AUTOMATIC ADJUSTING METHOD OF FOCUS POSITION OF ELECTRON BEAM

摘要

PURPOSE:To automate the adjustment of a focus position by scanning an electron beam across the seam of the object to be worked on each change of a focusing coil current and by finding the focusing coil current that the minimum value of the detected secondary energy is made minimum. CONSTITUTION:The secondary energy 9 detected by a collector 8 shows a change when an electron beam 3 is scanned so as to traverse the seam 7 of the object 4 to be worked, and the secondary energy amount is reduced at the part of the seam 7. This reduction ins made minimum at the time when the electron beam 3 is focused on the surface of the object to be worked and the focusing coil current of a focusing lens 5 at that time is made most suitable for the electron beam current at that time. This state is attained by adjusting repeatedly the action of a minimum value detection of the secondary energy 9 until the current of the focusing lens 5 is made minimum.