Design of an electrostatic ion optical system for microfabrication with 100 A resolution

A computer-aided design program (CAD) has been developed to provide rapid, interactive design of electron and ion optical systems. The CAD program simulates the focusing and deflection properties of systems consisting of cylinder electrodes and octupole deflectors. Ion optical systems for use with an H2+ gaseous field ion source were designed using the CAD program. The design goals were to produce a 100-A-diam probe capable of scanning a 0.2-mm-square field with an expected energy spread in the source of ΔE/E = 1/30 000. A system of five cylindrical electrodes (6-mm-diam bore) with the middle electrode containing double octupole deflectors would produce a 100-A-diam probe using an acceptance half-angle of 4 mrad when dynamic correction is used. Another sytem was calculated using cylinders with bores of 8-mm diam and somewhat larger lens elements to produce a 100-A-diam probe without dynamic corrections if a 2 mrad acceptance half-angle is used