| The emergence of secondary electron signals has an important value in the field of science and technology.As a most common imaging mode of scanning electron microscopy,it can reflect the in-situ material and morphology information under the influence of electron beam bombardment.Under the influence of experimental conditions and the material properties,several experimental contrast of the SE image is observed.Which can be used to obtain a variety of experimental observable contrasts.Therefore,SE has wide range of its applications.For example,the SE yield used to estimate the thickness of the thin film materials and the environmental scanning electron microscope is used for observation of biological samples.The development of secondary electrons is expected to become a characterization tool in more fields,and for achieving this goal a more detailed and accurate description of the secondary electron production model is needed.Based on the above research background,our research is focusing on the development of SE experimental measurement,this thesis has completed several of the following topics:Firstly,we introduced the progress of SEM,the experimental observation of SE imaging,and the theoretical model of the SE generation process.(1st Chapter)The transport and scattering processes of electrons in solids forms the physics basis for a variety of electron microscopic and spectroscopic analysis techniques.Thus,it is crucial to describe correctly the electron scattering processes and the corresponding cross sections for the simulation of electron-solid interaction.By careful analysis,two types of electron scattering processes have been described reasonably:the electron elastic scattering is treated by using Mott’s cross section and the electron inelastic scattering is considered with full Penn’s dielectric function.In implication of a simulation,justified random sampling and simulation procedures are necessary.We have treated reasonably the involved physical processes,i.e.electron elastic and inelastic scattering events,the step-length sampling and correction,the cascaded secondary electron production and the boundary corrections.(2nd Chapter)We have also introduced the finite element triangular mesh modelling to a smoothly varying curved shape structure with the space subdividing method to calculate scattering step length.By using Gmsh,a freely available GNU(General Public License)gridding software,a moderate wave-type structure can be constructed while the structural units may contain different mateials(vacuum,element alloy and compound).Gmsh uses a boundary representation to describe the geometric structure and structures are generated in a bottom up flow by successively defining points,lines surfaces and volumes.By appropriate correction to different physical parameters,such as step length,energy,transport direction and transmission probability,and by using high-efficiency MPI parallel algorithm,the simulation model can be practically used for the SEM image simulation of many complex samples.(3rd Chapter)Monte Carlo(MC)simulation techniques for the study of electron interaction with solids have been successfully applied to obtain the line-scan profiles in critical dimension scanning electron microscopy(CD-SEM).However,previous studies have been mostly concerned about the sample of simple geometries having sharp edges.In this work,we have extended the simulation to the study of wave-type structures with smooth curved shapes.In this work,the CD-SEM line-scan profiles of wave-type structures have been calculated by taking into account different experimental factors,e.g.primary beam energy,geometry parameters and material property.It is shown that with the decreasing the height of the structure,the double side peaks can shrink to merge into a single peak.This characteristic will pose a challenge to the CD characterization for the smoothed line structure.(4th Chapter)... |
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