チャージングを回避したSEMによる絶縁物の電子放出率の測定

概要

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Scanning electron microscope (SEM) observation of an insulator material often suffers an abnormal contrast image from a charging phenomenon, which is caused by accumulation of a part of primary electrons inside the material. In order to avoid the charging phenomenon, it is important to observe the insulator material under the primary electron energy condition that the total electron emission yield σ is equal to unity. In order to find out the above primary electron energy condition, we have measured the electron emission yield σ as a function of the primary electron energy Ep for several insulator materials. In this case the specimen (= the insulator material) has been heated up to 700 °C where the charging phenomenon disappears. The value of σ has been determined by measuring both the primary electron current (Ip) and the conduction electron current (Ia=Ip-σIp) flowing to the ground through the specimen stage. We also found that the primary electron energy corresponding to σ=1 can easily be determined by the condition that the conduction electron current Ia takes a minimum value. For example, the primary electron energy that gives the condition of σ=1 for Si3N4 has been found to be Ep=3.1 keV. We have also measured the secondary electron emission yield δ of the insulator material using the contrast method, which is based on the signal intensity ratio of the SEM image of the boundary between Au and the insulator material.
2006-12-01