| 摘要 |
PURPOSE:To improve operation efficiency without requiring hands by a method wherein the gains of the amplification of mark signals obtained by the initial scanning of a sample are adjusted on the basis of the dimensions of the mark signals, and the sample is positioned. CONSTITUTION:Electron rays 3 from an electron gun 6 are irradiated to a sample 16 on a sample base 14 through a focussing coil 8 and a deflection coil 10 for initial scanning, mark signals are detected by means of a secondary electron detector 12, the output is inputted to a wave-form memory storage 22 through a variable gain amplifier 18 and an AD transducer 20, the maximum level and the minimum level of wave-forms are obtained by means of a central processing unit 24, the optimum amplification rate of the amplifier 18 is decided, a switch-unit 182 is changed over and scanning for positioning is conducted. Thus, operation efficiency is improved because the dimensions of the mark signals are detected automatically and the optimum amplification rate of the amplifier is automatically computed and set. |
