JPH06280018A - Method and device for production of thin film superconductor - Google Patents

Abstract

(57) [Summary] [Objective] To provide a method for producing an oxide superconductor having a high superconducting critical current density. [Structure] As a Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _y vapor deposition source,
A high-frequency magnetron sputtering device including a target 13, a magnetron cathode 14, a shutter, and a high-frequency source, a hydrogen irradiation device is a small Kaufman type hydrogen ion gun with an acceleration voltage of 2 kV, and an oxygen treatment device is a plasma generation chamber 16 and a magnet. 18. Using an ECR oxygen plasma generator consisting of a microwave power source, etc., the processing conditions are as follows: microwave power 200 W, gas pressure 8.5 × 10 ⁻⁴
Torr, bias voltage 50V, 77K compared to the material without reactive hydrogen irradiation and oxygen treatment
, The superconducting critical current density could be improved about 10 times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for manufacturing a high temperature oxide superconductor, and in particular to Bi-Sr-C.
The present invention relates to a method and an apparatus for manufacturing a-Cu-O and Tl-Ba-Ca-Cu-O based thin film superconductors.

[0002]

2. Description of the Related Art The details of the superconducting mechanism of oxide superconducting materials represented by the Y-Ba-Cu-O system are not clear.
The transition temperature is as high as the temperature of liquid nitrogen or higher, and it is expected to be applied to various electronic fields such as quantum interference devices by thinning it.

The superconducting properties of this oxide superconducting material change depending on its crystal structure and production conditions, but it is said that the more well-controlled the crystallinity, the higher the superconducting transition temperature. Oxide superconductors with high crystallinity are excellent in initial characteristics at critical temperature and long-term stability, and good superconducting characteristics can be obtained by controlling crystallinity during production or immediately after production, and oxygen content. It is confirmed to bring.

However, the critical current density characteristics can be improved to some extent by controlling the crystallinity and optimizing the manufacturing conditions, but basically they are improved unless the arrangement of pinning centers in the crystal material can be designed. Can't hope

It is presumed that the pinning center in an oxide superconductor is a fine non-superconducting portion such as various crystal defects, crystal grain boundaries and impurities contained in the crystal, but it has been newly discovered. The pinning mechanism in high-temperature oxide superconductors has not been clarified at present.

In order to obtain this pinning effect, in the conventional case, when synthesizing a sintered material, impurities are mixed or impurities are precipitated by controlling firing conditions to obtain the effect of the pinning center. Attempts are being made. For example, in the case of a thin film material, various ions accelerated by a voltage of several tens of KV or higher, or high-energy particles such as fast neutrons are irradiated on the oxide thin film superconductor to cause defects in crystals or impurities. Attempts were made to inject or. Also, irradiation with energy beams such as X-rays, electron beams and ultraviolet rays was performed.

[0007]

Regarding the critical current density, which is one of the important characteristics required for thin film superconductors, detailed examination of the effect of irradiation with these energy beams has not yet been completed, and is not necessarily complete. It did not improve the characteristics. Moreover, even if the superconducting critical current is improved, the reason for this is still unknown.

That is, in general, Y-Ba-Cu-O
Bi-Sr-Ca-Cu-
There is no effect on O-based and Tl-Ba-Ca-Cu-O-based thin films, and it is difficult to form effective pinning centers with good controllability. The density could not be expected to improve easily.

On the other hand, in order to put such an oxide superconducting material into practical use, the Y-Ba-Cu-O system has an unstable oxygen defect structure, which causes problems in long-term stability and reliability. Therefore, the Bi-Sr-Ca-Cu-O system having a small superconducting temperature and a high superconducting critical temperature, and T
Utilization of the 1-Ba-Ca-Cu-O system is desired.

Further, in the conventional method, it is necessary to accelerate the ions at a high voltage and to use an X-ray apparatus, which is problematic in practical use, and the above-mentioned effects can be realized by a simple apparatus. Was wanted.

The present invention has been made in view of such conventional problems, and an object thereof is to provide a method for manufacturing an oxide superconductor having a high superconducting critical current density, and a simple and safe manufacturing apparatus. And

[0012]

The oxide thin film superconductor according to the present invention is irradiated with active hydrogen or reactive hydrogen such as hydrogen ions to react the oxide thin film superconductor with hydrogen to generate oxygen. It is possible to improve the crystallinity and precisely control the oxygen content in combination with heat treatment in an atmosphere or in active oxygen. In the present invention, such a hydrogen treatment is also performed during thin film production, during the thin film production, or while the thin film production is interrupted to perform oxygen treatment for promoting crystallization and supplying oxygen necessary for manifestation of superconductivity. During the thin film production or while the thin film production is interrupted, the above hydrogen treatment is performed together. In some cases, these treatments are performed by heating the produced thin film. As a simple method for hydrogen irradiation source, hydrogen ions are accelerated and used. In other words, a major feature is that high-performance thin film superconductors are realized with good controllability and stability by alternately repeating oxygen control by hydrogen treatment and oxygen treatment during thin film production, or by performing post-treatment after thin film production. There is.

[0013]

[Function] In the oxide superconductor, although the critical current density characteristics can be improved to some extent by controlling the crystallinity and optimizing the manufacturing conditions as described above, basically, the pinning in the crystalline material is performed. It is said that it is necessary to design a central arrangement.

The inventors of the present invention performed hydrogen irradiation during or after the above-mentioned oxide thin film superconductor was manufactured, and further performed appropriate oxygen treatment during or after the irradiation, to thereby remove oxide superconductor. Control the oxygen content,
It was found that an oxide thin film superconductor having excellent superconducting critical current characteristics can be realized with good controllability and stability.

Although the cause of this is not clear, the valence electrons of the Cu—O bond orbital are excited by hydrogen irradiation, the O ²⁻ is neutralized, and is removed from the crystal, resulting in the reduction of the Cu oxide. It is considered that the defective region with deteriorated superconducting properties acts as the pinning center.

Due to this action, the conventional Y-Ba-Cu-O
It is considered that the formation of the pinning center, which has been effective only in the system, is possible in the Bi system and the Tl system.

In the process, first, a non-superconducting region is formed by hydrogen treatment, and then oxygen treatment is performed to introduce oxygen into the defects in the planar Cu--O portion that controls superconductivity to make it superconducting. As a result, it is considered that crystal defects for pinning are controllably introduced into the positions of oxygen atoms other than the plane Cu—O in the thin film material, and this becomes the pinning center for the magnetic flux. Then, the invention was achieved by applying this to the production of a thin film superconductor.

This method has an advantage that a stable material can be supplied because the material is processed at a high temperature during oxygen treatment. In addition, when applied to thin film materials, it becomes easy to supply hydrogen to the entire thin film by hydrogen irradiation, and in particular, by performing hydrogen treatment for each extremely thin film deposition during thin film production, reactive hydrogen with low acceleration energy can be generated. It can be used, and it is possible to improve the characteristics with excellent uniformity, reproducibility, controllability, and reliability.

[0019]

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

Since the manufacturing method of the present invention performs hydrogen treatment and oxygen treatment, it requires a hydrogen irradiation device and an oxygen treatment device. Various devices can be used for hydrogen irradiation, but basically, a device that mainly uses active hydrogen and a device that mainly uses hydrogen ions can be distinguished. Since these can be obtained by ultraviolet irradiation, high frequency excitation, high frequency discharge, or thermal decomposition with a high heat filament,
A hydrogen source having such a function can be used. Further, as an apparatus for oxygen treatment, a heating furnace apparatus which can usually introduce a gas containing oxygen is generally used, but these hydrogen irradiation apparatuses can also be used for oxygen treatment.

First, an oxide thin film is formed by, for example, a sputtering method. In this case, as the substrate, a single crystal substrate is effective for producing an oxide thin film having high crystallinity,
A single crystal such as magnesium oxide, LaAlO ₃ , LaGaO ₃ , or strontium titanate is used.

When the oxide thin film is attached to the surface of the substrate, the present inventors need to have a substrate temperature range of 300 ° C. or higher in order to obtain a crystal structure having superconducting properties. Was confirmed to be appropriate. The optimum substrate temperature for optimizing the crystallinity, composition, and surface state of the oxide thin film exists in this range. A crystal structure of an oxide thin film superconductor is constructed under such a thin film production condition, and after depositing about 1000 Å, this is installed in, for example, a hydrogen ion irradiation device, an acceleration voltage of 1 KV, a current density of 0.
Irradiation is performed for 15 minutes under the condition of 6 mA / cm ² .

By this irradiation, the resistivity of the thin film shows a semiconductor-like response to the temperature change, and the value of about 10 ⁻⁴ Ω · cm at the superconducting critical temperature before hydrogen irradiation is 0.1 ohm by the irradiation.
・ It became about cm and no superconducting zero resistance was exhibited.

This sample was placed in a heating furnace introduced with oxygen gas, subjected to high temperature treatment at 800 ° C. for 5 hours, and subsequently, oxygen supply and crystallinity improvement were carried out by a slow cooling process at 80 ° C./hour. .

At the same time, it was possible to confirm the effect of the hydrogen treatment by placing the thin film sample not subjected to the hydrogen treatment at the same time in the heating furnace. That is, there was almost no change in the superconducting transition temperature between the sample subjected to the hydrogen treatment and the sample not subjected to the hydrogen treatment, but at the critical current density, for example, 1 × 1 at 77K.
0 ⁵ A / cm ² was improved about 10 times. The degree of this improvement depends on the conditions for forming the thin film, but the inventors have confirmed that the effect of hydrogen irradiation on a thin film having good crystallinity is more stable.

Such a treatment was carried out by taking out the sample from the apparatus after the thin film was formed. However, after the thin film preparation was completed, the sample was not taken out from the apparatus and the hydrogen treatment and the oxygen treatment were continuously carried out in the vacuum chamber. By this, it is considered that a more stable effect can be obtained.

Further, the inventors of the present invention have found that the oxide thin film superconductor having high crystallinity is excellent in initial characteristics and long-term stability, and the crystallinity and oxygen content can be controlled during or immediately after film formation. It was confirmed that it brings about better superconducting properties. Especially in the Y-based superconductor, once the thin film is taken out of the thin film production tank, water in the air is adsorbed on the surface,
Since the hydrogen treatment and the oxygen treatment react with the constituent elements of the thin film and deteriorate the characteristics, it is necessary to incorporate the hydrogen treatment and the oxygen treatment as part of the oxide thin film production process.

As a method of hydrogen treatment and oxygen treatment in the thin film manufacturing process, (1) the thin film deposition is performed at the same time, or (2) the thin film deposition is interrupted, that is, the thin film deposition process, the hydrogen treatment process and the oxygen treatment. (3) Only hydrogen irradiation is performed during thin film formation in an oxygen atmosphere. (4) A method of performing hydrogen treatment by switching to oxygen supply hydrogen irradiation during thin film formation in an oxygen atmosphere can be considered.

First, as a step corresponding to (1), the present inventors performed hydrogen irradiation during the production of an oxide thin film, introduced oxygen gas into the production tank immediately after the production of the thin film, and carried out the same process as the sintered body. It was confirmed that good superconducting properties can be obtained by performing oxygen treatment as a post-treatment by the slow cooling process.

The present inventors further found that defects were produced with good controllability by hydrogen irradiation and that oxygen was most effectively incorporated into the thin film by the oxygen treatment at a temperature lower than the substrate temperature for forming the thin film and higher than room temperature. It was discovered that the temperature range was limited, and that hydrogen treatment and oxygen treatment could be most efficiently and simply performed by performing the treatment in this temperature range for a certain period of time. The present inventors have confirmed that this effect can be obtained also in the step (2).

Since the temperature at which these hydrogen treatment and oxygen treatment should be performed differs depending on the type of the constituent elements of the thin film and the surface condition, it is necessary to select the optimum one for each case. It was confirmed that the temperature was below 300 ° C. The processing time also has an optimum value depending on the type of thin film, the film thickness, and the surface condition.

The inventors of the present invention carry out the hydrogen treatment and the oxygen treatment simultaneously with the thin film deposition, or when the thin film deposition is interrupted, that is, the thin film deposition step and the hydrogen treatment and the oxygen treatment step are alternately repeated. As a method of hydrogen treatment and oxygen treatment used in some cases, it is effective and convenient to treat with at least hydrogen gas or ions generated by discharge of oxygen gas, or to irradiate excited neutral atoms. I found that. For example, EC
Using the R plasma generator, a gas containing hydrogen or oxygen is introduced into the plasma generation chamber connected to the production tank,
By irradiating this gas with microwaves to generate discharge plasma and applying a magnetic field to this to increase the probability of ionization, it is possible to efficiently process the oxide thin film with ions and neutral atoms. I found it.

When such a treatment is carried out after forming an oxide thin film and used as a post-treatment step after being taken out from the vapor-deposition bowl, the critical temperature is improved in a short time, but with respect to the critical current density, oxygen treatment is more than ten. It takes time to order. This is considered to mean that the oxygen treatment is rate-controlled by the diffusion behavior of oxygen, and it takes a very long time to reach the entire complex oxide thin film. Oxygen treatment is performed at the same time as thin film deposition and hydrogen treatment, or by interrupting thin film deposition and hydrogen treatment, that is, performing thin film deposition step, hydrogen treatment step and oxygen treatment step alternately This enables effective processing.

From the point of view of performing hydrogen treatment and oxygen treatment, it is most desirable to perform these treatments at the same time as the thin film deposition, but the treatment temperature is limited to the deposition substrate temperature depending on the kind of the thin film deposition process. It was confirmed that the sufficient effect could not be obtained, or that high-energy particles might adversely affect.

The inventors of the present invention rather have the same or higher effect when the thin film deposition is interrupted, that is, the thin film deposition process and the hydrogen treatment and the oxygen treatment process are alternately repeated. It was confirmed that it was obtained.

In these thin film deposition processes, the respective constituent elements immediately after deposition are in an excited state, and in some cases, it takes a few minutes to stabilize,
In particular, in the case of a laminated structure, the deposition may be interrupted every time one period of the structure is deposited to stabilize the structure. It is considered that if hydrogen treatment and oxygen treatment are performed during such a deposition interruption time, ideal hydrogen treatment and oxygen treatment can be performed in a short time.

The present inventors have confirmed that a thin film superconductor having excellent characteristics can be obtained by interrupting every suitable deposition time and performing hydrogen treatment and oxygen treatment. Furthermore, it was confirmed that it is effective to set the deposition time interval such that the thickness of the thin film deposited during that time is 10 Å or more and 100 Å or less. Further, in such a process, hydrogen ions having a particularly low acceleration energy can be used, and 5 KV
It was confirmed that the following accelerating voltage is also effective.

Further, by adopting the treatment process including this hydrogen treatment, Bi effect, which has not been confirmed to be the conventional effect, is obtained.
It has been confirmed that the superconducting critical current is improved for the system and Tl superconductors. And, of course, it was confirmed that this new method and apparatus are effective even for the Y system composed of the conventional Ln (atomic numbers 63 to 71).

(Specific Example) In a thin film forming apparatus having such a structure, a magnesium oxide single crystal (100) surface was used as a substrate 11, and a high temperature oxide superconducting material was sintered by high frequency planar magnetron sputtering. The prepared target 13 is sputter-deposited in a mixed gas atmosphere of Ar and O ₂ , and crystalline Bi- is formed on the substrate.
It was deposited as a Sr-Ca-Cu-O thin film.

In this case, the gas pressure is 0.4 Pa, the sputtering power is 160 W, the sputtering time is 30 minutes,
The film thickness was 0.5 μm, and the substrate temperature was 600 ° C.

After the thin film was formed, the sample was divided into two, one sample was placed on the stage of the ion irradiation apparatus, the temperature of the stage was set between 10 ° C. and 500 ° C., and hydrogen generated by the Kauffman type ion source was used. Ions were accelerated and irradiated between 300 V and 2 KV.

Thereafter, both this sample and the sample not subjected to the hydrogen treatment were placed in an atmosphere containing oxygen and heat-treated at a temperature between 700 ° C. and 900 ° C., and a temperature of 100 ° C.
It was slowly cooled at less than / hour and taken out from the heat treatment furnace. These two
As a result of comparing two samples, as the conditions of hydrogen irradiation, the substrate heating was 100 ° C., the acceleration voltage was 1 KV, and the ion irradiation amount was 2.5.
In the case of × 10 ¹⁸ / cm ^2, the superconducting critical current density 1.0 × 10 ⁵ A / cm ² without hydrogen treatment at 77K is 1
It was improved about 0 times.

The crystallinity of these two samples was
As a result of examining the composition and composition, no change was observed. The X-ray diffraction pattern of the sample subjected to this heat treatment shows that Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _y with good crystallinity was produced, and there is no difference in this pattern between the two samples. It was

From this, it was confirmed that the active hydrogen species did not change the crystal structure of the oxide superconductor and was effective in improving the critical current characteristics. FIG. 1 is a diagram showing the temperature dependence of the critical current density when hydrogen treatment is performed and when hydrogen treatment is not performed.

It is considered that such an irradiation of hydrogen is such that hydrogen stays in the vicinity of the surface because the acceleration voltage is small and the effect is limited to the vicinity of the surface when the film thickness is large. It is considered that the effect can be made uniform in the film by increasing the accelerating voltage, but for that purpose, a large-scale ion implantation device is required. On the other hand, small ion guns, high-frequency excitation method, ECR plasma method, etc. are often used as a simple source for the source of elementary species, but from the above results, it is possible to use these sources of hydrogen species during thin film formation. It is expected to obtain the effect of improving the critical current.

When the hydrogen treatment and the oxygen treatment are incorporated as a part of the oxide thin film production process, the oxide thin film production apparatus has a device configuration as shown in FIG. A vapor deposition source, a device for hydrogen irradiation, and a device for oxygen treatment are attached, and a hydrogen supply port and an oxygen supply port are provided. In the example of FIG. 2, the target 13 and the magnetron cathode 14 are used as the vapor deposition source.
And a shutter, a high-frequency magnetron sputtering device including a high-frequency power source, a hydrogen ion gun for hydrogen irradiation, and a plasma generation chamber 16, a magnet 18, a microwave power source, etc. for oxygen treatment. An ECR oxygen plasma generator is used. Depending on the combination of the vapor deposition source, the apparatus for irradiating hydrogen, and the apparatus for oxygen treatment, the production tank is separated, a load lock mechanism is provided, and the substrate 11 can be moved together with the holder.

The oxygen treatment method uses the ECR plasma method, and the treatment conditions are as follows: microwave power 200 W, gas pressure 8.5 × 10 ⁻⁴
Torr was performed at a bias voltage of 50 V, and the hydrogen treatment was performed using a Kauffman type small ion gun at an acceleration voltage of 2 KV. In addition to this combination, an ozonizer with high-frequency excitation was used for oxygen treatment, and oxygen gas containing ozone obtained by flowing oxygen gas with high-frequency power of 800 W was introduced into the vacuum layer.

When the thin film deposition step, the hydrogen treatment step, and the oxygen treatment step are alternately repeated periodically, the thickness of the thin film to be deposited in one cycle and the hydrogen treatment time and the oxygen treatment time are
It was set to about 100Å, 5 minutes and 72 seconds, respectively. In this case, the thin film deposition is usually carried out in an oxygen atmosphere, so that it is not necessary to take a long time for the oxygen treatment depending on the thin film manufacturing conditions.

As a result of the thin film processing steps including the hydrogen treatment and the oxygen treatment performed in such a thin film forming apparatus, any of the thin film deposition step and the hydrogen treatment step of (1), (2) and (4) described above is performed. The present inventors have confirmed that even when a combination with an oxygen treatment step is used, a higher transition temperature can be obtained and a larger critical current density can be obtained as compared with the case where no hydrogen treatment and oxygen treatment are performed. On the other hand, in the case of (3), the composition of the thin film changed and the crystallinity deteriorated. However, even in this case by setting the optimum conditions, it can be inferred from the above-mentioned basic irradiation experiments by the inventors that there is a sufficient possibility that the characteristics can be improved.

As described above, the details of the changes in the optimum conditions of the hydrogen treatment and the oxygen treatment are not clear, but no improvement was observed by the conventional method. Bi-Sr-Ca-Cu-
There is no doubt that the critical current densities of O-based and Tl-Ba-Ca-Cu-O-based thin film superconductors can be improved, and the present invention establishes the hydrogen treatment and oxygen treatment steps in the production of thin film superconductors. Is.

[0051]

According to the present invention, A is Ln (atomic number 63 to 7).
1), at least one of Tl and Bi, and B is at least one element of alkaline earth group elements AB
Since it is a method of manufacturing a thin film superconductor in which an oxide thin film represented by -Cu-O is irradiated with reactive hydrogen and then further subjected to oxygen treatment, reliability of an element using an oxide high temperature superconductor, long-term A process for ensuring stability is provided, which has extremely great industrial value.

Since the superconductor used is homogeneous and thin-film single-crystallized as compared with the conventional thin film, an efficient and simple hydrogen treatment capable of realizing a very high-performance superconducting device according to the present invention. There is a big feature in finding the oxygen treatment process.

[Brief description of drawings]

FIG. 1 is a temperature dependence diagram of a superconducting critical current density between a sample subjected to hydrogen treatment and oxygen treatment and a sample subjected only to oxygen treatment.

FIG. 2 is a cross-sectional view of the basic structure of a thin-film superconductor manufacturing apparatus according to an embodiment of the present invention.

[Explanation of symbols]

11 substrate 13 target 14 magnetron cathode 19 O ₂ gas inlet

Claims (6)

[Claims] 1. A method for producing a thin film superconductor, which comprises irradiating an oxide thin film represented by AB-Cu-O with reactive hydrogen and further subjecting it to oxygen treatment. Where A
Is at least one of Ln (atomic numbers 63 to 71), Tl, and Bi, and B is at least one of the alkaline earth group elements. 2. Production of a thin film superconductor characterized by irradiating reactive hydrogen in a thin film producing step during the production of an oxide thin film represented by AB-Cu-O, and then further oxygen treatment. Method. Where A is Ln (atomic number 63
~ 71), at least one of Tl and Bi, and B represents at least one of the alkaline earth group elements. 3. The method for producing a thin film superconductor according to claim 1, wherein the reactive hydrogen is hydrogen ions accelerated at 5 KV or less. 4. The thin film manufacturing process is characterized in that a thin film deposition process and a hydrogen treatment process and an oxygen treatment process are alternately repeated, and the thickness of the thin film deposited in one thin film deposition process is 100 Å or less. The method for producing a thin film superconductor according to claim 2. 5. An evaporation source capable of producing an oxide thin film represented by AB-Cu-O, a heatable stage for setting a substrate for depositing the thin film, and a supply for supplying oxygen in a vacuum chamber. A thin-film superconductor manufacturing apparatus comprising a hole and a hydrogen supply hole for hydrogen irradiation. 6. A thin film superconductor according to claim 5, further comprising a hydrogen ion source capable of applying an electric field of 5 KV or less to a stage in which a substrate can be placed and heated in a vacuum chamber. apparatus.