JPH03215319A - 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] Industrial Field of Application The present invention relates to a method for producing a superconducting thin film. Especially in the formation of a multi-component thin film superconductor, the superconducting thin film has excellent controllability and higher performance. The present invention relates to a manufacturing method that provides excellent superconducting properties.

Conventional technology As a high-temperature superconductor, niobium nitride (NbN) and germanium niobium (Nb*Ge) are used as A15 type binary compounds.
etc., but the superconducting transition temperature of these superconducting materials was at most 24 K. An even higher transition temperature is expected compared to the ternary compounds of the 1X perovskite system.Ba-La-Cu-0 A system of high-temperature superconductors was proposed.
Page (J, G. Bendorz and K. A. Mul
ler, Zetshrift Furphysik
B- Condensed Matter 6
4, 189-193 (1986)].

Sara! Q Bi-Sr-Ca-Cu-0 material 7K
It was also discovered that it exhibits a transition temperature higher than IOOK [
27th volume, page 209 (H. Ma
eda, Y., Tanaka, M., Fukuto
mi and T, Asano, Japanese
Journal of Applied P
hyscs 27. L209-L210 (198
8)》 Ko.

Furthermore, it has a crystal structure similar to that of Bi-Sr-Ca-Cu-0 superconductor.TI has a superconducting transition temperature exceeding 120K.
-Ba-Ca-Cu-0 system was discovered.
dA. M. Hermann, Nature Vol.
．． 332. 138-139 (1988))].

Although the details of the superconducting mechanism of this type of material are not clear,
The transition temperature of this type of material can be higher than room temperature, and it is expected that this type of material will have more promising properties as a high-temperature superconductor than conventional binary compounds. (Melon) It is mainly formed through the process of sintering, and is often obtained in the form of ceramic powder or blocksb~ One person When this type of material is to be put to practical use in devices, etc., it must be processed into a thin film. Although there is a strong demand for this, various methods such as vacuum evaporation, magnetron sputtering, and plasma CVD are used to form thin films.
Thin films of oxide superconductors are being made.Special E, Bi-Sr-Ca-Cu-Oi Tl-B, which had many difficulties in producing thin films with good superconducting properties using conventional techniques.
In the a-Ca-Cu-0 system, there are several phases with different zeta superconducting transition temperatures, and it is extremely difficult to achieve a phase with a critical temperature of 100 K or more in the form of a thin film. It is said that it is very difficult to control the crystallinity and produce a single crystal with excellent crystallinity.9 This is influenced by the shape of the substrate, which tends to form an island-like crystal structure, which tends to reduce the current density. The main reason is that the superconducting properties tend to deteriorate easily, but for this reason, it is a high-performance superconducting thin film at a film thickness of about 100A, which is required when considering application to electronic devices, etc. The present invention was proposed to overcome the above-mentioned conventional problems, and it is possible to stack oxide superconducting thin films on a substrate with excellent reproducibility and crystallinity. It is an object of the present invention to provide a method for manufacturing a thin film superconductor of the present invention.A method for manufacturing a thin film superconductor of the present invention includes the following steps: A method for manufacturing a thin film superconductor of the present invention includes: A superconducting thin film of an oxide containing copper is formed on top of a layer of oxide containing bismuth. After trying to form various substances and considering the degree of layer diffusion, etc., we found that after first forming an oxide layer consisting of a substance containing copper and alkaline earth, 1;;Bi- 0 layer is formed, but when a composite oxide superconducting thin film containing copper is laminated on top of it, a single crystal thin film with almost no grains is formed, but this consists of the copper and alkaline earth that were initially formed on the substrate. Oxide ζ is formed on the heated substrate by spreading to fill the irregularities of the substrate. By subsequently forming a Bi-0 film, it is thought that a flat surface can be formed on the substrate surface. By periodically laminating oxide layers made of a substance containing the above-mentioned substances, diffusion between the layers can be suppressed and crystallinity can be improved.
The unevenness greatly affects the crystallinity of the thin film, so when forming a thin film, especially when forming an ultra-thin film device, it is necessary to use a material with small unevenness (to obtain a thin film with excellent properties and good crystallinity). Rare l.%
However, it is almost impossible to eliminate the unevenness due to the production process (~ It is believed that the crystallinity of superconducting thin films in particular has a large influence on the characteristics, and the first thing to do to improve current density is crystallinity. Although the surface roughness of the substrate can be improved, it is also easy to form crystal island structures, leading to a decrease in current density and transition temperature. However, according to the manufacturing method of the present invention, the layer which forms a layer mainly composed of copper oxide and alkaline earth oxide on the substrate preferentially adheres from the concave portion of the substrate.
It has the effect of flattening the substrate and improves the superconducting properties of the superconducting thin film formed thereon. To superconducting thin films Bismuth and alkaline earth (group IIa), or thallium (T1) and alkaline earth (group IIa), or yttrium (Y) and alkaline earth (group IIa), or neodymium (Nd) and alkali It is preferable to use an oxide thin film containing either an earth element (Group IIa) or lanthanum (La) or an alkaline earth element (Group Ila) because the superconducting properties are particularly good. Method for producing a thin film superconductor When forming a layer mainly composed of copper oxide and a layer mainly composed of alkaline earth oxide on a substrate, it is preferable to heat the substrate. When formed at temperatures between 550°C and 900°C, the effect of flattening the substrate surface is even greater.Also, materials containing copper and alkaline earth metals, which have been formed on various superconductors and whose crystal structures were investigated in detail, are A thin film with a perovskite structure is formed when the Bi-0 layer or TI-0 layer is directly formed on the substrate.The crystallinity is improved by several steps and grains are no longer observed.Especially for Bi-based materials, the temperature is below 650°C. In the Tl system, it was found that a critical temperature higher than LIOOK can be obtained by forming at 300°C.It also has good crystallinity, and can be formed by controlling and controlling it to distinguish it from superconducting phase crystals, etc., which have a critical temperature of 80K. Furthermore, the present invention has been shown to improve the crystallinity and superconducting properties of superconductors other than Big Tl-based superconductors. According to the manufacturing method of the present invention, it is possible to obtain a material with good reproducibility, even if it is necessary to periodically stack thin layers with a thickness of several A.A method of stacking materials with periodicity of several A As C on Conventional MBE
Although several methods have been considered, such as EB evaporation and sputtering, MBE and EB evaporation are suitable for achieving periodic stacking. This method was thought to be unsuitable for this reason (1) It is believed that this is due to the contamination of impurities caused by the high gas pressure during film formation and the damage caused by high-energy particles. They discovered that it was possible to produce a surprisingly good laminated film by laminating different thin layers.9 The reason for this was that the high oxygen gas pressure during sputtering and the sputtering discharge were favorable for the formation of a perovskite structure. This is thought to be due to the fact that it can be formed sufficiently by CVDa high-frequency sputtering method, which is not a periodic formation method in which sputtering is performed sequentially using multiple types of single materials as targets. In particular, the sputtering method is highly dependent on the composition of superconducting thin films, and although it is a manufacturing method with excellent controllability, we will also discuss an example in which the sputtering method was used for a bismuth-based film. *A CasCus target was sputtered alternately in a mixed gas of argon and oxygen, and periodically stacked on MgO substrates at various temperatures. When the substrates thus obtained were evaluated by X-ray diffraction, it was found that the substrate temperature was When the temperature is below 400°C, a peak corresponding to the laminated periodic structure is observed, but when the temperature is increased to 400°C to 550°C, the periodic structure becomes weaker and other phases appear.However, when the temperature is further increased to 550°C, the periodic structure becomes weaker. ~90
g at a substrate temperature in the range of 0°C;! , discovered that it is possible to create phases with critical temperatures higher than IOOK.

Furthermore, when comparing the case where Bi oxide is formed on the substrate by sputtering a Bi target and the case where Sr-Ca-Cu oxide is formed on the substrate by sputtering a Sr*Ca*Cu target, the latter They discovered that when an oxide of Sr-Ca-Cu was formed, the crystallinity of the thin film was much improved, no grains were seen, and the current density doubled. When the crystallinity of the film was examined, it was found that it depended markedly on the size of the irregularities on the substrate, and when the thickness of the Sr-Ca-Cu oxide was formed to a degree that exceeded the thickness of the irregularities on the substrate, the effect became remarkable. Also, due to this Sr-Ca-Cu oxide,
Although this effect is thought to be due to the flattening of the substrate, this effect is more pronounced as the film thickness becomes thinner. A schematic diagram of the vicinity of a base of a superconducting thin film formed by a method for manufacturing a conductive thin film is shown.

i on the substrate 11;; A of the Sr-Ca-Cu oxide 12;
A B layer of Bi oxide 13 is formed on this A layer, and a Bi-Sr-Ca-Cu oxide 1 is further formed on this B layer.
Even if the composite oxide superconducting thin films of No. 4 are laminated, if the sputtering rate of Bi and Sr2CaeCus is appropriately adjusted in the above temperature range, L will change depending on the lamination period.
A phase of OOK or higher appears and the crystallinity improves, especially at 550.
It was also discovered that when the temperature is between 900°C and 900°C, it is possible to produce a phase with very good crystallinity at a critical temperature of IOOK or higher. Thin films produced at substrate temperatures of 550°C to 900°C that are not deposited exhibit superconducting transition even in their original state, but heat treatment in oxygen at a substrate temperature of about 850°C more reliably transforms the superconducting transition to 100°C.
It has also been discovered that thin films having a critical temperature of K or higher and laminated at temperatures of 550 to 900 DEG C. are particularly excellent in reproducibility.

Example 1 Bi-0 target 21, Sr-Ca-
Cu-0 target 22, Bi-Sr-Ca-Cu-
Three types of 0 targets 23 are sputter-deposited using a planar magnetron sputtering method using a magnesium oxide single crystal (100) plane arranged so as to be focused on the base body 24, so that a crystalline layer is formed on the base body 24. At this time, the substrate 24, which has been deposited as a film, is heated to about 700°C with a heater 25 and exposed to Ar.
and 02 mixed gas atmosphere (gas mixture ratio: 5:1, pressure: 3 Pa) Sputtering current i for each target; J. ．． 100m of Bi-0 & 100m of Sr-Ca-Cu-0 & Bi
- Sr-Ca-Cu-0 was set at 150 mA, and the unevenness on the surface of the substrate 24 used in this example was estimated to be about 10 A. First, the shutter 26 was opened on the Sr-Ca-Cu-0 target 22 to give an electric current of about 3 OA. Next, open the shutter 12 on the Bi-0 target 21 and form LA for about 1 minute.
The shutter 26 was opened on the Bi-Sr-Ca-Cu-0 target 23 and sputtering was performed until the required film thickness was achieved.During these steps, the substrate was continued to be heated one row at a time, and periodic lamination was performed to form nine films. Thin film superconductor & friend formed by the manufacturing method of the invention Compared to the case where Bi-based superconductor is directly formed on the substrate, the zero resistance temperature rises by several tens of K, and the IOA of the irregularities of the substrate is Sr-Ca-Cu oxidized. It is thought that the crystalline layer of a composite oxide superconducting thin film having a belobedite structure similar to this Sr-Ca-Cu oxide is formed stably on the surface of the substrate after being flattened by the Sr-Ca-Cu oxide layer. According to surface observation of this thin film superconductor, which has approximately doubled Jc,
Even though the grain size increases, the reason for this increase in Jc is not clearly elucidated. Electrical conduction is thought to occur within the Cu-0 plane. This is thought to be due to improved connectivity and a reduction in the current barrier due to the increased grain size.
It is possible to create a phase with a critical temperature higher than LIOOK by changing the film thickness.The results of an analysis of the case where a thin film of about the same size as a superconductor was created by changing the film thickness. The composition was Bi:Sr:Ca:Cu=2:2:2:3.Even in this state, this thin film superconductor showed a superconducting transition of IOOK or better.Furthermore, it was heat-treated at 850℃ for 1 hour. When carried out in oxygen, the temperature at 100K is very reproducible.
By adding this heat treatment in oxygen to the production of the present invention, the oxidation of each metal element is promoted, and it is effective in stabilizing each layer to create this structure. However, in Example 2, sputter deposition was performed using a total of four targets of Bi, CaCq, and two Sr*Cu, focusing on the MgO (100) substrate. Each target was set up at an angle of about 30 degrees so that it would connect. There is a rotating shutter in front of the target, and by rotating the slit in it, the Sr*Cu
→CaCu→Srs Approximately 5 凰 in C cycle then Bi+ Srs Cu-b CaCu-+ Srt C
Sputter deposition was performed using a cycle of u-*CaCu-*Srs Cu-+Bi, and the nine substrates were heated to approximately 300°C with a heater, and the gas pressure was 3 Pa in a mixed atmosphere with an argon to oxygen ratio of 5:1. Sputtering was carried out on each target.
When periodic lamination was carried out with 0m input CaCu at 250mA and a shutter rotation period of 10 minutes with intervals, it was possible to create a phase with a critical temperature of 105K or more at a substrate temperature of 300℃. A thin film of about 100A was produced by vapor deposition, and the composition at this time was Bi:Sr:Ca:Cu=2:2:2:
3 Even in this state, this thin film is 105
By creating a thin film superconductor by setting a target for each layered structure, a thin film with higher crystallinity can be produced without being affected by the irregularities of the substrate. When a monocrystalline thin film is formed without gaps, and a manufacturing method with gaps as in t4 Example 2, crystallization progresses at lower temperatures compared to the case without gaps, and sharp peaks are observed when evaluated using X-rays, etc. This is thought to be because the structure of the constituent metals is well connected and is very useful for producing thin films with excellent crystallinity. The basic idea is to form a stable belobed structure on the surface with a part of the constituent composition of the holding plate.Although a high-performance superconducting thin film with good cohesiveness can be obtained, it is also a method of laminating different materials by sputter deposition. There is a method of sputtering multiple targets with different compositions.It is relatively easy to use a method of periodically controlling the erosion area by controlling the discharge position of one target with a composition distribution. Although this can be easily achieved, especially when sputter deposition is not used, it is recommended to introduce the 0 phase at least at some point after the film formation or during the intermittent period (~ In addition, it is recommended to introduce the 0 By irradiating the substrate with an ion beam or exposing it to Ot or Neo plasma, the crystallinity can be further improved and the critical current density can be increased.Also, sputtering methods such as laser beam sputtering or ion beam sputtering can be used. It can also be formed using sputtering, and by periodically moving multiple targets and periodically changing the targets irradiated with the beam, a periodic laminated film can be realized. It is possible to form the thin film superconductor of the present invention using MBE, multi-dimensional EB equipment, etc. In that case, it is possible to form the thin film superconductor of the present invention by oxygen ion beam plasma irradiation, etc., during at least one of the steps during formation or intermittently. , it is preferable to supply oxygen. In addition, in the above embodiment, an example was given for a Bi-based thin film superconductor. ) and copper-containing oxide thin air
or an oxide thin film containing at least yttrium (Y) and alkaline earths (Ila group) and copper; or at least neodymium (Nd) and alkaline earths (I
Similar results were obtained with an oxide thin film layer containing at least lanthanum (La) and alkaline earth (Ila group) and copper. Method for manufacturing the thin film superconductor of the invention
It provides a method for producing oxide superconducting thin films with good crystallinity and good reproducibility, and is of great industrial value.

[Brief explanation of drawings]

Figure 1 (Friend) A schematic diagram of a superconducting thin film formed according to an embodiment of the present invention Figure 2 (Friend) A basic configuration diagram of a magnetron sputtering apparatus for producing a thin film superconductor according to an embodiment of the present invention. 11.24---Basic 1 2...Sr-Ca-Cu
Oxidation IX 13...Bi oxidation I 1 4...Bi-
Sr-Ca-Cu oxide, 2l...Bi-0 target, 22...Sr-Ca-Cu-0 target, 23...Fist Bi-Sr-Ca-Cu-0 target, 25... Heater, 26...Shutter 0

Claims (5)

[Claims] (1) A layer A of an oxide containing copper and an alkaline earth is disposed on a substrate, a B layer of an oxide containing bismuth (Bi) is disposed on the A layer, and a layer B containing copper is disposed on the B layer. A method for producing a thin film superconductor, characterized by laminating composite oxide superconducting thin films. Here, alkaline earth refers to at least one or two or more elements of Group IIa elements. (2) A complex oxide superconducting thin film containing copper is made of bismuth (
Bi) and alkaline earth, thallium (Tl) and alkaline earth, yttrium (Y) and alkaline earth, neodymium (Nd) and alkaline earth, or lanthanum (La) and alkaline earth. 2. The method for producing a thin film superconductor according to claim 1, wherein the layer is a laminated layer containing layers. Here, alkaline earth refers to at least one or two or more elements of Group IIa elements. (3) A composite oxide superconducting thin film layer containing copper is formed by periodically layering an oxide layer containing bismuth, a layer mainly consisting of copper oxide, and a layer mainly consisting of alkaline earth oxide. 3. The method for producing a thin film superconductor according to claim 1, wherein the thin film superconductor is obtained by laminating layers. (4) The method for producing a thin film superconductor according to claim 1, wherein the evaporation of the composite oxide superconducting thin film is performed by sputtering. (5) When forming layer A on the substrate, the substrate is
The method for producing a thin film superconductor according to claim 1, characterized in that heating is performed to a temperature in the range of 900°C to 900°C.