Research On Charging And Discharging Mechanism Of Thin Dielectrics Irradiatedby Electron Beam

The charging and discharging effects of the dielectric thin film irradiated under high-energy electron beam(e-beam)are of great significance to improve the accuracy of detection in electron microscopy,the precision of micro machining and the radiation resistance of micro/nano devices.However,it is difficult to accurately reveal the dynamic mechanism of the charging and discharging under e-beam irradiation due to the imperfection of the existing numerical models.Through the analysis of the micro mechanism of the interaction between the e-beam and dielectrics,a numerical model is established in this dissertation.The charging effecst,discharging characteristics and e-beam induced conductivity of polymer films and SiO2 films irradiated b y high-energy penetrating e-beams are investigated.The main research contents are as follows:1.In this dissertation,a numerical model by considering electron scattering,transport,trapping,recombination and secondary electron(SE)emission is established.Here,according to the different energy,a Rutherford and Mott elastic scattering model are prposed respectively,and the fast secondary model and Penn dielectric function model are presented.The bulk defect trapping and interface trapping simulation system is constructed.The charge drift and diffusion model based on the current continuity equation is realized,and the transport,trapping and recombination,and tranmmision crrrent and induced current model based on the finite difference method is constructed.The trajectory of SEs is obtained by solving the numerical differential equation.2.Charge effects of PMMA films with ?m thickness are clarified under penetrating e-beam irradiation in this dissertation.Due to the SE emission from the surface,the space potential is positive on the surface.With the e-beam irradiation,the surface positive potential gradually increases to a stable value,the effective emission current and sample current respectively decreases and increases,and the transmission current basically remains unchanged with irradiation.With the increase of the film thickness,the positive surface potential decreases to a negative value,and the effective emission current and sample current increase.The surface potential,emission current and sample current decrease with the increase of the beam energy.The transmission current increases with the increase of the beam energy.The results have scientific significance and application value for improving the reliability in the polymer detection.3.The charging effect on SiO2/Si samples under penetrating e-beam irradiation is clarified.Due to SE emission and the charge transport,the space potential is positive near the surface,and negative inside the film.With the irradiation,the charging intensity decreases,and the electron beam induced current increases,meanwhile the effective emission current and transmission current remain basically unchanged.The transmission current gradually increases to the beam current with the increase of beam energy,and the induced current presents a maximum value at the beam energy of 15 keV.The induced current is approximately proportional to the beam current The results have practical significance for improving the reliability in the semiconductor detection.4.The mechanism of discharging of insulator/semiconductor films is investigated,and the optimal working conditions based on low-energy e-beam are revealed.Under the transport and recombination,the charging intensity in the film gradually decreases,and however the transient time becomes longer.Under the irradiation of low-energy e-beam with energy lower than the second critical energy,the positive charges are deposited inside the sample,and the negative charges are quickly neutralized.When the landing energy of incident electron is equal to the energy that the total yield is the maximum value,the transient time presents a minimum value.The transient time increases with increasing the beam current.The results have theoretical significance for improving the radiation performance of microelectronic devices.5.The induced conductivity of SiO2 and PMMA films irradiated by high-energy e-beam was investigated.Under the positive biases and the built-in electric field,the free electrons transport to the substrate,resulting in EBIC.The current gain of the film increases linearly with the increase of the positive bias,and the current gain of PMMA film is much lower than that of SiO2 film under the same irradiation condition.When the penetration depth of the e-beam is equal to the thickness of the film,the current gain presents the maximum valuable.The results are of scientific significance for understanding the induced conductivity of thin films.