The apparatus includes an electron source for generating an electron beam, a deflector for scanning generated electrons, an objective lens for focusing the electron beam upon the object, a grid disposed between the object and the objective lens, a wafer holder for holding the object, a sensor for detecting generated secondary electrons, {HEAD ~ a potential controller} for controlling {TAIL ~ the potential E0}, E1 and E2, and a storage for storing optimum potential conditions 
The apparatus includes an electron source for generating an electron beam , a deflector for scanning generated electrons , an objective lens for focusing the electron beam upon the object , a grid disposed between the object and the objective lens , a wafer holder for holding the object , a sensor for detecting generated secondary electrons , { HEAD ~ a potential controller } for controlling { TAIL ~ the potential E0 } , E1 and E2 , and a storage for storing optimum potential conditions
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH