材料分析Part B-2 掃描式電子顯微鏡(SEM)- SEM簡介

掃描式電子顯微鏡(Scanning Electron Microscopy, SEM)是材料分析最常使用、最容易操作的電子顯微鏡。傳統上，SEM的典型操作電壓為5 ~ 30 kV。近十幾年來，因應半導體元件製程上觀察光阻的趨勢，一部分SEM的發展走向低電壓 (1 kV or less) 和低真空的路線。SEM有二次電子影像(SEI) 和反射(背向散射)電子影像(BEI) 二種影像模式。供應表面層(數奈米~ 數微米)的形態、微結構、和成份(加裝EDS)訊息。SEI提供較淺層的材料訊息，而BEI提供較深層的材料訊息。由於聚焦電子束的收斂角很小，所以SEM影像有遠大於OM影像的景深。

SEM is the most popular and easy operation instrument for materials analysis. Traditionally, the SEM operation voltage is 5 to 30 KV. Some SEMs can be operated as low as 1 KV or even less because of the need of viewing PR in semiconductor manufacture. There are two types of SEM images, secondary electron image (SEI) and backscattered electron images (BEI), they offer materials information from volume several nano-meters to several micro-meters below the surface. SEI offers information close the surface, and BEI gives information deeper. The depth of field of SEM is much larger than that of OM due to the small converged angle of the electron beam. Composition information can be offered when an EDS system is attached.

SEM機台的基本結構如圖B-5示意圖所示。一個沒有畫出來的柱體提供一個可抽真空的環境和固定其他模組；電子鎗模組提供足夠亮度且穩定的光源；電磁透鏡與透鏡光圈用來調節電子束大小同於聚焦到試片表面，為不同模式和需求提供大小最適宜的電子束；偏折線圈控制電子束的掃瞄動作，和影像偵測器同步串聯；試片承載台用來承載試片，具有平移，傾轉，旋轉等改變試片位置和角度等功能；二次電子影像偵測器和反射電子影像偵測器分別用來接受二次電子和反射電子形成影像；EDS能譜儀接收X光訊號分析微區的組成，為選擇性附屬添加設備。

The basic configuration of a SEM is schematically shown in Fig. B-5. A column without being drawn will fix all modules and make a vacuum environment available. Electron gun module supplies a stable electron beam with enough intensity. Magnetic lenses and apertures are used to manipulate the electron beam to be different size and focus the electron beam on the specimen for different application. A stage is used to hold the specimen holder and to move/tilt/rotate the specimen to the right position and orientation. SEI and BEI detectors are used to collect SE and BE to form images respectively. EDS is usually an optional attachment for composition analysis.

圖B-5. SEM基本結構示意圖。