Method for depositing gold electrode on surface of BSCCO single crystal

Abstract

The invention discloses a method for depositing a gold electrode on the surface of a BSCCO single crystal, and belongs to the technical field of superconducting device preparation, and the method comprises the following steps: S1, cleaning a sapphire substrate; s2, placing the sapphire substrate in a vacuum pipeline, fixing the PDMS film adhered with the BSCCO single crystal on the sapphire substrate, and cleaving the BSCCO single crystal in the vacuum pipeline; s3, depositing a layer of gold film on the surface of the BSCCO single crystal fixed on the sapphire substrate by magnetron sputtering; s4, photoetching and transferring a gold electrode pattern on the surface of the BSCCO single crystal; s5, carrying out ion beam etching to remove the gold film outside the photoetching pattern; s6, evaporating a silicon oxide film as a protective layer; and S7, removing the photoresist by using an organic solvent. According to the method disclosed by the invention, the necessary steps of depositing the gold electrode on the BSCCO single crystal are completed in a vacuum environment, so that the influence of an organic reagent, water and air on the structure of the BSCCO single crystal is effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of superconducting device preparation, and particularly relates to a method for depositing gold electrodes on the surface of a BSCCO single crystal. Background Art

[0002] Superconducting nanowire single photon detectors (SNSPDs) have important application values in the fields of quantum communication, quantum computing, and high-precision optical sensing due to their high quantum efficiency, low time jitter, and fast response speed. As a typical high-temperature superconducting material, single crystals have become an ideal choice for preparing high-temperature and high-performance SNSPDs due to their relatively high superconducting transition temperature (Tc) and good physical properties. The high-temperature superconductivity of BSCCO enables it to operate at liquid nitrogen temperature, reducing the refrigeration cost and complexity; its anisotropic structural characteristics give it unique advantages in low-dimensional superconducting research; through mechanical exfoliation technology, ultra-thin single crystals with fewer defects can be prepared, which is beneficial to the research of low-dimensional superconducting properties and the preparation of superconducting electronics prototype devices. However, the research on BSCCO-based SNSPDs still faces challenges such as complex preparation processes and relatively high superconducting energy gap voltages that may affect the detection efficiency.

[0003] Currently, the main difficulties in depositing gold electrodes on the surface of BSCCO single crystals are as follows:

[0004] (1) After two-dimensional transfer, the surface of the BSCCO single crystal on the substrate will be exposed to air for a period of time, causing the surface layer of the single crystal to lose oxygen and the superconducting properties to degrade;

[0005] (2) After lithography, the electrode pattern is etched by an ion beam. However, during the etching process, some argon ion beams will penetrate into the interior of the BSCCO single crystal and damage its structure, resulting in the degradation of superconducting properties;

[0006] (3) After the BSCCO single crystal is etched, a protective layer needs to be added to its surface. However, during the transfer of the sample from the etching equipment to the protective layer evaporation equipment, the sidewalls of the single crystal contacting air will cause degradation. Summary of the Invention

[0007] Aiming at the above problems existing in the prior art, the technical problem to be solved by the present invention is to provide a method for depositing gold electrodes on the surface of a BSCCO single crystal, which has the advantages of greatly simplifying the steps of depositing gold electrodes on the surface of a BSCCO single crystal, effectively reducing the influence of organic reagents, water, and air on the structure of the BSCCO single crystal, and effectively improving the success rate and reliability of preparing superconducting nanowire single photon detectors.

[0008] Technical Solution: To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0009] A method for depositing a gold electrode on the surface of a BSCCO single crystal, comprising the following steps:

[0010] S1. Clean the sapphire substrate;

[0011] S2. Place the sapphire substrate in a vacuum pipeline, fix the PDMS film with the BSCCO single crystal adhered thereto on the sapphire substrate, and cleave the BSCCO single crystal in the vacuum pipeline;

[0012] S3. Use magnetron sputtering to deposit a gold film on the surface of the BSCCO single crystal fixed on the sapphire substrate;

[0013] S4. Photolithographically transfer the gold electrode pattern onto the surface of the BSCCO single crystal;

[0014] S5. Ion beam etching to remove the gold film outside the photolithographic pattern;

[0015] S6. In-situ transfer the sample to an electron beam evaporation device, and deposit a silicon oxide thin film as a protective layer;

[0016] S7. Remove the photoresist with an organic solvent.

[0017] Preferably, in the S1 cleaning step: put the sapphire substrate into an acetone solution and use ultrasonic cleaning for a cleaning time of T1, then use alcohol and deionized water to clean and remove the residues, dry it with a nitrogen gun, and then bake it on a baking table. The temperature of the baking table is D1, and the baking time of the sapphire substrate is T2.

[0018] Preferably, in the S2, use a high-temperature vacuum tape to fix the sapphire substrate on the sample tray, fix the sample tray on the trolley in the vacuum pipeline, fix the PDMS film with the BSCCO single crystal adhered thereto on the sapphire substrate, one end of the PDMS film is connected by a second tape, and the other end of the second tape is fixed on the cavity wall of the vacuum pipeline. By moving the trolley, utilize the inertia of the trolley movement to cleave the BSCCO single crystal in the pipeline.

[0019] Preferably, in the S3, magnetron sputtering deposits a gold film at a rate of 8 nm / min for 40 nm.

[0020] Preferably, in the S4, during the photolithography process, select the BSCCO single crystal thin film with a thickness of 10 nm to 20 nm for photolithography. The steps of photolithography exposure and development are as follows: spin-coat a layer of photoresist on the sample surface, and place the sample on a heating platform for baking. The temperature of the heating platform is D2, and the baking time of the sample is T3. Then use the microscope of the ultraviolet exposure machine to observe the sample surface, place the electrode pattern on the BSCCO single crystal thin film, perform development after the exposure is completed. The exposure time is T4, and the development time is T5.

[0021] Preferably, in step S5, the sample is fed into a vacuum pipeline and etched with a 300 V ion beam for 60 s.

[0022] Preferably, in step S6, the thickness of the silicon oxide thin film is 30 nm.

[0023] Preferably, after removing the photoresist in step S7, the sample is cleaned with acetone, rinsed with alcohol, and then dried with a nitrogen gun.

[0024] Advantages: Compared with the prior art, the present invention has the following advantages:

[0025] 1. This method cleaves the BSCCO single crystal in a vacuum environment using a pipeline, deposits a 40 nm gold film by magnetron sputtering, takes out the BSCCO single crystal sample covered with the gold film from the vacuum pipeline, and uses a 300 V ion beam for etching after ultraviolet exposure to transfer the electrode pattern. By controlling the etching time, the gold film outside the photolithography pattern is just removed without over-etching. Then, the sample is in-situ transferred to an electron beam evaporation coating system to deposit a 30 nm silicon oxide protective layer. By adopting metal mask technology, photolithography technology, electron beam evaporation technology, and magnetron sputtering technology, gold electrodes can be deposited while better protecting the BSCCO single crystal.

[0026] 2. The BSCCO single crystal is cleaved by the movement of a trolley in a vacuum pipeline, which is simple and efficient, ensuring that the cleaved sample is only in contact with the vacuum environment before evaporating the gold film, reducing degradation, and in-situ depositing the silicon oxide protective layer after the subsequent etching step is completed, avoiding the contact of the exposed single crystal sidewall with air during etching.

[0027] 3. All the necessary steps for depositing gold electrodes on the BSCCO single crystal are completed in a vacuum environment. This method can be applied to the deposition of gold electrodes on BSCCO single crystal thin films with a thickness of 10 nm to 20 nm. It has the advantages of greatly simplifying the steps of depositing gold electrodes on the surface of the BSCCO single crystal, effectively reducing the influence of organic reagents, water, and air on the BSCCO single crystal structure, weakening the degradation of the BSCCO single crystal surface during the electrode preparation process, improving the preparation success rate and performance of ultra-thin BSCCO single crystal samples, and laying a foundation for realizing superconducting nanodevices with higher working temperatures. Description of the Drawings

[0028] Figure 1 is the preparation flow chart of depositing gold electrodes on the surface of the BSCCO single crystal in the embodiment of the present invention;

[0029] Figure 2 is the front optical image of the sample prepared in the embodiment;

[0030] Figure 3 is the backlight optical image of the sample prepared in the embodiment;

[0031] Figure 4 It is a test chart of the resistance-temperature characteristics of the samples in the embodiments;

[0032] Figure 5 It is a diagram of the method for inertial cleavage of the trolley. Specific embodiments

[0033] The present invention will be further clarified below in conjunction with specific embodiments. The embodiments are implemented on the premise of the technical solution of the present invention. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0034] As Figure 1 shown, the method for depositing a gold electrode on the surface of a BSCCO single crystal in this embodiment includes the following steps:

[0035] S1. Clean the sapphire substrate. Place the sapphire substrate in acetone and ultrasonically clean it with 100 W. The cleaning time is T1. In this embodiment, T1 = 5 minutes. Then use alcohol and deionized water to remove the residues, and dry it with a nitrogen gun. Then bake it on a baking table. The temperature of the baking table is D1, 90°C ≤ D1 ≤ 98°C. In this embodiment, D1 = 95°C. The baking time of the sapphire substrate is T2, 3 minutes ≤ T2 ≤ 10 minutes. In this embodiment, T2 = 5 minutes.

[0036] S2. Place the sapphire substrate in the vacuum pipeline of the vacuum system. The vacuum location of the pipeline , attach the PDMS film with the BSCCO single crystal adhered to the sapphire substrate, and cleave the BSCCO single crystal in the vacuum pipeline. The specific process: As Figure 5 shown, in the vacuum pipeline, use a high-temperature vacuum tape (Teflon high-temperature tape) to fix the sapphire substrate on the sample tray. The sample tray is fixed on the trolley. Attach the PDMS film with the BSCCO single crystal adhered to the sapphire substrate. One end of the PDMS film is connected by a second tape (the second tape uses Scotch tape). The other end of the second tape is fixed on the cavity wall of the vacuum pipeline. By moving the trolley in the vacuum pipeline, when the trolley moves, the second tape connecting the cavity wall of the vacuum pipeline and the PDMS film will be straightened, and the PDMS film fixed on the sapphire substrate will be forced to fall off from the sapphire substrate, and the BSCCO single crystal remains on the sapphire substrate to form a sample.

[0037] S3. Use magnetron sputtering to deposit a layer of gold film on the surface of the BSCCO single crystal fixed on the sapphire substrate. The magnetron power is 150 W, the evaporation rate of the gold film is 8 nm / min, and a 40-nm gold film is deposited by evaporating for 5 min. Figure 1 as shown in (1) depositing the gold film in

[0038] S4. Transfer the gold electrode pattern onto the surface of the BSCCO single crystal by photolithography. Take the sample out of the vacuum pipeline and perform photolithography. During the photolithography process, since the backlight image of the BSCCO single crystal thin film can distinguish the thickness according to the color of BSCCO, and the colors from thin to thick are white - yellow - orange - black in sequence. Select the light - yellow BSCCO single crystal, and this thickness is expected to be in the range of 10 nm to 20 nm. Screen out the BSCCO single crystal thin film (light - yellow, thickness range 10 nm to 20 nm, and the thinner BSCCO single crystal thin film has better heat dissipation and is more conducive to making superconducting nanowires) for photolithography. The steps of photolithography exposure and development are as follows: Spin - coat a layer of photoresist on the sample surface. The photoresist used is AZ5214 photoresist. First, rotate at a low speed of 600 rpm for 10 s, then rotate at a high speed of 3000 rpm for 60 s, and place the sample on a heating platform for baking. The temperature of the heating platform is D2, where 90°C ≤ D2 ≤ 98°C. In this embodiment, D2 = 95°C. The baking time of the sample is T3, where 1 min ≤ T3 ≤ 5 min. In this embodiment, T3 = 2 minutes. Then, use the microscope of the ultraviolet exposure machine to observe the sample surface, place the electrode pattern on the photoresist layer, perform development after the exposure ends. The exposure time is T4, where 5 s ≤ T4 ≤ 10 s. In this embodiment, T4 = 7 s. The development time is T5, where 20 s ≤ T5 ≤ 30 s. In this embodiment, T5 = 22 s. Figure 1 As shown in (2) spin - coating and photolithography development.

[0039] S5. Ion beam etching, remove the gold film outside the photolithography pattern. Send the sample into the vacuum pipeline and use an ion beam with a voltage of 300 V (in the prior art, an ion beam voltage of 500 V is generally used. The speed and density of the argon ion beam are higher than those of 300 V, and the argon ion beam is likely to damage the deep - layer BSCCO single crystal) to etch the sample for 60 s to expose a fresh surface. Figure 1 As shown in (3) 300 V ion beam etching. If looking at the physical diagram from top to bottom, part of the BSCCO single crystal is under the gold film and part is exposed. In this step, the average rate of the argon ion beam is lower than that of the conventional 500 V ion beam etching. By controlling the etching time, over - etching can be avoided.

[0040] S6. Transfer the sample in - situ to an electron beam evaporation device and deposit a silicon oxide thin film as a protective layer. The thickness of the protective layer is greater than or equal to 20 nm. In this embodiment, the thickness of the silicon oxide thin film is 30 nm. Figure 1 As shown in (4) depositing a 30 nm silicon oxide protective layer.

[0041] S7. Remove the photoresist with an organic solvent. The organic solvent is acetone or ethanol. After removing the photoresist, clean the sample for 10 s, then rinse with alcohol, and then dry it with a nitrogen gun. (The photoresist is soluble in acetone, and the corresponding silicon oxide above also falls off after the photoresist disappears). Figure 1As shown in (5), the photoresist is removed using an organic solvent.

[0042] The performance of the prepared BSCCO single crystal film sample was tested as follows:

[0043] The optical image of the whole film sample was obtained using an optical microscope, as Figure 2 and Figure 3 shown, Figure 2 and Figure 3 The magnification is 50 times. The ion milling can fully etch away the gold film on the surface of the sapphire substrate without causing obvious damage to the surface of the BSCCO single crystal.

[0044] The current-voltage characteristics of the BSCCO single crystal were tested using a current source KEITHLEY 6221 and a voltmeter KEITHLEY 2182A. The results are as Figure 4 shown, Figure 4 In the figure, the ordinate R represents resistance in ohms, and the abscissa T represents temperature in Kelvin. The test results show that the R-T of the BSCCO single crystal is normal, and the superconducting transition temperature is about 80K, meeting the standard for preparing a high-temperature superconducting single-photon detector.

[0045] In this embodiment, the cleavage by a trolley in a vacuum pipeline is used to replace the existing cumbersome steps of thermal evaporation vacuum cleavage or cleavage with transparent tape (manual operation is not allowed in the vacuum pipeline). All important steps (S2, S3, and S5) are completed in a vacuum environment, saving the time for entering and exiting the vacuum system, avoiding the degradation of the BSCCO single crystal due to contact with air, and being applicable to the deposition of gold electrodes on BSCCO single crystal thin films with a thickness of 10 nm to 20 nm. (Once the BSCCO single crystal with a thickness of about 10 nm comes into contact with air, it will start to degrade), ensuring the quality of the BSCCO single crystal (which will be used to make a single-photon detector later, and there are high requirements for the heat dissipation of the sample, so the thickness of the BSCCO single crystal thin film must be between 10 nm and 20 nm).

[0046] The existing evaporation of gold film usually uses the vacuum thermal evaporation coating method, but the attraction between the thermally evaporated gold film and the substrate is weak. For the electrodes in this embodiment, acetone needs to be repeatedly used to clean the photoresist in very small areas, and the thermally evaporated gold film is likely to fall off. In this embodiment, magnetron sputtering is used to evaporate the gold film, and the contact resistance is about 50Ω, meeting the experimental requirements. At the same time, the gold electrode by magnetron sputtering can be well preserved when removing the glue.

[0047] This method realizes all the steps of depositing gold electrodes in a vacuum system, which improves the preparation success rate and performance of ultra-thin BSCCO single crystal samples, and can achieve a higher working temperature after processing superconducting nanowires (the superconducting transition temperature of the prior art is 50K, and in this embodiment, it exceeds 80K). The steps are relatively concise (instead of the originally cumbersome thermal evaporation vacuum cleavage steps, all steps are completed in the vacuum system, saving the time of entering and leaving the vacuum system, avoiding the degradation of BSCCO single crystal in contact with air, and ensuring the quality of BSCCO single crystal), and large-scale production can be achieved.

[0048] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for depositing a gold electrode on the surface of a BSCCO single crystal, characterized in that: The following steps are involved: S1. Cleaning the sapphire substrate; S2, placing the sapphire substrate in a vacuum pipe, fixing the PDMS film with the BSCCO single crystal on the sapphire substrate, and cleaving the BSCCO single crystal in the vacuum pipe; S3, depositing a gold film on the surface of the BSCCO single crystal fixed on the sapphire substrate using magnetron sputtering; S4, photolithography transfer of gold electrode pattern onto the surface of BSCCO single crystal; S5, ion beam etching to remove the gold film outside the photolithography pattern; S6, transferring the sample in situ to an electron beam evaporation device, and evaporating a silicon oxide film as a protective layer; S7. Remove the photoresist using an organic solvent.

2. The method for depositing a gold electrode on the surface of a BSCCO single crystal according to claim 1, characterized in that: The S1 cleaning step is as follows: the sapphire substrate is placed in an acetone solution and ultrasonically cleaned for a cleaning time of T1, then cleaned with alcohol and deionized water to remove residues, blown dry with a nitrogen gun, and then baked on a drying table at a drying table temperature of D1 and a sapphire substrate baking time of T2.

3. The method for depositing a gold electrode on the surface of a BSCCO single crystal according to claim 1, characterized in that: In S2, a high-temperature vacuum tape is used to fix the sapphire substrate on a sample tray, the sample tray is fixed on a trolley in a vacuum pipe, a PDMS film with a BSCCO single crystal adhered thereto is fixed on the sapphire substrate, one end of the PDMS film is connected by a second tape, the other end of the second tape is fixed to the wall of the vacuum pipe cavity, and the BSCCO single crystal is cleaved in the pipe by moving the trolley and utilizing the inertia of the trolley.

4. The method for depositing a gold electrode on the surface of a BSCCO single crystal according to claim 1, characterized in that: In S3, a 40 nm gold film is deposited by magnetron sputtering at a rate of 8 nm / min.

5. The method for depositing a gold electrode on the surface of a BSCCO single crystal according to claim 1, characterized in that: In the S4, during the photolithography process, a BSCCO single crystal film with a thickness of 10nm~20nm is screened for photolithography, and the steps of photolithography exposure and development are: spin coating a layer of photoresist on the surface of the sample, and placing the sample on a heating platform for baking, the heating platform temperature is D2, the sample baking time is T3, and then using a microscope of a UV exposure machine to observe the sample surface, placing an electrode pattern on the BSCCO single crystal film, and developing after the exposure is completed, the exposure time is T4, and the development time is T5.

6. The method for depositing a gold electrode on the surface of a BSCCO single crystal according to claim 1, characterized in that: In S5, the sample is sent into a vacuum pipe and treated with a 300V ion beam etching for 60 seconds.

7. The method for depositing a gold electrode on the surface of a BSCCO single crystal according to claim 1, characterized in that: In the S6, the thickness of the silicon oxide film is 30 nm.

8. The method for depositing a gold electrode on the surface of a BSCCO single crystal according to claim 1, characterized in that: After removing the photoresist in S7, the sample is cleaned with acetone, then rinsed with alcohol, and then blown dry with a nitrogen gun.

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