Measurement of specimen charging in scanning electron microscopy with a kelvin probe

Abstract

A vibrating Kelvin probe in form of a platinum wire loop is used to measure the surface potential Us on electron‐irradiated free‐floating metal and insulator specimens as a function of electron energy E. This allows an accurate measurement of the critical electron energy E2 for no charging. At energies below E2, the positive charging increases with decreasing energy to Us=2–5 eV at E=0.5 keV and switching off the collector bias of the Everhart‐Thornley detector. A two‐to threefold increase of Us is observed when the bias is switched on. For E > E2, the strong increase of a negative surface potential can be measured. Insulating films free‐supported on a conductive substrate show a steep decrease to small positive and negative Us when the film thickness becomes lower than the electron range at a critical energy E3 > E2. At insulating specimen the temporal decrease of charging can be measured when the electron beam is switched off. Copyright © 1994 Wiley Periodicals, Inc.