Single-Ion Micromechanics

Extract

This article describes the production of different types of microstructures using high-energy heavy-ion beams, a process called single-ion micromechanics. The formation of high-resolution “radiation shadows” using unfocused, high-energy heavy ions is first described, and the rest of the article discusses the production of microstructures using precisely aimed single ions and the technology underlying this process using a microprobe.

The process of using heavy ions for microlithography was initially developed at GSI (Gesellschaft für Schwerionen-forschung, Darmstadt, Germany) because of their property of traveling in straight lines within matter. Owing to their very high momentum, they tend to undergo very little lateral scattering. This is an even more pronounced characteristic for heavy ions than for light ions, such as MeV protons (as were discussed for lithography in the article by Watt et al.). Figure 1 shows an example of this behavior for 7.5-MeV per nucleon xenon ions in mica. To make the tracks visible, the irradiated mica was broken along the tracks. The length of the individual tracks from top to bottom is about 25 μm.

Such heavy, high-energy ions cause greater radiation damage than lighter ions. Their large rate of nuclear energy loss results in their displacing lattice nuclei with enough imparted energy that these nuclei create more displacements in subsequent collisions of their own. Therefore, high-energy heavy ions are very efficient for creating microstructures, compared with other types of radiation, because each individual ion can produce an observable irradiation effect, while it always takes more than one light ion, electron, x-ray, or light photon to render developable one volume element of the sample. Figure 2 shows the lattice disorder created by a single high-energy uranium ion in germanium sulfide.