JPH04193703A - Production of superconducting thin film - Google Patents

Abstract

PURPOSE:To produce the superconducting thin film of a single crystal having good smoothness on the surface with a large area by supplying gaseous oxygen contg. a specific concn. of ozone and specifying pressure in a vacuum chamber to a specific range at the time of producing the superconducting thin film by a vacuum vapor deposition method. CONSTITUTION:The substrate temp. is set at 550 to 650 deg.C higher than the crystallization temp. and the gaseous oxygen/ozone mixture having 5 to 20wt.% ozone concn. is so supplied that the gaseous pressure in the vacuum chamber attains 5X10<-5> to 6X10<-4> Torr at the time of producing the superconducting thin film by the vacuum vapor deposition method. The sufficiently activated oxygen is supplied to the substrate in the same manner as in the case of the constitution of the method for supplying the oxygen in the above-mentioned manner if the plasma is generated in the vacuum chamber at the time of supplying the gaseous oxygen/ozone mixture to the substrate and, therefore, the superconducting thin film of the single crystal having the large area is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industry> Second Field of Application The present invention relates to a method for producing an oxide superconducting thin film.

<Prior Art> Since the discovery of an oxide high-temperature superconductor that becomes superconducting at liquid nitrogen temperature (77 K), research into the basics and applications of this material has been actively conducted.

In recent years, 1n-
In-situ or as-depo film formation technology is attracting attention. These film-forming techniques include, for example, sputtering, laser evaporation, CVD, and reactive evaporation. In all of these methods, it is important to incorporate oxygen supplied to the substrate into the film. This is a major factor, and methods such as increasing the oxygen pressure during film formation, using oxygen plasma, and using atomic oxygen, ozone, and nitrous oxide, which are chemically more active than oxygen gas, as reaction gases, Efforts have been made to improve the stoichiometry of oxygen in the membrane.

For example, literature (Den-j-Information (1), Society Technical Research Report 1)
11S CE rtlj conductive electronics 1-ronics,■
○a, 89. No, 54. (1989) PP, II
~16) describes a method in which oxygen gas containing about 25% ozone is used as a reactive gas at a gas pressure of 3X10-"I'orr when producing a superconducting thin film by reactive vapor deposition. has been done.

In addition, literature (/Japanese Journal of Appraisal' Fixtures)
A i,, OFA P P I-I E I) P
IfYS IC8, Vori 28. No, 10°○CT
ORBER, (1989) PP.

L l 809-1. , l 8 ] ]), M
BE(Molecular Beam Epitaxy)
)-method in which 100% ozone is used as a reactive gas at a gas pressure of 3X] and 0-6 Torr.

- On the other hand, there is a tunnel-type Josephson device as a device using a superconducting thin film. This tunnel type N1
The superconducting thin film used in the Sefson element has a smooth surface.
Although it is required that the crystal has a crystal value of 〇, it is also advantageous to use an A-axis oriented film, a B-axis oriented film, a <1.10> axis oriented film, etc., which has a coherent length longer than the C-axis oriented film. I know that it is.

JP-A No. 83496 discloses that when a superconducting thin film is formed on a SrTi03M plate-1 having a (100) structure by sputtering, by controlling the acceleration voltage and ion current density of oxygen ions irradiated onto the substrate. , an example in which a superconducting thin film with A-axis orientation is formed is shown.

<Problems to be Solved by the Invention> A superconducting thin film has the property that it will not crystallize unless it is heated above a certain temperature, and oxygen will escape at high temperatures. Therefore, the superconducting thin film is generally produced by crystallizing the substrate during film formation by raising the temperature higher than the crystallization temperature, and then lowering the temperature and annealing in an oxygen atmosphere.

The above documents (IEICE technical research report SCE superconducting electronics 1 heronics, voQ, 89°No, 5/I
, (1989) I.] 11-16) also states that the effect of using ozone lies in the incorporation of oxygen into the film during cooling. Since the ozone concentration was as low as 25% relative to the gas, sufficient oxygen could not be incorporated into the film during film formation and cooling. Therefore, it was not possible to obtain a uniform single crystal thin film over the entire substrate.

In addition, Bunnan K (Nyapanese Journal Off-Applied Fixtures (JΔI) ANE S EJ
OU RN A l, OF A P I) L
IE DPI-IYS IC3, VoQ, 28. No
, ] 0゜○c'roRBER, (1989) PPL
In the method shown in I 809-L]8]]) 10
Since 0% ozone (Φ) is used, the degree of oxygen activation is high, or 3X] Because the film is formed under a low pressure of 0-6 Torr, it is possible to uniformly supply oxygen to the entire substrate. I can't do it. Therefore, it has been difficult to obtain a uniform tl crystal thin film over a large area.

Further, there is also the problem that the use of 100% ozone tends to corrode the manufacturing equipment, making it impractical for repeated manufacturing.

Furthermore, in the method described in JP-A-83496, the degree of activation of oxygen is low because the substrate is irradiated with oxygen gas plasma, and it is difficult to incorporate enough oxygen into the film. could not. Therefore, although it is possible to obtain a superconducting thin film partially oriented along the Δ axis, it is difficult to obtain a single crystal thin film over a large area! It was if.

An object of the present invention is to provide a method for manufacturing a large-area single-crystal superconducting thin film with good surface smoothness.

Means for Solving Problems> In order to achieve the above-mentioned object, in the present invention, when producing a superconducting thin film by a vacuum evaporation method, oxygen is removed during one operation by supplying a mixed gas of oxygen and ozone to the substrate surface. In the method of incorporating, the ozone concentration of the reaction gas is set to 5 to 2.
0wt%, and the gas pressure in the vacuum chamber is 5X]O'~
6X] O-'Torr.

Furthermore, in the present invention, for the purpose of +'+i+ purpose description,
When producing a superconducting thin film by vacuum evaporation, a plasma of the mixed gas was generated in a vacuum chamber in a method in which oxygen was introduced into the film by supplying a mixed gas of oxygen and ozone to the substrate surface.

<Operation> In order to obtain a large-area superconducting thin film in a single crystal state, it is first necessary to incorporate sufficient oxygen into the film during film formation.

In the present invention, the substrate temperature is set at 550°C to 550°C, which is higher than the crystallization temperature.
Set to 650°C and ozone concentration of 5 to 20W.
A mixed gas of oxygen gas and ozone having a concentration of
Since the gas is supplied to the substrate so that r r, highly reactive gas can be uniformly supplied to the substrate. Therefore, sufficient oxygen can be uniformly incorporated into the film during film formation.

However, as described above, if the substrate temperature is 550 to 650°C, a thin film in a crystalline form that does not exhibit superconducting properties can be obtained if the substrate temperature is 550 to 650°C. In order to further incorporate oxygen into this thin film and make it into a crystalline form that exhibits superconducting properties, it is necessary to lower the substrate temperature to 500°C and anneal it in an oxygen atmosphere. Without it, single crystallization cannot be achieved. In the present invention, since the conditions for supplying the reaction gas are configured as described above, even during annealing in the oxygen atmosphere, sufficient oxygen can be incorporated into the film, and the film exhibits good superconducting properties. A superconducting thin film can be obtained in the form of a single crystal.

Note that if the ozone concentration is less than 5 wt % with respect to oxygen gas, the amount of activated oxygen will be small, and oxygen will not be sufficiently incorporated into the film during film formation and cooling. In addition, when the osine concentration is 20% relative to oxygen gas,
If it exceeds wt%, problems such as corrosion of the manufacturing equipment and oxidation of the evaporation source will occur, such as the evaporation rate of the raw material becoming unstable.

In addition, the gas pressure is increased directly to the exhaust system by 5X]0-5T or
When it is lower than r, the concentration of the mixed gas supplied to the substrate becomes low, and oxygen is not sufficiently incorporated into the film. If it is higher than 6X 10-' Torr, a problem arises in that the quality of the produced superconducting thin film deteriorates.

Furthermore, when a mixed gas of oxygen and ozone is supplied to the substrate, if plasma is generated in the vacuum chamber 116 shown in FIG. Since the oxidized oxygen is supplied to the substrate, a large-area single-crystal superconducting thin film can be obtained.

<Example> Embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram of an apparatus used in an embodiment of the present invention. In the figure, 101 and 102 are melting holes for EB evaporation, and 103 is a port for resistance heating. That is, this device is equipped with two EB guns and one resistance heating device, and is capable of independently vapor depositing three elements. 1
04, 105, and 106 are film thickness monitors installed near each evaporation source, and are controlled by applying feedback to the input power so that the evaporation rate is always constant. 107, 108, and 109 are shutters installed near the evaporation source A, and 110 are shutters installed near the substrate I and J. When the evaporation rate monitored at 104, 105, and 106 becomes constant, By opening 107, 108, and 109, and finally opening 110, the controllability of the film composition is improved. 111 is a pipe for introducing a mixed gas of ozone and oxygen gas, and 112 is an RF coil for turning the mixed gas into plasma in the vacuum chamber 116.

113 is a substrate, 114 is a substrate boulder, and 1115 is a heater for heating the substrate. This board boulder-11
4 is used during film formation to improve the uniformity of the film] Or p
The mechanism is such that the substrate 113 is rotated at a rotation speed of m. 116 is a vacuum chamber in which the above equipment is installed, 117 is a vacuum cage for measuring the degree of vacuum in the chamber, and 118 is a pump for evacuating the vacuum chamber 116.

110-Example I The steps for making the superconducting thin film of the present invention will be described below. In this example, a superconducting thin film having a composition ratio of Y and Ba2Cu307-1 was fabricated.

First, Y and Ba metals are each placed in crucible 1 for EB deposition.
01.102, and Cu metal was installed in the resistance heating bow 1-103. The vacuum chamber 116 is pulled by the vacuum pump 218, and the vacuum level of the vacuum gauge 117 is 3XIO.
-OTorri: Now, gas introduction pipe 1
11] A mixed gas of oxygen gas and ozone containing Qwt% ozone was introduced, and the degree of vacuum was 5 × 10-”T or
It was made to be r.

Next, the substrate 113 placed on the substrate holder 114 was heated with a heater 115 and maintained at 600°C. Substrate 11
For No. 3, an Mg0 (1,00) single crystal substrate of 2Q mrn angle was used. Note that the substrate temperature is desirably set at 550°C to 650°C, and if the temperature is lower than 550°C, the superconducting thin film will be in an amorphous state. Furthermore, if the temperature exceeds 650°C, the flatness of the film surface deteriorates, and both conditions are inappropriate for obtaining a uniform thin film. 1- Gas introduction pipe III
and the substrate 113. It is preferable that the distance 7 is 10 to 30 mm, and in this example, it is 25 mm.

Distance between gas introduction pipe 111 and substrate +13], 0m
If the distance is less than 30 mm, the supply of oxygen to the board 113 will become uneven, and if it exceeds 30 mm, the amount of oxygen supplied to the substrate 113 will be insufficient.

Next, immerse power into the evaporation 1 source of +01, +02, and jo3, and create Ily ■3a: (
, u-]: the film thickness monitor 10 so that the composition ratio is 2:3.
4. While monitoring the evaporation rate of each evaporation source at 105 and 106, /Yatta107
, opened +08.109. Then, we opened the substrate (nearly 1J Nyatta 110) and started film formation.Finally, we formed a superconducting thin film with a thickness of 1.0 at a speed of 05 persons/sec.
One film was applied so that the number was 008. After film formation, cool to 500°C, and keep the temperature at 500°C (V) until the inside of the chamber reaches 3.
By introducing a mixed gas of oxygen and ozone at the mixing ratio shown below and annealing for 1 hour until the temperature reaches 00 Torr, the crystal form changes from a state that does not exhibit superconducting properties to a state that exhibits superconducting properties. It was. Thereafter, the chamber was allowed to cool down naturally, and the product was taken out from the vacuum chamber 11G. Below 1
A superconducting thin film was produced by the process of -.

FIG. 2 shows an X-ray diffraction pattern diagram of the j1α conductive thin film subjected to f'1 concentration according to this embodiment. In this example, as shown in the figure, Y 2 , B a 2Cu , O? A superconducting thin film with a composition ratio of −1 was obtained.

Furthermore, as a result of analyzing the film surface using electron beam diffraction, a C3 streak-like pattern was observed at arbitrary points on the substrate, indicating that the film was a single-crystal tW film over the entire substrate.

Furthermore, as a result of observing the film surface with an electron microscope, it was found that the film was a single-crystal thin film with no twins or grain boundaries observed over the entire substrate.

FIG. 3 shows the surface uniformity of the characteristics of this example.

As shown in the figure, it is shown in this example! The superconducting thin film produced by the J method uniformly exhibited good superconducting properties over the entire 20 mm square substrate with a zero resistance temperature Tc of -88K. In FIG. 3, the vertical axis represents the cell resistance of 418 degrees (the distance from the center of the substrate).

Further, the critical current density (, lc) was 6.5×l 06 A/cm 2 at a crystallinity of 77 K.

Example 2 Gas blowout from gas introduction pipe I11 [Pipe 111 is installed so that the distance between I1 and the center of the substrate is 10 mIT'l, and the degree of vacuum in the vacuum chamber is 5x], 0=
A superconducting thin film was fabricated in the same manner as in Example 1, except that Tor 88, the critical current density J at a temperature of 77K
c=6.5X], 06A/cm2 good superconducting properties were obtained.

Example 3 A superconducting thin film was fabricated using the same method as in Example 1 except that a 5rTi○ (100) single crystal Jj (plate was used as the substrate 113 and the substrate temperature was 550°C). The plate temperature is preferably 550 to 650°C, and 55
When the temperature drops below 0°C, the superconducting thin film becomes amorphous and 65
When the temperature is higher than 0°C, the superconducting thin film becomes polycrystalline. Fourth
The figure shows an X-ray diffraction pattern of a superconducting thin film formed on 5rTi○3 (100) obtained in this example. As shown in the figure, in this example, a completely A-axis oriented Y + B a 2Cu 307-X superconducting thin film was obtained.

Further, as a result of analysis using electron beam diffraction, a streak-like pattern was obtained at any point on the substrate, and it was found that single crystal thin films were laminated over the entire substrate.

Furthermore, in this example, as in Example 1, the substrate is 20 mm.
uniformly over the corner to zero resistance temperature Tc-8,8,7
Critical current density Jc-6,0XI06A/c at 7K
Good superconducting properties of m2 were obtained.

Example 4 A superconducting thin film was produced in the same manner as in Example 1 except that the substrate 113 was a SiT 1o3 (110) plane.

In this example, as in Example 3, the temperature range of the substrate is 55
0°C to 650°C is preferred.

FIG. 5 shows the X-ray diffraction pattern of the superconducting thin film obtained in this example. As shown in the figure, a superconducting thin film with (103) or (110) orientation was obtained. As in Example 1, this superconducting thin film has a uniform zero resistance temperature T c = 33 K, 7 over the entire 20 mm square substrate.
Critical current density Jc at 7K = 6. Good superconducting properties of 2 A/cm2 were obtained.

Example 5 RF coil 112 during film formation and cooling to 500°C
A superconducting thin film was produced in the same manner as in Example 1, except that plasma was generated with an RF power of 100 W. By generating plasma as described above, the number of oxygen active species increases, and the film becomes more easily oxidized, making it even more oxidized than when only a mixed gas of ozone and oxygen gas is supplied to the substrate.
A film with good surface flatness can be obtained. In this example, as in Example 1, the zero resistance temperature T
Good superconducting properties with c=9QK and critical current density Jc-7X106A/cm' were obtained.

As mentioned above, in any of the embodiments of the present invention, Y, Ba,
Although an oxide superconducting thin film of Cu30□-8 was fabricated, the composition is not limited to this, and other oxide superconductors (La
,−,M,) 2Cu 04 (M=B a .

Sr, Ca), Ln, Ba2Cu307-,.

Ln, Ba, Cu, O, (Ln=Nd, Pm, Sm.

Eu, Gd, Dy, Ho, Er, Tm, Yb).

B i, S r2Ca, Cu, ○IO+B il□P
bo25bo, +Ca2. oSr2. oCL12. sO
x+(B l67Pbo3)2S r2Ca, Cu30
．． o.

T I 2Ba2Ca2Cu30IO+ B a +
-xKxB I 03+Nd2-xCexCu○4-y
etc., uniform superconducting characteristics can be obtained over the entire substrate as in this embodiment.

In addition, as a substrate in this example, MgO (100), 5r
Although Ti03 (100) and (110) single crystal substrates were used, similar superconducting properties were obtained with LaAlO3 single crystal substrate, La Ga O3 single crystal substrate, yttrium stabilized zirconia (ysz) polycrystalline substrate, etc. .

<Effects of the Invention> Since the present invention is configured as follows, it produces the following effects.

In the present invention, when producing a superconducting thin film by a vacuum evaporation method,
In the method of introducing oxygen into the film by supplying a mixed gas of oxygen and ozone to the substrate surface, the ozone concentration of the reaction gas is set to 5 to 20 wt%, and the gas pressure in the vacuum chamber is set to 5 x 10-5. Since the value is 6×1 O −4 TOrr, sufficient oxygen can be incorporated into the film during film formation and cooling. Therefore, a single crystal superconducting thin film with good surface smoothness can be obtained over a large area.

Furthermore, in the method for producing a superconducting thin film of the present invention, when producing a superconducting thin film by vacuum evaporation, oxygen is introduced into the substrate surface by supplying a mixed gas of oxygen and ozone to the substrate surface. Since plasma of the mixed gas is generated, sufficient oxygen can be incorporated into the film. Therefore, a single crystal superconducting thin film with good surface smoothness can be obtained over a large area.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an apparatus according to an example of the present invention, FIG. 2 is an X-ray diffraction pattern diagram of a thin film obtained in Example 1, and FIG.
The figure is a diagram showing the substrate surface uniformity of the superconducting properties of the thin film obtained in Example 1, where the vertical axis is the zero resistance temperature and the horizontal axis is the distance from the center of the substrate. Figure 4 is an X-ray diffraction pattern diagram of the superconducting thin film obtained in Example 3, Figure 5 is an X-ray diffraction pattern diagram of the superconducting thin film obtained in Example 4, and Figure 6 is an X-ray diffraction pattern diagram of the superconducting thin film obtained in Example 5. FIG. 2 is an X-ray diffraction pattern diagram of a superconducting thin film. 101.102...Electron beam heating evaporation source 103...
・Resistance heating evaporation source, 104.105.106...Film thickness monitor, 107.1
08.109.110・Shutter 111... Gas introduction pipe, 112... RF coil, 113... Board,
114...Substrate boulder-1115...Heater, 116
・・・Vacuum cage, 117・Vacuum chamber, 118・Vacuum pump agent Patent attorney Ume 1) Masaru (and 2 others) Nichiyo Nuri〈Nichiyokan〈Takimiku〈) o Q o-, -, 30 shi ) wa 0 mi lopsided ku (y)

Claims (1)

[Claims] 1. In a method in which oxygen is incorporated into the film by supplying a mixed gas of oxygen and ozone to the substrate surface when producing a superconducting thin film by vacuum evaporation, the ozone concentration of the mixed gas is is set to 5 to 20 wt%, and the gas pressure in the vacuum chamber is set to 5 × 10^-^5 to 6 × 10^-
A method for producing a superconducting thin film characterized by setting the temperature to ^4 Torr. 2. When producing a superconducting thin film using the vacuum evaporation method, by supplying a mixed gas of oxygen and ozone to the substrate surface,
A method for producing a superconducting thin film, the method comprising: generating a plasma of the mixed gas in a vacuum chamber.