Method for manufacturing superconducting quantum devices

Abstract

The objective is to improve the Q-factor of a superconducting quantum device that incorporates a superconducting quantum circuit formed in a thin film region of an insulating film. [Solution] A method for manufacturing a superconducting quantum device comprises: an insulating film formation step of forming an insulating film on a substrate; a protective film formation step of forming a protective film on the insulating film; a thin film region formation step of etching from the back surface of the substrate using the protective film as a mask to form a thin film region on the insulating film formed on the surface of the substrate that is not supported by the substrate; a protective film removal step of removing the protective film after the thin film region has been formed; and a superconducting quantum circuit formation step of forming a superconducting quantum circuit on the thin film region.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a superconducting quantum device.

Background Art

[0002] Patent Document 1 below discloses an X-ray exposure mask including a silicon substrate held by a support, an X-ray transmission film formed on the silicon substrate, and an X-ray absorption layer pattern formed on the X-ray transmission film. In this mask, first, a silicon nitride or silicon carbide having a thickness of about 2 μm as a membrane is formed on a silicon substrate having a thickness of 0.5 to 2 mm by various CVDs, and then an X-ray absorber such as tungsten or a tungsten compound having a thickness of 0.5 to 1 μm is formed by sputtering. Further, a pattern of the X-ray absorber is formed. Thereafter, the silicon substrate is etched from the back surface with a KOH solution, and a glass support ring having a thickness of about 5 mm is adhered.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, a superconducting quantum device including a superconducting resonator is used in a quantum computer or the like. Improving the internal Q value in a superconducting resonator has been a major issue not only in the field of quantum computers but also in the fields of astronomy and optomechanics. Conventionally, a superconducting resonator prototyped on an insulating thin film, like the X-ray absorption layer pattern formed on the X-ray transmission film of Patent Document 1 above, has been prototyped for the purpose of coupling with a mechanical resonator. However, as an application of quantum information, the microwave characteristics of a superconducting resonator prototyped on an insulating thin film have not been paid much attention. In recent years, research has revealed that one of the advantages of fabricating superconducting resonant circuits on insulating thin films such as SiN (silicon nitride) is that it prevents phonons from propagating to the bulk substrate when high-energy waves (such as gamma waves) collide. However, the reported internal Q-factor of superconducting resonators is 10 5 This is on the order of magnitude lower than the Q-factor of superconducting resonators prototyped using conventional state-of-the-art methods, which is about one to two orders of magnitude lower.

[0005] The purpose of this disclosure is to provide a method for manufacturing superconducting quantum devices that solves the above-mentioned problems. [Means for solving the problem]

[0006] To address the above issues, this disclosure proposes the following measures. A method for manufacturing a superconducting quantum device according to this disclosure comprises: an insulating film formation step of forming an insulating film on a substrate; a protective film formation step of forming a protective film on the insulating film; a thin film region formation step of etching from the back surface of the substrate using the protective film as a mask to form a thin film region on the insulating film formed on the surface of the substrate that is not supported by the substrate; a protective film removal step of removing the protective film after the formation of the thin film region; and a superconducting quantum circuit formation step of forming a superconducting quantum circuit on the thin film region. [Effects of the Invention]

[0007] According to the above disclosure, the Q-factor of a superconducting quantum device comprising a superconducting quantum circuit formed in a thin film region of an insulating film can be improved. [Brief explanation of the drawing]

[0008] [Figure 1] This is a flowchart of the manufacturing method for a superconducting quantum device according to the minimum configuration example of this disclosure. [Figure 2] This is a schematic cross-sectional view of a superconducting quantum device according to one embodiment of the present disclosure. [Figure 3] This is an explanatory diagram of a method for manufacturing a superconducting quantum device according to one embodiment of the present disclosure. [Figure 4] This is an explanatory diagram of a method for manufacturing a superconducting quantum device according to one embodiment of the present disclosure. [Figure 5] This is an explanatory diagram of a method for manufacturing a superconducting quantum device according to one embodiment of the present disclosure. [Figure 6] This is a flowchart of the steps included in the superconducting quantum circuit formation process according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0009] A minimum configuration example of this disclosure will be described with reference to Figure 1. Figure 1 is a flowchart of the manufacturing method for a superconducting quantum device according to the minimum configuration example of this disclosure. As shown in Figure 1, the method for manufacturing the superconducting quantum device 1 of this disclosure comprises an insulating film formation step S1, a protective film formation step S2, a thin film region formation step S3, a protective film removal step S4, and a superconducting quantum circuit formation step S5.

[0010] In the insulating film formation step S1, an insulating film is formed on the substrate. In the protective film formation step S2, a protective film (protective resist) is formed on the insulating film. In the thin film region formation step S3, the protective film is used as a mask to etch from the back surface of the substrate, forming a thin film region (membrane) on the insulating film formed on the surface of the substrate that is not supported by the substrate. In the protective film removal step S4, the protective film is removed after the thin film region has been formed. In the superconducting quantum circuit formation step S5, a superconducting quantum circuit is formed on the thin film region.

[0011] Incidentally, when forming a superconducting quantum circuit in a thin film region of an insulating layer in the order disclosed in Patent Document 1, first, a SiN (silicon nitride) film is formed on a silicon substrate by LPCVD (low-pressure chemical vapor deposition). Next, after forming a superconducting quantum circuit on the SiN film, a thin film region of the SiN film is formed by etching from the back surface of the silicon substrate using DRIE (deep silicon reactive ion etching) and an aqueous KOH (potassium hydroxide) solution.

[0012] One problem with this conventional method is the poor compatibility between superconducting quantum circuits and KOH. When etching a bulk silicon substrate from the back with KOH, a protective film needs to be applied to protect the superconducting quantum circuit from KOH. This protective film contributes to the Q-factor of the superconducting quantum circuit formed on the SiN film as dielectric loss. In other words, if the superconducting quantum circuit is formed before etching the silicon substrate from the back, it is not possible to remove the protective film with a strong acid, leaving a source of dielectric loss on the surface of the superconducting quantum device.

[0013] In contrast, according to the method shown in Figure 1, after etching the back surface of the substrate (thin film region formation step S3), a superconducting quantum circuit is formed on the thin film region (membrane) of the insulating layer on the surface of the substrate (superconducting quantum circuit formation step S5). This allows for the removal of the protective film, which is a source of dielectric loss, by including the protective film removal step S4 before the superconducting quantum circuit formation step S5. Therefore, the dielectric loss sources remaining on the surface of the superconducting quantum circuit can be reduced, thereby improving the Q-factor of the superconducting quantum device.

[0014] Next, an embodiment of this disclosure will be described with reference to Figures 1, 2, and 6.

[0015] Figure 2 is a schematic cross-sectional view of a superconducting quantum device 1 according to one embodiment of the present disclosure. As shown in Figure 2, the superconducting quantum device 1 comprises a substrate 10, an insulating film 20, and a superconducting material film 30. The insulating film 20 (first insulating film 20A) and the superconducting material film 30 are sequentially laminated on the surface 10a of the substrate 10. The insulating film 20 (second insulating film 20B) is laminated on the back surface 10b of the substrate 10.

[0016] The substrate 10 is formed of a semiconductor material such as, for example, a silicon (Si) substrate. Note that the substrate 10 may be formed of an insulator material such as, for example, glass. The thickness of the substrate 10 is, for example, 10 μm to 500 μm (micrometers). The substrate 10 includes a surface 10a, a back surface 10b facing the side opposite to the surface 10a, and a through-hole 11 penetrating from the back surface 10b to the surface 10a.

[0017] The insulating film 20 is formed of an insulator material such as, for example, silicon nitride (SiN). Note that the insulating film 20 may be formed of other insulator materials such as, for example, silicon dioxide (SiO2). The thickness of the insulating film 20 is, for example, 100 nm to 150 nm (nanometers). The insulating film 20 includes a first insulating film 20A covering the surface 10a of the substrate 10 and a second insulating film 20B covering the back surface 10b of the substrate 10.

[0018] In the first insulating film 20A, a thin film region 21 (membrane) not supported by the substrate 10 is formed. The thin film region 21 is formed in a portion facing the opening of the through-hole 11. In the second insulating film 20B, a communication hole communicating with the through-hole 11 is formed. That is, in the through-hole 11, the surface 10a side of the substrate 10 is blocked by the thin film region 21, and the back surface 10b side of the substrate 10 is open.

[0019] The superconducting material film 30 is formed of a superconducting material such as, for example, niobium (Nb). Note that the superconducting material film 30 may be formed of other superconducting materials such as, for example, aluminum (Al) or titanium nitride (TiN). The thickness of the superconducting material film 30 is, for example, 0.1 μm to 0.5 μm (micrometers). In the superconducting material film 30, a superconducting quantum circuit 31 is formed.

[0020] The superconducting quantum circuit 31 forms, for example, a transmission line type superconducting resonator with a line length of 1 / 4 wavelength. The superconducting quantum circuit 31 may also be a superconducting resonator incorporating superconducting quantum interference devices (SQUIDs) including Josephson junctions. The superconducting quantum circuit 31 is formed on a thin film region 21 of the first insulating film 20A. With this configuration, when high-energy waves (such as gamma waves) collide, it is possible to prevent phonons from propagating to the substrate 10.

[0021] Next, a method for manufacturing the superconducting quantum device 1 with the above configuration will be described.

[0022] Figures 3 to 5 are explanatory diagrams of a method for manufacturing a superconducting quantum device 1 according to one embodiment of the present disclosure. Figure 6 is a flowchart of the steps included in the superconducting quantum circuit formation step S5 according to one embodiment of the present disclosure.

[0023] In this method, first, an insulating film 20 is formed on the substrate 10, as shown in Figure 3. Specifically, a substrate 10 (silicon substrate) is fabricated as shown in Figure 3(a). Then, as shown in Figure 3(b), an insulating film 20 (SiN film) is deposited on the front surface 10a and back surface 10b of the substrate 10 to a thickness of approximately 100 nm to 150 nm using LPCVD (low-pressure chemical vapor deposition) or the like.

[0024] Next, in this method, as shown in Figure 4(a), the protective film 40 is used as a mask to etch from the back surface 10b of the substrate 10, and a thin film region 21 that is not supported by the substrate 10 is formed in the insulating film 20 formed on the front surface 10a of the substrate 10. Specifically, the first protective film 40A is deposited on the first insulating film 20A, and a pattern is formed to create through-holes 11 in the second protective film 40B on the second insulating film 20B by photolithography or the like.

[0025] The protective film 40 can be a commercially available protective resist material. For example, the protective film 40 may be a resin composed of an acrylonitrile-styrene resin and an epoxy resin, with a silane coupling agent as the primer. Alternatively, the protective film 40 may be made of an acrylic resin-based resist material such as methyl methacrylate. In this case, the polymer itself has good adhesion to the metal and does not require a primer such as a silane coupling agent, so problems such as primer remaining on the device surface after resist removal with the cleaning solution described later are less likely to occur.

[0026] Next, using the second protective film 40B as a mask, the substrate 10 is etched from the back surface 10b using an aqueous KOH (potassium hydroxide) solution or DRIE (silicon deep reactive ion etching). This forms a through-hole 11 extending from the back surface 10b to the front surface 10a of the substrate 10, and a thin film region 21 that is not supported by the substrate 10 is formed in the first insulating film 20A. Note that TMAH (tetramethylammonium hydroxide) may be used instead of KOH.

[0027] Next, in this method, as shown in Figure 4(b), the protective film 40 is removed in the acidic cleaning solution 101 of the cleaning tank 100. This step is a cleaning process using a normal acid used in semiconductor manufacturing processes, such as RCA cleaning, piranha cleaning, or BHF cleaning. This cleaning removes the protective film 40, which is resistant to KOH and TMAH, preventing it from remaining as a dielectric loss source for the superconducting quantum circuit 31, which will be described later. In addition, organic matter other than the protective film 40 remaining on the surface of the insulating film 20 can also be removed by RCA cleaning or piranha cleaning.

[0028] After cleaning, in this method, a superconducting material film 30 is deposited on the first insulating film 20A, as shown in Figure 5(a). Then, a superconducting quantum circuit 31 is formed on the superconducting material film 30 using conventional photolithography. As a result, a superconducting quantum device 1 can be manufactured. Thus, with this method, the protective film 40, which is a dielectric loss source, is removed before the superconducting quantum circuit formation step S5, thereby improving the Q value of the superconducting quantum device 1.

[0029] The superconducting quantum circuit formation step S5 includes, as shown in Figure 6, a superconducting material film formation step S51, a second protective film formation step S52, a superconducting quantum circuit patterning step S53, and a second protective film removal step S54.

[0030] The superconducting material film formation step S51 is a step of forming a superconducting material film 30 on a thin film region 21, as shown in Figure 5(a). The second protective film formation step S52 is a step of forming a second protective film (not shown) on the superconducting material film 30 for drawing superconducting quantum circuits 31. The superconducting quantum circuit patterning step S53 is a step of patterning superconducting quantum circuits 31 on the superconducting material film 30 using the second protective film as a mask by RIE (reactive ion etching) or the like.

[0031] The second protective film removal step S54 is a step to remove the second protective film (mask). In the second protective film removal step S54, it is preferable to remove the second protective film with a cleaning solution that has a higher pH than that used in the protective film removal step S4 (a cleaning solution that is weaker acidic than that used in the protective film removal step S4). This prevents damage to the superconducting quantum circuit 31.

[0032] Incidentally, this method is characterized by back etching from the back surface 10b of the substrate 10, followed by patterning the superconducting quantum circuit 31 on a thin film region 21 of the insulating film 20 on the front surface 10a of the substrate 10. Since the area of ​​the thin film region 21 is small, the bending of the thin film region 21 has almost no effect, but in order to secure a large area for patterning the superconducting quantum circuit 31, a method to suppress the bending of the thin film region 21 may be adopted.

[0033] The thin film region 21 may bend due to gravity causing its center to sink downwards, or due to compressive stress acting on it because of the properties of the deposited superconducting material film 30, causing the thin film region 21 to bend vertically. To eliminate these causes and improve the bending of the thin film region 21, it is preferable to increase the magnitude of the tensile stress in the thin film region 21.

[0034] Therefore, for example, in the protective film formation step S2 described above, it is preferable to form a protective film 40 with a stoichiometric ratio of silicon to nitrogen of 3:4 by chemical vapor deposition. This is because the tensile stress of the SiN membrane is maximized when the SiN process-deposited by LPCVD is in a stoichiometric ratio (stoichiometric Si3N4).

[0035] Furthermore, for example, in the superconducting quantum circuit formation step S5 described above, it is preferable to deposit a superconducting material film 30 on the thin film region 21 that has a lower compressive stress than the thin film region 21. This reduces the compressive stress acting from the superconducting material film 30 on the thin film region 21, thereby suppressing the bending of the thin film region 21.

[0036] As described above, the manufacturing method of the superconducting quantum device 1 of this embodiment includes an insulating film formation step S1 for forming an insulating film 20 on a substrate 10, a protective film formation step S2 for forming a protective film 40 on the insulating film 20, a thin film region formation step S3 for etching from the back surface 10b of the substrate 10 using the protective film 40 as a mask to form a thin film region 21 on the insulating film 20 formed on the surface of the substrate 10 that is not supported by the substrate 10, a protective film removal step S4 for removing the protective film 40 after the thin film region 21 has been formed, and a superconducting quantum circuit formation step S5 for forming a superconducting quantum circuit 31 on the thin film region 21. This method makes it possible to improve the Q value of the superconducting quantum device 1 that has a superconducting quantum circuit 31 formed in the thin film region 21 of the insulating film 20.

[0037] Although embodiments of this disclosure have been described in detail above with reference to the drawings, the specific configurations are not limited to these embodiments and include design modifications that do not depart from the gist of this disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0038] Furthermore, some or all of the above embodiments may also be described as follows, but are not limited to the following.

[0039] (Note 1) An insulating film formation process in which an insulating film is formed on a substrate, A protective film forming step of forming a protective film on the insulating film, A thin film region formation step involves etching from the back surface of the substrate using the protective film as a mask to form a thin film region in the insulating film formed on the surface of the substrate that is not supported by the substrate, After forming the thin film region, a protective film removal step is performed to remove the protective film, The process includes a superconducting quantum circuit formation step of forming a superconducting quantum circuit on the thin film region. A method for manufacturing superconducting quantum devices.

[0040] (Note 2) In the protective film removal step, the protective film is removed with an acidic cleaning solution. A method for manufacturing a superconducting quantum device as described in Appendix 1.

[0041] (Note 3) The substrate is a silicon substrate. A method for manufacturing a superconducting quantum device as described in Appendix 1 or 2.

[0042] (Note 4) The aforementioned copolymer is silicon nitride. A method for manufacturing a superconducting quantum device as described in any one of the appendices 1 to 3.

[0043] (Note 5) In the protective film formation step, the protective film is formed by chemical vapor deposition, with a stoichiometric ratio of silicon to nitrogen of 3:4. A method for manufacturing a superconducting quantum device as described in any one of the appendices 1 to 4.

[0044] (Note 6) In the superconducting quantum circuit formation step, a superconducting material with a lower compressive stress than the thin film region is deposited on the thin film region. A method for manufacturing a superconducting quantum device as described in any one of the appendices 1 to 5.

[0045] (Note 7) In the superconducting quantum circuit formation step, niobium is deposited on the thin film region as a superconducting material. A method for manufacturing a superconducting quantum device as described in any one of the appendices 1 to 6.

[0046] (Note 8) The superconducting quantum circuit formation process is as follows: A superconducting material film formation step is to form a superconducting material film on the thin film region, A second protective film formation step, in which a second protective film is formed on the superconducting material film, The process includes a superconducting quantum circuit patterning step, in which the superconducting quantum circuit is patterned on the superconducting material film using the second protective film as a mask. A method for manufacturing a superconducting quantum device as described in any one of the appendices 1 to 7.

[0047] (Note 9) The superconducting quantum circuit formation step includes a second protective film removal step, which removes the second protective film after the superconducting quantum circuit patterning step. A method for manufacturing a superconducting quantum device as described in Appendix 8.

[0048] (Note 10) In the second protective film removal step, the second protective film is removed with a washing solution that has a higher pH than the protective film removal step. A method for manufacturing a superconducting quantum device as described in Appendix 9. [Explanation of Symbols]

[0049] 1. Superconducting quantum devices 10 circuit boards 10a surface 10b back side 11 Penetration 20 Insulating film 20A First insulating film 20B Second insulating film 21 Thin film area 30 Superconducting Material Films 31 Superconducting Quantum Circuits 40 Protective film 40A 1st protective film 40B 2nd protective film 100 Washing Tanks 101 Cleaning Solution S1 Insulating film formation process S2 Protective film formation process S3 Thin film region formation process S4 Protective film removal process S5 Superconducting Quantum Circuit Formation Process S51 Superconducting material film formation process S52 Second protective film formation process S53 Superconducting Quantum Circuit Patterning Process S54 Second protective film removal process

Claims

1. An insulating film formation process in which an insulating film is formed on a substrate, A protective film forming step of forming a protective film on the insulating film, A thin film region formation step involves etching from the back surface of the substrate using the protective film as a mask to form a thin film region in the insulating film formed on the surface of the substrate that is not supported by the substrate, After forming the thin film region, a protective film removal step is performed to remove the protective film, The process includes a superconducting quantum circuit formation step of forming a superconducting quantum circuit on the thin film region. A method for manufacturing superconducting quantum devices.

2. In the protective film removal step, the protective film is removed with an acidic cleaning solution. A method for manufacturing a superconducting quantum device according to claim 1.

3. The substrate is a silicon substrate. A method for manufacturing a superconducting quantum device according to claim 1 or 2.

4. The aforementioned copolymer is silicon nitride. A method for manufacturing a superconducting quantum device according to claim 1 or 2.

5. In the protective film formation step, the protective film is formed by chemical vapor deposition, with a stoichiometric ratio of silicon to nitrogen of 3:

4. A method for manufacturing a superconducting quantum device according to claim 1 or 2.

6. In the superconducting quantum circuit formation step, a superconducting material with a lower compressive stress than the thin film region is deposited on the thin film region. A method for manufacturing a superconducting quantum device according to claim 1 or 2.

7. In the superconducting quantum circuit formation step, niobium is deposited on the thin film region as a superconducting material. A method for manufacturing a superconducting quantum device according to claim 1 or 2.

8. The superconducting quantum circuit formation process is as follows: A superconducting material film formation step is to form a superconducting material film on the thin film region, A second protective film formation step, in which a second protective film is formed on the superconducting material film, The process includes a superconducting quantum circuit patterning step, in which the superconducting quantum circuit is patterned on the superconducting material film using the second protective film as a mask. A method for manufacturing a superconducting quantum device according to claim 1 or 2.

9. The superconducting quantum circuit formation step includes a second protective film removal step, which removes the second protective film after the superconducting quantum circuit patterning step. A method for manufacturing a superconducting quantum device according to claim 8.

10. In the second protective film removal step, the second protective film is removed with a washing solution having a higher pH than that used in the protective film removal step. A method for manufacturing a superconducting quantum device according to claim 9.

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