Monte Carlo Simulation Study On Scanning Electron Microscopy Images And Electron Elastic Peak Spectroscopy Analysis

Theoretical investigation is necessary to accommodate the fast development andwide application of the electron microscopic and electron spectroscopic analysis tech-niques. This thesis firstly introduces the basic principle and development of scan-ning electron microscope (SEM) and the related analysis techniques, the correspond-ing electron-solid interaction theories, and the application of Monte Carlo simulationmethod in respective field. Then, it is summarized the present status of the imagingsimulation study for scanning electron microscopy (SEM) and scanning Auger elec-tron microscopy (SAM); also it is stated the experimental and theoretical backgroundsfor quasi-elastic electron scattering spectroscopy as well as the charging effect in SEM.Thus, it has been pointed out the problems and the urgent works that to be carried out.(1st Chapter)The transport and scattering processes of electrons in solids forms the physics ba-sis for a variety of electron microscopic ad spectroscopic analysis techniques. Thus,it is crucial to describe correctly the electron scattering processes and the correspond-ing cross sections for the simulation of electron- solid interaction. By careful analysis,two types of electron scattering processes have been described reasonably: the electronelastic scattering is treated by using Mott's cross section and the electron inelastic scat-tering is considered with full Penn's dielectric function. In implication of a simulation,justified random sampling and simulation procedures are necessary. We have treatedreasonably the involved physical processes, i.e. electron elastic and inelastic scatteringevents, the step-length sampling and correction, the cascaded secondary electron pro-duction, the excitation and emission of Auger electrons and the boundary corrections.Furthermore, we have also introduced two constructive models of 3D structures: (1)the constructive solid geometry (CSG) modeling combining with the ray-tracing tech-nique to derive scattering step length; (2) the finite element triangle mesh modelingto a complex 3D structure with space subdividing method to calculate scattering steplength. By using these two methods, a moderate arbitrary complex 3D structure can beconstructed while the structure units may contain different materials (vacuum, element,alloy and compound). By appropriate correction to different physical quantities, suchas, step length, energy, transport direction and transmission probability, and by usinghigh efficiency MPI parallel algorithm, the simulation model can be practically used for the SEM image simulation of many complex samples. (2nd Chapter)Based on the above simulation model, the following works have been performedin this thesis:1. By the simulation of SEM images for nanometer linewidth, relationships be-tween the structural model and the simulated images have been given. The in?uence ofdifferent sample structural parameters and the instrumental parameters to the nanome-ter linewidth measurement are systematically analyzed. It has been pointed out that thebeam size, the angular parameters, roughness and charging effect are the main in?u-encing factors to the linewidth measurement. This study will be helpful to suggest anew algorithm for the linewidth measurement. (3rd Chapter)2. By combining a hydrodynamical simulation of charge distribution with the so-phisticated Monte Carlo simulation a theoretical framework and the simulation modelfor studying the charging effect in SEM have been founded. Furthermore, the excitationdepth distribution function and the emission depth distribution function of secondaryelectrons, which may be defined in a way analogous to that in Auger electron spec-troscopy, have been studied for various experimental conditions. These depth distribu-tion functions can be used to discuss the excitation and emission processes of secondaryelectrons quantitatively. (4th Chapter)3. By introducing the excitation and emission processes of Auger electrons rea-sonably, the Monte Carlo simulation method for calculating SEM image has been ex-tended to the calculation of SAM image, where the more accurate Casnati's inner-shellionization cross-section is employed. We have calculated the SAM images for dif-ferent systems under different experimental conditions to show the contrast formationmechanism in Auger electron images; the effect of different mechanisms to the artifactcontrast is analyzed. These results have demonstrated that the present simulation modelis universal and useful to explore the contrast mechanism of SAM image. (5th Chapter)4. Based on a classical model of binary collision to approach the energy loss inquasi-elastic electron scattering and by taking account of the Maxwell-Boltzmann ther-mal energy distribution of target atoms with a correction to anisotropic momentum dis-tribution of thermal vibration, we have performed simulations of electron elastic peakspectra and high energy re?ection electron energy loss spectra. Excellent agreementsbetween the calculation and experiments have been obtained on the peak position, peakwidth and the intensity ratio of the quasi-elastic peaks. The simulation shows that, thedominant contribution to quasi-elastic signals comes from the multiple scattering pro-cesses. Taking account of the multiple scattering effect can significantly improve the deviation on the intensity ratio of quasi-elastic peaks between a simple linear modeland experiment. This will be useful for quantitative surface analysis, such as, the quan-tification of elemental distribution, the depth profiling and the thickness determinationfor thin films, by the elastic peak spectroscopy. (6th Chapter)...