JPH07288346A - Formation of thin film and josephson element - Google Patents

Abstract

PURPOSE:To obtain a method for formation of thin films wherein a superconductive thin film and a non-superconductive thin film are formed on the flat surface of a substrate to manufacture a superconducting element using a simple process. CONSTITUTION:Thin film material is applied to a substrate 8 that, when it has crystallinity, delivers superconductive characteristics, and thin films are thereby grown. Previously and locally injected with inert gas, the substrate 8 has a region 3 where the inert gas has been injected and a region 4 where no inner gas has been injected. A superconductive thin film 12 of a thin film material having superconductive characteristics, is grown on the non-injection region 4. At the same time a non-superconductive film 11 of a thin film material having no superconductive characteristics, is formed on the injection region 3. This makes it possible to form a non-superconductive thin film without forming any step or trench on the surface of a substrate, and thus to manufacture a superconducting element, such as a Josephson element, with the surface of a substrate kept flat.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for forming a superconducting thin film and a Josephson device using the superconducting thin film.
The present invention relates to a thin film manufacturing method for simultaneously forming a superconducting thin film and a non-superconducting thin film on a substrate, and a Josephson device using the non-superconducting thin film obtained by the thin film manufacturing method as a barrier.

[0002]

2. Description of the Related Art Conventionally, a superconducting device such as a Josephson device, which makes a junction between a superconducting thin film and a non-superconducting thin film, has been manufactured, and a magnetic detection device utilizing superconducting characteristics has been put into practical use. Also, the production of superconducting computers has been attempted. As described above, it is expected that the superconducting device will be used in a wide range of applications, but the non-superconducting thin film and the superconducting thin film used for the superconducting device are conventionally manufactured by separate steps. Various compositions have been used, such as different compositions and different orientations.

However, recently, due to demands for ease of processing and improvement in device reliability, the same materials are used for the superconducting thin film and the non-superconducting thin film under the same film forming conditions.
At the same time, attempts have been made to grow both thin films to obtain superconducting devices.

As a conventional technique for growing two kinds of thin films at the same time, a part of the substrate surface is processed in advance, and a superconducting thin film is grown on the substrate surface other than the processed part. There is a method in which a non-superconducting thin film is grown on the substrate surface of the processed portion at the same time. An example of this conventional technique will be described with reference to the drawings.

FIG. 9A shows a thin film formed by a thin film manufacturing method called a step edge method. In the step-edge method, a step surface 102 is provided on the surface of a substrate 101 by a sputtering method, and superconducting thin films having different orientations are grown on the step surface 102 and flat surfaces 103 ₁ and 103 ₂ , and grain boundaries thereof are grown. (Grain Boundary) is configured to exhibit non-superconducting properties.

FIG. 9B shows a focused ion beam method (FIB).
Which are a superconducting thin film and a non-superconducting thin film, which are produced by a thin film manufacturing method called a thin film manufacturing method. A fine trench structure portion 112 is formed on the surface of a substrate 111, and the superconducting thin film is grown on flat surfaces 113 ₁ and 113 _2. Meanwhile, the trench structure portion 11
A non-superconducting thin film is formed on the film 2.

However, in each of these conventional thin film manufacturing methods, a three-dimensional step is formed on the surface of the substrate, and therefore, when integrated with other circuits or integrated, an obstacle such as inter-element wiring is generated. Will be. Further, since it is subjected to three-dimensional processing, it is not suitable for miniaturization of the element. Further, since the manufacturing process has to be complicated, there is a drawback that mass productivity is poor.

On the other hand, for example, the focused ion beam method (FI
Techniques such as B) have also been developed that do not require three-dimensional processing on the substrate surface and require only one film formation process. In this FIB method, a superconducting thin film is once entirely grown on a substrate surface, and then highly reactive ions such as gallium (Ga) and germanium (Ge) are selectively implanted into a desired portion of the superconducting thin film. , Is a technology for manufacturing a non-superconducting thin film by modifying the conduction characteristics of the injection portion to a non-superconducting property. With this, it is possible to manufacture a superconducting element with the superconducting thin film and the non-superconducting thin film. Is.

However, in this FIB method, so to speak, a superconducting thin film is post-treated to develop normal conductivity or insulating property, and it takes time to implant ions into a desired portion by a focused ion beam. I will end up. Therefore, the workability of manufacturing the non-superconducting thin film was poor, and the durability and reliability of the device obtained by this method were poor.

Further, since active ions such as Ga ions are implanted, a chemical reaction occurs with the thin film depending on the type of the thin film to be produced, so that the type of thin film that can be used is limited.

Further, since Ga ions are easily diffused, there is a disadvantage that when a thin film for which the substrate temperature must be raised is deposited in the film forming step, it diffuses on the substrate surface. In particular, Ga ions are implanted in a very narrow range,
Since a Josephson device cannot be obtained unless a narrow non-superconducting thin film is formed, the FIB method of implanting ions that easily diffuse is not suitable.

[0012]

The present invention was created in order to solve the above-mentioned disadvantages of the prior art, and its purpose is to achieve superconductivity by a simple process while maintaining the flatness on the substrate surface. A thin film manufacturing method capable of forming a thin film and a non-superconducting thin film, and a Josephson device using the superconducting thin film and the non-superconducting thin film formed by the thin film manufacturing method.

[0013]

In order to solve the above-mentioned problems, the method of the present invention according to claim 1 comprises: a step of introducing a material of a superconducting thin film onto a substrate; and a step of introducing the material introduced onto the substrate. In a thin film manufacturing method having a growth step of growing a thin film, an injection region is formed by previously implanting an inert gas in a desired region on the substrate, and a superconducting region is formed on a non-implantation region in which the inert gas is not implanted. Growing a superconducting thin film of said material exhibiting characteristics, growing a non-superconducting thin film of said material not exhibiting superconducting properties on said implantation region, and simultaneously depositing said superconducting thin film and said non-superconducting thin film The invention method according to claim 2 is the method for producing a thin film according to claim 1, wherein in the introducing step, laser light is applied to a target made of one or more components of the material. Irradiate the above Clusters of the same composition as Getto includes a laser beam irradiation step dislodge from the target,
4. The invention apparatus according to claim 3, wherein the growing step includes a deposition step of depositing the clusters on the substrate to form the superconducting thin film and the non-superconducting thin film. A Josephson device having a conductive thin film as a barrier and two superconducting thin films separated from each other with the barrier interposed therebetween, wherein the non-super-layer is formed by the thin film manufacturing method according to claim 1 or 2. A conductive thin film and a superconducting thin film are used as the barrier and the electrode, respectively.

[0014]

When an injection region in which an inert gas is injected is formed in a desired region on the surface of a substrate, a non-injection region in which the inert gas is not injected is also formed at the same time.

As described above, the ion-implanted portion (implanted region) and the non-implanted portion (non-implanted region) of the substrate surface
When X-ray diffraction analysis is applied to and and the surface state of both is observed, patterns 61 and 62 as shown in FIG. 8 are obtained. The pattern 61 shows the surface condition of the non-implanted region, and the pattern 62 shows the surface condition of the implanted region.

Comparing both patterns, the pattern 6
Since the peak of 1 is sharp, it can be seen that the portion of the non-implanted region of the substrate surface maintains crystallinity. On the other hand, since the peak of the pattern 62 is broad, it can be seen that the crystallinity is broken in the injection region portion of the substrate surface.

In this way, the same superconducting thin film material is introduced into the implanted region and the non-implanted region having different surface states to grow the thin film.

At this time, when the thin film growing on the non-implanted region is grown under the thin film growth condition capable of exhibiting superconducting properties, the superconducting thin film can be obtained on the non-implanted region,
A non-superconducting film can be obtained on the implantation region.

As a method for growing a thin film, in particular, a laser ablation method can be used, and a target composed of one or more components of a superconducting thin film material is irradiated with laser light to have the same composition as the target. Of the superconducting thin film material is introduced into the surface of the superconducting thin film to react with it, and the clusters are deposited on the substrate surface. A superconducting thin film can be formed on the region, and a non-superconducting thin film can be formed on the implantation region.

A superconducting device can be manufactured by etching the non-superconducting thin film and the superconducting thin film thus formed into desired shapes. In particular, when the non-superconducting thin film is used as a barrier and two electrodes separated from each other by the superconducting thin film sandwiching the barrier are provided, a Josephson junction can be obtained, so that a Josephson device can be manufactured. .

[0021]

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

FIGS. 1 (a) to 1 (d) are views showing steps of one embodiment of the method of the present invention. Referring to FIG. 1A, 1 is
Original substrate for growing thin film, magnesium oxide (M
(gO) single crystal is formed into an appropriate thickness and size.

On the surface of the original substrate 1, as shown in FIG. 1 (b),
A masking material 2 having a desired portion opened in a window was placed, and an inert gas, argon (Ar), was implanted from above the masking material 2 by an ion implantation method. Then, since the argon is injected into the surface of the substrate 1 at the window opening portion of the masking material 2, the injection region 3 is formed. On the other hand, in the portion of the surface of the original substrate 1 where the window is not opened and is covered with the masking material 2, the masking material 2 prevents the invasion of argon and creates a non-implanted region. It Therefore, the implantation region 3
The non-implanted region 4 into which argon is not implanted can be formed at the same time when the above is manufactured.

At this time, the implantation of argon by the ion implantation method was performed at an acceleration voltage of 100 kV, an ion source pressure of about 3 × 10 ⁻⁵ Torr, an extraction current of about 2 mA, an implantation angle of 7 °, a beam current of 200 μA, and a temperature of room temperature. The conditions are such that the implantation time and the beam current are 2 × 10 ¹⁷ (2 × 1) per 1 cm ² of the dose amount of argon on the implantation region.
It was adjusted to be 0 ¹⁷ / cm ² .

When the masking material 2 is removed after the ion implantation, the implanted region 3 and the non-implanted region 4 are exposed on the substrate surface 8 as shown in FIG. 1 (c).

Then, a thin film was grown on the surface of the substrate 8 by an excimer laser deposition method using a laser ablation apparatus as shown in FIG.

This excimer laser vapor deposition method will be described with reference to FIG. Referring to FIG. 2, reference numeral 41 denotes an excimer laser (Excim
er Laser) generator, wavelength 248n from KrF gas
The laser light 44 of m is generated. The laser light 44 is emitted as a pulse having a time width of 23 nsec to 24 nsec, and is condensed on the target 42 by the condenser lens 43. The energy density of the laser beam 44 was variable and was set to ² J / cm ² .

The target 42 is made of a sintered body of Bi ₂ Sr ₂ Ca ₁ Cu ₂ Ox which is a material of the superconducting thin film, and when the laser beam 44 is focused on the target 42, A cluster with the same composition as the target composition was ejected, and a plume composed of this cluster (Plum
e) 45 occurs.

On the surface of the substrate 8, the injection region 3
The surface where the non-implanted region 4 and the non-implanted region 4 face is arranged so as to face the plume 45, oxygen is introduced into the atmosphere in which the substrate 8 is placed, and the substrate 8 is heated by the heater 47 from 650 ° C. to 700 ° C. When heated to the range of ° C, clusters in the plume 45 are deposited on the implanted region 3 and the non-implanted region 4, and a thin film grows. In this laser ablation method, a single crystal thin film grows on the surface of a single crystal substrate. In addition, Bi ₂ which constitutes the target 42
Since the single crystal thin film of Sr ₂ Ca ₁ Cu ₂ Ox exhibits superconducting properties, the thin film grown on the non-implanted region 4 exhibits superconducting properties.

According to the laser ablation method,
Unlike the vacuum deposition method, the atmosphere in which the substrate is placed does not need to be in a high vacuum state, and various reactive gases other than oxygen can be added, so thin films of various compositions can be formed. It is possible.

A cross-sectional view of the thin film produced by the method of the present invention is shown in FIG. The superconducting thin film 12 showing the superconducting properties on the non-injection region 4 is grown, argon 1 cm ² per 2
A non-superconducting thin film 11 having no superconducting property was grown on the implanted region 3 having × 10 ¹⁷ implanted regions.

On the other hand, a substrate different from the original substrate 1 was prepared, and argon was added to the surface of the substrate 1 cm ² as a low injection amount region 5.
A substrate 9 having 5 × 10 ¹⁶ pieces implanted therein was produced. A thin film is grown on the surface of the substrate 9 under the same conditions as described above, and as shown in FIG.
Has grown up.

The non-superconducting thin film 11 and the superconducting thin film 1
2. The electrical characteristics of the comparative thin film 13 and the results of surface analysis will be described below.

FIG. 4 shows the pattern of the non-superconducting thin film 11 by reflection high-energy electron diffraction (RHEED), and FIG. 5 shows the patterns of the superconducting thin film 12 and the comparative thin film 13.
Shown in (a) and (b).

In the RHEED pattern, it is generally known that streaks are observed when the thin film is made of a single crystal, and rings are observed when the thin film is made of a polycrystal.

RH of the non-superconducting thin film 11 shown in FIG.
Since only the ring is observed in the EED pattern, it can be seen that the non-superconducting thin film 11 is polycrystalline.

On the other hand, in the patterns of the superconducting thin film 12 and the comparative thin film 13 of FIGS. 5 (a) and 5 (b), streak is observed together with the ring, which indicates that the film has single crystallinity.

As described above, when Ar is implanted into the MgO substrate and then a thin film of Bi ₂ Sr ₂ Ca ₁ Cu ₂ Ox is grown, the thin film has a superconducting property due to the difference in the surface concentration of argon on the substrate. It can be seen that it exhibits or does not exhibit superconducting properties. It can be seen that the boundary of the argon surface density exists between 5 × 10 ¹⁶ / cm ² and 2 × 10 ¹⁷ / cm ² .

FIG. 6 shows the pattern obtained by X-ray diffraction. The vertical axis of the graph of FIG. 6 is the X-ray intensity, which is on a logarithmic scale. The horizontal axis is the angle (2θ), and the unit is “degree”. A pattern 85, a pattern 86, and a pattern 87 are patterns of the non-superconducting thin film 11, the superconducting thin film 12, and the comparative thin film 13, respectively, and show the relationship between the diffraction angle and the intensity of the diffraction line (X-ray).

6 °, 17 °, 23 °, 29
Of the Bi ₂ Sr ₂ Ca ₁ Cu ₂ Ox film at the positions of
(002), (006), (008), (00 10 ), (00 1
The peak corresponding to 2 ) can be observed.

3 (a) and 3 (b) show the relationship between the temperature and the resistivity of these thin films. The horizontal axis of the graph in FIG. 3A is the absolute temperature (K), and the vertical axis is the resistivity (Ω cm). A curve 81 represents the temperature-resistivity of the non-superconducting thin film 11. From the curve 81, it can be seen that the non-superconducting thin film 11 does not exhibit superconducting characteristics even at a temperature of 20 K or lower.

In the graph of FIG. 3B, the horizontal axis represents the absolute temperature (K) and the vertical axis represents the resistivity (mΩcm).

A curve 82 shows the relationship between the temperature and the resistivity of the superconducting thin film 12, and a curve 83 shows the relationship between the temperature and the resistivity of the comparative thin film 13. It can be seen from the curves 82 and 83 that both the superconducting thin film 12 and the comparative thin film 13 exhibit superconducting characteristics.

The above data is summarized in the table below.

[0045]

[Table 1] Next, FIG. 7 shows a Josephson device manufactured using the thin film manufactured according to the above-mentioned embodiment. Referring to FIG. 7, 5
Reference numeral 1 denotes a single crystal substrate, which is provided with an implantation region 52 on the surface of the substrate 51 and non-implantation regions 53 ₁ and 53 ₂ and a non-superconducting film grows on the implantation region 52. A superconducting thin film is grown on the non-implanted regions 53 ₁ and 53 ₂ .

The non-superconducting thin film and the superconducting thin film are subjected to resist coating, exposure / development and etching to remove unnecessary portions, and a barrier 54 made of the non-superconducting thin film.
And electrodes 55 ₁ and 55 ₂ made of a superconducting thin film, which are located on both sides of the barrier 54.

At this time, if the width of the injection region 52, that is, the width of the barrier 54 is set to 1 μm or less, a Josephson junction is formed between the barrier 54 and the electrodes 55 ₁ and 55 ₂ , so that the Josephson junction is formed. The Son element 50 can be made.

Although the Josephson device 50 is a two-terminal device, a gate electrode is provided on the barrier 54,
A three-terminal element can be manufactured by using _{one of} the electrodes 55 ₁ and 55 ₂ as a source electrode and the other as a drain electrode.

In this embodiment, Bi ₂ Sr ₂ Ca ₁ C is used.
Although a sintered body of u ₂ Ox was used as the target, the target is not limited to this, and for example, Bi ₂ Sr ₂ Ca ₂ Cu ₃ Ox, which is an oxide superconductor material, or Y ₁ B ₂ C ₃ O. _x etc,
Various superconductor materials can be used.

Further, the inert gas to be injected is not limited to the argon gas, but may react with a substance constituting the substrate such as krypton (Kr) gas, xenon (Xe) gas, or nitrogen gas (N ₂ gas) in a certain case. Various gases that do not can be used.

Further, the substrate on which the thin film is grown is not only the magnesium oxide single crystal substrate but also strontium titanate (S).
It is possible to use various substrates on which a superconducting thin film can grow, such as TO), zircon oxide, and YSZ.

Furthermore, after implanting argon ions,
The method for growing the superconducting thin film and the non-superconducting thin film on the substrate at the same time is not limited to the laser ablation method, and the vacuum deposition method, the sputtering method, the molecular beam epitaxy method, the metal organic chemical vapor deposition method. The present invention can be widely applied to a method of growing a single crystal to form a superconducting thin film, such as a method. However, at present, the laser ablation method is considered optimal because of its good film quality.

[0053]

According to the present invention, since the superconducting thin film and the non-superconducting thin film can be grown without processing the substrate three-dimensionally, the substrate surface after film formation can be kept flat. You can

When wiring is provided between the superconducting elements on the surface of the substrate, it is not necessary to consider disconnection due to a step or deterioration of reliability. Further, the wiring is formed on the superconducting thin film or the non-superconducting thin film. It is possible to easily form a thin film such as a metal thin film.

Furthermore, since the non-superconducting thin film is not manufactured by post-processing after the growth of the thin film, the reliability of the superconducting element is improved.

[Brief description of drawings]

FIG. 1 is a process chart of an embodiment of the method of the present invention.

FIG. 2 Laser ablation device

FIG. 3A is a graph showing the relationship between the temperature and the resistivity of a thin film that does not show superconducting properties. FIG. 3B is a graph showing the relationship between the temperature and the resistivity of a thin film that shows superconducting properties.

FIG. 4 is an electron beam photograph of a RHEED pattern showing a crystal structure of a non-superconducting thin film.

FIG. 5 (a) RHEE showing the crystal structure of a superconducting thin film.
Electron micrograph of D pattern (b) Electron micrograph of RHEED pattern showing crystal structure of comparative thin film

FIG. 6 is an X-ray diffraction diagram of the thin film.

FIG. 7: Example of Josephson device of the present invention

FIG. 8: X-ray diffraction diagram of the substrate

9A is a sectional view of a substrate formed by a step edge method, and FIG. 9B is a sectional view of a substrate formed by a sputtering method.

[Explanation of symbols]

3, 52 ... Injection region 4, 53 ₁ , 53 ₂ ... Non-injection region 8, 51 ... Substrate 11 ... Non-superconducting thin film 12 ... Superconducting thin film 1
3 …… Comparative thin film 42 …… Plume (cluster of raw material) 44 ……
Laser light 45 …… Target 50 …… Josephson element 54 …… Barrier 55
₁ , 55 ₂ ...... Electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01L 39/24 B

Claims (3)

[Claims] 1. A thin film manufacturing method comprising: an introducing step of introducing a material of a superconducting thin film onto a substrate; and a growing step of growing a thin film of the material introduced onto the substrate. An injection region is formed by implanting an inert gas in the region of, and a superconducting thin film of the material having superconducting properties is grown on the non-injection region where the inert gas is not implanted, and the superconducting film is formed on the injection region. A method for producing a thin film, which comprises growing a non-superconducting thin film of the above-mentioned material which does not exhibit characteristics, and simultaneously forming the superconducting thin film and the non-superconducting thin film. 2. The introducing step comprises a laser light irradiation step of irradiating a target composed of one or more substances of the material with a laser beam, and projecting a cluster having the same composition as the target from the target. The thin film manufacturing method according to claim 1, wherein the growing step includes a deposition step of depositing the clusters on the substrate to form the superconducting thin film and the non-superconducting thin film. 3. A Josephson device comprising a non-superconducting thin film as a barrier and two superconducting thin films separated from each other with the barrier interposed therebetween as an electrode, wherein the thin film manufacturing method according to claim 1 or 2. A Josephson device, characterized in that the non-superconducting thin film and the superconducting thin film formed in step 1 are used as the barrier and the electrode, respectively.