CN112281141A - Method for inhibiting secondary electron emission coefficient of medium surface based on controllable carbon nano coating - Google Patents
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- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
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Abstract
The invention relates to a method for inhibiting secondary electron emission coefficient of a medium surface based on a controllable carbon nano coating, belonging to the technical field of inhibition of secondary electron emission coefficient of the medium surface. The invention realizes the method for inhibiting the secondary electron emission on the surface of the medium based on the controllable carbon nano coating under the multi-constraint condition, reduces the secondary electron emission coefficient on the surface by depositing the controllable carbon nano film on the atomic layer on the surface of the metal substrate, reduces the secondary electron emission coefficient by more than 60 percent, and has better application prospect in solving the micro-discharge effect of a medium microwave component and the electron cloud of a particle accelerator.
Description
Technical Field
The invention relates to a method for inhibiting a secondary electron emission coefficient on the surface of a medium based on a controllable carbon nano-coating, wherein the medium refers to a polyimide substrate, a polytetrafluoroethylene substrate, an alumina substrate or a silicon oxide substrate, and belongs to the technical field of inhibition of the secondary electron emission coefficient on the surface of the medium.
Background
With the development of aerospace technology, the effective load tends to be high-power, small-sized and light-weighted more and more so as to meet the requirements of the new generation of aerospace technology. The dielectric discharge of the microwave component is easily caused by the overlarge secondary electron emission coefficient of the dielectric surface, the surface of the microwave component is damaged once the secondary electron emission coefficient is too large, the noise level of a communication system is raised, the output power is reduced, the service life of the microwave component is shortened, and the microwave component is permanently failed to influence the normal progress of an aerospace task.
The dielectric micro-discharge surface treatment technology is an important means for suppressing discharge and improving a micro-discharge threshold, and comprises a surface low secondary electron emission coefficient coating film and a surface micro-nano trap structure, wherein the surface low secondary electron emission coefficient coating film treatment technology is the important part in research and development of related international digital navigation mechanisms. The U.S. Stanford university and the national Sian transportation university introduce the machining and integrated circuit micro-pattern ultraviolet lithography process into the surface local treatment of the microwave component, so that the surface of a regular porous array with large porosity is realized, and the SEY inhibition amplitude of the surface reaches 30%. Researchers also utilize surface gold plating, carbon black plating layer sputtering and oxide nano structure, so that the secondary electron emission coefficient of the surface is greatly inhibited. However, in order to meet the application of aerospace engineering, the suppression of the secondary electron emission coefficient on the surface of the medium needs to meet the requirements of multiple key technologies, including large suppression amplitude of the coating, strong binding force of the coating, high environmental stability and excellent medium characteristics. At present, the secondary electron emission coefficient suppression methods which can meet a plurality of key technical requirements are less.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method overcomes the problems of medium loss, poor controllability and weak binding force of a secondary electron emission inhibition coating caused by inhibiting the secondary electron emission coefficient, provides a medium surface secondary electron emission coefficient inhibition method based on a controllable carbon nano coating, and realizes the result of reducing the controllable inhibition of the secondary electron emission coefficient on the medium surface under multiple constraint conditions.
The technical solution of the invention is as follows:
a method for inhibiting secondary electron emission coefficient of a medium surface based on a controllable carbon nano coating comprises the following steps:
(1) ultrasonically cleaning a medium substrate by using alcohol and isopropanol, and blow-drying by using nitrogen, wherein the medium is a polyimide substrate, a polytetrafluoroethylene substrate, an alumina substrate or a silica substrate;
(2) the cleaned medium substrate is placed in an ion etching system, residual organic matters on the surface are thoroughly removed, the strong binding force between a carbon film and the surface of the substrate is guaranteed, the film is prevented from falling off, the ion etching cleaning surface comprises two etching technologies, and the first etching technology is as follows: etching the substrate by argon-hydrogen plasma at near room temperature, and performing high-temperature annealing after the etching is finished, wherein the second etching technology is as follows: etching with inert gas ions;
a first etching technique: adopting a remote plasma system, introducing argon-hydrogen mixed gas with the ratio of 1:3-2:1 and the pressure of 20-100Pa, the power of the plasma being 50-100w, etching the surface of the medium substrate for 10-30 minutes at 50-80 ℃, then closing the plasma, raising the temperature to 200-300 ℃, and annealing for 30-60 minutes;
the second etching technique: cleaning the surface of the medium substrate by adopting high-purity argon ions with energy of 400-600eV, wherein the cleaning process is executed in multiple stages, the phenomenon that the surface temperature is too high due to long-time etching is avoided, the single cleaning stage is 20-40s, after 20-40s, the next cleaning stage is executed, and the cleaning time is accumulated for 2-3 minutes;
(3) conveying the medium substrate into an atomic layer deposition reaction cavity through a pre-vacuum chamber, vacuumizing the atomic layer deposition reaction cavity to 0.1-5Pa, introducing high-purity nitrogen with the purity of 99.99%, maintaining the air pressure at 30-50Pa, and heating the reaction cavity to 150-250 ℃;
(4) conveying the medium substrate to a pre-vacuum chamber, performing carbon film deposition in an atomic layer deposition reaction cavity, wherein two reaction source precursors are used during the carbon film deposition, one of the two reaction source precursors is benzene, toluene, xylene or p-terphenyl as a carbon reaction source precursor, the other one is iodomethane, heating the reaction cavity to 150 ℃ and 250 ℃, the pulse time of the carbon source precursor is 0.2-1s, the waiting time is 5-30s, the pulse time of the iodomethane is 0.1-0.5s, the waiting time is 20-60s, and the carbon film deposition process is performed for 10-20 cycles to obtain a stable carbon film deposition environment and improve the film deposition quality;
(5) conveying a medium substrate to an atomic layer deposition reaction cavity, performing carbon film deposition on the surface of the medium substrate, wherein two reaction source precursors are used during the carbon film deposition, one of the two reaction source precursors is benzene, toluene, xylene or p-terphenyl as a carbon reaction source precursor, the other one is iodomethane, heating the reaction cavity to 150 ℃ and 250 ℃, the pulse time of the carbon source precursor is 0.2-1s, the waiting time is 5-30s, the pulse time of the iodomethane is 0.1-0.5s, and the waiting time is 20-60s, and the carbon film deposition process is performed for 10-100 cycles to generate a carbon film with the target thickness;
(6) conveying the medium substrate to a pre-vacuum chamber, cooling to room temperature, taking out the medium substrate to obtain the medium substrate with the secondary electron emission coefficient inhibited, and performing the following operations aiming at the atomic layer deposition reaction cavity for the convenience of next use: and closing the two reaction source precursor valves, and executing 5-15 gas washing cycles by using the two reaction source precursors participating in the gas path, wherein the gas washing cycles refer to the pulse time of the carbon source precursor of 0.2-1s, the waiting time of 5-30s, the pulse time of iodomethane of 0.1-0.5s and the waiting time of 20-60 s.
The invention has the beneficial effects that:
(1) the method for inhibiting the secondary electron emission coefficient of the medium surface based on the carbon nano-coating of the controllable carbon has the advantages that the atomic layer deposited carbon film has good conformality and is suitable for surfaces with different appearances and complex structures, the quasi-continuous regulation and control of the secondary electron emission coefficient of the medium surface are realized by depositing the controllable carbon nano-coating on the atomic layer of the medium substrate surface, and the inhibition amplitude of the secondary electron emission coefficient exceeds 60 percent.
(2) The atomic layer deposition reaction source and reaction parameters are optimized, and the preparation method of the carbon film with the compatible process and the strong binding force of the medium microwave component is realized.
(3) By optimizing the process parameters, the carbon-carbon bonding mode and the dielectric property in the carbon film are regulated, and the ultrathin controllable thickness of the carbon film is beneficial to weakening or eliminating the increase of the dielectric loss of a dielectric microwave component caused by conventional coating.
(4) The amplitude regulation of the secondary electron emission coefficient of the surface of the medium is realized by regulating the thickness of the atomic layer deposition carbon film, and the coating process parameter with the thickness of 4-6 nanometers suitable for improving the power threshold of the microwave part of the medium is optimized.
Drawings
FIG. 1 is a simplified flow diagram of a process scheme;
FIG. 2 is a top view of a carbon film microtopography magnified 5 thousand times Atomic Force Microscope (AFM) image;
FIG. 3 is a top view of a carbon film microtopography magnified 10 thousand times Atomic Force Microscope (AFM) image;
FIG. 4 is carbon film Raman spectroscopy characterization data;
FIG. 5 shows that the secondary electron emission SEY varies with the incident electron energy for different carbon film thicknesses;
fig. 6 shows that the maximum value of the secondary electron emission coefficient SEY varies with the thickness of the carbon film.
Detailed Description
The invention is further illustrated by the following figures and examples.
As shown in fig. 1, the method of the present invention is as follows:
a method for inhibiting secondary electron emission on the surface of a medium based on a controllable carbon nano-coating is characterized by comprising the following steps:
(1) ultrasonically cleaning medium polyimide, polytetrafluoroethylene, alumina and silicon oxide substrates by using alcohol and isopropanol, and drying by using nitrogen.
(2) The medium substrate is placed in an ion etching system, residual organic matters on the surface are thoroughly removed, strong bonding force between the carbon film and the substrate surface is guaranteed, and the film is prevented from falling off. The ion etching and surface cleaning comprises two etching technologies, namely argon-hydrogen plasma near room temperature etching + annealing and inert gas ion etching. For the argon-hydrogen plasma surface treatment process, a remote plasma system is adopted, argon-hydrogen mixed gas with the proportion of 1:3-2:1 and the pressure of 20-100Pa is introduced, the plasma power is 50-100w, the surface of the substrate is etched for 10-30 minutes at 50-80 ℃, then the plasma is closed, the temperature is raised to 200-300 ℃, and annealing is carried out for 30-60 minutes. For the inert ion etching surface treatment process, high-purity argon ions with the energy of 400-600eV are adopted to clean the surface of the sample piece, the cleaning process is executed in multiple stages, the phenomenon that the surface temperature is too high due to long-time etching is avoided, the single cleaning stage is 20-40s, after 20-40s, the next cleaning stage is executed, and the cleaning time is accumulated for 2-3 minutes.
(3) Conveying a substrate into an atomic layer deposition reaction cavity through a pre-vacuum chamber, vacuumizing the system to 0.1-5Pa, introducing high-purity nitrogen with the purity of 99.99%, maintaining the air pressure at 30-50Pa, selecting benzene, toluene, xylene and p-terphenyl as carbon reaction source precursors, selecting iodomethane as a second reaction source precursor, heating the reaction cavity to 150 ℃ and 250 ℃, setting the pulse time of the carbon source precursor to 0.2-1s, the waiting time to be 5-30s, the pulse time of the iodomethane to be 0.1-0.5s and the waiting time to be 20-60 s;
(4) the sample is transmitted to a pre-vacuum chamber, and the reaction chamber executes 10-20 circulating pre-reaction gas washing processes to obtain a stable carbon film deposition environment and improve the film deposition quality;
(5) conveying the sample to a reaction chamber, and performing 10-100 atomic layer deposition cycles to generate a carbon film with a target thickness;
(6) and (3) conveying the sample to a pre-vacuum chamber, closing a reaction source valve, executing 5-15 gas washing cycles in the reaction chamber, closing the system, cooling the sample to room temperature, taking out and storing.
Further, the medium is a variety of base materials such as polyimide, polytetrafluoroethylene, alumina, and silica.
Furthermore, the method for cleaning the surface by ion etching, enhancing the bonding force between the carbon film and the surface of the substrate and preventing the film from falling off comprises the following steps: for the argon-hydrogen plasma surface treatment process, a remote plasma system is adopted, argon-hydrogen mixed gas with the proportion of 1:3-2:1 and the pressure of 20-100Pa is introduced, the plasma power is 50-100w, the surface of the substrate is etched for 10-30 minutes at 50-80 ℃, then the plasma is closed, the temperature is raised to 200-300 ℃, and annealing is carried out for 30-60 minutes. For the inert ion etching surface treatment process, high-purity argon ions with the energy of 400-600eV are adopted to clean the surface of the sample piece, the cleaning process is executed in multiple stages, the phenomenon that the surface temperature is too high due to long-time etching is avoided, the single cleaning stage is 20-40s, after 20-40s, the next cleaning stage is executed, and the cleaning time is accumulated for 2-3 minutes.
Further, benzene, toluene, xylene and p-terphenyl are selected as a carbon reaction source precursor, iodomethane is selected as a second reaction source precursor, the reaction cavity is heated to 250 ℃ with the temperature of 150-.
Further, the sample is conveyed to a pre-vacuum chamber, and the reaction chamber executes 10-20 circulating pre-reaction gas washing processes to obtain a stable carbon film deposition environment, so that the occurrence of a common chemical vapor deposition process in the carbon film deposition process is avoided, and the film deposition quality is improved.
Further, the sample is transferred to the reaction chamber, 10-100 atomic layer deposition cycles are performed, a carbon film of a target thickness is generated, the atomic layer deposition carbon film has extremely high controllability, the thickness of the deposited carbon film is about 0.1 nm during each cycle within the reaction window, and the thickness of the carbon film is strictly controlled by changing the number of deposition cycles.
Further, the sample is conveyed to a pre-vacuum chamber, a reaction source valve is closed, 5-15 gas washing cycles are executed in the reaction chamber, and residual reaction sources in the gas path are completely removed to prevent the cavity and the gas path from being polluted.
The present invention will be described in detail below with reference to the accompanying drawings.
A method for suppressing secondary electron emission on the surface of a medium based on a controllable carbon nano-coating comprises the following steps of: ultrasonically cleaning and drying a substrate → ionically cleaning the surface, enhancing the bonding force of the carbon film and the surface of the substrate → preferably selecting reaction source precursors such as benzene, p-terphenyl and the like, preferably selecting atomic layer deposition reaction parameters → executing a pre-reaction cycle, improving the quality of the carbon film → performing an atomic layer deposition reaction, generating the carbon film with a target thickness → executing a gas washing reaction cycle, taking out the substrate and storing.
A method for inhibiting secondary electron emission on the surface of a medium based on a controllable carbon nano-coating. The method adopts an atomic layer deposition method to directly grow the controllable carbon nano film material on the surface of the medium sample piece. The method provided by the technical scheme has the advantages of simple process, good controllability of the carbon film, high stability, strong binding force, large and adjustable secondary electron emission inhibition amplitude, capability of preventing the surface dielectric property from being degraded by the controllable ultrathin carbon film, and clean and pollution-free introduction process of the carbon film.
The preferable scheme of the method specifically comprises the following steps:
(1) ultrasonically cleaning medium polyimide, polytetrafluoroethylene, alumina and silicon oxide substrates by using alcohol and isopropanol, and drying by using nitrogen. (2) Placing a dielectric substrate in an ion etching system, introducing argon-hydrogen mixed gas with the proportion of 1:2 and the pressure of 50Pa by adopting a remote plasma system, etching the surface of the substrate for 20 minutes at the temperature of 60 ℃ with the plasma power of 80w, then closing the plasma, raising the temperature to 250 ℃, and annealing for 40 minutes to thoroughly remove residual organic matters on the surface, thereby ensuring that the carbon film has strong bonding force with the surface of the substrate and preventing the film from falling off.
(3) Conveying a substrate into an atomic layer deposition reaction cavity through a pre-vacuum chamber, vacuumizing the system to 1Pa, introducing high-purity nitrogen with the purity of 99.99%, maintaining the air pressure at 40Pa, selecting benzene, toluene, xylene and p-terphenyl as carbon reaction source precursors, selecting monoiodomethane as a second reaction source precursor, heating the reaction cavity to 200 ℃, setting the pulse time of the carbon source precursor to be 0.5s, waiting for 20s, the pulse time of the monoiodomethane to be 0.3s and waiting for 40 s;
(4) the sample is transmitted to a pre-vacuum chamber, and the reaction chamber executes 15 circulating pre-reaction gas washing processes to obtain a stable carbon film deposition environment and improve the film deposition quality;
(5) conveying the sample to a reaction chamber, and performing 50 atomic layer deposition cycles to generate a carbon film with a target thickness;
(6) and (3) conveying the sample to a pre-vacuum chamber, closing a reaction source valve, executing 10 gas washing cycles in the reaction chamber, closing the system, cooling the sample to room temperature, taking out and storing.
FIGS. 2 and 3 are atomic force microscope images of a carbon film having a grain size of 20-80 nm, wherein the microscopic pattern top view of the carbon film is magnified 5-thousand times and 10-thousand times, respectively. The carbon film prepared by atomic layer deposition has extremely high uniformity and process uniformity, and can realize high-quality controllable coating on the surfaces of dielectric substrates and parts.
Fig. 4 is carbon film raman spectrum rectification data. The carbon-carbon bonding mode in the carbon film determines the conductivity of the carbon film, and the larger the sp2 bonding proportion is, the closer the carbon film is to the characteristics of graphene, the better the conductivity is; the larger the sp3 bonding specific gravity, the closer the carbon film is to the properties of diamond, and the better the insulation. Considering that the graphene coating will increase the surface loss of the medium and deteriorate the electrical characteristics of the medium microwave component; pure diamond coatings are difficult to effectively suppress the secondary electron emission coefficient, and therefore the carbon-carbon bonding mode must be strictly controlled. The Raman spectrum characterization result shows that the carbon-carbon bonding mode in the carbon film is mainly sp3 bonding and is mixed with a small part of sp2 bonding.
FIG. 5 shows the variation of the secondary electron emission coefficient of the surface of PTFE with the incident electron energy after atomic layer deposition of carbon films of different thicknesses.
FIG. 6 shows the SEY maximum value of the surface secondary electron emission coefficient of polytetrafluoroethylene as a function of the thickness of the carbon film. The maximum value of the secondary electron emission coefficients of the dielectric materials of Polytetrafluoroethylene (PTFE) and an alumina substrate is about 3.7 and 3.5. Depositing 10-100 cycles carbon film on the surface of the medium substrate, and the film thickness is about 1-10 nm by combining the AFM analysis technology. The secondary electron emission coefficient test result shows that after 1 nanometer carbon film is deposited on the surfaces of the medium alumina and the polytetrafluoroethylene, the secondary electron emission coefficients are respectively reduced by about 2.7 and 2.6; after the 2 nanometer carbon film is deposited, the secondary electron emission coefficient is reduced to about 2.1 and 2.0; after 3 nanometers of deposition, the secondary electron emission coefficient is reduced to about 1.5; after the 4 nanometer carbon film is deposited, the secondary electron emission coefficient is reduced to about 1.3; after 5 nanometers of deposition, the secondary electron emission coefficient is reduced to about 1.25; after 8 nm deposition, the secondary electron emission coefficient decreased to around 1.23. As the carbon film is continuously increased, the secondary electron emission coefficient is basically kept stable and is about 1.20, and the reduction amplitude exceeds 60 percent. Comprehensively analyzing the inhibition effect, dielectric property, coating cost, production efficiency and space flight reliability of the carbon film on the surface of the medium, and preferably selecting a 4-6 nanometer carbon film coating for improving the micro-discharge threshold of the medium microwave component.
The preparation of the film based on the atomic layer deposition technology is a chemical reaction deposition process for generating one sub-atomic layer in one period, so that the density and the uniformity of the surface carbon film are high, and the roughness of the surface of the microwave component level substrate can not be changed. The atomic layer deposition reaction is completed in a gaseous environment, the precursor source in the reaction window is uniformly adsorbed on the surface of the substrate of the part to be deposited in a chemical adsorption mode, and the surface can be a plane, a curved surface, a trap structure surface with a larger depth-to-width ratio and the like.
Claims (6)
1. A method for suppressing secondary electron emission coefficient on the surface of a medium, wherein the medium is a polyimide substrate, a polytetrafluoroethylene substrate, an alumina substrate or a silica substrate; the method is characterized by comprising the following steps:
(1) cleaning the medium substrate with an organic solvent and drying;
(2) placing the cleaned medium substrate in an ion etching system to remove residual organic matters on the surface;
(3) conveying the medium substrate into an atomic layer deposition reaction cavity through a pre-vacuum chamber, vacuumizing the atomic layer deposition reaction cavity to 0.1-5Pa, introducing nitrogen, maintaining the air pressure at 30-50Pa, and heating the reaction cavity to 150-250 ℃;
(4) conveying the medium substrate to a pre-vacuum chamber, performing carbon film deposition in an atomic layer deposition reaction cavity, wherein two reaction source precursors are used during the carbon film deposition, one of the two reaction source precursors is benzene, toluene, xylene or p-terphenyl as a carbon reaction source precursor, the other one is iodomethane, heating the reaction cavity to 150 ℃ and 250 ℃, the pulse time of the carbon source precursor is 0.2-1s, the waiting time is 5-30s, the pulse time of the iodomethane is 0.1-0.5s, the waiting time is 20-60s, and the carbon film deposition process is performed for 10-20 cycles;
(5) conveying a medium substrate to an atomic layer deposition reaction cavity, performing carbon film deposition on the surface of the medium substrate, wherein two reaction source precursors are used during the carbon film deposition, one of the two reaction source precursors is benzene, toluene, xylene or p-terphenyl as a carbon reaction source precursor, the other one is iodomethane, heating the reaction cavity to 150 ℃ and 250 ℃, the pulse time of the carbon source precursor is 0.2-1s, the waiting time is 5-30s, the pulse time of the iodomethane is 0.1-0.5s, and the waiting time is 20-60s, and the carbon film deposition process is performed for 10-100 cycles to generate a carbon film with the target thickness;
(6) and conveying the medium substrate to a pre-vacuum chamber, cooling to room temperature, and taking out to obtain the medium substrate with the suppressed secondary electron emission coefficient.
2. The method for suppressing secondary electron emission coefficient of a dielectric surface according to claim 1, wherein: in the step (1), the medium substrate is ultrasonically cleaned by alcohol and isopropanol and is dried by nitrogen.
3. The method for suppressing secondary electron emission coefficient of a dielectric surface according to claim 1, wherein: in the step (2), the ion etching and surface cleaning comprises two etching methods, wherein the first etching method comprises the following steps: and (3) performing argon-hydrogen plasma near room temperature etching, and performing high-temperature annealing after the etching is finished, wherein the second etching method comprises the following steps: and etching by inert gas ions.
4. The method for suppressing secondary electron emission coefficient of a dielectric surface according to claim 3, wherein: the first etching method comprises the following steps: adopting a remote plasma system, introducing argon-hydrogen mixed gas with the ratio of 1:3-2:1 and the pressure of 20-100Pa, etching the surface of the medium substrate for 10-30 minutes at 50-80 ℃ with the plasma power of 50-100w, then closing the plasma, raising the temperature to 200-.
5. The method for suppressing secondary electron emission coefficient of a dielectric surface according to claim 3, wherein: the second etching method comprises the following steps: the surface of the medium substrate is cleaned by adopting high-purity argon ions with energy of 400-600eV, the cleaning process is executed in a plurality of stages, the single cleaning stage is 20-40s, after 20-40s, the next cleaning stage is executed, and the cleaning time is accumulated for 2-3 minutes.
6. The method for suppressing secondary electron emission coefficient of a dielectric surface according to claim 1, wherein: in the step (6), for the convenience of next use of the atomic layer deposition reaction cavity, the following operations are performed: and closing the two reaction source precursor valves, and executing 5-15 gas washing cycles by using the two reaction source precursors participating in the gas path, wherein the gas washing cycles refer to the pulse time of the carbon source precursor of 0.2-1s, the waiting time of 5-30s, the pulse time of iodomethane of 0.1-0.5s and the waiting time of 20-60 s.
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