CN113003535A - Glue removing method of superconducting quantum bit air bridge and chip thereof - Google Patents

Abstract

The invention provides a method for removing glue of a superconducting qubit air bridge, which comprises the step of spraying photoresist on a multi-superconducting qubit air bridge by using a mixed solution of acetone and N-methylpyrrolidone. The method successfully removes the photoresist in the superconducting qubit air bridge process, and solves the problem of the photoresist removal by the original soaking method. Tests show that the multi-quantum bit performance obtained by applying the process of the invention reaches the corresponding level in the world.

Description

Glue removing method of superconducting quantum bit air bridge and chip thereof

Technical Field

The invention belongs to the field of superconducting quanta, and particularly relates to a glue removing method of a superconducting quantum bit air bridge and a chip thereof.

Background

Superconducting qubits are based on nonlinear resonant circuits consisting of capacitors and nonlinear inductances of josephson junctions. The quantum bit is well balanced in the aspects of quantum bit service life, expandability, easiness in controllability and easiness in processing. Is a scheme that is recognized to most probably realize a general quantum computer.

Therefore, superconducting quantum computing has become one of the key fields in competition among the medical technology countries worldwide, and China has also listed quantum computing as a significant scientific research direction of the national strategic level. As a core superconducting quantum chip for superconducting quantum computation, the preparation process and the technology are the key for success or failure of superconducting quantum computation, and as the number of bits on a superconducting quantum bit chip increases, the use of the superconducting quantum computation technology is severely restricted by the mutual interference among the bits.

At present, two mainstream methods for solving the mutual interference among a plurality of bits on the superconducting qubit chip are available worldwide, one is to weld a micron-sized metal wire at a specific position on the superconducting qubit chip by using a manual ultrasonic spot welding machine, and the other is to directly prepare 1000-1500 micron-sized metal Bridge bridges, namely an Air Bridge process (Air Bridge), at a specific position on the superconducting qubit chip by using a micro-nano processing means.

The first method, because of manual welding, has low precision and success rate, and very limited final effect, and the whole sample is also discarded due to carelessness. The second method has higher precision and success rate, but a wet etching process (reference 2) of micro-nano processing or a micro-nano processing process (reference 2) of highly toxic gas etching is needed in the preparation process, and the remaining photoresist of the highly toxic gas etching process is less but the process is complicated, harmful and not suitable for use. An important step in the wet etching process is to remove the photoresist on the prepared superconducting qubit chip.

The existing glue removing method mainly comprises a chemical glue removing agent soaking method, a microwave plasma bombardment method and a plasma enhanced etching method, but for preparing the superconducting quantum bit chip for completing the air bridge, the microwave plasma bombardment method and the plasma enhanced etching method can cause irreversible damage to the micron-sized air bridge, so that the glue can be removed only by the chemical glue removing agent soaking method. However, in the actual process, the inevitable denaturation of the surface layer of the photoresist results in unsatisfactory photoresist removing effect of the soaking method of the chemical photoresist remover due to the air bridge micro-nano processing technology. After the superconducting qubit chip is soaked in the chemical degumming agent for 48 hours, more residual glue still remains on the superconducting qubit chip.

In summary, the following problems exist in the existing available photoresist removing process:

1. the photoresist removing process is long;

2. the photoresist removal effect is not good.

Disclosure of Invention

Therefore, the invention aims to overcome the defects in the prior art and provide a glue removing method of a superconducting qubit air bridge, a product and a chip thereof.

In order to achieve the above object, a first aspect of the present invention provides a method for removing photoresist from a superconducting qubit air bridge, wherein the method comprises a step of performing a spraying process on the photoresist on the superconducting qubit air bridge by using a mixed solution of acetone and N-methylpyrrolidone.

According to the glue removing method of the first aspect of the invention, the volume ratio of the acetone to the N-methyl pyrrolidone in the mixed solution of the acetone and the N-methyl pyrrolidone is as follows: 0.2 to 5, preferably 0.5 to 3, most preferably 1: 1.

the photoresist removing method according to the first aspect of the invention, wherein the photoresist is selected from one or more of the following: s1813, SPR955, SPR220-7.0, SPR220-4.5, SPR220-3.0, SPR220-1.5 and SPR 220-1.2.

The glue removing method according to the first aspect of the invention, wherein the method comprises the following steps:

(1) fixing the prepared superconducting quantum bit chip of the air bridge;

(2) adjusting an included angle between the multi-superconducting qubit chip in the step (1) and the vertical direction;

(3) vertically spraying a multi-superconducting qubit chip by using a mixed solution of acetone and N-methylpyrrolidone;

(4) and (4) adjusting the position of the multi-superconducting qubit chip, repeating the step (3), and spraying other positions of the multi-superconducting qubit chip where the photoresist exists.

The glue removing method according to the first aspect of the invention, wherein in the step (2), the included angle ranges from 30 ° to 60 °, preferably from 40 ° to 50 °, and most preferably 45 °.

The degumming method according to the first aspect of the invention, wherein in the step (3), the spraying flow rate of the acetone and N-methyl pyrrolidone mixed solution is 0.10ml/s to 0.50ml/s, preferably 0.20ml/s to 0.40ml/s, and most preferably 0.35 ml/s; and/or

The spraying time of the acetone and N-methyl pyrrolidone mixed solution is 1min to 4min, preferably 2min to 3min, and most preferably 2.5 min.

The glue removing method according to the first aspect of the invention, wherein the method further comprises the steps of:

(5) repeating the step (4) until the acetone and N-methyl pyrrolidone mixed solution is sprayed and traverses the multi-superconducting quantum bit chip;

(6) vertically traversing and spraying the multi-superconducting quantum bit chip by using analytically pure isopropanol liquid;

(7) and vertically traversing and spraying the multi-superconducting qubit chip by using deionized water.

The degumming method according to the first aspect of the invention, wherein in the step (6), the analytically pure isopropanol liquid is sprayed at a flow rate of 0.40ml/s to 1.20ml/s, preferably 0.60ml/s to 1.00ml/s, and most preferably 0.80 ml/s; and/or

The spraying time of the isopropanol solution is 1-5 min, preferably 2-4 min, and most preferably 3 min.

The degumming method according to the first aspect of the invention, wherein in the step (7), the flow rate of the deionized water spray is 0.80 ml/s-1.60 ml/s, preferably 1.00 ml/s-1.40 ml/s, and most preferably 1.20 ml/s; and/or

The spraying time of the deionized water is 1-4 min, preferably 2-3 min, and most preferably 2.5 min.

A second aspect of the present invention provides a superconducting qubit chip, which includes one or more air bridges, and which performs glue removal of the air bridges by using the glue removal method of the first aspect.

The degumming method of the invention can have the following beneficial effects:

the method successfully removes the photoresist in the superconducting qubit air bridge process, and solves the problem of the photoresist removal by the original soaking method. Tests show that the multi-quantum bit performance obtained by applying the process of the invention reaches the corresponding level in the world.

Drawings

Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:

FIG. 1 shows the effect of removing the gel by the conventional dipping method in test example 1; in which fig. 1A is a partially enlarged photograph and fig. 1B is a photograph of a smaller magnification.

Fig. 2 shows an air bridge electron microscope photograph prepared by a microwave plasma bombardment method or a plasma enhanced etching method in experimental example 1.

Fig. 3 shows a diagram of niobium-based planar multi-superconducting qubits and air bridges (small-magnification aerial photographs) prepared in experimental example 1 according to the method described in example 1 of the present invention.

Fig. 4 shows a diagram of niobium-based planar multi-superconducting qubits and air bridges (magnified partial photographs) prepared in experimental example 1 according to the method described in inventive example 1.

Fig. 5 shows a diagram of a niobium-based planar multi-superconducting qubit and an air bridge (a single air bridge structure photograph) prepared according to the method described in inventive example 1 in experimental example 1.

Fig. 6 shows the results of testing crosstalk between superconducting qubits for samples prepared using the process of example 1 using the QND measurement method for ten superconducting qubits spaced apart by 384 microns for the sample under test, where fig. 6A shows crosstalk between bits No. 3 and 6 (less than 1%), fig. 6B shows crosstalk between bits No. 4 and 5 (less than 1%), fig. 6C shows crosstalk between bits No. 5 and 6 (less than 1%), and fig. 6D shows crosstalk between bits No. 1 to 10.

Detailed Description

The invention is further illustrated by the following specific examples, which, however, are to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

This section generally describes the materials used in the testing of the present invention, as well as the testing methods. Although many materials and methods of operation are known in the art for the purpose of carrying out the invention, the invention is nevertheless described herein in as detail as possible. It will be apparent to those skilled in the art that the materials and methods of operation used in the present invention are well within the skill of the art, provided that they are not specifically illustrated.

The reagents used in the following examples are as follows: reagent:

acetone, N-methylpyrrolidone, isopropanol, from Physics, Inc.

Example 1

This example is used to illustrate the stripping method of the present invention.

The method is suitable for the superconducting qubits which comprise air bridges and are made of niobium-based and aluminum-based superconducting qubit chips, and the niobium-based superconducting qubit chips are adopted in the following embodiments.

Step 1: and fixing the niobium-based superconducting qubit chip with the prepared air bridge on a fixing clamp with good grounding.

The preparation method of the air bridge comprises the following steps:

1. spin-coating SPR 2203.0 at 4000rpm for 60 s;

2. baking on a hot plate at 115 deg.C for 1 min;

3. exposing a window connecting the second layer of aluminum and the first layer of aluminum by using laser direct writing;

4. baking on a hot plate at 115 deg.C for 1 min;

5. developing with ZX238 (available from Suzhou research micro-nano technology Co., Ltd.) positive photoresist developer for 60s, fixing with deionized water for 30s, and drying with nitrogen;

6. baking on a hot plate at 140 deg.C for 3min to make the glue flow sufficiently;

7. evaporating aluminum about 300nm in electron beam evaporation;

8. spin coating S1813 at 4000rpm for 60S;

9. baking on a hot plate at 115 deg.C for 1 min;

10. using laser to directly write and expose the part of the second layer of aluminum to be removed;

11. developing with ZX238 (available from Suzhou research micro-nano technology Co., Ltd.) positive photoresist developer for 60s, fixing with deionized water for 30s, and drying with nitrogen;

12. the aluminum to be removed was etched in ZX238 (available from suzhou research micro-nano technologies ltd).

Step 2: after the step 1, adjusting the included angle between the niobium-based superconducting qubit chip and the vertical direction to be within the adjustable range of 30-60 degrees, preferably within the range of 40-50 degrees, and most preferably within the range of 45 degrees.

And step 3: after the step 2, the position of the niobium-based superconducting qubit chip is vertically sprayed for 1min to 5min, preferably for 2min to 4min, and most preferably for 3min at a flow rate of 0.10ml/s to 0.50ml/s, preferably at a flow rate of 0.20ml/s to 0.40ml/s, and most preferably at a flow rate of 0.35ml/s, using a mixed solution of analytically pure acetone and analytically pure N-methylpyrrolidone (volume ratio 1: 1).

And 4, step 4: after the step 3, adjusting the position of the niobium-based superconducting qubit chip to enable the mixed solution of analytically pure acetone and analytically pure N-methylpyrrolidone to be sprayed to other positions with the photoresist, and repeating the step 3.

And 5: and (4) repeating the step (4) until the mixed solution of the analytically pure acetone and the analytically pure N-methyl pyrrolidone is sprayed to traverse the niobium-based superconducting qubit chip.

Step 6: after step 5, the niobium-based superconducting qubit chip is sprayed vertically in a traversal pattern using analytically pure isopropanol liquid at a flow rate of 0.40-1.20 ml/s, preferably 0.60-1.00 ml/s, most preferably 0.80ml/s for 1-5 min, preferably 2-4 min, most preferably 3 min.

And 7: after step 6, deionized water is used for vertically and transversely spraying the niobium-based superconducting qubit chip for 1min to 4min, preferably 2min to 3min, and most preferably 2.5min at a flow rate of 0.80ml/s to 1.60ml/s, preferably at a flow rate of 1.00ml/s to 1.40ml/s, and most preferably at a flow rate of 1.20 ml/s.

The steps 1 to 5 are removing of the photoresist after the air bridge is prepared, and the steps 5 to 7 are removing of impurities which are not beneficial to the performance of the niobium-based superconducting qubit, such as analytically pure acetone and analytically pure N-methyl pyrrolidone mixed solution, dust and the like, remained on the niobium-based superconducting qubit chip.

Test example 1

This test example is intended to illustrate the effect of the stripping method of the present invention.

In order to further illustrate the effect of the photoresist removing method, the inventor adopts the existing soaking method to remove the photoresist of the air bridge. The method comprises the following steps: soaking in acetone liquid or N-methyl pyrrolidone liquid or their mixture for 24-48 hr.

FIG. 1 shows the effect of removing glue by the existing soaking method (soaking for 48 hours at room temperature by using analytically pure acetone liquid), and it is evident that there is more glue residues (wherein, FIG. 1A is a partially enlarged photograph, and FIG. 1B is a photograph of a smaller multiple).

Fig. 2 shows an electron microscope photograph of an air bridge (irreversible damage to the air bridge of micron order) prepared by microwave plasma bombardment or plasma enhanced etching.

Fig. 3 to 5 are photographs showing niobium-based planar multi-superconducting qubits and air bridge structures prepared according to the method of example 1 of the present invention, with no resist residue visible, wherein fig. 3 is a small-magnification partial photograph, fig. 4 is a large-magnification partial photograph, and fig. 5 is a single air bridge structure photograph.

Test example 2

This test example is intended to illustrate the effect of the niobium-based superconducting qubit prepared by the process of the invention.

Fig. 6 shows the measurement of crosstalk between the superconducting qubits of the sample prepared by applying the process of example 1 by using the conventional QND measurement method (the obtained conclusion is that the crosstalk between the superconducting qubits is less than 0.00004 in the frequency range in which the superconducting qubits operate), and it can be seen that the performance of the multi-qubit obtained by applying the process reaches the corresponding level in the world. The samples tested had ten superconducting qubits spaced 384 microns apart, with fig. 6A showing crosstalk between bits No. 3 and 6 (less than 1%), fig. 6B showing crosstalk between bits No. 4 and 5 (less than 1%), fig. 6C showing crosstalk between bits No. 5 and 6 (less than 1%), and fig. 6D showing crosstalk between bits No. 1 and 10. The driving signal is added to the No. 2 bit, the correspondence of all 10 bits is observed, the larger the crosstalk is, the larger the reaction of other bits is, the non-quantitative result of the test is, and only the condition that the global crosstalk is small is displayed.

Although the present invention has been described to a certain extent, it is apparent that appropriate changes in the respective conditions may be made without departing from the spirit and scope of the present invention. It is to be understood that the invention is not limited to the described embodiments, but is to be accorded the scope consistent with the claims, including equivalents of each element described.

Claims (10)

1. A method for removing photoresist of a superconducting qubit air bridge is characterized by comprising the step of spraying photoresist on a multi-superconducting qubit air bridge by using a mixed solution of acetone and N-methylpyrrolidone.

2. The method for removing glue according to claim 1, wherein the volume ratio of acetone to N-methyl pyrrolidone in the mixed solution of acetone and N-methyl pyrrolidone is as follows: 0.2 to 5, preferably 0.5 to 3, most preferably 1: 1.

3. a method according to claim 1 or 2, wherein the photoresist is selected from one or more of the following: s1813, SPR955, SPR220-7.0, SPR220-4.5, SPR220-3.0, SPR220-1.5 and SPR 220-1.2.

4. A glue removal method according to any one of claims 1 to 3, characterized in that it comprises the following steps:

(1) fixing the prepared superconducting quantum bit chip of the air bridge;

(2) adjusting an included angle between the multi-superconducting qubit chip in the step (1) and the vertical direction;

(3) vertically spraying a multi-superconducting qubit chip by using a mixed solution of acetone and N-methylpyrrolidone;

(4) and (4) adjusting the position of the multi-superconducting qubit chip, repeating the step (3), and spraying other positions of the multi-superconducting qubit chip where the photoresist exists.

5. The method according to claim 4, wherein in step (2) the included angle is in the range of 30 ° to 60 °, preferably 40 ° to 50 °, most preferably 45 °.

6. The method according to claim 4 or 5, wherein in the step (3), the mixed solution of acetone and N-methyl pyrrolidone is sprayed at a flow rate of 0.10ml/s to 0.50ml/s, preferably 0.20ml/s to 0.40ml/s, and most preferably 0.35 ml/s; and/or

The spraying time of the acetone and N-methyl pyrrolidone mixed solution is 1min to 4min, preferably 2min to 3min, and most preferably 2.5 min.

7. The method according to any one of claims 4 to 6, characterized in that the method further comprises the steps of:

(5) repeating the step (4) until the acetone and N-methyl pyrrolidone mixed solution is sprayed and traverses the multi-superconducting quantum bit chip;

(6) vertically traversing and spraying the multi-superconducting quantum bit chip by using analytically pure isopropanol liquid;

(7) and vertically traversing and spraying the multi-superconducting qubit chip by using deionized water.

8. The method according to claim 7, wherein in step (6), the analytically pure isopropanol liquid spray is at a flow rate of 0.40 to 1.20ml/s, preferably 0.60 to 1.00ml/s, most preferably 0.80 ml/s; and/or

The spraying time of the isopropanol solution is 1-5 min, preferably 2-4 min, and most preferably 3 min.

9. The method according to claim 7 or 8, wherein in step (6), in step (7), the flow rate of the deionized water spray is 0.80ml/s to 1.60ml/s, preferably 1.00ml/s to 1.40ml/s, and most preferably 1.20 ml/s; and/or

The spraying time of the deionized water is 1-4 min, preferably 2-3 min, and most preferably 2.5 min.

10. A superconducting qubit chip comprising one or more air bridges, wherein the air bridges are removed by the method of any one of claims 1 to 9.

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