JPH0818915B2 - Preparation method of oxide superconducting polycrystalline thin film - Google Patents

Description

The present invention relates to a method for producing an oxide superconducting polycrystalline thin film. In particular, the present invention relates to a method for producing an oxide superconductor polycrystalline thin film having a very high degree of crystal orientation and ordered crystal grain boundaries.

[Prior Art] Conventionally, when forming a polycrystalline thin film of an oxide superconductor,
The degree of orientation of crystal grains forming the thin film becomes a problem. In particular, in the case of a process of promoting crystal growth by heat treatment after depositing an amorphous thin film, crystal nucleation occurs randomly in the film, resulting in a polycrystalline film with a very low degree of orientation. There are many. Even in the crystal film forming process that does not require heat treatment, depending on the film forming conditions, a film having a low degree of orientation or a film having a high degree of orientation but a very small crystal grain size may be formed.

A feature of oxide superconducting materials is that when an amorphous film or a crystalline film deposited on a substrate is heat-treated at a high temperature near its melting point, a highly oriented film is obtained, and in many cases the C axis is oriented perpendicular to the substrate. The obtained film is obtained. However, when the heat treatment is performed at a high temperature close to the melting point, a chemical reaction or mutual diffusion occurs between the substrate material and the film, which deteriorates the superconducting property of the film. In addition, the crystal grain sizes of the obtained alignment film are not uniform.

For a film with a low degree of crystal orientation or a film with uneven crystal grain size,
The surface of the film is so rough that it can be confirmed with the naked eye, and is not suitable for producing a laminated element.

Further, also in the production of a weak grain boundary type device using a polycrystalline film, if the distribution of the crystal grain size is random, the existence probability of defects that obstruct the flow of the tunnel current becomes high, which is not preferable.

[Problems to be Solved by the Invention] In order to solve the above technical problems, the present invention aims to provide a method for producing an oxide superconductor polycrystalline thin film having the following characteristics. To do.

That is, a. The size, shape and distribution of grown crystal grains in the oxide polycrystalline thin film are made uniform.

b. The size of the crystal grains that compose the oxide superconductor polycrystalline thin film is controlled according to the purpose.

c. The shape of the grain boundaries formed in the obtained polycrystalline thin film,
Control number, position and distribution.

d. Increase the degree of crystal orientation in the oxide superconducting polycrystalline thin film grown on the substrate.

e. The surface of the obtained polycrystalline thin film is made flat and the surface roughness is tens of degrees.
Get closer to nm or less.

Therefore, it is an object of the present invention to provide a method capable of producing an oxide superconductor polycrystalline thin film having a very high degree of crystal orientation and ordered grain boundaries. Accordingly, the present invention has a high degree of crystal orientation and a controlled size, shape, etc. of crystal grains, so that a superconducting device to which weak grain boundary coupling is applied, for example, an oxidation that can be used for the production of Josephson devices. An object of the present invention is to provide a method for producing a superconductor polycrystalline thin film. Further, the present invention further enables multi-step crystal growth to be repeated to form a thick film, and enables the production of a superconducting tape-shaped wire consisting of highly oriented crystal grains, which has a high critical current and a high critical magnetic field. It is an object to provide a method capable of producing a wire rod or a superconducting antenna.

[Structure of the Invention] [Means for Solving the Problems] In order to solve the above-mentioned technical problems, the present invention provides a method for forming an oxide superconductor polycrystalline thin film on a substrate. On the substrate, at least the same cation composition as the desired oxide superconductor, an alloy or amorphous thin film having an average composition is formed to a thickness of 5 nm or more and 20 nm or less,
The thin film thus formed is exposed to air or a mixed gas atmosphere of an inert gas and oxygen at a temperature of 400 ° C. to 1200 ° C.
By heat-treating for more than a minute, a plurality of predetermined fine superconductor crystal (hereinafter also referred to as seed crystal) particles are formed, and the crystal of the oxide superconductor is grown on the substrate with these seed crystal particles as nuclei. At most, based on the crystal arrangement and orientation of the fine crystal grains, a single-layer polycrystalline thin film in which the grain size and grain boundary distribution of the grown crystal grains are determined is formed. A method for producing a crystal thin film is provided. Further, it is preferable to form a multi-layered polycrystalline thin film by repeating the crystal growth operation on the seed crystal particles a plurality of times. Further, before the heat treatment of the thin film for forming the seed crystal, it is preferable that the thin film is preliminarily separated and divided into a shape to be formed by the seed crystal on the surface of the substrate. Furthermore, it is preferable that the partition area to be partitioned in advance is a circle having a diameter of 10 μm or less or a rectangle having a short side of 10 μm or less. The seed crystal is one or more kinds of cations or anions from a desired oxide superconductor crystal composition,
An alloy having a thickness of 5 nm to 20 nm, which is partially or completely absent, or an amorphous thin film is deposited on the substrate or on an oxide superconductor polycrystalline thin film that has already been formed, and is absent where the seed crystal is formed. After injecting a desired dose amount of the ion species thus prepared, by performing the crystallization treatment by the heat treatment, only a desired portion, that is, only an ion-implanted portion,
The method of forming is preferred. In addition, the ion implantation location is
It is preferable that the shape is a dot shape having a diameter of 10 μm or less or a rectangle having a short side of 10 μm or less, and the size and dispersion state of the formed seed crystal are controlled by the size and shape and the interval thereof. Further, the growth of the oxide superconductor crystal on the seed crystal is performed by cation compensation on the seed crystal with compensation of a cation composition within an error of at least 10% from the desired composition or a cation composition deviation in the subsequent step. An alloy thin film or amorphous thin film having a composition is deposited to a thickness of 10 nm or more, and the thin film is heat-treated in the temperature range of 400 ° C to 1200 ° C for 1 minute or more in air or in an atmosphere of a mixed gas of an inert gas and oxygen. , In a mixed gas of oxygen and inert gas to adjust the amount of oxygen in the grown crystal
By heat-treating at a temperature of 1200 ° C or less for 1 minute or more,
It is preferable that a crystal growth process is performed using the seed crystal as a nucleus, and if desired, the steps of depositing on the seed crystal and crystallization are repeated a plurality of times. Further, the treatment for growing the crystal on the seed crystal is performed continuously using a thin film deposition apparatus capable of heating the substrate while heating the substrate to a temperature of 300 ° C. or higher in an atmosphere containing oxygen. It is preferable to advance crystal growth on the seed crystal.

The present invention, in order to solve the above technical problems, in a method of forming an oxide superconductor polycrystalline thin film on a substrate, a. In advance of crystal growth of a desired oxide superconductor on the substrate A plurality of fine crystal grains (hereinafter also referred to as seed crystals) to be seeds are formed, b. The seed crystal grains serve as nuclei for growing oxide superconductor crystals on the substrate, and c. A method for producing an oxide superconductor polycrystalline thin film, which comprises forming a single-layer polycrystalline thin film in which the grain size and grain boundary distribution of grown crystal grains are determined based on the crystal arrangement and orientation. Further, it is preferable to form an oxide superconductor polycrystalline thin film by forming a multilayer polycrystalline thin film by repeating the crystal growth operation on the seed crystal particles a plurality of times. In addition, the seed crystal is formed on the substrate by forming an alloy, an amorphous or laminated thin film having an average composition having at least the same cation composition as or close to that of the desired oxide superconductor, in a thickness of 5 nm or more and 20 nm or less. A fine superconductor crystal obtained by heat-treating the formed thin film is preferable. The heat treatment used for forming the seed crystal is preferably performed by holding the formed thin film in the air or a mixed gas of an inert gas and oxygen at 400 ° C. to 1200 ° C. for 1 minute or more. The heat treatment for forming the seed crystal can be performed by spotwise heat treatment using an energy beam such as a laser beam, an electron beam, or a converged infrared ray under an energy condition corresponding to the treatment temperature. The energy beam for the heat treatment has a diameter of 10 μm or less, and the size of the formed seed crystal can be defined by this size.
Then, the energy beam can define the dispersion state of the seed crystal to be formed by performing the scanning shape in a dot shape or a linear shape. Further, after the seed crystal is formed, or before the heat treatment for forming the thin film therefor, the shape of the seed crystal to be formed is formed on the surface of the substrate.
It is preferable to partition in advance. The divided area to be divided in advance is a circle with a diameter of 10 μm or less, or
A rectangular shape having a short side of 10 μm or less is preferable in terms of control. Further, the seed crystal is an alloy, amorphous or laminated thin film having a thickness of 5 nm to 20 nm or less, in which one or more kinds of cations or anions are partially or completely absent from the desired oxide superconductor crystal composition, on the substrate. Alternatively, by depositing on the already formed oxide superconductor polycrystalline thin film, injecting a desired dose of the missing ionic species into the portion where the seed crystal is to be formed, and then performing the crystallization treatment by the heat treatment described above. It is preferable that it is formed only at a desired portion, that is, only at an ion implantation portion. And
The ion-implanted portion is a dot having a diameter of 10 μm or less or a rectangle having a short side of 10 μm or less, and the size and shape of the formed seed crystal and the dispersed state can be controlled by the size and shape and the interval thereof. In addition, the growth of the oxide superconductor crystal on the seed crystal has at least a desired composition and an error on the seed crystal.
An alloy thin film having a cation composition within 10% or a cation composition that compensates for the deviation of the cation composition in the subsequent step,
Deposit an amorphous thin film or a laminated thin film with a thickness of 10 nm or more, and deposit this thin film in air or in a mixed gas of an inert gas and oxygen.
Heat treatment at 0 ℃ ~ 1200 ℃ for 1 minute or more, and then to adjust the amount of oxygen in the grown crystal, by heat treatment at a temperature of 1200 ℃ or less in the mixed gas of oxygen and inert gas for 1 minute or more. , With the seed crystal as a nucleus, a crystal growth process is performed,
Further, if desired, it is preferable to repeat the steps of depositing on the seed crystal and crystallization a plurality of times. Then, for the treatment for growing the crystal on the seed crystal, a thin film deposition apparatus capable of heating the substrate is used to deposit the substrate in an atmosphere containing oxygen.
It is preferable to continuously advance crystal growth on the seed crystal while heating at 300 ° C. or higher.

In order to solve the above problems in the production of an oxide superconductor polycrystalline thin film, the present invention first forms fine crystal grains of a desired oxide superconductor on a substrate and uses them as seeds. This is to grow crystals of oxide superconductor.

That is, according to the present invention, in the step of forming a polycrystalline thin film of an oxide superconductor on a substrate, a plurality of fine seed crystals to be seeds of desired oxide superconductor crystal growth are previously formed on the substrate. Individually formed, these seed crystals serve as nuclei to advance the crystal growth of the oxide superconductor on the substrate, and finally, the grain diameter of the grown crystal grains and the grain boundary It is intended to obtain a single-layer polycrystalline thin film in which the distribution is arbitrarily defined and the crystallographic orientation of each grown grain is also defined based on the crystallographic orientation of the seed crystal. At this time, the desired oxide superconductor itself is used as the seed crystal. Furthermore, by repeating the above operation a plurality of times, a polycrystalline thin film in which the grain size, grain boundary distribution, and crystal orientation are controlled can be prepared, and further superconducting substances of different types can be laminated in multiple layers. In this way, a Josephson tunnel junction device having a crystal grain boundary as a barrier layer can be produced by using the oxide superconductor polycrystalline thin film thus produced.

Furthermore, in the above-described method for producing an oxide superconductor polycrystalline thin film, the seed crystal is first formed on the substrate or on the already formed oxide superconductor polycrystalline thin film, and the desired oxide superconductor is formed. Deposit an alloy or amorphous or laminated thin film with a thickness of 5 nm or more and 20 nm or less having an average thin film composition with at least the same cation composition (this is called the initial thin film), and then heat treat this thin film with oxide superoxide. A plurality of seed crystals are formed on the substrate by crystallizing the conductor. By utilizing the contraction of deposition of the thin film material that occurs during this crystallization, desired oxide superconducting microcrystals can be grown in an island shape on the substrate.

Further, this heat treatment is held in air or in a mixed gas of inert gas and oxygen (0 to 100% oxygen) at 400 ° C to 1200 ° C for 1 minute or more, and subsequently, the amount of oxygen in the grown crystal is increased. The heat treatment for adjustment is carried out in a mixed gas of oxygen and an inert gas (oxygen 0 to 100%) at a temperature of 1200 ° C. or lower for 1 minute or more, and individual crystal particles are formed of a desired oxide superconductor. Independent fine crystal grains (that is, a plurality of seed crystals) having a crystal structure are obtained. In this way, a uniformly dispersed seed crystal having a crystal grain size of 5 μm or less can be obtained.

Here, the substrate is a common material used for forming an oxide superconductor thin film, such as single crystal MgO or single crystal SrTiO 3.
₃ substrates or their polycrystalline substrates can be used,
In particular, it is not limited. In addition, suitable means in heat treatment for forming the oxide superconductor thin film, for example, means for preventing various phenomena that are expected to occur during the heat treatment, for example, chemical reaction between the superconductor thin film and the substrate. ,
It is also possible to use a substrate provided with a buffer layer and an intermediate layer in order to prevent mutual diffusion, mismatch of lattice constants, mismatch of thermal expansion coefficients, and the like.

In the present invention, the seed crystal, which is the first key, is a desired oxide superconductor, for example, an amorphous film or an alloy film or a laminated film having a cation composition of Y ₁ Ba ₂ Cu ₃ O _7-z. Was deposited very thinly, and the superconductor material of these films was crystallized by heat treatment to grow a large number of independent microcrystals of oxide superconductor (Y ₁ Ba ₂ Cu ₃ O _7-z ). It can be created by At this time, in order to obtain dispersed crystal fine particles (that is, seed crystals), the thickness of the thin film to be deposited first is
It is preferably 20 nm or less. The initial thin film for seed crystal preparation for this purpose can be deposited, for example, by physical vapor deposition (PVD) such as sputtering, or chemical vapor deposition (CVD).

The heat treatment for producing the seed crystal can be simply performed by electric furnace heating or infrared heating. It is also possible to use a method other than this, for example, a method such as laser irradiation. The heat treatment temperature, heat treatment energy, or heat treatment time is adjusted according to the desired type of oxide superconductor. For example, when an amorphous film of Y ₁ Ba ₂ Cu ₃ O _7-z is crystallized by heat treatment, if electric furnace heating is used, in air or in a mixed gas of an inert gas and oxygen (oxygen 0 to 100%), 700
By heat treatment that can include slow cooling to 400 ° C. or less in oxygen at 1 ° C. to 1200 ° C. for 1 minute or more, a uniformly dispersed seed crystal having a particle size of submicron to micro order can be obtained. The particle diameter depends on the thickness of the thin film and the heat treatment conditions, and a particle diameter of up to about 5 μm can be obtained.

The seed crystallization of the thin film for crystallizing the superconducting thin film of this initial formation is spot-wise for crystallizing the oxide superconducting substance by using an energy beam such as a laser beam, an electron beam, and a focused infrared ray. It can be performed by heat treatment under an energy condition corresponding to the required temperature.
In these methods, the heat treatment position and region can be arbitrarily controlled within the thin film surface. By utilizing this, the growth position of the seed crystal on the substrate, that is, the dispersed state of the seed crystal can be defined.

Further, the diameter of the energy beam is set to 10 μm or less, and this size defines the size of the seed crystal to be grown. Further, the scanning shape of the energy beam can be dispersed in a dot shape or a linear shape.

Further, before seed crystallization, the initially formed thin film is partitioned into a required shape in advance by a normal patterning technique (wet etching or dry etching method), and the heat treatment method described above By crystallizing the thin film portion, the dispersed state of the seed crystal can be adjusted.

In the above step of crystallizing the formed oxide superconductor thin film, the shape of the partition region is a circle with a diameter of 10 μm or less or a rectangle with a length of 10 μm or less and a length of a short side or more, The size and dispersion state of the seed crystal can be controlled by the size and shape of the partition and the distance between the partitions.

To form a seed crystal by first forming an oxide superconductor thin film on the surface of a substrate and then heat-treating it, one or more cations or anions from the desired oxide superconducting crystal composition can be used. Part or all missing thickness 5 nm or more 20 nm
The following alloy or amorphous or laminated thin film is deposited on the substrate or on the already formed oxide superconductor polycrystalline thin film, and ions are injected into the portion where the seed crystal is to be formed by the ion implantation method. After a predetermined dose is implanted, a crystallization process by heat treatment is performed to form seed crystals of the oxide superconductor material only at the ion-implanted site, that is, at a desired site. At this time, ion implantation can be performed directly on the substrate before thin film deposition.

In such an ion implantation process, spots having a diameter of 10 μm or less or a length of a quadrangle side of 10 μm is applied to an ion implanted portion.
In the following, a rectangle having a long side longer than the length of the short side is used, and the size of the seed crystal and the dispersion state are controlled according to the size and shape of the ion-implanted portions and their intervals.

As described above, the final target cation and anion composition of the oxide superconductor can be obtained within an error of 10%, and a seed crystal having a desired crystal structure can be obtained.

Next, on a given seed crystal, an alloy having a cation composition which is at least equal to the desired oxide superconductor within an error of 10% or a cation composition capable of compensating for cation deviation in the subsequent step. Alternatively, deposit an amorphous or laminated thin film with a thickness of 10 nm or more, and deposit this thin film in air or in a mixed gas of inert gas and oxygen (oxygen 0-100%)
Heat-treat at 1200 ℃ for 1 minute, and then adjust the amount of oxygen in the grown crystal in a mixed gas of oxygen and inert gas (oxygen 0-100%) at a temperature of 1200 ℃ or less for 1 minute. By performing the heat treatment as described above, crystal growth with seed crystals as nuclei proceeds. Further, a stacked or thick oxide polycrystalline thin film can be prepared by repeating the steps of depositing on the seed crystal and crystallization a plurality of times.

The growth of the oxide superconductor crystal on the seed crystal, which is the second key in the method for forming a polycrystalline thin film of a superconductor according to the present invention, is performed by forming a desired oxide superconductor, that is, a seed crystal on the seed crystal. An amorphous film or a platinum film or a laminated film having the same cation composition of an oxide superconductor as the above is deposited by physical vapor deposition (PVD) such as sputtering or chemical vapor deposition (CDV),
The heat treatment can be performed by promoting crystallization with the seed crystal as a nucleus. At this time, the temperature of the heat treatment is preferably equal to or lower than the treatment temperature at the time of forming the seed crystal. For example, a seed crystal with a thickness of 10
700 when deposited with a 0 nm Y ₁ Ba ₂ Cu ₃ O _7-z amorphous film
Approximately 1μ in particle size by processing at 5 ℃ to 900 ℃ for 5 minutes
It is possible to obtain tabular grains of m having a high orientation in the same direction as the seed crystal.

That is, the crystal growth on the seed crystal is performed continuously on the seed crystal while heating the substrate to about 300 ° C. or higher in an oxygen-containing atmosphere in the apparatus using a thin film deposition apparatus capable of heating the substrate. The crystal growth can be promoted by using the seed crystal as a nucleus. In this case, the crystal growth of the seed crystal is controlled because the crystal growth of the seed crystal is memorized, and the crystal growth direction of the seed crystal is controlled. By utilizing this effect, the oxide superconductivity having extremely high crystal orientation and flatness is obtained. A polycrystal thin film can be prepared. That is, by aligning the crystal orientation of the seed crystal with a certain specific orientation, the crystal orientation, that is, the orientation of the finally obtained polycrystalline thin film can be defined.

In addition, when a seed crystal is formed, its grain size, grain boundary arrangement, and crystal orientation degree can be controlled to improve the characteristics of the grain boundary Josephson device using the formed grain boundary. Therefore, the control of the film quality of the polycrystalline thin film can be achieved by defining or controlling the seed crystal distribution state at the position where the desired particle spacing and particle arrangement can be obtained. At this time, the particle diameter and the grain boundary are determined by the position of the seed crystal, that is, the nucleus of the particle.

Further, the oxide superconductor obtained by the present invention is composed of a simple layered or composite layered compound containing a metal-oxygen two-dimensional square lattice or a metal-oxygen two-dimensional pseudo-square lattice as the basis of its crystal structure. is there. For example, a copper oxide superconducting material is a material having this crystal structure, and a superconductor polycrystalline thin film can be prepared by the present invention.

That is, as a method of promoting crystal growth using a seed crystal as a nucleus, there is a method of repeating deposition and heat treatment in several times in addition to a method of depositing a film having a required thickness at a time and performing heat treatment. If a thick film, for example, a film thickness of 300 nm or more is deposited at one time on the seed crystal and then heat-treated, new nuclei are generated in the parts other than the seed crystal, and the effect of the seed crystal cannot be obtained. However, the film has a low degree of orientation. Therefore, in order to obtain the effect obtained by the present invention with a thick film, it is preferable to carry out the crystal growth on the seed crystal in a number of times. Even in the case of a thin film, the crystallinity and the crystal orientation of the obtained thin film are better when the deposition and the heat treatment are performed plural times.

As a method of growing a crystal on a seed crystal, it is possible to continuously grow a crystal on a seed crystal while heating the substrate using a film deposition apparatus capable of heating the substrate as described above. is there.

The method for producing the superconductor polycrystalline thin film according to the present invention described above is schematically shown in FIGS. 1 and 2. According to the method of the present invention, the seed crystal 3 is formed on the substrate 2 and the superconductor polycrystalline thin film 5 is formed by the series of steps shown on the left side of FIG. 1 as shown in FIG. It is a thing. That is, the amorphous thin film 1 is formed on the surface of the substrate 2,
When heat-treated, a plurality of island-shaped fine seed crystals 3 are formed on the substrate 2, then an amorphous thin film 4 is formed thereon, and when heat-treated, a polycrystalline thin film 5 is formed. On the other hand, in the conventional method of forming a thin film, as shown in the right side of FIG. 1, an amorphous thin film 4 is formed on the substrate 2, and when it is heat-treated, microcrystals having no orientation are shown. It is only randomly formed.

Further, FIG. 2 is a cross-sectional view showing an example of repeated crystal growth of an oxide superconductor according to the present invention. That is, a plurality of seed crystals 3 are obtained by forming an amorphous thin film 1 on a substrate 2 and heat-treating it, and using the seed crystals as nuclei, crystal growth is performed and a polycrystalline thin film 5 is grown. It is a thing.

The grain size control and grain boundary control of each single crystal grain in the polycrystalline thin film, which is the third key of the method for producing a superconductor polycrystalline thin film of the present invention, can be carried out by the following method. That is, these controls are mainly based on a method of dispersing seed crystals that are initially formed and a particle growth rate adjustment using the method as a nucleus.

That is, the adjustment of the dispersed state of the seed crystal is performed by first of all, adjusting the thickness of the film deposited on the substrate, the processing temperature for crystal growth,
This can be done by adjusting the processing time. In the case of this method, the seed crystal can be dispersed with a uniform particle size and a uniform particle interval by the crystallization treatment, as shown in FIG. By changing the initial film thickness and processing conditions,
The size and spacing of the seed crystals can be adjusted, but the dispersed state is random. By this method, the seed crystal prepared is a polycrystalline thin film having a highly uniform orientation with a substantially uniform particle size,
It is suitable for obtaining a wide range of substrates.

The ordered arrangement of the seed crystals can be performed by performing seed crystallizing of the initial formation film by spot heat treatment using an energy beam such as a laser beam, an electron beam, or a converged infrared ray. Also in this case, similarly to the above, the crystallinity and the grain size of the seed crystal to be formed can be determined by the processing conditions such as the initial film thickness, the beam energy, the irradiation time and the irradiation diameter.

Prior to the method of adjusting the dispersed state of the seed crystal, the thin film before the seed crystallization is divided into the necessary shapes in advance by a normal patterning technique (wet or dry etching),
The dispersion state of the seed crystal can be adjusted by crystallizing the thin film portion in the compartment by the above dispersion state adjusting method.

Contrary to the above adjusting method, it is also possible to pattern the formed seed crystal so that only necessary portions remain.

The multi-step crystal growth method of the oxide superconductor polycrystalline thin film according to the present invention is that the seed crystal material and the crystal material grown by using the seed crystal material as the nucleus are of the same kind. Therefore, as a method for producing a seed crystal that satisfies the condition, an initial film deposition method is used in which a part or all of one or more cations or anions is missing from a desired oxide superconductor crystal composition. It is also possible to form a seed crystal of an oxide superconductor material only at an ion-implanted portion, that is, a desired portion by performing a crystallization treatment after implanting a predetermined dose of the seed. At this time, ion implantation can also be performed directly on the substrate before thin film deposition.

As described above, the method of promoting crystal growth with the seed crystal having the ordered array thus prepared as a nucleus can also be performed by depositing the superconductor material while heating the substrate as described above.

INDUSTRIAL APPLICABILITY The method for producing an oxide superconductor polycrystalline thin film of the present invention can be applied to the production of almost any kind of oxide superconductor polycrystalline thin film, and in particular, the superconducting substance is not limited. . However, the effect of obtaining a highly oriented polycrystalline thin film according to the present invention is to produce a substance having a high anisotropy in the crystal structure, for example, a polycrystalline thin film of a Y-Ba-Cu-O-based oxide superconductor. It is remarkably effective.

The method for producing an oxide superconducting thin film of the present invention can be further used for forming a superconducting crystal thin film for products such as Josephson junctions, infrared detectors and optical switches.

Next, the method for producing the oxide superconducting polycrystalline thin film of the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.

In Example 1 of the MgO crystal substrate (100) surface was examined _{Y 1 Ba 2 Cu 3 O 7} -z oxide superconductor uniformly create conditions a seed crystal of the crystal.

An amorphous film having a cation composition of Y ₁ Ba ₂ Cu ₃ was formed on the (100) plane of the MgO crystal substrate by using a multi-source sputtering device without heating the substrate, and the film thickness was 5 nm, 10 nm, 1 nm, respectively.
Five kinds of 5 nm, 20 nm, and 50 nm were deposited and prepared, and after heat treatment, the states of the obtained crystal particles were compared.

The multi-source sputtering system used consisted of independent high frequency magnetron sputtering guns of yttrium metal, copper metal and BaCu alloy, and the composition of the deposited film was adjusted by the power input to each gun. The sputtering gas was pure argon, and the gas pressure was 4 Pa.

As a result of X-ray diffraction observation of the obtained deposited thin film, it was confirmed to be amorphous.

The deposited amorphous thin film was heat-treated in a horizontal tubular furnace. Flowing pure nitrogen as atmosphere gas, 800 ℃
After holding for 5 minutes, the atmosphere gas was switched to pure oxygen, the temperature was lowered to 200 ° C. or lower in about 2 hours, and the sample was taken out.

The shape of crystal grains of each thin film after the heat treatment was observed by a scanning electron microscope. The results are shown in Table 1.

From Table 1, it was found that in order to obtain a dispersed seed crystal, it is preferable that the thickness of the deposited amorphous thin film is at least 20 nm or less. Further, in order to obtain a seed crystal having a uniform grain size and a dispersed state, the deposition thickness needs to be 10 nm or less. In the sample with a thickness of 50 nm, the seed crystals could not be created because the crystal grains were connected together.

Therefore, the seed crystal used in the following examples has a deposited film thickness of 10
nm.

In Example 2 of the MgO crystal substrate (100) on the _{Y 1 Ba 2 Cu 3 O 7} -z seed crystals created on the surface, the amorphous film having a cation composition ratio of Y1Ba2Cu3, the multi-source sputtering method Deposited,
Heat treatment was performed. Two types of samples were prepared, with a deposited thin film thickness of 100 nm and 300 nm. The seed crystal used was an initially deposited thin film having a thickness of 10 nm, which gave good results in Example 1.

The heat treatment condition of the amorphous thin film deposited on the seed crystal was set to 800 ° C. for 5 minutes in a pure nitrogen flow as in Example 1, and the cooling step was gradually cooled in a pure oxygen atmosphere for about 3 hours. .

For comparison, the MgO crystal substrate without seed crystal ((1
The amorphous thin film deposited to a thickness of about 300 nm on the (00) surface was heat-treated under the same conditions.

The surface condition of each sample after the heat treatment was observed with a scanning electron microscope (SEM). Further, the crystal orientation of the sample film was observed by X-ray diffraction (XRD).

FIG. 3 is a SEM photograph of a seed crystal before thin film deposition,
That is, it is a SEM photograph of a seed crystal obtained by heat-treating an amorphous Y ₁ Ba ₂ Cu ₃ O _7-z thin film having a thickness of 10 nm formed on the (100) plane of an MgO crystal substrate. From this, it is clear that submicron-order microcrystalline particles are uniformly dispersed on the substrate. The step seen in the photograph is the cleavage step of MgO single crystal.

FIG. 4 is an SEM photograph of the thin film deposited on the seed crystal after heat treatment. FIG. 4 is a SEM photograph of a Y ₁ Ba ₂ Cu ₃ O _7-z polycrystalline thin film grown with seed crystals as nuclei on the (100) plane of a MgO crystal substrate, and FIG. FIG. 4B shows the case where the thin film has a thickness of 100 nm and 300 nm.

Fig. 5 shows Y ₁ Ba grown to a thickness of about 300 nm directly on the (100) plane of a MgO crystal substrate without making a seed crystal.
₂ is an SEM photograph of a ₂ Cu ₃ O _7-z polycrystalline thin film. That is, a SEM photograph after heat treatment of a thin film having a thickness of 300 nm prepared without using a seed crystal is shown.

That is, in the thin film polycrystals produced according to the present invention, all the thin films produced on the seed crystal are arranged so that tabular grains having a grain size of 1 to 2 μm are spread and lined up. In contrast to these, in a seed crystal-free film, tabular grains are grown in completely random directions.

The tabular plane of the tabular grain corresponds to the ab plane of the Y ₁ Ba ₂ Cu ₃ O _7-z crystal. As a result of observation by X-ray diffraction, a strong (00n) diffraction peak appears preferentially in the thin-film polycrystal prepared using the seed crystal, whereas the thin film polycrystal formed using the seed crystal has a (00n) diffraction peak. Was weak, and peaks other than those, such as (103) and (013) diffraction peaks, appeared strongly.
That is, it is clear that the crystal orientation of the thin film is high due to the effect of using the seed crystal.

The bright contrast portion in the photograph of FIG. 4A is the exposed portion of the substrate, which can be improved by further studying the heat treatment conditions.

FIG. 6 is an X-ray diffraction pattern of a Y ₁ Ba ₂ Cu ₃ O _7-z polycrystalline thin film grown with a seed crystal formed on the (100) plane of an MgO crystal substrate as a nucleus. The thickness of the deposited thin film is 100 nm, and the figure below is for the deposited film thickness of 300 nm. From this X-ray diffraction pattern, it is clear that the formed Y ₁ Ba ₂ Cu ₃ O _7-z thin film polycrystal grows while being oriented vertically to the substrate surface. Thickness 10
In the 0 nm sample, almost only the (00n) diffraction peak is seen, whereas in the sample with a thickness of 300 nm, other than (00n) (10
3) and (013) diffraction peaks are seen. This cause is 300n
In the thin film of m, new nucleation occurred randomly except in the seed crystal prepared in advance.

From the above results, according to the present invention, Y ₁ Ba ₂ C was formed on the seed crystal.
It is clear that by promoting the crystal growth of u ₃ O _7-z , a polycrystalline thin film having a high degree of crystal orientation and a uniform grain size was obtained. The superconducting critical temperature (onset) of these polycrystalline thin films was about 85K.

[Example 3] An amorphous thin film having a film thickness of 20 nm was deposited on a Y ₁ Ba ₂ Cu ₃ O _7-z seed crystal formed on the (100) plane of a MgO crystal substrate, and after heat treatment, the film thickness was further 20 nm. The amorphous thin film was deposited and heat treated to form a crystalline thin film with a thickness of about 50 nm including the thickness (height) of the seed crystal. The method of depositing this amorphous thin film and the method of heat treatment were the same as in Examples 1 and 2, but the holding time of the heat treatment was 30 minutes.

Figure 7 shows Y ₁ Ba prepared on (100) plane of MgO crystal substrate.
_{2 is} an X-ray diffraction pattern of a polycrystalline thin film obtained by performing crystal growth on a ₂ Cu ₃ O _7-z seed crystal in multiple steps. The total thin film thickness is about 500 nm. From this X-ray diffraction pattern, a strong (00n) diffraction peak is seen, indicating that the effect of multistep growth is high. These diffraction peak intensities are
It is relatively stronger than the sample of Example 2 with the film thickness of 100 nm and 300 nm. However, in this embodiment, the amorphous thin film composition in order to deviated from the _{Y 1 Ba 2 Cu 3 O 7} -z , in the thin film, a phase other than _{Y 1 Ba 2 Cu 3 O 7} -z is generated. That is, in FIG. 7? It is a peak indicated by a mark.

Superconducting critical temperature (onset) of these polycrystalline thin films
Was about 85K.

[Advantages of the Invention] The following remarkable technical effects were obtained by the method for producing an oxide superconductor polycrystalline thin film of the present invention.

First, it provides a method for producing an oxide superconductor polycrystalline thin film in which the grain size, grain boundaries, and crystal orientation are controlled.

Secondly, therefore, since the oxide superconductor polycrystalline thin film can be obtained by controlling each parameter and condition, it is possible to obtain an oxide superconductor polycrystalline film suitable for application to a superconducting thin film component. did it.

Third, that is, by forming an oxide superconductor polycrystalline thin film having crystal grain boundaries with a very high degree of crystal orientation, a superconducting element using weak grain boundary coupling, for example, Josephson element, etc. A method for producing an oxide superconductor that can be used for

Fourthly, by repeating multi-step crystal growth to form a thick film, it becomes possible to prepare a superconducting tape-shaped wire made of highly oriented crystal particles, and a superconducting wire having a high critical current and a high critical magnetic field. Alternatively, the present invention provides a method for producing an oxide superconductor capable of producing a superconducting antenna or the like.

[Brief description of drawings]

FIG. 1 is a schematic view sequentially showing a method for producing an oxide superconductor polycrystalline thin film according to the present invention. FIG. 2 is a schematic diagram showing the crystal growth when the crystal growth of the oxide superconductor is repeated on the seed crystal according to the present invention. FIG. 3 is a SEM photograph showing a crystal structure of a Y ₁ Ba ₂ Cu ₃ O _7-z seed crystal formed on the (100) plane of an MgO crystal substrate according to the present invention. FIG. 4 is a SEM photograph showing a crystal structure of a Y ₁ Ba ₂ Cu ₃ O _7-z polycrystalline thin film grown by using a seed crystal on a (100) plane of an MgO crystal substrate as a nucleus according to the present invention. is there. Fig. 5 shows (1) of MgO crystal substrate directly without seed crystal formation.
₃ is a SEM photograph showing the crystal structure of a Y ₁ Ba ₂ Cu ₃ O _7-z polycrystalline thin film grown on the (00) plane. FIG. 6 is an X-ray diffraction pattern of a Y ₁ Ba ₂ Cu ₃ O _7-z polycrystalline thin film grown with seed crystals on the (100) plane of an MgO crystal substrate as nuclei. FIG. 7 is an X-ray diffraction pattern of a polycrystalline thin film formed by dividing the crystal growth of Y ₁ Ba ₂ Cu ₃ O _7-z on the (100) plane of the MgO crystal substrate in plural times.

Claims (8)

[Claims] 1. A method of forming a polycrystalline oxide superconductor thin film on a substrate, which comprises firstly forming an alloy or an alloy having the same average cation composition as the desired oxide superconductor on the substrate. An amorphous thin film is formed with a thickness of 5 nm or more and 20 nm or less, and the formed thin film is heat-treated at a temperature of 400 ° C. to 1200 ° C. for 1 minute or more in air or a mixed gas atmosphere of an inert gas and oxygen. As a result, a plurality of desired fine superconductor crystal (hereinafter also referred to as seed crystals) particles are formed, and the seed crystal particles serve as nuclei to grow a crystal of an oxide superconductor on the substrate. A method for producing a polycrystalline thin film of an oxide superconductor characterized by forming a single-layer polycrystalline thin film in which the grain size and grain boundary distribution of grown crystalline grains are determined based on the crystal arrangement and orientation of the grains. . 2. The oxide superconductor polycrystal according to claim 1, further comprising repeating the crystal growth operation on the seed crystal particles a plurality of times to form a multi-layer polycrystal thin film. How to make a thin film. 3. Before the heat treatment of the thin film for forming the seed crystal, the thin film is preliminarily cut and divided into a shape on which the seed crystal is to be formed on the surface of the substrate. The method for producing an oxide superconductor polycrystalline thin film according to claim 1. 4. The partition area to be partitioned in advance has a diameter of
The method for producing a polycrystalline thin film of an oxide superconductor according to claim 3, which is a circle having a diameter of 10 µm or less or a rectangle having a short side of 10 µm or less. 5. The seed crystal is an alloy having a thickness of 5 nm to 20 nm or an amorphous thin film in which one or more kinds of cations or anions are partially or completely absent from a desired oxide superconductor crystal composition, After depositing on the substrate or on the already formed oxide superconductor polycrystal thin film and injecting a desired dose of the missing ionic species into the portion where the seed crystal is formed, the crystallization treatment by the heat treatment is performed. The method for producing an oxide superconductor polycrystalline thin film according to claim 1, wherein the oxide superconductor polycrystalline thin film is formed only at a desired portion, that is, only at an ion-implanted portion. 6. The ion-implanted portion is a dot with a diameter of 10 μm or less or a rectangle with a short side of 10 μm or less. The size and shape of the formed seed crystal and the dispersion state can be determined depending on the size and shape and their intervals. The method for producing an oxide superconductor polycrystalline thin film according to claim 5, wherein the method is controlled. 7. The growth of the oxide superconductor crystal on the seed crystal is such that at least a desired composition and a cation composition within an error of 10% or a deviation of the cation composition in a subsequent step are caused on the seed crystal. Deposit an alloy thin film or amorphous thin film with a compensated cation composition to a thickness of 10 nm or more, and deposit this thin film in air or in a mixed gas atmosphere of inert gas and oxygen at 400 ℃ ~ 1200 ℃
In order to adjust the amount of oxygen in the grown crystal, the heat treatment is performed in a mixed gas of oxygen and an inert gas at a temperature of 1200 ° C. or less for 1 minute or more, so that the seed Crystal growth is performed using the crystals as nuclei, and
The method for producing an oxide superconductor polycrystalline thin film according to any one of claims 1 to 6, wherein the steps of depositing on the seed crystal and crystallization are repeated a plurality of times if desired. 8. The process for growing a crystal on the seed crystal is performed by using a thin film deposition apparatus capable of heating a substrate while heating the substrate to a temperature of 300 ° C. or higher in an atmosphere containing oxygen. The method for producing an oxide superconductor polycrystalline thin film according to claim 7, wherein the crystal growth is continuously advanced on the seed crystal.