SINGLE-PARTICLE TECHNIQUES

The high radiation damage of MeV heavy ions does not only destroy targets, it can also be used to produce microstructures in an unusually wide range of materials by a combination of irradiation and chemistry. Unlike any other type of radiation used for microlithography, already a single ion is able to produce a microstructure, usually an etch cone of various opening angles. If one is able to control the position, the length and the shape of an etched nuclear track, this method may be a valuable complement to the already existing microlithographic tools. Unfortunately microlithography with heavy ions does not work the usual way: The use of irradiation masks is hampered by the fact that masks of sufficient thickness cannot be produced economically and, if they could be produced, every ion scattered in the mask could give rise to a defect. Therefore we decided to avoid the use of masks and to write microstructures directly by a heavy ion microbeam which has the additional advantage that it can be almost free of scattered particles. To compensate for the economic disadvantage of that slow writing method, we started using single precisely aimed ions, because there are microstructures which can exclusively be produced that way. As it turned out later, other applications in microelectronics and biology may also profit from single particle techniques and the tools developed for single-particle techniques may be useful for a much wider range of applications.