<title>Influence of first lens on magnification optimization method in two-lens FIB optical system</title>

Abstract

Focused ion beam (FIB) tools are widely used for scanning ion microscope (SIM) image observation and for ion milling in semiconductor and other industries. The demands for a higher resolution in SIM and for a more intensive beam in ion milling are increasing. Limiting in 2 lenses FIB optical system, we studied the influence of the first lens's properties, particularly magnification M<SUB>1</SUB> and extraction voltage V<SUB>ext</SUB>, on the attainable beam diameter through an optimizing calculation. From this point of view, we investigated the attainable smallest beam size in the low current region by varying the parameters of the first lens, and found out that the lower extraction voltage has an advantage for getting a smaller beam. It is of big concern, as far as emission is possible, how much the extraction voltage can be minimized. It is related to M<SUB>1</SUB>, and the change of V<SUB>ext</SUB> between 5 and 12 kV produces the beam size variation of about 1 to approximately 1.5 nm. It is not negligible compared with the beam size of approximately 5 nm, which is attainable today. Therefore, we have a possibility to reduce the beam size by reviewing the first lens properties including V<SUB>ext</SUB>. Finally, a guide line is shown for the FIB column design from this point of view.