The interaction between electron beam and sample is an important research topic in current scanning electron microscope imaging and detection, electron beam probe micro-analysis and electron beam exposure technology 1101. Among them, the charging effect of insulating samples due to electron beam irradiation will change from the sample surface The state of motion of the emitted secondary electrons and incident electrons 1113, which affects the accuracy of imaging, detection and micromachining 11416. Although this charging effect can be suppressed 11718 in low-energy electron beam devices with an energy of less than 5keV, it cannot be completely eliminate. On the other hand, the charging effect of electron beam irradiation has useful prospects. For example, the buried microstructure 11923 and the deep trap 241 of the electrically insulating sample have been observed by scanning electron microscopy. Parameter measurement 1251 and imaging 126 of semiconductor samples have been tried. The charging effect of electron beam irradiation on an insulated sample is caused by the imbalance between the electron beam current of the incident sample and the secondary electron current (including intrinsic secondary electrons and backscattered electrons) leaving the sample and the leakage current. The charging process is affected by both the sample conditions and the incident electron beam conditions, which is a very complicated process. 21. For bulk-insulated samples or non-conductive substrate-insulated samples, the leakage current is approximately zero, so the charged state is mainly caused by the incident electrons. The condition of the beam is determined. When the electron beam energy is greater than the second critical energy that makes the secondary electron yield equal to 1, the electron beam current will be greater than the secondary electron current exiting from the sample surface, so the sample is negatively charged 1181. For the above The negatively charged process of thick insulating samples with negligible leakage current has been theoretically analyzed in recent years 127281, MonteCarlo simulation 129301 and the net charge density (negative space charge density) determined by electrons is maximum at the right edge of the scattering region, and then along the depth It gradually decreases to zero. This distribution is caused by electron migration, and at the same time provides the electric field from the substrate to the scattering area and the electron density gradient field required for electron migration (including diffusion). Here, the incident electrons It takes a certain time to travel from the edge of the scattering area to the substrate, so different electron beam irradiation time will This results in different charge distributions, which also shows that electron migration is a slower process than electron scattering. Further, as shown in (c), after 60-core electron beam irradiation for a longer time, there is a bottom of the 500nm thick film The net negative charge distribution generated by the electrons indicates that the incident electrons have reached the grounded substrate to form a leakage current. The last point, as shown in (c), when the electron beam irradiation time is 10Ms, the net charge density first appears near z = 140nm A large value, and then a minimum value near z = 150nm. The reason for this phenomenon is that near the edge of the scattering region at z = 140nm, the electron density decreases before the hole density due to the migration effect, but at z Near 150nm, the hole density drops sharply to zero and the electron density decreases slowly.
The similarity of ilM in the two directions of r1 indicates that the space charge density bookmark9 of aM electrons in the sample wishis film is a simulation result of the carrier density and the net space charge density distributed along the radial r direction on the film surface. It can be seen from this that the electron scattering area in the r direction is about 180 nm. This is because the radius of the incident electron beam will make the r direction scattering area slightly larger than the z direction scattering area. In addition, the density of holes and electrons is relatively high in the scattering region with a radius of 180nm; in the region of r> 180nm, the hole density is zero, and the electron density is not zero. There is also a negative space charge distribution formed by electrons; charge competition The density has a minimum value at z = 180nm. The reasons for the formation of these carrier and charge density distributions can be explained by analysis of related results. Here, the electron distribution is approximately hemispherical inside the product. However, since the scale of the z-direction of the film is generally much smaller than the scale of the r-direction, the migration characteristics of electrons in the z-direction play a more important role in the negative charging process of the insulating film under a certain scattering region.
The negative space charge distribution from the outside of the scattering area to the substrate formed by the migration of incident electrons is a key link of the charging effect of the low-energy electron beam irradiation on the grounded insulating film. The influence law of electron beam energy and current and electron migration rate on the net charge density distribution in the depth z direction under long-term irradiation of electron beam is given. It can be seen from (a) that as the energy of the electron beam increases, the simulation results of the electron scattering region show that although the electron beam current is different, the final negative space charge distribution is almost the same, that is, the net insulation film determined by (11) The amount of negative charge (hereinafter collectively referred to as the amount of negative space charge) is equal.
(C) shows that the higher the electron migration rate, the less negative space charge in the film, and the lower the negative charge. At this time, the increase in the electron migration rate will directly lead to an increase in the average drift velocity of the electrons and produce a stronger leakage current, but the incident electron beam current is constant, so the negative space charge left inside the film will be reduced.
Negative charging process and its balance mechanism From the above results and analysis, it can be seen that the generation and changes of leakage current directly affect the negative charging process of the film and the amount of negative space charge. The following describes the simulation results of the leakage current, the amount of negative space charge and the surface potential of the electron beam irradiation center point (hereinafter referred to as the surface potential) during electronegative irradiation.
The time-varying characteristics of leakage current, negative space charge and surface potential under different film thickness conditions are given. First of all, it can be seen that the leakage current and the amount of negative space charge in the charging process increase with the irradiation of the electron beam, and the surface potential decreases with the irradiation time, both of which appear to reach equilibrium from the transient state to the steady state. From (a), the thicker the film, the longer the delay time of the leakage current, and the longer the transit time from the occurrence of the leakage current to the electron drift from the edge of the scattering region to the formation of the leakage current of the substrate, and as shown in (b) , The more internal negative space charge, the longer the transition time. Here, the negatively charged transient effect and the equilibrium process and the delay effect of leakage current obtained through simulation in this paper can explain the similar phenomenon of the recent scanning electron microscope image of negatively charged microstructures in the insulating film sample with electron beam irradiation.
After the negatively charged transient process tends to stabilize, as shown in (a), the leakage current balance value is the same when the film thickness is different. This can be explained by the current balance conditions in and out of the film.
Since the electron current Is leaving the sample and the incident electron beam current / pe satisfy / s = pe, the condition that the net current of the film is zero becomes ―S). The longer the Cuan day of equilibrium state. This is because the thicker the film, the smaller the thickness H, the negatively charged black and the different insulating film thickness H, (a) vent: / PE is related to the secondary electron yield S. Therefore, when the electron beam current is fixed, the energy of the electron beam is constant, s is constant, and the leakage current balance value is unchanged. On the other hand, the delay time of the leakage current corresponding to the thick film is longer, and the transition time to the steady state is also longer. At this time, more electrons will be injected into the film. As a result, as shown in (b) and (c), the negative space charge increases and the film surface potential decreases. After the leakage current is generated, part of the electrons collected near the edge of the electron scattering area in the film is lost by migration into the substrate, and the surface potential will tend to stabilize. Therefore, the final negative space charge amount and the absolute value of the surface equilibrium potential will increase as the film thickness increases.
The series of results show that the leakage current and its evolution characteristics are important factors affecting the negative charging process and intensity. When the leakage current increases so that the net current flowing into the membrane is zero, the negative charging process then stops and reaches a stable equilibrium state. Among them, the spatial scale of the formation and evolution of negative charge is only equivalent to the area near the surface in the bulk insulating thick sample. Unlike the case of thick samples, the electron scattering area in this paper is comparable to the thickness of the film, so the electron migration characteristics will have a greater impact on the negative charging process. In addition, as can be seen from (b) and (c), the maximum negative space charge at this time is composed of only about 830 electrons. Although the number of electrons is not large, the electron beam energy is 2keV, the film thickness is 500nm, and the electron mobility is 105cm2V Under the condition of 1, a surface equilibrium potential of about 5V can still be generated.
The simulation results also show that the stronger the incident electron beam current, the shorter the leakage current, negative space charge amount, and surface potential from irradiation start to equilibrium. This is because when the electron beam current is strong, there are more negative space charges accumulated in the film, the electric field and the electron density gradient field from the substrate to the scattering region are stronger, and the electron drift from the edge of the scattering region to the substrate transit time and The transition time to reach equilibrium will be shortened. However, the electron beam current does not change the surface equilibrium potential. This is because, as shown in (b), when the electron beam is irradiated for a long time to reach equilibrium, it is known from equation (12) that the leakage current increases proportionally with the electron beam current. The charge distribution will not change the incidence, and the amount of negative space charge generated in the film and the surface equilibrium potential formed will not change, that is, the negative charge intensity will not change. In short, the electron beam current only changes the speed of the negative charging process, and does not affect the negative charging result.
Similarly, the higher the electron migration rate of the insulating film, the shorter the time for leakage current, negative space charge, and surface potential to reach equilibrium. This is because the higher the electron migration rate, the greater the electron drift velocity and leakage current, and the shorter the leakage current delay time and the transition time of the leakage current to its equilibrium value. However, from equation (12), the leakage current balance has nothing to do with the electron migration rate. On the other hand, as is not the case, the amount of negative space charge generated by the incident electrons in the film decreases as the electron migration rate increases, the absolute value of the corresponding surface equilibrium potential decreases, and the negatively charged intensity becomes weaker. For semiconductor materials with high migration rate
600V DC Electronic Load System have options for 39600W/52800W/66000W , the highest power will be 2400A.It supports list function. RS232, RS485 and USB is the standard communication interfaces. LAN&GPIB communication card is optional. This series DC electronic load can be applied to battery discharge, DC charging station and power electronics and other electronics products.BTW, expect 600V DC Electronic Load System can cover 200V DC Electronic Load System, also it can have high voltage options for 1200V DC electronic load System.
Kinly check below features for your reference:
â— Flippable front panel and color touch screen allow convenient access and operation
â— Provides four kinds of basic working mode such as CV/CC/CR/CP, and CV+CC/CV+CR/CR+CC complex operating modes
â— Adjustable current slew rate, adjustable CV loop speed
â— Ultra high precision voltage & current measurement
â— 50kHz high-speed CC/CR dynamic mode
â— 500kHz high-speed voltage and current sampling rate
â— Timing & discharging measurement for batteries
â— Short circuit test mode
â— Auto mode function provides an easy way to do complicated test
â— V-monitor/I-monitor
â— Full protection: OCP, OPP, OTP, over voltage and reverse alarm
â— Front panel USB interface supports data import and export
â— Using standard SCPI communication protocol
â— Smart fan control with lower noise and better for environment
600V DC Electronic Load System
600V list mode DC E-load, 600V dynamic mode DC electronic load, 500kHz sampling rate DC electronic load
APM Technologies (Dongguan) Co., Ltd , https://www.apmpowersupply.com