Josephson junction element and method for manufacturing a Josephson junction element

Abstract

In a Josephson junction device, the aim is to suppress variations in the junction area within the substrate while avoiding the inclusion of impurities at the junction between the superconducting film and the insulating film. [Solution] A first wiring made of superconductor and a first electrode made of superconductor connected to the first wiring are formed on a substrate. A resist mask is formed to cover at least the first wiring. The surface of the first electrode is etched using the resist mask. An insulating film is formed on the surface of the first electrode using the resist mask. A second electrode made of superconductor is formed on the surface of the insulating film using the resist mask.

Description

Technical Field

[0001] The disclosed technology relates to Josephson junction devices and methods for manufacturing the same.

Background Art

[0002] As technologies related to methods for manufacturing Josephson junction devices, the following technologies are known. For example, Patent Document 1 describes a manufacturing method including forming a lower superconducting layer and an insulating layer on a substrate in this order, forming an edge structure having an inclination on the surface of the insulating layer, and forming a superconducting thin film via a barrier layer on the inclined surface of the insulating layer.

[0003] Patent Document 2 describes a manufacturing method including attaching a first superconducting layer to the surface of a substrate, attaching a dielectric layer to the first superconducting layer, forming an inclined edge inclined with respect to the surface of the substrate in the first superconducting layer and the dielectric layer, attaching a second superconducting layer on the inclined edge, attaching a barrier layer on the second superconducting layer, and attaching a third superconducting layer on the barrier layer.

[0004] Patent Document 3 describes a manufacturing method including a step of forming a first YBCO superconducting thin film and an insulating layer thin film on an oxide single crystal substrate, a step of forming a first photoresist pattern on the insulating layer thin film, and a step of removing the exposed insulating layer thin film and the first superconducting thin film in an inclined shape by etching, a step of forming a non-superconducting cubic YBCO barrier thin film, a second YBCO superconducting thin film, and a protective layer thin film on the entire surface of the substrate, a step of forming a second photoresist pattern that exposes the opposite side of the portion etched in an inclined shape on the protective layer thin film, and a step of etching the protective layer thin film, the second YBCO superconducting thin film continuously exposed in an inclined shape, and the non-superconducting cubic YBCO barrier thin film.

[0005] Patent Document 4 describes that after applying a photoresist material to a target region, an edge at a required angle is formed using photolithography and ion milling.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-173246 [Patent Document 2] Japanese Patent Application Publication No. 11-31853 [Patent Document 3] U.S. Patent No. 6004907 [Patent Document 4] U.S. Patent No. 6476413 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In superconducting circuits, qubits are comprised of Josephson junctions. A Josephson junction has a structure in which an insulating film, which functions as a barrier layer, is sandwiched between two superconducting films. The so-called oblique deposition method is known as a method for manufacturing Josephson junctions. The oblique deposition method is a method in which deposition is performed multiple times using a single resist mask while changing the orientation of the substrate relative to the deposition source. The insulating film, which functions as a barrier layer, is formed by oxidizing the surface of the superconducting film formed by the first deposition in the deposition apparatus.

[0008] The oblique deposition method allows for the formation of superconductor / insulator / superconductor films in a continuous vacuum process within a common vacuum chamber. Furthermore, the patterning of the three-layer structure consisting of superconductor / insulator / superconductor films can be performed using a single resist mask. Therefore, the oblique deposition method avoids exposure of the three-layer structure to the atmosphere and prevents impurities resulting from resist patterning from entering the interface between the superconductor and insulator films.

[0009] On the other hand, with oblique deposition, the inclination angle of the path from the deposition source to each position on the substrate changes depending on the position on the substrate. As a result, the area of ​​the overlapping region (junction area) of the three layers—superconductor film / insulator film / superconductor film—changes depending on the position on the substrate. Consequently, the properties of the qubit composed of the three-layer structure may become non-uniform within the substrate surface.

[0010] The disclosed technology was developed in view of the above-mentioned points, and aims to suppress variations in the junction area within the substrate surface while avoiding the inclusion of impurities in the junction between the superconducting film and the insulating film in a Josephson junction device. [Means for solving the problem]

[0011] A method for manufacturing a Josephson junction element according to the disclosed technology includes forming a first wiring made of a superconductor and a first electrode made of a superconductor connected to the first wiring on a substrate, forming a resist mask that covers at least the first wiring, etching the surface of the first electrode using the resist mask, forming an insulating film on the surface of the first electrode using the resist mask, and forming a second electrode made of a superconductor on the surface of the insulating film using the resist mask. [Effects of the Invention]

[0012] In Josephson junction devices, it becomes possible to suppress variations in the junction area within the substrate while avoiding the inclusion of impurities at the junction between the superconducting film and the insulating film. [Brief explanation of the drawing]

[0013] [Figure 1] This is a plan view showing an example of the configuration of a Josephson junction element according to an embodiment of the disclosed technology. [Figure 2] This is a cross-sectional view along line 2-2 in Figure 1. [Figure 3A] This is a plan view showing an example of a method for manufacturing a Josephson junction element according to an embodiment of the disclosed technology. [Figure 3B]It is a plan view showing an example of a method for manufacturing a Josephson junction device according to an embodiment of the disclosed technology. [Figure 3C] It is a plan view showing an example of a method for manufacturing a Josephson junction device according to an embodiment of the disclosed technology. [Figure 3D] It is a plan view showing an example of a method for manufacturing a Josephson junction device according to an embodiment of the disclosed technology. [Figure 3E] It is a plan view showing an example of a method for manufacturing a Josephson junction device according to an embodiment of the disclosed technology. [Figure 3F] It is a plan view showing an example of a method for manufacturing a Josephson junction device according to an embodiment of the disclosed technology. [Figure 3G] It is a plan view showing an example of a method for manufacturing a Josephson junction device according to an embodiment of the disclosed technology. [Figure 4A] It is a cross-sectional view taken along line 4A-4A in FIG. 3A. [Figure 4B] It is a cross-sectional view taken along line 4B-4B in FIG. 3B. [Figure 4C] It is a cross-sectional view taken along line 4C-4C in FIG. 3C. [Figure 4D] It is a cross-sectional view taken along line 4D-4D in FIG. 3D. [Figure 4E] It is a cross-sectional view taken along line 4E-4E in FIG. 3E. [Figure 4F] It is a cross-sectional view taken along line 4F-4F in FIG. 3F. [Figure 4G] It is a cross-sectional view taken along line 4G-4G in FIG. 3G. [Figure 5A] It is a cross-sectional view showing an example of a method for manufacturing a Josephson junction device using an oblique evaporation method. [Figure 5B] It is a cross-sectional view showing an example of a method for manufacturing a Josephson junction device using an oblique evaporation method. [Figure 6A] It is a perspective view showing an example of a method for manufacturing a Josephson junction device using an oblique evaporation method. [Figure 6B] It is a cross-sectional view showing an example of a method for manufacturing a Josephson junction device using an oblique evaporation method. [Figure 6C] This is a cross-sectional view showing an example of a method for manufacturing a Josephson junction element using oblique deposition. [Figure 7] This is a cross-sectional view showing an example of the configuration of a Josephson junction element according to another embodiment of the disclosed technology. [Figure 8A] This is a cross-sectional view showing an example of a method for manufacturing a Josephson junction element according to another embodiment of the disclosed technology. [Figure 8B] This is a cross-sectional view showing an example of a method for manufacturing a Josephson junction element according to another embodiment of the disclosed technology. [Figure 8C] This is a cross-sectional view showing an example of a method for manufacturing a Josephson junction element according to another embodiment of the disclosed technology. [Figure 8D] This is a cross-sectional view showing an example of a method for manufacturing a Josephson junction element according to another embodiment of the disclosed technology. [Figure 9] This is a cross-sectional view showing an example of a method for manufacturing a Josephson junction element according to another embodiment of the disclosed technology. [Modes for carrying out the invention]

[0014] Hereinafter, an example of an embodiment of the disclosed technology will be described with reference to the drawings. In each drawing, identical or equivalent components and parts will be given the same reference numerals, and redundant descriptions will be omitted.

[0015] [First Embodiment] Figure 1 is a plan view showing an example of the configuration of a Josephson junction element 10 according to an embodiment of the disclosed technology. Figure 2 is a cross-sectional view along line 2-2 in Figure 1. The Josephson junction element 10 includes a substrate 11, a first wiring 12, a first electrode 13, an insulating film 14, a second electrode 15, and a second wiring 16. The first wiring 12, the first electrode 13, the second electrode 15, and the second wiring 16 are each formed using a material made of a superconductor. The first wiring 12 is provided on the substrate 11. The first electrode 13 is provided on the substrate 11 and connected to the first wiring 12. The insulating film 14 is provided on the surface of the first electrode 13. The second electrode 15 is provided on the surface of the insulating film 14. That is, the insulating film 14 is sandwiched between the first electrode 13 and the second electrode 15, which are each made of a superconductor. The second wiring 16 is provided on the substrate 11 and connected to the second electrode 15.

[0016] When the first electrode 13 and the second electrode 15, both made of superconductors, are weakly coupled through an insulating film 14, a phenomenon is observed in which superconducting electron pairs (Cooper pairs) tunnel through the insulating film 14. This phenomenon is called the Josephson effect, and the weak coupling between superconductors is called a Josephson junction.

[0017] The method for manufacturing the Josephson junction element 10 will be described below. Figures 3A, 3B, 3C, 3D, 3E, 3F, and 3G are plan views showing an example of the method for manufacturing the Josephson junction element 10. Figure 4A is a cross-sectional view along the line 4A-4A in Figure 3A. Figure 4B is a cross-sectional view along the line 4B-4B in Figure 3B. Figure 4C is a cross-sectional view along the line 4C-4C in Figure 3C. Figure 4D is a cross-sectional view along the line 4D-4D in Figure 3D. Figure 4E is a cross-sectional view along the line 4E-4E in Figure 3E. Figure 4F is a cross-sectional view along the line 4F-4F in Figure 3F. Figure 4G is a cross-sectional view along the line 4G-4G in Figure 3G.

[0018] First, a first wiring 12 made of superconductor is formed on the substrate 11 (Figures 3A and 4A). The substrate 11 is preferably an insulator, and may be, for example, an undoped silicon substrate, a sapphire substrate, or a magnesium oxide substrate.

[0019] The first wiring 12 may be made of a metal that exhibits superconductivity at low temperatures. For example, Nb, Al, TiN, NbN, or Nb3Al can be used as the material for the first wiring 12. For example, the first wiring 12 can be formed by forming a resist patterned by lithography on a substrate 11, forming a superconducting film on the substrate 11 on which the resist has been formed by sputtering or deposition, and removing the excess superconducting film together with the resist. Alternatively, the first wiring 12 can be formed by forming a superconducting film over the entire surface of the substrate 11, covering the surface of the superconducting film with a resist mask having a pattern corresponding to the pattern of the first wiring 12, and removing the exposed portion of the superconducting film by dry etching. The type of gas used in dry etching is appropriately selected depending on the material of the resist mask and the superconducting film.

[0020] Next, a resist mask 20 is formed for patterning the first electrode 13, which is made of superconductor and connected to the first wiring 12, by lift-off (Figures 3B and 4B). The resist mask 20 has openings 21 corresponding to the pattern of the first electrode 13, and the surface of the substrate 11 and the ends of the first wiring 12 are exposed at the openings 21.

[0021] Next, a superconducting film 30 constituting the first electrode 13 is formed by vapor deposition or sputtering. The superconducting film 30 is formed on the surface of the substrate 11 exposed at the opening 21 of the resist mask 20, and also on the surface of the resist mask 20 (Figures 3C and 4C). The material of the first electrode 13 may be the same as that of the first wiring 12. The thickness of the superconducting film 30 is, for example, several tens of nanometers to several hundred nanometers. The orientation of the substrate 11 during vapor deposition or sputtering is set to face the vapor deposition source or sputtering source. That is, the superconducting film 30 constituting the first electrode 13 is formed by a method different from oblique vapor deposition.

[0022] Next, the excess superconducting film 30 deposited on the resist mask 20 is removed along with the resist mask 20. This patterns the first electrode 13 (Figures 3D and 4D).

[0023] Next, a resist mask 40 is formed for patterning the second electrode 15 and the second wiring 16 by lift-off (Figures 3E and 4E). The resist mask 40 has openings 45 corresponding to the patterns of the second electrode 15 and the second wiring 16. The surface of the first electrode 13 is exposed in the portion of the opening 45 corresponding to the second electrode 15, and the surface of the substrate 11 is exposed in the portion of the opening 45 corresponding to the second wiring 16. Part of the first electrode 13 and the entirety of the first wiring 12 are covered by the resist mask 40. In addition, the surface of the substrate 11 is covered by the resist mask 40, except for the portion corresponding to the second wiring 16.

[0024] Next, the surface of the first electrode 13 exposed at the opening 45 of the resist mask 40 is etched by dry etching or wet etching (Figures 3E and 4E). This removes impurities such as residue from the resist mask 40 adhering to the surface of the first electrode 13, and cleans the surface of the first electrode 13. In addition, this etching may remove a portion of the surface of the first electrode 13 to thin the first electrode 13.

[0025] Next, an insulating film 14 is formed on the surface of the first electrode 13 exposed at the opening 45 of the resist mask 40 (Figures 3F and 4F). The insulating film 14 may also be formed by modifying the surface of the first electrode 13. For example, an oxide film may be formed as the insulating film 14 by exposing the surface of the first electrode 13 to oxygen gas. The oxygen partial pressure at this time is about 1 Pa to 10 kPa, and the exposure time is 1 minute to 10 hours. The substrate temperature is preferably set to a range in which the resist mask 40 does not harden, for example, about 25°C to 200°C. Alternatively, an oxide film, nitride film, or oxynitride film may be formed as the insulating film 14 by exposing the surface of the first electrode 13 to oxygen plasma or nitrogen plasma. The material of the insulating film 14 is preferably selected appropriately according to the material of the first electrode 13, and the type of gas used to obtain the desired insulating film 14 is appropriately selected.

[0026] Alternatively, a superconducting film different from the first electrode 13 may be formed on the surface of the first electrode 13, and then the surface of the superconducting film may be modified to form an insulating film. This method makes it possible to form an insulating film containing materials not included in the first electrode 13. For example, if Nb is used as the material for the first electrode 13, an Al film can be formed on the surface of the first electrode 13, and the surface of the Al film can be oxidized to form an Nb / Al / AlO film. X A layered structure consisting of these is obtained.

[0027] Furthermore, the insulating film 14 may be formed by sputtering. In this case, the material for the insulating film 14 may be, for example, aluminum oxide (AlO X ), aluminum nitride (AlN) or niobium oxide (NbO X ) can be used.

[0028] Next, a superconducting film 50 constituting the second electrode 15 and the second wiring 16 is formed by vapor deposition or sputtering. The superconducting film 50 is formed on the surface of the substrate 11 and the insulating film 14 exposed at the opening 45 of the resist mask 40, as well as on the surface of the resist mask 40 (Figures 3G and 4G). The material of the second electrode 15 and the second wiring 16 may be the same as that of the first electrode 13 and the first wiring 12. The thickness of the superconducting film 50 is, for example, several tens of nanometers to several hundred nanometers. The orientation of the substrate 11 during vapor deposition or sputtering is set to face the vapor deposition source or sputtering source. In other words, the superconducting film 50 constituting the second electrode 15 and the second wiring 16 is formed by a method different from conventional oblique vapor deposition.

[0029] Next, the excess superconducting film 50 deposited on the resist mask 40 is removed along with the resist mask 40. This patterns the second electrode 15 and the second wiring 16, completing the Josephson junction device (Figures 1 and 2).

[0030] The steps of etching the surface of the first electrode 13 (Figures 3E and 4E), forming an insulating film 14 on the surface of the first electrode 13 (Figures 3F and 4F), and forming the second electrode 15 on the surface of the insulating film 14 and forming the second wiring 16 on the substrate 11 (Figures 3G and 4G) are carried out continuously in a common vacuum chamber. The inside of the vacuum chamber is not exposed to the atmosphere from the start to the end of the above three steps. The resist mask 40 masks the surfaces of the substrate 11 and the first wiring 12 throughout the above three steps.

[0031] Figures 5A and 5B are cross-sectional views showing an example of a method for manufacturing a Josephson junction element using the oblique deposition method in a comparative example. In the oblique deposition method, a resist mask 70 having an overhang structure is used.

[0032] First, the orientation of the substrate 11 is set so that the flight path of the particles to be deposited from the deposition source, which will be the material for the superconducting film, to the substrate 11 is inclined with respect to the substrate surface, and the first deposition is performed. The particles to be deposited fly in from an oblique direction with respect to the substrate surface and are deposited on the substrate 11. As a result, the superconducting film 30 constituting the first electrode is formed on the substrate 11. The superconducting film 30 is formed with a pattern corresponding to the resist mask 70 (Figure 5A). Next, an insulating film 14 is formed on the surface of the superconducting film 30 by oxidizing the surface of the superconducting film 30.

[0033] Next, the orientation of the substrate 11 is set so that the flight path of the particles to be deposited is inclined in a different direction relative to the substrate surface than during the first deposition, and the second deposition is performed. The particles to be deposited fly in from a different oblique direction relative to the substrate surface than during the first deposition and are deposited on the substrate 11. As a result, the superconducting film 50 constituting the second electrode is formed on the substrate 11 and the insulating film 14. The superconducting film 50 is formed with a pattern corresponding to the resist mask 70 (Figure 5B). The same resist mask 70 is used for both the first and second depositions. By changing the orientation of the substrate 11 between the first and second depositions, the area shadowed by the resist mask 70 on the substrate 11 changes, making it possible to form the superconducting films 30 and 50 at different positions on the substrate 11.

[0034] According to the oblique deposition method, the superconducting film 30, insulating film 14, and superconducting film 50 can be formed in a continuous vacuum process within a common vacuum chamber. Furthermore, the patterning of the three-layer structure consisting of the superconducting film 30, insulating film 14, and superconducting film 50 can be performed using a single resist mask 70. Therefore, the oblique deposition method avoids exposure of the three-layer structure to the atmosphere and prevents impurities resulting from resist patterning from being introduced at the interface between the superconducting film and the insulating film.

[0035] On the other hand, with the oblique deposition method, as shown in Figure 6A, the inclination angle θ of the flight path of the deposition target particles from the deposition source 80 to each position on the substrate 11 changes depending on the position on the substrate 11. As a result, the size of the overlapping area (junction area) of the three layers of superconducting film 30 / insulating film 14 / superconducting film 50 changes depending on the position on the substrate 11. Figure 6B is a cross-sectional view of the three-layer structure formed on the substrate 11 at a position where the inclination angle θ is relatively large. At a position where the inclination angle θ is relatively large, the overlapping area (junction area) of the three layers of superconducting film 30 / insulating film 14 / superconducting film 50 becomes relatively small. Figure 6C is a cross-sectional view of the three-layer structure formed on the substrate 11 at a position where the inclination angle θ is relatively small. At a position where the inclination angle θ is relatively small, the overlapping area (junction area) of the three layers of superconducting film 30 / insulating film 14 / superconducting film 50 becomes relatively large. Thus, with the oblique deposition method, the area (junction area) of the overlapping portion of the three layers—superconducting film 30, insulating film 14, and superconducting film 50—changes depending on the position on the substrate 11. Therefore, the properties of the qubit composed of the three-layer structure may become non-uniform within the substrate surface.

[0036] On the other hand, a method for manufacturing a Josephson junction element according to an embodiment of the disclosed technology includes the steps of forming a first wiring 12 made of a superconductor and a first electrode 13 made of a superconductor connected to the first wiring 12 on a substrate 11; forming a resist mask 40 that covers at least the first wiring 12; etching the surface of the first electrode 13 using the resist mask 40; forming an insulating film 14 on the surface of the first electrode 13 using the resist mask 40; and forming a second electrode 15 made of a superconductor on the surface of the insulating film 14 using the resist mask 40.

[0037] According to the manufacturing method of the embodiment of the disclosed technology, in deposition or sputtering for forming the first electrode 13 and the second electrode 15, the orientation of the substrate 11 is set to face the deposition source or sputtering source. That is, the superconducting films constituting the first electrode 13 and the second electrode 15 are formed using a method different from oblique deposition. This makes it possible to make the angle of the flight path of the particles to be deposited with respect to the substrate surface substantially uniform over the entire surface of the substrate. This makes it possible to suppress variations in the area (junction area) of the overlapping portion of the three layers of superconducting film / insulating film / superconducting film within the substrate surface. As a result, the uniformity of the properties of the qubit composed of the Josephson junction element 10 within the substrate surface can be improved.

[0038] Furthermore, according to the manufacturing method of a Josephson junction element according to an embodiment of the disclosed technology, the first electrode 13 and the second electrode 15 are formed using different resist masks. That is, the resist mask 40 for forming the second electrode 15 is formed after the formation of the first electrode 13. Therefore, the surface of the first electrode 13 may be contaminated with impurities such as residue from the resist mask 40. In the manufacturing method according to this embodiment, the surface of the first electrode 13 exposed at the opening 45 of the resist mask 40 is etched before the insulating film 14 is formed on the surface of the first electrode 13. This removes impurities such as residue from the resist mask 40 that have adhered to the surface of the first electrode 13, and cleans the surface of the first electrode 13. Furthermore, the etching of the surface of the first electrode 13, the formation of the insulating film 14, and the formation of the second electrode 15 and the second wiring 16 are performed by a vacuum integrated process. This makes it possible to avoid the incorporation of impurities into the junction between the first electrode 13 and the insulating film 14, and into the junction between the insulating film 14 and the second electrode 15. Thus, according to the method for manufacturing a Josephson junction element as described in the disclosed technology, it is possible to suppress variations in the junction area within the substrate surface while avoiding the incorporation of impurities into the junction between the superconducting film and the insulating film.

[0039] [Second Embodiment] Figure 7 is a cross-sectional view showing an example of the configuration of a Josephson junction element 10A according to a second embodiment of the disclosed technology. In the Josephson junction element 10A, the first electrode 13 has a continuously changing thickness from one end to the other and a sloped surface. The first wiring 12 is connected to the end of the first electrode 13 where the thickness is relatively larger. The insulating film 14 and the second electrode 15 are laminated on the sloped surface of the first electrode 13. The second wiring 16 is connected to the second electrode 15 on the side of the end of the first electrode 13 where the thickness is relatively smaller.

[0040] The method for manufacturing the Josephson junction element 10A will be described below. Figures 8A, 8B, 8C, and 8D are cross-sectional views showing an example of the method for manufacturing the Josephson junction element 10A. The steps of forming the first wiring 12, forming a resist mask for patterning the first electrode 13, forming a superconducting film constituting the first electrode 13, and removing the resist mask to pattern the first electrode 13 are the same as those in the manufacturing method according to the first embodiment described above, so their explanation will be omitted.

[0041] After the patterning of the first electrode 13 is completed, a resist mask 40 is formed for patterning the second electrode 15 and the second wiring 16 by lift-off (Figure 8A). The resist mask 40 has a first portion 41 that covers the surface of the first wiring 12, a second portion 42 that covers the surface of the first electrode 13, and a third portion 43 that covers the area of ​​the substrate 11 corresponding to the second wiring 16. The first portion 41 may include a portion that covers the end of the first electrode 13 on the first wiring 12 side. The second portion 42 has a continuously changing thickness from one end to the other and a sloped surface. More specifically, the second portion 42 has a continuously increasing thickness from the end on the second wiring 16 side to the end on the first wiring 12 side. The thickness of the third portion 43 is less than the thickness of the first portion 41.

[0042] Grayscale exposure can be used as a technique to form multiple areas of varying thickness on a resist. Grayscale exposure is a technique that directly forms a three-dimensional shape on a resist by exposing it using a grayscale mask with varying shades. For example, in a positive-type resist, the thickness of the resist after development becomes relatively smaller in areas where the intensity of the light irradiated during exposure is relatively high.

[0043] Next, the surface of the first electrode 13 is etched through the resist mask 40 by dry etching or wet etching (Figure 8B). The first electrode 13 is etched sequentially starting from the areas where the thickness of the resist mask 40 covering its surface is relatively thin. Therefore, a three-dimensional shape corresponding to the three-dimensional shape of the second portion 42 of the resist mask 40 is formed on the first electrode 13. That is, in this etching process, the first electrode 13 is formed into a shape in which the surface is sloped so that the thickness changes continuously from one end to the other. In addition, in this etching process, impurities such as residue of the resist mask 40 adhering to the surface of the first electrode 13 are removed, and the surface of the first electrode 13 is cleaned. Since the area on the surface of the substrate 11 corresponding to the second wiring 16 is covered by the third portion 43 of the resist mask 40, damage to the above area due to etching is suppressed.

[0044] At the completion of etching, the resist mask 40 has its second portion 42 and third portion 43 removed, leaving only the first portion 41. That is, openings 45 corresponding to the patterns of the second electrode 15 and the second wiring 16 are formed in the resist mask 40. The surface of the first electrode 13 is exposed in the portion of the opening 45 corresponding to the second electrode 15, and the surface of the substrate 11 is exposed in the portion of the opening corresponding to the second wiring 16.

[0045] Next, an insulating film 14 is formed on the inclined surface of the first electrode 13 that is exposed at the opening 45 of the resist mask 40 (Figure 8C). The insulating film 14 is formed in the same manner as in the first embodiment described above.

[0046] Next, a superconducting film 50 constituting the second electrode 15 and the second wiring 16 is formed by vapor deposition or sputtering. The superconducting film 50 is formed on the surface of the insulating film 14 and the substrate 11 that are exposed at the opening 45 of the resist mask 40, as well as on the surface of the resist mask 40. The second electrode 15 is formed along the inclined surface of the first electrode 13 (Figure 8D). The orientation of the substrate 11 during vapor deposition or sputtering is set to face the vapor deposition source or sputtering source.

[0047] Next, the excess superconducting film 50 deposited on the resist mask 40 is removed along with the resist mask 40. This patterns the second electrode 15 and the second wiring 16, completing the Josephson junction element 10A (Figure 7).

[0048] According to the manufacturing method of the Josephson junction element 10A as described in the second embodiment of the disclosed technology, similar to the manufacturing method according to the first embodiment, it is possible to suppress variations in the bonding area within the substrate surface while avoiding the incorporation of impurities into the bonding area between the superconducting film and the insulating film.

[0049] Furthermore, in the Josephson junction element 10A according to the second embodiment of the disclosed technology, the first electrode 13 has a structure in which the thickness changes continuously from one end to the other and the surface is sloped. When the thickness of the first electrode 13 is constant, a step is formed at the end of the first electrode 13, and the superconducting film constituting the second electrode 15 and the second wiring 16 covers the stepped portion. In the stepped portion, it becomes difficult for the superconducting film to deposit, resulting in insufficient thickness of the superconducting film in the stepped portion, which increases the risk of disconnection in the second wiring 16. Moreover, it may be difficult to remove impurities such as residue from the resist mask in the stepped portion.

[0050] The inclined structure of the first electrode 13 reduces the step formed at the end of the first electrode 13. This makes it less likely for areas with insufficient thickness to occur in the superconducting film 50 constituting the second electrode 15 and the second wiring 16, thereby suppressing the risk of wire breakage in the second wiring 16. Furthermore, the reduction of the step makes it easier to remove impurities.

[0051] Furthermore, if, for example, the thickness of the first electrode 13 is thin and the step formed at the edge of the first electrode 13 is not a problem, the thickness of the second portion 42 of the resist mask 40 may be constant, as shown in Figure 9. In the example shown in Figure 9, the thickness of the second portion 42 and the third portion 43 of the resist mask 40 is smaller than the thickness of the first portion 41. In this case, the shape of the first electrode 13 after etching will be a flat shape without inclined surfaces. A resist mask 40 having multiple portions with different thicknesses in this way can be formed by grayscale exposure.

[0052] The following additional information is disclosed regarding the first and second embodiments described above. (Note 1) A first wiring made of a superconductor and a first electrode made of a superconductor connected to the first wiring are formed on a substrate. A resist mask is formed that covers at least the first wiring, The surface of the first electrode is etched using the resist mask, Using the resist mask, an insulating film is formed on the surface of the first electrode. Using the resist mask, a second electrode made of a superconductor is formed on the surface of the insulating film. A method for manufacturing a Josephson junction element, including the following.

[0053] (Note 2) The resist mask has a first portion that covers the surface of the first wiring and a second portion that covers the surface of the first electrode, wherein the thickness of the second portion changes continuously. The manufacturing method described in Appendix 1.

[0054] (Note 3) The resist mask has a first portion that covers the surface of the first wiring and a second portion that covers the surface of the first electrode. The thickness of the second part is smaller than the thickness of the first part. The manufacturing method described in Appendix 1.

[0055] (Note 4) The resist mask is formed by grayscale exposure. The manufacturing method described in Appendix 2 or Appendix 3.

[0056] (Note 5) By etching the surface of the first electrode through the resist mask, a slope corresponding to the shape of the second portion is formed on the surface of the first electrode. The manufacturing method described in Appendix 2.

[0057] (Note 6) The etching of the surface of the first electrode, the formation of the insulating film, and the formation of the second electrode are performed continuously in a common vacuum chamber. The manufacturing method described in any one of the appendices 1 to 5.

[0058] (Note 7) The resist mask has a third portion that covers the region of the substrate surface corresponding to the second wiring made of a superconductor connected to the second electrode, The thickness of the third portion is less than the thickness of the first portion. Using the resist mask, the surface of the first electrode is etched while the third portion is removed. Using the resist mask, a second electrode is formed on the surface of the insulating film, and the second wiring is formed on the surface of the substrate. The manufacturing method described in Appendix 2 or Appendix 3.

[0059] (Note 8) A first electrode provided on a substrate, the thickness of which changes continuously from one end to the other, An insulating film provided on the surface of the first electrode, A second electrode provided on the surface of the insulating film, A second wiring is provided on the substrate and connected to the second electrode at the end of the first electrode where the thickness is relatively smaller, A Josephson junction element. [Explanation of symbols]

[0060] 10, 10A Josephson junction element 11 circuit boards 12 1st wiring 13 1st electrode 14 Insulator film 15 2nd electrode 16 2nd wiring 40 Resist Masks 41 Part 1 42 Part 2 43 Part 3

Claims

1. A first wiring made of a superconductor and a first electrode made of a superconductor connected to the first wiring are formed on a substrate. A resist mask is formed that covers at least the first wiring, The surface of the first electrode is etched using the resist mask. Using the resist mask, an insulating film is formed on the surface of the first electrode. Using the resist mask, a second electrode made of a superconductor is formed on the surface of the insulating film. A method for manufacturing a Josephson junction element, including the following.

2. The resist mask has a first portion that covers the surface of the first wiring and a second portion that covers the surface of the first electrode, wherein the thickness of the second portion changes continuously. The manufacturing method according to claim 1.

3. The resist mask has a first portion that covers the surface of the first wiring and a second portion that covers the surface of the first electrode. The thickness of the second portion is smaller than the thickness of the first portion. The manufacturing method according to claim 1.

4. The resist mask is formed by grayscale exposure. The manufacturing method according to claim 2 or claim 3.

5. By etching the surface of the first electrode through the resist mask, a slope corresponding to the shape of the second portion is formed on the surface of the first electrode. The manufacturing method according to claim 2.

6. The etching of the surface of the first electrode, the formation of the insulating film, and the formation of the second electrode are performed continuously in a common vacuum chamber. The manufacturing method according to claim 1.

7. The resist mask has a third portion that covers the region of the substrate surface corresponding to the second wiring made of a superconductor connected to the second electrode, The thickness of the third portion is less than the thickness of the first portion. Using the resist mask, the surface of the first electrode is etched while the third portion is removed. Using the resist mask, a second electrode is formed on the surface of the insulating film, and the second wiring is formed on the surface of the substrate. The manufacturing method according to claim 2 or claim 3.

8. A first electrode provided on a substrate, the thickness of which changes continuously from one end to the other, An insulating film provided on the surface of the first electrode, A second electrode provided on the surface of the insulating film, A second wiring is provided on the substrate and connected to the second electrode at the end of the first electrode where the thickness is relatively smaller, A Josephson junction element.

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