Achromatic two-stage E x B mass filter for a focused ion beam column with collimated beam

A two-stage achromatic E x B mass seperator has been desinged for a high-current focused ion beam column with collimated beam. The seperator consists of two homogeneous field E x B filters, a stigmator and the seperation aperture. The second-order geometrical and chromatic aberration coefficients are derived and their dependence on magnetic pole piece and electrode geometry are investigated in performing electric and magnetic field calculations. The influence of the mass seperator on the spatial resolution of the column is discussed.