Contact configuration processing method of carbon nanotube field effect transistor and field effect transistor

Abstract

The application provides a contact configuration processing method of a carbon nanotube field effect transistor and the field effect transistor. In the process of manufacturing a source electrode and a drain electrode, after a metal film is deposited and grown, annealing treatment is performed by heating to an interface reaction temperature in vacuum or inert gas and maintaining for a set time length. Solid phase reaction occurs between the carbon nanotube and the metal by using the solubility of carbon in the metal, carbon atoms diffuse into the metal to form a chemical bond connection, and the problem that the resistance sharply increases when the size is reduced due to the connection between the existing side contact structure, the source electrode, the drain electrode and the carbon nanotube array is solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a contact configuration fabrication method for a carbon nanotube field-effect transistor and the field-effect transistor itself. Background Technology

[0002] Silicon-based complementary metal-oxide-semiconductor (CMOS) technology is nearing its physical limits, making the search for new materials and devices as continuation and alternatives urgent. Carbon nanotubes (CNTs), due to their excellent electrical properties, quasi-one-dimensional lattice structure, and high carrier mobility, have become one of the ideal semiconductor channel materials for constructing novel CMOS transistors and integrated circuits. Further developments indicate that high-purity, high-density, parallel-aligned carbon nanotube arrays (ACNTs) are considered ideal materials for constructing high-performance, low-power carbon nanotube field-effect transistors (CNTFETs).

[0003] In ACNT FETs, the contact resistance of the source and drain electrodes directly affects the device's performance and power consumption. With the development of carbon nanotube field-effect transistors (CNTFETs), the mainstream contact method is currently side contact, where metal is directly deposited onto the carbon nanotube array, and the interaction between the metal and the carbon nanotube array is van der Waals. Studies have found that the contact resistance in side contact (… ) and contact length ( )follow ( Quantum resistance; The channel resistivity; (where the radius is the carbon nanotube) The contact resistance is inversely proportional to the contact length. This leads to a rapid increase in contact resistance as the contact length decreases. Especially when the contact length is below 50 nm, the contact between the metal and carbon nanotube fluctuates greatly due to the exposed crystal planes of the metal and the large fluctuations in the contact ratio between the metal and the carbon nanotube, making it difficult for side contact schemes to meet the contact resistance requirements of advanced ACNT FET nodes. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide a contact configuration fabrication method for carbon nanotube field-effect transistors and a field-effect transistor, in order to eliminate or improve one or more defects existing in the prior art, and solve the problem that the resistance increases sharply when the size is reduced due to the use of side contact structure in the prior art, which connects the source and drain electrodes with the carbon nanotube array based on van der Waals force.

[0005] One aspect of the present invention provides a method for fabricating contact configurations for carbon nanotube field-effect transistors, the method comprising: The carbon nanotube channels arranged in the first preset pattern array on the substrate are cut and cleaned to remove invalid parts; Photoresist is spin-coated onto the carbon nanotube channel, and ultraviolet lithography is used to perform photolithography according to the second preset pattern. The exposed areas are removed with developer to define the source and drain positions. The coating method is based on magnetron sputtering or electron beam evaporation, and a first type of metal is used to deposit a metal thin film. The first type of metal has a miscibility of greater than or equal to 0.1% with the carbon nanotubes in an inert gas environment above the interfacial reaction temperature. The remaining photoresist and the metal film on it are removed using a photoresist solvent, leaving the substrate, the carbon nanotube channel based on the first preset pattern, and the metal film based on the second preset pattern. The material is heated to the interface reaction temperature between the first type of metal and carbon in a vacuum or inert gas environment, maintained for a first set time, and then cooled to room temperature to complete the annealing, so that the source electrode, the drain electrode, and the carbon nanotube are connected by chemical bonds through solid-state reaction.

[0006] In some embodiments, the deposition of a metal thin film using a first type of metal includes: depositing the metal thin film using a magnetron sputtering device in DC sputtering mode at a power of 500 watts, a pressure of 2 millitor, and a velocity greater than 27 nm / min.

[0007] In some embodiments, after heating to the interfacial reaction temperature between the first type of metal and carbon in a vacuum or inert gas environment, maintaining the temperature for a first set time, and then cooling to room temperature, the method further includes: The macroscopic morphology of the metal film and the carbon nanotube channels was examined by scanning electron microscopy, and the metal carbide phase of the carbon nanotubes was characterized by X-ray diffraction. If no metal carbide phase is formed, repeat the annealing process or extend the high-temperature holding time.

[0008] In some embodiments, heating to the interface reaction temperature of the first type of metal and carbon in a vacuum or inert gas environment, maintaining it for a first set time, and then cooling to room temperature includes: At a vacuum degree of 10 -3 Under Pa conditions, nitrogen or argon is introduced as a protective gas, and the temperature is raised to the interface reaction temperature. After maintaining this temperature for at least 1 hour, the mixture is cooled to room temperature to complete the annealing process.

[0009] In some embodiments, molybdenum is used as the first type of metal in the method; Then, heating to the interface reaction temperature of the first type of metal and carbon in a vacuum or inert gas environment, maintaining it for a first set time, and then cooling to room temperature includes: At a vacuum degree of 10 -5 Under Pa conditions, the temperature was increased to 850°C at a heating rate of 27.5 °C / min, held for 1 hour, and then cooled to room temperature to complete the annealing.

[0010] In some embodiments, spin-coating photoresist onto the carbon nanotube channels includes: The rotation speed is increased in a stepwise manner to spin-coat the photoresist, and the dwell time at each rotation speed increases with the increase of rotation speed until the photoresist reaches a set thickness; Bake the glue at the set temperature for the second set time.

[0011] In some embodiments, spin-coating photoresist onto the carbon nanotube channels includes: The photoresist was maintained at a rotation speed of 600 rad / min for 10 s, and at a rotation speed of 4000 rad / min for 30 s until the photoresist thickness reached 1.2 μm. Then, the photoresist was baked at 105 °C for 3 min.

[0012] In some embodiments, after heating to the interface reaction temperature of the first type of metal and carbon in a vacuum or inert gas environment, maintaining it for a first set time, and then cooling to room temperature to complete the annealing, the process further includes: Polymethyl methacrylate was spin-coated onto the substrate, the carbon nanotube channels, and the metal film as a support. The silicon dioxide on the surface of the substrate, which had undergone thermal oxidation, was etched using hydrofluoric acid solution, while retaining the carbon nanotube channels and the metal film. After rinsing with deionized water, the film was lifted out using a microgrid and dried at 60°C for transfer.

[0013] On the other hand, the present invention also provides a field-effect transistor based on carbon nanotubes, comprising: Substrate; A carbon nanotube channel arranged in a first preset pattern array, wherein the carbon nanotube channel is grown on the substrate; The source electrode, located at one end of the carbon nanotube, is used to input current; The drain electrode, located at the other end of the carbon nanotube, is used to output current; The gate and dielectric layer are deployed in a top-gate structure, a bottom-gate structure, or a surrounding gate structure to control the conduction and shutdown of the carbon nanotube channels; The source and drain are fabricated using the contact configuration processing method described above for carbon nanotube field-effect transistors, and the source, drain, and carbon nanotube are connected by chemical bonds formed through a solid-state reaction.

[0014] In some embodiments, the substrate is a silicon wafer with a silicon dioxide layer of 50-300 nm grown on it, and the gate is made of a heterogeneous bimetallic material.

[0015] The beneficial effects of the present invention are at least as follows: The contact configuration fabrication method and field-effect transistor of the carbon nanotube field-effect transistor described in this invention, in the process of fabricating the source and drain electrodes, after depositing and growing a metal thin film, annealing is performed by heating to the interface reaction temperature in a vacuum or inert gas and maintaining it for a set time. By utilizing the solubility of carbon in metal, the carbon nanotubes and metal undergo a solid-phase reaction, and carbon atoms diffuse into the metal to form chemical bonds. This solves the problem that the resistance increases sharply when the size is reduced due to the existing side contact structure connecting the source and drain electrodes to the carbon nanotube array.

[0016] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows, and will also become apparent in part to those skilled in the art upon studying the description, or may be learned by practice of the invention. The objects and other advantages of the invention can be realized and obtained by means of the structures specifically pointed out in the description and drawings.

[0017] Those skilled in the art will understand that the objectives and advantages achievable with the present invention are not limited to those specifically described above, and that the above and other objectives achievable with the present invention will become clearer from the following detailed description. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, are not intended to limit the scope of the invention. In the drawings: Figure 1 This is a schematic flowchart of a contact configuration fabrication method for carbon nanotube field-effect transistors according to an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram illustrating the transfer method of carbon nanotubes and metal thin films in a contact configuration fabrication method for carbon nanotube field-effect transistors according to an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram illustrating the detection results of molybdenum carbide under different annealing methods using XRD combined with transfer-low-pressure aberration-corrected transmission electron microscopy in an embodiment of the present invention.

[0021] Figure 4(a) is a characterization diagram of the contact configuration of molybdenum carbide and carbon nanotube array using an 80 kV aberration-corrected transmission electron microscope according to an embodiment of the present invention.

[0022] Figure 4(b) is the nano diffraction pattern of Figure 4(a).

[0023] Figure 4(c) is an enlarged view of the part in the yellow box in Figure 4(a). Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments and accompanying drawings. Here, the illustrative embodiments and descriptions of this invention are used to explain the invention, but are not intended to limit the invention.

[0025] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the structures and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0026] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, element, step, or component, but does not exclude the presence or addition of one or more other features, elements, steps, or components.

[0027] It should also be noted that, unless otherwise specified, the term "connection" in this article can refer not only to a direct connection, but also to an indirect connection involving an intermediary.

[0028] In the current mainstream source and drain structures of carbon nanotube field-effect transistors, the metal and the channel material carbon nanotubes adopt a side contact structure. With the reduction of transistor size, the channel resistance increases sharply, making it difficult to meet the technical requirements of future nodes.

[0029] This invention proposes an end-contact scheme. The principle of this scheme is based on the solubility of carbon in metals. At high temperatures, carbon nanotubes and metals undergo a solid-state reaction, with carbon atoms diffusing into the metal. Metals with good miscibility with carbon, such as molybdenum and nickel, have been proven to chemically bond with carbon nanotubes after the high-temperature solid-state reaction, replacing the side contact method of van der Waals interactions. Metal electrical tests show that carbon nanotube field-effect transistors using molybdenum as the end-contact metal (with a single carbon nanotube) achieve a contact resistance as low as 11 ohms at a contact length of 10 nm. Furthermore, the uniformity is good. Currently, this type of end contact has only been reported in single carbon nanotube transistors, and the end contact lacks characterization, the microstructure is still unclear, and it has not been applied to carbon nanotube field-effect transistors (ACNT FETs).

[0030] Specifically, this invention provides a method for fabricating contact configurations for carbon nanotube field-effect transistors, such as... Figure 1 As shown, the method includes steps S101 to S105: Step S101: Cut and clean the carbon nanotube channels arranged in the first preset pattern array on the substrate to remove invalid parts.

[0031] Step S102: Spin-coat photoresist onto the carbon nanotube channel, and perform photolithography according to the second preset pattern using an ultraviolet lithography machine, and remove the exposed areas with developer to define the source and drain positions.

[0032] Step S103: Based on the coating method of magnetron sputtering or electron beam evaporation, a metal thin film is deposited using a type I metal. The type I metal has a miscibility of greater than or equal to 0.1% with carbon nanotubes in an inert gas environment above the interface reaction temperature.

[0033] Step S104: Use photoresist solvent to remove the remaining photoresist and the metal film on it, leaving the substrate, the carbon nanotube channel based on the first preset pattern, and the metal film based on the second preset pattern.

[0034] Step S105: Heat to the interface reaction temperature of the first type of metal and carbon in a vacuum or inert gas environment, maintain for a first set time, and then cool to room temperature to complete the annealing, so that the source, drain and carbon nanotubes are connected by chemical bonds through solid-state reaction.

[0035] Steps S101 to S105 mainly focus on the fabrication scheme for the contact configuration of the source and drain electrodes of carbon nanotube field-effect transistors.

[0036] In step S101, the substrate is a silicon wafer that has undergone thermal oxidation. The silicon wafer is cleaned using the RCA cleaning method to remove organic contaminants, metal ions, and dust from its surface. RCA cleaning is a standardized wet cleaning process for cleaning silicon wafer surfaces, first developed by engineers at RCA Corporation of America in 1965. This method is still widely used today, especially in semiconductor manufacturing processes, where it is the primary means of removing various contaminants from the silicon wafer surface.

[0037] RCA cleaning typically involves three main steps, each using a different chemical solution: SC-1 cleaning, using a solution of ammonia, hydrogen peroxide, and water in a 1:1:5 ratio, reacting at 75-80°C for 10-15 minutes to remove organic contaminants and particles; HF immersion, using a solution of hydrofluoric acid and water in a 1:50 to 1:100 ratio, to remove the natural oxide layer for 1-2 minutes; and SC-2 cleaning, using a solution of ammonia, hydrogen peroxide, and water in a 1:1:6 ratio, reacting at 75-80°C for 10-15 minutes to remove metal ion contamination. After cleaning, the silicon wafer can be thermally oxidized at a reaction temperature of 1000-1200°C to grow a silicon dioxide layer 50-300 nm thick, isolating the silicon substrate from the electric field.

[0038] Carbon nanotubes can be grown in situ or transferred externally to a substrate. In-situ growth methods use chemical vapor deposition (CVD) to directly grow carbon nanotubes on a substrate. The CVD process typically involves: coating a catalyst (such as iron, cobalt, or nickel nanoparticles) onto the substrate, heating it to 700-900°C, introducing a carbon source gas (such as methane, acetylene, or ethylene) into an inert gas environment (such as argon or hydrogen), decomposing the carbon source, and depositing carbon atoms to form single-walled or multi-walled carbon nanotubes (SWCNTs or MWCNTs).

[0039] External transfer methods are used to transfer carbon nanotube powders or films from pre-prepared materials. Solution methods disperse carbon nanotubes in a solvent (such as SDS solution), and then transfer them onto a substrate via solution coating, drop casting, or spraying. Dry transfer methods transfer carbon nanotube films to a target substrate through a PDMS (polydimethylsiloxane) support layer.

[0040] Furthermore, carbon nanotube channels are patterned using photolithography or electron beam lithography to define the channel regions. Photoresist is then applied, and the layers are exposed and developed using a mask to leave the channel regions. Plasma etching is then used to remove the carbon nanotubes from the non-channel regions.

[0041] In step S102, first ensure the carbon nanotube channel surface is clean and dust-free. If necessary, plasma cleaning or solvent cleaning can be used to remove organic residues and other contaminants from the surface. Spin-coat photoresist uniformly onto the carbon nanotube channels. SU-8 2021 negative photoresist is commonly used. The spin-coating speed and time need to be carefully controlled to ensure a uniform and appropriate photoresist layer thickness. Place the spin-coated sample on a hot plate to bake, removing the solvent from the photoresist. This step is typically performed at 110°C to 130°C for approximately 1 minute. Expose the sample using a UV lithography machine. During exposure, a pre-designed mask containing a second preset pattern is used to define the positions of the source and drain electrodes. The exposure time and UV light intensity need to be adjusted according to the type and thickness of the photoresist. After exposure, bake the sample again on a hot plate to complete the crosslinking reaction of the photoresist. This step is typically performed at a slightly higher temperature; for example, for SU-8 2021 photoresist, baking at 95°C for approximately 1 minute is recommended. Use an appropriate developer to remove the photoresist from the exposed areas. For positive photoresist, the exposed areas will dissolve in the developer; for negative photoresist like SU-8 2021, the unexposed areas will dissolve, while the exposed areas will remain to form the desired pattern. The development process must be performed under controlled temperature conditions to avoid over- or under-development. After development, thoroughly rinse the sample with deionized water or other suitable solvent to remove residual developer. Finally, dry the sample using a nitrogen gun or other drying method.

[0042] In some embodiments, spin-coating photoresist onto the carbon nanotube channels includes steps S1021-S1022: Step S1021: Increase the rotation speed in steps to spin-coat the photoresist. The dwell time at each rotation speed increases with the increase of rotation speed until the photoresist reaches the set thickness.

[0043] Step S1022: Bake the glue at the set temperature for the second set time.

[0044] In some embodiments, spin-coating photoresist onto carbon nanotube channels includes: selecting AZ5214 photoresist, maintaining a spin speed of 600 rad / min for 10 s, maintaining a spin speed of 4000 rad / min for 30 s, until the photoresist thickness is 1.2 μm, and baking the photoresist at 105 °C for 3 min.

[0045] The exposed photoresist will selectively dissolve in the developer, ZX-238, with a development time of 35 seconds. After development, it is fixed in deionized water for 1 minute and finally dried with a nitrogen gun.

[0046] In step S103, the present invention uses molybdenum or nickel as the first metal. Of course, depending on the application scenario, titanium, palladium, gold, platinum, etc., can also be selected as the first metal. Appropriate magnetron sputtering or electron beam evaporation equipment is selected based on the specific metal type and thin film requirements. For magnetron sputtering, parameters such as sputtering power, gas pressure, and target type need to be set; for electron beam evaporation, parameters such as electron beam energy, evaporation rate, and vacuum level need to be set.

[0047] In some embodiments, a first-type metal deposition method is used, comprising: depositing a metal thin film using a magnetron sputtering system in DC sputtering mode at a power of 500 watts, a gas pressure of 2 millitor, and a deposition rate greater than 27 nm / min. A higher deposition rate is chosen here to disrupt the intrinsic carbon nanotube structure beneath the metal through the kinetic energy of the metal atoms, which is beneficial for the formation of chemical bonds in subsequent solid-phase reactions.

[0048] In step S104, the photoresist solvent can be an NMP solution, i.e., an N-methylpyrrolidone solution. After dissolving the photoresist and the metal film attached to it, it is rinsed with deionized water and dried.

[0049] In step S105, the first type of metal and carbon nanotubes undergo a solid-state reaction through annealing. The different reactivity of different metals with carbon determines the starting temperature of the solid-state reaction.

[0050] Highly reactive metals (such as titanium (Ti), vanadium (V), and palladium (Pd): These metals readily form metal carbides with carbon at relatively low temperatures, typically in the range of 400–600 °C.

[0051] Moderately reactive metals (such as nickel (Ni), tungsten (W), and molybdenum (Mo): These metals may react chemically with carbon nanotubes at temperatures of 600-800°C.

[0052] Low-reactive metals (such as gold (Au), silver (Ag), and platinum (Pt): These metals can only react with carbon nanotubes at relatively high temperatures, and are even relatively stable above 1000℃.

[0053] The different chemical stability of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) can also affect the onset temperature of solid-state reactions.

[0054] For example, the interface reaction temperature of titanium with carbon is 400~600℃, the interface reaction temperature of nickel with carbon is 600~800℃, and the interface reaction temperature of palladium with carbon is 300~500℃.

[0055] In this invention, heating to the interface reaction temperature of a first type of metal and carbon under a vacuum or inert gas environment, maintaining it for a first set time, and then cooling to room temperature includes: heating to a vacuum of 10... -3 Under Pa conditions, nitrogen or argon is introduced as a protective gas, and the temperature is raised to the interface reaction temperature. After maintaining this temperature for at least 1 hour, the mixture is cooled to room temperature to complete the annealing process.

[0056] In some embodiments, when molybdenum is used as the first metal in the method, heating to the interface reaction temperature between the first metal and carbon under vacuum or inert gas conditions, maintaining this temperature for a first set time, and then cooling to room temperature includes: [the process is described in the original text, but the provided excerpt ends here.] -5 Under Pa conditions, the temperature was increased to 850°C at a heating rate of 27.5 °C / min, held for 1 hour, and then cooled to room temperature to complete the annealing.

[0057] In some embodiments, after heating to the interface reaction temperature between the first type of metal and carbon in a vacuum or inert gas environment, maintaining it for a first set time, and then cooling it to room temperature, the method further includes steps S201-S202: Step S201: The macroscopic morphology of the metal thin film and carbon nanotube channels is examined by scanning with an electron microscope, and the metal carbide phase is verified by X-ray diffraction of the carbon nanotubes.

[0058] Step S202: If no metal carbide phase is formed, repeat the annealing or extend the high temperature holding time.

[0059] In some embodiments, after heating to the interface reaction temperature of the first type of metal and carbon in a vacuum or inert gas environment, maintaining it for a first set time, and then cooling to room temperature to complete the annealing, as follows: Figure 2 As shown, the method also includes: spin-coating polymethyl methacrylate as a support on the substrate, carbon nanotube channels and metal film; etching the silicon dioxide on the surface of the substrate after thermal oxidation with hydrofluoric acid solution to retain the carbon nanotube channels and metal film; cleaning with deionized water and then lifting it with a microgrid; drying and transferring it at 60°C.

[0060] On the other hand, the present invention also provides a field-effect transistor based on carbon nanotubes, comprising: Substrate; A carbon nanotube channel arranged in a first preset pattern array, wherein the carbon nanotube channel is grown on the substrate; The source electrode, located at one end of the carbon nanotube, is used to input current; The drain electrode, located at the other end of the carbon nanotube, is used to output current; The gate and dielectric layer are deployed in a top-gate structure, a bottom-gate structure, or a surrounding gate structure to control the conduction and shutdown of the carbon nanotube channels; The source and the drain are fabricated using the contact configuration processing method for carbon nanotube field-effect transistors described in steps S101 to S105 above, and the source, the drain, and the carbon nanotube are connected by chemical bonds formed through a solid-state reaction.

[0061] In some embodiments, the substrate is a silicon wafer with a silicon dioxide layer of 50-300 nm grown on it; the gate is made of a heterogeneous bimetallic material. The dielectric layer typically uses a high dielectric constant material, such as hafnium oxide. Alumina Barium aluminate titanate (BST) is used to enhance the electric field effect.

[0062] Specifically, the gate can adopt a top-gate structure, a bottom-gate structure, or a gate-all-around structure.

[0063] In a top-gate structure, the gate electrode is fabricated after the source and drain electrodes. This is commonly used in carbon nanotube field-effect transistors (CNT-FETs) and organic thin-film transistors (OTFTs).

[0064] In bottom-gate structures, the gate and dielectric layer are usually fabricated first. This is common in traditional silicon-based FETs and some thin-film transistors (TFTs).

[0065] In a gate-all-around structure, the gate electrode surrounds the channel material, providing stronger electric field control. It is commonly used in advanced nanowire FETs and next-generation high-performance transistors.

[0066] The present invention will now be described with reference to a specific embodiment: This embodiment provides a contact configuration fabrication method for carbon nanotube field-effect transistors, comprising the following steps: (1) Cutting and cleaning carbon nanotube array substrate: Cut the carbon nanotube wafer substrate to facilitate subsequent cleaning, coating and other operations. Use organic solvents (such as acetone, isopropanol, etc., preferably organic solvents that leave less residue on the wafer after drying) and deionized water to clean the carbon nanotube array substrate. After cleaning, use light microscope and scanning electron microscope to observe to ensure the cleanliness of the wafer.

[0067] Specifically, the carbon nanotube wafer substrate is cut, and the cut substrate is immersed in an acetone solution and heated at 65°C for 3 minutes. Then, it is immersed in deionized water for 3 minutes. After cleaning, it is observed using an optical microscope and a scanning electron microscope to ensure the cleanliness of the wafer.

[0068] (2) Spin coating of photoresist: Select AZ5214 photoresist, maintain rotation at 600 rad / min for 10 s, maintain rotation at 4000 rad / min for 30 s, photoresist thickness 1.2 μm, bake at 105 ℃ for 3 min.

[0069] (3) Photolithography and development: The customized pattern is transferred onto the carbon nanotube substrate using an ultraviolet lithography machine. The exposed photoresist will selectively dissolve in the developer. A specific developer is used to remove the photoresist in the exposed area.

[0070] Specifically, AZ5214 photoresist is selected to transfer the customized pattern onto the carbon nanotube substrate. After exposure, the photoresist will selectively dissolve in the developer ZX-238, with a development time of 35 seconds. After development, the substrate is fixed in deionized water for 1 minute and finally dried with a nitrogen gun.

[0071] (4) Coating: Metal thin films are deposited on the substrate surface using magnetron sputtering or electron beam evaporation equipment. The thickness and shape of the metal thin film can be designed according to the requirements (carbon nanotube array density / device structure). The type of metal thin film should be a metal with high miscibility with carbon and a low solid-state reaction temperature with carbon. A larger coating rate is selected to destroy the intrinsic carbon nanotube structure under the metal through the kinetic energy of the metal atoms, which is beneficial to the formation of chemical bonds in the subsequent solid-state reaction.

[0072] Specifically, in a DE-500 magnetron sputtering system, DC mode, 500 W power, 2 mtorr air pressure, it took 1.5 minutes to deposit 40 nm of molybdenum.

[0073] (5) Stripping: Immerse the coated sample in a solution that can dissolve the photoresist to remove the remaining photoresist and the metal film on it, leaving the exposed patterned part.

[0074] Specifically, the coated sample is immersed in an NMP solution to remove the remaining photoresist and the metal film on it, leaving the exposed patterned portion.

[0075] (6) Inspection: Inspect the effects of photolithography, coating, and stripping under a scanning electron microscope. Compare the coating results with the layout to confirm that the pattern is correct.

[0076] (7) Annealing: The inspected metal / carbon nanotube substrate is placed into the annealing equipment, ensuring a vacuum level of 10. -3 After the pressure drops below 1 Pa, a protective gas (nitrogen or argon) is introduced, and the mixture is heated to the required temperature and maintained for a period of time, followed by cooling to room temperature. Heating is only to provide sufficient energy for the reaction; there are no restrictions on the heating method itself. Tube furnace annealing, RTP annealing, and even laser annealing can all meet the requirements under suitable parameters.

[0077] Specifically, for a 40 nm thick layer of metallic molybdenum, vacuum annealing requires a vacuum level of 10. -5 Pa, purging with an atmosphere can appropriately reduce the vacuum requirement. The temperature was raised to 850℃ at a rate of 27.5℃ / min, held at this high temperature for 1 h, and then cooled to room temperature.

[0078] (8) Phase characterization: Preliminary characterization was performed under a scanning electron microscope to characterize the macroscopic morphology of the metal thin film and the arrayed carbon nanotubes. Subsequently, X-ray diffraction was performed on the carbon nanotube substrate to confirm the formation of the molybdenum carbide phase. If no carbide phase was formed or carbon nanotubes remained under the metal, the annealing experiment should be repeated or the high-temperature holding temperature of the annealing experiment should be extended.

[0079] (9) Transfer: PMMA is spin-coated onto the metal / array carbon nanotubes as a support, and SiO2 is etched using a certain concentration of HF solution to retain the array carbon nanotubes and metal film. After washing with deionized water three times, the film is lifted with a microgrid and completely dried at 60°C.

[0080] (10) Microscopic characterization: The specific contact structure of molybdenum carbide and carbon nanotube array was observed under an 80 kV transmission electron microscope.

[0081] In this embodiment, as Figure 3 As shown, characterization was performed using XRD combined with transfer-low-pressure aberration-corrected transmission electron microscopy. Under annealing conditions, distinct Mo2C peaks appeared at 36.4° and 39.5°, macroscopically confirming the formation of the molybdenum carbide phase. As shown in Figures 4(a) to (c), the microscopic contact structure of the arrayed carbon nanotubes and molybdenum carbide was clearly defined. Compared to traditional side contact structures, the end contact structure constructed on the arrayed carbon nanotubes in this embodiment is formed at high temperature. The metal and the contacting carbon nanotubes form carbides, maintaining a relatively uniform morphology at a small size, thus resulting in more stable transistor performance. The end contact structure can be directly patterned according to the transistor shape without introducing additional processing steps.

[0082] In summary, the contact configuration fabrication method and field-effect transistor of the carbon nanotube field-effect transistor of the present invention, in the process of fabricating the source and drain electrodes, after depositing and growing a metal thin film, annealing is performed by heating to the interface reaction temperature in a vacuum or inert gas and maintaining it for a set time. By utilizing the solubility of carbon in metal, the carbon nanotubes and metal undergo a solid-state reaction, and carbon atoms diffuse into the metal to form chemical bonds. This solves the problem that the resistance increases sharply when the size is reduced due to the existing side contact structure connecting the source and drain electrodes to the carbon nanotube array.

[0083] Those skilled in the art will understand that the exemplary components, systems, and methods described in conjunction with the embodiments disclosed herein can be implemented in hardware, software, or a combination of both. Whether implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this invention. When implemented in hardware, it can be, for example, electronic circuits, application-specific integrated circuits (ASICs), appropriate firmware, plug-ins, function cards, etc. When implemented in software, the elements of this invention are programs or code segments used to perform the desired tasks. The programs or code segments can be stored in a machine-readable medium or transmitted over a transmission medium or communication link via data signals carried in a carrier wave.

[0084] It should be clarified that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of the present invention.

[0085] In this invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with or in place of features of other embodiments.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations of the embodiments of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating contact configurations for carbon nanotube field-effect transistors, characterized in that, The method includes: The carbon nanotube channels arranged in the first preset pattern array on the substrate are cut and cleaned to remove invalid parts; On the carbon nanotube channel, the rotation speed is increased stepwise to spin-coat photoresist. The dwell time at each rotation speed increases with the increase of rotation speed until the photoresist reaches a set thickness. The photoresist is baked at a set temperature for a second set time, and a UV lithography machine is used to perform photolithography according to a second preset pattern. The exposed areas are removed with developer to define the source and drain positions. The deposition method is based on magnetron sputtering or electron beam evaporation. A magnetron sputtering instrument is used in DC sputtering mode to deposit a metal thin film based on molybdenum at a power of 500 watts, a gas pressure of 2 millitor, and a velocity greater than 27 nm / min. The molybdenum has a miscibility of greater than or equal to 0.1% with the carbon nanotubes in an inert gas environment above the interfacial reaction temperature. The remaining photoresist and the metal film on it are removed using a photoresist solvent, leaving the substrate, the carbon nanotube channel based on the first preset pattern, and the metal film based on the second preset pattern. At a vacuum degree of 10 -5 Under Pa conditions, the source electrode, drain electrode, and carbon nanotube are heated to 850°C at a heating rate of 27.5 °C / min, held for 1 hour, and then cooled to room temperature to complete the annealing process, so that the source electrode, drain electrode, and carbon nanotube are connected by chemical bonds through solid-state reaction. The macroscopic morphology of the metal film and the carbon nanotube channels was examined by scanning electron microscopy, and the metal carbide phase of the carbon nanotubes was verified by X-ray diffraction. If no metal carbide phase was formed, the annealing was repeated or the high temperature holding time was extended.

2. The contact configuration fabrication method for carbon nanotube field-effect transistors according to claim 1, characterized in that, The spin coating of the photoresist is performed by progressively increasing the spin speed, with the dwell time at each spin speed increasing as the spin speed increases, until the photoresist reaches a set thickness. Then, the photoresist is baked at a set temperature for a second set time, including: The photoresist was maintained at a rotation speed of 600 rad / min for 10 s, and at a rotation speed of 4000 rad / min for 30 s until the photoresist thickness reached 1.2 μm. Then, the photoresist was baked at 105 °C for 3 min.

3. The contact configuration fabrication method for carbon nanotube field-effect transistors according to claim 2, characterized in that, After annealing by heating to the interfacial reaction temperature of the molybdenum and carbon metal in a vacuum or inert gas environment, maintaining the temperature for a first set time, and then cooling to room temperature, the process further includes: Polymethyl methacrylate was spin-coated onto the substrate, the carbon nanotube channels, and the metal film as a support. The silicon dioxide on the surface of the substrate, which had undergone thermal oxidation, was etched using hydrofluoric acid solution, while retaining the carbon nanotube channels and the metal film. After rinsing with deionized water, the film was lifted out using a microgrid and dried at 60°C for transfer.

4. A field-effect transistor based on carbon nanotubes, characterized in that, include: Substrate; A carbon nanotube channel arranged in a first preset pattern array, wherein the carbon nanotube channel is grown on the substrate; The source electrode, located at one end of the carbon nanotube, is used to input current; The drain electrode, located at the other end of the carbon nanotube, is used to output current; The gate and dielectric layer are deployed in a top-gate structure, a bottom-gate structure, or a surrounding gate structure to control the conduction and shutdown of the carbon nanotube channels; The source and the drain are fabricated using the contact configuration fabrication method for carbon nanotube field-effect transistors as described in any one of claims 1 to 3, and the source, the drain, and the carbon nanotube are connected by chemical bonds formed through a solid-state reaction.

5. The field-effect transistor based on carbon nanotubes according to claim 4, characterized in that, The substrate is a silicon wafer with a silicon dioxide layer of 50-300 nm grown on it, and the gate is made of a heterogeneous bimetallic material.

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