A maskless plasma patterning method and device for carbon nanotube thin films

Abstract

The application belongs to the field of micro-nano processing technology, and particularly relates to a mask-free plasma patterning method and device for carbon nanotube film. The method comprises the following steps: fixing a substrate carrying the carbon nanotube film on a controllable two-dimensional motion platform; introducing oxygen-containing working gas into a plasma jet head and exciting to generate a stable plasma beam current; generating a scanning path program according to a preset pattern; controlling the substrate to move under the plasma beam current according to the program, so that the carbon nanotubes in the target area are selectively oxidized and removed to form a pattern. Through the synergistic effect of the plasma beam current and the controllable two-dimensional motion platform, selective oxidation etching of the carbon nanotube film is realized. The method does not need a mask and a wet chemical step, and through controlling the plasma power, the jet-sample distance and the scanning speed within a specific range, the patterning can be realized on rigid and flexible polymer substrates, and the heat input in the process can be effectively controlled.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano processing technology, specifically relating to a maskless plasma patterning method and apparatus for carbon nanotube thin films. Background Technology

[0002] Carbon nanotube films, due to their excellent electrical, optical, and mechanical properties, have shown great application potential in fields such as flexible electronics, transparent conductors, and sensors. To realize device functions, continuous carbon nanotube films must be processed into predetermined fine patterns.

[0003] Currently, the mainstream technology for achieving this type of patterning is photolithography. However, photolithography involves multiple wet chemical steps such as spin coating, exposure, development, and resist removal. The chemical reagents used are prone to remain in the porous structure of carbon nanotubes, leading to a significant deterioration in the electrical properties of the thin film. Furthermore, the process is complex, costly, and has poor compatibility with flexible substrates.

[0004] Existing technologies include processing devices that combine plasma nozzles with CNC motion platforms, such as CN108081031A for polishing optical components and CN210237680U for quenching metal surfaces. CN108081031A discloses an atmospheric plasma processing device that uses fluorine-containing gases (such as SF6 and CF4) to chemically react with optical glass to remove materials; the plasma power is 300-600W, and the nozzle-sample distance is 2-5mm. CN210237680U discloses a CNC plasma quenching machine that uses a plasma torch to directionally heat the surface of a metal workpiece to achieve surface hardening. While both patents combine plasma with a motion platform, their processing objects are bulk materials such as optical glass or metals; the working gas is fluorine-containing gas or a gas that does not involve chemical reactions; and the process parameters are high power and small spacing. Their technical purposes are polishing and surface quenching, respectively, which are fundamentally different from the patterning requirements of carbon nanotube films.

[0005] Carbon nanotube films, as nanoporous structures, are heat-sensitive and require the removal of the target area while preserving the conductivity of the untreated areas. Directly applying existing techniques using fluorine-containing gases or high-power, small-pitch parameters will lead to thermal damage, electrical performance failure, or blurred pattern edges. Therefore, developing a maskless patterning method specifically for carbon nanotube films, capable of achieving patterning without compromising their electrical properties, has become a pressing technical problem in this field. Summary of the Invention

[0006] The purpose of this invention is to address the problem that existing technologies lack a method for maskless patterning without damaging the electrical properties of carbon nanotube films. Specifically, it aims to overcome the problems of chemical contamination in photolithography, the inability of existing plasma processing techniques to pattern the films, and the film damage or performance failure caused by the mismatch between existing CNC plasma processing equipment and the patterning requirements of carbon nanotube films in this invention, due to the mismatch between the processing object, gas type, process parameters and the patterning requirements of carbon nanotube films in this invention.

[0007] Furthermore, the present invention also aims to address the issues of controlling heat input during the process to avoid carbon nanotube agglomeration or substrate overheating, as well as simplifying the process flow and reducing equipment costs.

[0008] The technical solution of the present invention is as follows: On one hand, a maskless plasma patterning method for carbon nanotube thin films is provided, comprising the following steps: S1: Fix the substrate carrying the carbon nanotube film to be patterned onto the stage; S2: Install the stage onto a controllable two-dimensional motion platform; S3: Provide a plasma nozzle, introduce working gas into the plasma nozzle to generate a stable plasma beam, the direction of the plasma beam is towards the stage; S4: Generate a motion path program to control the controllable two-dimensional motion platform based on a preset patterned graphic; S5: Execute the motion path program to drive the stage to move the substrate under the plasma beam, so that the target area to be removed on the carbon nanotube film passes through the action area of ​​the plasma beam in sequence. The carbon nanotubes in the corresponding area are selectively removed by the chemical reaction between the active oxygen species in the plasma beam and the carbon nanotubes, thereby forming a pattern composed of the retained carbon nanotubes on the substrate. The working gas is nitrogen, or a mixture of nitrogen and an inert gas. The working pressure of the plasma nozzle is 0.15~0.2MPa; The vertical distance between the outlet of the plasma nozzle and the surface of the carbon nanotube film is 30~40mm; The stage moves at a speed of 10~30 mm / s.

[0009] Preferably, the inert gas includes argon; the volume ratio of nitrogen to inert gas in the mixed gas is 1:(1~4).

[0010] Preferably, the working pressure of the plasma nozzle is 0.18 MPa.

[0011] Preferably, the vertical distance between the outlet of the plasma nozzle and the surface of the carbon nanotube film is 35 mm.

[0012] Preferably, the movement speed of the stage is 20 mm / s.

[0013] Preferably, the thickness of the carbon nanotube film is 10~100nm.

[0014] Preferably, the substrate is a rigid substrate, including glass, quartz, or silicon wafer.

[0015] On the other hand, an apparatus for implementing the above-described method of carbon nanotube thin film plasma patterning is provided, comprising: The plasma generating unit includes a plasma nozzle, a gas supply module connected to the plasma nozzle, and a power supply connected to the electrodes of the plasma nozzle, for generating and outputting a plasma beam with a stable direction. The two-dimensional motion unit includes a stage and a controllable two-dimensional motion platform. The stage is used to fix the substrate carrying the carbon nanotube film and is mounted on the controllable two-dimensional motion platform. The controllable two-dimensional motion platform can drive the stage to move independently in two mutually perpendicular directions in the horizontal plane. The motion control unit is electrically connected to the controllable two-dimensional motion platform and is used to receive preset pattern graphic information, generate and send control commands to drive the controllable two-dimensional motion platform to move along a preset scanning trajectory.

[0016] Preferably, the plasma nozzle is an atmospheric pressure radio frequency plasma nozzle with an operating frequency of 13.56MHz.

[0017] Compared with the prior art, the advantages of the present invention are: (1) Nitrogen plasma can be used for selective etching of carbon nanotube films without causing degradation of the electrical properties of the retained area. When nitrogen is used as the working gas, the resistance of the retained area after plasma treatment is 520kΩ, which is basically the same as 500kΩ before treatment; while when oxygen is used as the working gas, the resistance of the retained area after treatment is greater than 50MΩ, indicating that nitrogen plasma treatment can avoid degradation of the electrical properties of carbon nanotubes.

[0018] (2) By limiting the working gas pressure to 0.15~0.2MPa, the nozzle-sample distance to 30~40mm, and the scanning speed to 10~30mm / s, the complete etching of carbon nanotube films and the effective control of thermal damage were achieved. This parameter range is the optimal parameter obtained through a large number of experiments: below the lower limit, the etching is incomplete (residual), and above the upper limit, thermal damage (carbon nanotube agglomeration and failure of electrical properties) is caused, which provides a reliable process guarantee for the non-destructive patterning of carbon nanotube films.

[0019] (3) This method does not require photoresist masks and wet chemical steps, thus avoiding the decline in electrical performance caused by photoresist residue (Comparative Example 1 shows that the resistance rises to 700kΩ after photolithography process), and the process time is significantly shorter than that of photolithography process.

[0020] (4) The device has a clear structure and integrates plasma generation, precision motion and control functions. It is designed specifically to realize the above methods, ensuring the repeatability and stability of the process. The carbon nanotube film pattern has clear boundaries, which can meet the needs of early research and development and small-batch production where the precision requirements are not high. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a three-dimensional structural schematic diagram of an embodiment of the carbon nanotube thin film plasma patterning device of the present invention; Figure 2 As described in this invention Figure 1 A top view of the controllable two-dimensional motion platform section of the device; Figure 3 An optical microscope photograph of the processed sample in Example 1 of the present invention; Figure 4 As described in this invention Figure 3 Scanning electron microscope (SEM) image of the mid-boundary region; Figure 5 This is a SEM image of the initial morphology of the carbon nanotube film described in this invention; Figure 6 This is a SEM image processed when the parameters described in this invention deviate from the optimal range (e.g., the air pressure is too low); Figure 7 SEM images processed when the parameters described in this invention deviate from the optimal range (e.g., excessively high air pressure / excessively close distance / excessively slow speed); Figure 8 This is a microscopic image of the original normal morphology before the local high-temperature treatment described in this invention. Figure 9 This is a microscopic image showing the abnormal morphology observed after local high-temperature treatment as described in this invention.

[0022] The components include: 1. Plasma nozzle; 2. Gas pipeline; 3. Stage; 4. Guide rail. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments.

[0024] Example 1

[0025] like Figure 1 As shown, this embodiment provides a method for patterning carbon nanotube thin films using plasma under optimal process conditions. The specific steps are as follows: S1. Provide the sample to be patterned: A uniform single-walled carbon nanotube film is prepared by vacuum filtration and then wet-transferred onto a clean glass substrate (25mm x 25mm) to obtain a substrate bearing a continuous carbon nanotube film. The film thickness is approximately 30nm and the sheet resistance is approximately 500Ω / sq.

[0026] S2. Sample clamping: Securely attach the above-mentioned substrate to the center of a metal stage 3 using high-temperature resistant tape. The stage 3 is mounted on a controllable two-dimensional motion platform.

[0027] S3. Start the plasma system: Turn on the nitrogen gas source and introduce pure nitrogen as the working gas into an atmospheric pressure plasma nozzle (RF excitation, frequency 13.56MHz). Set the gas flow rate to 3 slm (standard liters per minute) and adjust the working pressure to 0.18MPa. Turn on the RF power supply and set the power to 200W to generate a stable, visible pale blue oxygen plasma plume at the nozzle outlet.

[0028] S4. Execute the patterning program: Using a computer numerical control (CNC) system, call the preset circular pattern processing program (5mm diameter). For example... Figure 2 As shown, the program-controlled two-dimensional motion platform causes the stage 3 to move the substrate along a circular trajectory in the horizontal plane at a speed of 20 mm / s. The plasma nozzle remains stationary, and its outlet is fixed at a height of 35 mm above the surface of the carbon nanotube film.

[0029] S5. Pattern Formation: During the movement of the stage 3, carbon nanotubes are removed in the areas traversed by the circular trajectory under the action of nitrogen plasma, forming a clear circular pattern on the glass substrate, while carbon nanotubes are retained in the areas not traversed.

[0030] S6. Post-processing and inspection: After processing, turn off the plasma and gas. Remove the sample and observe the pattern morphology using an optical microscope (e.g., Figure 3 As shown in the image, a clear circular boundary is visible, with no diffusion halo or blurred areas at the edge, indicating that the plasma beam has good directionality and no significant lateral diffusion has occurred. SEM observation of the boundary region (e.g.) Figure 4 As shown in the image, the carbon nanotubes in the treated area on the left were completely removed, exposing a smooth glass substrate; the carbon nanotube film in the untreated area on the right was continuous and dense, with no etching marks or signs of thermal damage. Figure 5The initial morphology comparison showed that the carbon nanotube network structure in the untreated area remained intact, with no significant changes in tube diameter and distribution density, proving that nitrogen plasma treatment did not damage the preserved area.

[0031] Example 2

[0032] In this embodiment, to verify the importance of optimizing process parameters, the same sample as in Example 1 was used, but some parameters were changed, and the results were observed.

[0033] (1) Low air pressure: Adjust the working air pressure to 0.10 MPa, and keep other conditions the same as in Example 1. Figure 6 As shown, SEM observation after treatment reveals a large number of carbon nanotubes remaining in the treated area, exhibiting a discontinuous network structure with blurred edges. This is because the concentration of active particles in the plasma is low under low pressure, resulting in insufficient bombardment energy to completely break carbon-carbon bonds. The presence of numerous carbon nanotubes in the treated area indicates incomplete etching.

[0034] (2) Excessive air pressure: Adjust the working air pressure to 0.25 MPa, with other conditions the same as in Example 1. Figure 7 As shown in the figure, SEM observation after treatment revealed that although carbon nanotubes were removed from the treated area, obvious carbon nanotube aggregation was observed in the surrounding untreated area, forming island-like clusters, indicating that local overheating led to the migration and aggregation of carbon nanotubes. Figure 8 and Figure 9 Comparing the original normal morphology with the thermally damaged morphology, it can be seen that the thermally damaged area is darker in color and denser in structure, which is a manifestation of increased graphitization of carbon nanotubes, which will lead to a decrease in electrical properties.

[0035] (3) Too close a distance: Reduce the nozzle-sample distance to 10 mm, and keep other conditions the same as in Example 1. Thermal damage morphology still appears after treatment, and the substrate shows obvious local heating, indicating that the energy density is too high and the heat cannot diffuse in time.

[0036] (4) Too slow speed: Reduce the stage movement speed to 5 mm / s, and keep other conditions the same as in Example 1. Thermal damage was also observed after the treatment, and the etching line width increased by about 30% compared with the optimal value, indicating that the dwell time was too long, resulting in heat accumulation and lateral heat diffusion.

[0037] (5) Using oxygen as the working gas: The working gas was changed to pure oxygen, and other conditions were the same as in Example 1. After treatment, the resistance of the retained area was measured with a multimeter. The resistance value was found to be more than 50 MΩ, which was much greater than the 500 kΩ before treatment, indicating that the electrical properties of the carbon nanotubes had failed. SEM observation showed that although the morphology of the carbon nanotubes changed, it was not significant, indicating that although oxygen plasma can remove carbon nanotubes, it will cause irreversible damage to the retained carbon nanotubes.

[0038] Example 3

[0039] To determine the range of process parameters suitable for patterning carbon nanotube films, a series of experiments were conducted using single-walled carbon nanotube films (approximately 30 nm thick) on glass substrates. With other conditions fixed, the plasma working pressure (P), nozzle-sample distance (Z), scanning speed (V), and working gas were varied. The results are shown in Table 1.

[0040] Table 1: Influence of process parameters on patterning effect

[0041] As shown in Table 1, the optimal process parameters for achieving effective and non-destructive patterning are: working gas pressure 0.15~0.20MPa, nozzle-sample distance 30~40mm, and scanning speed 10~30mm / s. Nitrogen or a nitrogen-argon mixture is preferred as the working gas; oxygen should be avoided. Specific analysis follows: 1. Working gas pressure: When the gas pressure is below 0.15MPa, the plasma energy density is insufficient, resulting in incomplete etching (e.g., Figure 6 As shown, carbon nanotube residues remain in the treated area. When the gas pressure exceeds 0.20 MPa, the energy is too strong; although complete etching is possible, it leads to over-etching at the pattern edges and substrate heating. When the gas pressure reaches 0.25 MPa, partial failure of the film's electrical properties occurs. Therefore, 0.15–0.20 MPa is an effective and safe range, with 0.18 MPa being the optimal value.

[0042] 2. Nozzle-sample spacing: When the spacing is less than 30mm (e.g., 10mm), the energy is too concentrated, resulting in over-etching of the pattern edges, significant heating of the substrate, and partial failure of electrical properties. When the spacing is greater than 40mm (e.g., 50mm), the plasma beam diverges, the energy density decreases, resulting in incomplete etching and blurred pattern edges. Therefore, 30~40mm is the effective range, with 35mm being the optimal value.

[0043] 3. Scanning speed: When the speed is below 10 mm / s (e.g., 5 mm / s), the plasma dwell time in the unit area is too long, and heat accumulation leads to carbon nanotube aggregation, over-etching of pattern edges, and partial failure of electrical properties; when the speed is above 30 mm / s (e.g., 50 mm / s), the dwell time is insufficient, and the etching is incomplete. Therefore, 10~30 mm / s is the effective range, with 20 mm / s being the optimal value.

[0044] 4. Working Gas: Using pure nitrogen or a nitrogen-argon mixture (N2:Ar=1:2) can achieve complete etching, clear patterns, and normal electrical properties. However, using pure oxygen, although complete etching is possible, the resistivity of the retained area rises to >50MΩ (approximately 500kΩ before processing), indicating that the electrical properties of the carbon nanotubes have irreversibly failed. Therefore, this invention must use nitrogen or a nitrogen-based mixture, which is crucial for achieving non-destructive patterning.

[0045] The determination of the above parameter range is not a simple optimization, but rather based on a deep understanding of the properties of carbon nanotube materials and extensive experimental screening. For example, if only the completeness of etching is considered, a parameter combination of 0.25 MPa, 10 mm, and 5 mm / s can be used, but this combination will lead to thermal damage; if only safety is considered, 0.10 MPa, 50 mm, and 50 mm / s can be used, but the etching will not be complete. Only within the range of 0.15~0.20 MPa, 30~40 mm, and 10~30 mm / s defined in this invention can the synergistic effect of the three parameters simultaneously achieve "complete etching" and "damage-free preservation". Figures 3-9 It visually demonstrates the morphological differences between inside and outside the range of this parameter.

[0046] Extensive experiments have revealed that when nitrogen is used as the working gas, high-energy nitrogen particles (such as N2) in the plasma... + N2 + The process primarily involves bombarding carbon nanotubes through physical sputtering, causing their carbon-carbon bonds to break and detach in the form of atoms or small molecular clusters. Meanwhile, due to the relatively inert chemical properties of nitrogen, it does not undergo a strong chemical reaction with the carbon nanotubes, thus causing no chemical damage to the carbon nanotube structure in the preserved region. Figure 4 SEM images show that the treated area has clear boundaries, while the morphology of the carbon nanotubes in the untreated area is similar to that in the untreated area. Figure 5 The initial morphology was completely consistent, and resistance measurements also confirmed that the electrical properties remained unchanged (500kΩ before treatment and 520kΩ after treatment).

[0047] Conversely, if oxygen from Example 2 is used as the working gas, oxygen free radicals will undergo a violent oxidation reaction with carbon nanotubes to generate CO2. Although this can remove the target area, the reaction is exothermic and reactive oxygen diffuses, leading to partial oxidation and etching of the carbon nanotubes in the retained area. This results in a sharp decrease in electrical properties (resistance > 50 MΩ), while the morphological changes are not obvious (difficult to distinguish with SEM), indicating that the chemical damage is latent and can only be detected through electrical testing. Therefore, the choice of gas type has a crucial impact on the experimental results.

[0048] Furthermore, the three process parameters of this invention (gas pressure, spacing, and speed) are interrelated and synergistic. The working gas pressure determines the density and energy of active particles in the plasma; the nozzle-sample spacing affects the focusing degree of the beam and the energy density reaching the sample surface; and the scanning speed controls the plasma residence time per unit area. The matching relationship between these three directly affects the etching effect: below the lower limit, insufficient energy leads to residue (e.g., ...). Figure 6 As shown), when the energy exceeds the upper limit, excessive energy can cause thermal damage (such as...). Figures 7-9 ).

[0049] In summary, the process method of this invention achieves high-precision, selective, and low-damage dry patterning of carbon nanotube thin films by combining an oxygen-containing gas plasma beam with precision numerical control motion. This parameter range ensures the feasibility, flexibility, and adaptability to different substrates (especially flexible substrates), solving the technical problems of chemical contamination, thermal damage, or insufficient patterning accuracy encountered when directly applying traditional photolithography or existing numerical control plasma processing techniques to such nanomaterial thin films.

[0050] Comparative Example 1 This comparative example uses traditional photolithography to pattern the same carbon nanotube thin film samples, with the target clusters being circular.

[0051] Steps: Spin-coating positive photoresist onto carbon nanotube film → pre-baking → UV exposure through mask → alkaline development → forming photoresist pattern → dry etching of exposed carbon nanotubes using oxygen plasma (overall etching) → immersion in acetone and ultrasonic removal of photoresist.

[0052] Results: Circular patterns were eventually obtained. However, observations revealed residual photoresist contaminants at some pattern edges, and the conductivity of the retained areas decreased by approximately 40% compared to the product of Example 1 (resistance increased to approximately 700kΩ). The process took approximately five times longer than that of Example 1 and involved the use of various chemicals and wet processing steps.

[0053] Comparative Example 2 Referring to typical parameters used for polishing optical components: power P = 400 W, spacing Z = 2 mm, speed V = 5 mm / s, and N2 / CF4 mixed gas was used. After processing the carbon nanotube film / glass sample, local overheating of the substrate was observed. The carbon nanotubes were completely removed, but the pattern boundaries were blurred, and the resistivity of the retained area increased significantly (>10 MΩ), indicating that the performance of the carbon nanotubes was impaired.

[0054] The above embodiments are merely illustrative of the technical concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of the present invention is defined by the appended claims rather than the foregoing description, and thus all changes falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention.

Claims

1. A maskless plasma patterning method for carbon nanotube thin films, comprising the following steps: S1: Fix the substrate carrying the carbon nanotube film to be patterned onto the stage; S2: Install the stage onto a controllable two-dimensional motion platform; S3: Provide a plasma nozzle, introduce working gas into the plasma nozzle to generate a stable plasma beam, the direction of the plasma beam is towards the stage; S4: Generate a motion path program to control the controllable two-dimensional motion platform based on a preset patterned graphic; S5: Execute the motion path program to drive the stage to move the substrate under the plasma beam, so that the target area to be removed on the carbon nanotube film passes through the action area of ​​the plasma beam in sequence. The carbon nanotubes in the corresponding area are selectively removed by the chemical reaction between the active oxygen species in the plasma beam and the carbon nanotubes, thereby forming a pattern composed of the retained carbon nanotubes on the substrate. The working gas is nitrogen, or a mixture of nitrogen and an inert gas. The working pressure of the plasma nozzle is 0.15~0.2MPa; The vertical distance between the outlet of the plasma nozzle and the surface of the carbon nanotube film is 30~40mm; The stage moves at a speed of 10~30 mm / s.

2. The maskless plasma patterning method for carbon nanotube thin films according to claim 1, characterized in that, The inert gas includes argon; the volume ratio of nitrogen to inert gas in the mixed gas is 1:(1~4).

3. The maskless plasma patterning method for carbon nanotube thin films according to claim 1, characterized in that, The working pressure of the plasma nozzle is 0.18 MPa.

4. The maskless plasma patterning method for carbon nanotube thin films according to claim 1, characterized in that, The vertical distance between the outlet of the plasma nozzle and the surface of the carbon nanotube film is 35 mm.

5. The maskless plasma patterning method for carbon nanotube thin films according to claim 1, characterized in that, The stage moves at a speed of 20 mm / s.

6. The maskless plasma patterning method for carbon nanotube thin films according to claim 1, characterized in that, The thickness of the carbon nanotube film is 10~100nm.

7. The maskless plasma patterning method for carbon nanotube thin films according to claim 1, characterized in that, The substrate is a rigid substrate, including glass, quartz, or silicon wafer.

8. A carbon nanotube thin film plasma patterning apparatus for implementing the method of any one of claims 1 to 7, characterized in that, include: The plasma generating unit includes a plasma nozzle, a gas supply module connected to the plasma nozzle, and a power supply connected to the electrodes of the plasma nozzle, for generating and outputting a plasma beam with a stable direction. The two-dimensional motion unit includes a stage and a controllable two-dimensional motion platform. The stage is used to fix the substrate carrying the carbon nanotube film and is mounted on the controllable two-dimensional motion platform. The controllable two-dimensional motion platform can drive the stage to move independently in two mutually perpendicular directions in the horizontal plane. The motion control unit is electrically connected to the controllable two-dimensional motion platform and is used to receive preset pattern graphic information, generate and send control commands to drive the controllable two-dimensional motion platform to move along a preset scanning trajectory.

9. The carbon nanotube thin film plasma patterning device according to claim 8, characterized in that, The plasma nozzle is an atmospheric pressure radio frequency plasma nozzle with an operating frequency of 13.56MHz.

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