Material Shaping by Ion and Electron Nanobeams

Abstract

Beams of electrons and ions of energies ranging from a few keV to over 100keV and diameters in the single nanometers have become standard nanofabrication tools. Electron beams are routinely used to expose resist down to dimensions of 10nm. In principle, ion beams can be and have been used similarly to expose resist. However, what motivates this chapter is that both ion beams and electron beams can be used to directly produce structures without the usual multistep lithography process. Ion beams can simply locally sputter a surface, i.e., carve predesigned structures. In addition both electron beams and ion beams can be used to deposit material if a suitable precursor gas is adsorbed on the surface. The beam causes the adsorbed molecules to dissociate leaving some constituent behind. Similarly, if the adsorbate is a reactive gas, such as Cl₂ or XeF₂, a chemical reaction is induced where the beam is incident, and the material is locally etched. These material shaping techniques have found many applications and there are many types of structures have been built. However, the beam solid-interaction is complicated and factors other than the diameter of the beam limit the size of the structure that can be fabricated. In addition, these point-by-point fabrication techniques are slow. Typically to add or remove 1cm³ may require several tens of seconds. The finer the resolution needed the longer the fabrication time. Nevertheless these electron and ion nanobeam tools are widely used in research and in industry.