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Study of Secondary Electron Image Contrast of Sample Surfaces Scanned by Focused Ion Beams

聚焦离子束扫描样品表面二次电子图像对比度研究

基本信息

批准号：
14550026
负责人：
OHYA Kaoru
金额：
$ 1.22万
依托单位：
The University of Tokushima
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

项目摘要

A scanning ion microscope (SIM) has been employed both by scanning a gallium (Ga) focused ion beam (FIB) on a sample surface and by detecting secondary electrons (SEs) emitted from the sample. Although the image formation mechanism present in the SIM is similar to that in a scanning electron microscope (SEM) there are some differences in image properties for materials, surface topography, grain contrast, and so on. In order to study the difference between STM and SEM images, a Monte Carlo simulation of ion-induced and electron-induced secondary electron emission was performed for 17 metals with atomic numbers, Z_2, of 4 -79 under Ga ion and electron bombardment with energies of several tens of and several keV. The SEs are produced in the SIM through collisions with three different collision partners : projectile ions, recoiled target atoms, and target electrons. The basic concept of our Monte Carlo model is to simulate all the trajectories of collision partners.The SE yield for Ga ion bombardment generally decreases with increasing Z_2, whereas the SE yield for electron bombardment increases. This explains the origin of the opposite trend in the material contrast between SIM and SEM. The lateral distribution of SEs escaped from the surface, which was much narrower for Ga ions than for electrons, indicates that the spatial resolution of SE images is better for SIM than SEM. For comparison between topographic contrasts in SIM and SEM, pseudo-images of semicircular rods with different radii were reconstructed from a line profile of the SE intensity obtained by the beam scan on the pattern. They revealed the topographic contrast for heavy metals is clearer in SIM than in SEM, whereas for light metals both contrasts are similar to each other. When scanning a step with large height and small wall angle, the bright area on the step caused by an edge effect was less for Ga ions than for electrons, so that the inclined wall is clearly observed in the SIM.

扫描离子显微镜(SIM)既可以扫描样品表面的镓(Ga)聚焦离子束(FIB)，也可以检测样品发射的二次电子(Ses)。虽然SIM的成象机理与扫描电子显微镜相似，但在材料的成象性质、表面形貌、颗粒对比度等方面有所不同。为了研究扫描隧道显微镜(STM)和扫描电子显微镜(SEM)图像的差异，对原子序数为4-79的17种金属的离子诱导和电子诱导二次电子发射进行了蒙特卡罗模拟。SIM中的SES是通过与三个不同的碰撞伙伴碰撞而产生的：投射离子、反冲目标原子和目标电子。蒙特卡罗模型的基本思想是模拟碰撞对的所有轨迹，一般情况下，Ga离子轰击的SE产额随着Z_2的增加而降低，而电子轰击的SE产额则增加。这解释了SIM和SEM在材料对比上出现相反趋势的原因。从表面逸出的Se的横向分布表明，SIM图像的空间分辨率比扫描电子图像的空间分辨率要好。为了比较SIM和扫描电子显微镜的形貌对比，利用光束扫描获得的SE强度的线状轮廓重建了不同半径的半圆棒的伪像。结果表明，在SIM中，重金属的地形对比度比在扫描电子显微镜中更明显，而对于轻金属，这两种对比度彼此相似。在扫描高度较大、壁角较小的台阶时，由边缘效应引起的台阶上的亮区对Ga离子的影响小于对电子的影响，因此在SIM中可以清楚地观察到斜壁。