Preparation method of room temperature high-quality buffer layer-free alpha-phase tantalum film and preparation method of tantalum film quantum device

Abstract

The application provides a preparation method of a room-temperature high-quality buffer layer-free alpha-phase tantalum film, wherein a substrate is loaded into a sample loading chamber and vacuumized to below 6e-8 Torr; the substrate is transmitted to a film coating chamber, the substrate is arranged opposite to a tantalum target, the normal line of the substrate and the normal line of the plane where the tantalum target is located form an angle of 0°, the substrate sample and the tantalum target are kept at a predetermined interval, and the vacuum of the film coating chamber is extracted to below 5e-10 Torr; inert gas is pre-injected in a vacuum environment, so that the chamber reaches and maintains a predetermined air pressure; a specific power is output to perform sputtering film coating, after a predetermined sputtering time, the power output and the inert gas input are stopped; the substrate coated with the alpha-phase tantalum film is transmitted from the film coating chamber back to the sample loading chamber, and nitrogen or argon is used to break the vacuum and take out. The application provides a process flow for preparing a high-quality factor resonator quantum device from the prepared tantalum film. The application improves the yield, improves the device performance, and has a wide application field, including but not limited to the field of quantum computing.

Description

TECHNICAL FIELD

[0001] The present application relates to quantum device manufacturing technology, in particular to a method for preparing a room-temperature high-quality buffer-free alpha-phase tantalum film and a method for preparing a tantalum film quantum device. BACKGROUND

[0002] Currently, the integration of precisely controlled superconducting quantum bits has reached hundreds of quantum bits, and is increasingly close to the application of quantum computers. This progress is achieved by breakthroughs in superconducting materials, circuit design, manufacturing processes, packaging architectures, and the like to improve coherence time. Among them, the quality of the superconducting thin film material plays an important role. Compared with niobium film, aluminum film, etc., the oxide of the tantalum film is single, and the alpha-phase tantalum film has lower loss, so the quantum device prepared therefrom has excellent performance. Generally, there are two ways to grow alpha-phase tantalum film, one of which requires high-temperature heating, and the other of which requires growing a niobium film as a buffer layer between the tantalum film and the substrate, and then the alpha-phase tantalum film can be grown at room temperature. These two ways of growing tantalum film have high cost, long cycle, complicated steps, and high requirements for equipment.

[0003] In addition, the etching of the tantalum film is difficult. In the article "New material platform for superconducting transmon qubits with coherence times exceeding 0.3 milliseconds" published in Nature Communications journal in 2021 by Alexander P.M. Place et al. of Princeton University, wet etching is used to obtain qualified quantum devices. However, wet etching has poor controllability, and isotropic etching can easily form overhangs and inclined walls, and the photoresist is often etched during the etching process; while the pattern sidewall is rough after dry etching, which affects the performance of the quantum device. The surface treatment of the quantum device sample in the process flow is also a difficulty, and improper treatment can easily contaminate the sample, and the surface oxide treatment and the cleaning method of the sample affect the performance of the sample. SUMMARY

[0004] The purpose of the present application is to provide a method for growing a buffer-free alpha-phase tantalum film at room temperature by magnetron sputtering, which does not require high-temperature growth and does not require a buffer layer, greatly reducing the equipment requirements for thin film growth. At the same time, an etching method for tantalum film is provided, which combines dry etching and wet etching to ensure etching rate, reduce etching cost, etc., avoid the shortcomings of the two etching methods, and at the same time have the advantages of the two etching methods.

[0005] The technical solution for achieving the purpose of the present application is: a method for preparing a room-temperature high-quality buffer-free alpha-phase tantalum film, comprising the following steps:

[0006] Step 1, providing a substrate;

[0007] Step 2, loading the substrate into a sample chamber and vacuumizing to below 6e-8 Torr;

[0008] Step 3, transferring the substrate to a coating chamber, the substrate is arranged opposite to a tantalum target, and the angle between the normal line of the substrate and the normal line of the plane where the tantalum target is located is 0°, adjusting the substrate sample and the tantalum target to be kept at a predetermined interval, and vacuumizing the coating chamber to below 5e-10 Torr;

[0009] Step 4, pre-feeding inert gas in a vacuum environment, so that the chamber reaches and maintains at a predetermined gas pressure;

[0010] Step 5, outputting a specific power for sputtering coating, after sputtering for a predetermined sputtering time, stopping the power output and the inert gas input;

[0011] Step 6, transferring the substrate coated with the alpha-phase tantalum film from the coating chamber back to the sample chamber, and breaking the vacuum with nitrogen or argon for taking out.

[0012] Further, in step 3, the substrate is transferred to the coating chamber, the substrate is arranged opposite to the tantalum target, and the angle between the normal line of the substrate and the normal line of the plane where the tantalum target is located is 0°, adjusting the substrate sample and the tantalum target to be kept at a predetermined interval, and vacuumizing the coating chamber to below 5e-10 Torr, wherein:

[0013] The interval between the substrate and the target is 60mm-80mm, so as to better realize the sputtering effect and good film thickness uniformity.

[0014] Further, in step 4, the inert gas is pre-fed in a vacuum environment, so that the chamber reaches and maintains at a predetermined gas pressure, wherein:

[0015] The inert gas is argon, the gas flow is 10sccm-30sccm, the sputtering gas pressure of the coating chamber is 1mTorr-3mTorr, and the gas flow is low at low gas pressure.

[0016] Further, in step 5, a specific power is outputted for sputtering coating, after sputtering for a predetermined sputtering time, the power output and the inert gas input are stopped, wherein:

[0017] The sputtering power is 30W-80W, and the sputtering time is 500s-1500s, which is low-power sputtering and long sputtering time.

[0018] A preparation method of a tantalum film quantum device, based on the preparation method of the room-temperature high-quality buffer-free alpha-phase tantalum film, the tantalum film is prepared, comprising the following steps:

[0019] Step 1, annealing the sapphire substrate at 1000-1400℃;

[0020] Step 2, growing a tantalum film with a thickness of 150-250nm on the sapphire substrate at room temperature;

[0021] Step 3, cleaning the tantalum film with piranha solution, then rinsing with deionized water, ultrasonic cleaning, and rinsing again to remove the residual piranha solution on the surface of the tantalum film;

[0022] Step 4, coating photoresist, exposing, and developing;

[0023] Step 5, dry etching 85-100% of the depth, then wet etching the remaining depth and slightly over-etching to form an external circuit, and obtaining a quantum device sample containing a tantalum film;

[0024] Step 6, removing the photoresist, coating the photoresist, and dicing the sample;

[0025] Step 7, ultrasonic cleaning with N-methyl pyrrolidone solution, then replacing the solution and standing for 15 hours, followed by rinsing the sample with acetone, isopropyl alcohol, and deionized water;

[0026] Step 8, cleaning the sample with piranha solution again, then rinsing with deionized water, ultrasonic cleaning, and rinsing again to remove the residual piranha solution on the surface of the sample;

[0027] Step 9, immersing the sample in BOE solution for about 20min to etch away part of the oxide on the surface of the tantalum film, then rinsing with deionized water, ultrasonic cleaning, and rinsing again to remove the residual BOE solution on the surface of the sample.

[0028] Further, in Step 1, the sapphire substrate is annealed at 1000-1400℃, wherein:

[0029] The high-temperature annealing is performed using compressed air high-temperature annealing.

[0030] Further, in Step 3, the tantalum film substrate is cleaned with piranha solution, then rinsed with deionized water, ultrasonic cleaned, and rinsed again to remove the residual piranha solution on the surface of the sample, wherein:

[0031] The piranha solution is a mixture of 98% concentrated sulfuric acid and 30% hydrogen peroxide with a volume ratio of 2:1, and the heating temperature is 150℃, and the piranha solution is cleaned for 20min.

[0032] Further, in Step 4, the photoresist is coated, exposed, and developed, wherein:

[0033] The photoresist model is S1813, and the exposure dose is 115 mJ / m2~120 mJ / m2. The lower exposure dose makes the circuit line width after exposure wider than the designed line width, and the line width after subsequent etching is consistent with the designed width.

[0034] Further, in step 5, 85%~100% of the depth is etched by dry etching, and the remaining depth is etched by wet etching for a short time to form an external circuit, thereby obtaining a quantum device sample containing a tantalum film.

[0035] The wet etching time is 3 sec~10 sec, and the wet etching solution is a mixed solution with a volume ratio of HNO3:HF:H2O=1:1:1. The remaining depth is etched by wet etching for a short time, and the slight over-etching of wet etching makes the rough sidewall after dry etching smooth and flat, thereby improving the performance of the quantum device.

[0036] Further, in step 8, the piranha solution is heated to clean the sample again, and then the sample is rinsed with deionized water, ultrasonic cleaning, and then rinsed to remove the residual piranha solution on the surface of the sample.

[0037] The piranha solution is a mixture of 98% concentrated sulfuric acid and 30% hydrogen peroxide with a volume ratio of 2:1, and the heating temperature is 60~80℃. The piranha solution is cleaned for 20 min. The lower heating temperature can prevent the solution from reacting violently, thereby preventing the sample from being contaminated.

[0038] Compared with the prior art, the present application has the following advantages: 1) the tantalum film is a buffer layer-free tantalum film with an alpha phase and a crystal direction, which is grown at room temperature by a magnetron sputtering chamber, does not need high-temperature growth, and does not need a buffer layer, thereby greatly reducing the equipment requirements for thin film growth, having a large process window, being stable and repeatable, improving the yield and device performance, and greatly reducing the time cost and economic cost; 2) the etching of the tantalum film combines dry etching and wet etching, removes the residual photoresist in the circuit, well guarantees the etching rate, reduces the etching cost, avoids the shortcomings of the two etching methods, and has the advantages of both etching methods; 3) the two times of piranha solution passivation of the film form a stable and low-loss amorphous tantalum oxide layer on the film, and the second piranha cleaning removes the organic solvent pollution remaining on the surface of the sample; 4) the BOE solution removes part of the oxides on the surface of the tantalum film, thereby improving the quality factor of the quantum device; and 5) the cleaning method of deionized water rinsing-ultrasonic cleaning-deionized water rinsing effectively removes the organic and inorganic solution residues. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is a preparation process schematic diagram of a high-quality buffer layer-free alpha phase tantalum film grown at room temperature.

[0040] Figure 2is the XRD result diagram of the thin film.

[0041] Figure 3 is the SEM result diagram of the root thin film.

[0042] Figure 4 is the preparation flowchart of the tantalum-containing film quantum device. DETAILED DESCRIPTION

[0043] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application.

[0044] Please refer to Figure 1 In view of the deficiencies of the prior art, the present inventors have long studied and practiced and have finally proposed the technical solutions of the present application, which mainly grow the alpha-phase tantalum film by a method without high-temperature heating, without growing a buffer layer, low sputtering gas pressure and low power. The following is the preparation method of the room-temperature high-quality buffer-layer-free alpha-phase tantalum film, which uses the Xiamen Wenmao double-chamber magnetron sputtering equipment for film plating and includes the following steps:

[0045] Step 1, providing a substrate; the substrate sample is made of sapphire.

[0046] Step 2, loading the substrate into the sample chamber and vacuumizing to below 6e-8 Torr.

[0047] Step 3, transmitting the substrate to the film plating chamber, the substrate is arranged opposite to the target material, the normal line of the substrate sample and the normal line of the plane where the target material is located form an angle of 0°, the substrate sample and the target material are adjusted to be kept at a predetermined interval, and the vacuum of the film plating chamber is vacuumized to below 5e-10 Torr; the target material is a tantalum target material, and the interval between the substrate and the target material is 60mm-80mm, so as to better achieve the sputtering effect and good film thickness uniformity.

[0048] Step 4, pre-feeding inert gas in the vacuum environment, so that the chamber reaches and maintains at a predetermined gas pressure; the inert gas is argon, the gas flow is 10sccm-30sccm, the sputtering gas pressure of the film plating chamber is 1mTorr-3mTorr, and the gas flow is low.

[0049] Step 5, outputting a specific power for sputtering film plating, stopping the power output and gas input after sputtering for a predetermined sputtering time; the sputtering power is 30W-80W, the sputtering time is 500s-1500s, and the sputtering is low in power and long in time.

[0050] Step 6, the substrate is transferred from the coating chamber to the sample chamber. After the substrate is transferred from the coating chamber to the sample chamber, the sample coated with the alpha phase tantalum film is taken out by breaking the vacuum using nitrogen or argon.

[0051] Figure 2 is an XRD result diagram of a film according to an embodiment of the present application, and the crystal direction of the film is mainly alpha-110 phase of tantalum. Figure 3 is an SEM result diagram of a film according to an embodiment of the present application. Under the observation of a scanning electron microscope (SEM), the surface grains of the film are dense and uniform, and have obvious microstructure characteristics of alpha phase tantalum.

[0052] Please refer to Figure 4 The present application also provides a new process flow for preparing a quantum device based on the tantalum film, which has great improvement and innovation in the etching method of the tantalum film and the substrate processing. The process flow is as follows:

[0053] Step 1, sapphire substrate is annealed at 1300℃ for pretreatment; the high-temperature annealing is compressed air high-temperature annealing, and the annealing time is 3 hours.

[0054] Step 2, a tantalum film with a certain thickness is grown on the sapphire substrate at room temperature, and the tantalum film is prepared by the above preparation method; the thickness of the tantalum film is 200 nm.

[0055] Step 3, piranha solution is used to clean the tantalum film at a higher temperature; deionized water is used for washing, ultrasonic cleaning, and then rinsing to remove the residual piranha solution on the surface of the tantalum film; the piranha solution is a mixture of 98% concentrated sulfuric acid and 30% hydrogen peroxide (volume ratio H2SO4:H2O2=2:1), the heating temperature is 150℃, and the piranha solution cleaning time is 20 min.

[0056] Step 4, photoresist is coated, exposed at a lower exposure dose, and developed; the type of photoresist is S1813, and the lower exposure dose is 115mJ / ㎡-120mJ / ㎡. The lower exposure dose makes the circuit line width after exposure wider than the designed line width, and the line width after the subsequent over-etching is consistent with the designed width.

[0057] Step 5, dry etching is first used to etch 100% of the depth, and then wet etching is used for a short time to form an external circuit, and a quantum device sample containing a tantalum film is obtained; the wet etching solution is a mixed solution with a volume ratio of HNO3:HF:H2O=1:1:1, and the wet etching time is 3-5 seconds. The slight over-etching of the wet etching for a short time makes the rough sidewall after the dry etching smooth and flat.

[0058] Step 6, the sample is subjected to photoresist removing, photoresist uniformizing, and wafer dicing.

[0059] Step 7, after ultrasonic degumming in N-methyl pyrrolidone solution, the solution was replaced and the sample was left to stand for 15 hours. Subsequently, the sample was cleaned by washing with acetone, isopropyl alcohol and deionized water;

[0060] Step 8, the piranha solution was heated at a lower temperature to clean the sample again; the sample surface was cleaned by washing with deionized water, ultrasonic cleaning and washing again to remove the residual piranha solution on the sample surface; the piranha solution was a mixture of 98% concentrated sulfuric acid and 30% hydrogen peroxide (volume ratio H2SO4:H2O2=2:1), and the lower heating temperature was 60-80°C. The lower heating temperature can prevent the solution from reacting violently, thereby preventing the sample from being contaminated by being overturned.

[0061] Step 9, the sample was immersed in a BOE solution for about 20 minutes to remove the oxide on the surface of the tantalum film. The sample surface was cleaned by washing with deionized water, ultrasonic cleaning and washing again to remove the residual BOE solution on the sample surface. The BOE solution was a conventional buffered oxide etching (BOE) solution (HF:NH4F=1:6), and the sample was immersed in the BOE solution for 20 minutes.

[0062] In addition, after the tantalum film sample is subjected to the above process, a resonator is prepared by wire packaging. Table 1 is a table of the change of the quality factor Q of two resonators with different frequencies prepared by using the new process for preparing quantum devices after the tantalum film is prepared by using the preparation method of room-temperature high-quality buffer-free α-phase tantalum film provided by the embodiment of the present application, from a higher power to a lower power. i

[0063] Table 1 Table of the change of the quality factor Q i

[0064] Resonator frequency (MHz) Q i (about -100 dB) Q i (-141dB) 3625 About 8600 k About 1600 k 3697 About 10540 k About 1290 k

[0065] In the table, Q i represents the internal quality factor of the circuit, Q i is a dimensionless physical quantity, Q i 1 / Q i can be directly used to quantify the loss of the circuit. As can be seen from Table 1, the resonator prepared by using the preparation process for quantum devices provided by the present application has a very excellent quality factor, which indicates that the thin film prepared by the preparation method of the present application has high quality and good application prospect.

[0066] The technical features of the above embodiments can be combined in any manner. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described, but as long as the combinations of the technical features do not exist, they should be considered as the scope of the present application.

[0067] ​​The above-described embodiments are merely illustrative of several embodiments of the present application, which are described in more detail and in a specific manner, but should not be construed as limiting the scope of the present application. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method for preparing high-quality α-phase tantalum film without buffer layer at room temperature, characterized in that: The following steps are involved: Step 1, providing a substrate; Step 2: Load the substrate into the loading chamber and evacuate the chamber to below 6e-8 Torr. Step 3: Transfer the substrate to the coating chamber. Place the substrate and the tantalum target opposite each other, with the angle between the substrate normal and the tantalum target plane normal being 0°. Adjust the substrate sample and the tantalum target to maintain a predetermined distance, and evacuate the coating chamber to below 5e-10 Torr. Step 4: Pre-introduce inert gas into the vacuum environment to make the chamber reach and maintain a predetermined pressure, wherein: The inert gas is argon, the gas flow rate is 10sccm~30sccm, and the sputtering pressure in the coating chamber is 1mTorr~3mTorr; Step 5: Output a specific power to perform sputtering coating. After the predetermined sputtering time is completed, stop the power output and the inert gas input, wherein: The sputtering power is 30W to 80W, and the sputtering time is 500s to 1500s; In step 6, the substrate coated with the α-phase tantalum film is transferred from the coating chamber back to the sample loading chamber, and is taken out by breaking the vacuum using nitrogen or argon gas.

2. The method for preparing a high-quality buffer-free α-phase tantalum film at room temperature according to claim 1, characterized in that: Step 3: Transfer the substrate to the coating chamber. The substrate and the tantalum target are arranged relative to each other, and the angle between the normal line of the substrate and the normal line of the plane where the tantalum target is located is 0°. The substrate sample and the tantalum target are adjusted to maintain a predetermined distance, and the vacuum of the coating chamber is evacuated to below 5e-10Torr, wherein: The distance between the substrate and the target is 60mm to 80mm to achieve better sputtering effect and good film thickness uniformity.

3. A method for preparing a tantalum film quantum device, characterized in that: The method for preparing a high-quality buffer-free α-phase tantalum film at room temperature according to any one of claims 1 to 2 comprises the following steps: Step 1: pre-treating the sapphire substrate by annealing at a temperature of 1000° C. to 1400° C. Step 2, growing a tantalum film with a thickness of 150 nm to 250 nm on a sapphire substrate at room temperature; Step 3: The tantalum membrane is cleaned with a heated piranha solution, and then rinsed with deionized water, ultrasonicated, and rinsed again to remove any piranha solution residue on the surface of the tantalum membrane; Step 4, performing photoresist coating, exposure, and development; Step 5: first dry-etching to remove 85% to 100% of the depth, then wet-etching to remove the remaining depth, and slightly over-etching to form an external circuit, thereby obtaining a quantum device sample containing a tantalum film; Step 6, performing degumming, coating, and dicing on the sample; Step 7: ultrasonically remove the glue using N-methylpyrrolidone solution, then replace the solution and let it stand for 15 hours. Then, rinse the sample with acetone, isopropyl alcohol, and deionized water; Step 8: The sample is washed again with heated piranha solution, and then rinsed with deionized water, ultrasonically cleaned, and rinsed again to remove any piranha solution residue on the sample surface; Step 9: Immerse the sample in BOE solution for about 20 minutes to etch away part of the oxide on the surface of the tantalum film, then rinse with deionized water, ultrasonically clean, and rinse again to remove the BOE solution residue on the sample surface.

4. The method for preparing a tantalum film quantum device according to claim 3, wherein: Step 1: pre-treating the sapphire substrate by annealing at a temperature of 1000° C. to 1400° C., wherein: High temperature annealing pretreatment uses compressed air high temperature annealing.

5. The method for preparing a tantalum film quantum device according to claim 3, wherein: Step 3: Heating the piranha solution to clean the tantalum film substrate, then rinsing with deionized water, ultrasonicating, and then rinsing again to remove the piranha solution residue on the surface of the substrate, wherein: The piranha solution is a mixture of 98% concentrated sulfuric acid and 30% hydrogen peroxide in a volume ratio of 2:

1. The heating temperature is 150°C and the piranha solution is used for cleaning for 20 minutes.

6. The method for preparing a tantalum film quantum device according to claim 3, wherein: Step 4, performing photoresist coating, exposure, and development, wherein: The photoresist model is S1813, and the exposure dose is 115mJ / ㎡~120mJ / ㎡.

7. The method for preparing a tantalum film quantum device according to claim 3, wherein: Step 5: First, dry-etch 85% to 100% of the depth, and then wet-etch the remaining depth and slightly over-etch to obtain a quantum device sample containing a tantalum film, wherein: The wet etching time is 3 sec to 10 sec, and the wet etching solution is a mixed solution with a volume ratio of HNO3:HF:H2O=1:1:

1.

8. The method for preparing a tantalum film quantum device according to claim 3, wherein: Step 8: Heat the piranha solution to clean the sample again, then rinse with deionized water, ultrasonically clean, and rinse again to remove any piranha solution residue on the surface of the sample, wherein: The piranha solution is a mixture of 98% concentrated sulfuric acid and 30% hydrogen peroxide in a volume ratio of 2:

1. The heating temperature is 60-80°C, and the piranha solution is used for cleaning for 20 minutes.

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