扫描电子显微学中二次电子发射过程的蒙特卡洛模拟

利用蒙特卡洛模拟固体中电子散射轨迹的计算方法，系统地研究了扫描电镜中二次电子信号的发射过程。该模拟电子与固体相互作用的蒙特卡洛模型包含了级联二次电子产生的过程，并且采用光学介电函数方法描述电子的能量损失和相伴的二次电子激发。由于模拟计算可以给出背散射电子和二次电子的绝对产额，以及它们随加速电压和样品的原子序数的变化关系，因此可以用于模拟元素衬度和形貌衬度像。还计算得到了关于二次电子产生和发射的其它分布，并与实验结果作了比较。     

绝缘膜负带电时的表面局部电场与二次电子返回特性

为分析IC多层版图扫描电镜(SEM)对准检测所利用的负带电成像原理,采用Mott弹性散射截面和修正的Bethe非弹性碰撞公式,对点照射入射电子在绝缘膜中的散射过程进行了Monte Carlo模拟,得到负带电绝缘物表面的局部电位分布.在此基础上计算了二次电子从表面出射后在局部场作用下的运动轨迹,获得了SEM像的二次电子信号电流.结果表明,在弱负带电条件下,照射点处表面电位越低,返回表面的二次电子就越多,对应的二次电子信号电流越弱.此结果与SEM实验中图像亮度随照射时间的变化规律相符.     

绝缘膜负带电时的表面局部电场与二次电子返回特性

为分析IC多层版图扫描电镜(SEM)对准检测所利用的负带电成像原理,采用Mott弹性散射截面和修正的Bethe非弹性碰撞公式,对点照射入射电子在绝缘膜中的散射过程进行了Monte Carlo模拟,得到负带电绝缘物表面的局部电位分布.在此基础上计算了二次电子从表面出射后在局部场作用下的运动轨迹,获得了SEM像的二次电子信号电流.结果表明,在弱负带电条件下,照射点处表面电位越低,返回表面的二次电子就越多,对应的二次电子信号电流越弱.此结果与SEM实验中图像亮度随照射时间的变化规律相符     

基于光电子显微镜的X射线近吸收边结构研究

利用基于第三代同步辐射光源的光电子显微镜图像[1,2 ] (图 1) ,我们测量了银的L3 全电子产生几率模式的X射线近吸收边结构谱 ,同Burattini等的透射实验结果比较[3 ,4] ,二者十分吻合 ,说明反射、透射模式的X射线近吸收边结构谱均能很好地描述材料的非占有电子态结构。进一步利用描述电子在固体内的散射过程及级联产生的二次电子过程的蒙特卡罗模型[5] 计算了银的L3 吸收边上、下的X光子激发的光电子、俄歇电子及其级联产生的二次电子对全部出射电子的贡献。全电子产生几率同实验结果接近 ,同时在吸收边两侧全电子产生几率的比值也同实验…     

采用法拉第杯评价ESEM的电荷环境

采用环境扫描电镜（ESEM），非导体及含水样品不经过表面喷金或喷碳处理就能直接观察。在ESEM样品室中，电子-离子-样品相互作用，构成了一个复杂的动态电荷环境：入射电子（PE），二次电子（SE）、背散射电子（BSE）受到气体的散射作用；气体分子被PE、SE、BSE电离产生正离子流向样品表面运动，并与电子中和；离子场对SE的场助发射作用等。因此测量及评价ESEM的电荷环境，可为消除荷电效应，或利用荷电效应成像提供依据。     

碳纳米管材料和碳纳米管基器件的扫描电镜成像

本文探讨了在扫描电镜中单壁碳纳米管的成像问题.一般情况下碳纳米管的像衬度随入射电子能量,扫描速度,样品基底和环境而变,情况非常复杂.但在一定厚度的SiO2绝缘基底上且与金属电极相连的单壁碳纳米管的成像机理则相对简单.单壁碳纳米管像衬度的贡献主要来源于二次电子而不是背散射电子.像衬度产生的机理主要为SiO2绝缘基底在成像过程中的电荷积累导致的表面电势的变化对于碳纳米管以及周围SiO2基底二次电子发射效率的影响.     

环形固体背散射探测器的最佳检测距离

当入射电子与物质相互作用后又能返回表面逸出，则这部份原入射电子称为背散射电子。通常以能量小于50eV的电子称为二次电子，大于50eV而小于E0的电子称为背散射电子，用背散射电子来扫描成像所获得的图像称为背散射电子像。     

多级降压收集极CAD中的二次电子发射模型

多级降压收集极被广泛应用于提高微波放大器件效率.多级降压收集极中的二次电子发射对其效率有重要影响.该文探讨了真二次电子、弹性反射电子、非弹性反射电子3种二次电子发射模型,对发射率、发射角度以及能量分布情况进行了深入分析,并对考虑二次电子后的收集极模拟计算收敛条件进行了讨论.上述结果在多级降压收集极CAD软件中得到应用,定量分析了其对多级降压收集极效率的影响.     

高分辨二次电子像中的成份衬度

高分辨二次电子像中的成份衬度徐军陈文雄张会珍（北京大学电镜实验室，北京１００８７１）在传统的扫描电子显微学的概念中，二次电子像中包含的是形貌衬度，而背散射电子像中包含的是成份衬度。但实际上二次电子的产额是和样品的成份有关的，不过样品表面极易玷污，样品...     

扫描电子显微镜中吸收电流像的应用

扫描电镜(SEM)具有多种成像模式,二次电子像和背散射电子像是最常用的模式。这两种像的衬度均与试样—检测器的几何位置有关,具有不同程度的阴影效应。吸收电流像与试样—检测器的几何位置无关,无阴影效应。对均匀的电惰性材料,吸收电流像与发射电流像(二次电子像和背散射电子像)的衬度互补。对半导体和磁性材料,没有这种互补关系。本文根据吸收电流像的特点,对均匀电惰性材料用吸收电流信号作为附加模式,用两次曝光技术对二次电子像中不易得到的形貌细节补偿,获得了清晰的图像。图1—4是对黄铜试样垫上的激光孔补偿前后的对比。我们还用吸收电流像观察了多相合金表面成份分布和半导体材料中的势垒电子伏特效应。实验结果表明吸收电流像主要有以下几种应用:     

Energy exchange via electron-electron scattering in many-valley semiconductors

The theoretical treatment of electron-electron (e-e) scattering in semiconductor transport has always posed formidable problems, due to the long range and to the non-linearity of the interaction. Here we present a Monte Carlo study of the e-e interaction based on a molecular-dynamics approach. The full long range of the Coulomb interaction is accounted for, and no assumptions are needed on the screening process. This is particularly important when different valleys are involved, and a multi-component plasma has to be simulated. The Monte Carlo algorithm is applied to the study of the relaxation of photo-excited electrons in GaAs looking in particular at the energy exchange between electrons in different valleys. Such type of interaction has never been considered up to now in Monte Carlo simulations. The dependence of the e-e interaction on the electron density is discussed in detail. A comparison with a different approach, that treats the e-e scattering in k-space using a screened potential formulation, is also presented.     

低能电子束散射模拟在邻近效应修正中的应用

文章运用Monte Carlo方法模拟具有高斯分布特征的低能入射电子束斑在PMMA-村底中的复杂散射过程，分别得到了电子束在抗蚀剂中的穿透深度和能量沉积分布圈，并利用模拟结果进行邻近效应的修正．得到修正后的剂量数据文件。结果表明：采用修正后的剂量曝光，光刺胶中的能量沉积比较均匀．曝光分辨率有较大幅度的提高。该研究将对低能电子束曝光技术的定量研究和邻近效应修正技术的探索具有较高的理论指导意义。     

低能电子束对抗蚀剂曝光的Monte Carlo模拟

考虑二次电子的产生和散射，利用Monte Carlo方法模拟了具有高斯分布特征的低能入射电子束斑在抗蚀剂中的散射过程，分别得到了电子束在抗蚀剂中的穿透深度和能量沉积的分布图。发现在能量小于2．5keV范围内的模拟结果与实验结果相吻合，这比用传统的不考虑二次电子的Bethe公式得到的模拟结果更加符合实际的电子散射过程，精度更高。另外还发现电子束能量越低，曝光的分辨率和效率越高，这一结果也与实验相吻合。结果表明，二次电子的产生和散射对电子束曝光起了重要的作用，需考虑它们的影响。     

The influence of ion beam parameters on pattern resolution

In nanofabrication the generation of phonons and secondary electrons by an incoming ion in a specimen gets important in limiting the resolution of the fabricated structures. A model is presented for calculating the effect of ion beam parameters (mass and energy) on the resolution and the production yield. In this model the phonon and secondary electron effect are calculated based on results for the scattering of the ions obtained with the Monte Carlo simulation program TRIM. The fabrication resolution is simulated for implantation, sputtering and beam induced etching and beam induced deposition.

Some preliminary results are given which show that the best resolution can be obtained for ions with high mass at low energy for all discussed fabrication techniques, while even the production yield is relatively high at these parameters.     

电子束曝光的Morte Carlo模拟

建立一个更为严格地描述电子散射过程的物理模型，运用Monte Carlo方法模拟高斯分布电子束在靶体PMMA-衬底中的散射过程，研究不同曝光条件对沉积能密度的影响，获得的沉积能分布规律是：有利于降低邻近效应的高束能、薄胶层，提高曝光分辩率。     

Quantitative measurements of intervalley and carrier-carrier scattering in GaAs with hot (e,A) luminescence

We have used photoluminescence from nonequilibrium electrons recombining at neutral acceptors to quantitatively measure hot electron kinetics in GaAs. Values have been obtained for intervalley scattering rates as a function of electron kinetic energy and the scattering rate of a single nonequilibrium electron in the presence of a sea of thermalized carriers. These measurements demonstrate the power of this new probe of nonequilibrium carrier relaxation in direct gap semiconductors.     

基于散射模型的霓虹现象研究

霓和虹是天空中常见的大气光学现象,采用几何光学理论能够较准确地解释其成因。然而,几何光学理论的物理模型相对简单,不能说明雨滴尺度等因素对霓、虹形成的影响。本文采用散射理论研究了不同尺度水汽粒子的散射相函数以及雨滴粒子集群的角向色散特性,从散射的角度解释了霓和虹的成因,最后对散射理论和几何光学理论做了对比。研究结果为大气光学现象的研究提供了新的思路。     

Phase measurement of atomic resolution image using transport of intensity equation

Since the Transport Intensity Equation (TIE) has been applied to electron microscopy only recently, there are controversial discussions in the literature regarding the theoretical concepts underlying the equation and the practical techniques to solve the equation. In this report we explored some of the issues regarding the TIE, especially bearing electron microscopy in mind, and clarified that: (i) the TIE for electrons exactly corresponds to the Schr?dinger equation for high-energy electrons in free space, and thus the TIE does not assume weak scattering; (ii) the TIE can give phase information at any distance from the specimen, not limited to a new field; (iii) information transfer in the TIE for each spatial frequency g will be multiplied by g2 and thus low frequency components will be dumped more with respect to high frequency components; (vi) the intensity derivative with respect to the direction of wave propagation is well approximated by using a set of three symmetric images; and (v) a substantially larger defocus distance than expected before can be used for high-resolution electron microscopy. In the second part of this report we applied the TIE down to atomic resolution images to obtain phase information and verified the following points experimentally: (i) although low frequency components are attenuated in the TIE, all frequencies will be recovered satisfactorily except the very low frequencies; and (ii) using a reconstructed phase and the measured image intensity we can correct effectively the defects of imaging, such as spherical aberrations as well as partial coherence.     

Radar image study of simulated breaking waves

Radar images of electromagnetic scattering from one-dimensional simulated ocean breaking waves are described. Backscatter results from 10-14 GHz at 60/spl deg/ to 80/spl deg/ incident angles are considered for surfaces that satisfy an impedance boundary condition. The generalized forward-backward method with spectral accelerations was used as an exact numerical solution to obtain backscatter returns from several surface profiles, and radar images are formed through back-projection tomography. Detailed investigations of the images are provided to clarify major and secondary scattering events, as well as the polarization dependence, and a ray-tracing analysis is performed to interpret multipath scattering mechanisms. By adding surface roughness outside the breaking region, small-scale roughness scattering effects are also investigated.