Air bridge preparation method and quantum chip

Abstract

The invention discloses an air bridge preparation method and a quantum chip, and is applied to the technical field of quantum, and the method comprises the steps: arranging a first photoresist layer on the surface of a substrate; arranging a second photoresist layer on the surface of the first photoresist layer; the viscosity of the second photoresist layer is smaller than that of the first photoresist layer; preparing a bridge support based on the laminated photoresist structure of the first photoresist layer and the second photoresist layer; preparing the air bridge based on the bridge support. The bridge support is prepared by using a laminated structure of two layers of photoresist, the viscosity of the first photoresist layer which is located on the lower layer and is not in direct contact with the air bridge is large, a good supporting effect can be achieved, and it is guaranteed that the air bridge has a large span and a high size; the viscosity of the second photoresist layer which is positioned on the upper layer and is in direct contact with the air bridge is relatively small, so that the internal stress of the bridge support can be effectively reduced, the problems of deformation, fracture and the like of the air bridge caused by stress change after photoresist removal are avoided, and the air bridge is ensured to have a good shape.

Description

Technical Field

[0001] The invention relates to the field of quantum technology, and in particular to an air bridge preparation method and a quantum chip. Background Art

[0002] The circuit of the superconducting quantum chip is a coplanar waveguide (CPW) transmission line, and the ground of the CPW is often connected through an air bridge to eliminate the potential difference and the slot line mode. As the number of bits in the superconducting quantum chip continues to increase, the air bridge is also used to connect different circuit elements. As a result, a new design with a large span and increased size is proposed for the structure of the air bridge, which brings challenges to the processing technology of the air bridge. At present, the height of the air bridge prepared in the field of superconducting quantum chips is usually within 5um, and the span is within 50um, which is increasingly inconsistent with the design requirements of large-span and increased-size air bridges. Therefore, how to provide a technical solution for preparing a large-span and increased-size air bridge is a problem that technicians in this field urgently need to solve. Summary of the invention

[0003] The object of the present invention is to provide a method for preparing an air bridge, which can prepare an air bridge with a large span and increased size; another object of the present invention is to provide a quantum chip having an air bridge with a large span and increased size.

[0004] In order to solve the above technical problems, the present invention provides an air bridge preparation method, comprising:

[0005] Disposing a first photoresist layer on the surface of the substrate;

[0006] Disposing a second photoresist layer on the surface of the first photoresist layer; the viscosity of the second photoresist layer is less than the viscosity of the first photoresist layer;

[0007] Prepare a bridge based on the stacked photoresist structure of the first photoresist layer and the second photoresist layer;

[0008] Air bridges are prepared based on the bridge struts.

[0009] Optionally, the thickness of the first photoresist layer is greater than the thickness of the second photoresist layer.

[0010] Optionally, preparing a bridge based on a stacked photoresist structure of the first photoresist layer and the second photoresist layer includes:

[0011] Expose and develop the stacked photoresist structure to expose the position of the substrate corresponding to the bridge pier;

[0012] After exposure and development, the stacked photoresist structure is heated for reflow to form a bridge support of an arch structure.

[0013] Optionally, the reflux temperature for heating the stacked photoresist structure ranges from 140° C. to 160° C., the heating time ranges from 3 min to 5 min, and the height of the bridge ranges from 6 μm to 10 μm.

[0014] Optionally, preparing the air bridge based on the bridge support includes:

[0015] After the bridge support is manufactured, a superconducting layer covering the bridge support is arranged on the surface of the substrate; the superconducting layer covers the bridge support and the position of the bridge pier exposed on the surface of the substrate;

[0016] Removing the superconducting layer outside the area where the air bridge is located defined on the surface of the substrate; the area where the air bridge is located includes the area where the bridge pier is located and the area where the bridge support is located;

[0017] The bridge support is removed.

[0018] Optionally, providing a first photoresist layer on the surface of the substrate includes:

[0019] Spin coating a first photoresist on the surface of the substrate;

[0020] The first photoresist is baked to be cured to form the first photoresist layer.

[0021] Optionally, the viscosity of the first photoresist ranges from 400 PC to 800 PC; the temperature for baking the first photoresist ranges from 100° C. to 120° C.; and the thickness of the first photoresist layer ranges from 6 μm to 10 μm.

[0022] Optionally, providing a second photoresist layer on the surface of the first photoresist layer includes:

[0023] Spin coating the second photoresist on the surface of the first photoresist layer;

[0024] The second photoresist is baked to be cured to form the second photoresist layer.

[0025] Optionally, the viscosity of the second photoresist ranges from 100 PC to 300 PC; the temperature for baking the second photoresist ranges from 100° C. to 120° C.; and the thickness of the second photoresist layer ranges from 2 μm to 4 μm.

[0026] The present invention also provides a quantum chip, comprising an air bridge prepared by any of the air bridge preparation methods described above.

[0027] The present invention provides a method for preparing an air bridge, comprising: setting a first photoresist layer on the surface of a substrate; setting a second photoresist layer on the surface of the first photoresist layer; the viscosity of the second photoresist layer is less than the viscosity of the first photoresist layer; preparing a bridge support based on a stacked photoresist structure of the first photoresist layer and the second photoresist layer; and preparing an air bridge based on the bridge support.

[0028] The bridge support is prepared by using a stacked structure of two layers of photoresist, wherein the first photoresist layer located in the lower layer and not in direct contact with the air bridge has a higher viscosity and a higher thickness, and can play a good supporting role after reflow, thereby ensuring that the air bridge has a large span and a high size; the second photoresist layer located in the upper layer and in direct contact with the air bridge has a lower viscosity, which can effectively reduce the internal stress of the bridge support, thereby avoiding deformation, fracture and other problems caused by changes in stress of the air bridge after degumming, and ensuring that the air bridge has a good morphology.

[0029] The present invention also provides a quantum chip, which also has the above-mentioned beneficial effects, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 A flow chart of a method for preparing an air bridge provided by an embodiment of the present invention;

[0032] Figures 2 to 9 A process flow chart of a specific air bridge preparation method provided in an embodiment of the present invention.

[0033] In the figure: 1. substrate, 2. first photoresist layer, 3. second photoresist layer, 4. bridge support, 5. superconducting layer, 6. third photoresist layer. DETAILED DESCRIPTION

[0034] The core of the present invention is to provide a method for preparing an air bridge. In the prior art, the size of the air bridge is relatively small. The height of the air bridge prepared in the field of superconducting quantum chips is usually within 5um and the span is within 50um, which is increasingly inconsistent with the design requirements of air bridges with large spans and increased heights.

[0035] The present invention provides a method for preparing an air bridge, comprising: setting a first photoresist layer on the surface of a substrate; setting a second photoresist layer on the surface of the first photoresist layer; the viscosity of the second photoresist layer is less than the viscosity of the first photoresist layer; preparing a bridge support based on a stacked photoresist structure of the first photoresist layer and the second photoresist layer; and preparing an air bridge based on the bridge support.

[0036] The bridge support is prepared by using a stacked structure of two layers of photoresist, wherein the first photoresist layer located in the lower layer and not in direct contact with the air bridge has a higher viscosity and a higher thickness, and can play a good supporting role after reflow, thereby ensuring that the air bridge has a large span and a high size; the second photoresist layer located in the upper layer and in direct contact with the air bridge has a lower viscosity, which can effectively reduce the internal stress of the bridge support, thereby avoiding deformation, fracture and other problems caused by changes in stress of the air bridge after degumming, and ensuring that the air bridge has a good morphology.

[0037] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] Embodiment 1

[0039] Please refer to Figure 1 , Figure 1 The present invention provides a flow chart of a method for preparing an air bridge.

[0040] See also Figure 1 In an embodiment of the present invention, the air bridge preparation method includes:

[0041] S101: Disposing a first photoresist layer on the surface of a substrate.

[0042] The substrate 1 may be a wafer substrate provided with some or all of the bottom-layer circuits or no bottom-layer circuits. The specific content of the bottom-layer circuits may be set according to actual conditions and is not specifically limited here. The complete structure of the corresponding bottom-layer circuits may be performed before or after the preparation of the air bridge, which is also not specifically limited here.

[0043] In this step, a first photoresist layer 2 is disposed on the surface of the substrate 1. The first photoresist layer 2 needs to have a relatively large viscosity to ensure that the first photoresist layer 2 can have a relatively high thickness. In this embodiment, the first photoresist layer 2 mainly plays a supporting role to facilitate the formation of a large-span, high-size air bridge, so the first photoresist layer 2 needs to have a relatively large viscosity.

[0044] S102: Disposing a second photoresist layer on the surface of the first photoresist layer.

[0045] In an embodiment of the present invention, the viscosity of the second photoresist layer 3 is less than the viscosity of the first photoresist layer 2. In this step, the second photoresist layer 3 is disposed on the surface of the first photoresist layer 2 to form a laminated photoresist structure. The second photoresist layer 3 needs to have a relatively low viscosity to ensure that the stress at the position where the subsequently formed bridge support 4 is combined with the air bridge is relatively small. The second photoresist layer 3 is mainly used to ensure that the finally formed air bridge will not be deformed due to the excessive viscosity of the bridge support 4. When the viscosity of the bridge support 4 is too high, it will have a relatively high stress inside. The preparation of the air bridge ultimately requires the removal of the bridge support 4. When the internal stress of the bridge support 4 is too high, the air bridge will be deformed after the bridge support 4 is removed due to the significant change in stress, which affects the quality of the air bridge.

[0046] The second photoresist layer 3 is provided in this step to reduce the stress inside the final bridge support 4, thereby ensuring that the air bridge will not be greatly deformed or broken after the bridge support 4 is removed. In this embodiment, the thickness of the first photoresist layer 2 is usually greater than the thickness of the second photoresist layer 3, so that the main structure of the bridge support 4 with a height greater than 5μm and a span greater than 50μm is prepared through the first photoresist layer 2, and the structure in contact with the air bridge in the bridge support 4 is formed through the second photoresist, so as to form an air bridge with a height greater than 5μm and a span greater than 50μm.

[0047] S103: preparing a bridge based on the stacked photoresist structure of the first photoresist layer and the second photoresist layer.

[0048] In this step, a bridge support 4 will be prepared based on the stacked structure of the above-mentioned two layers of photoresist. This step usually requires exposing and developing the stacked photoresist structure to prepare the bridge support 4, and reflowing the bridge support 4 to form an arch shape, etc. The specific content will be described in detail in the following invention embodiments and will not be repeated here.

[0049] S104: preparing an air bridge based on the bridge support.

[0050] In this step, a superconducting layer 5 is usually provided on the surface of the bridge support 4, and finally the laminated photoresist structure forming the bridge support 4 needs to be removed to form an air bridge. The specific content of this step will be described in detail in the following embodiments, and will not be repeated here.

[0051] The present embodiment provides a method for preparing an air bridge, in which a bridge support 4 is prepared by using a stacked structure of two layers of photoresist, wherein the first photoresist layer 2 located in the lower layer and not in direct contact with the air bridge has a higher viscosity and a higher thickness, and can play a good supporting role after reflow, thereby ensuring that the air bridge has a large span and a high size; the second photoresist layer 3 located in the upper layer and in direct contact with the air bridge has a lower viscosity, and can effectively reduce the internal stress of the bridge support 4, thereby avoiding deformation, fracture and other problems caused by changes in stress of the air bridge after degumming, thereby ensuring that the air bridge has a good morphology.

[0052] The specific contents of the air bridge preparation method provided by the present invention will be described in detail in the following invention examples.

[0053] Embodiment 2

[0054] Please refer to Figures 2 to 9 , Figures 2 to 9 A process flow chart of a specific air bridge preparation method provided in an embodiment of the present invention.

[0055] See also Figure 2 In an embodiment of the present invention, the air bridge preparation method includes:

[0056] S201: Spin-coating a first photoresist on the surface of the substrate.

[0057] See also Figure 3 In this step, the first photoresist is firstly spin-coated on the surface of the substrate 1. The viscosity of the first photoresist ranges from 400PC to 800PC. It is mainly used as a supporting glue for the air bridge. It usually needs to maintain a high thickness in the subsequent baking process and reflow process. Due to its high viscosity, it can keep its deformation small in the subsequent baking process and reflow process. The first photoresist with high viscosity can be AZ4000 series photoresist, preferably AZ4620 photoresist. In the spin coating process of this step, the coating speed is usually between 1200rpm and 3000rpm, and the spin coating time is usually about 60 seconds.

[0058] S202: baking the first photoresist to solidify it and form a first photoresist layer.

[0059] In this step, a hot plate can be used to bake the first photoresist. The temperature range for baking the first photoresist is usually 100°C to 120°C, and the baking time for baking the first photoresist is usually 2 minutes to 5 minutes to preliminarily solidify the first photoresist. The thickness range of the first photoresist layer 2 is usually 6μm to 10μm.

[0060] S203: Spin-coat a second photoresist on the surface of the first photoresist layer.

[0061] See also Figure 4 In this step, a second photoresist is spin-coated on the surface of the first photoresist layer 2. The viscosity of the second photoresist ranges from 100 PC to 300 PC, which is mainly used to alleviate the stress effect caused by the high-viscosity photoresist after curing, and at the same time obtain a good arched reflow effect. When the viscosity of the photoresist is high, the high-viscosity photoresist is prone to produce a large stress inside the glue when it is reflowed into an arch, and in the final degumming process, that is, when the bridge support 4 is removed, the stress disappears, which causes the shape of the arched air bridge to be deformed by the stress change. And this step can alleviate the stress effect caused by only setting the high-viscosity photoresist by setting the second photoresist, and at the same time obtain a good arched reflow effect, ensuring the high-quality preparation of the air bridge.

[0062] The second photoresist with low viscosity can be SPR220 series photoresist, preferably SPR220-3.0 photoresist. In the spin coating process of this step, the coating speed is usually between 1500 rpm and 2700 rpm, and the spin coating time is usually about 35 seconds.

[0063] S204: baking the second photoresist to solidify it and form a second photoresist layer.

[0064] In this step, a hot plate can be used to bake the second photoresist. The temperature range for baking the second photoresist is usually 100°C to 120°C, and the baking time for baking the second photoresist is usually 1 minute to 3 minutes to preliminarily cure the second photoresist. The thickness range of the second photoresist layer 3 is usually 2μm to 4μm.

[0065] S205: exposing and developing the stacked photoresist structure to expose the position of the substrate corresponding to the bridge pier.

[0066] See also Figure 5 In this step, the above-mentioned laminated photoresist structure will be exposed and developed in sequence, that is, the laminated photoresist structure will be patterned, the purpose of which is to expose the position of the air bridge pier corresponding to the surface of the substrate 1. That is, in this step, the air bridge pier pattern of the above-mentioned laminated photoresist structure will be exposed on the photolithography machine, and after exposure, it will be developed to expose the area on the surface of the substrate 1 corresponding to the pier position. The above-mentioned photolithography machine can be a MA6 or a laser direct writing one, and the span of the above-mentioned pier pattern is usually between 50μm and 100μm, so that the span of the final air bridge can be between 50μm and 100μm. The developer used in the above-mentioned development process can be set according to actual conditions, and no specific limitation is made here. The above-mentioned pier pattern usually includes the positions of at least two piers, and the laminated photoresist structure between two adjacent piers will be made into piers in subsequent steps.

[0067] S206: After exposure and development, the stacked photoresist structure is heated for reflow to form a bridge support of an arched structure.

[0068] See also Figure 6 In this step, a hot plate can be used to bake the developed substrate 1. The purpose of heating in this step is to make the laminated photoresist structure fully reflow to form an arch, that is, to form a bridge support 4 of an arch structure. During the reflow process, the deformation of the first photoresist layer 2 is usually smaller than that of the second photoresist layer 3. Since the viscosity of the second photoresist layer 3 is small, it can form a good arch during reflow. The second photoresist layer 3 with a smaller viscosity and a larger deformation will be located in the upper layer, so that the entire bridge support 4 has an arch structure.

[0069] In this step, the reflow temperature for heating the laminated photoresist structure is usually in the range of 140° C. to 160° C., the heating time in this step is usually 3 min to 5 min, and the height of the arch bridge 4 after reflow is in the range of 6 μm to 10 μm.

[0070] S207: After the bridge support is formed, a superconducting layer covering the bridge support is disposed on the surface of the substrate.

[0071] See also Figure 7 In this embodiment, the superconducting layer 5 covers the bridge support 4 and the position of the bridge pier exposed on the surface of the substrate 1 .

[0072] In this step, superconducting material can be deposited on the surface of the substrate 1 to form a superconducting layer 5. The superconducting layer 5 will cover the surface of the bridge support 4 and the position where the bridge pier is exposed on the surface of the substrate 1, that is, the superconducting layer 5 will contact the substrate 1 at the bridge pier to be fixedly connected. In this step, the thickness of the superconducting layer 5 is generally in the range of 400nm to 700nm. The specific material of the superconducting layer 5 can be set according to actual conditions and is not specifically limited here.

[0073] S208: removing the superconducting layer outside the area where the air bridge is defined on the substrate surface.

[0074] See also Figure 8 In this embodiment, the area where the air bridge is located includes the area where the bridge pier is located and the area where the bridge support 4 is located. In this step, the redundant superconducting layer 5 on the surface of the substrate 1 can be removed by photolithography and etching, that is, the superconducting layer 5 outside the area where the bridge pier is located and the area where the bridge support 4 is located can be removed.

[0075] Specifically, in this step, a third photoresist such as AZ4620 or SPR220-3.0 can be spin-coated on the surface of the superconducting layer 5, and then the third photoresist is baked to form a third photoresist layer 6. After baking, the thickness of the third photoresist layer 6 is usually about 5 μm. After baking, the newly spin-coated third photoresist layer 6 is exposed to the air bridge etching window pattern using a photolithography machine, and then developed after exposure to expose the bridge body etching position. The air bridge etching window pattern usually covers and protects the superconducting layer 5 located at the bridge pier position and the superconducting layer 5 located on the surface of the bridge support 4, and the corresponding exposed bridge body etching position is the position outside the air bridge.

[0076] Afterwards, in this step, the etching window pattern may be etched. Specifically, the etching window pattern may be etched using an etching process such as wet etching or dry etching to remove the superconducting layer 5 outside the air bridge.

[0077] S209: Remove the bridge support.

[0078] See also Fig. 9 In this step, the etched air bridge is specifically debonded, that is, the bridge support 4 and the residual photoresist layer on the surface of the substrate 1 are removed, so as to obtain a large-span, heightened air bridge, whose height can be 5μm to 10μm, and whose span can be 50μm to 100μm.

[0079] An air bridge preparation method provided by an embodiment of the present invention prepares a bridge support 4 by using a stacked structure of two layers of photoresist, wherein the first photoresist layer 2 located in the lower layer and not in direct contact with the air bridge has a higher viscosity and a higher thickness, and can play a good supporting role after reflow, thereby ensuring that the air bridge has a large span and a high size; the second photoresist layer 3 located in the upper layer and in direct contact with the air bridge has a lower viscosity, which can effectively reduce the internal stress of the bridge support 4, thereby avoiding deformation, fracture and other problems caused by changes in stress of the air bridge after degumming, thereby ensuring that the air bridge has a good morphology.

[0080] Embodiment 3

[0081] A quantum chip provided by an embodiment of the present invention is introduced below. The quantum chip described below and the air bridge preparation method described above can be referenced to each other.

[0082] In this embodiment, the quantum chip includes an air bridge, and the air bridge is an air bridge prepared by an air bridge preparation method provided by any of the above embodiments. The specific content of the air bridge preparation method has been described in detail in the above invention embodiments, and will not be repeated here.

[0083] Since the quantum chip of this embodiment includes an air bridge prepared by an air bridge preparation method provided by any of the above embodiments, and because its air bridge can have a higher size and a larger span, the quantum chip can be provided with more quantum bits and has higher performance.

[0084] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0085] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0086] The above is a detailed introduction to the air bridge preparation method and quantum chip provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing an air bridge, characterized in that: include: Disposing a first photoresist layer on the surface of the substrate; Disposing a second photoresist layer on the surface of the first photoresist layer; The viscosity of the second photoresist layer is less than the viscosity of the first photoresist layer; Prepare a bridge based on the stacked photoresist structure of the first photoresist layer and the second photoresist layer; Air bridges are prepared based on the bridge struts.

2. The method according to claim 1, characterized in that The thickness of the first photoresist layer is greater than the thickness of the second photoresist layer.

3. The method according to claim 1, characterized in that Preparing a bridge support based on a stacked photoresist structure of the first photoresist layer and the second photoresist layer includes: Expose and develop the stacked photoresist structure to expose the position of the substrate corresponding to the bridge pier; After exposure and development, the stacked photoresist structure is heated for reflow to form a bridge support of an arch structure.

4. The method according to claim 3, characterized in that The reflux temperature for heating the stacked photoresist structure ranges from 140° C. to 160° C., the heating time ranges from 3 min to 5 min, and the height of the bridge ranges from 6 μm to 10 μm.

5. The method according to claim 3, characterized in that: The preparation of the air bridge based on the bridge support comprises: After the bridge support is manufactured, a superconducting layer covering the bridge support is arranged on the surface of the substrate; the superconducting layer covers the bridge support and the position of the bridge pier exposed on the surface of the substrate; Removing the superconducting layer outside the area where the air bridge is located defined on the surface of the substrate; the area where the air bridge is located includes the area where the bridge pier is located and the area where the bridge support is located; The bridge support is removed.

6. The method according to claim 1, characterized in that Providing a first photoresist layer on the surface of the substrate comprises: Spin coating a first photoresist on the surface of the substrate; The first photoresist is baked to be cured to form the first photoresist layer.

7. The method according to claim 6, characterized in that The viscosity of the first photoresist ranges from 400 PC to 800 PC; the temperature for baking the first photoresist ranges from 100° C. to 120° C., and the thickness of the first photoresist layer ranges from 6 μm to 10 μm.

8. The method according to claim 6, characterized in that Providing a second photoresist layer on the surface of the first photoresist layer comprises: Spin coating the second photoresist on the surface of the first photoresist layer; The second photoresist is baked to be cured to form the second photoresist layer.

9. The method according to claim 8, characterized in that The viscosity of the second photoresist ranges from 100 PC to 300 PC; the temperature for baking the second photoresist ranges from 100° C. to 120° C.; and the thickness of the second photoresist layer ranges from 2 μm to 4 μm.

10. A quantum chip, characterized in that: It comprises an air bridge prepared by the air bridge preparation method according to any one of claims 1 to 9.

Images