFa, for example, is introduced into the ion source 31 of FIG. 3, and a high frequency signal is applied to electrodes 32 and 33 facing each other with this gas in between to generate plasma. A magnetic field generation source 34 for forming a magnetic field in this plasma is disposed, and the efficiently generated fluorine ions and plasma are transferred to the substrate table 35 on which the base 11 on which the composite compound coating is formed and the plasma of the ion source. By applying a voltage between them, fluorine ions are extracted from the ion source and irradiated onto the coating 12. At this time, plasma and substrate stand 3
If the voltage applied between 5 and 5 is 2KV or less, the coating 12
Although the surface 13 of the film was slightly sputtered, it was confirmed that the inside of the film could be effectively replaced with oxygen by fluorine. Further, heating of the substrate during fluorine treatment is performed by a heater 36.

In FIG. 4, for example, CF a gas is introduced into a plasma generation chamber 41, and microwaves generated by a microwave power source 42 are introduced into the gas through a waveguide 43 to cause a discharge, thereby generating fluorine plasma. to occur. A magnetic field is applied to the fluorine plasma by a magnetic field generating source 34 to improve the ionization efficiency of fluorine ions, and this is used as an ion source.

In this case, if a 2.45 GHz microwave is normally used in the microwave source 42 and the magnetic field strength is set to about 875 Gauss, electron cyclotron resonance will occur, thereby increasing the ionization efficiency of fluorine. The structure is such that fluorine ions and plasma extracted by this ion source are irradiated onto the composite compound coating 12 placed on the substrate stand 35 in the sample chamber 44 . In this case, high-energy fluorine ions efficiently ionized by microwaves and fluorine plasma drawn by a divergent magnetic field are irradiated onto the compound film 12 with good controllability. In order to further improve controllability, the energy of fluorine ions in the fluorine plasma can be controlled by applying a voltage between the plasma generation chamber 41 and the sample chamber 44 via the insulating section 45. in this way,
It is possible to control fluorine ions by applying an accelerating voltage, and to control fluorine ions and fluorine plasma by microwave power.

In addition to this, the treatment equipment also introduces a gas containing fluorine into a vacuum chamber, applies high frequency waves to the gas to discharge it to parallel electrodes, places a composite compound coating in this discharge plasma, and performs the fluorine treatment. You can also. The inventors confirmed that this method improves the superconducting properties of the coating. However, in this method, since the coating is directly exposed to plasma, the state of the coating surface is likely to change, so the plasma ion extraction method described above is more preferable.

It is also possible to combine these devices as sources of fluorine ions and plasma, and in this case there is an advantage that controllability is further improved.

This kind of composite compound superconductor (A+-xBx) 2cu
The details of changes in superconducting properties due to changes in constituent elements A and B of 04 are not clear. Although the explanation has been given with reference to Nd as an element, the use of Ss, Pr, or a combination containing at least one of these does not change the essential characteristics of the invention, except to the extent that the superconducting transition temperature changes.

Further, regarding element B, even if a combination containing Th or at least one of these instead of Ce0 changes the superconducting transition temperature, it does not change the essential characteristics of the invention.

Furthermore, it has been confirmed that if the value of X is in the range O≦X≦0.2, the superconducting transition temperature changes, but the essential characteristics of the invention do not change.

Effects of the Invention According to the present invention, it has become possible to obtain a high-quality, high-performance thin film superconductor having an N dzCuo a-type crystal structure with good reproducibility. The irradiation effect with fluorine ions or fluorine plasma is well controllable, does not cause major damage to the film, and can be easily processed under conditions of 500° C. or lower.

Therefore, a damage-free thin film superconductor can be realized very easily and at low temperature according to the present invention. The manufacturing method of the present invention includes:
This is essential for applications such as devices using this type of material, and the industrial value of the present invention is high.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the basic concept of a thin film superconductor manufactured according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of the temperature dependence of electrical resistance of the thin film superconductor realized according to the present invention, and FIG. 4 are schematic cross-sectional views showing the schematic structure of a fluorine treatment apparatus used in the present invention. 11... Substrate, 12... Composite compound coating, 13...
・Surface, 31... Ion source, 32, 33... Electrode, 34... Magnetic field generation source, 35... Substrate stand, 36
...Heater, 41...Plasma generation chamber, 42...
Microwave power supply, 43... Waveguide, 44... Sample chamber, 45... Insulating section.

Claims (11)

[Claims] (1) The main component is (A
_1_-_xB_x)_2 A composite compound film represented by CuO_4 is irradiated with fluorine ions or fluorine plasma (here, A is at least one of Nd, Sm, and Pr, and B is at least one of Ce and Th). and x is a numerical value in the range of 0≦x≦0.2. (2) The method for producing a thin film superconductor according to claim 1, characterized in that the composite compound film is heated during irradiation with fluorine ions or fluorine plasma. (3) The method for producing a thin film superconductor according to claim 2, characterized in that the composite compound coating upon irradiation with fluorine ions or fluorine plasma is heated while being maintained at a predetermined temperature of 500° C. or less. (4) The method for producing a thin film superconductor according to claim 1, wherein plasma generated by discharging a gas containing at least fluorine in a vacuum chamber is used as the fluorine ion or fluorine plasma source. (5) As a fluorine ion or fluorine 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 a fluorine ion or fluorine 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) A claim characterized in that fluorine ions generated by electric discharge in a vacuum chamber are accelerated and irradiated by applying a voltage between the plasma in the vacuum chamber and a sample stage on which a composite compound coating is installed. 4. The method for producing a thin film superconductor according to 4. (8) An electrode set to a predetermined potential is installed between the plasma generated by applying a high frequency voltage to a gas containing at least fluorine and the sample stage, and irradiation with fluorine ions is performed. A method for producing thin film superconductors. (9) The method for manufacturing a thin film superconductor according to claim 7, characterized in that a DC voltage of 2 KV or less is applied between the plasma and the sample stage. (10) The method for manufacturing a thin film superconductor according to claim 7, characterized in that the composite compound coating is placed in plasma generated by applying a high frequency voltage to a gas containing at least fluorine. (11) F_2, SF as a gas containing at least fluorine
5. The method for producing a thin film superconductor according to claim 4, wherein _6, SF_4, CF_4, and BF_3 are used.