Measurement of virtual crossover in liquid gallium ion source

Abstract

Gallium ion probes of 50 keV obtained from a liquid metal ion source are recorded on silicon and gallium arsenide substrates by using the method of ion bombardment enhanced etching. The minimum linewidth obtained in line exposures is about 20 nm for both substrates which corresponds to the lateral spread of the implanted ions. For a specified value of the lens acceptance half-angle, the line dose varies as a square function of the linewidth, which means that the distribution of the current density in the focused beam is Gaussian. From the theoretical evaluation of the full widths at half-maximum of these distributions, the virtual crossover diameter of the source is estimated to be 40–45 nm independently of the emission current ranging from 4 to 12 μA, and of the value of the needle apex radius of the source in the range 1–3 μm.