DX-5型实验扫描电子显微镜

An Expeimental Scanning Electron Microscope DX-5

本文主要叙述我厂最近试制成的DX-5型扫描电镜的性能,电子光学设计方面的一些考虑。该仪器的二次电子象的分辨率为60A～70A,有较完善的视频信号处理系统,并可配两道X光分光光谱仪一个能谱仪和一个光学显微镜。该仪器是非对称物镜,用通常的对称透镜的计算参数加以修正得到正确的象差系数。物镜磁路用近似场的假设计算。扫描线圈的设计主要在大偏转范围内给出均匀场以减少低放大倍数下的畸变。为了有效的收集二次电子,在样品附近放置一个小电极加上15V～30V的电压。一个意外的噪音来源来之于电子枪附近的背反射电子通过真空管道达探测器。为了实现电子束的合轴,在电子束交叉点附近放置一个电磁对中线圈,加上瓷瓶的精确定位可以方便合轴。文章也叙述了在调试中排除了一些问题后达到60A的分辨率。

A new model Scanning Electron Microscope was developed recentlyon the basis of the first Chinese DX-3 SEM, which has been placed on the marketsince 1975. The resolution of this new model DX-5 is 60A for SE image. It isequipped with a variety of video signal processing devices. The high voltage sourcesupplies a maximum acceleration voltage of 30kV, and the Wehnelt bias, is contro-lled photoelectrically. The specimen chamber is capable of accepting a dual fullyfocused linear-type crystal spectrometer with optical microscope. The size of theelectron optical column is much smaller than the old model DX-3. A vacuum lineartube with three apertures goes through the bores of the lenses. The specimenstage has five degrees of freedom, and the whole column is mounted on airbuffers to minimize vibration problem. In this paper the performances andcharacteristics of this SEM are given. Some aspects of the electron optical systemdesign, such as reduction of objective abberation, calculation of magnetic circuitusing our coaxial-cylinder approximate model, Schlesinger deflection coil of semi-concentrated distribution, centering of electron gun with a single set deflecting aredescribed. Finally, some difficuit problems of tunning up this instrument to achievehigh performances are briefly discussed.