Method of manufacturing a qubit device

Abstract

A disclosed method of manufacturing a qubit device includes bonding a diamond substrate to a first region of a first substrate, and forming a first film on the first substrate and the diamond substrate, the first film being an optically transparent film; grinding or polishing the first film to expose the diamond substrate; bonding the first film and the exposed diamond substrate to a second substrate through a second film, the second film being an optically transparent film; and removing the first substrate to expose the first film and the diamond substrate.

Description

METHOD OF MANUFACTURING A QUBIT DEVICE

[0001] The disclosures discussed herein relate to a method of manufacturing a qubit device.

[0002] The related art technologies disclose a diamond substrate manufacturing method that includes depositing a diamond thin film on a substrate material having a prescribed degree of smoothness; adhering a support to the diamond thin film; and removing the substrate material by etching or mechanical polishing after adhering the support (See, e.g., Patent Document 1).

[0003] [PTL 1]　　Japanese Laid-Open Patent Publication No. H07-172989

[0004] However, in a diamond thin film produced by such a diamond substrate manufacturing method, one surface can be flattened, but the other surface is not flattened. Therefore, when the diamond substrate is used for a qubit, light reflection or loss occurs, making it difficult to fabricate a qubit with good operating properties.

[0005] Therefore, it is desirable to provide a qubit device manufacturing method capable of fabricating a qubit device with good operating properties.

[0006] According to an aspect of an embodiment of the present disclosure, a method of manufacturing a qubit device is provided. The method includes bonding a diamond substrate to a first region of a first substrate, and forming a first film on the first substrate and the diamond substrate, the first film being an optically transparent film; grinding or polishing the first film to expose the diamond substrate; bonding the first film and the exposed diamond substrate to a second substrate through a second film, the second film being an optically transparent film; and removing the first substrate to expose the first film and the diamond substrate.

[0007] According to an embodiment of the present disclosure, a qubit device manufacturing method capable of fabricating a qubit device with good operating properties may be provided.

[0008] Fig. 1 is a view illustrating an example of a planar configuration of a quantum computer 1 according to an embodiment.Fig. 2 is a view illustrating an example of a cross-sectional structure of the quantum computer 1.Fig. 3A is a view illustrating an example of a manufacturing step of a nanobeam resonator 20.Fig. 3B is a view illustrating an example of a manufacturing step of a nanobeam resonator 20.Fig. 3C is a view illustrating an example of a manufacturing step of a nanobeam resonator 20.Fig. 3D is a view illustrating an example of a manufacturing step of a nanobeam resonator 20.Fig. 3E is a view illustrating an example of a manufacturing step of a nanobeam resonator 20.Fig. 3F is a view illustrating an example of a manufacturing step of a nanobeam resonator 20.Fig. 4A is a cross-sectional view illustrating a comparative nanobeam resonator 20.Fig. 4B is a cross-sectional view illustrating a nanobeam resonator 20 according to an embodiment.Fig. 5A is a view illustrating an example of simulation results of a distribution of stress generated in the comparative nanobeam resonator 20 and a wafer substrate 110 illustrated in Fig. 4A.Fig. 5B is a view illustrating an example of simulation results of a distribution of stress generated in the comparative nanobeam resonator 20 and the wafer substrate 110 illustrated in Fig. 4A.Fig. 6A is a view illustrating an example of simulation results of a distribution of stress generated in the nanobeam resonator 20 according to the embodiment and the wafer substrate 110 illustrated in Fig. 4B.Fig. 6B is a view illustrating an example of simulation results of a distribution of stress generated in the nanobeam resonator 20 according to the embodiment and the wafer substrate 110 illustrated in Fig. 4B.Fig. 7A is a view illustrating an example of simulation results of a distribution of stress generated in the nanobeam resonator 20 according to the embodiment and the wafer substrate 110.Fig. 7B is a view illustrating an example of simulation results of a distribution of stress generated in the nanobeam resonator 20 according to the embodiment and the wafer substrate 110.

[0009] Hereafter, a description will be given of an embodiment to which a method of manufacturing a qubit device according to the present disclosure is applied.

[0010] <Embodiment> Fig. 1 is a view illustrating an example of a planar configuration of a quantum computer 1 according to an embodiment. The XYZ coordinate system is defined and described below. A direction parallel to the X axis (X direction), a direction parallel to the Y axis (Y direction), and a direction parallel to the Z axis (Z direction) are orthogonal to each other. The plan view means to view in XY plane. In addition, the length, the width, and the thickness of each part may be highlighted to facilitate understanding of the structure below.

[0011] The quantum computer 1 includes an optical waveguide 10 (10X, 10Y, 10S), a movable waveguide 150 (150A, 150B), a nanobeam resonator 20, a beam splitter 30, a coupler 40, and a photodetector 50. The nanobeam resonator 20 is an example of a qubit device. Of these, the optical waveguide 10 (10X, 10Y, 10S) is fabricated by micromachining, for example, a sapphire substrate or a silicon substrate. The optical waveguide 10 is also disposed under the nanobeam resonator 20. The movable waveguide 150 (150A, 150B) is implemented by MEMS (Micro Electro Mechanical Systems). The nanobeam resonator 20 is implemented by a diamond qubit using a diamond color center. The quantum computer 1 is a diamond qubit quantum computer.

[0012] The optical waveguide 10 has optical waveguides 10X, 10Y, and 10S. The optical waveguides 10X, 10Y, and 10S are waveguides in which light can propagate. Multiple optical waveguides 10X extend in the X direction. Multiple optical waveguides 10Y extend in the Y direction. The optical waveguides 10X and 10Y intersect. Note that the spacing G1 between the optical waveguide 10Y located at the end in the -X direction and the optical waveguide 10S is approximately 500 μm, as an example, and the same applies to the spacing between adjacent optical waveguides 10X and also to the spacing between adjacent optical waveguides 10Y.

[0013] The optical waveguide 10S is disposed in an approximately rectangular ring shape to surround the optical waveguides 10X and 10Y. The four corners of the optical waveguide 10S are curved in a curved shape in plan view to allow light to propagate inside. Both ends of each of the optical waveguides 10X and 10Y are not directly connected to the optical waveguide 10S, and the movable waveguide 150 forms an optical path through which light can propagate. When the optical waveguides 10X, 10Y, and 10S are not specifically distinguished, they are simply referred to as the optical waveguide 10.

[0014] The movable waveguide 150A is disposed between the optical waveguides 10X and 10Y and the nanobeam resonator 20. By being moved in the optical directional coupler to be described later, the movable waveguide 150A is switched to either a connected state in which the optical waveguides 10X and 10Y are connected to the nanobeam resonator 20 or to a disconnected state in which the optical waveguides 10X and 10Y are not connected to the nanobeam resonator 20. Hereinafter, being able to switch between the connected and disconnected states is referred to as detachable.

[0015] The movable waveguide 150B is disposed between both ends of each of the optical waveguides 10X and 10Y and the optical waveguide 10S. By being moved in an optical directional coupler to be described later, the movable waveguide 150B is switched to either a connected state in which the end of the optical waveguide 10X or 10Y is connected to the optical waveguide 10S or a disconnected state in which the end of the optical waveguide 10X or 10Y is not connected to the optical waveguide 10S.

[0016] The movable waveguides 150A and 150B have a similar configuration. Hereinafter, when the movable waveguides 150A and 150B are not specifically distinguished, they are simply referred to as the movable waveguides 150.

[0017] The nanobeam resonators 20 are disposed along the optical waveguides 10X and 10Y. The nanobeam resonators 20 are implemented with a diamond qubit using a diamond color center and keep qubits. The qubits are the three of electron spin, nuclear spin and photon, or alternatively, electron spin and photon.

[0018] The beam splitters 30 are connected around the optical waveguide 10S. The beam splitter 30 each have two optical waveguides (not illustrated). One coupler 40 is connected to one end of each of the optical waveguides. In addition, one movable waveguide 150 is detachably disposed on the other end of a corresponding one of the two optical waveguides. When one of the two movable waveguides 150 becomes connectable, the optical waveguide 10S is connected.

[0019] The coupler 40 is an optical coupler that couples between the beam splitter 30 and the photodetector 50. The photodetector 50 detects light input through the coupler 40. The photodetector 50 can use, for example, an avalanche photodiode (APD) or a superconducting nanowire photon detector (SNSPD). In the case of detecting photons directly from the optical waveguide 10S, the coupler 40 may not be required.

[0020] <Cross-Sectional Structure of Quantum Computer 1> Fig. 2 is a view illustrating an example of a cross-sectional structure of the quantum computer 1. Fig. 2 is a view illustrating an example of a cross-sectional structure taken along a line A-A in Fig. 1.

[0021] In Fig. 2, the quantum computer 1 includes a wafer substrate 110 and a nanobeam resonator 20. The wafer substrate 110 is an example of a second wafer substrate, and includes a substrate 111, and optical waveguides 10X and 10A. The wafer substrate 110 also includes optical waveguides 10Y and 10S illustrated in Fig. 1. The optical waveguide 10A is disposed under the nanobeam resonator 20. As an example, the wafer substrate 110 is made of silicon (Si).

[0022] <Manufacturing Method of Nanobeam Resonator 20> Figs. 3A to 3F are views each illustrating an example of a manufacturing step of a nanobeam resonator 20.

[0023] First, as illustrated in Fig. 3A, a diamond substrate 20A is bonded to the surface of a sapphire wafer substrate 70 by metal melt bonding using solder 21. The wafer substrate 70 is an example of a first wafer substrate. As the wafer substrate 70, a wafer substrate made of silicon, SiC (silicon carbide) or quartz may be used. In addition, direct bonding, diffusion bonding, pressure bonding or bonding through resin may be used instead of metal fusion bonding by solder 21.

[0024] Then, as illustrated in Fig. 3B, a SiN (silicon nitride) film 80 is formed by CVD (Chemical Vapor Deposition) to cover the surface of the wafer substrate 70 and the entire diamond substrate 20A. The SiN film 80 is an example of a first film. The thickness of the SiN film 80 may be greater than that of the diamond substrate 20A. Instead of the SiN film 80, a SiO2(silicon dioxide), TiO2(titanium oxide), Al2O3(alumina), MgO (magnesium oxide), etc. film may be used. Besides CVD, sputtering or vapor deposition may also be used as a manufacturing process.

[0025] Next, the SiN film 80 and the diamond substrate 20A are ground by back-grinding and polished by CMP (Chemical Mechanical Polishing) to obtain the SiN film 80 and the diamond substrate 20A with flattened upper surfaces as illustrated in Fig. 3C. Because the flattening is thus performed by the semiconductor process, the flatness of the upper surface of the diamond substrate 20A is extremely high. Note that the lap polishing may be used as another polishing method. When one of grinding by the back-grinding or polishing by CMP can be used to flatten the surfaces, only one of these methods may be used.

[0026] Then, by reversing the top and bottom of the wafer substrate 70, the SiN film 80, and the diamond substrate 20A illustrated in Fig. 3C, the flat surfaces of the SiN film 80 and the diamond substrate 20A are bonded to the upper surface of the wafer substrate 110 as illustrated in Fig. 3D. In Fig. 3D, an optical waveguide 10 is disposed in an upper surface portion of the wafer substrate 110. The optical waveguide 10 is not disposed in the entire upper surface of the wafer substrate 110, but is disposed in a portion where, for example, the optical waveguides 10X, 10Y, and 10S illustrated in Fig. 1 and the optical waveguide 10A illustrated in Fig. 2 are located. In Fig. 3D, a dashed frame illustrates a position where the optical waveguides 10X, 10Y, 10S, and 10A can be formed in the upper surface portion of the wafer substrate 110.

[0027] Moreover, the flat surfaces of the SiN film 80 and the diamond substrate 20A can be bonded to the upper surface of the wafer substrate 110 through a TiO2film 90. The TiO2film 90 is an example of a second film. Since the second film may be made of a material with an elastic modulus lower than that of the diamond substrate 20A and that of the wafer substrate 110, and may be optically transparent, the second film is not limited to the TiO2film 90, but may be a film such as a SiO2, SiN, or MgO film. The thickness of the second film may be 10 nm or more, which is thinner than that of the nanobeam resonator 20 and that of the optical waveguide 10.

[0028] By bonding the diamond substrate 20A and the wafer substrate 110 through the second film, which has an elastic modulus lower than that of the diamond substrate 20A and that of the wafer substrate 110, and is optically transparent, the occurrence of misalignment is reduced and stress is reduced. Accordingly, when the nanobeam resonator 20 is fabricated by processing the diamond substrate 20A later, property degradation can be reduced. In addition, since the nanobeam resonator 20 and the optical waveguide 10 are fabricated last, they can be fabricated without misalignment. Moreover, since the second film has optical transparency, the optical transparency between the nanobeam resonator 20 and the optical waveguide 10 can be ensured.

[0029] Next, the wafer substrate 70 and the solder 21 are removed by etching, and the upper surfaces of the SiN film 80 and the diamond substrate 20A are ground by back-grinding and polished by CMP to obtain the SiN film 80 and the diamond substrate 20A whose upper surfaces are flattened as illustrated in Fig. 3E. The diamond substrate 20A has both the upper and lower surfaces in Fig. 3E flattened by semiconductor process polishing. The etching may be performed by dry etching or wet etching. Lap polishing may be used instead of CMP. In addition, when one of grinding by the back-grinding or polishing by CMP can be used to flatten the surfaces, only one of these methods may be used.

[0030] Finally, nanobeam resonators 20 are fabricated by lithography using electron beam exposure, as illustrated in Fig. 3F. In Fig. 3F, cross sections of six nanobeam resonators 20 are illustrated as an example, but when two nanobeam resonators 20 are arranged side by side as illustrated in Fig. 2, two nanobeam resonators 20 may be fabricated.

[0031] Moreover, although not illustrated in Figures, the cross-sectional structure illustrated in Fig. 2 can be fabricated by removing the SiN film 80 and the TiO2film 90 from the state illustrated in Fig. 3F by etching. The SiN film 80 and the TiO2film 90 may be left unremoved as illustrated in Fig. 3F.

[0032] <Simulation Results> Fig. 4A is a cross-sectional view illustrating a comparative nanobeam resonator 20. Fig. 4B is a cross-sectional view illustrating a nanobeam resonator 20 according to an embodiment. In Fig. 4A, the nanobeam resonator 20 is formed directly on the wafer substrate 110, and in Fig. 4B, the nanobeam resonator 20 is formed on the wafer substrate 110 via a TiO2film 90. In Figs. 4A and 4B, illustration of the optical waveguide 10 is omitted.

[0033] Figs. 5A and 5B are views each illustrating an example of simulation results of a distribution of stress generated in the comparative nanobeam resonator 20 and the wafer substrate 110 illustrated in Fig. 4A. Fig. 5A illustrates an overall distribution of stress throughout the nanobeam resonator 20 and the wafer substrate 110, and Fig. 5B illustrates a distribution of stress at the end of the nanobeam resonator 20 in an enlarged manner. The stress generated at the boundary between the comparative nanobeam resonator 20 and the wafer substrate 110 was the maximum, at 10 GPa.

[0034] Figs. 6A and 6B are views each illustrating an example of simulation results of a distribution of stress generated at the nanobeam resonator 20 according to the embodiment and the wafer substrate 110 illustrated in Fig. 4B. The thickness of the TiO2film 90 is 10 nm. Fig. 6A illustrates an overall distribution of stress throughout the nanobeam resonator 20 and the wafer substrate 110, and Fig. 6B illustrates a distribution of stress at the end of the nanobeam resonator 20 in an enlarged manner. The stress generated at the boundary between the nanobeam resonator 20 according to the embodiment and the wafer substrate 110 was the maximum, at 6.8 GPa. The stress was reduced by approximately 30% by disposing a TiO2film 90 with a thickness of 10 nm.

[0035] Figs. 7A and 7B are views each illustrating an example of simulation results of a distribution of stress generated in the nanobeam resonator 20 according to the embodiment and the wafer substrate 110. The simulation results illustrated in Figs. 7A and 7B illustrate a distribution of stress in the nanobeam resonator 20 and the wafer substrate 110 bonded through a SiO2film with a thickness of 10 nm instead of the TiO2 film 90. Fig. 7A illustrates an overall distribution of stress throughout the nanobeam resonator 20 and the wafer substrate 110, and Fig. 7B illustrates a distribution of stress at the end of the nanobeam resonator 20 in an enlarged manner.

[0036] The stress generated at the boundary between the nanobeam resonator 20 according to the embodiment and the wafer substrate 110 bonded through the SiO2film was the maximum, 4.2 GPa. By bonding the nanobeam resonator 20 according to the embodiment and the wafer substrate 110 through the SiO2film with a thickness of 10 nm, the stress was reduced by approximately 60%. Thus, this indicates that by bonding the nanobeam resonator 20 and the wafer substrate 110 through the TiO2film 90 or through the SiO2film, the stress could be greatly reduced.

[0037] <Effect> A method of manufacturing a qubit device includes: bonding a diamond substrate 20A to a surface of a wafer substrate 70, and forming an optically transparent SiN film 80 on the surface of the wafer substrate 70 and over the diamond substrate 20A; flattening the SiN film 80 and the diamond substrate 20A by grinding or polishing; bonding flat surfaces of the flattened SiN film 80 and diamond substrate 20A to a surface of a wafer substrate 110 through an optically transparent TiO2film 90; and removing the wafer substrate 70 by grinding or polishing and flattening the surface opposite to the flat surfaces of the SiN film 80 and the diamond substrate 20A by grinding or polishing. Forming a diamond substrate 20A with flattened both sides can provide a nanobeam resonator 20 as a qubit device with good operating properties.

[0038] Therefore, it is possible to provide a method of manufacturing a qubit device (nanobeam resonator 20) with good operating properties. Since a qubit device (nanobeam resonator 20) requires arrangement accuracy at a several tens of nm level, which is shorter than the wavelength of light, it is difficult to ensure such accuracy by a pick-and-place arrangement method using a probe. It is also considered that a qubit device may be fabricated from bulk by anisotropic dry etching, but it appears difficult to flatten the back side of a beam-like structure. However, the method of manufacturing a qubit device according to the embodiment is capable of fabricating a diamond substrate 20A both sides of which are flattened using the flattening process by semiconductor fabrication technology, so that a diamond substrate 20A with extremely high flatness can be fabricated with an accuracy at a several tens of nm level. In addition, when a beam is formed in a qubit device fabricated from bulk by anisotropic dry etching, a hollow structure is formed on the underside of the beam. The hollow structure is vulnerable to stress at the support point, resulting in property degradation. However, the method of manufacturing a qubit device according to the embodiment is resistant to stress and can prevent property degradation because such a beam structure is not formed.

[0039] In addition, since the method of manufacturing a qubit device further includes forming a qubit device (nanobeam resonator 20) by processing the diamond substrate 20A on the wafer substrate 110 and forming an optical waveguide 10 in the wafer substrate 110, the method of manufacturing a qubit device is capable of fabricating a qubit device (nanobeam resonator 20) with good operating properties using the diamond substrate 20A having flat both sides.

[0040] In addition, since the first film is a silicon nitride film, a silicon dioxide film, a titanium oxide film, an alumina film or a magnesium oxide film, the use of the first film can reduce the deformation (warpage) of the wafer substrate 110 due to the thermal expansion mismatch between the wafer substrate 110 and the nanobeam resonator 20 at extremely low temperatures, and can obtain good operating properties.

[0041] In addition, the TiO2film 90 is a film made of a material with an elastic modulus lower than that of the diamond substrate 20A and that of the wafer substrate 110. By bonding the diamond substrate 20A and the wafer substrate 110 through a second film that has an elastic modulus lower than that of the diamond substrate 20A and that of the wafer substrate 110 and that is optically transparent, the occurrence of misalignment is reduced and stress is reduced. Accordingly, when the nanobeam resonator 20 is fabricated by processing the diamond substrate 20A later, property degradation can be prevented. Since the nanobeam resonator 20 and the optical waveguide 10 are fabricated last, they can be fabricated without misalignment. Moreover, since the second film has optical transparency, the optical transparency between the nanobeam resonator 20 and the optical waveguide 10 can be ensured.

[0042] In addition, since the thickness of the second film, such as the TiO2film 90, is 10 nm or more, the occurrence of misalignment between the diamond substrate 20A and the wafer substrate 110 can be effectively reduced, and when the nanobeam resonator 20 is fabricated by processing the diamond substrate 20A later, property degradation can be effectively prevented by reducing the stress.

[0043] Although the method of manufacturing a qubit device, which is the illustrative embodiment of the present disclosure, has been described above, the present disclosure is not limited to the specific disclosed embodiment and various modifications and alterations can be made without departing from the scope of the claims.

[0044] 10,10A,10S,10X,10Y　　optical waveguide 20　　nanobeam resonator (an example of a qubit device) 20A　　diamond substrate 70　　wafer substrate (an example of a first wafer substrate) 80　　SiN film (an example of a first film) 90　　TiO2film (an example of a second film) 110　　wafer substrate (an example of a second wafer substrate)

Claims

1. A method of manufacturing a qubit device, the method comprising: 　　　　bonding a diamond substrate to a first region of a first substrate, and forming a first film on the first substrate and the diamond substrate, the first film being an optically transparent film; 　　　　grinding or polishing the first film to expose the diamond substrate; 　　　　bonding the first film and the exposed diamond substrate to a second substrate through a second film, the second film being an optically transparent film; and 　　　　removing the first substrate to expose the first film and the diamond substrate.

2. The method according to claim 1, further comprising: 　　　　forming an optical waveguide in the second substrate; and 　　　　processing the diamond substrate on the second substrate to form a qubit device.

3. The method according to claim 1, wherein the first film is a silicon nitride film or a silicon dioxide film.

4. The method according to claim 1, wherein the second film is a film made of a material with an elastic modulus lower than that of the diamond substrate and that of the second substrate.

5. The method according to claim 1, wherein a thickness of the second film is 10 nm or more.