PARTICLE-OPTICAL APPARATUS COMPRISING A DETECTOR FOR SECONDARY ELECTRONS

摘要

The focusing device 8 for the primary beam in a scanning electron microscope (SEM) consists in known manner of a combination of a magnetic gap lens 34 and a monopole lens 38. The secondary electrons released from the specimen are detected in accordance with the invention by a detector whose actual detecting elements 64, 66, are arranged in a field-free space between the gap lens and the monopole lens. This space is rendered field-free by a screening plate 44 arranged underneath the gap lens. In order to achieve a high detector efficiency and a large field of vision, the pole tip of the focusing device 8 is provided with an attraction electrode 42 whose potential is higher than that of the specimen.