Method for producing an air bridge and quantum chip

Abstract

This invention discloses a method for fabricating an air bridge and a quantum chip. The method includes: providing a substrate with a first photoresist layer; forming at least three vias on the first photoresist layer, with their center points sequentially connected to form a closed pattern; forming a first metal structure filling each via, and removing the first photoresist layer; forming a second photoresist layer flush with the surface of the first metal structure on the substrate, and forming a third photoresist layer covering the second photoresist layer, forming an opening on the third photoresist layer exposing the entire first metal structure; forming a second metal structure connected to the entire first metal structure within the opening; and removing the second and third photoresist layers to obtain the air bridge. Because there are at least three piers, and all piers support the bridge deck, the structural strength is enhanced, thereby improving the structural stability of the air bridge. Structural damage is less likely during photoresist removal, and the air bridge is less prone to collapse after photoresist removal.

Description

Technical Field

[0001] This invention relates to the field of quantum chip manufacturing technology, and in particular to a method for preparing an air bridge and a quantum chip. Background Technology

[0002] Quantum chips contain numerous coplanar waveguides. Due to limitations in manufacturing processes, the morphology of these waveguides is not perfect and always contains imperfections, such as poor symmetry, uneven edges, and discontinuities. Furthermore, as the number of qubits on a quantum chip increases, the number of coplanar waveguides also increases, making their wiring increasingly complex. To correct these imperfections and facilitate their wiring, existing processes have introduced air bridges to connect the grounding bands on both sides of the coplanar waveguide.

[0003] Current air bridge manufacturing processes, such as Figure 1 As shown, Figure 1 In the diagram, a to e represent the process flow. First, a photoresist P1 for support is formed on the substrate S. Then, an arched photoresist P2 is obtained through heating and reflow. A metal layer M is deposited on the photoresist P2, and excess metal is etched away. Finally, the photoresist P2 is removed by ultrasonic cleaning or other methods, leaving a metal structure that forms an air bridge. However, because the thickness at the edges and corners of this air bridge is very small, its structural stability is poor. Ultrasonic cleaning and other processes can easily cause the air bridge to break, and the lack of support after photoresist removal can easily cause it to collapse. Summary of the Invention

[0004] The purpose of this invention is to provide a method for fabricating an air bridge and a quantum chip, so as to solve the problem of poor structural stability of air bridges in the prior art and improve the structural stability of air bridges.

[0005] To solve the above-mentioned technical problems, the present invention provides a method for preparing an air bridge, comprising:

[0006] Provide a substrate having a first photoresist layer;

[0007] At least three through-holes with their center points connected in sequence to form a closed pattern are formed on the first photoresist layer;

[0008] A first metal structure is formed to fill each of the vias, and the first photoresist layer is removed;

[0009] A second photoresist layer flush with the surface of the first metal structure is formed on the substrate, and a third photoresist layer is formed covering the second photoresist layer, with an opening in the third photoresist layer exposing the entire second photoresist layer.

[0010] A second metal structure is formed within the opening, which is connected to all of the first metal structures.

[0011] Remove the second and third photoresist layers to obtain an air bridge.

[0012] Preferably, the step of forming at least three vias with their center points connected in pairs to form a closed pattern on the first photoresist layer includes:

[0013] At least three through-hole patterns with their center points connected in sequence to form a closed pattern are exposed on the first photoresist layer.

[0014] Each of the via patterns is developed to form a via.

[0015] Preferably, the step of forming a second photoresist layer flush with the surface of the first metal structure on the substrate, forming a third photoresist layer covering the second photoresist layer, and forming an opening on the third photoresist layer exposing the entire first metal structure includes:

[0016] A second photoresist layer is formed by coating photoresist onto the substrate, which is flush with the surface of the first metal structure.

[0017] A third photoresist layer is formed by coating photoresist onto the second photoresist layer;

[0018] An opening pattern is exposed on the third photoresist layer;

[0019] The opening pattern is developed to expose the entire first metal structure.

[0020] Preferably, before the step of forming a second metal structure connected to all of the first metal structures within the opening, the preparation method further includes:

[0021] Remove the natural oxide layer from the surface of the first metal structure within the opening.

[0022] Preferably, the opening is annular.

[0023] Preferably, the center line of the projection shape of the opening on the substrate coincides with the projection of the closed pattern on the substrate.

[0024] Preferably, the second photoresist layer and the third photoresist layer are removed by ultrasonic cleaning.

[0025] Preferably, the number of through holes is four.

[0026] Preferably, both the closed shape and the through hole are rectangular.

[0027] To address the aforementioned technical problems, the present invention also provides a quantum chip comprising an air bridge prepared according to any of the preceding claims, wherein the substrate comprises a substrate and a coplanar waveguide formed on the substrate, at least one first metal structure of the air bridge is located on one grounding band of the coplanar waveguide, the remaining first metal structures are located on another grounding band of the coplanar waveguide, the central conductor of the coplanar waveguide passes through the gap between the first metal structures on the two grounding bands, and a second metal structure between the first metal structures on the two grounding bands spans over the central conductor.

[0028] Unlike existing technologies, the method for fabricating an air bridge provided by this invention first provides a substrate with a first photoresist layer. At least three through-holes with their center points connected sequentially to form a closed pattern are formed on the first photoresist layer. Next, a first metal structure is filled into each through-hole, and the first photoresist layer is removed. Then, a second photoresist layer flush with the surface of the first metal structure is formed, and a third photoresist layer covering the second photoresist layer is formed. An opening exposing the entire first metal structure is formed on the third photoresist layer. Finally, a second metal structure connected to the entire first metal structure is formed within the opening, and the second and third photoresist layers are removed to obtain the air bridge. The first metal structure serves as the bridge pier, and the second metal structure serves as the bridge deck. Since there are at least three piers, and all piers support the bridge deck, the structural strength is enhanced, thereby improving the structural stability of the air bridge. Structural damage is less likely during photoresist removal, and the air bridge is less prone to collapse after photoresist removal.

[0029] The quantum chip provided by this invention includes an air bridge obtained according to the aforementioned air bridge preparation method, and has the same technical effect, which will not be repeated here. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the fabrication process of an air bridge in the prior art.

[0031] Figure 2 This is a schematic flowchart of the method for preparing an air bridge according to an embodiment of the present invention.

[0032] Figure 3 A process flow diagram for fabricating an air bridge.

[0033] Figure 4 for Figure 2 The diagram shows the specific process flow of step S2 in the preparation method shown.

[0034] Figure 5 for Figure 2 The diagram shows the specific process flow of step S4 in the preparation method shown.

[0035] Figure 6Another process flow diagram for the fabrication of air bridges.

[0036] Figure 7 This is a schematic diagram showing the positional relationship between the projection of the opening and the through hole on the substrate.

[0037] Figure 8 This is a partial structural schematic diagram of the quantum chip provided in an embodiment of the present invention. Detailed Implementation

[0038] The specific embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. The advantages and features of the present invention will become clearer from the following description and claims. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0039] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0040] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0041] Please refer to the reference. Figure 2 and Figure 3 , Figure 3 In this paper, a to g represent the process flow. This invention provides a method for preparing an air bridge. The method includes the following steps:

[0042] S1: Provide a substrate with a first photoresist layer.

[0043] The first photoresist layer can be formed by coating photoresist, for example, by first coating photoresist onto a substrate using a spin-coating method, and then curing the photoresist to form the first photoresist layer. Figure 3 Figure a shows a schematic diagram of a substrate having a first photoresist layer. The substrate 11 has a first photoresist layer 21.

[0044] S2: Form at least three through holes on the first photoresist layer, with their center points connected in sequence to form a closed pattern.

[0045] In this embodiment, the center point of the through-hole is the geometric center of its shape. If the through-hole is circular, the center point is the center of the circle; if the through-hole is rectangular, the center point is the intersection of its diagonals. The center points of at least three through-holes constitute the vertices of the closed shape, and connecting any pair of the center points of these three through-holes forms the edges of the closed shape. The number of through-holes can be arbitrarily set; for example, three through-holes form a triangle, four through-holes form a quadrilateral, and six through-holes form a hexagon. In this embodiment, four through-holes are preferred. Furthermore, the closed shape can be a rectangle, rhombus, or other shapes; in this embodiment, a rectangle, especially a square, is preferred. The through-hole can be any shape, such as a rectangle, circle, rounded rectangle, triangle, etc. Again, in this embodiment, a rectangle, especially a square, is preferred. Figure 3 Figure b shows a schematic diagram after through-holes are formed on the first photoresist layer. Four through-holes 211 are formed on the first photoresist layer 21. The through-holes 211 are square, and the lines connecting the center points of the four through-holes 211 in pairs also form a square.

[0046] S3: Form a first metal structure that fills each via and remove the first photoresist layer.

[0047] Since the first metal structure fills the through hole, its cross-sectional shape is the same as the through hole's shape. The thickness of the first metal structure can be set according to actual needs; it can exceed the depth of the through hole or not exceed it.

[0048] like Figure 3 Figure c shows a schematic diagram after the formation of the first metal structure. The first metal structure 31 is formed within the through hole 211.

[0049] The first metallic structure can be formed using deposition processes such as magnetron sputtering and evaporation. During the deposition of the metallic material, the thickness of the deposited metal is the same at each location, so the thickness of the first metallic structure within the four through-holes is identical. For example... Figure 3 Figure d shows a schematic diagram after the first photoresist layer 21 has been removed. After the first photoresist layer 21 is removed, only the first metal structure 31 remains on the substrate 11, and the four first metal structures 31 have the same thickness.

[0050] S4: A second photoresist layer flush with the surface of the first metal structure is formed on the substrate, and a third photoresist layer covering the second photoresist layer is formed, and an opening exposing the entire first metal structure is formed on the third photoresist layer.

[0051] The second and third photoresist layers can be formed by coating photoresist. For example, photoresist can be first coated onto the substrate by spin coating, with the spin coating thickness being the same as that of the first metal structure. After the photoresist cures, a second photoresist layer is formed. Then, photoresist can be further spin-coated onto the second photoresist layer. After the photoresist cures, a third photoresist layer is formed. Figure 3 Figure e shows a schematic diagram after the formation of the second and third photoresist layers. The second photoresist layer 22 is formed on the substrate 11. The second photoresist layer 22 has the same height as the first metal structure 31, so the first metal structure 31 is not covered by the second photoresist layer 22. The third photoresist layer 23 covers the second photoresist layer 22 and has an opening 231 that exposes the four first metal structures 31.

[0052] S5: A second metal structure is formed within the opening, which is connected to all the first metal structures.

[0053] Since the second metal structure fills the opening, its cross-sectional shape is identical to the opening's shape. The thickness of the second metal structure can be set according to actual needs; it can exceed the depth of the opening or not. The second metal structure can be formed using deposition processes such as magnetron sputtering or evaporation. Figure 3 Figure f shows a schematic diagram after the second metal structure is formed. The second metal structure 32 is formed within the opening 231.

[0054] S6: Remove the second and third photoresist layers to obtain an air bridge.

[0055] The second and third photoresist layers can be removed using various methods, such as ultrasonic cleaning and reactive ion etching. In this embodiment, ultrasonic cleaning is preferred for removing the second and third photoresist layers. Since the first metal structure serves as the pier of the air bridge and the second metal structure serves as the bridge deck, and because there are at least three piers supporting the bridge deck, the structural strength of the air bridge is enhanced, resulting in high structural stability. Therefore, removing the second and third photoresist layers using processes such as ultrasonic cleaning is less likely to cause structural damage, and the air bridge is less prone to collapse after removal of the second and third photoresist layers. Figure 3 Figure g shows a schematic diagram after the removal of the second and third photoresist layers. After the second photoresist layer 22 and the third photoresist layer 23 are removed, only the first metal structure 31 and the second metal structure 32 remain on the substrate 11.

[0056] The method for fabricating an air bridge provided by the present invention firstly uses a layer of photoresist to create at least three first metal structures, then uses two layers of photoresist to create second metal structures on all the first metal structures, and finally removes the photoresist to obtain the air bridge. The first metal structures serve as bridge piers, and the second metal structures serve as the bridge deck. Since there are at least three bridge piers, and all the bridge piers support the bridge deck, the structural strength is enhanced, thereby improving the structural stability of the air bridge. When removing the photoresist, it is not easy to cause structural damage, and it is not easy to collapse after removing the photoresist.

[0057] In some embodiments of this application, before the step of forming a second metal structure connected to all the first metal structures within the opening, i.e., step S5, the preparation method further includes: removing the natural oxide layer on the surface of the first metal structure within the opening. After the first metal structure comes into contact with air, its surface may be oxidized, preventing it from forming a complete metal structure with the second metal structure. Therefore, it is necessary to remove the natural oxide layer on the surface of the first metal structure. The natural oxide layer can be removed using methods such as ion beam etching (IBE).

[0058] In some embodiments of this application, please refer to Figure 4 Step S2, which involves forming at least three vias with their center points connected sequentially to form a closed pattern on the first photoresist layer, includes:

[0059] S21: Expose at least three through-hole patterns on the first photoresist layer, with their center points connected in sequence to form a closed pattern.

[0060] Specifically, at least three via patterns, whose center points are sequentially connected to form a closed pattern, can be exposed on the first photoresist layer using a photomask. The via pattern has the same shape as the via.

[0061] S22: Develop each through-hole pattern to form through-holes.

[0062] In this process, the portion of each via pattern on the first photoresist layer can be etched away by developing, thereby forming at least three vias whose center points are connected in sequence to form a closed pattern.

[0063] In some embodiments of this application, please refer to Figure 5 Step S4 includes the following steps: forming a second photoresist layer flush with the surface of the first metal structure on the substrate, forming a third photoresist layer covering the second photoresist layer, and forming an opening on the third photoresist layer that exposes the entire first metal structure.

[0064] S41: Coating photoresist on the substrate to form a second photoresist layer flush with the surface of the first metal structure.

[0065] S42: Coating photoresist onto the second photoresist layer to form a third photoresist layer.

[0066] S43: Expose the opening pattern on the third photoresist layer.

[0067] An opening pattern can be exposed on the third photoresist layer using a photomask. The opening pattern matches the shape of the opening.

[0068] S44: Develop the opening pattern to form an opening that exposes the entire first metal structure.

[0069] In this process, the portion of the third photoresist layer containing the opening pattern can be etched away by developing, thereby forming the opening. By controlling the developing time and speed, only the area of ​​the third photoresist layer within the opening pattern can be removed without affecting the underlying second photoresist layer.

[0070] In some embodiments of this application, the opening is annular. Furthermore, the center line of the projection shape of the opening onto the substrate coincides with the projection of the closed pattern onto the substrate. For example, when the closed pattern is circular, the opening is annular; when the closed pattern is rectangular, the opening is annular, formed by two concentric rectangles. Because the area of ​​the second metal structure in the aforementioned embodiments is relatively large, the second photoresist layer beneath it is obscured and difficult to etch. By making the opening annular, more of the second photoresist layer can be exposed after the second metal structure is formed. Figure 6 As shown, Figure 6 The process flow represented by a to f in the middle can be replaced Figure 3 The process flow represented by a to f in the diagram is as follows: Figure 6 a to d and Figure 3 The numbers a through d are the same. Figure 6 In equation e, the opening 231 formed on the third photoresist layer 23 is annular. For example... Figure 7 The diagram shows the positional relationship between the projections of the openings and through holes on the substrate. The projections of the four through holes 211 are squares, and the inner and outer contours of the projection of the opening 231 are also squares. The center line of the projection of the opening 231 (the square dashed box in the figure) is also a square, and the center line of the projection of the opening 231 coincides with the preset quadrilateral. Figure 6 In f, since the opening 231 is annular, the second metal structure 32 formed is a hollow structure, and the hollow region is the area surrounded by the opening 231. Figure 8 The bridge deck of the air bridge obtained in g is a hollow structure.

[0071] Please refer to Figure 8 The present invention also provides a quantum chip, the quantum chip comprising an air bridge obtained by the air bridge fabrication method according to the foregoing embodiments. Figure 6Taking the obtained air bridge as an example, the substrate 11 includes a substrate 110 and a coplanar waveguide 120 formed on the substrate 110. At least one first metal structure 31 of the air bridge is located on one grounding strip 121 of the coplanar waveguide 120, and the remaining first metal structures 31 are located on another grounding strip 121 of the coplanar waveguide 120. The center conductor 122 of the coplanar waveguide 120 passes through the gap between the first metal structures 31 on the two grounding strips 121, and the second metal structure 32 between the first metal structures 31 on the two grounding strips 121 spans over the center conductor 122.

[0072] As a preferred embodiment, two adjacent first metal structures 31 of the air bridge are located on one grounding strip 121, and the other two first metal structures 31 are located on another grounding strip 121. Since the air bridge has four piers, there is a gap between any two adjacent piers. There is no need to specifically set the direction of the air bridge. It is only necessary to ensure that the center conductor of the coplanar waveguide passes through the gap between any two adjacent piers. For coplanar waveguides with two mutually perpendicular wiring directions, the air bridge preparation method of this embodiment is more applicable than the traditional air bridge preparation method, especially when the quadrilateral is preset to be a square. This is because coplanar waveguides with both wiring directions can use the air bridge that is compatible with this embodiment. It is only necessary to ensure that the central axis of the closed shape is parallel (preferably overlapping) with the center line of the coplanar waveguide.

[0073] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," or "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0074] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the protection scope of the present invention.

Claims

1. A method for producing an air bridge, characterized by, include: Provide a substrate having a first photoresist layer; At least three vias are formed on the first photoresist layer, with their center points connected in sequence to form a closed pattern; A first metal structure is formed to fill each of the vias, and the first photoresist layer is removed; A second photoresist layer flush with the surface of the first metal structure is formed on the substrate, and a third photoresist layer is formed covering the second photoresist layer, and an opening exposing the entire first metal structure is formed on the third photoresist layer; A second metal structure is formed within the opening, which is connected to all of the first metal structures. Remove the second and third photoresist layers to obtain an air bridge.

2. The production method according to claim 1, characterized by, The step of forming at least three vias with their center points connected in sequence to form a closed pattern on the first photoresist layer includes: At least three through-hole patterns with their center points connected in sequence to form a closed pattern are exposed on the first photoresist layer. Each of the via patterns is developed to form a via.

3. The preparation method according to claim 1, characterized in that, The steps of forming a second photoresist layer flush with the surface of the first metal structure on the substrate, forming a third photoresist layer covering the second photoresist layer, and forming an opening on the third photoresist layer that exposes the entire first metal structure include: A second photoresist layer is formed by coating photoresist onto the substrate, which is flush with the surface of the first metal structure. A third photoresist layer is formed by coating photoresist onto the second photoresist layer; An opening pattern is exposed on the third photoresist layer; The opening pattern is developed to expose the entire first metal structure.

4. The preparation method according to claim 1, characterized in that, Prior to the step of forming a second metal structure connected to all of the first metal structures within the opening, the preparation method further includes: Remove the natural oxide layer from the surface of the first metal structure within the opening.

5. The preparation method according to claim 1, characterized in that, The opening is annular.

6. The preparation method according to claim 5, characterized in that, The center line of the projection shape of the opening on the substrate coincides with the projection of the closed shape on the substrate.

7. The preparation method according to claim 1, characterized in that, The second and third photoresist layers are removed by ultrasonic cleaning.

8. The preparation method according to claim 1, characterized in that, The number of through holes is four.

9. The preparation method according to claim 8, characterized in that, Both the closed shape and the through hole are rectangular in shape.

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