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

Abstract

The invention provides a preparation method for growing an alpha-phase tantalum film at room temperature and high quality without a buffer layer, which comprises the following steps of: loading a substrate into a sample introduction chamber, and vacuumizing to be below 6e-8Torr; the substrate is conveyed to a coating chamber, the substrate and the tantalum target material are oppositely arranged, the included angle between the normal of the substrate and the normal of the plane where the tantalum target material is located is 0 degree, the substrate sample and the tantalum target material are adjusted to be kept at a preset distance, and the coating chamber is vacuumized to be below 5e-10Torr; inert gas is pre-introduced into the vacuum environment, so that the chamber reaches and is maintained at the preset air pressure; specific power is output for sputter coating, and power output and inert gas input are stopped after sputter is completed for a preset sputter time; and the substrate plated with the alpha-phase tantalum film is conveyed back to the sample injection chamber from the film plating chamber, and nitrogen or argon is used for breaking vacuum and taking out the substrate. The invention provides a technological process for preparing a high-quality-factor resonator quantum device from the prepared tantalum film. According to the invention, the yield is improved, the device performance is improved, and the method has wide application fields including but not limited to the fields of quantum calculation and the like.

Description

Technical Field

[0001] The invention relates to a quantum device manufacturing technology, and in particular to a method for preparing a high-quality buffer-free α-phase tantalum film grown at room temperature and a method for preparing a tantalum film-containing quantum device. Background Art

[0002] At present, the integration level of precisely controlled superconducting quantum bits has reached hundreds of quantum bits, which is getting closer and closer to the application of quantum computers. This progress is achieved by improving the coherence time through breakthroughs in superconducting materials, circuit design, manufacturing processes, packaging architecture, etc. Among them, the quality of superconducting thin film materials plays an important role. Compared with niobium film, aluminum film, etc., tantalum film oxide is single, and the α-phase tantalum film has lower loss, so the quantum devices prepared with it have excellent performance. Usually there are two ways to grow α-phase tantalum film, one requires high-temperature heating, and the other is to grow a layer of niobium film between the tantalum film and the substrate as a buffer layer, and then the α-phase tantalum film can be grown at room temperature. These two methods of growing tantalum films are costly, have a long cycle, and have cumbersome steps, and have high requirements for equipment.

[0003] In addition, tantalum films are difficult to etch. Alexander PMPlace and others from Princeton University used wet etching in the article "New material platform for superconducting transmon qubits with coherence times exceeding 0.3 milliseconds" published in the journal Nature Communications in 2021 to obtain qualified quantum devices. However, wet etching has poor controllability, and its isotropic etching easily forms overhangs and sloping walls, and the photoresist is often etched off during the etching process; while dry etching makes the side walls of the pattern rough after etching, affecting the performance of the quantum device. Surface treatment of quantum device samples in the process flow is also a difficult point. Improper treatment can easily contaminate the samples. The surface oxide treatment and sample cleaning methods affect the performance of the samples. Summary of the invention

[0004] The purpose of the present invention is to propose a method for growing a buffer-free α-phase tantalum film at room temperature by magnetron sputtering, which does not require high-temperature growth or adding a buffer layer, greatly reducing the equipment requirements for thin film growth. At the same time, a tantalum film etching method is provided, which combines dry etching with wet etching to ensure etching rate, reduce etching costs, avoid the disadvantages of the two etching methods, and have the advantages of both etching methods.

[0005] The technical solution to achieve the purpose of the present invention is: a method for preparing a high-quality buffer-free α-phase tantalum film at room temperature, comprising the following steps:

[0006] Step 1, providing a substrate;

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

[0008] Step 3, transferring the substrate to the coating chamber, the substrate and the tantalum target are arranged opposite 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°, adjusting the substrate sample and the tantalum target to maintain a predetermined distance, and the vacuum of the coating chamber is pumped to below 5e-10Torr;

[0009] Step 4, pre-introducing an inert gas into the vacuum environment to allow the chamber to reach and maintain a predetermined pressure;

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

[0011] Step 6: Transfer the substrate coated with the α-phase tantalum film from the coating chamber back to the sample injection chamber, and take it out by breaking the vacuum with nitrogen or argon.

[0012] Further, in step 3, the substrate is transferred to the coating chamber, the substrate and the tantalum target are arranged opposite 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 pumped to below 5e-10Torr, wherein:

[0013] The distance between the substrate and the target is 60 mm to 80 mm to achieve better sputtering effect and good film thickness uniformity.

[0014] Further, in step 4, an inert gas is introduced into the vacuum environment to make the chamber reach and maintain a predetermined pressure, wherein:

[0015] The inert gas is argon, the gas flow rate is 10sccm~30sccm, the sputtering gas pressure in the coating chamber is 1mTorr~3mTorr, and the lower the gas pressure, the lower the gas flow rate.

[0016] Further, in step 5, a specific power is output for sputtering coating, and after 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, low power sputtering and long sputtering time.

[0018] A method for preparing a tantalum film-containing quantum device, based on the method for preparing a high-quality α-phase tantalum film grown without a buffer layer at room temperature, prepares a tantalum film, comprising the following steps:

[0019] Step 1, performing high temperature annealing pretreatment at 1000° C. to 1400° C. on the sapphire substrate;

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

[0021] Step 3, heating the piranha solution to clean the tantalum membrane, and then rinsing with deionized water, ultrasonicating, and then rinsing again to remove the piranha solution residue on the surface of the tantalum membrane;

[0022] Step 4, performing photoresist coating, exposure, and development;

[0023] 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;

[0024] Step 6, performing degumming, coating and dicing on the sample;

[0025] Step 7, using N-methylpyrrolidone solution for ultrasonic degumming, replacing the solution and letting it stand for 15 hours, and then rinsing the sample with acetone, isopropanol and deionized water;

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

[0027] 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 surface of the sample.

[0028] Further, in step 1, the sapphire substrate is subjected to a high temperature annealing pretreatment at 1000° C. to 1400° C., wherein:

[0029] High temperature annealing pretreatment uses compressed air high temperature annealing.

[0030] Further, in step 3, the tantalum film substrate is cleaned with a heated piranha solution, and then rinsed with deionized water, ultrasonicated, and rinsed again to remove the piranha solution residue on the surface of the substrate, wherein:

[0031] 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.

[0032] Further, step 4, photoresist coating, exposure, and development are performed, wherein:

[0033] The photoresist model is S1813, and the 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 subsequent etching is consistent with the designed width.

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

[0035] 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. Wet etching can remove the remaining depth in a short time, and the slight over-etching of wet etching can make the rough side wall after dry etching smooth and flat, thus improving the performance of quantum devices.

[0036] Further, in step 8, the sample is washed again with the piranha solution after heating, and then rinsed with deionized water, ultrasonically cleaned, and rinsed again to remove the piranha solution residue on the surface of the slice, wherein:

[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°C. The piranha solution is used for cleaning for 20 minutes. The lower heating temperature can prevent the solution from reacting violently, thereby overturning the sample and causing contamination.

[0038] Compared with the prior art, the present invention has the following significant advantages: 1) The tantalum film is a tantalum film grown at room temperature by magnetron sputtering, has no buffer layer, and has an α-phase crystal orientation. It does not require high-temperature growth or a buffer layer, greatly reduces the equipment requirements for film growth, has a large process window, and has excellent stability and repeatability, improves the yield rate, improves device performance, and greatly reduces time costs and economic costs. 2) The etching of the tantalum film adopts a combination of dry etching and wet etching to remove residual photoresist in the circuit, well ensures the etching rate, reduces the etching cost, avoids the disadvantages of the two etching methods, and has the advantages of both etching methods. 3) The film is passivated by two piranha solutions to form a stable and low-loss amorphous tantalum oxide layer on the film, and the second piranha cleaning removes the organic solvent contamination remaining on the sample surface. 4) The BOE solution removes part of the oxide on the surface of the tantalum film, improving the quality factor of the quantum device. 5) The cleaning method of deionized water rinsing-ultrasound-deionized water rinsing effectively removes organic and inorganic solution residues. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0042] Figure 4 It is a schematic diagram of the preparation process of tantalum film quantum devices. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0044] Please refer to Figure 1 In view of the shortcomings of the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice, which mainly grows α-phase tantalum film by a method without high-temperature heating, without growing a buffer layer, low sputtering pressure, and low power. The following is a preparation method for such a high-quality α-phase tantalum film grown without a buffer layer at room temperature, using Xiamen Yunmao dual-chamber magnetron sputtering equipment for coating, including the following steps:

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

[0046] Step 2: Load the substrate into the injection chamber and evacuate the chamber to below 6e-8 Torr.

[0047] Step 3, transfer the substrate to the coating chamber, the substrate and the target are arranged opposite to each other, and the angle between the normal of the substrate and the normal of the plane where the target is located is 0°, adjust the substrate sample and the target to maintain a predetermined distance, and evacuate the vacuum of the coating chamber to below 5e-10Torr; the target is a tantalum target, and the distance between the substrate and the target is 60mm to 80mm, so as to better achieve the sputtering effect and good film thickness uniformity.

[0048] Step 4, pre-introducing an inert gas into the vacuum environment to make the chamber reach and maintain a predetermined gas pressure; the inert gas is argon, the gas flow rate is 10sccm~30sccm, the sputtering pressure of the coating chamber is 1mTorr~3mTorr, and the lower the gas pressure, the lower the gas flow.

[0049] Step 5, output a specific power for sputtering coating, and stop the power output and gas input after the predetermined sputtering time; the sputtering power is 30W to 80W, the sputtering time is 500s to 1500s, low power sputtering, and long sputtering time.

[0050] Step 6: The substrate is transferred from the coating chamber back to the sample injection chamber. After the substrate is transferred from the coating chamber back to the sample injection chamber, nitrogen or argon gas is used to break the vacuum and take out the sample coated with the α-phase tantalum film.

[0051] Figure 2 3 is an XRD result diagram of the film according to an embodiment of the present invention. The crystal orientation of the film is mainly tantalum α-110 phase. Figure 3 Observation under a scanning electron microscope (SEM) shows that the surface grains of the film are dense and uniform, and have obvious α-phase tantalum microstructure characteristics.

[0052] Please refer to Figure 4 The embodiment of the present invention also provides a new process flow for preparing quantum devices based on the above-mentioned tantalum film, which makes great improvements and innovations in the tantalum film etching method and substrate processing. The process flow is as follows:

[0053] Step 1, the sapphire substrate is pretreated by high temperature annealing at 1300° C. The high temperature annealing adopts compressed air high temperature annealing for 3 hours.

[0054] Step 2: growing a tantalum film of a certain thickness on a sapphire substrate at room temperature, wherein the tantalum film is prepared by the above-mentioned preparation method; the thickness of the tantalum film is 200 nm.

[0055] Step 3, heating the piranha solution at a relatively high temperature to clean the tantalum film; rinsing with deionized water, ultrasonication, and then rinsing to remove the piranha solution residue 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°C, and the piranha solution is cleaned for 20 minutes.

[0056] Step 4, photoresist coating, low exposure dose exposure, and development; the photoresist model is S1813, and the low exposure dose is 115mJ / ㎡~120mJ / ㎡. The low 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.

[0057] Step 5, first dry-etching to remove 100% of the depth, then wet-etching for a short time to form an external circuit, and obtain a quantum device sample containing a tantalum film; 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 3sec to 5sec. The slight over-etching in the short time of wet etching makes the rough side wall after dry etching smooth and flat.

[0058] Step 6, performing degumming, coating and dicing on the sample;

[0059] Step 7, ultrasonically remove the glue with N-methylpyrrolidone solution, then replace the solution and let it stand for 15 hours. Then, rinse the sample with acetone, isopropanol and deionized water;

[0060] Step 8, heating the piranha solution at a lower temperature to clean the sample again; rinsing with deionized water, ultrasonication, and then rinsing to remove the piranha solution residue on the surface of the sample; the piranha solution is a mixture of 98% concentrated sulfuric acid and 30% hydrogen peroxide (volume ratio H2SO4:H2O2=2:1), and the lower heating temperature is 60-80°C. The lower heating temperature can prevent the solution from reacting violently, thereby overturning the sample and causing contamination.

[0061] Step 9, immerse the sample in BOE solution for about 20 minutes to remove the oxide on the surface of the tantalum film. Rinse with deionized water, ultrasonically clean, and then rinse again to remove the BOE solution residue on the surface of the sample. BOE solution is an existing buffered oxide etching (BOE) solution (HF: NH4F = 1: 6), and the sample is immersed in the BOE solution for 20 minutes.

[0062] In addition, after the tantalum film sample has gone through the above process flow, the resonator is prepared by wire bonding and packaging. Table 1 shows the quality factors Q of two resonators of different frequencies from higher power to lower power obtained by using the new process flow for preparing quantum devices after the tantalum film is prepared by the method for preparing high-quality α-phase tantalum film without buffer layer at room temperature provided by the embodiment of the present invention. i table of changes.

[0063] Table 1 Quality factor Q i Table of changes

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

[0065] Q i Represents the internal quality factor of the circuit, Q i is a dimensionless physical quantity, Q i The inverse of 1 / Q i It can be directly used to quantify the loss of the circuit. As shown in Table 1, the room temperature high-quality buffer-free α-phase tantalum film obtained by the preparation method of the present invention has a very excellent resonator quality factor after being prepared by the preparation process of the quantum device provided by the present invention, indicating that the film has high quality and good application prospects.

[0066] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0067] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations 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 shall be subject to the attached claims.

Claims

1. A method for preparing a high-quality buffer-free α-phase tantalum film at room temperature, characterized in that: The following steps are involved: Step 1, providing a substrate; Step 2, loading the substrate into the injection chamber and evacuating the chamber to below 6e-8Torr; Step 3, transferring the substrate to the coating chamber, the substrate and the tantalum target are arranged opposite 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°, adjusting the substrate sample and the tantalum target to maintain a predetermined distance, and the vacuum of the coating chamber is pumped to below 5e-10Torr; Step 4, pre-introducing an inert gas into the vacuum environment to allow the chamber to reach and maintain a predetermined pressure; Step 5, outputting a specific power for sputtering coating, and stopping the power output and the inert gas input after the predetermined sputtering time is completed; Step 6: Transfer the substrate coated with the α-phase tantalum film from the coating chamber back to the sample injection chamber, and take it out by breaking the vacuum with nitrogen or argon.

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, transferring the substrate to the coating chamber, the substrate and the tantalum target are arranged opposite 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°, adjusting the substrate sample and the tantalum target to maintain a predetermined distance, and the vacuum of the coating chamber is pumped to below 5e-10Torr, wherein: The distance between the substrate and the target is 60 mm to 80 mm to achieve better sputtering effect and good film thickness uniformity.

3. The method for preparing a high-quality buffer-free α-phase tantalum film at room temperature according to claim 1, characterized in that: Step 4, pre-introducing 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 to 30sccm, and the sputtering pressure in the coating chamber is 1mTorr to 3mTorr.

4. The method for preparing a high-quality buffer-free α-phase tantalum film at room temperature according to claim 1, characterized in that: Step 5, output a specific power for sputtering coating, and after the predetermined sputtering time, stop the power output and the inert gas input, wherein: The sputtering power is 30W~80W, and the sputtering time is 500s~1500s.

5. 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 4 is used to prepare a tantalum film, comprising the following steps: Step 1, performing high temperature annealing pretreatment at 1000° C. to 1400° C. on the sapphire substrate; Step 2, growing a tantalum film with a thickness of 150 nm to 250 nm on a sapphire substrate at room temperature; Step 3, heating the piranha solution to clean the tantalum membrane, and then rinsing with deionized water, ultrasonicating, and then rinsing again to remove the 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, using N-methylpyrrolidone solution for ultrasonic degumming, replacing the solution and letting it stand for 15 hours, and then rinsing the sample with acetone, isopropanol and deionized water; Step 8, heating the piranha solution to clean the sample again, then rinsing with deionized water, ultrasonic cleaning, and then rinsing again to remove the piranha solution residue on the surface of the sample; 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 surface of the sample.

6. The method for preparing a tantalum-containing film quantum device according to claim 5, characterized in that: Step 1, pre-treating the sapphire substrate by high temperature annealing at 1000° C. to 1400° C., wherein: High temperature annealing pretreatment uses compressed air high temperature annealing.

7. The method for preparing a tantalum-containing film quantum device according to claim 5, characterized in that: Step 3, heating the piranha solution to clean the tantalum film substrate, and then rinsing with deionized water, ultrasonic, and then rinsing 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.

8. The method for preparing a tantalum-containing film quantum device according to claim 5, characterized in that: Step 4, performing photoresist coating, exposure, and development, wherein: The photoresist model is S1813, and the exposure dose is 115mJ / ㎡~120mJ / ㎡.

9. The method for preparing a tantalum-containing film quantum device according to claim 5, characterized in that: 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 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.

10. The method for preparing a tantalum-containing film quantum device according to claim 6, characterized in that: Step 8, heating the piranha solution to clean the sample again, then rinsing with deionized water, ultrasonic cleaning, and then rinsing to remove the piranha solution residue on the surface of the slice, 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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