Method of making air bridges and superconducting quantum chips

Abstract

The application relates to a preparation method of an air bridge and a superconducting quantum chip. The method comprises the following steps: coating at least two photoresist layers on a substrate, and the photoresist photosensitivity of the photoresist layer far from the substrate is greater; performing exposure and etching treatment on at least two bridge regions of the at least two photoresist layers to form at least two bridge preparation structures with different bridge support structures in the at least two bridge regions; when etching the bridge top regions of the bridge support structures with different structures, different exposure doses capable of etching different photoresist layers are respectively adopted, so that the bridge support structures with different structures respectively include photoresists with different numbers of photoresist layers; depositing a superconducting film layer on the at least two bridge preparation structures; and performing a photoresist removing treatment on the bridge preparation structures with the deposited superconducting film layer to form at least two air bridges with different heights. The above method can be used for preparing the superconducting quantum chip, and can effectively improve the preparation efficiency of the air bridges with different heights prepared on the same substrate.

Description

Technical Field

[0001] This application relates to the field of circuit structure, and in particular to a method for fabricating an air bridge and a superconducting quantum chip. Background Technology

[0002] An air bridge is a three-dimensional structure that spans a coplanar waveguide transmission line and connects the ground planes on both sides of the transmission line. It can shield signals, reduce crosstalk between different coplanar waveguides, and connect the ground planes on both sides of the coplanar waveguide. When two coplanar waveguides cannot be avoided from intersecting, an air bridge can be used as a signal line from one coplanar waveguide to cross over the other.

[0003] Traditional air bridge fabrication technology can only fabricate air bridges of a single height on the same substrate at a time. When two different heights of air bridges need to be fabricated on the same substrate, they can only be fabricated in multiple separate processes, resulting in low fabrication efficiency. Summary of the Invention

[0004] Therefore, it is necessary to address the aforementioned technical problems by providing a method for fabricating air bridges of different heights on the same substrate, which can improve the fabrication efficiency of air bridges of different heights, and a superconducting quantum chip with air bridges of different heights.

[0005] In a first aspect, this application provides a method for preparing an air bridge, comprising:

[0006] At least two photoresist layers are coated on the substrate, and the photoresist layer farther away from the substrate has greater photosensitivity.

[0007] Exposure and etching are performed on at least two bridge regions of the at least two photoresist layers to form at least two bridge structures with different types of bridge support structures in the at least two bridge regions; and when etching the bridge top regions of the different types of bridge support structures, exposure doses that can etch to different photoresist layers are used respectively, so that the different types of bridge support structures include photoresist with different numbers of photoresist layers.

[0008] Superconducting films are deposited in the at least two bridging structures respectively;

[0009] The bridging structure with the deposited superconducting film is subjected to a debinding process to form air bridges of at least two heights.

[0010] Secondly, this application provides a superconducting quantum chip, which includes a substrate, quantum circuits integrated on the substrate, and air bridges of at least two heights, wherein the air bridges of at least two heights are prepared using the above-described air bridge preparation method.

[0011] The above-mentioned method for fabricating air bridges involves coating at least two layers of photoresist onto a substrate, and then performing exposure etching on at least two bridge regions of the at least two photoresist layers to form at least two types of bridging structures with different types of bridging structures. When etching the bridge top regions of the different types of bridging structures, different exposure doses are used to etch different photoresist layers, resulting in different bridging structures comprising photoresist with different numbers of photoresist layers. Since the photoresist layer farther from the substrate has higher photosensitivity, exposure etching on the photoresist layer farther from the substrate achieves higher etching efficiency, while exposure etching on the photoresist layer closer to the substrate achieves higher etching precision. This achieves a balance between etching efficiency and etching precision during the etching process for different types of bridging structures. By depositing superconducting films on at least two bridging structures and performing photoresist removal on the bridge structures with deposited superconducting films, at least two types of air bridges of different heights can be rapidly and accurately formed on the same substrate. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic cross-sectional view of the air bridge in the air bridge fabrication method provided in one embodiment;

[0014] Figure 2 This is a schematic diagram of an air bridge in a method for preparing an air bridge provided in one embodiment;

[0015] Figure 3 This is a schematic diagram of an air bridge in a method for preparing an air bridge provided in another embodiment;

[0016] Figure 4 This is a flowchart illustrating the preparation process of an air bridge in one embodiment.

[0017] Figure 5 This is a schematic diagram comparing the mask plate and the bridge region in the air bridge fabrication method provided in one embodiment;

[0018] Figure 6 This is a schematic diagram showing the width of different regions within the bridge area in the air bridge fabrication method provided in one embodiment;

[0019] Figure 7 This is a schematic diagram illustrating the changes in exposure dose in different areas within the bridge region during the air bridge fabrication method provided in one embodiment.

[0020] Figure 8 This is a schematic diagram of one of the bridge structures after exposure and etching of two photoresist layers in the air bridge fabrication method provided in one embodiment;

[0021] Figure 9 This is a schematic diagram illustrating the deposition effect of the superconducting film layer in the air bridge fabrication method provided in one embodiment;

[0022] Figure 10 This is a schematic diagram of the air bridge after adhesive removal in the air bridge preparation method provided in one embodiment;

[0023] Figure 11 This is a schematic diagram illustrating the relationship between etching depth and exposure dose in the air bridge fabrication method provided in one embodiment;

[0024] Figure 12 This is a schematic diagram illustrating the relationship between the remaining adhesive thickness and the exposure dose in the air bridge fabrication method provided in one embodiment;

[0025] Figure 13 This is a schematic diagram comparing the effects of reshaping and non-reshaping in the air bridge fabrication method provided in one embodiment.

[0026] Figure 14 This is a three-dimensional schematic diagram of the air bridge in the superconducting quantum chip in one embodiment of the air bridge fabrication method. Detailed Implementation

[0027] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0028] First, a brief introduction to the terms used in the embodiments of this application:

[0029] An air bridge is a circuit structure used to bridge planar circuits using a three-dimensional bridge-like structure. Air bridges are fabricated using micro-nano fabrication methods. Introducing air bridge structures into circuits can solve problems such as low inductance and low edge capacitance cross-interconnection, offering significant advantages over traditional wire bonding techniques. The key to fabricating air bridges is ensuring their structural robustness, allowing them to maintain their shape without collapsing or breaking.

[0030] Air bridges can be applied to various chips, such as superconducting quantum chips. Illustratively, for superconducting quantum chips, adding an air bridge structure at a suitable location in the superconducting circuit has many benefits: 1. Effectively improves impedance matching of chip connections; 2. Increases wiring space for quantum bit samples; 3. Relocates some lossy devices or processes out of the bit region to improve bit decoherence under complex processes; 4. Increases isolation between bit controls, especially in flip-chip chips, effectively increasing the isolation between the substrate and the top substrate.

[0031] Bridge Structure: In the process of constructing an air bridge, a bridge structure must first be constructed. This structure includes the bridge bracing structure to support the bridge deck and the pier area to connect the bridge deck to the foundation. In other words, when constructing an air bridge, the bridge structure must first be constructed, and then the air bridge structure is created based on this structure. Finally, the bridge bracing structure within the bridge structure is released, resulting in an independent air bridge.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0033] It should be understood that the singular forms of “a,” “an,” and “ / the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that terms such as “comprising / including” or “having” specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, in this specification, the term “and / or” includes any and all combinations of the associated listed items.

[0034] Indicative Figure 1 This application provides a cross-sectional structure of an air bridge according to an exemplary embodiment. The air bridge 100 includes a bridge top structure 110, an arch structure 120, a pier structure 130, and a bridge support structure 140 introduced during fabrication. The air bridge 100 is entirely situated on a base 150. When the bridge support structure 140 is released, the air bridge 100 is obtained, and the area where the bridge support structure 140 was originally located becomes an air or vacuum region 160. The distance from the base 150 to the bridge top structure 110 is the bridge height, and the arch structure 120 forms a certain angle θ with the base 150. The cross-sectional view of the bridge support structure can be a trapezoidal structure.

[0035] Figure 2 and Figure 3 This is a top view of an air bridge provided in an exemplary embodiment of this application, such as... Figure 2 As shown, an air bridge is a three-dimensional structure that spans a coplanar waveguide transmission line and connects the ground planes on both sides of the transmission line. It can shield signals, reduce crosstalk between different coplanar waveguides, and connect the ground planes on both sides of the coplanar waveguide. Air bridges can also be used as crossovers. Figure 3 As shown by the air bridge in the middle, when two coplanar waveguides cannot be avoided from intersecting, the air bridge can be used as a signal line of one coplanar waveguide to cross over the other coplanar waveguide.

[0036] In related technologies, air bridges in the field of superconducting qubits are currently typically fabricated using aluminum. There are two common air bridge fabrication techniques: based on the bridging material, air bridges can be divided into adhesive air bridges and SiO2 (silicon dioxide) air bridges. Adhesive air bridge fabrication requires multiple photolithography steps, making the process complex. It also relies on the reflow properties of special photoresists, imposing strict limitations on the photoresist. The superconducting film etching steps also impose limitations on the photoresist and the air bridge material itself. SiO2 air bridge fabrication requires multiple photolithography and stripping processes, making the process complex. It carries a significant risk of vHF (gaseous hydrogen fluoride) exposure and also imposes limitations on the air bridge material itself. Only air bridges of a single height can be fabricated on the same substrate at a time. Furthermore, the angle between the arch of SiO2 and adhesive air bridges and the substrate is usually small, which is detrimental to the release of the bridging structure and the removal of the adhesive.

[0037] Figure 4 This is a flowchart of a method for preparing an air bridge according to an exemplary embodiment of this application, as shown below. Figure 4 As shown, the fabrication process of this air bridge includes:

[0038] Step 402: Apply at least two photoresist layers to the substrate, and the photoresist layer farther away from the substrate has greater photoresist sensitivity.

[0039] The substrate is the basic material of the printed circuit board. Specifically, it can be a semi-finished product that integrates some electronic circuit structures. For example, taking a superconducting quantum chip as an example, the substrate can be a semi-finished product that integrates quantum circuits.

[0040] A photoresist layer is a film formed on a substrate using photoresist. Photoresist, also known as photoresist, is a thin-film etching material whose solubility changes upon exposure to ultraviolet light, electron beams, ion beams, X-rays, etc. Photoresist is a photosensitive liquid mixture composed of three main components: photosensitive resin, sensitizer, and solvent. It is used as an anti-corrosion coating material in the photolithography process. When semiconductor materials are processed on the surface, using appropriate selective photoresists can produce the desired image. Photoresists are classified into two main categories based on the image they form: positive and negative. In the photoresist process, after exposure and development, the exposed areas dissolve, while the unexposed areas remain; this type of coating material is called a positive photoresist. If the exposed areas remain while the unexposed areas dissolve, the coating material is called a negative photoresist.

[0041] Photoresists that use X-rays, electron beams, or ion beams as exposure sources are collectively referred to as radiation-line photoresists. Because the wavelengths of X-rays, electron beams, or ion beams are shorter than deep ultraviolet light, they exhibit almost no diffraction, thus achieving higher resolution in integrated circuit fabrication. Radiation-line photoresists are designed for processing techniques with linewidths less than 0.1 μm, while electron beam and ion beam lithography are suitable for nanometer-scale linewidths. Electron beam lithography involves high-speed, high-energy (typically 10-20 keV) particle streams colliding with resist molecules. The energy lost in inelastic collisions is absorbed by the molecules, inducing a chemical reaction. Resist molecules and atoms absorb this energy, releasing secondary and tertiary electrons. Due to the excitation of resist molecules, they lose energy and gradually become low-energy electrons. During the energy loss process of electron beam lithography, various ions and atomic groups (chemical free radicals) are generated, causing cross-linking of resist molecules (negative photoresist) or degradation (positive photoresist). The difference in solubility and dissolution rate between exposed and unexposed areas in the solvent is utilized to obtain an image after development. Electron beam lithography requires the resist to have high photosensitivity, contrast, and selectivity against dry etching. In this embodiment, the photoresist can be an electron beam photoresist or an ultraviolet photoresist, etc.

[0042] Photosensitivity, also known as light sensitivity, is the minimum exposure dose of light of a certain wavelength required to produce a good pattern on a photoresist. The unit of photosensitivity is mJ / cm². 2(mJ / cm²). The sensitivity of photoresist is particularly important for shorter wavelengths such as deep ultraviolet (DUV) and extreme ultraviolet (EUV). Negative photoresists typically require 5 to 15 seconds of exposure time, while positive photoresists require 3 to 4 times longer. Sensitivity reflects the degree to which a photoresist material responds to a specific wavelength of light. Different photoresists are selective for different wavelengths of light. High yields require short exposure times, thus placing increasingly higher demands on the photosensitivity of photoresists. Exposure dose can be used as an indicator of photoresist photosensitivity; the lower the exposure dose required to etch a certain depth onto the photoresist, the higher its photosensitivity.

[0043] Specifically, after applying the first layer of photoresist to the substrate, the first layer can be baked to allow it to solidify on the substrate as quickly as possible. Once the first layer is solidified, a second layer is applied over it, and this second layer can also be baked. This process is repeated until the required number of photoresist layers are applied.

[0044] The baking temperatures for the first and second photoresist layers can be determined based on the relative critical temperatures for forming the first and second photoresist layers. When the critical temperature for forming the first photoresist layer is higher than that for forming the second photoresist layer, the baking temperature for the first photoresist layer can be higher than that for the second photoresist layer.

[0045] Furthermore, since each photoresist layer is obtained by coating with photoresist materials of different photosensitivity, in order to make the photosensitivity of the photoresist layer farther away from the substrate greater, before coating each photoresist layer, the different photoresist materials can be sorted in advance according to their photosensitivity. This way, when coating different photoresist layers, the photoresist materials can be directly coated layer by layer in order of increasing photosensitivity, so that the coated photoresist layers change in order of distance from the substrate.

[0046] Step 404: Exposure and etching are performed on at least two bridge regions of at least two photoresist layers to form at least two bridge structures with different types of bridge support structures in at least two bridge regions; and when etching the bridge top regions of different types of bridge support structures, exposure doses that can etch to different photoresist layers are used respectively, so that different types of bridge support structures include photoresist with different numbers of photoresist layers.

[0047] The bridge region is the area used to form air bridges. There is a one-to-one correspondence between bridge regions and air bridges; one air bridge can be formed in each bridge region. Specifically, the bridge region is the area used for exposure etching to form the bridge structure and create the air bridge. The specific location of the bridge region is determined based on the desired location of the air bridge. To reduce the error between the actual exposed area and the desired bridge region, this can be achieved by precisely controlling the exposure position of the electron beam, or by covering at least two photoresist layers with a mask.

[0048] Specifically, a photomask is overlaid on at least two photoresist layers to expose at least two bridge regions based on the photomask. When the photoresist layer is positive, the bridge regions are the cut-out areas on the photomask. In some embodiments, since the locations of the individual air bridges to be fabricated are discontinuous and independent regions, using positive photoresist and a cut-out photomask makes the photomask a continuous whole, effectively improving the accuracy of the exposure etching positions of the bridge regions. Furthermore, the top view shape of the formed air bridge depends on the mask shape of the bridge regions. Figure 5 As shown, Figure 5 The image above is a schematic diagram of a cutout area in a cutout mask. Figure 5 The image below is a top view of the air bridge. The shape of this top view is the same as the shape of the hollow area. Specifically, for the hollow area and the top view, the left and right parts are the pier areas in the bridge area, and the middle part is the bridge body area and the arch area in the bridge area.

[0049] In some embodiments, such as Figure 6 As shown, the width of the bridge deck area can be smaller than the width of the pier area to increase the contact area between the air bridge and the foundation, thereby increasing the stability of the air bridge. The arch area connects the bridge deck area and the pier area. From the bridge deck area to the pier area, the width of the arch area can remain constant, for example, maintaining the same width as the bridge deck area. The width of the arch area can also gradually increase, specifically ranging from the width of the bridge deck area to the width of the pier area.

[0050] Exposure etching is a process that utilizes the photosensitivity of a photoresist layer to selectively remove portions of the photoresist. For example, it can remove the portion of the photoresist layer that is not masked by a photomask, resulting in a pattern that is completely identical to the one on the photomask.

[0051] Specifically, in the fabrication of the air bridge, the exposure etching process includes exposure, development, and fixing. The desired pattern is copied onto the photoresist layer, or a pattern is directly drawn onto the photoresist layer using an electron beam. After baking, the originally liquid photoresist solidifies on the substrate surface, facilitating exposure. Before exposure, the photosensitive agent DQ in the positive photoresist is insoluble in the developer and also inhibits the dissolution of phenolic resin in the developer. During exposure, the photosensitive agent DQ undergoes a chemical reaction to become ketene. Ketene is chemically unstable and further hydrolyzes to indenecarboxylic acid. Carboxylic acid has a solubility in alkaline solvents that is approximately 100 times higher than that of the unexposed photosensitive agent, and it also promotes the dissolution of phenolic resin. The difference in solubility between the exposed and unexposed photoresist in alkaline solutions is utilized to achieve the effect of exposure etching.

[0052] The bridge-making structure is the basic structure for fabricating an airbridge. It includes a strut structure to support the bridge deck and pier areas to connect the bridge deck to the base. Specifically, in fabricating an airbridge, the bridge-making structure is first fabricated, and then the airbridge structure is created based on it. Finally, the strut structure within the bridge-making structure is released, resulting in an independent airbridge. The shape of the bridge-making structure matches the shape of the airbridge; by depositing superconducting material on the bridge-making structure, a precisely shaped airbridge can be obtained.

[0053] Specifically, the bridge structure includes partially etched bridge support structures and fully etched bridge pier areas. The bridge support structures correspond to the bridge crown area and the bridge arch area. Different types of bridge support structures can be bridge support structures comprising photoresist layers of different thicknesses. Since the photoresist thickness varies with the different photoresist layers, different types of bridge support structures will at least have different photoresist thicknesses. In other embodiments, different types of bridge support structures can have different dimensions, such as different spans or different widths, i.e., the length and width in the top view of the air bridge.

[0054] The etching depth can be achieved by controlling the exposure dose. Different photoresist layers have different photosensitivity to the exposure dose, so the degree of change with the exposure dose will also be different. The bridge top region of the bridge support structure is the highest region in the bridge structure. By exposing the bridge top region of the bridge support structure with an exposure dose that can etch to different photoresist layers, different depths of etching can be achieved in the bridge top region of different bridge support structures, so that different types of bridge support structures include photoresist with different numbers of photoresist layers.

[0055] Specifically, by adjusting the exposure intensity, different exposure doses are applied to different locations within the bridge area. For positive photoresist, the exposure dose at the piers is required to be greater than that at the bridge top, and the exposure dose at the arch is between that of the piers and the bridge top. The exposure dose at the arch varies with the location gradient. The exposure dose of the air bridge is as follows: Figure 7 As shown. The effect after exposure etching is as follows. Figure 8 As shown, a bridge structure is formed, including a bridge bracing structure and a pier area. The bridge bracing structure is used to support the arch and body of the subsequent air bridge.

[0056] Step 406: Deposit superconducting films on at least two bridging structures respectively.

[0057] The superconducting film can be made of materials such as Al (aluminum), Nb (niobium), or TiN (titanium nitride). The deposition location of the superconducting film can be a local area encompassing each bridging region, or the entire area containing at least two photoresist layers after exposure and etching. Local deposition saves material used for superconducting film deposition, while global deposition allows for uniform deposition, resulting in a simple and efficient process. In a specific application, global deposition of the superconducting film can be achieved through vapor deposition. Vapor deposition is a process that uses heating and evaporation to evaporate the coating material, causing it to vaporize and the particles to condense on the surface of the deposition target, forming a film. The deposition effect of the superconducting film is as follows: Figure 9 As shown.

[0058] Step 408: At least the superconducting film layer of the bridging structure is debonded to form air bridges of at least two heights.

[0059] Photoresist, as a mask material, plays a role in pattern replication and transfer in semiconductor processing. Once the etching process is complete, it must be completely removed; this process is called resist stripping. Resist stripping specifically includes wet resist stripping. Wet resist stripping involves immersing the substrate with photoresist in a suitable organic solvent to dissolve or decompose the photoresist, removing it from the substrate surface. Before wet etching, the surface of the photoresist undergoes surface hardening treatment, making it insoluble or difficult to completely dissolve in most resist stripping solutions. In such cases, plasma can be used to remove the top layer of resist before wet resist stripping.

[0060] In a specific application, such as Figure 10 As shown, the substrate with the deposited superconducting film is placed in the photoresist stripping solution. The film suspended above the photoresist will detach from the substrate as the photoresist dissolves, while the superconducting film that is adhered to the substrate will be retained. The morphology after stripping is as follows. Figure 10 As shown, this is an air bridge structure.

[0061] The aforementioned method for fabricating air bridges involves coating at least two layers of photoresist onto a substrate, followed by exposure etching of at least two bridge regions within the photoresist layers. This forms at least two different bridging structures with varying bridging support structures in these regions. During the etching of the bridge top regions of the different bridging structures, different exposure doses are used to etch different photoresist layers, resulting in different photoresist layers for each bridging structure. Since the photoresist layer farther from the substrate has higher photosensitivity, this method achieves higher etching efficiency in the photoresist layer farther from the substrate and higher etching precision in the photoresist layer closer to the substrate. This balances etching efficiency and precision for different bridging structures. Furthermore, by depositing superconducting films on at least two bridging structures and removing the superconducting film from the bridging structure, at least two air bridge heights can be rapidly and accurately formed on the same substrate.

[0062] In some embodiments, the method for preparing an air bridge further includes: determining the number of photoresist layers to be coated and the required coating thickness of each photoresist layer based on the bridge height of the air bridges of different heights to be prepared; coating at least two photoresist layers on the substrate, including: coating photoresist layers layer by layer on the substrate according to the required coating thickness of each photoresist layer.

[0063] In this context, the height of an air bridge refers to the distance from the top of the fabricated air bridge to the substrate. Air bridges used for different purposes generally have different heights. For example, taking an air bridge in a superconducting quantum chip as an example, the height of an air bridge used to connect the two ground planes in a superconducting quantum chip is typically on the order of micrometers (e.g., 1 μm). For an air bridge used as a quantum bit capacitor (C = 80 fF), assuming the bridge area is S = 50 μm x 50 μm and the vacuum permittivity ε = 8.85E-12 F / m, the bridge height can be simply calculated as εS / C = 276 nm.

[0064] To accurately fabricate air bridges of various heights, the number of photoresist layers to be coated is determined according to the type of air bridge. Specifically, the number of photoresist layers to be coated can be equal to or less than the number of types of air bridges with different heights, so that each photoresist layer corresponds to at least one type of air bridge. This ensures accurate fabrication of each type of air bridge while avoiding increased coating time due to additional photoresist layers, thus improving fabrication efficiency. The specific coating thickness required for each photoresist layer can be determined based on the height of the air bridge.

[0065] In a specific application, there are two types of air bridges with different heights to be fabricated, with heights of 1µm and 276nm respectively. Therefore, the number of photoresist layers to be applied is determined to be two. The first type of air bridge, with a height of 276nm, is fabricated based on the first photoresist layer. The coating thickness of the first photoresist layer needs to be greater than the height of the first type of air bridge. The second type of air bridge, with a height of 1µm, is fabricated based on the superposition of the first and second photoresist layers. The cumulative coating thickness of the first and second photoresist layers needs to be greater than the height of the second type of air bridge. For example, the coating thickness of the first photoresist layer can be 400nm, and the coating thickness of the second photoresist layer can be 800nm, satisfying the conditions 400nm > 276nm and 400nm + 800nm ​​> 1µm. Then, photoresist layers are applied layer by layer on the substrate according to the required coating thickness for each layer.

[0066] In this embodiment, the number of photoresist layers to be coated and the required coating thickness of each photoresist layer are determined by the bridge height of the air bridges of different heights to be prepared. This ensures the accurate preparation of air bridges of different heights while avoiding the increase in coating time caused by applying too many or too thick photoresist layers, thereby improving the preparation efficiency of air bridges of different heights.

[0067] In some embodiments, the number of photoresist layers to be coated and the required coating thickness for each photoresist layer are determined based on the bridge height of the air bridges of different heights to be prepared, including:

[0068] The number of photoresist layers to be coated is determined according to the number of different types of air bridges of different heights to be prepared; the air bridges of different heights to be prepared are sorted according to their respective bridge heights to obtain the bridge height sorting result; based on the bridge height sorting result, the range of values ​​for the required coating thickness of each photoresist layer is determined in turn, and the target value is selected from the range as the required coating thickness of the photoresist layer corresponding to the range.

[0069] The range of values ​​for the required coating thickness of each photoresist layer can be determined based on the cumulative value of the required coating thickness of the already determined photoresist layer and the bridge height data currently being processed.

[0070] For example, if there are three types of air bridges with different heights to be prepared, namely 1µm, 200nm, and 2µm, then the number of photoresist layers to be coated is determined to be three. The air bridges of different heights are then sorted from lowest to highest, resulting in a bridge height sorting of 200nm, 1µm, and 2µm. For the 200nm high air bridge, the required coating thickness of the photoresist layer is in the range of (200nm, 400nm), and 300nm is selected as the required coating thickness for the first photoresist layer. For the 1µm high air bridge, the cumulative required coating thickness of the photoresist layer is in the range of 1µm to 1.5µm, where the required coating thickness for the first photoresist layer is 300nm. Therefore, the required coating thickness for the second photoresist layer is in the range of 0.7µm to 1.2µm, and 1µm is selected as the required coating thickness for the second photoresist layer. For an air bridge with a height of 2µm, the cumulative required coating thickness of the photoresist layer is between 2µm and 3µm. The cumulative required coating thickness of the first and second photoresist layers is 1.3µm. Therefore, the required coating thickness of the third photoresist layer is between 0.7µm and 1.7µm. 1.2µm is selected as the required coating thickness of the third photoresist layer.

[0071] In this embodiment, based on the bridge height sorting results, the range of values ​​for the required coating thickness of each photoresist layer is determined sequentially. The target value is selected from the range as the required coating thickness of the photoresist layer corresponding to the range. This can accurately obtain the required coating thickness of each photoresist layer, and effectively improve the exposure etching efficiency when fabricating bridge support structures of different heights.

[0072] In some embodiments, photoresist layers are applied layer by layer on the substrate according to the required coating thickness of each photoresist layer, including: for each target photoresist layer to be coated, using the target photoresist material required for the target photoresist layer, cyclically performing spin coating of the target photoresist material and baking of the spin-coated target photoresist material, until the coating thickness of the target photoresist material reaches the required coating thickness of the target photoresist layer.

[0073] During the photoresist coating process, the required coating thickness for different photoresist layers may vary, and the greater the required coating thickness, the more difficult the coating process becomes. To achieve accurate coating thickness for each photoresist layer, a small-batch, multiple-layer coating method can be used for each layer. Each coating process includes coating and baking to ensure rapid setting of the photoresist in a single application. The baking temperature of the photoresist can be determined based on the critical temperature for forming the photoresist material of the corresponding layer. For example, if the critical temperature is 180℃, the baking temperature of the photoresist should be higher than a target value of a certain threshold above the critical temperature, such as 180℃ + 10℃ = 190℃.

[0074] Furthermore, the photoresist material can be applied using methods such as spin coating, vapor deposition, and blade coating. Spin coating, also known as spin coating, can be achieved using a spin coater. The spin coating process includes three steps: material preparation, high-speed rotation, and evaporation to form a film. The film thickness is controlled by adjusting the spin coating time, rotation speed, drop volume, and the concentration and viscosity of the solution used.

[0075] In a specific application, the process of coating two photoresist layers on a substrate includes: spin-coating 500nm PMMA (polymethyl methacrylate) electron beam photoresist onto the substrate, baking at 180°C for 10 minutes, and repeating this cycle multiple times until the target thickness of the first photoresist layer is achieved. Then, spin-coating 900nm MAA (methyl methacrylate) electron beam photoresist on top of this, baking at 180°C for 10 minutes, and repeating this cycle multiple times until the target thickness of the second photoresist layer is achieved. Specifically, using PMMA as the first photoresist layer allows for precise control of the bridge height at the nanometer scale, serving as the capacitance of the qubit. Using MAA as the second photoresist layer increases the bridge support thickness, serving as the spanning line at the micrometer scale.

[0076] PMMA is polymerized from MMA. MMA monomers have a molecular weight of 100, while the number of monomers composing the polymer chain can reach thousands, with a molecular weight on the order of 100,000. The physicochemical properties of PMMA polymers largely depend on their molecular weight. The covalent bonds between atoms forming PMMA polymers can be broken by high-energy radiation. PMMA is sensitive to radiation with wavelengths λ of 1 nm or shorter and electron radiation with energies of 20 keV or higher, exhibiting photosensitive properties. Under electron beam exposure conditions, the PMMA backbone breaks down to form low-molecular-weight polymer fragments, which are used as positive photoresists. However, the exposure energy required for backbone breakage is relatively high, resulting in relatively low photosensitivity. When the exposure energy is sufficiently high, PMMA cross-links to form negative photoresists, achieving a maximum resolution of 10 nm. In this embodiment, by using a small-batch, multiple-batch spin-coating and baking process for each photoresist layer, the spin-coated photoresist material can be rapidly set, improving the stability of the photoresist layer.

[0077] In some embodiments, the bridge region includes a bridge top region, at least two bridge pier regions, and at least two bridge arch regions that respectively connect the bridge top region and the at least two bridge pier regions; exposure etching is performed on at least two bridge regions with at least two photoresist layers, including: for each bridge region with at least two photoresist layers, applying different exposure doses to the bridge pier regions, bridge arch regions, and bridge top regions to expose and etch the bridge regions to form a bridge structure.

[0078] Within the same bridge region, there can be one or more bridge crest regions. Bridge arch regions connect the bridge crest regions and the pier regions. Pier regions and bridge arch regions can exist in pairs, meaning the number of pier regions can be the same as the number of bridge pier areas. Alternatively, the number of pier regions can be less than the number of bridge pier areas, for example, multiple bridge arch regions can connect a single pier region to the bridge crest region. For ease of explanation, the following embodiments will use an example where the number of bridge crest regions is 1, and the number of pier regions and bridge arch regions are both 2.

[0079] The bridge structure fabrication process includes: applying different exposure doses to the pier area, the arch area, and the top area of ​​the bridge, and then developing the exposed bridge area to achieve exposure etching, thereby forming the bridge structure.

[0080] Development is a photolithography technique in which the photoresist in the exposed areas of positive photoresist and the unexposed areas of negative photoresist is dissolved in a developing solution, forming a three-dimensional pattern on the photoresist. Development is a crucial step in creating patterns in the photoresist on the substrate surface. Soluble areas on the photoresist are dissolved by a chemical developer, leaving visible islands or window patterns on the substrate surface. The development process may specifically include spinning, spraying, wetting, and then development, followed by rinsing the substrate with deionized water and drying. The unexposed photoresist areas do not undergo a chemical reaction during exposure, and therefore, there is no acid-base neutralization during development, so these areas are retained. The exposed positive photoresist gradually dissolves, and the neutralization reaction only occurs on the surface, making it relatively less affected by the developing solution. For negative photoresist, the unexposed areas first form a gel in the developing solution and then decompose, resulting in the entire negative photoresist layer being thoroughly soaked in the developing solution. After being soaked, the exposed negative photoresist areas will expand and deform.

[0081] In this embodiment, since the pier area is a fully etched area and the bridge top area is a partially etched area, there is a height difference between the pier area and the bridge top area. In order to connect the pier and the bridge body of the fabricated air bridge, a bridge arch with varying height is required to connect the pier and the bridge body. By applying different exposure doses to the pier area, the bridge arch area, and the bridge top area respectively, the bridge area is exposed and etched to form the bridge structure, ensuring the stability of the air bridge fabricated in the bridge area.

[0082] In some embodiments, different exposure doses are applied to the pier area, the arch area, and the crown area, including:

[0083] A first exposure dose is applied to the bridge top area, and the first exposure dose is different for different types of bridge structures; a second exposure dose that can completely etch at least two layers of photoresist is applied to the bridge pier area; in the bridge arch area, an intermediate exposure dose that gradually increases with the increase of the distance between the arch area and the bridge top area is applied, and the intermediate exposure dose is greater than the first exposure dose and less than the second exposure dose.

[0084] The first exposure dose is determined by the height of the air bridge to be prepared. The higher the height of the air bridge to be prepared, the smaller the first exposure dose; the lower the height of the air bridge to be prepared, the larger the first exposure dose. The first exposure dose is inversely correlated with the height of the air bridge to be prepared and positively correlated with the etching depth of the photoresist layer.

[0085] In one specific application, in the bridge arch region, as the distance between the current exposure position and the bridge top region increases, an intermediate exposure dose with a linearly increasing dose is applied within the bridge arch region. This causes the bridge arch region to descend at a uniform rate from the etching depth from the bridge top region to the bridge pier region. In this case, the cross-section of the bridge support structure is trapezoidal. In another specific application, in the bridge arch region, as the distance between the current exposure position and the bridge top region increases, an intermediate exposure dose with a gradually increasing dose increase rate is applied within the bridge arch region. This causes the bridge arch region to descend slowly and then rapidly from the etching depth from the bridge top region to the bridge pier region. This results in a larger angle between the bridge arch region and the substrate, improving the stability of the air bridge.

[0086] In this embodiment, by applying an intermediate exposure dose that gradually increases with the increase in distance between the follower and the bridge top region, and by making the intermediate exposure dose greater than the first exposure dose and less than the second exposure dose, a stable connection between the bridge top region and the bridge pier region can be ensured, thereby improving the structural stability of the air bridge.

[0087] In some embodiments, the method for fabricating air bridges further includes: obtaining a target relationship curve between etching degree and exposure dose, the target relationship curve comprising at least two sequentially connected sub-curves corresponding one-to-one with the photoresist layer; the sub-curves characterize the change of etching degree with the change of exposure dose, and the sub-curve corresponding to the photoresist layer with higher photosensitivity has a greater rate of change; and performing exposure etching processing on at least two bridge regions of at least two photoresist layers, including: performing exposure etching processing on at least two bridge regions of at least two photoresist layers based on the target relationship curve.

[0088] The degree of etching can be specifically represented by either the etching depth or the remaining resist thickness. A greater etching depth or a smaller remaining resist thickness indicates a greater degree of etching, while a smaller etching depth or a larger remaining resist thickness indicates a smaller degree of etching. The target relationship curve between the degree of etching and the exposure dose can be established by creating an air bridge. The target relationship curve is related to the type, order, and thickness of the photoresist layers coated on the substrate. When at least one of the type, order, or thickness of the photoresist layers coated on the substrate changes, it may be necessary to re-obtain the corresponding target relationship curve.

[0089] The target relationship curve consists of at least two sequentially connected sub-curves, each corresponding to a photoresist layer. The inflection point between the two sub-curves is the contact surface of the two directly contacting photoresist layers. When the x-axis of the target relationship curve represents the exposure dose and the y-axis represents the etching degree, the sub-curve corresponding to the photoresist layer with higher photosensitivity will have a greater rate of change, i.e., a steeper slope.

[0090] In practical applications, based on the target relationship curve, exposure etching is performed on at least two bridge regions of at least two photoresist layers to accurately understand the etching degree corresponding to each exposure dose and improve the accuracy of the exposure etching process.

[0091] In some embodiments, the process of constructing the target relationship curve includes: applying various exposure doses with different dosages to a measurement substrate coated with at least two layers of photoresist; measuring the etching depth or remaining photoresist thickness of the measurement substrate after applying different exposure doses to construct the target relationship curve.

[0092] The multiple exposure doses applied can be exposure doses applied separately at different locations on the measurement substrate, or multiple exposure doses that are gradually increased and applied sequentially to the same location at different time points. For example, an exposure dose is applied once at a certain location and a development process is performed, then the etching degree parameter is measured, and then an exposure dose with an increased dose is applied at the same location.

[0093] The target relationship curve includes at least one of the following: the relationship curve between remaining resist thickness and exposure dose, and the relationship curve between etching depth and exposure dose. The remaining resist thickness is the thickness of the photoresist left in the photoresist layer after the exposure and etching are completed, and the etching depth is the thickness of the photoresist etched away in the photoresist layer after the exposure and etching are completed. The combination of the remaining resist thickness and the etching depth is the total thickness of the photoresist layer.

[0094] In this embodiment, by applying different exposure doses to the measurement substrate, at least one of the following curves is constructed: the relationship between the remaining adhesive thickness and the exposure dose, and the relationship between the etching depth and the exposure dose. Based on a small number of experiments, the etching depth or remaining adhesive thickness corresponding to each exposure dose can be obtained through curve fitting. This is beneficial for accurately determining the exposure dose at each position during the subsequent fabrication of air bridges.

[0095] In some embodiments, multiple exposure doses with different dosages are applied to a measurement substrate coated with at least two photoresist layers. This includes: when two photoresist layers are coated on the measurement substrate, multiple exposure doses with sequentially increasing dosages are applied to the measurement substrate. The multiple exposure doses are divided into multiple exposure dose groups arranged sequentially. The dose interval between adjacent exposure doses in the same exposure dose group is the same. The maximum exposure dose in the previous exposure dose group is less than the minimum exposure dose in the next exposure dose group, and the dose interval in the previous exposure dose group is less than the dose interval in the next exposure dose group.

[0096] For example, when two photoresist layers are coated on the measurement substrate, multiple exposure doses are applied to the measurement substrate, with the dose gradually increasing from the minimum exposure dose to the first exposure dose according to a first dose interval, and multiple exposure doses gradually increasing from the first exposure dose to the second exposure dose according to a second dose interval; wherein, the second exposure dose is the dose that can completely etch the two photoresist layers, and the first dose interval is smaller than the second dose interval.

[0097] Since the photoresist layer farther from the substrate has greater photosensitivity, the etching degree of the photoresist layer farther from the substrate will also vary more for the same exposure dose interval. By setting different dose intervals, the photoresist layer farther from the substrate can have a smaller dose interval, thus obtaining an accurate sub-curve. Since the photoresist layer closer to the substrate has lower photosensitivity to exposure dose, increasing the dose interval can effectively reduce the number of measurements on the photoresist layer closer to the substrate while obtaining a more accurate sub-curve, thus obtaining an accurate target relationship curve.

[0098] In some embodiments, depositing superconducting films on at least two bridging structures includes: depositing superconducting films on at least two photoresist layers including at least two bridging structures; and performing a photoresist stripping process on at least the bridging structures with deposited superconducting films to form air bridges of at least two heights, including: immersing a substrate coated with at least two photoresist layers and on which superconducting films are deposited into a photoresist stripping solution to dissolve the at least two photoresist layers and cause the superconducting film layer in the unetched areas deposited on the at least two photoresist layers to detach with the dissolution of the photoresist, thereby forming air bridges of at least two heights that adhere to the substrate.

[0099] By directly depositing a superconducting film on at least two photoresist layers, it is possible to ensure that each bridging structure in the at least two photoresist layers can be deposited with a superconducting film, without needing to determine the specific location of each of the at least two types of bridging structures in the at least two photoresist layers. This ensures the precise deposition of the superconducting film on the bridging structures. By placing the substrate coated with at least two photoresist layers and on which the superconducting film is deposited into a stripper solution, the at least two photoresist layers dissolve in the stripper solution. This allows the superconducting film in the unetched areas deposited on the at least two photoresist layers to detach as the photoresist dissolves, while the superconducting film adhering to the substrate is retained, forming air bridges of at least two heights. This simplifies the process complexity of depositing the superconducting film.

[0100] In some embodiments, when different removers are required to dissolve photoresists with different photosensitivity, the dissolution process of at least two photoresist layers includes: placing a substrate coated with at least two photoresist layers and having a superconducting film layer deposited thereon into the remover required for the target photoresist layer furthest from the substrate, so that the target photoresist layer dissolves and the superconducting film layer in the unetched area deposited on the target photoresist layer detaches as the target photoresist layer dissolves; for the undissolved remaining photoresist layers on the substrate, in order from farthest to near the substrate, placing the substrate containing at least one remaining photoresist layer into the remover required for each remaining photoresist layer in order of distance from the substrate, so that each remaining photoresist layer dissolves in sequence until at least two air bridges of different heights are formed that adhere to the substrate.

[0101] In one specific embodiment, taking at least two photoresist layers, including a first photoresist layer and a second photoresist layer, as an example, if the stripper solution for the first photoresist layer is the same as that for the second photoresist layer, the substrate coated with at least two photoresist layers and deposited with a superconducting film layer can be directly placed into the same stripper solution. If the stripper solution for the first photoresist layer is different from that for the second photoresist layer, the substrate coated with at least two photoresist layers and deposited with a superconducting film layer is first placed into the stripper solution required for the second photoresist layer. After removing the second photoresist layer and the suspended superconducting film layer, the substrate with the bridging structure and the first photoresist layer is placed in the stripper solution for the first photoresist layer, forming air bridges of at least two different heights.

[0102] In this embodiment, the substrate containing at least one remaining photoresist layer is sequentially placed into the photoresist remover solution required for each remaining photoresist layer in order from farthest to near the substrate, so as to remove the photoresist layer layer by layer and achieve effective stripping of the photoresist layer.

[0103] In some embodiments, the method for fabricating an air bridge further includes: performing a high-temperature baking process on at least two photoresist layers that have undergone exposure etching to reshape the bridging structure in at least two bridging structures; and depositing a superconducting film layer on each of the at least two bridging structures, including: depositing a superconducting film layer on each of the at least two bridging structures having the reshaped bridging structure.

[0104] In practical applications, since the edges of the bridging structures in the air bridge may have gradient changes, a high-temperature photoresist baking step is added before depositing the superconducting film after exposure etching to reshape the edges of the bridging structures in order to make the bridging more continuous at the arch. This results in a larger angle between the arch and the substrate, higher stability of the air bridge, and better removal of the photoresist from the bridging structures, thereby improving the removal efficiency and effect.

[0105] In one embodiment, this application also provides a superconducting quantum chip, which includes a substrate, quantum circuitry integrated on the substrate, and air bridges of at least two heights. The air bridges of at least two heights are fabricated using the air bridge fabrication methods described in the above embodiments. Fabricating air bridges of at least two heights using the air bridge fabrication methods described in the above embodiments can effectively improve the fabrication efficiency of the superconducting quantum chip.

[0106] Furthermore, the air bridges of at least two heights include air bridges used as coplanar waveguide spans and air bridges used as capacitors for qubits, with the height of the air bridge used as a coplanar waveguide span being greater than the height of the air bridge used as a capacitor for qubits.

[0107] It should be understood that although the steps in the flowcharts of the above embodiments are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the above embodiments may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0108] This application also provides a specific application scenario for the fabrication of air bridges in superconducting quantum chips, which utilizes the aforementioned air bridge fabrication method. Specifically, the application of this air bridge fabrication method in the application scenario of air bridges in superconducting quantum chips is as follows:

[0109] Taking the fabrication of air bridges in superconducting quantum chips as an example, the height of an air bridge used to connect the two ground planes in a superconducting quantum chip is typically on the order of micrometers (e.g., 1 μm). For an air bridge used as a qubit capacitor (assuming C = 80 fF), assuming the bridge area is S = 50 μm x 50 μm and the vacuum permittivity ε = 8.85E-12 F / m, the height of the bridge can be simply calculated as εS / C = 276 nm.

[0110] In the superconducting quantum chip, there are two types of air bridges of different heights to be fabricated, with heights of 1µm and 276nm respectively. Therefore, two photoresist layers need to be applied. The first type of air bridge, with a height of 276nm, is fabricated based on the first photoresist layer. The coating thickness of the first photoresist layer needs to be greater than the height of the first type of air bridge. The second type of air bridge, with a height of 1µm, is fabricated by stacking the first and second photoresist layers. The cumulative coating thickness of the first and second photoresist layers needs to be greater than the height of the second type of air bridge. For example, the coating thickness of the first photoresist layer could be 400nm, and the coating thickness of the second photoresist layer could be 800nm, satisfying the conditions 400nm > 276nm and 400nm + 800nm ​​> 1µm. Then, photoresist layers are applied layer by layer on the substrate according to the required coating thickness for each layer.

[0111] Furthermore, it was determined that using PMMA as the first photoresist layer allows for precise control of the bridge height at the nanometer scale, serving as the capacitance of the qubit. Using MAA as the second photoresist layer increases the bridge support thickness, serving as the span at the micrometer scale.

[0112] To accurately understand the relationship between different photoresist layers and exposure records, exposure tests were performed on substrates coated with a first photoresist layer and a second photoresist layer. Specifically, the process of coating two photoresist layers on the substrate included: spin-coating 500nm PMMA electron beam photoresist onto the substrate, baking at 180°C for 10 minutes, and repeating this cycle multiple times until the target thickness of the first photoresist layer of 400nm was achieved. Then, spin-coating 900nm MAA (methyl methacrylate) electron beam photoresist onto this substrate, baking at 180°C for 10 minutes, and repeating this cycle multiple times until the target thickness of the second photoresist layer of 800nm ​​was achieved.

[0113] At different locations on the measurement substrate, multiple exposure doses are applied, with the dose gradually increasing from the minimum exposure dose to the first exposure dose according to a first dose interval, and multiple exposure doses gradually increasing from the first exposure dose to the second exposure dose according to a second dose interval; wherein, the second exposure dose is the dose that can completely etch the two photoresist layers, and the first dose interval is smaller than the second dose interval.

[0114] Develop with a developer solution of MIBK (methyl isobutyl ketone):IPA (isopropanol) = 1:3 for 60 seconds. Measure the thickness of the etched photoresist using a profilometer or atomic force microscope to establish the relationship between etching depth and exposure dose. Figure 11 As shown. The relationship between the remaining thickness of the photoresist and the exposure dose is as follows. Figure 12 As shown, the etching depth (remaining resist thickness) is divided into two stages based on the exposure dose. Stage 1 represents the portion of the data points along the first fitted curve, and Stage 2 represents the portion of the data points distributed along the second fitted curve. Stage 1 corresponds to the etching of MAA photoresist, and Stage 2 corresponds to the etching of PMMA photoresist. MAA photoresist is more sensitive to exposure dose, while PMMA photoresist is less sensitive. Therefore, it is easier to achieve nanometer-level control of the remaining resist thickness using PMMA photoresist.

[0115] The fabrication of the air bridge involves several processes, including spin-coating photoresist on the substrate, exposure etching, photoresist reshaping, deposition of a superconducting film, and lift-off.

[0116] In the spin-coating stage of photoresist on the substrate, the coating parameters of the photoresist layer on the substrate are the same as those on the test substrate. Specifically, the process of coating two photoresist layers on the substrate includes: spin-coating 500nm PMMA electron beam photoresist on the substrate, baking at 180℃ for 10 minutes, and repeating this cycle multiple times until the target thickness of the first photoresist layer of 400nm is achieved. Then, spin-coating 900nm MAA (methyl methacrylate) electron beam photoresist on this substrate, baking at 180℃ for 10 minutes, and repeating this cycle multiple times until the target thickness of the second photoresist layer of 800nm ​​is achieved.

[0117] In the exposure etching stage, either electron beam lithography or ultraviolet lithography can be used. By adjusting the exposure intensity, different exposure doses are applied to different locations in the bridge area. The exposure dose at the piers is required to be greater than that at the bridge top, and the exposure dose at the arch is between that of the piers and the bridge top. The exposure dose at the arch varies with the position gradient. Specifically, at least two bridge structures with different types of bridge support structures are formed in at least two bridge areas. Furthermore, when etching the bridge top areas of the different types of bridge support structures, exposure doses capable of etching different photoresist layers are used, ensuring that each type of bridge support structure includes photoresist with a different number of photoresist layers.

[0118] Photoresist reshaping can be an additional step. The high-temperature baking step reshapes the photoresist of the bridge structure after exposure and etching, making the edges of the bridge structure smoother. See [link to details]. Figure 13 .

[0119] In the superconducting film deposition stage, the material of the superconducting film can be Al (aluminum), Nb (niobium), TiN (titanium nitride), etc. The deposition location of the superconducting film can be a local area including each bridging region, or it can be the entire area containing at least two photoresist layers after exposure and etching. Local deposition can save the material required to deposit the superconducting film, while global deposition can perform the deposition process uniformly, making the process simple and efficient.

[0120] During the stripping stage, if the stripping solution for the first photoresist layer is the same as that for the second photoresist layer, the substrate with at least two photoresist layers and a superconducting film deposited can be directly placed into the same stripping solution. If the stripping solution for the first and second photoresist layers is different, the substrate with at least two photoresist layers and a superconducting film deposited is first placed into the stripping solution required for the second photoresist layer. After removing the second photoresist layer and the suspended superconducting film, the substrate with the bridging structure and the first photoresist layer is placed in the stripping solution for the first photoresist layer, forming air bridges of at least two different heights. The three-dimensional morphology and height of the air bridges are shown below. Figure 14 As shown, the height of the air bridge can be precisely controlled using the above method. A single process on the same substrate can achieve air bridges with heights ranging from nanometers to micrometers, adapting to application scenarios that require the fabrication of air bridges with different heights on the same substrate.

[0121] In the description of this specification, the references to terms such as "some embodiments," "other embodiments," "ideal embodiments," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example that are included in at least one embodiment or example of this application. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0122] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features of the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0123] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing an air bridge, characterized in that, include: At least two photoresist layers are coated on the substrate, and the photoresist layer farther away from the substrate has greater photosensitivity. Based on the target relationship curve between etching degree and exposure dose, exposure etching is performed on at least two bridge regions of the at least two photoresist layers to form at least two bridge structures with different types of bridge support structures in the at least two bridge regions; and when etching the bridge top regions of different types of bridge support structures, exposure doses that can etch to different photoresist layers are used respectively, so that different types of bridge support structures include photoresist with different numbers of photoresist layers. Superconducting films are deposited in the at least two bridging structures respectively; The bridging structure with the deposited superconducting film is subjected to a desizing process to form air bridges of at least two heights, including micron-sized air bridges and nano-sized air bridges. The target relationship curve includes at least two sequentially connected sub-curves corresponding one-to-one with the photoresist layer. The target relationship curve is constructed by applying multiple exposure doses with sequentially increasing doses to a measurement substrate coated with at least two photoresist layers, and measuring the etching depth or remaining photoresist thickness of the measurement substrate after applying different exposure doses to construct the target relationship curve. The multiple exposure doses are divided into multiple exposure dose groups arranged sequentially. The dose interval between adjacent exposure doses in the same exposure dose group is the same. The maximum exposure dose in the previous exposure dose group is less than the minimum exposure dose in the next exposure dose group, and the dose interval in the previous exposure dose group is less than the dose interval in the next exposure dose group.

2. The method for preparing an air bridge according to claim 1, characterized in that, The method for preparing the air bridge further includes: Based on the bridge height of the air bridges of different heights to be prepared, the number of photoresist layers to be coated and the required coating thickness of each photoresist layer are determined. The process of coating at least two layers of photoresist on the substrate includes: Photoresist layers are applied layer by layer on the substrate according to the required coating thickness of each photoresist layer.

3. The method for preparing an air bridge according to claim 2, characterized in that, The determination of the number of photoresist layers to be coated and the required coating thickness for each photoresist layer based on the bridge height of the air bridges of different heights to be prepared includes: The number of photoresist layers to be applied is determined according to the number of different types of air bridges of varying heights to be prepared. The air bridges of different heights to be prepared are sorted according to their respective bridge heights to obtain the bridge height sorting results; Based on the bridge height sorting results, the range of values ​​for the required coating thickness of each photoresist layer is determined sequentially, and the target value is selected from the range as the required coating thickness of the photoresist layer corresponding to the range.

4. The method for preparing an air bridge according to claim 2, characterized in that, The step of coating photoresist layers onto the substrate layer by layer according to the required coating thickness of each photoresist layer includes: For each target photoresist layer to be coated, the target photoresist material required for the target photoresist layer is used, and the spin coating of the target photoresist material and the baking of the spin-coated target photoresist material are performed cyclically until the coating thickness of the target photoresist material reaches the coating thickness required for the target photoresist layer.

5. The method for preparing an air bridge according to claim 1, characterized in that, The bridge area includes a bridge top area, at least two bridge pier areas, and at least two bridge arch areas that respectively connect the bridge top area and the at least two bridge pier areas; The exposure etching process for at least two bridge regions of the at least two photoresist layers includes: For each bridge region of the at least two photoresist layers, different exposure doses are applied to the pier region, the arch region, and the top region to perform exposure etching processing on the bridge region to form a bridge structure.

6. The method for preparing an air bridge according to claim 5, characterized in that, Applying different exposure doses to the bridge pier area, the bridge arch area, and the bridge top area respectively includes: A first exposure dose is applied to the top region of the bridge; the first exposure dose varies depending on the type of bridge structure. A second exposure dose capable of completely etching the at least two photoresist layers is applied to the pier area; In the arch region, as the distance between the arch and the top region increases, an intermediate exposure dose that gradually increases is applied, the intermediate exposure dose being greater than the first exposure dose and less than the second exposure dose.

7. The method for preparing an air bridge according to claim 6, characterized in that, In the bridge arch region, as the distance from the bridge crown region increases, an intermediate exposure dose that gradually increases in dose is applied, including: As the distance from the bridge crown region increases, an intermediate exposure dose with a linearly increasing dose is applied within the bridge arch region; Alternatively, as the distance between the bridge crown region and the bridge arch region increases, an intermediate exposure dose with a gradually increasing dose increase rate is applied within the bridge arch region.

8. The method for preparing an air bridge according to claim 1, characterized in that, The sub-curve represents the change in etching degree as the exposure dose changes, and the sub-curve corresponding to the photoresist layer with higher photosensitivity changes at a greater rate.

9. The method for preparing an air bridge according to claim 8, characterized in that, The target relationship curve includes at least one of the relationship curves between remaining adhesive thickness and exposure dose, and the relationship curve between etching depth and exposure dose.

10. The method for preparing an air bridge according to claim 1, characterized in that, The deposition of superconducting films on the at least two bridging structures includes: Deposit a superconducting film layer on at least two photoresist layers including the at least two bridging structures; The process of removing the adhesive from the bridging structure, which at least has a deposited superconducting film, to form air bridges of at least two heights includes: The substrate coated with at least two layers of photoresist and deposited with the superconducting film is placed in a photoresist remover solution to dissolve the at least two layers of photoresist and cause the superconducting film in the unetched area deposited on the at least two layers of photoresist to detach as the photoresist dissolves, forming air bridges of at least two heights that adhere to the substrate.

11. The method for preparing an air bridge according to claim 10, characterized in that, The step of placing a substrate coated with at least two layers of photoresist and deposited with a superconducting film into a resist remover solution to dissolve the at least two layers of photoresist and cause the superconducting film in the unetched areas deposited on the at least two layers of photoresist to detach as the photoresist dissolves, forming air bridges of at least two heights adhered to the substrate, includes: When different photoresists with different photosensitivity require different removers, a substrate coated with at least two photoresist layers and with a superconducting film layer deposited is placed in the remover required for the target photoresist layer furthest from the substrate, so that the target photoresist layer dissolves and the superconducting film layer in the unetched area deposited on the target photoresist layer is detached as the target photoresist layer dissolves. For the undissolved remaining photoresist layer on the substrate, the substrate containing at least one remaining photoresist layer is sequentially placed into the remover solution required for each remaining photoresist layer in order from farthest to near the substrate, so that each remaining photoresist layer is dissolved sequentially until at least two air bridges of different heights are formed that adhere to the substrate.

12. The method for preparing an air bridge according to any one of claims 1 to 11, characterized in that, The method for preparing the air bridge further includes: The at least two photoresist layers that have undergone the exposure and etching process are subjected to high-temperature baking to reshape the bridge support structure in the at least two bridge-making structures. The deposition of superconducting films on the at least two bridging structures includes: Superconducting films are deposited on each of the at least two bridging structures having the reshaped bridging structure.

13. A superconducting quantum chip, characterized in that, The superconducting quantum chip includes a substrate, quantum circuitry integrated on the substrate, and air bridges of at least two heights, wherein the air bridges of at least two heights are prepared by the method of any one of claims 1 to 12.

14. The superconducting quantum chip according to claim 13, characterized in that, The air bridges of at least two heights include a first type of air bridge used as a coplanar waveguide crossover and a second type of air bridge used as a capacitor for a quantum bit; the height of the first type of air bridge is greater than the height of the second type of air bridge.

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