JPH02298085A - Manufacture of josephson device - Google Patents

Abstract

PURPOSE:To prevent characteristic deterioration of the superconductive film surface by providing a microslit part on a part of a double-layer film formed by piling a first metal film on a metal oxide superconductive film formed on a substrate by etching to divide the film into two electrode parts while piling a second metal film on a slit part for forming a junction part. CONSTITUTION:A metal oxide superconductive film 12 is formed on a substrate 11 and immediately thereafter a first metal film 13 is piled to form a double- layer film 15. A beam resist is applied on this double-layer film 15 followed by baking while forming a slit part into a resist film by an electron beam exposure development. Having this resist film as a mask, a slit part 17 is formed on the double-layer film 15 by an ion beam etching to divide the double-layer film 15 into two electrode parts 16. Next, a second metal film 14 is vapor- deposited allover the sample surface, thereon a negative type photoresist is applied followed by baking while irradiating ultra-violet rays on the resist to form a pattern for forming a junction part 18 by developing. Next, the second metal film 14 is etched by ion beam etching in order to form the junction part 18.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a Josephson device, which is a superconducting application technology.

BACKGROUND OF THE INVENTION Among oxide superconductors discovered in recent years, some have superconducting transition temperatures exceeding liquid nitrogen temperatures (77.3 K), greatly expanding the field of application of superconductors.

Regarding the Josephson element, which is one of its practical applications,
A break-type Josephson device in which an oxide superconductor is split in half and brought back into slight contact, and a bridge that utilizes so-called grain boundary bonding, which actively utilizes the phenomenon of grain growth that occurs during the fabrication of oxide superconducting films. 2. Description of the Related Art A proximity effect type (SNS type) Josephson element in which oxide superconductors are connected with a noble metal such as Au Ag has been prototyped in the past. In addition, Y-Ba-Cu-0 and Bi-Sr-Ca-
Tunnel-type Josephson devices have been prototyped using oxide superconductors such as Cu-0 and Ti-Ba-Ca-Cu-0 and metal superconductors such as Nb and Pb.

In a Josephson device using a metal oxide superconducting film,
The problem with the break type and grain boundary bonding type is that the reproducibility during production is extremely poor.

In addition, tunnel-type di-N-Sefson junctions require two superconductors to be brought very close together (a few nanometers or less) via an insulator, and with current technology, when using oxide high-temperature superconductors, it is difficult to manufacture them. It is difficult.

On the other hand, a proximity effect type (SNS type) Josephson junction is a phenomenon in which when a superconductor and a normal conducting metal are brought into direct contact, a pair of Coopers, which carry superconducting current, penetrate into the normal conducting metal. (proximity effect) is used. A Josephson junction is formed by weakly coupling superconductors by bringing them close to each other with a normal conducting metal in between. This proximity effect type Josephson junction allows the superconductors to be relatively spaced apart (several hundreds of nanometers or more) compared to the tunnel type Josephson junction, which requires the superconductors to be very close to each other. This has the advantage that restrictions on manufacturing accuracy are relaxed.

Problems to be Solved by the Invention However, metal oxide superconductors are susceptible to chemical damage, particularly due to reactions between the superconductor and moisture in the air and the release of oxygen, which is a constituent element of the superconductor. The superconducting properties of the superconductor surface may deteriorate or the superconductivity may be lost, and preventing these effects is an important issue. In particular, in the case of Josephson devices that utilize the proximity effect, a major problem is that if an insulator or semiconductor-like layer is formed at the interface between the superconductor and the metal, the characteristics of the device will deteriorate dramatically. In order to manufacture a Josephson device with good performance and controllability, prevention of deterioration of characteristics at the superconductor interface is an issue that must be solved.

In addition, in order to form a SNS type J-E Sefson junction,
Usually, a three-layer laminated structure of a superconducting film (gold WA) and a superconducting film has been used. In order to construct this structure using a metal oxide superconducting thin film, it is often necessary to heat the substrate during thin film fabrication, or to perform heat treatment with high salt after film deposition.

Therefore, it is currently extremely difficult to form a multilayer film containing a metal oxide superconductor due to interdiffusion between films and deterioration of already deposited films due to heat treatment. Therefore, the development of new methods for forming SNS junctions is also an important issue.

The present invention aims to solve the problems of the prior art.

Means for Solving the Problems In the method for manufacturing a Josephson device according to the first aspect of the present invention (claim 1), on a metal oxide superconducting film formed on a substrate,
By providing a minute slit in a part of the two-layer film formed by depositing the first metal film, the second
The layered film is divided into two electrode parts, and a second metal film is deposited on a part of the slit so as to electrically connect the two electrode parts to form a joint part, thereby forming a Josephson element. Manufacture. It is also effective to form a joint by etching after depositing the second metal film, or to form the second metal film at the joint by a lift-off method. When a transition metal is used as the material for the first and second metal films, gold,
It is also effective when using noble metals such as platinum and silver.

In the method for manufacturing a Josephson device according to the second aspect of the present invention (claim 4), a minute line portion is provided in a part of a metal film deposited on a substrate, and a metal oxide superconducting film is formed on the metal film. By providing a slit portion in the metal oxide superconducting film across the line portion, the metal oxide superconducting film is divided into two electrode portions, and a joint portion is formed, thereby forming a Josephson device. Manufacture. It is also effective to use a material containing a transition metal element such as platinum, palladium, nickel, or an alloy of these metals as the metal film.

As the metal oxide superconducting film, one containing a copper element is used, or one in which some of the oxygen atoms in the metal oxide superconducting film containing the copper element are replaced with sulfur atoms or fluorine atoms is used. It is also effective to use an AB-Cu-0 composite compound as the metal oxide superconducting film containing the copper element. Here, A is SC,
Y, la.

and La series elements (atomic number 57.59-60, E3
2 to 71), B is E3a, Sr
At least one of the Ha group elements such as A and B elements and the Cu element satisfy the following relationship: 0.5≦(A+B)/Cu≦2.5. Furthermore, as the metal oxide superconducting film containing the copper element, a Bi-Sr-Ca-Cu-0 compound or a compound in which a part of the Sr atoms in the Bi-3r-Ca-Cu-0 compound are replaced with Pb. , or Ti-Ba-C
a-Cu-Q compound or the above TI-Ba-Ca-C
It is also effective to use a compound in which some of the Ba atoms in the u-0 compound are substituted with Pb''r, or a Nd-Ce-Cu-0 compound.

The inventors confirmed that it is extremely important to keep the interface between the superconductor and metal clean in order to form a good bond in the Josephson device manufacturing method that uses the proximity effect. are doing.

Therefore, the first step in the manufacturing method of the present Jirosefson device is
In the present invention, immediately after forming the metal oxide superconducting film,
By using a two-layer film in which the first metal film is deposited on the metal oxide superconducting film, the interface between the metal oxide superconducting film and the metal film is not directly exposed during the manufacturing process. This makes it possible to prevent deterioration of the characteristics of the superconducting film surface.

In addition, in order to form a minute slit part in the two-layer film by etching or the like, and to form a joint part with a second metal film so as to electrically short-circuit a part of the slit l, the superconducting film is multilayered. The bond can be formed using conventional microfabrication and thin film fabrication techniques.

In addition, in the second invention, the inventors have discovered that a metal oxide superconducting film with good characteristics can be fabricated on a metal film such as platinum, palladium, or nickel, and the above-mentioned metal film is placed on a substrate. After fabrication, a minute line portion is provided in the metal film as a bonding portion, a metal oxide superconducting film is deposited thereon, and a minute slit portion is provided in the metal oxide superconducting film so as to cross the line portion. As a result, we found that a Josephson junction can be formed through the metal film underlying the metal oxide superconducting film due to the proximity effect. Also in this manufacturing method, the interface between the metal oxide superconducting film and the metal film is not exposed, and furthermore, the metal film only needs to be deposited once on the substrate, which simplifies the manufacturing process.

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

Example 1 The structure of a girosefson device manufactured by an embodiment of the method for manufacturing a girosefson device of the first invention is shown in FIG.
Its cross section is shown in FIG. Mg0 (100) front substrate 11
Metal oxide superconducting film 1 made of Y-Ba-Cu-0 on top
2 (thickness: 300 nm) was formed by RF magnetron sputtering, and immediately thereafter gold (50 nm) was deposited as the first metal film 13 by vacuum evaporation to form a two-layer film 15. On this two-layer film 15, an electron beam resist 0EBR-1000 is applied by spin coating, and after baking, electron beam exposure and development are performed to approximately 0.0. A slit portion with a width of 5 μm was formed in the resist film. Using this resist film as an etching mask, Ar ion beam etching (ion acceleration voltage 550
V, ion beam current density 570 μA/cm2,
For about 10 minutes), a slit portion 17 with a width of about 500 nm was formed in the two-layer film 15, and the two-layer film 15 was divided into two electrode portions 16. After etching, the resist film remaining on the surface was removed by ashing using oxygen plasma.

Next, a second metal film 14 of gold (5
0 nm) was vacuum evaporated, a negative photoresist 0MR87 (manufactured by Tokyo Ohka) was applied thereon by spin coating, and baked.

The resist was irradiated with ultraviolet rays by a contact exposure method using a chrome mask, and developed to form a pattern for forming the bonding portion 18 . Ar ion beam etching (acceleration voltage 560V1 ion current density 570μA/cm
The second metal film 14 was etched for 2.5 minutes to form a bonding portion 18.

In forming the metal oxide superconducting film 12, the substrate is heated to about 600°C.
A high frequency power of 150 W was applied to a mixed gas of argon and oxygen (partial pressure ratio 2:1) at a pressure of 064 Pa, and sputtering was performed for about 20 minutes. This metal oxide superconducting film showed good superconducting properties (superconducting transition temperature of approximately 90 K) without any particular heat treatment after formation, and the film surface had a surface flatness that was sufficiently suitable for microfabrication. .

This sample was cooled to below the superconducting transition temperature of the metal oxide superconducting film 12, and the voltage-current characteristics between the two electrode parts 16 were measured. As a result, a superconducting current was confirmed, and nonlinear characteristics peculiar to the proximity effect type Josephson junction were observed. It was confirmed that In addition, microwaves with a frequency around 20 GHz are applied to the joint 18.
When irradiated with irradiation, a voltage jump (Shapiro step) due to the Josephson effect was observed on the current-voltage characteristic curve, clearly confirming the formation of a Josephson junction.

In the embodiment described above, in order to form the joint part 18, a method was used in which the second metal film 14, which had been deposited in advance on the entire surface of the two-layer film 15, was patterned by Ar ion beam etching. For this, slit part 1
Since it is sufficient to connect 7 with a metal film having a minute width, it is also possible to form a bond by a normal lift-off method. In fact, after forming the slit portion 17 in the two-layer film 15, the present inventors spin-coded a positive photoresist MP1400-17 (manufactured by Sibley Co., Ltd.) suitable for lift-off, and used a photophosphorography technique. , a pattern from which only the joint 18 is removed is formed on the resist, and metal tantalum (approximately 50 nm) is sputter-deposited on it, and tantalum is immersed in acetone to remove unnecessary portions of tantalum by lift-off.
was formed. In this example, the metal tantalum, which is easy to lift off, was used, but if the shape of the side surface of the resist film is good, it is also possible to use other metal films such as gold, and a metal that is difficult to etch may be used as the first material. It has been confirmed that it can also be used as the metal film 14 of No. 2. In addition,
When the first metal film 13 was formed continuously in the same vacuum after the formation of the metal oxide superconducting film 12, an element with even better characteristics was obtained.

In addition to gold and tantalum, it is also effective to use transition metals as materials for the first and second metal films.

When noble metals such as gold, platinum, and silver are used as the transition metal, the surface of the two-layer film becomes particularly chemically stable and there is no interaction with the metal oxide superconducting film, making it extremely effective. I've confirmed it.

Example 2 FIG. 3 shows the structure of a Josephson device manufactured by an example of the method for manufacturing a Josephson device according to the second invention. Platinum (50 nm) was formed as a metal film 32 on an Mg0 (100) plane substrate 31 by DC magnetron sputtering. On this metal film 32 made of platinum, a positive photoresist microposit 1400-17 is placed.
(manufactured by Shipley), and the resist was developed by irradiating ultraviolet rays through contact exposure using a chrome mask. Using this patterned resist film as a mask, the metal film 3 is etched by Ar ion beam etching.
After forming a minute line portion 35 as shown in FIG. 3 on 2, the resist film was peeled off using acetone. A metal oxide superconducting film 33 was formed on the metal film 32 by RF magnetron sputtering. This metal oxide superconducting film 33 (approximately 300 nm) was manufactured under the same conditions as in the previous example. Further, on the metal oxide superconducting film 33, a positive resist for electron beam 0EBR-too is applied.
oc (manufactured by Tokyo Ohka) was applied, and a slit-like pattern with a width of about 0.5 μm was formed by electron beam lithography. Using the resist film as an etching mask, only the metal oxide superconducting film layer 33 is etched by reactive ion etching using chlorine gas to form a slit portion 36 as shown in FIG. The physical superconducting film 33 was divided into two electrode portions 34 to form a joint. After removing the resist film remaining on the metal oxide superconducting film 33 using an oxygen plasma asher, a gold electrode was provided by vacuum evaporation, and the electrical characteristics of the bond were observed. As a result, it was confirmed that the Josephson element manufactured by this manufacturing method also exhibited the same characteristics as the Josephson element manufactured by the method of Example 1 above.

In this example, reactive ion etching was used to form the slit portion 3S, but the method is not limited to this, and Ar ion beam etching, which is said to cause less damage to metal oxide superconductors, may be used. It is also possible to use However, unlike reactive ion etching, Ar ion beam etching is characterized in that the difference in etching rate depending on the type of material is small. Therefore, in order to etch the metal oxide superconducting film 33, the underlying metal film 32 is also etched to some extent. Therefore, when using Ar ion beam etching, the thickness of the metal film 32 is set to 1100 nm or more, so that the gold ryt film 32 is completely etched when the metal oxide superconducting film 33 is etched. It has been confirmed that the line portion 35 can be prevented from being cut.

In addition, although platinum is used as the metal film 32, materials containing transition metal elements such as palladium and nickel or metal alloys thereof may also be used as metal oxides that exhibit good properties. It has been confirmed that a superconducting film 33 can be formed and that a Josephson device having similar characteristics can be formed.

In Examples 1 and 2, a Y-Ba-Cu-0 thin film was used as the metal oxide superconducting film, but it is not limited to this type of superconductor, and metal oxides containing a copper element may also be used. When using a superconducting film or a metal oxide superconducting film in which some of the oxygen atoms in the metal oxide superconducting film containing the above-mentioned copper element are replaced with sulfur atoms or fluorine atoms, a di-1-Sefson junction with similar characteristics can be achieved. It has been confirmed that it can be produced. In this way, it has been confirmed that a relatively stable superconducting film can be obtained by replacing oxygen atoms in a metal oxide superconducting film with sulfur atoms or fluorine atoms. As the metal oxide superconducting film containing the above copper element, A-B
It has been confirmed that a method using a -Cu-◯ composite compound is also effective. Here, A is Sex Y, La
, and La series elements (atomic number 57.59-60
．． 62 to 71), B is at least one of group IIa elements such as Ba and Sr, and the concentrations of the A and B elements and the Cu element are 0, 5≦(A+B)/Cu≦
It is 2.5. Furthermore, as the metal oxide superconducting film containing the copper element, a Bi-Sr-Ca-Cu-0 compound or a compound in which a part of Sr atoms in the Bi-Sr-Ca-Cu-0 compound is replaced with Pb. , or Ti-Ba-C
a-Cu-Q compound or the above Ti-Ba-Ca-Cu
It has been confirmed that the use of a compound in which some of the Ba atoms in the -0 compound are substituted with Pb is also effective. Furthermore, even if a Nd-Ce-Cu-0 compound, which is a metal oxide superconductor characterized by the fact that carriers in a normal conductive state are electrons, is used as a metal oxide superconducting film, the Josephson film has similar characteristics. It has been confirmed that the device can be obtained.

In addition, although Ar ion beam etching and reactive ion etching have been described in the examples as etching methods for forming slit portions in metal oxide superconducting films, they are not limited to these methods; There is no particular problem as long as it can be etched, and techniques such as reactive ion beam etching and focused ion beam etching are also applicable. In particular, focused ion beam etching is a maskless process, which simplifies the device manufacturing process and improves manufacturing accuracy.

Effects of the Invention As described above, according to the present invention, the interface between the metal oxide superconducting film and the metal film is not directly exposed to the surface during the device fabrication process. Josephson devices can be fabricated with extremely good reproducibility and controllability without degrading the interface characteristics during the device fabrication process.

Further, in the method for manufacturing a Josephson device of the present invention, there is no need to form a multilayer film of superconductors, which is often required when forming a conventional proximity effect type junction. Therefore, there is no deterioration of previously formed superconducting films or metal films due to heat treatment associated with superconducting film fabrication, and Josephson junctions can be formed with sufficient controllability at the current technological level.

By using a Josephson device manufactured based on the manufacturing method of the present invention, a superconducting quantum interferometer or the like that operates at a temperature higher than liquid nitrogen temperature can be constructed. It is also expected to be applied to high-speed photodetectors and microwave mixers.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a Josephson device manufactured based on an embodiment of the method for manufacturing a Josephson device of the first invention, FIG. 2 is a cross-sectional view of the Josephson device, and FIG. FIG. 3 is a perspective view of a Josephson device manufactured based on another embodiment of the Josephson device manufacturing method of the present invention. 11.31...One substrate, 12.33I...Metal oxide superconducting film, 13 tatami Φ-first total 1! ! iM, 14 battles, urn second metal film, 15 fists, 112 layer film, 16.34...fist π
Pole portion, 32.II metal film, 18...junction, 17.
3Bφφ slit part, 35φ pot line part. Name of agent: Patent attorney Shigetaka Awano, 1 person/JWL Envy Section 12 Figure 1 δ Seikan Department

Claims (1)

[Claims] (1) A minute slit portion is provided by etching in a portion of a two-layer film formed by depositing a first metal film on a metal oxide superconducting film formed on a substrate. The two-layer film is divided into two electrode parts, and a second metal film is deposited on a part of the slit part so as to electrically connect the two electrode parts, thereby forming a joint part. 1. A method for manufacturing a Josephson element, characterized by forming a Josephson element. (2) The method for manufacturing a Josephson device according to claim 1, wherein a transition metal is used as a material for the first and second metal films. (3) The method for manufacturing a Josephson element according to claim 2, wherein a noble metal such as gold, platinum, or silver is used as the transition metal. (4) A minute line portion is provided in a portion of the metal film deposited on the substrate, a metal oxide superconducting film is formed on the metal film, and the metal oxide superconducting film is etched across the line portion. The method is characterized in that the metal oxide superconducting film is divided into two electrode parts and a joint part is formed by providing a minute slit part and leaving a part of the metal film in the line part. A method for manufacturing a Josephson element. (5) The method for manufacturing a Josephson element according to claim 4, wherein the metal film is made of a material containing a transition metal element such as platinum, palladium, or nickel, or an alloy of these metals. (6) The method for manufacturing a Josephson device according to claim 1 or 4, wherein the metal oxide superconducting film contains a copper element. (7) The method for manufacturing a Josephson device according to claim 6, characterized in that part of the oxygen atoms in the metal oxide superconducting film are replaced with sulfur atoms or fluorine atoms. (8) A-B-Cu-O composite compound is used as the metal oxide superconducting film (here, A is Sc, Y, La, and La series elements (atomic numbers 57, 59-60, 62-71
), B is at least one of Group IIa elements such as Ba and Sr, and the concentration of A, B elements and Cu element is 0.5≦(A+B)/Cu≦2.5). 7. The method for manufacturing a Josephson device according to claim 6. (9) As a metal oxide superconducting film, Bi-Sr-Ca-
Cu-O compound or the Bi-Sr-Ca-Cu-
A compound in which some of the Sr atoms in the O compound are replaced with Pb, or a Ti-Ba-Ca-Cu-O compound, or a part of the Ba atoms in the Ti-Ba-Ca-Cu-O compound is replaced with Pb. or a compound substituted with Nd-Ce
9. The method for manufacturing a Josephson device according to claim 8, wherein a -Cu-O compound is used.