Effect of the Einzel Lens Structure in Microcolumn

Electron beam microcolumn system is thought to be attractive because of its potential applications as a miniaturized electron source and various equipments based on it. Einzel lens is composed of three lens electrodes and used to focus the electron beam. The structure of an Einzel lens has been reported to have a great influence on the final output beam properties. The influence of the lens thickness and the focusing voltage on its operation has been investigated. Simulation analysis was performed with FCM by varying the electrode thickness from 2 to 100 µm and the focusing voltage from 1500 to 2300 V in an accelerating mode. Both probe beam diameter and working distance decrease with the increase of the focusing voltage and the relation between these two variables shows a linear dependency. The result also indicate that both probe beam diameter and working distance decrease with the increase of the thickness of electrode. The change of the electrode thickness from 2 µm to 100 µm show 20%–40% decreasing of the beam diameter. Most of all, Einzel lens composed of thicker lens offers smaller probe beam and more stable operation rather than conventional 2 µm thin lens system. This result suggests that the high performance of as well as easier fabrication can be achieved through optimization of the Einzel lens structure.