Method for manufacturing quantum device and quantum device

Abstract

To provide a method of manufacturing a quantum device capable of improving reliability of mechanical strength of a first conductive film and a second conductive film.SOLUTION: A method of manufacturing a quantum bit device includes a step of forming a second groove on a second surface of a quantum bit substrate, a step of forming a second conductive film on a bottom surface and a side surface of the second groove, a step of forming a first groove reaching a part of the bottom surface of the second groove on a first surface after the step of forming the second conductive film, a step of forming a first conductive film on a bottom surface and a side surface of the first groove, and a step of forming a quantum bit on the first surface.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a quantum device and a quantum device. [Background technology]

[0002] In quantum devices, a configuration is known in which the upper and lower surfaces of a substrate are electrically connected by forming a conductive film in a through hole provided from the upper surface to the lower surface (e.g., Non-Patent Document 1).A configuration is also known in which the upper and lower surfaces of a substrate are electrically connected by forming a conductive film on the inner surface of a groove provided in each of the upper and lower surfaces (e.g., Patent Documents 1 and 2).Furthermore, a configuration is also known in which a conductive film is formed in a groove provided on one surface of the substrate and this conductive film is capacitively coupled to a metal film provided on the other surface (e.g., Patent Documents 3 and 4). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-85020 [Patent Document 2] Special Publication No. 2008-532319 [Patent Document 3] Japanese Patent Publication No. 2022-32990 [Patent Document 4] US Patent Application Publication No. 2019 / 0165237 [Non-patent literature]

[0004] [Non-Patent Document 1] JAAlfaro-Barrantes and 5 others, “Highly-Conformal Sputtered Through-Silicon Vias With Sharp Superconducting Transition”, JOURNAL OFMICROELECTRONECHANICAL SYSTEMS, VOL.30, NO.2, April 2021, pp253-261 Summary of the Invention [Problem to be solved by the invention]

[0005] In quantum devices, a configuration is desired in which a conductive film extending from the first surface to the second surface of a quantum bit substrate electrically connects the first surface and the second surface on which the quantum bits are provided. In this case, it is conceivable to form a through-hole penetrating from the first surface to the second surface with a vertical side, and then form a conductive film on the side surface of the through-hole from both the first surface side and the second surface side, thereby electrically connecting the first surface and the second surface via the conductive film. However, the thickness of the conductive film formed on the first surface side and the conductive film formed on the second surface side becomes thinner near the center of the through-hole, which poses a problem in terms of the electrical connection of the conductive film.

[0006] In order to prevent the film thickness from becoming thin near the center of the through hole, it is conceivable to make the side surfaces of the through hole tapered from the first and second surfaces toward the center of the through hole. However, in this case, the contact area between the conductive film formed on the first surface side and the conductive film formed on the second surface side becomes small, leaving room for improvement in terms of the electrical connection of the conductive films.

[0007] To improve the reliability of the electrical connection, a first groove is formed on the first surface of the quantum bit substrate, and a first conductive film is formed on the inner surface of the first groove. A second groove is formed on the second surface, reaching the first groove, and a second conductive film is formed on the inner surface of the second groove, connecting to the first conductive film. This improves the reliability of the electrical connection because the first and second conductive films are connected at the bottom surfaces of the first and second grooves, respectively. However, this may reduce the mechanical strength of the first and second conductive films.

[0008] In one aspect, an object is to suppress a decrease in the mechanical strength of the first conductive film and the second conductive film while maintaining electrical connection. [Means for solving the problem]

[0009] In one aspect, a method for manufacturing a quantum device including a quantum bit and a quantum bit substrate having a first surface on which the quantum bit is formed includes the steps of: forming a second groove on the second surface of the quantum bit substrate; forming a second conductive film on the bottom and side surfaces of the second groove; after the step of forming the second conductive film, forming a first groove on the first surface that reaches a portion of the bottom surface of the second groove; forming a first conductive film on the bottom and side surfaces of the first groove; and forming the quantum bit on the first surface.

[0010] In one aspect, a quantum device comprises a quantum bit substrate, a quantum bit provided on a first surface of the quantum bit substrate, a second groove provided on a second surface of the quantum bit substrate, a second conductive film provided on a bottom surface and side surfaces of the second groove, a first groove provided on the first surface and reaching a portion of the bottom surface of the second groove, and a first conductive film provided on the bottom surface and side surfaces of the first groove. [Effects of the Invention]

[0011] As one aspect, it is possible to suppress a decrease in the mechanical strength of the first conductive film and the second conductive film while maintaining electrical connection. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a plan view of a quantum device according to a first embodiment. [Figure 2] FIG. 2(a) is a cross-sectional view of the quantum device according to the first embodiment, and FIG. 2(b) is an enlarged view of the vicinity of the first trench and the second trench in FIG. 2(a). [Figure 3] FIG. 3(a) is a plan view of the Josephson device in Example 1, and FIG. 3(b) and FIG. 3(c) are AA and BB cross-sectional views of FIG. 3(a). [Figure 4] 4(a) to 4(c) are cross-sectional views (part 1) illustrating a method for manufacturing a quantum device according to the first embodiment. [Figure 5]5(a) to 5(c) are cross-sectional views (part 2) illustrating the method for manufacturing the quantum device according to the first embodiment. [Figure 6] 6(a) to 6(c) are cross-sectional views (part 3) illustrating the method for manufacturing the quantum device according to the first embodiment. [Figure 7] 7(a) to 7(c) are diagrams (part 1) showing a method for manufacturing a Josephson device in Example 1. FIG. [Figure 8] 8(a) and 8(b) are diagrams (part 2) showing a method for manufacturing a Josephson device in Example 1. FIG. [Figure 9] 9(a) is a plan view showing a connection portion between the first groove and the second groove in Example 1, and FIG. 9(b) is a plan view showing a contact portion between the first conductive film and the second conductive film in Example 1. [Figure 10] 10(a) to 10(c) are cross-sectional views (part 1) showing a method for manufacturing a quantum device according to a comparative example. [Figure 11] 11(a) and 11(b) are cross-sectional views (part 2) showing a method for manufacturing a quantum device according to a comparative example. [Figure 12] 12(a) to 12(c) are cross-sectional views (part 1) illustrating a method for manufacturing a quantum device according to the second embodiment. [Figure 13] 13(a) and 13(b) are cross-sectional views (part 2) illustrating a method for manufacturing a quantum device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0014] Fig. 1 is a plan view of a quantum device 100 in accordance with Example 1. Fig. 2(a) is a cross-sectional view of the quantum device 100 in accordance with Example 1, and Fig. 2(b) is an enlarged view of the vicinity of a first groove 50 and a second groove 60 in Fig. 2(a). In Fig. 1, the first conductive film 21 and the third conductive film 23 are hatched for clarity.

[0015] As shown in FIG. 1 , quantum bits 30 and coupling wires 40 are provided on the top surface 11 of a quantum bit substrate 10, which is, for example, a silicon (Si) substrate. The quantum device 100 is used in quantum computers and operates in a superconducting state at extremely low temperatures, for example, several tens of millikelvins (mK). The quantum bits 30 are elements that form a coherent two-level system using superconductivity. The quantum bits 30 include a Josephson junction 31 connected between a central electrode 13 and a peripheral electrode 14, and a capacitor 32 formed by the central electrode 13 and the peripheral electrode 14 facing each other. That is, the quantum bits 30 include a Transmon quantum bit circuit in which the Josephson junction 31 and the capacitor 32 are connected in parallel. The coupling wires 40 are electrostatically coupled to the quantum bits 30, coupling adjacent quantum bits 30. As a result, each quantum bit 30 creates a quantum entangled state with its neighboring quantum bits 30, thereby performing quantum operations.

[0016] Fig. 3(a) is a plan view of a Josephson device 31 in Example 1, Fig. 3(b) is a cross-sectional view taken along line AA in Fig. 3(a), and Fig. 3(c) is a cross-sectional view taken along line BB in Fig. 3(a). In Fig. 3(a) to Fig. 3(c), directions parallel to and perpendicular to the top surface 11 of the quantum bit substrate 10 are defined as the X-axis direction and the Y-axis direction, and the normal direction to the top surface 11 is defined as the Z-axis direction. In Fig. 3(a), the insulating film 35 provided on the surface of the superconducting film 33 is not shown.

[0017] 3(a) to 3(c), a Josephson element 31 includes a superconducting film 33 extending in the X-axis direction, a superconducting film 34 extending in the Y-axis direction, and an insulating film 35 provided between the superconducting films 33 and 34 in an overlapping region. The region where the superconducting films 33 and 34 overlap with the insulating film 35 interposed therebetween forms a Josephson junction 36.

[0018] The superconducting films 33 and 34 are made of a superconducting material that exhibits superconductivity at a temperature equal to or lower than a predetermined critical temperature. The insulating film 35 is provided, for example, to cover the surface of the superconducting film 33. The superconducting films 33 and 34 are, for example, aluminum (Al) films. The insulating film 35 is, for example, an aluminum oxide (Al2O3) film. The Josephson element 31 is connected between the central electrode 13 and the peripheral electrode 14 by connecting one of the superconducting films 33 and 34 to the central electrode 13 and the other to the peripheral electrode 14.

[0019] As shown in FIGS. 1, 2(a), and 2(b), a third conductive film 23 is provided on the top surface 11 of the quantum bit substrate 10. The third conductive film 23 is patterned to form a central electrode 13, a peripheral electrode 14, and a coupling wire 40. The portions of the third conductive film 23 other than the central electrode 13, the peripheral electrode 14, and the coupling wire 40 are connected to, for example, ground. The third conductive film 23 is formed of a superconducting material that exhibits superconductivity at a temperature below a predetermined critical temperature, such as a titanium nitride (TiN) film. A first groove 50 is provided on the top surface 11 of the quantum bit substrate 10. A second groove 60 is provided on the bottom surface 12 of the quantum bit substrate 10. The first groove 50 and the second groove 60 form a through via. The through via provides electrical conductivity between the top surface 11 and the bottom surface 12, thereby fixing the ground potential and serving as a readout electrode for reading out signals from the quantum bit 30.

[0020] The first groove 50 is provided so as to overlap the second groove 60 in a plan view, and is connected to only a portion of the bottom surface 61 of the second groove 60. Therefore, the diameter L1 of the bottom surface 51 of the first groove 50 is smaller than the diameter L2 of the bottom surface 61 of the second groove 60. For example, the diameter L1 is not less than 1 / 5 and not more than 1 / 2 of the diameter L2. Furthermore, the depth D1 of the first groove 50 is smaller than the depth D2 of the second groove 60. For example, the depth D1 is not more than 1 / 10 of the depth D2.

[0021] The side surface 52 of the first groove 50 and the side surface 62 of the second groove 60 are both tapered. That is, a first angle α formed between the side surface 52 of the first groove 50 and the top surface 11 of the quantum bit substrate 10, and a second angle β formed between the side surface 62 of the second groove 60 and the bottom surface 12 of the quantum bit substrate 10 are both obtuse angles. The first angle α is greater than the second angle β. Therefore, the side surface 52 of the first groove 50 has a gentler slope than the side surface 62 of the second groove 60.

[0022] A first conductive film 21 is provided on a bottom surface 51 and a side surface 52 of the first groove 50. The first conductive film 21 is provided from the side surface 52 of the first groove 50 to the third conductive film 23, and is in contact with the upper surface of the third conductive film 23. A gap 24 is formed inside the first conductive film 21 in the first groove 50. The first conductive film 21 is formed of a superconducting material that exhibits superconductivity at a temperature equal to or lower than a predetermined critical temperature, and is, for example, a titanium nitride (TiN) film.

[0023] A second conductive film 22 is provided on the bottom surface 61 and side surface 62 of the second groove 60. The second conductive film 22 is provided from the side surface 62 of the second groove 60 to the lower surface 12 of the quantum bit substrate 10. In the second groove 60, a gap 25 is formed inside the second conductive film 22. The second conductive film 22 is formed from a superconducting material that exhibits superconductivity at a temperature equal to or lower than a predetermined critical temperature, such as a titanium nitride (TiN) film.

[0024] The first conductive film 21 and the second conductive film 22 are in contact at the point where the first groove 50 and the second groove 60 are connected. That is, the first conductive film 21 and the second conductive film 22 are in surface contact. The first conductive film 21 and the second conductive film 22 are connected to ground, for example. The bottom surface 51 of the first groove 50 is flush with the bottom surface 61 of the second groove 60. Therefore, the plane of the first conductive film 21 closest to the second groove 60 and the plane of the second conductive film 22 closest to the first groove 50 are flush with each other.

[0025] The quantum bit substrate 10 may be a semiconductor substrate or an insulating substrate other than a silicon substrate, such as a sapphire substrate. The first conductive film 21, the second conductive film 22, and the third conductive film 23 may be made of a superconducting material other than titanium nitride, such as an aluminum (Al) film, a niobium (Nb) film, or a tantalum (Ta) film.

[0026] [Manufacturing method] 4(a) to 6(c) are cross-sectional views illustrating a manufacturing method of the quantum device 100 according to the first embodiment. As shown in FIG. 4(a), a metal film 79 such as an aluminum film is formed on the lower surface 12 (the upper surface in FIG. 4(a)) and the upper surface 11 (the lower surface in FIG. 4(a)) of a quantum bit substrate 10, which is, for example, a silicon substrate. Next, a patterned resist film 70 is formed on the lower surface 12 of the quantum bit substrate 10. A protective resist film 71 is formed on the upper surface 11 of the quantum bit substrate 10. A second groove 60 having a bottom surface 61 and a side surface 62 is formed on the lower surface 12 of the quantum bit substrate 10 using the resist film 70 as a mask. The second groove 60 is formed by dry etching, for example, reactive ion etching using the Bosch process. For example, the second groove 60 is formed by alternately repeating etching of the quantum bit substrate 10 using SF6 gas or the like and forming a protective film using C4F8 gas. The depth D2 of the second groove 60 may be, for example, greater than ½ or greater than ¾ of the distance between the top surface 11 and the bottom surface 12 of the quantum bit substrate 10 (i.e., the thickness of the quantum bit substrate 10). As an example, when the thickness of the quantum bit substrate 10 is 300 μm, the depth D2 is 250 μm or greater and 290 μm or less. The diameter L2 of the second groove 60 at the bottom surface 61 is, for example, 70 μm or greater and 80 μm or less, and the diameter L3 at the bottom surface 12 is, for example, 140 μm or greater and 160 μm or less.

[0027] As shown in FIG. 4(b), after removing the resist films 70 and 71 and the metal film 79, a second conductive film 22, such as a titanium nitride film, is formed on the lower surface 12 of the quantum bit substrate 10 and the bottom surface 61 and side surface 62 of the second groove 60. Scallops formed on the side surface 62 of the second groove 60 may be removed before or after removing the metal film 79. The second conductive film 22 is formed, for example, using atomic layer deposition (ALD). By using the ALD method, variations in the thickness of the second conductive film 22 formed on the bottom surface 61 and side surface 62 of the second groove 60 are reduced even when the depth D2 is large. A gap 25 is formed inside the second conductive film 22 in the second groove 60. The thickness of the second conductive film 22 is, for example, 50 nm to 500 nm.

[0028] 4(c), the second conductive film 22 is patterned using photolithography and etching, for example, by reactive ion etching using CF4 gas.

[0029] 5(a), a third conductive film 23, which is, for example, a titanium nitride film, is formed by, for example, sputtering on the upper surface 11 of the quantum bit substrate 10. The thickness of the third conductive film 23 is, for example, 50 nm to 500 nm.

[0030] As shown in FIG. 5(b), the third conductive film 23 is patterned using photolithography and etching. The etching is performed by reactive ion etching using, for example, CF4 gas. By patterning the third conductive film 23, the central electrode 13, the peripheral electrode 14, and the coupling wires 40 (see FIG. 1) are formed.

[0031] As shown in FIG. 5(c), a Josephson device 31 is formed on the upper surface 11 of the quantum bit substrate 10, thereby forming a quantum bit 30 (see FIG. 1).

[0032] 7(a) to 8(b) are diagrams illustrating a method for manufacturing a Josephson device 31 in Example 1. The upper diagrams of FIGS. 7(a) to 8(b) are plan views illustrating the method for manufacturing a Josephson device 31. The middle diagrams are cross-sectional views taken along line AA of the upper diagrams, and the lower diagrams are cross-sectional views taken along line BB of the upper diagrams. Similarly to FIGS. 3(a) to 3(c), the X-axis, Y-axis, and Z-axis directions are indicated in FIGS. 7(a) to 8(b). For clarity, the superconducting films 33, 34, and insulating films 35 formed in the gaps 83 are hatched in the upper plan views of FIGS. 7(a) to 8(b).

[0033] As shown in FIG. 7(a), a patterned laminated resist film 72 is formed on the upper surface 11 of the quantum bit substrate 10. The laminated resist film 72 has an upper layer 73 and a lower layer 74. A pattern 80 including an opening 81, an opening 82, and a void 83 is formed in the laminated resist film 72. The opening 81 extends in the X-axis direction, and the opening 82 extends in the Y-axis direction, intersecting the opening 81, and both are formed in the upper layer 73. The void 83 is formed in the lower layer 74. The void 83 is located below the openings 81 and 82, and has a shape that is larger than the openings 81 and 82 in a planar view. The widths of the openings 81 and 82 are, for example, 100 nm to 300 nm.

[0034] 7(b), using the laminated resist film 72 as a mask, a superconducting film 33 is formed on the upper surface 11 of the quantum bit substrate 10 by oblique vacuum deposition from above in the −X direction, as indicated by arrow 85. Since the superconducting film 33 is formed by oblique vacuum deposition from above in the −X direction, by setting the width dimension of the opening 82 to an appropriate size, only the superconducting film 33 extending in the X-axis direction is formed within the void 83. The superconducting film 33 is, for example, an aluminum film, and has a thickness of, for example, 30 nm to 50 nm and a width of, for example, 100 nm to 300 nm.

[0035] As shown in FIG. 7(c), while maintaining the vacuum state when the superconducting film 33 was formed, oxygen is introduced into the chamber to oxidize the surface of the superconducting film 33, and an insulating film 35 made of, for example, aluminum oxide is formed on the surface of the superconducting film 33.

[0036] As shown in FIG. 8( a), using the laminated resist film 72 as a mask, a superconducting film 34 is formed on the upper surface 11 of the quantum bit substrate 10 by oblique vacuum deposition from above in the +Y direction, as indicated by arrow 86. Since the superconducting film 34 is formed by oblique vacuum deposition from above in the +Y direction, the width dimension of the opening 81 is set to an appropriate size, so that only the superconducting film 34 extending in the Y-axis direction is formed within the void 83. The superconducting film 34 is, for example, an aluminum film, and has a thickness of, for example, 50 nm to 70 nm and a width of, for example, 100 nm to 300 nm. This forms a region 84 where the superconducting film 33 extending in the X-axis direction and the superconducting film 34 extending in the Y-axis direction overlap with the insulating film 35 interposed therebetween.

[0037] 8(b), the laminated resist film 72, and the superconducting film 33, insulating film 35, and superconducting film 34 formed on the laminated resist film 72 are removed by a lift-off method. A region 84 where the superconducting film 33 extending in the X-axis direction and the superconducting film 34 extending in the Y-axis direction overlap with the insulating film 35 interposed therebetween becomes a Josephson junction 36.

[0038] As shown in FIG. 6( a), a patterned resist film 75 is formed on the top surface 11 of the quantum bit substrate 10. Using the resist film 75 as a mask, a first groove 50 having a bottom surface 51 and side surfaces 52 is formed on the top surface 11 of the quantum bit substrate 10. The first groove 50 is formed by dry etching, e.g., reactive ion etching. For example, the quantum bit substrate 10 is etched using CF4 gas and O2 gas to form the first groove 50. The first groove 50 is formed so as to reach only a portion of the bottom surface 61 of the second groove 60. As a result, a portion of the second conductive film 22 formed on the bottom surface 61 of the second groove 60 is exposed from the bottom surface 51 of the first groove 50. In forming the first groove 50, the second conductive film 22 can be used as an etching stopper layer. The depth D1 of the first groove 50 is, for example, less than ½, or may be less than ¼, the distance between the top surface 11 and the bottom surface 12 of the quantum bit substrate 10. For example, when the thickness of the quantum bit substrate 10 is 300 μm, the depth D1 is 10 μm or more and 50 μm or less. The diameter L1 of the first groove 50 at the bottom surface 51 is, for example, 40 μm or more and 60 μm or less, and the diameter L4 at the top surface 11 is, for example, 140 μm or more and 160 μm or less.

[0039] 9(a) is a plan view showing a connection portion between the first groove 50 and the second groove 60 in Example 1. Since the first groove 50 is formed so as to reach only a portion of the second groove 60, as shown in FIG. 9(a), the area S1 of the bottom surface 51 of the first groove 50 is smaller than the area S2 of the bottom surface 61 of the second groove 60. For example, the area S1 of the bottom surface 51 of the first groove 50 is 1 / 25 to 1 / 4 times the area S2 of the bottom surface 61 of the second groove 60.

[0040] As shown in FIG. 6(b), after removing the resist film 75, a patterned resist film 76 is formed on the upper surface 11 of the quantum bit substrate 10. Using the resist film 76 as a mask, a first conductive film 21, such as a titanium nitride film, is formed by, for example, vacuum deposition. The first conductive film 21 is formed from the bottom surface 51 and side surface 52 of the first groove 50 to the upper surface of the third conductive film 23, and is in contact with the third conductive film 23. A gap 24 is formed in the first groove 50, inside the first conductive film 21. The thickness of the first conductive film 21 is 50 nm or more and 500 nm or less.

[0041] FIG. 9B is a plan view showing a contact portion between the first conductive film 21 and the second conductive film 22 in Example 1. As shown in FIG. 9B, the first conductive film 21 and the second conductive film 22 are in surface contact. This improves the reliability of the electrical connection between the first conductive film 21 and the second conductive film 22. The area S3 of the plane 26 of the first conductive film 21, which is the surface that is closest to the second groove 60 and in contact with the second conductive film 22, is smaller than the area S4 of the plane 27 of the second conductive film 22, which is the surface that is closest to the first groove 50 and in contact with the first conductive film 21. For example, the area S3 of the plane 26 of the first conductive film 21 is 1 / 25 to 1 / 4 times the area S4 of the plane 27 of the second conductive film 22.

[0042] 6(c), the resist film 76 and the first conductive film 21 formed on the resist film 76 are removed by lift-off. In this way, the quantum device 100 according to the first embodiment is formed.

[0043] [Comparative Example] 10(a) to 11(b) are cross-sectional views showing a method for manufacturing a quantum device according to a comparative example. As shown in FIG. 10(a), a groove 150 having a bottom surface 151 and side surfaces 152 is formed on the top surface 111 of a quantum bit substrate 110 using photolithography and etching. The groove 150 is formed by reactive ion etching using, for example, the Bosch process. For example, if the thickness of the quantum bit substrate 110 is 300 μm, the depth D3 of the groove 150 is 200 μm or more and 250 μm or less. Then, a conductive film 121 is formed on the top surface 111 of the quantum bit substrate 110 and the bottom surface 151 and side surfaces 152 of the groove 150. The conductive film 121 is formed using, for example, the ALD method. The thickness of the conductive film 121 is, for example, 50 nm or more and 500 nm or less.

[0044] As shown in FIG. 10(b), the conductive film 121 is patterned using photolithography and etching.

[0045] 10(c), a groove 160 having a bottom surface 161 and side surfaces 162 is formed on the lower surface 112 of the quantum bit substrate 110 (the upper surface in FIG. 10(c)) using photolithography and etching. The groove 160 is formed so that the bottom surface 161 is larger than the bottom surface 151 of the groove 150. Therefore, the entire conductive film 121 provided on the bottom surface 151 of the groove 150 is exposed from the bottom surface 161 of the groove 160.

[0046] 11(a), a conductive film 122 is formed on the lower surface 112 (the upper surface in FIG. 11(a)) of the quantum bit substrate 110 using, for example, a sputtering method. The thickness of the conductive film 122 is, for example, 50 nm or more and 500 nm or less. Thereafter, the conductive film 122 is patterned using photolithography and etching.

[0047] As shown in Figure 11(b), a Josephson device 131 is formed on the upper surface 111 of the quantum bit substrate 110. The Josephson device 131 is formed by the same method as in Figures 7(a) to 8(b). In this way, a quantum device according to the comparative example is formed.

[0048] In the comparative example, as shown in FIG. 10(c), the entire conductive film 121 provided on the bottom surface 151 of the groove 150 is exposed from the bottom surface 161 of the groove 160. Therefore, as shown in FIG. 11(a), the contact area between the conductive film 121 and the conductive film 122 increases, improving the reliability of the electrical connection. However, in FIG. 10(c), the conductive film 121 provided on the bottom surface 151 of the groove 150 is not in contact with the quantum bit substrate 110 and is in a floating state. Because the thickness of the conductive film 121 is thin, at 50 nm or more and 500 nm or less, the conductive film 121 provided on the bottom surface 151 of the groove 150 has low strength. Therefore, when a physical external force is applied to the conductive film 121, for example, during the manufacturing process, the conductive film 121 is easily damaged. 11(a), the thickness of the conductive film 122 formed in the groove 160 is also thin, at 50 nm or more and 500 nm or less, so even after the conductive film 122 is formed, the strength of the conductive films 121 and 122 on the bottom surface 151 of the groove 150 is weak. Therefore, when a physical external force is applied to the conductive films 121 and 122, for example, during or after the manufacturing process, they are likely to be damaged. Thus, in the comparative example, the mechanical strength of the conductive films 121 and 122 is weak.

[0049] On the other hand, according to Example 1, as shown in FIG. 4(a), a second groove 60 is formed on the lower surface 12 (second surface) of the quantum bit substrate 10. As shown in FIG. 4(b), a second conductive film 22 is formed on the bottom surface 61 and side surface 62 of the second groove 60. As shown in FIG. 6(a), after the second conductive film 22 is formed, a first groove 50 is formed on the upper surface 11 (first surface) of the quantum bit substrate 10, reaching a portion of the bottom surface 61 of the second groove 60. As shown in FIG. 6(b), a first conductive film 21 is formed on the bottom surface 51 and side surface 52 of the first groove 50. In this way, the first groove 50 is formed so as to reach a portion of the bottom surface 61 of the second groove 60, and therefore, as shown in FIG. 6(a), the area of ​​the second conductive film 22 exposed from the bottom surface 51 of the first groove 50 is small. The portion of the second conductive film 22 provided on the bottom surface 61 of the second groove 60 that is not exposed from the bottom surface 51 of the first groove 50 is in contact with the quantum bit substrate 10. This prevents the second conductive film 22 from decreasing in strength, making it less susceptible to breakage. Furthermore, as shown in FIG. 6( b), even after the first conductive film 21 is formed, the areas of the first conductive film 21 and the second conductive film 22 that are not in contact with the quantum bit substrate 10 are small, so that the decrease in strength of the first conductive film 21 and the second conductive film 22 is prevented. Therefore, according to the first embodiment, it is possible to prevent the decrease in mechanical strength of the first conductive film 21 and the second conductive film 22.

[0050] 1, 2(a), and 2(b), quantum bits 30 are provided on the upper surface 11 (first surface) of a quantum bit substrate 10. A second groove 60 is provided on the lower surface 12 (second surface) of the quantum bit substrate 10. A second conductive film 22 is provided on a bottom surface 61 and a side surface 62 of the second groove 60. A first groove 50 is provided on the upper surface 11 of the quantum bit substrate 10, reaching a part of the bottom surface 61 of the second groove 60. A first conductive film 21 is provided on the bottom surface 51 and a side surface 52 of the first groove 50. With this configuration, it is possible to suppress a decrease in the mechanical strength of the first conductive film 21 and the second conductive film 22.

[0051] 4(a) and 6(a), the second grooves 60 are formed with a depth D2 that is greater than the depth D1 of the first grooves 50. This prevents the diameter L4 of the first grooves 50 on the top surface 11 of the quantum bit substrate 10 from becoming too large. This makes it possible to ensure a region for forming the quantum bits 30 and the like without increasing the size of the quantum bit substrate 10.

[0052] From the viewpoint of preventing the diameter L4 from becoming large, the depth D2 is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more of the distance between the upper surface 11 and the lower surface 12. From the viewpoint of preventing the second groove 60 from penetrating the quantum bit substrate 10 due to manufacturing variations or the like, the depth D2 is preferably 95% or less of the distance between the upper surface 11 and the lower surface 12, more preferably 90% or less, and even more preferably 85% or less.

[0053] In Example 1, as shown in FIG. 2(b), the second groove 60 is formed such that the second angle β formed between the side surface 62 of the second groove 60 and the lower surface 12 of the quantum bit substrate 10 is an obtuse angle. The first groove 50 is formed such that the first angle α formed between the side surface 52 of the first groove 50 and the upper surface 11 of the quantum bit substrate 10 is larger than the second angle β. Because the second angle β is obtuse, it becomes easier to form the second conductive film 22 of a desired thickness on the side surface 62 of the second groove 60. Furthermore, because the second angle β is smaller than the first angle α, the diameter L3 (see FIG. 4(a)) of the second groove 60 at the lower surface 12 of the quantum bit substrate 10 is prevented from becoming large, and the quantum bit substrate 10 can be prevented from becoming large. Because the first angle α is greater than the second angle β, the first conductive film 21 can be easily formed with a desired thickness on the bottom surface 51 and side surface 52 of the first groove 50, even if the diameter L1 of the bottom surface 51 of the first groove 50 is small. The thicknesses of the first conductive film 21 and the second conductive film 22 can affect the occurrence of a phenomenon known as superconducting transition, in which a transition to a superconducting state occurs. However, according to this embodiment, the first conductive film 21 and the second conductive film 22 can be formed with a desired thickness, and therefore, variations in read characteristics can be suppressed, particularly when the first conductive film 21 and the second conductive film 22 are used as read electrodes.

[0054] From the viewpoint of forming the second conductive film 22 with a desired thickness, the second angle β is preferably 95° or greater, more preferably 98° or greater, and even more preferably 100° or greater. From the viewpoint of preventing the diameter L3 from increasing, the second angle β is preferably 110° or less, more preferably 107° or less, and even more preferably 103° or less. Furthermore, from the viewpoint of forming the first conductive film 21 with a desired thickness, the first angle α is preferably 130° or greater, more preferably 135° or greater, and even more preferably 140° or greater. From the viewpoint of preventing the diameter L4 of the first groove 50 on the upper surface 11 of the quantum bit substrate 10 from increasing, the first angle α is preferably 150° or less, more preferably 145° or less, and even more preferably 140° or less.

[0055] 9(a), in Example 1, the area S1 of the bottom surface 51 of the first groove 50 is 1 / 25 to 1 / 4 times the area S2 of the bottom surface 61 of the second groove 60. The area S1 of the bottom surface 51 of the first groove 50 is 1 / 25 to 1 / 4 times the area S2 of the bottom surface 61 of the second groove 60, thereby improving the reliability of the electrical connection between the first conductive film 21 and the second conductive film 22. The area S1 of the bottom surface 51 of the first groove 50 is 1 / 4 to 1 / 4 times the area S2 of the bottom surface 61 of the second groove 60, thereby preventing a decrease in the mechanical strength of the first conductive film 21 and the second conductive film 22.

[0056] From the viewpoint of reliability of electrical connection, the area S1 of the bottom surface 51 of the first groove 50 is preferably 1 / 20 times or more, more preferably 1 / 15 times or more, and even more preferably 1 / 10 times or more of the area S2 of the bottom surface 61 of the second groove 60. From the viewpoint of suppressing a decrease in mechanical strength, the area S1 of the bottom surface 51 of the first groove 50 is preferably 1 / 5 times or less, more preferably 1 / 6 times or less, and even more preferably 1 / 8 times or less of the area S2 of the bottom surface 61 of the second groove 60.

[0057] In Example 1, the thickness of the second conductive film 22 is 50 nm or more and 500 nm or less. In such a case, in the comparative example, the strength of the second conductive film 22 is reduced, making it more susceptible to breakage. Therefore, in such a case, it is preferable to use Example 1. The thickness of the second conductive film 22 may be 50 nm or more and 300 nm or less.

[0058] In Example 1, as shown in FIG. 4( a), the second groove 60 is formed using a Bosch process, which involves repeatedly performing an etching process and a protective film formation process. After the second groove 60 is formed, the Josephson element 31 constituting the quantum bit 30 is formed on the upper surface 11 of the quantum bit substrate 10, as shown in FIG. 5( c). When the Bosch process is used to form the second groove 60, scallops are generated on the side surface 62 of the second groove 60. Therefore, the scallops are removed using an etchant to flatten the side surface 62. By forming the Josephson element 31 after the second groove 60, the Josephson element 31 is not affected by the etchant used to remove the scallops. This suppresses changes in the characteristics of the Josephson element 31. Furthermore, although a temperature rise occurs during the formation of the second groove 60, by forming the Josephson element 31 after the formation of the second groove 60, the Josephson element 31 is not affected by the temperature rise, thereby suppressing changes in its characteristics.

[0059] In Example 1, as shown in FIGS. 4(a) to 6(a), Josephson elements 31 constituting quantum bits 30 are formed on the upper surface 11 of the quantum bit substrate 10 after the second grooves 60 are formed and before the first grooves 50 are formed. By forming the Josephson elements 31 before the formation of the first grooves 50, no grooves are formed on the upper surface 11 of the quantum bit substrate 10 when the Josephson elements 31 are formed. This reduces the variation in the film thickness of the laminated resist film 72 shown in FIGS. 7(a) to 8(a). This reduces the variation in the width and thickness of the superconducting films 33 and 34 in the Josephson elements 31, thereby reducing the variation in the characteristics of the Josephson elements 31.

[0060] 2(b), in Example 1, the bottom surface 51 of the first groove 50 is flush with the bottom surface 61 of the second groove 60. This allows the first conductive film 21 and the second conductive film 22 to be in good contact with each other, improving the reliability of the electrical connection. Furthermore, since the depth D2 of the second groove 60 is greater than the depth D1 of the first groove 50, it is possible to prevent the diameter L4 (see FIG. 6(a)) of the first groove 50 from becoming larger. [Example]

[0061] The plan view and cross-sectional view of the quantum device according to the second embodiment are the same as those of the first embodiment shown in FIGS. 1, 2(a) and 2(b), and therefore will not be illustrated or described.

[0062] [Manufacturing method] 12(a) to 13(b) are cross-sectional views showing a method for manufacturing a quantum device according to Example 2. As shown in Fig. 12(a), the same steps as those shown in Fig. 4(a) to 5(b) in Example 1 are performed to form a third conductive film 23 on the upper surface 11 of the quantum bit substrate 10. A second conductive film 22 is formed on the lower surface 12 of the quantum bit substrate 10 and on the bottom surface 61 and side surface 62 of the second groove 60.

[0063] As shown in FIG. 12(b), a patterned resist film 77 is formed on the upper surface 11 of the quantum bit substrate 10. Using the resist film 77 as a mask, a first groove 50 having a bottom surface 51 and a side surface 52 is formed on the upper surface 11 of the quantum bit substrate 10. As in Example 1, the first groove 50 is formed so as to reach only a portion of the bottom surface 61 of the second groove 60. As a result, a portion of the second conductive film 22 formed on the bottom surface 61 of the second groove 60 is exposed from the bottom surface 51 of the first groove 50. The plan view of the connection portion between the first groove 50 and the second groove 60 is the same as that shown in FIG. 9(a).

[0064] As shown in FIG. 12(c), after removing the resist film 77, a patterned resist film 78 is formed on the upper surface 11 of the quantum bit substrate 10. Using the resist film 78 as a mask, the first conductive film 21 is formed by, for example, vacuum deposition. The first conductive film 21 is formed from the bottom surface 51 and side surface 52 of the first groove 50 to the upper surface of the third conductive film 23, and is in contact with the third conductive film 23. A gap 24 is formed inside the first conductive film 21 in the first groove 50. The plan view of the contact portion between the first conductive film 21 and the second conductive film 22 is the same as that shown in FIG. 9(b).

[0065] As shown in FIG. 13(a), the resist film 78 and the first conductive film 21 formed on the resist film 78 are removed by lift-off.

[0066] As shown in Figure 13(b), a quantum bit 30 (see Figure 1) is formed by forming a Josephson device 31 on the upper surface 11 of the quantum bit substrate 10. The Josephson device 31 is formed by the same method as in Figures 7(a) to 8(b). In this way, a quantum device according to Example 2 is formed.

[0067] According to the second embodiment, as shown in FIG. 12(a), a second groove 60 is formed on the lower surface 12 (second surface) of the quantum bit substrate 10. A second conductive film 22 is formed on the bottom surface 61 and side surface 62 of the second groove 60. As shown in FIG. 12(b), after the second conductive film 22 is formed, a first groove 50 is formed on the upper surface 11 (first surface) of the quantum bit substrate 10, reaching a portion of the bottom surface 61 of the second groove 60. As shown in FIG. 12(c), a first conductive film 21 is formed on the bottom surface 51 and side surface 52 of the first groove 50. In this way, since the first groove 50 is formed so as to reach a portion of the bottom surface 61 of the second groove 60, a decrease in the mechanical strength of the first conductive film 21 and the second conductive film 22 can be suppressed, as in the first embodiment.

[0068] In Example 2, as shown in FIGS. 12(a) to 13(b), the Josephson elements 31 that constitute the quantum bits 30 are formed on the upper surface 11 of the quantum bit substrate 10 after the second grooves 60 and the first grooves 50 are formed. Because the Josephson elements 31 are formed after the second grooves 60 are formed, they are not affected by the etchant used to remove scallops generated in the Bosch process, as in Example 1, and changes in the characteristics of the Josephson elements 31 can be suppressed. By forming the Josephson elements 31 after the first grooves 50, a resist film or the like is not formed on the Josephson elements 31. For example, if a protective film such as a silicon oxide film is provided between the resist film 77 used to form the first grooves 50 and the Josephson elements 31, the protective film is not formed on the Josephson elements 31. Therefore, the Josephson elements 31 are less likely to be damaged. Furthermore, by forming the Josephson elements 31 after the second grooves 60 and the first grooves 50, changes in the characteristics of the Josephson elements 31 due to aging can be suppressed.

[0069] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims.

[0070] In addition, the following supplementary notes are provided in relation to the above description. (Appendix 1) A method for manufacturing a quantum device comprising a quantum bit and a quantum bit substrate having a first surface on which the quantum bit is formed, the method comprising the steps of: forming a second groove in the second surface of the quantum bit substrate; forming a second conductive film on a bottom surface and side surfaces of the second groove; after the step of forming the second conductive film, forming a first groove in the first surface, the first groove reaching a part of the bottom surface of the second groove; forming a first conductive film on the bottom surface and side surfaces of the first groove; and forming the quantum bit on the first surface. (Appendix 2) The method for manufacturing a quantum device according to Appendix 1, wherein the step of forming the second trench forms the second trench having a depth greater than that of the first trench. (Appendix 3) The method for manufacturing a quantum device described in Appendix 1 or 2, characterized in that the step of forming the second groove forms the second groove such that a second angle formed between the side surface of the second groove and the second surface is an obtuse angle, and the step of forming the first groove forms the first groove such that a first angle formed between the side surface of the first groove and the first surface is larger than the second angle. (Appendix 4) The method for manufacturing a quantum device according to appendix 1 or 2, wherein the step of forming the first trench forms the first trench such that the area of ​​the bottom surface of the first trench is 1 / 25 to 1 / 4 times the area of ​​the bottom surface of the second trench. (Appendix 5) The method for manufacturing a quantum device according to appendix 1 or 2, wherein the second conductive film has a thickness of 50 nm or more and 500 nm or less. (Appendix 6) A method for manufacturing a quantum device according to Appendix 1, wherein the step of forming the second groove uses a Bosch process in which an etching step and a protective film formation step are repeatedly performed to form the second groove, and the step of forming the quantum bit forms the quantum bit on the first surface after forming the second groove. (Appendix 7) A method for manufacturing a quantum device as described in Appendix 1, characterized in that the step of forming the quantum bit is performed after the step of forming the second groove and before the step of forming the first groove, thereby forming the quantum bit on the first surface. (Appendix 8) The method for manufacturing a quantum device according to appendix 1, wherein the step of forming the quantum bit includes forming the quantum bit on the first surface after forming the first groove. (Supplementary Note 9) The method for manufacturing a quantum device according to any one of Supplementary Notes 6 to 8, wherein the quantum bit includes a Josephson element. (Appendix 10) A quantum device comprising: a quantum bit substrate; a quantum bit provided on a first surface of the quantum bit substrate; a second groove provided on a second surface of the quantum bit substrate; a second conductive film provided on a bottom surface and a side surface of the second groove; a first groove provided on the first surface and reaching a part of the bottom surface of the second groove; and a first conductive film provided on a bottom surface and a side surface of the first groove. (Appendix 11) The quantum device described in Appendix 10, characterized in that the bottom surface of the first groove is flush with the bottom surface of the second groove, and the depth of the second groove is greater than the depth of the first groove. [Explanation of symbols]

[0071] 10...qubit substrate, 11...top surface, 12...bottom surface, 13...central electrode, 14...peripheral electrode, 21...first conductive film, 22...second conductive film, 23...third conductive film, 24...gap, 25...gap, 26...plane, 27...plane, 30...qubit, 31...Josephson element, 32...capacitor, 33...superconducting film, 34...superconducting film, 35...insulating film, 36...Josephson junction, 40...coupling wiring, 50...first groove, 51...bottom surface, 52...side surface, 60...second groove, 61...bottom surface, 62...side surface, 70...resist film, 7 1...resist film, 72...laminated resist film, 73...upper layer, 74...lower layer, 75...resist film, 76...resist film, 77...resist film, 78...resist film, 79...metal film, 80...pattern, 81...opening, 82...opening, 83...void, 84...region, 100...quantum device, 110...qubit substrate, 111...upper surface, 112...lower surface, 121...conductive film, 122...conductive film, 131...Josephson element, 150...groove, 151...bottom surface, 152...side surface, 160...groove, 161...bottom surface, 162...side surface,

Claims

1. A method for manufacturing a quantum device including a quantum bit and a quantum bit substrate having a first surface on which the quantum bit is formed, comprising: forming a second groove in a second surface of the quantum bit substrate; forming a second conductive film on the bottom and side surfaces of the second groove; forming a first groove in the first surface, the first groove reaching a portion of the bottom surface of the second groove, after the step of forming the second conductive film; forming a first conductive film on the bottom and side surfaces of the first trench; forming the quantum bit on the first surface.

2. 2. The method for manufacturing a quantum device according to claim 1, wherein the step of forming the second trench comprises forming the second trench to have a depth greater than a depth of the first trench.

3. the step of forming the second groove includes forming the second groove such that a second angle formed between the side surface of the second groove and the second surface is an obtuse angle; 3. The method for manufacturing a quantum device according to claim 1, wherein the step of forming the first groove includes forming the first groove such that a first angle formed between the side surface of the first groove and the first surface is larger than the second angle.

4. 3. The method for manufacturing a quantum device according to claim 1, wherein the step of forming the first trench includes forming the first trench such that the area of ​​the bottom surface of the first trench is 1 / 25 to 1 / 4 times the area of ​​the bottom surface of the second trench.

5. the step of forming the second groove includes forming the second groove using a Bosch process in which an etching step and a protective film forming step are repeatedly performed; The method for manufacturing a quantum device according to claim 1 , wherein the step of forming the quantum bit comprises forming the quantum bit on the first surface after forming the second groove.

6. 2. The method for manufacturing a quantum device according to claim 1, wherein the step of forming the quantum bit comprises forming the quantum bit on the first surface after the step of forming the second groove and before the step of forming the first groove.

7. 2. The method for manufacturing a quantum device according to claim 1, wherein the step of forming the quantum bit includes forming the quantum bit on the first surface after forming the first groove.

8. 8. The method for manufacturing a quantum device according to claim 5, wherein the quantum bit includes a Josephson element.

9. a qubit substrate; a quantum bit provided on a first surface of the quantum bit substrate; a second groove provided on a second surface of the quantum bit substrate; a second conductive film provided on the bottom and side surfaces of the second groove; a first groove provided on the first surface and reaching a portion of the bottom surface of the second groove; a first conductive film provided on the bottom and side surfaces of the first trench.

10. the bottom surface of the first groove is flush with the bottom surface of the second groove; 10. The quantum device of claim 9, wherein the depth of the second trench is greater than the depth of the first trench.

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