Space charge effects in focused ion beams

Focused ion beams have significant advantages (over other directed energy beams) in terms of resist response and direct materials processing. However, the low value of q/m raises questions about space charge effects—particularly the stochastic effects which limit high throughput e‐beam systems. We have modified the space charge simulation program originally set up for electrons to allow for a greater number of particles and the effect of energy spreading in the source accelerating region. Beams of 50 keV Ga ions suffer serious spreading at currents above 1 nA (α=2 mrad); 50 keV protons suffer similar spreading at currents above 50 nA.