JPH05343754A - Superconductive device and manufacture thereof - Google Patents

Abstract

PURPOSE:To firmly connect a metallic conductive layer to become connecting wiring, etc., with a passive element and a normally conductive circuit with an oxide superconductor besides having made it exhibit the property of the oxide superconductor in an active element, a wiring section, or the like. CONSTITUTION:This is an oxide superconductive layer 2, which is equipped with a stoichiometrically properly composition ratio and a metallic conductive layer 5 connected to this oxide superconductor layer 2. The deposits of metallic elements exist in the vicinity 6 of the connection face with the oxide superconductor layer 2 of the oxide superconductor layer 2. The metallic deposits are made by depositing the metallic elements after selectively introducing metallic elements into one part of the oxide superconductor layer 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting device using an oxide superconductor and a method for manufacturing the same.

[0002]

2. Description of the Related Art In order to apply a superconductor to the field of electronics, it is necessary that an active element can be constituted by the superconductor and appropriate wiring can be provided for signal transmission. It is desirable that the wiring be made of a superconductor in order to take advantage of the features such as high speed and low power consumption of the superconducting element. On the other hand, in constructing a circuit, it is important to incorporate an appropriate passive element such as a resistance element. For example, a superconducting quantum interferometer (SQUID) is an electronic device that includes one or two Josephson junctions in a closed loop formed by a superconducting line. When a SIS type junction is used as a Josephson junction. In order to eliminate the hysteresis characteristic of the Josephson junction, a resistance element (shunt resistor) made of a metal conductor having a finite resistance value is installed in parallel with the junction.

Oxide superconductors have attracted attention as a material exhibiting superconductivity at high temperatures as compared with conventionally used metallic superconductors such as Pb and Nb, and are expected to be applied to electronic devices. As an oxide superconductor,
For example, a compound having a composition such as YBa ₂ Cu ₃ O _7-x is known, and is generally a compound composed of multiple elements. Such an oxide superconductor does not exhibit superconductivity unless its composition is appropriately controlled and it has a predetermined crystal structure. Therefore, when manufacturing a superconducting element using an oxide superconductor, it is important to secure the composition ratio of the constituent elements and realize a predetermined crystal structure.

In order to form a Josephson junction using such an oxide superconductor and to install the above shunt resistor in parallel with the junction, connection portions (contact holes) are provided at both ends of the junction, It is necessary to connect the oxide superconductor and the metal conductor through this contact hole. Specifically, an appropriate insulating layer is formed on the oxide superconductor pattern, contact holes are provided at the portions corresponding to both ends of the junction of the insulating layer, and metal conduction is performed through the contact holes by a vacuum deposition method or the like. By depositing a body thin film, the oxide superconductor and the metal conductor are connected. As the metal conductor forming the resistance element or the like, a noble metal or a refractory metal is generally used so as not to react with the oxide superconductor to impair the superconductivity of the oxide superconductor.

However, when the oxide superconductor and the metal conductor are connected by the method as described above, the oxide superconductor and the metal conductor thin film are not firmly connected to each other at the connection portion, and peeling occurs. However, there is a problem in that electrical characteristics such as contact resistance and maximum current value that can flow are not constant.

[0006]

As described above, in producing an electronic device using an oxide superconductor, it is necessary to electrically connect the oxide superconductor pattern and the metal conductor. However, by simply depositing a metal conductor thin film on an oxide superconductor as in the conventional method, the oxide superconductor and the metal conductor thin film are often not firmly connected at the connection portion, and There was a problem that the electrical characteristics of that part were not constant. On the other hand, in order to fully exhibit the characteristics of the oxide superconductor, it is important to optimize its composition ratio and crystal structure.

The present invention has been made in order to solve such a problem, and makes full use of the characteristics of an oxide superconductor which becomes an active element, a wiring portion, etc., and then a passive element and a normal conduction circuit. It is an object of the present invention to provide a superconducting device capable of firmly connecting an oxide superconductor to a metal conductive layer which will be a connection wiring or the like, and a manufacturing method thereof.

[0008]

A superconducting device of the present invention comprises an oxide superconductor layer having a stoichiometrically proper composition ratio, and a metal conductive layer connected to the oxide superconductor layer. In the superconducting device described above, a deposit of a metal element is present in the vicinity of a connection surface of the oxide superconductor layer with the metal conductive layer.

Further, the method for manufacturing a superconducting device of the present invention comprises a step of selectively introducing a metal element into a part of the oxide superconductor layer having a stoichiometrically proper composition ratio, and the oxide. In the portion where the metal element of the superconductor layer is introduced,
It has a step of forming a deposit of the metal element, and a step of depositing a metal conductive layer on at least a portion of the oxide superconductor layer where the deposit of the metal element is formed. ..

[0010]

In the superconducting device of the present invention, since the precipitate of the metal element is present in the vicinity of the connection surface of the oxide superconductor layer with the metal conductive layer, the oxide of the metal element precipitates through the precipitate of the metal element. It is possible to firmly connect the superconductor layer and the metal conductive layer. Further, this strong connection makes it possible to obtain a connection exhibiting electrically stable characteristics. And since the precipitate of the metal element is formed only near the connection surface with the metal conductive layer, the stoichiometric amount of the active element of the oxide superconductor layer, the wiring, etc. Theoretically appropriate composition ratio is maintained, and good superconducting characteristics can be obtained.

[0011]

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

FIG. 1 is a cross-sectional view showing a main structure of a superconducting device according to an embodiment of the present invention. In the figure,
Reference numeral 1 is an insulator substrate made of SrTiO ₃ single crystal or the like. On this insulator substrate 1, an oxide superconductor layer 2 patterned into a desired shape, such as a YBa ₂ Cu ₃ O _7-x film (hereinafter , Y-Ba-Cu-O film) is formed. The oxide superconductor layer 2 is covered with an insulating film 3 made of SiO or the like, and the insulating film 3 is provided with an opening 4 serving as a contact hole. On the insulating film 3, a metal conductive layer 5 connected to the oxide superconductor layer 2 through the opening 4 is formed. The metal conductive layer 5 serves as, for example, a shunt resistor or a connection wiring with a normal conduction circuit.
It consists of precious metals such as u and Ag and refractory metals such as Mo and W.

Then, in a portion corresponding to the inside of the opening 4 of the oxide superconductor layer 2, that is, in the vicinity 6 of the connection surface with the metal conductive layer 5, as shown in FIG. Exists. The metal precipitate 7 plays a role of strengthening the connection with the metal conductive layer 5. In other words, the oxide superconductor layer 2 and the metal conductive layer 5 are the metal precipitates 7 described above.
Is firmly connected via. Also, this strong connection provides a connection exhibiting electrically stable characteristics.
As the metal element forming the metal precipitate 7, the constituent metal element of the oxide superconductor used, for example, copper, yttrium, barium, gold, silver, white when a Y-Ba-Cu-O film is used. Noble metal elements such as metal group elements are used, and these can be used as a mixture of two or more kinds.

By the way, it is important that the portion 8 of the oxide superconductor layer 2 other than the vicinity 6 of the connecting surface is substantially free of metal precipitates and has a stoichiometrically proper composition ratio. .. That is, the metal deposit as described above can also be formed by preliminarily containing any of the metal elements forming the oxide superconductor layer 2 in excess of the stoichiometric appropriateness value. However, in the method described above, metal deposits are present in the entire oxide superconductor layer 2. In such an oxide superconductor containing a large amount of metal precipitates, the critical current that can be flowed is reduced, etc.
There are problems that the superconducting characteristics are deteriorated and the electric characteristics of the device become unstable due to the trapping of magnetic flux, as compared with the case where the composition ratio is stoichiometrically appropriate. Further, when a Josephson junction device or the like is manufactured by using an oxide superconductor containing such a metal precipitate as a whole, there is a problem that the leak current is large and the function of the device cannot be sufficiently exhibited.

From the above, in the above-described embodiment, the metal precipitate 7 is allowed to exist only in the vicinity 6 of the connection surface with the metal conductive layer 5, and the other portion 8 has a stoichiometrically suitable composition. By providing the ratio, the superconducting characteristics of the oxide superconductor 8 which actually functions as an active element, wiring, etc. are secured.

As described above, as a method of forming the metal precipitate 7 only in the vicinity 6 of the connecting surface of the oxide superconductor layer 2 to the metal-group conductive layer 5, the following method can be mentioned. Be done. FIG. 3 is a sectional view showing an essential part of a manufacturing process of a superconducting device according to an embodiment of the present invention. A method of manufacturing the superconducting device of this embodiment will be described with reference to FIG. In this example, a case where a gold thin film shunt resistor that connects between patterned Y-Ba-Cu-O 2 films is manufactured as a metal conductive layer will be described.

First, in an atmosphere containing an appropriate amount of oxygen, 6
On the SrTiO ₃ single crystal substrate 1 heated to 00 ° C to 800 ° C,
Y-Ba-Cu-O film with a thickness of 300 nm using the sputtering method 2
And then patterning the Y-Ba-Cu-O film 2 using a known photolithography technique.
Separated Y-Ba-Cu-O film patterns 2a and 2b were formed (FIG. 1-a).

Next, the above Y-Ba-Cu-O film patterns 2a, 2
By depositing the SiO insulating film 3 on the entire surface of the SrTiO ₃ single crystal substrate 1 having b by a vacuum deposition method or the like, and selectively etching the insulating film 3 using a photolithography technique, Y-Ba-Cu -O film patterns 2a and 2b are formed with openings 4a and 4b, respectively, and Y-Ba-Cu-O of the portions is formed.
Membrane 2 was exposed. After that, apply the ion implantation method,
Ion implantation of about 1 × 10 ²² / cm ² of copper was carried out at an acceleration voltage of 200 keV (FIG. 1-b).

In this state, only the surface of the Y-Ba-Cu-O film 2 exposed by the openings 4a and 4b was irradiated with an energy beam such as a laser beam for a short time (FIG. 1-c).
By this laser beam irradiation, Y-Ba-Cu-O of the irradiated part
The surface of the film 2 is once melted and then re-solidified, but in the process of re-solidification, the ion-implanted copper is deposited and Y-Ba-Cu-O
The vicinity of the connection surface including the surface of the film 2 was formed to contain fine copper deposits. At this time, the energy beam to be irradiated can be adjusted in focus so that energy can be applied only to the surface portion of the Y-Ba-Cu-O film, so that it does not affect other portions. It was possible to melt and re-solidify only a necessary portion, that is, the vicinity of the surface, to deposit copper.

After that, a 100 nm-thickness is formed on the entire surface by a vacuum deposition method or the like.
By depositing a gold thin film 5 of a certain degree and patterning the gold thin film 5 using a photolithography technique, Y-Ba-
A resistance element connecting the Cu-O film patterns 2a and 2b was formed (FIG. 1-d).

According to the method for manufacturing a superconducting device described above, the energy beam is applied only to the surface of the Y-Ba-Cu-O film 2 exposed by the openings 4a and 4b serving as the connection surface with the gold thin film 5. In addition, since the injected copper is finely precipitated by melting and re-solidifying only in the vicinity of the surface, it does not affect the part that actually functions as an active element such as Josephson junction, and the vicinity of the connecting surface Only copper deposits could be formed. The copper deposits firmly connect the Y-Ba-Cu-O film 2 and the gold thin film 5 through the copper deposits, and a connection showing electrically stable characteristics can be obtained. did it. In addition, in the step shown in FIG. 1D, in order to secure the electrical coupling between the Y-Ba-Cu-O film 2 and the gold thin film 5, an opening is formed before forming the gold thin film 5. It is desirable to clean the surface of the Y-Ba-Cu-O film 2 exposed by the portions 4a and 4a by argon sputtering or the like.

By the way, in the manufacturing process of the above-described embodiment, the Y-Ba-Cu-O film 2 exposed by the openings 4a and 4b.
After copper is ion-implanted into the surface portion of, the portion is melted and re-solidified by irradiating with an energy beam for a short time. In such a method, in order to melt and re-solidify only a necessary portion of the Y-Ba-Cu-O film 2 without affecting other portions of the Y-Ba-Cu-O film 2 when the energy beam is irradiated, the Focus is adjusted so that energy can be applied only to the surface portion of the -O film 2, and only the portion of the Y-Ba-Cu-O film 2 exposed by the openings 4a and 4b is irradiated with the light. It is necessary to aim and irradiate the apertures 4a and 4b.

Next, a method of manufacturing a superconducting device in which the complexity associated with the irradiation of the energy beam is alleviated will be described with reference to FIG. FIG. 4 is a diagram showing a manufacturing process of a superconducting device according to another embodiment of the present invention.

First, Y-Ba-Cu-O film patterns 2a and 2b which are separated from each other are formed on the SrTiO ₃ single crystal substrate 1 in the same manner as in the above-mentioned embodiment, and thereafter, the S-TiO ₃ single crystal substrate 1 is subjected to S vapor deposition or the like.
The iO insulating film 3 was deposited on the entire surface (FIG. 4-a).

Next, using photolithography technology,
A photoresist film pattern 12 having an upper surface covered with a metal film 11 such as a thin film of aluminum or silver was formed. Next, using the photoresist film pattern 12 as a mask, the insulating film 3 is etched to form the openings 4a and 4b, and the Y-Ba-Cu-O film 2 in each of the openings is exposed (see FIG. 4). -B). The photoresist film 12 whose upper surface is covered with the metal film 11 can be formed, for example, as follows.

That is, a positive type photoresist is used as the photoresist film 12, the photoresist film 12 is applied on the entire surface, and then the metal film 1 is formed thereon by a vacuum deposition method or the like.
Put on 1. Next, a photoresist (not shown) is applied again thereon, exposed and developed to pattern the upper photoresist. At this time, since the lower photoresist film 12 is covered with the metal film 11, it is not affected by exposure and development. Next, the metal film 11 is patterned using the upper photoresist pattern as a mask. In this state, the photoresist film 1 is exposed again and developed using the metal film 11 as a mask.
2 is patterned. If the photoresist on the upper side is a positive type, it is removed at the same time during this exposure and development, and the state shown in FIG. 4B is obtained.

In this state, using the ion implantation method, 1 × 10
^After ion-implanting about ²² / cm ² of copper at an acceleration voltage of 200 keV (FIG. 4-c), an energy beam, for example, a laser beam is irradiated for a short time (FIG. 4-d) to open the hole 4a,
The surface portion of the Y-Ba-Cu-O film 2 exposed by 4b was melted and solidified again. By this ion implantation and energy beam irradiation, the surface of the Y-Ba-Cu-O film 2 was formed containing fine copper precipitates. Here, the laser beam is reflected by the metal film 11 in the portion where the metal film 11 exists, and the portion of the Y-Ba-Cu-O film 2 located therebelow is not affected by the laser beam. The entire surface can be irradiated with a laser beam.

Then, the photoresist film 12 is removed by washing with ascent or the like, and at the same time, the metal film 1 on the photoresist film 12 is removed.
By removing 1 as well, the openings 4a, 4
Y-Ba-Cu-O film patterns 2a and 2b containing fine copper precipitates were obtained only in the vicinity of the surface exposed by b.
After that, by forming and patterning the gold thin film 5 in the same manner as in the above-described embodiment, the superconducting device in which the Y-Ba-Cu-O film patterns 2a and 2b are connected by the resistance element made of the gold thin film 5. Was produced (FIG. 1-d).

Also in the superconducting device thus obtained, the Y-Ba-Cu-O film 2 and the gold thin film 5 were firmly connected, as in the above-mentioned embodiment. Further, in the manufacturing method as described above, laser beam irradiation is performed in a self-aligned manner on the portion of the Y-Ba-Cu-O film 2 into which the copper ions have been implanted,
Since the portion of the Y-Ba-Cu-O film 2 that does not require beam irradiation is covered with the metal film 11, the respective openings 4 are
It is possible to avoid the complexity of irradiating with aiming at a and b. In addition, the need for narrowing down the diameter of the laser beam to be irradiated is reduced, and the process margin is increased, so that the entire surface of the substrate can be processed by collective beam irradiation.

In the above embodiment, the metal film 1
If 1 is removed by the subsequent dissolution treatment without affecting the Y-Ba-Cu-O film 2 or the like, the formation of the photoresist film 12 therebelow can be omitted. However, it is generally known that oxide superconductors have poor resistance to acids and alkalis and are easily corroded. Therefore, it is desirable to adopt the structure described above.

Further, in the manufacturing method of each of the above-mentioned embodiments, the laser beam is used as the energy beam for melting and re-solidifying the surface of the oxide superconductor, but other energy beams such as infrared rays, electron beams, X-rays or the like may be used. The method using energy beam irradiation as a means for forming metal deposits is superior to other methods such as high-temperature treatment using a heating furnace in that the influence of the treatment does not reach unnecessary portions.

In each of the above embodiments, an example using a Y-Ba-Cu-O film as an oxide superconductor has been described, but the present invention is not limited to this, and Bi-Sr- C
The same can be applied to a-Cu-O system and other oxide superconductors. Further, in such a case, each constituent metal element or noble metal element can be used as an element to be ion-implanted to form a metal precipitate. Further, the present invention is applied to a connection between a metal film pattern having an element function such as a resistance element as described above and an oxide superconductor pattern, and also on a oxide superconductor pattern for a protective film or other purposes. The present invention can also be applied to a portion that needs to be covered with a metal film, for example, the production of a bonding pad.

[0033]

As described above, according to the present invention, in producing a superconducting device using an oxide superconductor, an oxide having a stoichiometrically appropriate composition ratio and exhibiting excellent superconducting properties. It is possible to form active elements, wirings, etc. with a solid superconductor, and to firmly connect the oxide superconductor layer and the metal conductive layer, and obtain a connection showing electrically stable characteristics. .. Therefore, it is possible to provide a superconducting device having excellent characteristics in both the connecting portion and the substantial oxide superconducting layer.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a main part of a superconducting device according to an embodiment of the present invention.

2 is an enlarged view showing a connection between an oxide superconductor layer and a metal conductive layer in the superconducting device shown in FIG.

FIG. 3 is a cross-sectional view showing a manufacturing process of a superconducting device according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a manufacturing process of a superconducting device according to another embodiment of the present invention.

[Explanation of symbols]

 1 ... Insulator substrate 2 ... Oxide superconductor layer 3 ... Insulation film 4 ... Opening part to be a contact hole 5 ... Metal conductive layer 6 ... Connection of oxide superconductor layer to metal conductive layer Near surface 7 ... Precipitates of metallic elements

Claims (2)

[Claims] 1. A superconducting device comprising: an oxide superconductor layer having a stoichiometrically proper composition ratio; and a metal conductive layer connected to the oxide superconductor layer. 2. A superconducting device, characterized in that precipitates of a metal element are present in the vicinity of the connection surface with the metal conductive layer. 2. A step of selectively introducing a metal element into a part of the oxide superconductor layer having a stoichiometrically proper composition ratio, and the step of introducing the metal element in the oxide superconductor layer. A step of forming a deposit of the metal element on a portion where the metal element is deposited, and a step of depositing a metal conductive layer on at least a portion of the oxide superconductor layer where the deposit of the metal element is formed. And a method for manufacturing a superconducting device.