Josephson junction, superconducting quantum chip preparation method and related products

Abstract

The invention discloses a Josephson junction, a superconducting quantum chip preparation method and a related product. The preparation method of the Josephson junction comprises the following steps: spin-coating a first layer of photoresist on a substrate and baking; spin-coating a second layer of photoresist again and baking; exposing the first layer of photoresist and the second layer of photoresist, developing after exposure, and forming patterns with crossed gaps in the first layer of photoresist and the second layer of photoresist; cleaning the photoresist left in the cross-shaped gap of the developed substrate by using plasma; then the substrate is put into a TMAH solution to be soaked so as to remove the photoresist left in the cross-shaped gap; mutually crossed metal deposition layers are evaporated in the crossed gaps; and stripping the residual first layer of photoresist and the second layer of photoresist to obtain the Josephson junction. According to the method, under the condition that the size of the side wall of the photoresist of the barrier layer is not influenced basically, the residual photoresist in the cross-shaped gap can be well removed, and the preparation quality of the Josephson junction and the performance of the superconducting quantum chip are improved.

Description

Technical Field

[0001] The present invention relates to the field of superconducting quantum technology, and in particular to a Josephson junction, a superconducting quantum chip preparation method and related products. Background Art

[0002] In the field of quantum computing, superconducting quantum chips are the core components of superconducting quantum computers.

[0003] The Josephson junction is an important component in superconducting quantum chips. It can be used to construct superconducting quantum bits and form superconducting circuits together with other superconducting elements.

[0004] A Josephson junction is usually composed of two layers of superconducting material with an extremely thin insulating layer sandwiched between them, presenting a microscopic structure similar to a "sandwich".

[0005] Since the Josephson junction is an important component of the functional circuit of the superconducting quantum chip, the preparation quality of the Josephson junction may have an important impact on the performance of the superconducting quantum chip and even the entire superconducting quantum computer.

[0006] In the prior art, during the preparation of the Josephson junction, after the photoresist layer is exposed and developed, the formed physical mask portion is placed in a UV cleaning machine, UV light is generated by the UV lamp of the UV cleaning machine, and the physical mask portion is placed in an ozone environment for a set time to remove the residual photoresist material. However, in the above method, while using UV to remove the residual photoresist material at the photoresist hollow pattern portion, the UV light will also greatly affect the size and morphology of the barrier layer photoresist, which will affect the subsequent processing quality of the Josephson junction, thereby possibly reducing the preparation quality of the final Josephson junction. Summary of the invention

[0007] In view of the above problems, the present invention is proposed to provide a Josephson junction, a superconducting quantum chip preparation method and related products that overcome the above problems or at least partially solve the above problems.

[0008] In a first aspect, an embodiment of the present invention provides a method for preparing a Josephson junction in a superconducting quantum chip, comprising:

[0009] Spin coating a first layer of photoresist on the substrate and baking it;

[0010] Spin coating a second layer of photoresist on the substrate covered with the first layer of photoresist and baking;

[0011] Exposing the first layer of photoresist and the second layer of photoresist using an electron beam, and developing the exposed portion using a developer after the exposure to form a pattern of cross-shaped gaps in the first layer of photoresist and the second layer of photoresist;

[0012] For the developed substrate, using plasma to clean the photoresist remaining in the cross-shaped gap;

[0013] The substrate cleaned by plasma is immersed in a tetramethylammonium hydroxide solution to remove the photoresist remaining in the cross-shaped gap;

[0014] The substrate from which the residual photoresist in the cross-shaped gap has been removed is placed in an electron beam evaporation device to evaporate metal deposition layers that intersect each other in the cross-shaped gap;

[0015] For the substrate on which the metal deposition layer has been evaporated, the remaining first photoresist layer and second photoresist layer are stripped off to obtain a Josephson junction.

[0016] In one embodiment, exposing the first layer of photoresist and the second layer of photoresist with an electron beam includes:

[0017] Exposing the first layer of photoresist and the second layer of photoresist using an exposure amount of 200 to 500 μC / cm2 on a 100 to 125 kV electron beam lithography device;

[0018] The step of developing the exposed portion using a developer after exposure comprises:

[0019] At room temperature, the exposed portion is developed using a developer prepared by mixing methyl isobutyl ketone and isopropyl alcohol in a ratio of 1:3 for a set time.

[0020] In one embodiment, after development, the residual photoresist in the cross-shaped gap is cleaned using plasma, comprising:

[0021] Use plasma cleaning equipment for cleaning, with a cleaning power of 100-200W, an oxygen flow rate of 0.1L / min-0.5L / min, and a preset cleaning time;

[0022] Soak in tetramethylammonium hydroxide solution, including:

[0023] The substrate is placed in a tetramethylammonium hydroxide solution having a concentration of 1% to 2.38% and soaked for a preset time.

[0024] In one embodiment, the cross-shaped gap includes a first gap and a second gap that intersect each other;

[0025] Accordingly, placing the electron beam evaporation device in the cross-shaped gap to evaporate the metal deposition layers that intersect each other comprises:

[0026] Depositing a bottom superconducting metal layer in a first gap of the cross-shaped gap by physical vapor deposition at a first angle θ1;

[0027] The surface of the bottom Al layer is oxidized to form an in-situ oxide layer on the bottom superconducting metal layer;

[0028] Depositing a top superconducting metal layer in the second gap of the cross-shaped gap by physical vapor deposition at a second angle θ2; the top superconducting metal layer intersects with the bottom superconducting metal layer on which the in-situ oxide layer is prepared;

[0029] The bottom superconducting metal layer and the top superconducting metal layer are metal aluminum layers.

[0030] In one embodiment, stripping the first photoresist layer and the second photoresist layer to obtain a Josephson junction includes:

[0031] The substrate on which the metal deposition layers have been evaporated and intersected is immersed in an N-methylpyrrolidone solution for a preset time, and the remaining first layer of photoresist and second layer of photoresist are removed to obtain a Josephson junction.

[0032] In one embodiment, after the step of immersing in a tetramethylammonium hydroxide solution to remove the photoresist remaining in the cross-shaped gap, the method further comprises:

[0033] Soak in deionized water for 1 to 5 minutes;

[0034] After the step of stripping off the remaining first layer of photoresist and second layer of photoresist to obtain a Josephson junction, the method further comprises:

[0035] Soaking the substrate from which the first and second photoresist layers have been removed in an isopropyl alcohol solution for a preset time to remove organic matter;

[0036] Blow dry with nitrogen.

[0037] In one embodiment, the first layer of photoresist is methyl methacrylate or poly(α-methylstyrene-co-α-methylchloroacrylate);

[0038] The second layer of photoresist is polymethyl methacrylate.

[0039] In a second aspect, an embodiment of the present invention provides a method for preparing a superconducting quantum chip, wherein the method for preparing a superconducting quantum chip comprises the step of preparing a Josephson junction using the aforementioned method for preparing a Josephson junction in a superconducting quantum chip.

[0040] In a third aspect, an embodiment of the present invention provides a Josephson junction, wherein the Josephson junction is prepared according to the preparation method of the Josephson junction in the superconducting quantum chip as described above.

[0041] In a fourth aspect, an embodiment of the present invention provides a superconducting quantum chip, wherein the superconducting quantum chip includes a Josephson junction as described above.

[0042] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0043] The Josephson junction, superconducting quantum chip preparation method and related products provided by the embodiments of the present invention, in the process of preparing the Josephson junction, after exposing and developing the two layers of photoresist, first use plasma to clean the photoresist remaining in the cross-shaped gap, and then put it into a certain concentration of tetramethylammonium hydroxide (TMAH) solution for immersion to remove the photoresist remaining in the cross-shaped gap. By utilizing a large number of active particles in the plasma to quickly react chemically with organic matter remaining on the surface or physically impact it to separate it from the surface of the object, the cleaning of the residual organic matter on the side wall of the cross-shaped gap and the surface of the substrate can be achieved; and because TMAH can increase the solubility of certain organic compounds by increasing the polarity of the solution or changing the dielectric constant of the solvent, in combination with plasma pretreatment, the photoresist residue at the hollow pattern (cross-shaped gap) can be removed without substantially affecting the size of the side wall of the barrier layer photoresist, avoiding the adverse effects of the residual photoresist material on the substrate substrate and the side wall of the cross-shaped gap on subsequent processes, improving the preparation quality of the Josephson junction, improving the problems of unstable bit frequency and reduced decoherence time of the superconducting quantum chip caused by the cleanliness of the interface between the Josephson junction and the substrate substrate, and improving the performance of the superconducting quantum chip where the Josephson junction is located.

[0044] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0045] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0047] Figure 1 Flow chart of a method for preparing a Josephson junction in a superconducting quantum chip according to an embodiment of the present invention;

[0048] Figure 2 Schematic diagram of the vertical cross-sectional changes of the first photoresist layer and the second photoresist layer after exposure and development in an embodiment of the present invention;

[0049] Figure 3 A schematic diagram of the morphology of the first and second photoresist layers after exposure in an embodiment of the present invention;

[0050] Figure 4 It is a three-dimensional schematic diagram of evaporating a bottom superconducting metal layer and a top superconducting metal layer in the first gap and the second gap respectively with θ1 and θ2 in an embodiment of the present invention;

[0051] Figure 5 Schematic diagram of evaporating a bottom superconducting metal layer in a first gap at an angle θ1 in an embodiment of the present invention;

[0052] Figure 6 is a schematic diagram of evaporating a top superconducting metal layer in the second gap at an angle θ2 in an embodiment of the present invention;

[0053] Figure 7 The figure is a schematic diagram of the morphology of a Josephson junction obtained after removing the remaining first layer of photoresist and second layer of photoresist in an embodiment of the present invention. DETAILED DESCRIPTION

[0054] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0055] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", "far", "near", "front", "back" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0056] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0057] The inventors of the present invention have found that in the field of quantum computing, the Josephson junction is the core building block of superconducting quantum chips; superconducting quantum bits utilize the quantum properties of the Josephson junction in the superconducting state, and their energy levels can be regulated by external electric and magnetic fields, and can exhibit key quantum phenomena such as quantum superposition and quantum entanglement, providing a physical basis for the encoding, processing and storage of quantum information. The preparation quality of the Josephson junction will greatly affect the performance of quantum chips and quantum computers using quantum chips. Therefore, improving the preparation quality of the Josephson junction is a key issue in ensuring the performance of quantum chips and quantum computers.

[0058] In order to solve the problem in the prior art that the use of UV to remove the residual photoresist material at the photoresist hollow pattern portion may affect the quality of the Josephson junction preparation, the embodiment of the present invention provides a method for preparing a Josephson junction in a superconducting quantum chip, referring to Figure 1 As shown, the method comprises the following steps:

[0059] S11, spin coating a first layer of photoresist on the substrate and baking;

[0060] S12, spin coating a second layer of photoresist on the substrate covered with the first layer of photoresist and baking;

[0061] S13, exposing the first layer of photoresist and the second layer of photoresist using an electron beam, and developing the exposed portion using a developer after the exposure to form a cross-shape gap pattern in the first layer of photoresist and the second layer of photoresist;

[0062] S14, cleaning the photoresist remaining in the cross-shaped gap by using plasma on the developed substrate;

[0063] S15, placing the substrate cleaned by plasma into a tetramethylammonium hydroxide solution to remove the photoresist remaining in the cross-shaped gap;

[0064] S16, placing the substrate from which the residual photoresist in the cross-shaped gap has been removed into an electron beam evaporation device to evaporate metal deposition layers that intersect each other in the cross-shaped gap;

[0065] S17, for the substrate on which the metal deposition layer has been evaporated, the remaining first layer of photoresist and second layer of photoresist are peeled off to obtain a Josephson junction.

[0066] In order to improve the preparation quality of the Josephson junction in the superconducting quantum chip, the inventors of the present application found that in the preparation process of the Josephson junction, since the main part of the Josephson junction is mainly in the cross-shaped gap, it is obtained by evaporating mutually intersecting superconducting metal layers (also called superconducting thin film layers) on the substrate of the cross-shaped gap, and the preparation quality of the superconducting metal layer is closely related to the side wall of the cross-shaped gap after the photoresist is exposed and developed, and the cleanliness, smoothness and surface damage of the substrate at the bottom of the cross-shaped gap. Therefore, if the quality of the side wall of the cross-shaped gap and the substrate surface after the photoresist is exposed and developed can be improved, the quality of the finally prepared Josephson junction can be well improved.

[0067] Based on this, in the method for preparing a superconducting Josephson junction proposed by the inventor of the present application, after exposing and developing the two layers of photoresist, the photoresist remaining in the cross-shaped gap is first cleaned using plasma, and then immersed in a tetramethylammonium hydroxide (TMAH) solution of a certain concentration to remove the photoresist remaining in the cross-shaped gap. By utilizing a large number of active particles in the plasma to quickly react chemically with organic matter remaining on the surface or physically impact it to separate it from the surface of the object, the cleaning of the residual organic matter on the side wall of the cross-shaped gap and the surface of the substrate can be achieved; and because TMAH can increase the solubility of certain organic compounds by increasing the polarity of the solution or changing the dielectric constant of the solvent, in combination with plasma pretreatment, the photoresist residue at the hollow pattern (cross-shaped gap) can be removed without substantially affecting the size of the side wall of the barrier layer photoresist, avoiding the adverse effects of the residual photoresist material on the substrate substrate and the side wall of the cross-shaped gap on subsequent processes, improving the preparation quality of the Josephson junction, improving the problems of unstable bit frequency and reduced decoherence time of the superconducting quantum chip caused by the cleanliness of the interface between the Josephson junction and the substrate substrate, and improving the performance of the superconducting quantum chip where the Josephson junction is located.

[0068] The principle of plasma cleaning is as follows: In plasma cleaning equipment, a radio frequency electric field is applied to the electrodes in the reaction chamber through a radio frequency power supply. The power supply outputs radio frequency energy of a certain power, which ionizes the gas in the chamber (such as argon, oxygen and other commonly used process gases), breaks the original chemical bonds of the gas molecules, and generates plasma. The particles in the plasma react quickly with the pollutants chemically (such as oxidation, reduction, decomposition, etc.) or physically impact them to separate them from the surface of the object, thereby achieving the cleaning of the residual organic matter on the surface of the cross-shaped gap.

[0069] The power used by the plasma cleaning equipment directly determines the degree of gas ionization and the density and energy state of active particles (such as ions, electrons, free radicals, etc.) in the generated plasma.

[0070] In one embodiment, in the above step S14, the developed substrate is cleaned by a plasma cleaning device, the cleaning power is 100-200W, the oxygen flow rate is 0.1L / min-0.5L / min, and the cleaning time is 3-5min, so that more oxygen molecules can be ionized to form oxygen free radicals with strong oxidizing properties, thereby more efficiently decomposing and removing organic pollutants.

[0071] In one embodiment, in the above step S15, the concentration of the tetramethylammonium hydroxide solution (TMAH) may be, for example, 1% to 2.38%, and the time for which the substrate is immersed in the TMAH solution after plasma cleaning may be, for example, 60 to 90 seconds.

[0072] For multi-layer photoresists such as PMMA / MMA photoresists, TMAH solution can utilize the difference in solubility of different polymers to selectively remove the upper photoresist layer without affecting the underlying material, thereby achieving precise removal of specific photoresist layers and meeting the needs of complex processes. In addition, since TMAH solution has good fluidity and wettability, it can fully contact various parts of the substrate surface, rinse off the residual photoresist, and will not leave obvious impurities or residues on the substrate surface, thereby ensuring the cleanliness of the substrate surface.

[0073] In the embodiment of the present invention, the photoresist spin-coated in step S11 and step S12 is electron beam photoresist.

[0074] In one embodiment, in the above step S11, a first layer of photoresist is spin-coated on the substrate and baked. The first layer of photoresist can be spin-coated by, for example, a coating machine, a spin coater, etc. During the spin coating process, the photoresist is evenly spread on the substrate surface under the action of centrifugal force. As the rotation speed increases, the thickness of the photoresist gradually becomes thinner and the distribution becomes more uniform. The rotation speed and the spin coating time of the coating machine and the spin coater can be set according to the amount of photoresist to be spin-coated and the final thickness of the photoresist to be achieved.

[0075] After the spin coating is completed, the purpose of baking the photoresist is to remove the solvent in the photoresist and make the photoresist more dense and stable. Baking can be done on a hot plate or in an oven.

[0076] For example, the baking temperature in a hot plate may be set to 170-210° C. and the baking time may be 2-4 minutes.

[0077] In one embodiment, the first layer of photoresist may be, for example, methyl methacrylate, i.e., MMA, or poly(α-methylstyrene-co-α-methyl chloroacrylate), for example, CSAR62. CSAR62 is a positive electron beam photoresist produced by Allresist of Germany, and its main component is poly(α-methylstyrene-co-α-methyl chloroacrylate).

[0078] In one embodiment, in the above step S12, the steps and principles of spin coating the second layer of photoresist are similar to those of the first layer of photoresist. After spin coating, for example, a hot plate can be used for baking. The baking temperature can be set to 170-210° C., and the baking time is 3-5 minutes.

[0079] In one embodiment, the second layer of photoresist may be, for example, polymethyl methacrylate, ie, PMMA.

[0080] In the above step S13, when the first and second photoresist layers are exposed using an electron beam, it can be achieved, for example, by the following steps: the first and second photoresist layers are exposed using an exposure amount of 200 to 500 μC / cm2 on an electron beam lithography device of 100 to 125 kV.

[0081] The principle of electron beam exposure is to directly hit the photoresist surface with a focused electron beam spot to change the chemical properties of the photoresist. The electron beam can scan the photoresist surface according to the pre-required pattern. When the electron beam irradiates the photoresist surface, the molecules in the photoresist absorb the energy of the electrons and undergo a chemical reaction, thereby changing the solubility of the photoresist. During the development process, the exposed area will be dissolved by the developer, while the unexposed area will remain, forming the desired hollow pattern.

[0082] In one embodiment, a developer prepared by mixing methyl isobutyl ketone (MIBK) and isopropyl alcohol (IPA) in a ratio of 1:3 may be used to develop the exposed portions of the first and second photoresist layers according to a set time.

[0083] Since the sensitivity of the first photoresist layer and the second photoresist layer to the electron beam is different, after the exposed part of the photoresist is developed using a developer in step S13, the first photoresist layer and the second photoresist layer can be formed as follows: Figure 2 The gap shown is narrow at the top and wide at the bottom.

[0084] Figure 2 Schematic diagram of the cross-sectional changes of the first layer of photoresist and the second layer of photoresist in the vertical direction after exposure and development. Figure 2It can be seen that due to different sensitivities to the electron beam, the width of the first layer of photoresist (brown part) removed is larger than the width of the second layer of photoresist (green part) removed.

[0085] From a bird's-eye view, the overall shape after exposure can be referred to Figure 3 As shown, from Figure 3 It can be seen that after electron beam exposure and development, a hollow pattern with cross-shaped gaps can be formed.

[0086] In one embodiment, the cross-shaped gap includes a first gap and a second gap that intersect each other. In the step S16, the cross-shaped gap is placed in an electron beam evaporation device to evaporate metal deposition layers that intersect each other in the cross-shaped gap to form a Josephson junction, which includes the following steps:

[0087] 1) depositing a bottom superconducting metal layer in a first gap of the cross-shaped gap by physical vapor deposition at a first angle θ1;

[0088] 2) performing oxidation treatment on the surface of the bottom Al layer to generate an in-situ oxide layer on the bottom superconducting metal layer;

[0089] 3) depositing a top superconducting metal layer in the second gap of the cross-shaped gap by physical vapor deposition at a second angle θ2; the top superconducting metal layer intersects with the bottom superconducting metal layer on which the in-situ oxide layer has been prepared;

[0090] Specifically, the above θ1 and θ2 are respectively the angles between the incident directions of the two evaporation deposition materials (such as metal aluminum atoms) and the normal direction of the substrate surface.

[0091] The substrate plane is regarded as the reference plane, and its normal is perpendicular to the upward (or downward) direction of this plane. When the deposited material flies toward the substrate, the angle formed by rotating counterclockwise from the substrate normal direction to the incident direction of the deposited material is the angle corresponding to this deposition process (i.e., the aforementioned θ1 and θ2).

[0092] Figure 4 A three-dimensional schematic diagram is shown of the cross-shaped gap obtained after exposure and development, in which a bottom superconducting metal layer and a top superconducting metal layer are evaporated in the first gap and the second gap at two angles θ1 and θ2 respectively.

[0093] The green part shows the second photoresist layer PMMA, the brown part shows the first photoresist layer MMA, and the gray part shows the substrate part (Substrate) exposed at the bottom of the formed cross-shaped gap.

[0094] Further, refer to Figure 5 As shown, the bottom superconducting metal layer is evaporated in the first gap at θ1.

[0095] The superconducting metal layer may be, for example, a metal aluminum AL layer or other superconducting metal layers.

[0096] The evaporation of the bottom metal aluminum layer can usually be achieved by physical vapor deposition (PVD) technology. The presence of the in-situ oxide layer on the bottom metal aluminum layer can prevent further oxidation of the superconducting metal aluminum layer and can serve as an insulating layer in the Josephson junction.

[0097] Reference Figure 6 As shown, a top superconducting metal layer is evaporated in the second gap at another angle θ2.

[0098] Similar to the bottom superconducting metal layer, the top superconducting metal layer may be a metal aluminum AL layer or other superconducting metal layers.

[0099] In the embodiment of the present invention, by depositing metal aluminum at different angles, complex metal connections can be formed in a three-dimensional structure, which is crucial for the manufacture of multi-layer electronic devices.

[0100] In one embodiment, in the above step S17, the substrate on which the metal deposition layers intersecting each other have been evaporated is immersed in an N-methylpyrrolidone (NMP) solution for a preset time, and the remaining first layer of photoresist and second layer of photoresist are removed to obtain a Josephson junction.

[0101] NMP has a strong dissolving ability and can dissolve photoresist quickly and effectively. This helps to completely remove residual photoresist after the photolithography process, improve cleaning efficiency, and reduce the impact of residual photoresist on subsequent processes. In addition, NMP has low solubility in the underlying substrate material or other adjacent materials. This selective dissolving property allows the integrity of the underlying material and device structure to be protected to the greatest extent during the photoresist removal process, which is conducive to the realization of high-precision, complex micro-nano processing.

[0102] In one embodiment, after removing the remaining first photoresist layer and the second photoresist layer to obtain the Josephson junction, the following steps may be further performed:

[0103] The substrate from which the first layer of photoresist and the second layer of photoresist have been removed is immersed in an isopropyl alcohol (IPA) solution for a preset time to remove organic matter; and is blown dry using nitrogen gas.

[0104] The use of isopropyl alcohol solution can further remove organic matter generated or remaining in the previous steps to ensure the cleanliness of the prepared Josephson junction, improve the quality and performance of the Josephson junction, and improve the yield rate.

[0105] Figure 7The figure shows the morphology of the Josephson junction obtained after removing the remaining first and second photoresist layers. The light green represents the top superconducting metal layer, the dark green represents the bottom superconducting metal layer, and there is an in-situ oxide layer between the top superconducting metal layer and the bottom superconducting metal layer. Figure 7 In the example shown, the Josephson junction uses AL / ALO X The composition of Al, that is, the bottom and top layers are superconducting metal aluminum layers, and the middle is ALO X layer (i.e. in-situ oxide layer).

[0106] The following specific example illustrates the method for preparing the Josephson junction.

[0107] In this specific embodiment, the preparation process of the Josephson junction is as follows:

[0108] 1) Spin-coat the electron beam photoresist on the substrate at a coating speed of 1500-2000 rpm for 60 seconds. After coating, bake on a hot plate at 170-210°C for 2-4 minutes.

[0109] 2) Spin-coat the electron beam photoresist on the substrate again, with a coating speed of 1000-2000 rpm for 60 seconds, and bake on a hot plate at 170-210° C. for 3-5 minutes.

[0110] 3) Setting the exposure dose to 200 to 500 μC / cm2 on a 100-125 kV electron beam lithography device, and starting exposure after the baking in step 2) is completed.

[0111] 4) After exposure, a mixed solution of MIBK:IPA 1:3 is used as a developer for development at room temperature for 60 to 90 seconds.

[0112] 6) After development, the substrate is cleaned with plasma. The power of plasma cleaning is 100-200W, the amount of oxygen introduced is 0.1L / min to 0.5L / min, and the cleaning time is 3 to 5 minutes.

[0113] 7) After plasma cleaning, the substrate is immersed in a TMAH 2.38% solution for 60s to 90s.

[0114] 8) Soak in deionized water for 2 to 3 minutes.

[0115] 9) The cleaned substrate is placed in an electron beam evaporation device to evaporate the Josephson junction. The evaporation rate can be set to 3A to 10A / s.

[0116] The specific evaporation process can refer to the above Figure 5 and Figure 6 Description.

[0117] 10) Place the substrate on which the Josephson junction has been evaporated into an NMP solution to remove the photoresist for 3 to 5 hours, and then peel off the Josephson junction.

[0118] 11) Soak the Josephson junction in IPA for 10 minutes.

[0119] 12) Use a nitrogen gun to blow dry the surface.

[0120] Based on the same inventive concept, an embodiment of the present invention further provides a method for preparing a superconducting quantum chip, which includes the step of preparing a Josephson junction using the aforementioned method for preparing a Josephson junction in a superconducting quantum chip.

[0121] The preparation method of other functional circuits in the superconducting quantum chip can be prepared by referring to the preparation method of the Josephson junction in the superconducting quantum chip provided in the embodiment of the present invention, or by adopting the preparation method in the prior art, which is not limited in the embodiment of the present invention.

[0122] The embodiment of the present invention further provides a Josephson junction, which is prepared according to the aforementioned method for preparing a Josephson junction in a superconducting quantum chip.

[0123] An embodiment of the present invention further provides a superconducting quantum chip, wherein the superconducting quantum chip includes the aforementioned Josephson junction.

[0124] The specific implementation method of the method for preparing the Josephson junction in the superconducting quantum chip can refer to the above-mentioned embodiment and will not be described in detail here.

[0125] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a Josephson junction in a superconducting quantum chip, characterized in that: include: Spin coating a first layer of photoresist on the substrate and baking it; Spin coating a second layer of photoresist on the substrate covered with the first layer of photoresist and baking; Exposing the first layer of photoresist and the second layer of photoresist using an electron beam, and developing the exposed portion using a developer after the exposure to form a pattern of cross-shaped gaps in the first layer of photoresist and the second layer of photoresist; For the developed substrate, using plasma to clean the photoresist remaining in the cross-shaped gap; The substrate cleaned by plasma is immersed in a tetramethylammonium hydroxide solution to remove the photoresist remaining in the cross-shaped gap; The substrate from which the residual photoresist in the cross-shaped gap has been removed is placed in an electron beam evaporation device to evaporate metal deposition layers that intersect each other in the cross-shaped gap; For the substrate on which the metal deposition layer has been evaporated, the remaining first photoresist layer and second photoresist layer are stripped off to obtain a Josephson junction.

2. The method according to claim 1, characterized in that Exposing the first photoresist layer and the second photoresist layer with an electron beam includes: Exposing the first layer of photoresist and the second layer of photoresist using an exposure amount of 200 to 500 μC / cm2 on a 100 to 125 kV electron beam lithography device; The step of developing the exposed portion using a developer after exposure comprises: At room temperature, the exposed portion is developed using a developer prepared by mixing methyl isobutyl ketone and isopropyl alcohol in a ratio of 1:3 for a set time.

3. The method according to claim 1, characterized in that After development, the residual photoresist in the cross-shaped gap is cleaned using plasma, including: Use plasma cleaning equipment for cleaning, with a cleaning power of 100-200W, an oxygen flow rate of 0.1L / min-0.5L / min, and a preset cleaning time; Soak in tetramethylammonium hydroxide solution, including: The substrate is placed in a tetramethylammonium hydroxide solution having a concentration of 1% to 2.38% and soaked for a preset time.

4. The method according to any one of claims 1 to 3, characterized in that: The cross-shaped gap includes a first gap and a second gap that intersect each other; Accordingly, placing the electron beam evaporation device in the cross-shaped gap to evaporate the metal deposition layers that intersect each other comprises: Depositing a bottom superconducting metal layer in a first gap of the cross-shaped gap by physical vapor deposition at a first angle θ1; The surface of the bottom Al layer is oxidized to form an in-situ oxide layer on the bottom superconducting metal layer; Depositing a top superconducting metal layer in the second gap of the cross-shaped gap by physical vapor deposition at a second angle θ2; the top superconducting metal layer intersects with the bottom superconducting metal layer on which the in-situ oxide layer is prepared; The bottom superconducting metal layer and the top superconducting metal layer are metal aluminum layers.

5. The method according to any one of claims 1 to 3, characterized in that: The first photoresist layer and the second photoresist layer are stripped off to obtain a Josephson junction, including: The substrate on which the metal deposition layers have been evaporated and intersected is immersed in an N-methylpyrrolidone solution for a preset time, and the remaining first layer of photoresist and second layer of photoresist are removed to obtain a Josephson junction.

6. The method according to any one of claims 1 to 3, characterized in that After the step of immersing in a tetramethylammonium hydroxide solution to remove the photoresist remaining in the cross-shaped gap, the method further comprises: Soak in deionized water for 1 to 5 minutes; After the step of stripping off the remaining first layer of photoresist and second layer of photoresist to obtain a Josephson junction, the method further comprises: Soaking the substrate from which the first and second photoresist layers have been removed in an isopropyl alcohol solution for a preset time to remove organic matter; Blow dry with nitrogen.

7. The method according to any one of claims 1 to 3, characterized in that: The first layer of photoresist is methyl methacrylate or poly(α-methylstyrene-co-α-methyl chloroacrylate); The second layer of photoresist is polymethyl methacrylate.

8. A method for preparing a superconducting quantum chip, characterized in that: The method for preparing the superconducting quantum chip includes the step of preparing a Josephson junction using the method for preparing a Josephson junction in a superconducting quantum chip as described in any one of claims 1 to 7.

9. A Josephson junction, characterized in that: The Josephson junction is prepared according to the method for preparing a Josephson junction in a superconducting quantum chip as described in any one of claims 1 to 7.

10. A superconducting quantum chip, characterized in that: The superconducting quantum chip comprises the Josephson junction as claimed in claim 9.

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