Superconducting device and method of manufacturing the same

Abstract

To provide a superconducting device and a method of manufacturing the same that suppresses the generation of intermetallic compounds between first and second metal bumps that constitute a bump bond.SOLUTION: In a superconducting device that utilizes the characteristics of superconductivity, a diffusion prevention layer 5 is formed at the interface of a joint between a first metal bump 2 formed on a first superconducting circuit chip 1 provided with a functional circuit and a second metal bump 4 formed on a second superconducting circuit chip 3 connected to the first superconducting circuit chip 1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a superconducting device and a method for manufacturing the same.

Background Art

[0002] Patent Document 1 discloses a technique related to a bump bond that connects first and second quantum chips each having a functional circuit. The bump bond has a configuration in which a first bump pad made of, for example, Al (aluminum) provided on the first chip side and a second bump pad made of, for example, In (indium) provided on the second chip side are pressed against each other. In addition to the Al and In, materials having superconductivity such as Ni (niobium) and Sn (tin) are used for the bump pads.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the bump bond described in Patent Document 1 above, when different metals are used for the first bump pad and the second bump pad, an intermetallic compound between the dissimilar metals may be generated on these bonding surfaces. Although materials having superconductivity are used for both the first and second bump pads, the intermetallic compound does not necessarily have the same superconductivity as these superconducting materials. In addition, since the intermetallic compound may have various characteristics depending on conditions such as temperature and pressure during the press bonding (including not only during the press bonding but also the history of pressure and temperature changes before and after), even if it has superconductivity, it is not easy to suppress the variation in its superconducting characteristics within a predetermined range.

[0005] The object of the present invention is to suppress the generation of intermetallic compounds in bump bonds used for connecting a plurality of superconducting chips constituting a superconducting device.

Means for Solving the Problem

[0006] In order to solve the above problems, the present invention proposes the following means. The superconducting device according to the present invention is a superconducting device using superconducting characteristics, characterized in that a diffusion prevention layer is formed at the interface of the joint between a first metal bump formed on a first superconducting circuit chip provided with a functional circuit and a second metal bump formed on a second superconducting circuit chip connected to the first superconducting circuit chip.

[0007] Further, a method for manufacturing a superconducting device according to the present invention is a method for manufacturing a superconducting device using superconducting characteristics, characterized by having a step of forming a diffusion prevention layer at the interface of the joint between a first metal bump formed on a first superconducting circuit chip provided with a functional circuit and a second metal bump formed on a second superconducting circuit chip connected to the first superconducting circuit chip.

Advantages of the Invention

[0008] According to the present invention, the generation of intermetallic compounds associated with the bonding between the first and second metal bumps can be suppressed.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] The superconducting device according to the minimum configuration example of the present invention will be described with reference to FIG. 1. This superconducting device is a superconducting device using superconducting characteristics, and includes a first metal bump 2 formed on a first superconducting circuit chip 1 provided with a functional circuit, and a second superconducting circuit chip 3 connected to the first superconducting circuit chip 1. A diffusion prevention layer 5 is formed at the interface of the joint with the second metal bump 4 formed thereon.

[0011] According to the above configuration, when the first superconducting circuit chip 1 and the second superconducting circuit chip 3 are joined to perform bump bonding, the diffusion prevention layer 5 is interposed between the first metal bump 2 and the second metal bump 4 that are pressed against each other. Therefore, it is possible to prevent the diffusion of molecules between the metal material constituting the first metal bump 2 and the metal material constituting the second metal bump 4. Therefore, generation of an intermetallic compound between the first metal bump 2 and the second metal bump 4 can be suppressed, and a decrease in superconductivity or variation caused by generation of the intermetallic compound in bump bonding using the first metal bump 2 and the second metal bump 4 can be suppressed.

[0012] A method for manufacturing a superconducting device according to a minimum configuration example of the present invention is a method for manufacturing a superconducting device using superconducting characteristics, and includes a step of forming a diffusion prevention layer 5 on an interface of a joint portion between a first metal bump 2 formed on a first superconducting circuit chip 1 provided with a functional circuit and a second metal bump 4 formed on a second superconducting circuit chip 3 connected to the first superconducting circuit chip 1.

[0013] According to the above configuration, between a step of facing the first superconducting circuit chip 1 and the second superconducting circuit chip 3 with each other and a step of press-bonding the first metal bump 2 and the second metal bump 4 therebetween, a diffusion prevention layer 5 for preventing diffusion of metals constituting the first metal bump 2 and the second metal bump 4 can be formed, generation of an intermetallic compound in bump bonding in which the first metal bump 2 and the second metal bump 4 are integrated can be suppressed, and a decrease in superconductivity or variation can be suppressed.

[0014] A first embodiment of the present invention will be described with reference to FIGS. 2 to 6. FIG. 2 shows a superconducting device according to the first embodiment, in which a first metal bump 20 is provided on a lower surface of a first superconducting circuit chip 10 provided with a functional circuit using superconducting characteristics (including an interposer composed of a superconducting conductor circuit for connection to a circuit board or the like as well as a logic circuit), and a second metal bump 40 is provided on an upper surface of a second superconducting circuit chip 30 connected to the functional circuit of the first superconducting circuit chip 10 and provided with a functional circuit using superconducting characteristics, and has a basic configuration in which a diffusion prevention layer 50 for preventing diffusion of metal molecules between different metals is provided between the first metal bump 20 and the second metal bump 40. Note that FIG. 2 shows the separated state of each of the elements constituting the superconducting device before they are integrally joined for convenience of explanation. By pressing these elements against each other vertically (in the direction opposite to each other between the first and second superconducting circuit chips 10 and 30, i.e., the vertical direction in FIG. 2), an integrated superconducting device as exemplified in FIG. 1 is formed.

[0015] The first metal bump 20 and the second metal bump 40 are bump pads for establishing a bump bond by being integrally joined. For example, they are made of Nb (niobium), Al (aluminum), Sn (tin), In (indium). In the illustrated example, the cross-section is circular and the tip is formed flat. Also, in the first embodiment, Al is used as the material of the first metal bump 20 and In is used as the material of the second metal bump 40. That is, in the first embodiment, the first and second metal bumps 20 and 40 are made of different metals.

[0016] The diffusion prevention layer 50 is made of metals such as Al (aluminum) and In (indium) and their compounds, inorganic materials such as Si (silicon) oxide film, and organic materials, and has the same planar shape as the cross-section (tip surface) of the first and second metal bumps 20 and 40. More specifically, as materials that can be used for the diffusion prevention layer 50, metal oxides and semi-metal oxides such as aluminum oxide, indium oxide, niobium oxide, titanium oxide, tin oxide, tantalum oxide, silicon oxide, metal nitrides and semi-metal nitrides such as aluminum nitride, indium nitride, titanium nitride, tin nitride, tantalum nitride, silicon nitride, oxynitrides such as silicon oxynitride and titanium oxynitride, or other ceramics, etc. can be mentioned. Also, organic resin materials such as epoxy, phenol, acrylic, urethane, styrene, polyimide, and polyamide may be used. Also, the thickness of the diffusion prevention layer 50 needs to be set to a thickness that does not exceed the coherence length of the constituent material in order to ensure superconductivity equal to or higher than that of the metals constituting the first and second metal bumps 20 and 40. Note that the coherence length of the materials that can be adopted for the diffusion prevention layer 50 is as shown in the table in FIG. 12, for example.

[0017] The anti-diffusion layer 50 is set to a thickness (vertical dimension in FIG. 2 etc.) not exceeding the coherence length ξ capable of obtaining the upper critical magnetic field H calculated by the following formula (1) in order to realize a superconducting state according to the materials exemplified in the table shown in FIG. 12. H = φ0 / πξ 2 ……Formula (1) However, φ0 is 2.0678×10 -15 T·m 2 [Tesla·meter squared] That is, as shown in formula (1), since the upper critical magnetic field H is inversely proportional to the square of the coherence length ξ, the thickness of the anti-diffusion layer 50 is set to a value equal to or less than a value at which the upper critical magnetic field H in the superconducting state becomes a desired value or more.

[0018] Further, the anti-diffusion layer 50 is not limited to a member separated from the first and second metal bumps 20 and 40. As shown in Modification 1 of FIG. 3, the anti-diffusion layer 50 may be integrally formed at the tip of the second metal bump 40 and pressed against the upper first metal bump 20 in this state. Also, as shown in Modification 2 of FIG. 4, the anti-diffusion layer 50 may be integrally formed at the tip of the first metal bump 20 and pressed against the lower second metal bump 40 in this state.

[0019] As shown in Modifications 1 and 2, as a method of forming an anti-diffusion layer in a predetermined range (range in contact during pressing) of the first and second metal bumps 20 and 40, a method of forming a compound serving as an anti-diffusion layer only in a predetermined region (region at the tip of the first metal bump 20 to be left as the anti-diffusion layer 50A) of a metal material on whose surface no oxide film or the like has occurred is common. In addition to this common method, as shown in Modification 3 of FIGS. 5 and 6, a method of removing a part (outer peripheral part excluding the end face) of the anti-diffusion layer 50 covering the entire surface of the first (or second) metal bump 20 (40) and leaving only the joint surface may be adopted. More specifically, when the surface is covered with an oxide film (diffusion prevention layer) 50A due to contact with the atmosphere, a method may be adopted in which the oxide film on the outer periphery of the first or second metal bump 20(40) made of Al is removed by machining or chemical treatment in a non-oxidizing environment such as a vacuum chamber or an inert gas chamber, and a part thereof is left as the diffusion prevention layer 50A as shown in FIG. 6. Further, when the first (or second) metal bump 20(40) is not made of a metal material having the property of generating an oxide film in the atmosphere, the material to be the first (or second) metal bump 20(40) is placed in a gas in an oxidizing atmosphere, or immersed in an oxidizing liquid, or applied to the surface to form an oxide film (diffusion prevention layer) 50A as shown in FIG. 5, and a part thereof is removed to form the diffusion prevention layer 50A only at the tip of the first (or second) metal bump 20(40).

[0020] FIG. 7 shows a second embodiment of the present invention. In the figure, the same reference numerals are given to the components common to FIGS. 2 to 6, and the description is simplified. In this second embodiment, the first metal bump 20A is configured to have a larger diameter (a shape in which the circle formed by the cross section has a larger diameter) than the second metal bump 40A. Also in this second embodiment, it is assumed that Al is adopted as the first metal bump 20A and In having a lower melting point than the Al is adopted as the second metal bump 40A. Regarding the thickness of the diffusion prevention layer 50A as well, similar to the first embodiment, it is set to a predetermined value in consideration of the coherence length inherent to the material so as to satisfy the required superconductivity.

[0021] According to the configuration of the second embodiment, by forming the first metal bump 20A to have a larger diameter than the second metal bump 40B, when these first and second metal bumps 20A (40A) are pressed in the vertical direction of FIG. 7, even if the tip of the second metal bump 40A with a low melting point is deformed (so that the diameter expands) due to the pressing, since the diameter of the diffusion prevention layer 50A at the tip of the first metal bump 20A is large, when pressing the first and second metal bumps 20A and 40B, the relatively low melting point metal (In) constituting the second metal bump 40A melts or deforms and wraps around the outer peripheral surface of the first metal bump 20A (the surface where the diffusion prevention layer 50A is not formed), contacts and diffuses into the metal constituting the first metal bump 20A on this outer peripheral surface, and the phenomenon of forming an intermetallic compound between these metals can be more reliably prevented.

[0022] FIG. 8 shows a second embodiment of the present invention. Components common to FIGS. 2 to 7 in the figure are denoted by the same reference numerals, and the description is simplified. In this third embodiment, similar to the second embodiment, the first metal bump 20B is formed to have a larger diameter (a shape in which the circle formed by the cross-section is larger in diameter) than the second metal bump 40B. Furthermore, in the third embodiment, the surface of the lower end (diffusion prevention layer 50B) of the first metal bump 20B is formed as a concave surface, and the tip of the second metal bump 40B is formed as a convex surface corresponding to the concave surface (although it is expressed as a curved shape in the cross-section shown in FIG. 8, three-dimensionally, it is a curved surface with a radius of curvature corresponding to the diffusion prevention layer 50B). Also in this second embodiment, it is assumed that Al is adopted as the first metal bump 20B and In with a lower melting point than the Al is adopted as the second metal bump 40B. Regarding the thickness of the diffusion prevention layer 50B as well, it is set to a predetermined value to have the same superconductivity as in the first embodiment.

[0023] According to the configuration of the third embodiment, by forming the first metal bump 20B to have a larger diameter than the second metal bump 40B, when the first and second metal bumps 20A(40A) are pressed in the vertical direction of FIG. 7, even if the tip of the second metal bump 40A with a lower melting point is deformed (such that the diameter expands) due to the pressing, the diameter of the diffusion prevention layer 50B at the tip of the first metal bump 20B is large, and moreover, it has a concave surface so as to cover the surface of the second metal bump. Therefore, when the first and second metal bumps 20B and 40B are pressed, the relatively low melting point metal (In) constituting the second metal bump 40A can be more reliably prevented from flowing around and contacting the outer peripheral surface of the first metal bump 20B (the surface where the diffusion prevention layer 50B is not formed) to form an intermetallic compound.

[0024] FIG. 9 shows a fourth embodiment of the present invention. Components common to FIGS. 2 to 8 in the figure are denoted by the same reference numerals, and the description is simplified. This fourth embodiment has a configuration in which the upper surface and the outer periphery of the tip (the upper end in FIG. 9) of the second metal bump 40 are covered by a diffusion prevention layer 50C. The diffusion prevention layer 50C has a shape in which the tip of a cylindrical portion 51 covering the outer periphery of the end of the second metal bump 40C is covered by a flat portion 52 integral therewith. The flat portion 52 is formed to have a thickness with a predetermined superconductivity, similar to the first embodiment.

[0025] In the fourth embodiment described above, since the entire tip of the second metal bump 40 is covered by the diffusion prevention layer 50C, when the first and second metal bumps 20 and 40 are pressed, the metal constituting the second metal bump 40 does not come into contact with the metal constituting the first metal bump 20. Therefore, the generation of intermetallic compounds due to the contact of the first and second metal bumps 20 and 40 can be prevented. Note that the diffusion prevention layer 50C may be provided on the first metal bump 20 instead of the second metal bump 40, or may be provided on both the first and second metal bumps 20 and 40. With this configuration, it is possible to more reliably prevent the generation of intermetallic compounds due to the diffusion of metal between the first and second metal bumps 20 and 40 than in the example of FIG. 8.

[0026] FIG. 10 shows a fifth embodiment of the present invention. In the figure, the same reference numerals are given to the components common to FIGS. 2 to 9 to simplify the description. This fifth embodiment has a configuration in which the tips of the first and second metal bumps 20 and 40 are covered with a diffusion prevention layer 50D. The diffusion prevention layer 50D includes a cylindrical portion 53 that covers the entire outer periphery of the first and second metal bumps 20 and 40, and a flat portion 52 that is formed integrally with the cylindrical portion 53 and is disposed between the first and second metal bumps 20 and 40. The cylindrical portion 53 has a cylindrical shape that covers the outer peripheries of the first and second metal bumps 20 and 40, and the flat portion 52 is disposed so as to cross the cylindrical portion 53.

[0027] According to the diffusion prevention layer 50D, direct contact between the first and second metal bumps 20 and 40 can be prevented, and the generation of intermetallic compounds between them can be prevented.

[0028] In the above first to fifth embodiments, the cross-sections (end faces) of the first and second metal bumps 20 and 40 etc. have been described as being circular, but they are not limited to perfect circles and may have a shape as shown in FIG. 11. FIG. 11(a) shows a first modification in which the first metal bump 20C is formed in a square shape with a side length larger than that of the second metal bump 40C. FIG. 11(b) shows a second modification in which the first metal bump 20D is square, the second metal bump 40D is circular with a diameter smaller than the inscribed circle of the square, and a third modification in which the second metal bump 40D is square and the first metal bump 20D is circular with a diameter larger than the circumscribed circle of the square. FIG. 11(c) shows a fourth modified example in which the first metal bump 20E is hexagonal and the second metal bump 40E is circular with a diameter smaller than the inscribed circle of the hexagon, and a fifth modified example in which the second metal bump 40E is hexagonal and the first metal bump is circular with a diameter larger than the circumscribed circle of the hexagon.

[0029] In these first to fifth modified examples, by covering the tip surfaces of the first metal bumps 20C to 20E and / or the second metal bumps 40C to 40E with a diffusion prevention film of the same shape, generation of an intermetallic compound can be prevented, similar to the first to fifth embodiments. Also, for the shapes of the first and second metal bumps exemplified in the first to fifth modified examples, it is desirable to select an appropriate shape according to the shape of the conductor pads and the shape of the conductor patterns of the superconducting circuit chips to be joined thereby.

[0030] In addition to indium (In) and aluminum (Al) employed in the embodiment, materials that can be used as the first metal bumps 20 (20A to 20E) and the second metal bumps 40 (40A to 40E) include, for example, tin (Sn), niobium (Nb), bismuth (Bi), yttrium (Y), lead (Pb), and alloys thereof. Also, the number, arrangement, constituent material, shape, and combinations thereof of the bump portions are not limited to those of the above embodiment.

[0031] As described above, the embodiments of the present invention have been described in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and also includes design changes and the like within the scope not departing from the gist of the present invention. The embodiments of the present invention can also be applied to superconducting devices using devices (quantum devices) that utilize quantum mechanical phenomena or chips (quantum chips) incorporating circuits that utilize quantum mechanical phenomena, but are not limited thereto.

[0032] Some or all of the above embodiments can also be described as in the following supplementary notes, but are not limited to the aspects specified in the supplementary notes. (Supplementary Note 1) A superconducting device using superconducting characteristics, characterized in that a diffusion prevention layer is formed at an interface of a joint portion between a first metal bump formed on a first superconducting circuit chip provided with a functional circuit and a second metal bump formed on a second superconducting circuit chip connected to the first superconducting circuit chip. (Appendix 2) The superconducting device according to Appendix 1, wherein the first metal bump and the second metal bump are superconducting materials. (Appendix 3) The superconducting device according to Appendix 2, wherein the thickness of the diffusion prevention layer is equal to or less than the coherence length of the first and second metal bumps. (Appendix 4) The superconducting device according to any one of Appendix 2 or 3, wherein, in addition to indium (In) and aluminum (Al), for example, tin (Sn), niobium (Nb), bismuth (Bi), yttrium (Y), lead (Pb), and alloys thereof, or a combination of two of these are selected as the first metal bump and the second metal bump. (Appendix 5) The superconducting device according to any one of Appendix 1 to 4, wherein niobium (Nb) is selected as the diffusion prevention layer. (Appendix 6) The superconducting device according to any one of Appendix 1 to 5, characterized in that the shapes of the first metal bump and the second metal bump in a plan view are different from each other. (Appendix 7) The superconducting device according to any one of Appendix 1 to 6, wherein the cross section of the first metal bump is circular, and the cross section of the second metal bump is circular with a smaller diameter than that of the first metal bump. (Appendix 8) The superconducting device according to any one of Appendix 1 to 7, characterized in that one of the surfaces of the first metal bump and the second metal bump facing each other is convex and the other is concave. (Appendix 9) The superconducting device according to any one of Appendix 1 to 8, characterized in that a diffusion prevention layer is provided on at least a part of the joint surface and the side surface of the first metal bump and the second metal bump. (Appendix 10) The superconducting device according to any one of Appendices 1 to 9, wherein the first metal bump and the second metal bump are made of different materials. (Appendix 11) The diffusion prevention layer is a metal oxide or a semi-metal oxide such as aluminum oxide, indium oxide, niobium oxide, titanium oxide, tin oxide, tantalum oxide, silicon oxide, a metal nitride or a semi-metal nitride such as aluminum nitride, indium nitride, titanium nitride, tin nitride, tantalum nitride, silicon nitride, an oxynitride such as silicon oxynitride, titanium oxynitride, or other ceramics, or an organic resin material such as epoxy, phenol, acrylic, urethane, styrene, polyimide, polyamide. The superconducting device according to any one of Appendices 1 to 3. (Appendix 12) A method for manufacturing a superconducting device using superconducting characteristics, the method comprising a step of forming a diffusion prevention layer at an interface of a joint between a first metal bump formed on a first superconducting circuit chip provided with a functional circuit and a second metal bump formed on a second superconducting circuit chip connected to the first superconducting circuit chip. (Appendix 13) The step of forming the diffusion prevention layer is a step of interposing the diffusion prevention layer in a region where at least one of the first metal bump and the second metal bump is pressure-bonded to the other. The method for manufacturing a superconducting device according to Appendix 12. (Appendix 14) The step of forming the diffusion prevention layer is a step of removing an oxide film formed on at least one of the surfaces of the first metal bump and the second metal bump in a region excluding these joint surfaces. The method for manufacturing a superconducting device according to Appendix 12. (Appendix 15) The step of forming the diffusion prevention layer is a step of forming an oxide film on the joint surfaces of at least one of the surfaces of the first metal bump and the second metal bump that are not covered with an oxide film. The method for manufacturing a superconducting device according to Appendix 12.

Industrial Applicability

[0033] The present invention can be used for superconducting device apparatuses and their manufacturing.

Explanation of Signs

[0034] 1 First superconducting circuit chip 2 First metal bump 3 Second superconducting circuit chip 4 Second metal bump 5 Diffusion prevention layer 10 First superconducting circuit chip 20, 20A, 20B, 20C, 20D, 20E First metal bump 30 Second superconducting circuit chip 40, 40A, 40B, 40C, 40D, 40E Second metal bump 50, 50A, 50B, 50C, 50D Diffusion prevention layer 51, 53 Cylindrical part 52 Planar part

Claims

1. A superconducting device using superconducting characteristics, characterized in that a diffusion prevention layer is formed at the interface of the joint between a first metal bump formed on a first superconducting circuit chip provided with a functional circuit and a second metal bump formed on a second superconducting circuit chip connected to the first superconducting circuit chip.

2. The superconducting device according to claim 1, wherein the first metal bump and the second metal bump are superconducting materials.

3. The superconducting device according to claim 2, wherein the thickness of the diffusion prevention layer is equal to or less than the coherence length of the first and second metal bumps.

4. The superconducting device according to claim 1, wherein the shapes of the first metal bump and the second metal bump in plan view are different from each other.

5. The superconducting device according to claim 1, wherein one of the surfaces of the first metal bump and the second metal bump facing each other is convex and the other is concave.

6. The superconducting device according to claim 1, comprising a diffusion prevention layer on at least a part of the joint surface and the side surface of the first metal bump and the second metal bump.

7. The superconducting device according to claim 1, wherein the first metal bump and the second metal bump are made of different materials.

8. A method for manufacturing a superconducting device using superconducting characteristics, characterized by having a step of forming a diffusion prevention layer at the interface of the joint between a first metal bump formed on a first superconducting circuit chip provided with a functional circuit and a second metal bump formed on a second superconducting circuit chip connected to the first superconducting circuit chip.

9. The method for manufacturing a superconducting device according to claim 8, wherein the step of forming the diffusion prevention layer is a step of removing an oxide film formed on at least one of the surfaces of the first metal bump and the second metal bump in a region excluding these joint surfaces.

10. The method for manufacturing a superconducting device according to claim 8, wherein the step of forming the diffusion prevention layer is a step of forming an oxide film on the joint surfaces of at least one of the surfaces of the first metal bump and the second metal bump not covered with an oxide film.

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