The Simulation Of Secondary Electron Emission By Monte Carlo Method

The emergence of secondary electron (SE) signal has an important value in the field of science and technology. The SE can be response to material and shape infor-mation in situ within the scope of electron beam bombardment as the most common imaging mode of Scanning Electron Microscope (SEM). Under the influence of experi-mental conditions and the material, the varietal experimental contrast of the SE image is observed. Take into account this, the SE is applied in a wide range. For example, the SE yield used to estimation for thickness of film material, environmental scanning electron microscope (ESEM) is used to observe biological sample , etc. The SE is expected to be a characterization tool in more fields, and the realization of this goal depends on a more detailed and accurate description of the SE signal physical model. Based on the above research background, our research 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 and the numerical sim-ulation method. (1st Chapter)This research is based on the theory of electron-solid interaction and the Monte Carlo model with the SE cascade handle method. The electrons impact surface of the sample, and interac with atoms and electrons in the material by series of elastic or in-elastic scattering. elativistic Mott differential scattering cross section describes elastic scattering. Dielectric function theory used to describe the inelastic scattering of elec-trons within the material and Full Penn algorithm is used to extend the energy loss function of momentum dependent from experimental optical energy loss function. The inelastic scattering cross section and the inelastic scattering mean free path is calculated by full Penn method. The SE excitation can be divided into single electron excitation and plasmon excitation. (2nd Chapter)The surface sensitivity of the emission signal is a major problem in surface anal-ysis technique. The definition of SE average escape depth becomes more complicated due to the SE cascade. Traditional escape depth calculation is roughly estimated by inelastic scattering mean free path or maximum escape depth. This definition covers two different processes of SE excitation and emission. In this thesis, we introduce the excitation depth distribution function, emission depth distribution function, and depth distribution function used to define the escape depth of SE. The average escape depth of solid materials of C, A], Si, Cu, Pt, Ag and Au is calculated. The calculation results of different experimental conditions and the definition of precise average escape depth make up for the difficulty in the experimental measurement. SE escape from the subsur-face area of the shallow surface, so their escape depth is more localized than expected.(3rd Chapter)Critical dimension (CD) measurement has always been one of the most challenging problems in the field of nanoscale precision measurement. The value of CD control has doubled as the size of the nanodevice has halved. CD-SEM is a critical measurement tool commonly used in industry. However, the edge detection algorithm has a signif-icant influence on the stability and accuracy of the CD measurement. Model based libary (MBL) following the physical principle of SE has been proved to be superior to an arbitary threshold method and other experience methods. The MBL method is more complicated than traditional threshold method. In this chapter, we have studied in detail the MBL method to measure the CD and give a complete simulation process.The MBL of Au element was constructed, and used for CD measurement of CD-SEM image of the matching of experimental conditions. CD obtained by MBL method is not only the single value of the line width, but also the detection of the 3D morphology of specimen. The main purpose of this research is standard the MBL method for CD measurements. We consider details problem in standardization of CD measurement by MBL method, and finally formed the draft of this standard. This topic was submitted to the international standardization organization-microbeam analysis technology com-mittee (ISO/TC202). The "Method for Evaluating Critical Dimensions by cd-sem" was voted and approved by the International Standardization Organization (ISO/AWI 21466(ISO/TC202/SC4)) on June 2, 2016. It is expected to be released by June 2, 2019. (4th Chapter)The SE signal generation involves the transport, excitation and scattering of elec-trons within the material, and the SE emission intensity depends on the greater depth of the target material. If the excited electrons encounter another element in the process of moving through the material, then the SE intensity will change even from a uniform surface of chemical composition. Based on experimental observation results of rela-tionship between the SE intensity with layer structure of sample , we studied the SE emission from uniform surface but inhomogeneity in depth. We built more complex samples with multilayer structure with alternating layer of Ni - C elements placed Si substrate, and change the layer structure and thickness of the top layer, and then sepa-rately calculate the SE yield from the specimen surface. SE yield is affected by layer structure and thickness of the top layer more complicatedly. The calculation results of multi-layer structure specimens are consistent with the experimental observation on the overall change trend. We explain the reason of thickness contrast by SE signal genera-tion progress. (5th Chapter)The SE simulation and interpretation of the contrast mechanism in the environ-mental state is very interesting problem. ESEM can observe the "original" surface of the sample is different from traditional SEM. For biological samples and water-bearing samples, the SE image can be observed directly under the state of nature without de-hydration and conduction. SE susceptibility to experimental conditions and material changes, so variety of the experimental observable can contrast can be obtained. The simulation of SEM image contrast in a different environment is helpful for the analysis of experimental SE image contrast and obtains more material information. The spec-imen structure constituted by graphene, liquid water medium and Au element sample was constructed with reference to ESEM environment sample chamber. We studied the dependence of the SE yield on the incident electron energy in the complex environment,and the SE yield under the influence of medium layer thickness of the liquid water and the of the thickness of Au specimen. (6th Chapter)...