JPH03197321A - Production of superconductor of thin film - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing thin film superconductors applied to electronic devices, particularly oxide thin film superconductors.

Conventional technology It has been proposed that the Y-B a-Cu-0 system is a high-temperature superconductor with a superconducting transition temperature exceeding 90K [M, K, Wu, et al. 1- Letters (Physical Re-vie)
w Letters) Vol, 58. No, 9,90
8-910 (19B?)], which has made it higher than the boiling point (77K) of liquid nitrogen, making it promising for practical use. Furthermore, after that, Bi-5r-Ca-Cu-0 series material which becomes a superconductor at 100 or more, and T l-B
A-Ca-Cu-0 based materials have been discovered one after another. Although the details of the superconducting mechanism of these oxide superconducting materials are not clear, their transition temperatures may be higher than room temperature, and they are expected to have more promising properties as high-temperature superconductors than conventional binary compounds.

When such oxide superconductors are to be put to practical use as electronic devices, it is strongly desired that they be made into thin films. Methods for thinning oxide superconductors include sputtering,
Vacuum deposition method, CVD (chemical vapor deposition) method, etc. are used.

Invention tries to solve! When putting thin films into practical use as devices, stabilizing the properties of the thin film and lowering the temperature of the formation process are considered to be fundamental issues.

However, with the sputtering method, although it is formed at a low temperature,
Film formation is carried out by exposing the substrate to plasma; therefore,
The film surface is easily damaged, and the film thickness distribution occurs depending on the plasma distribution state, making it difficult to make the entire film uniform, making it difficult to achieve stable characteristics.

There are many complicated parameters such as substrate temperature, gas pressure, gas mixture ratio, distance between the substrate and target, and input power, and it is quite difficult to match the film composition.

Furthermore, when using a single target, the target composition changes as time passes during sputtering deposition.
Poor reproducibility. Newly discovered oxide superconductors have different properties due to differences in their composition, so in this respect 7.
However, the sputtering method is inconvenient for realizing stable characteristics.

Furthermore, it has been confirmed that the electrical conductivity of this type of superconducting material is greatly influenced by the content of oxygen, which is a constituent element. In conventional vacuum deposition methods, the oxygen concentration in the deposited film is insufficient. Therefore, in order to supplement oxygen, high-temperature heat treatment at 800° C. or higher is performed in an oxygen atmosphere after film formation. When considering integration with semiconductor devices, high process temperatures may destroy the elements.
This high temperature treatment is disadvantageous. This heat treatment itself also has problems, such as subtle differences in characteristics depending on the treatment conditions and complicated operations. In addition, as a method of supplementing oxygen after film formation, there is a method of plasma oxidation at about 300 to 400°C, but at most O,OS μm from the surface
Since the treatment was limited to a certain extent, it was insufficient to oxidize the entire film. It is known that the oxidation of the film, especially the oxidation of the constituent element copper, affects the superconducting properties.

In the CVD method, CVD raw material metal compounds include halides, organometallic compounds, organometallic complexes, and the like. In the case of halides, it is difficult to lower the synthesis temperature because the decomposition temperature for gasification generally requires a high temperature of 1000° C. or higher. Furthermore, although the gasification temperature of organometallic compounds and organometallic complexes is as low as 120 to 240°C, a high-quality superconducting thin film could not be obtained unless the substrate temperature was as high as 800°C or higher.

The present invention promotes the oxidation of the constituent element copper by a combination method of vacuum evaporation, which allows the film composition to be adjusted relatively easily, and irradiation with a plasma flow of oxygen-based gas and copper compound gas, or with an ion flow. The purpose of this invention is to provide a method for forming a thin film superconductor without damage.

Means for Solving the Problems The method for manufacturing a thin film superconductor according to the present invention according to claim 1 includes:
At least one type of evaporation source is installed in a vacuum chamber, and a plasma flow or ion flow of a mixed gas of an evaporation flow from the evaporation source, an oxygen-based gas, and a copper compound gas is irradiated onto the substrate installed in the vacuum chamber. By doing so, it is attempted to form a thin film.

Another method for producing a superconducting thin film according to the present invention according to claim 4 includes installing at least one evaporation source in a vacuum chamber,
A thin film is formed by independently irradiating the evaporation flow from the evaporation source and the plasma flow or ion flow of oxygen-based gas and copper compound gas onto the substrate placed in the vacuum chamber. .

The present invention according to claim 1 uses plasma or ion irradiation of a mixed gas of an oxygen-based gas with a high electron temperature and a high degree of dissociation and a copper compound gas of an organometallic complex during vapor deposition, so that the oxidation of the constituent element copper is avoided. It is possible to provide a method for forming a thin film superconductor that accelerates the formation process, lowers the formation process temperature, and causes no damage. This makes it possible to form electronic devices using superconducting thin films with excellent properties.

In addition, the present invention according to claim 4 is capable of promoting oxidation of copper, lowering the formation process temperature, and forming a film without damage, as well as the method of manufacturing a superconducting thin film, and the irradiated oxygen-based gas and copper compound gas Since the ions and plasma can be controlled independently, the film properties can be more controlled.

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

FIG. 1 shows a conceptual diagram of a manufacturing apparatus used in the method of manufacturing a thin film superconductor according to the present invention.

The vacuum chamber 1 includes an ion source 2 that generates plasma or ions of oxygen-based gas and copper compound gas, and one or more types of evaporators [3]. A film is formed by irradiating a plasma flow/ion flow of a mixed gas of an oxygen-based gas and a copper compound gas from an ion source 2 while evaporating metal from an evaporation source 3 onto a substrate 4 set in a vacuum chamber 1. Do this. When using this apparatus, it is evacuated in advance to approximately 10<-7 >Torr in the direction of arrow 5.

The frequency of 2.45 G generated by the microwave power supply 6 is shown in FIG.
Hz microwave is passed through the waveguide 7 to the plasma generation chamber 8.
to be introduced. In this case, a solenoid-type electromagnet 9 placed around the plasma generation chamber 8 generates a central magnetic field of B 75
By applying a magnetic field to a Gaussian level, electron cyclotron resonance is generated within the plasma generation chamber 8. The configuration is such that the oxygen-based gas can be introduced into the vicinity of the substrate 4 and into the plasma generation chamber 8, and the copper compound gas can be introduced into the plasma generation chamber 8.

By setting the mixed gas pressure of oxygen-based gas and copper compound gas in the plasma generation chamber 8 to 1O-5 to 10''3 Torr, a mixed gas plasma with high activity and high ionization rate can be obtained. It is pulled out into the vacuum chamber l by the divergent magnetic field of the electromagnet 9.

An example of forming a G d-B a-Cu-0 based superconducting thin film using this apparatus will be described. (100) plane Mg
Using O as the substrate 4, the evaporation source 3 is heated by electron beam heating.
Gd-B on the substrate 4 by irradiating a highly active oxygen and copper plasma stream or ion stream from the ion slag 2 using 7-electron cyclotron resonance while depositing Gd and Ba metals on the substrate 4. An a-Cu-0 based thin film can be formed. In this case, the output of the electron beam evaporation control power source was controlled using a crystal film thickness monitor, and the composition of the formed film was set to CdBa2CutO. The temperature of the substrate 4 was set to 600° C., and oxygen was introduced into the plasma generation chamber 8 using oxygen as the oxygen-based gas and Cu(Cz H+eO2)2 as the copper compound gas. In addition, Cu(C+ + H1902
)2 gas is gasified by placing the container in a thermostat kept at 150°C. The total deposition rate of each metal was set to 2.0/sec under the conditions of microwave power of 400 W, oxygen gas flow rate of 5 SCGI, and mixed gas pressure of 3 x 10-'Torr. A GdBa film with a thickness of about 2000A was formed under these conditions.
The 2Cu308 film exhibited superconductivity, with an onset of 94K and a zero resistance temperature of 84K. Further, the formed film was C-axis oriented and exhibited good crystallinity.

For comparison, a film formed by vacuum deposition in an oxygen and copper compound gas atmosphere without using an ion source will be described. The formation conditions were as follows: (100) plane MgO was used as the substrate, the substrate temperature was 800°C in a mixed gas atmosphere with a gas pressure of 3 x 10-'Torr, and the total deposition rate was 1. OA/se
c and the film thickness is approximately 200 OA. As before, although the formed film showed C-axis orientation, the superconducting transition temperature onset was 93, but the zero resistance temperature was as low as 68.

This was confirmed by comparing the lengths of the C-axes identified by X-ray diffraction, which showed that the oxygen concentration in the film was insufficient compared to that using an ion source.

Therefore, by depositing the metal component and irradiating it with ions or plasma of a mixed gas of oxygen-based gas and copper compound gas to form a film, we were able to lower the deer's crystallization temperature by about 200 degrees. It can be seen that the oxidation of the constituent steel is promoted, and the oxygen necessary for exhibiting good superconducting properties is incorporated into the formed film.

Further, an example in which oxygen gas is introduced from near the base 4 will be described. In this case as well, as the base 4 (100)
Using planar MgO, the total evaporation rate of each metal was set to 2.0% under the conditions of microwave power of 40OW and total gas pressure of 3 x 10-'Torr. GdBa2Cu as OA/sec
An aOx film was formed to a thickness of about 20 OA. Base temperature is 600
℃, the formed film is a C-axis oriented film and exhibits superconductivity, with a superconducting transition temperature of onset 94 and a zero resistance temperature of 86.
It was. As a result, it can be said that the zero resistance temperature is slightly improved. This is considered to be because the oxygen concentration in the formed film is further increased by increasing the oxygen gas pressure near the substrate.

Furthermore, an example will be shown in which generated oxygen and copper ions are accelerated by a DC electric field. Under the same conditions as above,
Film formation was performed by applying an accelerating voltage of 60 V between the plasma generation chamber 8 and the substrate 4.

A C-axis oriented superconducting thin film was obtained at a substrate temperature of 550°C. The superconducting critical temperature was 93K (Oncera) and the zero resistance temperature was 82. In this case, by applying an accelerating voltage, the substrate temperature could be lowered by about 50 degrees.

Next, FIG. 3 shows a conceptual diagram of another superconducting thin film manufacturing apparatus according to the present invention. The vacuum chamber l includes an ion source 11 that generates oxygen-based gas plasma or ions, and an ion source 12 that generates copper compound gas plasma or ions.
and one or more evaporation sources 3. This makes it possible to independently control oxygen plasma ions and copper plasma ions.

FIG. 4 shows a case where a plasma processing apparatus is used as the ion sources 11 and 12, which generates plasma by applying a magnetic field and microwaves so as to satisfy electron cyclotron resonance conditions. Plasma and ion generation are as described above.

An example of forming a Cd-Ba-Cu-0 based superconducting thin film using the apparatus shown in FIG. 4 will be described. The substrate 4 is made of (100) plane MgO in the same manner as described above, and each metal of Gd and Ba is deposited from deposition i1!3 by electron beam heating.
Ion sources 11 and 1 using electron cyclotron resonance
A G d-B a-Cu-0 thin film can be formed on the substrate 4 by independently irradiating copper and oxygen plasma ions generated in Step 2 and drawn out by a divergent magnetic field.

In this case, oxygen was used as the oxygen-based gas, CD (C mouth HI902) 2 was used as the copper compound gas, and the substrate temperature was 600°C.
, Cu(C++H+eO2)2 in the plasma generation chamber 13
Gas pressure 2 x 10-'Torrs Oxygen gas flow rate 5
5CC-, oxygen gas pressure in the plasma generation chamber 14
10-'Torr, about 250 at microwave power 400W
0A vapor deposition was performed. The formed film is a C-axis oriented film and exhibits superconductivity, and the superconducting transition temperature is 93K, zero resistance temperature 81
It was. In addition, under the same conditions as above, a DC voltage of 50 V was applied between the copper compound gas plasma generation chamber 13 and the base 4, showing an example in which the generated oxygen and copper ions are independently accelerated by a DC electric field. An acceleration voltage of 60 V was applied between the oxygen gas plasma generation chamber 14 and the substrate 4 to form a film. Substrate temperature is 520
A C-axis oriented superconducting thin film was obtained at . The superconducting critical temperature was 93K (Oncera) and the zero resistance temperature was 84K. By applying an accelerating voltage, in this case, 8
It can be said that the substrate temperature was lowered to about 0 degrees, and the zero resistance temperature was slightly improved.

Next, a case will be described in which 03 (ozone) or N20 (nitrous oxide) is used instead of 020 as the oxygen-based gas. For 03, 02 was generated at a concentration of 5% using an ozonizer. The difference between 03 and N20 and oxygen only is that, for example, when a microwave plasma source using electron cyclotron resonance is used as ion R2, the microwave power supplies the oxygen concentration in the formed film with lower power. For example, when using 5%03, the G d B a2Cu30 K thin film has the effect that the substrate temperature is 5%.
The temperature was 50°C, the total gas pressure was I x 10-' Torr, and gas was introduced through the introduction tubes 5 and 11, and the generated ions were
Under the condition that 0V accelerating voltage is applied, the microwave power is
At a minimum of 200W, the superconducting transition temperature is 94K,
A film with a zero resistance temperature of 85% was formed. Also, N
When using a microwave power of 30 W, the same film properties as above can be obtained with a microwave power of 150 W.
If ζ is rubbed for more than 0 W, the superconducting properties will deteriorate due to the influence of nitrogen plasma and ions.

However, it was confirmed that in the range of 150 to 300 W, there was no effect on the superconducting properties or the orientation of the film.

When Cu(Cs HF 602)2 gas is used as the copper compound gas, the essential aspect of the present invention is achieved by lowering the holding temperature by about 40 degrees to obtain the same gas vapor pressure as Cu(C++H+902)2 gas. This does not change the characteristics. Furthermore, when the DC voltage applied between the plasma generation chamber 8 and the substrate 4 is set to 100 V, the C-axis orientation is exhibited at the substrate temperature of 490°C, and the superconducting property also has a transition temperature of 100 V. )9
1K and zero resistance temperature of 79K were obtained. DC voltage is 15
In the case of 0 V, it was confirmed that C-axis orientation was exhibited at a substrate temperature of 400° C., and superconductivity was exhibited even at a substrate temperature of 400° C., although the onset temperature was 92 K and the zero resistance temperature was a low value of 48.

In this manner, in each invention, superconductivity can be achieved at a predetermined temperature of the substrate during thin film formation of 400 to 700°C.

Note that as a method for evaporating the evaporation source, an evaporation method using electron beam heating or resistance heating may be used.

Effects of the Invention The method for manufacturing a thin film superconductor of the present invention uses a mixed gas of an oxygen-based gas and a copper compound gas in addition to a combined method of evaporation and plasma/ion irradiation that can lower the formation process temperature and form a film without damage. Since the oxidation of copper is promoted using plasma ions, it is possible to form superconducting thin films with excellent properties. By using a superconducting thin film formed by the method of the present invention, it is possible to realize an element with stable characteristics.

Another method for producing a superconducting thin film of the present invention is a combined method of vapor deposition and plasma ion irradiation, and by independently irradiating plasma ion streams of oxygen-based gas and copper compound gas, film characteristics can be better controlled. This makes it possible to form a superconducting thin film with even better properties.

In particular, there is a possibility that the transition temperature of the oxide superconductor is higher than room temperature, so the practical scope of the present invention is wide and the industrial value of the present invention is extremely high.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of an embodiment of the thin film superconductor manufacturing apparatus according to the present invention, and FIG. 2 is a schematic cross-sectional view of an ion source in FIG. 1 in which a magnetic field and microwave are applied so as to satisfy the electron cyclotron resonance conditions. FIG. 3 is a schematic cross-sectional view when using a plasma processing apparatus that generates plasma by
FIG. 4 is a schematic cross-sectional view showing the concept of another superconducting thin film manufacturing apparatus of the present invention, and the ion source in FIG. 3 generates plasma by applying a magnetic field and microwaves so as to satisfy the electron cyclotron resonance conditions. FIG. 2 is a schematic cross-sectional view showing the concept of using a plasma processing apparatus that allows l...Vacuum chamber, 2.11.12...Ion source, 3.
... Evaporation source, 4... Substrate, 6... Microwave power source,
7... Waveguide, 8.13.14... Plasma generation chamber, 9... Magnet.

Claims (5)

[Claims] (1) At least one type of evaporation source is installed in a vacuum chamber, and an evaporation flow from the evaporation source and a plasma flow of a mixed gas of an oxygen-based gas and a copper compound gas or A method for producing a thin film superconductor, characterized by forming a thin film by irradiating an ion stream. (2) The method for manufacturing a thin film superconductor according to claim 1, characterized in that the thin film is formed by introducing an oxygen-based gas into the vicinity of the substrate. (3) The method for producing a thin film superconductor according to claim 1, wherein the thin film is formed by controlling the ion flow of a mixed gas of an oxygen-based gas and a copper compound gas using a DC electric field. (4) At least one type of evaporation source is installed in a vacuum chamber, and an evaporation flow from the evaporation source and a plasma flow or ion flow of oxygen-based gas and copper compound gas are applied onto the substrate installed in the vacuum chamber. A method for producing a thin film superconductor, characterized by forming a thin film by irradiating each independently. (5) The method for producing a thin film superconductor according to claim 4, characterized in that the thin film is formed by controlling the ion flows of the oxygen-based gas and the copper compound gas independently using a DC electric field.