A method for controlling surface potential of insulating materials under high vacuum

Abstract

The present invention discloses a method for controlling the surface potential of an insulating material under high vacuum, which uses an ultraviolet light source to irradiate an insulating material sample to generate radiation-induced conductivity, and discharges the charge by discharging the charge to the ground. In the present invention, an ultraviolet light source is used to irradiate an insulating material sample to generate radiation-induced conductivity, and discharges the charge by discharging the charge to the ground, which can effectively eliminate the surface potential formed by the accumulated charge on the surface of the insulating material sample, without the need to additionally equip expensive equipment such as electron guns and ion sources, thereby reducing the cost of potential control, eliminating complex external circuit design, and increasing test reliability; ultraviolet irradiation is used to achieve surface potential control of the insulating material under high vacuum conditions, and the surface potential neutralization operation can be completed without contacting the sample surface, thereby avoiding damaging the sample surface morphology and thus affecting its secondary electron emission characteristics, increasing test stability, and improving the accuracy of secondary electron emission coefficient measurement.

Description

Technical Field

[0001] The present invention relates to the field of insulating material microelectronic technology, and in particular to a method for controlling the surface potential of an insulating material under high vacuum. Background Art

[0002] The charging parameters of materials are crucial for spacecraft charging evaluation, protection design, and fault diagnosis. First, they provide input parameters for charging simulation analysis, yielding on-orbit material charging evaluation results for use in spacecraft material and structural design. Second, during ground-based charging simulation and verification testing, material charging characteristic parameters are fundamental to understanding and interpreting test results. Therefore, the necessity and importance of measuring the charging parameters of aerospace materials for spacecraft charging evaluation and protection design are readily apparent. The secondary electron emission coefficient of a material, as one of the most important parameters determining charging outcomes, has long attracted significant attention from researchers. Secondary electrons, in this context, refer to electrons emitted from a material surface when particles of a certain energy interact with it. Incident electrons are also called primary electrons (sometimes referred to as source electrons in literature), while electrons emitted from the material surface are called secondary electrons. Escaped secondary electrons are generally classified into backscattered electrons and true secondary electrons based on their energy. Backscattered electrons are further divided into elastically scattered electrons and inelastically scattered electrons. Secondary electron measurement is a complex technology. Firstly, according to theoretical analysis and experimental results, true secondary electron energies are relatively low, typically on the order of a few to tens of eV, generally far lower than the incident electron energy (typically tens to thousands of eV). Collection typically requires bias voltage settings, but achieving high-energy resolution is difficult, making obtaining a secondary electron energy spectrum challenging. Secondly, secondary electron emission is often accompanied by backscattered electrons generated by the interaction of the incident electron with the material, further complicating measurement.

[0003] More critically, when measuring the secondary electron emission coefficient of insulating materials, in addition to conventional techniques such as secondary electron collection, weak signal measurement, scattered electron filtering, and electrical noise suppression, it is crucial to carefully consider and control the impact of the surface potential formed by incident electrons accumulating on the insulating material's surface. This influence generally arises from three aspects. First, the surface potential formed by accumulated charge on the insulating material sample directly affects the energy of the incident electron. Experimental studies have shown that failure to neutralize the surface potential can significantly alter the measurement results. When the secondary electron emission coefficient of the material being measured is less than 1, negative charge accumulates on the material's surface, lowering the surface potential and reducing the energy of the incident electron. Conversely, if the secondary electron emission coefficient of the material being measured is greater than 1, positive charge accumulates, raising the surface potential and increasing the energy of the incident electron. Therefore, regardless of the type of charge accumulated on the surface of the material being measured, it will affect the measurement accuracy; the greater the accumulated charge, the greater the error. When measuring the secondary electron emission coefficient of insulating materials, the change in the surface potential of the material being measured must be as small as possible at a given point. This requires that the amount of velocity charge incident on the surface of the material be minimized during measurement. On the other hand, due to the poor conductivity of insulating materials, the charge accumulated on the surface of the material to be measured will cause errors in the next measurement point. As a result of the accumulation, it will cause increasingly larger measurement errors. Secondly, under vacuum or even high vacuum conditions (10 -5 Pa~10 -7 Pa), in order to maintain the background vacuum during measurement, the use of catalysts such as plasma to neutralize the surface potential cannot be used, and the charge accumulated on the insulating material is extremely difficult to eliminate. At the same time, according to existing test results, the surface potential of the sample decays very slowly under vacuum conditions; finally, to ensure a high background vacuum, the diameter of the test container is generally not too large. At the same time, to ensure that the secondary electrons emitted from the surface of the test sample can be completely collected, the collecting electrode is generally made into a hemispherical shape and the radius is also as small as possible, which greatly limits the existing and mature surface potential testing methods.

[0004] In order to study the method of controlling the surface potential of insulating materials under high vacuum, Tong Linsu et al. published an article entitled "A New Experimental Method for Measuring the Secondary Electron Emission Coefficient" in the 6th issue of Volume 4 of the Journal of Vacuum Science and Technology in November 1984. The article introduced a method for measuring the secondary electron emission coefficient of materials using a continuous pulse method with three electron guns. In this method, one electron gun is used as the main electron gun to charge the sample, and the other two are used as auxiliary electron guns. Electrons of corresponding energy are used to irradiate the sample to stabilize the surface potential of the sample within a certain range, thereby achieving the purpose of regulating the surface potential of the sample. Huang Jianguo et al. introduced in Chinese Patent 201210219891.0 a method for measuring the secondary electron emission coefficient, in which an automatic voltage regulating circuit is provided between the sample standby level and the ground line, so that the sample surface potential relative to the potential between the electron guns remains constant, thereby compensating for the charging potential of the test sample. Bu Ren'an et al. introduced in Chinese Patent 201410636027.X a method for eliminating the surface charge of a material in a vacuum, using a mechanical device to translate and rotate the charged material surface to contact the conductive adhesive, so that the sample surface charge is discharged to the ground, thereby achieving the purpose of potential elimination.

[0005] However, the above methods still have some problems during the measurement process. First, the test process requires multiple electron guns or a voltage regulation circuit between the sample and the ground line, which increases system complexity and reduces test reliability. In addition, the surface potential of the insulating material cannot be restored to zero potential or within the controlled voltage range. Second, some methods require contact with the sample surface when eliminating (controlling) the surface potential, which may damage the sample surface morphology and affect the material's secondary electron emission characteristics. Therefore, the present invention proposes a method for controlling the surface potential of insulating materials under high vacuum. Summary of the Invention

[0006] The purpose of the present invention is to solve the above problems and to propose a method for controlling the surface potential of an insulating material under high vacuum.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for controlling the surface potential of an insulating material under high vacuum conditions uses an ultraviolet light source to irradiate an insulating material sample to generate radiation-induced conductivity, and discharges the charge by discharging the charge to the ground. The method specifically includes the following steps:

[0009] S1. When the expected secondary electron emission coefficient of the insulating material sample is less than 1 by emitting primary electrons through the electron gun, the surface voltage of the insulating material sample is measured by a voltmeter connected to the sample stage, and the surface potential of the insulating material sample is increased to V1;

[0010] S2. Turn off the electron gun and use a potential probe to record the decay curve of the surface potential of the insulator sample over time;

[0011] S3. Then test the effect of the ultraviolet light source on eliminating the surface potential. First, measure the initial values of the surface resistance and volume resistance of the insulator.

[0012] S4. Increase the potential of the insulator sample surface to V1 again through the electron gun, then turn off the electron gun, turn on the ultraviolet light source, set the wavelength of the ultraviolet light source as λ1 and the intensity as I1, irradiate the insulator surface, and record the decay of the surface potential of the insulator sample over time.

[0013] S5. After ultraviolet irradiation, after a period of recovery, measure the values of the surface resistance and volume resistance of the insulator, compare with the values before irradiation, and record the change amount Δ.

[0014] S6. Replace the insulator sample, measure the initial values of the surface resistance and volume resistance of the insulator, change the above-mentioned ultraviolet light source wavelength, and the test method is the same as in step S4 and step S5, and record the decay of the surface potential over time when irradiated with different ultraviolet light source wavelengths.

[0015] S7. Replace the insulator sample, measure the initial values of the surface resistance and volume resistance of the insulator, change the above-mentioned ultraviolet light source intensity, and the test method is the same as in step S4 and step S5, and record the decay of the surface potential over time when irradiated with different ultraviolet light source intensities.

[0016] S8. Analyze the required discharge time t of the surface potential according to the test process 0， According to the test results of step S6 and step S7, when the surface charging potential V drops to V0, the required time Δt < t0, that is, the setting of the ultraviolet light source meets the requirements at this time, and it can be used to determine the minimum energy and minimum intensity of the required ultraviolet light source.

[0017] S9. Analyze and obtain the allowable change range Δ 10 、Δ 20 of the surface resistance and volume resistance according to the physical properties of the insulator sample. Measure the values of the surface resistance and volume resistance of the insulator sample after each ultraviolet irradiation and after a period of recovery, and the change amounts Δ1 and Δ2 compared with the initial values. If Δ1 < Δ 10 and Δ2 < Δ 20 are considered that the damage of the insulator sample is within the acceptable range, and this can be used to determine the maximum energy and maximum intensity that the energy and intensity of the ultraviolet light source can allow.

[0018] Preferably, the energy of the electrons emitted by the electron gun in step S1 is not greater than 5 eV, which can neutralize the potential on the surface of the insulator sample, and the potential on the surface of the processed insulator sample does not exceed -5 V, which can be ignored.

[0019] Preferably, during the process of testing the surface voltage of the insulator sample, the insulator sample is placed on the upper surface of the sample table, the potential probe is electrically connected to the voltmeter and is located on the upper surface of the insulator sample, and the electron gun and ultraviolet light source are both placed above the insulator sample.

[0020] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0021] 1. In the present application, a method for controlling the surface potential of an insulating material under high vacuum conditions by using ultraviolet irradiation is provided. An ultraviolet light source is used to irradiate an insulating material sample to generate radiation-induced conductivity. The charge is discharged by discharging the charge to the ground, which can effectively eliminate the surface potential formed by the accumulated charge on the surface of the insulating material sample and reduce the impact on the energy of the incident electrons. During the test process, there is no need to equip additional expensive equipment such as electron guns and ion sources, which reduces the cost of potential control, eliminates the need for complex external circuit design, and increases test reliability.

[0022] 2. In this application, ultraviolet irradiation is used to achieve surface potential control of insulating materials under high vacuum conditions, so as to eliminate the influence of the surface potential formed by the accumulated charge on the surface of the insulating material sample on the energy of the incident electrons. The surface potential neutralization operation can be completed without contacting the sample surface, avoiding damage to the sample surface morphology and thus affecting its secondary electron emission characteristics, increasing the test stability and improving the accuracy of the secondary electron emission coefficient measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic structural diagram of eliminating surface potential by ultraviolet radiation in a method for controlling surface potential of an insulating material under high vacuum provided by an embodiment of the present invention is shown.

[0024] Legend:

[0025] 1.1. Electron gun; 1.2. UV light source; 1.3. Potential probe; 1.4. Insulator sample; 1.5. Sample stage; 1.6. Voltmeter. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0027] See also Figure 1 , the present invention provides a technical solution:

[0028] A method for controlling the surface potential of an insulating material under high vacuum irradiates an insulating material specimen with an ultraviolet light source 1.2 to generate radiation-induced conductivity, and discharges charges by means of charge discharge to the ground. The specific steps are as follows:

[0029] S1. Emitting primary electrons through an electron gun 1.1, when the expected secondary electron emission coefficient of the insulating material sample is less than 1, measuring the surface voltage of the insulator sample 1.4 through a voltmeter 1.6 connected to a sample stage 1.5, and increasing the potential on the surface of the insulator sample 1.4 to V1;

[0030] S2. Turning off the electron gun 1.1 and using a potential probe 1.3 to record the decay curve of the surface potential of the insulator sample 1.4 over time;

[0031] S3. Then testing the effect of the ultraviolet light source 1.2 on eliminating the surface potential. First, measuring the initial values of the surface resistance and volume resistance of the insulation;

[0032] S4. Increasing the potential on the surface of the insulator sample 1.4 to V1 again through the electron gun 1.1, then turning off the electron gun 1.1, turning on the ultraviolet light source 1.2, setting the wavelength of the ultraviolet light source 1.2 to λ1 and the intensity to I1, irradiating the surface of the insulator, and recording the decay of the surface potential of the insulator sample 1.4 over time;

[0033] S5. After ultraviolet irradiation, after a period of recovery, by measuring the values of the surface resistance and volume resistance of the insulation, comparing with the values before irradiation, and recording the change amount Δ;

[0034] S6. Replacing the insulator sample 1.4, measuring the initial values of the surface resistance and volume resistance of the insulation, changing the wavelength of the above-mentioned ultraviolet light source 1.2, and the test method is the same as in steps S4 and S5, and recording the decay of the surface potential over time when irradiated with different wavelengths of the ultraviolet light source 1.2;

[0035] S7. Replacing the insulator sample 1.4, measuring the initial values of the surface resistance and volume resistance of the insulation, changing the intensity of the above-mentioned ultraviolet light source 1.2, and the test method is the same as in steps S4 and S5, and recording the decay of the surface potential over time when irradiated with different intensities of the ultraviolet light source 1.2;

[0036] S8. Analyzing the required discharge time t of the surface potential according to the test process 0， According to the test results of steps S6 and S7, when the time Δt required for the surface charging potential V to drop to V0 is less than t0, that is, the setting of the ultraviolet light source 1.2 at this time meets the requirements, and it can be used to determine the minimum energy and minimum intensity of the required ultraviolet light source 1.2;

[0037] S9. Analyzing and obtaining the allowable change ranges Δ 10 、Δ20 , measure the surface resistance and volume resistance of the insulator sample 1.4 after each UV irradiation and after a period of recovery, and the change of Δ1 and Δ2 from the initial value. If Δ1<Δ 10 , Δ2<Δ 20 , it is believed that the damage to the insulator sample 1.4 is within an acceptable range, which can be used to determine the maximum energy and maximum intensity that can be used for the energy and intensity of the ultraviolet light source 1.2.

[0038] Specifically, during the secondary electron emission test, when the expected secondary electron emission coefficient of the insulating material sample is greater than 1, its surface potential relative to the measurement ground is positive. At this time, the main method of neutralizing the surface potential effect is generally to use an electron gun to emit low-energy electrons (generally no more than 5eV) to neutralize the surface, which can ensure that the surface potential after treatment does not exceed -5V. This residual surface potential has little impact on subsequent measurement results and can be ignored.

[0039] When the expected secondary electron emission coefficient of an insulating material sample is less than 1, its surface potential is negative relative to the measurement ground. When measuring the secondary electron emission coefficient, it is necessary to pay attention to controlling the impact of the accumulated potential on the material surface on the measurement results.

[0040] Specifically, such as Figure 1 As shown, during the process of testing the surface voltage of the insulator sample 1.4, the insulator sample 1.4 is placed on the upper surface of the sample table 1.5, the potential probe 1.3 is electrically connected to the voltmeter 1.6 and is located on the upper surface of the insulator sample 1.4, and the electron gun 1.1 and the ultraviolet light source 1.2 are both placed above the insulator sample 1.4.

[0041] To sum up, the present embodiment provides a method for controlling the surface potential of an insulating material under high vacuum, which uses a certain wavelength (the specific wavelength needs to be determined in combination with the specific sample to be tested, and cannot cause irreversible damage to the sample during the irradiation process) to irradiate the insulating material sample to generate radiation-induced conductivity, and discharge the charge by discharging the charge to the ground, so as to eliminate the influence of the surface potential formed by the accumulated charge on the surface of the insulating material sample on the energy of the incident electrons, thereby improving the accuracy of the secondary electron emission coefficient measurement; the present invention uses ultraviolet irradiation to instantly change the conductivity of the sample to increase the discharge rate of the accumulated charge of the insulating material sample to the ground.

[0042] The above description of the embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling the surface potential of an insulating material under high vacuum, characterized in that: An ultraviolet light source (1.2) is used to irradiate an insulating material sample to generate radiation-induced conductivity, and the charge is discharged by discharging the charge to the ground, specifically comprising the following steps: S1. When the electron gun (1.1) emits primary electrons and the expected secondary electron emission coefficient of the insulating material sample is less than 1, the surface voltage of the insulating material sample (1.4) is measured by a voltmeter (1.6) connected to the sample stage (1.5) to increase the surface potential of the insulating material sample (1.4) to V1; S2. Turn off the electron gun (1.1) and use the potential probe (1.3) to record the decay curve of the surface potential of the insulator sample (1.4) over time; S3. Then test the UV light source (1.2) to test the surface potential elimination effect. First, measure the initial values ​​of the insulation surface resistance and bulk resistance. S4. Increase the potential on the surface of the insulator sample (1.4) to V1 again through the electron gun (1.1), then turn off the electron gun (1.1), turn on the ultraviolet light source (1.2), set the wavelength of the ultraviolet light source (1.2) to λ1 and the intensity to I1, irradiate the surface of the insulator, and record the decay of the surface potential of the insulator sample (1.4) over time; S5. After a period of recovery after UV irradiation, measure the insulation surface resistance and bulk resistance, compare them with the values ​​before irradiation, and record the change Δ; S6. Replace the insulator sample (1.4), measure the initial values ​​of the insulation surface resistance and bulk resistance, change the wavelength of the ultraviolet light source (1.2), and conduct the same test as steps S4 and S5. Record the decay of the surface potential over time when irradiated with different wavelengths of the ultraviolet light source (1.2); S7. Replace the insulator sample (1.4), measure the initial values ​​of the insulation surface resistance and volume resistance, change the intensity of the ultraviolet light source (1.2), and conduct the same test as steps S4 and S5. Record the decay of the surface potential over time when irradiated with different intensities of the ultraviolet light source (1.2); S8. Analyze the required discharge time t of the surface potential according to the test process 0， According to the test results of step S6 and step S7, the time Δt required for the surface charging potential V to drop to V0 is less than t0, that is, the setting of the ultraviolet light source (1.2) meets the requirements at this time and can be used to determine the minimum energy and minimum intensity of the required ultraviolet light source (1.2); S9. Based on the physical properties of the insulator sample (1.4), analyze and obtain the allowable variation range of surface resistance and volume resistance Δ 10 , Δ 20 , measure the surface resistance and volume resistance of the insulator sample (1.4) after each UV irradiation and after a period of recovery, and the change of Δ1 and Δ2 from the initial value. If Δ1<Δ 10 , Δ2<Δ 20 , it is considered that the damage to the insulator sample (1.4) is within the acceptable range, which can be used to determine the maximum energy and maximum intensity that can be used for the energy and intensity of the ultraviolet light source (1.2).

2. The method for controlling the surface potential of an insulating material under high vacuum according to claim 1, wherein: The energy of the electrons emitted by the electron gun (1.1) in step S1 is no more than 5 eV, which can neutralize the potential on the surface of the insulator sample (1.4). The potential on the surface of the insulator sample (1.4) after treatment does not exceed -5 V and can be ignored.

3. The method for controlling the surface potential of an insulating material under high vacuum according to claim 1, wherein: During the process of testing the surface voltage of the insulator sample (1.4), the insulator sample (1.4) is placed on the upper surface of the sample table (1.5), the potential probe (1.3) is electrically connected to the voltmeter (1.6) and is located on the upper surface of the insulator sample (1.4), and the electron gun (1.1) and the ultraviolet light source (1.2) are both placed above the insulator sample (1.4).

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