Automatic focusing unit for scanning electron microscope and so on

Abstract

Abstract PURPOSE: To search automatically a focus to improve the operational efficiency of a scanning electron microscope by providing a means, which detects the defocusing of the smaple image obtained by scanning a smaple by electron beam, and constituting this unit so that focusing may be started on a basis of output signals of this means. CONSTITUTION: Secondary electrons generated from sample 3 by electron beam 1 are detected by detector 6, and the output signals are sent to display device 8. Meanwhile, pulse generator circuit 16 is triggerred to operate automatic focusing unit 9, and change components of detection signals obtained every one horizontal scanning are integrated. Then, the current value of object lens 2 is obtained when the integrated value is maximum, and this value is held in peak hold circuit 12. Here, when defocusing has occurred, the integrated value sent to comparator 14 is reduced; and when this value becomes smaller than a prescribed value sent from potentiometer 15, circuit 16 is triggerred to start the operation of unit 9, and circuit 12 is cleared. As a result, when the focus has gotten worse than the initial focusing state, unit 9 is operated automatically to obtain always good-quality images COPYRIGHT: (C)1979,JPO&Japio

Inventors

• 👤 Takao Namae

Bibliographic Details