JP2742418B2 - Method for producing oxide superconducting thin film - Google Patents

Description

The present invention relates to a method for producing an oxide superconducting thin film applicable as a superconducting device such as a Josephson device or a superconducting memory device.

[Background Art] In recent years, oxide-based superconductors have been discovered in which a critical temperature (Tc) at which a transition from a normal conducting state to a superconducting state is higher than the temperature of liquid nitrogen is high.

Conventionally, methods for producing a thin film made of this kind of oxide superconductor include, for example, a vacuum deposition method, a sputtering method, an MBE (molecular beam epitaxy) method, a CVD (chemical vapor deposition) method, and an IVD (ion vapor deposition). Various film forming methods such as the method are known. Each of these film forming methods is performed under a low pressure of 1 Torr or less, and furthermore, in order to supply oxygen to the thin film, the atmosphere is changed to an oxygen gas atmosphere or an oxygen gas and an inert gas. It is a mixed gas atmosphere such as an atmosphere.

However, in the above-mentioned conventional method, since the partial pressure of oxygen in the atmosphere is low, it is difficult to introduce a desired amount of oxygen into the crystal of the film formed on the substrate, and the crystal composition is changed from the stoichiometric composition. There is a problem of deviation, and a film body having low superconducting characteristics such as critical current density tends to be generated.

Therefore, conventionally, at the time of film formation or after film formation, the film body is subjected to a heat treatment of heating to about 600 to 1000 ° C. in an oxygen atmosphere to adjust the crystal structure of the film body, and adjust the oxygen concentration to adjust the superconductivity of the film body. Is performed.

In order to perform the above-described heat treatment, for example, as shown in FIG. 4, a heater 3 is provided inside a substrate holder 2 arranged opposite to a sputtering target 1 to heat a substrate 4 mounted on the substrate holder 2. The heater 3 heats the film body through the substrate 4.

As another method for performing the above-described heat treatment, a substrate is placed inside a vacuum chamber, and a film on the substrate is irradiated with infrared rays from outside the vacuum chamber through a transparent window provided in the vacuum chamber. There are known a method of heating a film, a method of providing an infrared lamp inside a vacuum chamber, and heating the film by the infrared lamp.

“Problem to be Solved by the Invention” In the conventional method performed using the heater 3,
Since the heater 3 is used in an atmosphere where oxygen is present, there is a problem that the life of the heater 3 is shortened. Further, in order to heat the substrate to a sufficiently high temperature, it is necessary to use the heater 3 having a large heat capacity. However, when the heat capacity of the heater 3 is large, the power supply is stopped when the superconducting thin film is rapidly cooled after heating. Nevertheless, there is a problem that the cooling rate cannot be increased because the heater 3 dissipates residual heat, and the superconductivity tends to deteriorate after film formation. For this reason, conventionally, it has been necessary to heat-treat the superconducting thin film in a separate step after forming the superconducting thin film, adjust the crystal structure of the superconducting thin film, and adjust the oxygen concentration. Furthermore, when heating is performed using the heater 3, a part of the constituent material of the heater 3 evaporates and mixes as an impurity in the superconducting thin film on the substrate 4, which causes a problem of deteriorating the superconducting characteristics of the superconducting thin film. .

On the other hand, in the conventional method of heating using infrared light, the irradiation range is limited by the size of the transparent window because the film is irradiated with infrared light through the transparent window formed in the vacuum chamber. Is difficult to heat to a sufficiently high temperature, and in particular, when the irradiation range of infrared rays is narrow, there is a problem that uniform heating cannot be performed. Furthermore,
Due to the formation of the transparent window in the vacuum chamber, the degree of vacuum inside the vacuum chamber cannot be increased, and in some cases, the degree of vacuum in the vacuum chamber is reduced due to the transparent window.

When an infrared lamp is provided inside the vacuum chamber and heating is performed, the size of the infrared lamp that can be installed is limited due to the limitation of the internal space of the vacuum chamber,
This limits the maximum temperature that can be heated,
There is a problem that it cannot be heated to a desired temperature.

The present invention has been made in order to solve the above-mentioned problems, and can be heated to a temperature high enough to improve the superconducting properties by adjusting the crystal shape, and it is also easy to control the temperature and to perform a rapid cooling process. Accordingly, it is an object of the present invention to provide a method for manufacturing an oxide superconducting thin film without mixing impurities.

"Means for solving the problem" The first invention uses a base material at least partially formed of a conductor or a dielectric,
In a state where the base material is subjected to high-frequency induction heating, an oxide superconducting thin film is formed on the base material using both the source of the constituent elements of the oxide superconducting thin film and the supply source of oxygen. Is stopped to cool the substrate.

The second invention uses a substrate formed at least in part from a conductor or a dielectric to solve the problem,
Forming an oxide superconducting thin film on this substrate, then heating the substrate by high-frequency induction heating to heat the oxide superconducting thin film, stopping the high-frequency induction heating after cooling for a required time, and cooling the substrate. It is.

[Function] Heat treatment of the superconducting thin film is performed by high-frequency induction heating of the base material, the crystal structure of the superconducting thin film is adjusted, and the amount of oxygen in the superconducting thin film is adjusted. Further, it is not necessary to provide a heater having a large heat capacity in the vicinity of the substrate in order to generate heat in the substrate itself, and the superconducting thin film can be rapidly cooled after heating. Furthermore, since there is no need to provide a heater near the base material, impurities do not enter the superconducting thin film.

 Hereinafter, the present invention will be described in more detail.

FIG. 1 shows an example of an apparatus used for forming an oxide superconducting thin film by applying the sputtering method using an ion source to form an oxide superconducting thin film. 2 shows a plate-like base material to be formed.

As shown in FIG. 2, the base material 11 is formed on a plate-shaped main body 12 made of a metal material such as a nickel-based alloy such as stainless steel, Hastelloy, and superalloy, and on the upper surface of the main body 12. coating layer 13 made MgO, ZrO, etc. BaTiO ₃
It is composed of The constituent material of the coating layer 13 is as follows:
As described later, a material having low reactivity with constituent elements of the oxide superconducting thin film H formed on the substrate 11 and being chemically stable is selected, and the coating layer 13 is formed by a film forming method such as a high-frequency magnetron sputtering method. Thereby, it is formed on the upper surface of the main body 12. At least one of the main body 12 and the coating layer 13 is formed of a conductor or a dielectric that generates heat by a high-frequency induction heating method. Note that the shape of the base material 11 is not limited to a plate shape, and any shape such as a linear shape, a tape shape, and a tubular shape can be used.

On the other hand, as shown in FIG. 2, the oxide superconducting thin film H formed on the base material 11 is specifically ABCD (where A is Sc, Y, La, Ce, Pr). , Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, E
R, Tm, Yb, Lu, etc., represent at least one group IIIa element of the periodic law, and B represents one of the group IIa elements of the periodic table, such as Sr, Ba, Ca, Be, Mg, Ra. In the above, C represents two or more elements including Cu or Cu among elements of the group Ib of the periodic table such as Cu, Ag, and Au and Nb, and D represents O, S, Se, Te, Po. And O or two or more elements containing O among the Group VIb elements of the periodic table such as F and Br, I, and At. ) System. For example, in the case of a Y-Ba-Cu-O-based superconductor, the composition ratio of each constituent element of this oxide-based superconductor is Y: Ba: Cu: O = 1: (2-3) :( 3-3 4): (7
To δ) are preferable, and δ is preferably in the range of 0 to 5.

Means for forming the superconducting thin film H on the substrate 11 include a vacuum evaporation method, a sputtering method, an MBE (molecular beam epitaxy) method, a CVD chemical vapor deposition (IVD) method, an IVD (ion vapor deposition) method, a cluster ion Various film formation methods such as a beam method can be applied. In this example, a sputtering method using an ion source is performed.

In the apparatus shown in FIG. 1, a substrate 11 and a target 15 (a supply source of the constituent elements of the oxide superconducting thin film) are arranged inside a vacuum vessel so as to face each other. The first ion source 16 (supply source for the constituent elements of the oxide superconducting thin film) is provided as described above, and the second ion source 17 (supply source for oxygen) is provided on the side of the target 15 so as to face the substrate 11. Furthermore, a high-frequency coil 19 of a high-frequency induction heating device 18 is provided in the vicinity of the substrate 11 so that the substrate 11 can be heated by high-frequency.

The target 15 is made of a material containing an element constituting the above-described oxide superconductor. Therefore, ABCD
A target composed of an ABCD-based superconductor produced by calcining and sintering a mixed powder containing each element of the system, or a target consisting of A, B, C and D , Etc. can be used.

The first ion source 16 is a device for irradiating the target 15 with accelerated ions to strike out constituent atoms of the target 15 and form a film on the substrate 11. The second ion source 17 is a device that irradiates the substrate 11 with oxygen in the form of ions, atoms, molecules, or the like. These ion sources 16 and 17 are provided with an ion generator and an ion extraction electrode, and are configured so that ions generated by the ion generator can be accelerated and irradiated by the extraction electrode.

Next, a case of manufacturing an oxide superconducting thin film using the apparatus shown in FIG. 1 will be described.

In order to manufacture an oxide superconducting thin film using the apparatus shown in FIG. 1, first, the base material 11 and the target 15 are set at predetermined positions inside a vacuum vessel, and the inside of the vacuum vessel is evacuated to reduce the internal pressure. After increasing the pressure to 10 ^-1 Pa or higher, the ion source
Activate 7 Further, the base material 11 is
The substrate 11 is heated to about 600 to 1000 ° C. by applying a high frequency to the substrate 11.

By the above operation, the ion source 16 irradiates the target 15 with ions to perform sputtering, and AB on the substrate 11.
-A superconducting thin film H of the CD type is generated.

Further, the oxide superconducting thin film H can be generated while supplying a sufficient amount of oxygen by irradiating the ion source 17 with oxygen ions. During film formation, the internal pressure of the vacuum
^{When the} value is lower than ^-1 Pa, when a high frequency is applied to the base material 11, plasma is generated by glow discharge inside the vacuum vessel, and ion ions of the plasma collide with the superconducting thin film H formed on the substrate and become superconductive. There is a problem that a lattice defect or a composition deviation is introduced into the thin film H, and the film formation rate is further reduced. Therefore, it is preferable to set the pressure in the vacuum chamber to a high value of 10 ^-1 Pa or more.

When the superconducting thin film H having a predetermined thickness is formed on the base material 11, the irradiation of ions by the ion sources 16 and 17 is stopped, and the high-frequency heating of the base material 11 is stopped immediately after film formation or after a predetermined time has elapsed. The substrate 11 is cooled.

When the irradiation of oxygen ions from the oxygen ion source 17 is not performed, there is a possibility that a superconducting thin film deviating from a desired stoichiometric composition may be generated due to a lack of oxygen inside crystals of the generated superconducting thin film. . Such a superconducting thin film lacking oxygen has a disadvantage that the superconducting properties are inferior. If oxygen ions are supplied from the ion source 17 at this point, the oxygen deficiency can be eliminated and the superconducting thin film H excellent in characteristics of the target composition conforming to the stoichiometric composition can be obtained.

Further, since the superconducting thin film H is formed while performing high-frequency heating on the base material 11, there is an effect that the superconducting thin film H can be heated to a sufficiently high temperature. Then, after high-frequency heating, the superconducting thin film H
Is cooled, the base material 11 can be rapidly cooled because there is no member having a large heat capacity in the vicinity of the base material 11 as compared with the conventional method of heating with a heater having a large heat capacity. Therefore, the crystal structure of the formed superconducting thin film H can be adjusted, and the ratio of oxygen in the crystal can be set to a desired value. is there. Further, according to the method of the present invention, since it is not necessary to use the heater used in the conventional method, no impurities are mixed into the superconducting thin film H. In addition, since it is not necessary to use infrared rays for heating the superconducting thin film H, it is not necessary to provide a transparent window for transmitting infrared rays on the outer wall of the vacuum vessel, and the degree of vacuum of the vacuum vessel does not decrease.

On the other hand, in the second invention, the object is achieved by heating the substrate 11 by high frequency heating after forming the superconducting thin film H.

That is, in a state where the high-frequency heating is stopped, the superconducting thin film H is formed in a state where the base material 11 is heated to a required temperature by a heating device such as an infrared lamp, and after the superconducting thin film H is formed, the heating by the infrared lamp or the like is stopped. Then, high-frequency heating is performed on the substrate 11 to adjust the crystal structure of the superconducting thin film H and adjust the amount of oxygen. By performing such a method, the amount of oxygen in the superconducting thin film H can be adjusted, and the crystal structure of the superconducting thin film H can be adjusted.

FIG. 3 shows another example of the substrate used in the method of the present invention.

The base material 20 shown in FIG. 3 is an element having low reactivity with the constituent elements of the superconducting thin film, and is made of a chemically stable metal material. It is possible.

In the above-described example, it is free to provide an infrared lamp or the like for preheating the superconducting thin film H in the vacuum container.
Of course, a temperature control device or the like for adjusting the temperature of the entire inside of the vacuum vessel may be provided.

"Example" A tape-shaped base material was prepared by forming a coating layer having a thickness of 1 µm on a tape-shaped main body made of stainless steel and having a width of 10 mm and a thickness of 0.5 mm. Next, using the apparatus having the configuration shown in FIG.
Using a Y-Ba-Cu-O-based composite oxide as a sputtering target, a sputtering method using an ion source is performed to form an oxide superconductor represented by Y-Ba-Cu-O on the substrate. The elements were sputtered and simultaneously irradiated with oxygen ions, and a high frequency of 30 to 100 kHz was applied to the substrate to generate heat and the substrate was heated to 700 ° C. to form a superconducting thin film. At this time, the ion acceleration voltage of the ion source is 1000 V, the ion current is 100 mA, and the degree of vacuum of the atmosphere is 5 × 10
^-1 Pa.

After sputtering for 4 hours under the above conditions,
The sputtering and energization were stopped, and the substrate was cooled to obtain a superconducting thin film. In this case, the time required for lowering the substrate temperature from 700 ° C. to 100 ° C. and the critical temperature (Tc) of the formed superconducting thin film were measured and are shown in Table 1 below.

Further, using an apparatus configured by adding an ion source to the conventional apparatus having the configuration shown in FIG. 4, using a Y-Ba-Cu-O-based sputtering target and heating the substrate to 700 ° C. with a heater, Under the same conditions as in the previous example, ion sputtering and oxygen ion irradiation are simultaneously performed to form an oxide superconducting thin film, and after film formation, the power to the heater is stopped and the substrate is cooled to obtain an oxide superconducting thin film. Was.

In this case, the time required for lowering the temperature of the substrate from 700 ° C. to 100 ° C. and the critical temperature of the formed oxide superconducting thin film were measured and are shown in Table 1.

As is clear from Table 1, when the substrate was heated at a high frequency, it was found that the cooling time could be greatly reduced as compared with the case where the substrate was heated using a heater, and that rapid cooling treatment was possible. In addition, it was also found that the manufacturing time of the superconducting thin film was improved because the cooling time could be significantly reduced.
In addition, it was found that the oxide superconducting thin film manufactured by rapid cooling after high-frequency heating had a high critical temperature.

[Effects of the Invention] As described above, the present invention can heat the oxide superconducting thin film by high-frequency heating of the base material, so that the superconducting thin film can be heated to a sufficiently high temperature. Since a member having a large heat capacity can be eliminated in the vicinity of the substrate as compared with the conventional method in which the substrate is heated by a large heater, the substrate can be rapidly cooled. Therefore, the crystal shape of the oxide superconducting thin film can be adjusted, and the amount of oxygen in the crystal can be adjusted by using an oxygen supply source without causing oxygen shortage. This has the effect of producing an oxide superconducting thin film excellent in the above. Further, since it is not necessary to use a heater, no impurity element is mixed into the superconducting thin film from the atmosphere. Further, since there is no need to use infrared rays for heating the superconducting thin film, it is not necessary to provide a transparent window on the outer wall of the vacuum vessel, and the vacuum degree of the vacuum vessel does not decrease. There is an effect that the film can be implemented.

[Brief description of the drawings]

FIG. 1 is a structural view showing an example of an apparatus used for carrying out the method of the present invention, FIG. 2 is a cross-sectional view showing an example of a substrate used for carrying out the method of the present invention, and FIG. FIG. 4 is a cross-sectional view showing another example of a substrate to be used, and FIG. 4 is a configuration diagram for explaining a conventional method. 11,20 Base material, 12 Body part, 13 Coating layer, 15 Target, 16 First ion source, 17 Second ion source, 18, High frequency heating device, 19 ... High frequency coil, H ... Superconducting thin film.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01B 13/00 565 H01B 13/00 565D H01L 39/24 ZAA H01L 39/24 ZAAB (72) Inventor Satoshi Kono Kiba, Koto-ku, Tokyo 1-5-1, Fujikura Electric Wire Co., Ltd. (56) References JP-A-62-1154 (JP, A) JP-A-61-104077 (JP, A) JAPANESE JOURNAL OF APPLIED PHYSIC S.S. VOL. 26, NO. 7, JULY, 1987, PP. L1199-L1201 edited by the Ministry of International Trade and Industry, Ministry of Industry and Industry, “All about Superconductivity” Maruzen Co., Ltd., January 31, 1988, p. 109−123

Claims (2)

(57) [Claims] 1. A substrate, at least a part of which is formed of a conductor or a dielectric, is used, and both the supply source of the constituent elements of the oxide superconducting thin film and the supply source of oxygen are used in a state where the substrate is subjected to high-frequency induction heating. To form an oxide superconducting thin film on the substrate,
A method for producing an oxide superconducting thin film, wherein heating of the substrate is stopped after the formation of the oxide superconducting thin film to cool the substrate. 2. An oxide superconducting thin film is formed by using a substrate formed at least in part of a conductor or a dielectric, forming an oxide superconducting thin film on the substrate, and thereafter heating the substrate by high-frequency induction heating. A method for producing an oxide superconducting thin film, comprising heating a substrate, heating for a required time, and then stopping high-frequency induction heating to cool the substrate.