Ion beam lithography with single ions

Abstract

Although sub-micron structures have been fabricated with ion beam lithography using focused MeV ions, the best resolution of the method has not yet been approached. The best resolution is potentially around 10 nm which is the diameter of latent damage produced by the passage of a single fast ion through sensitive materials where the ion range could be tens of micrometres. In principle, the latent damage can be developed to create very high aspect ratio nanostructures. We call this technique single ion nanolithography. In order to approach the ultimate resolution of lithography with single ions we investigate the resist material, the exposure as a function of ion type and development parameters. To implement the technique we have developed a novel strategy that employs a resist film on an active substrate that functions as a detector sensitive to single ion impacts. Together with a focused microbeam, the precise control of ion fluence attained by counting ion impacts allows us to perform a convenient systematic study of the track formation and seek conditions where single ion tracks can be produced. We report here the current status of the investigations using PMMA and CR-39 resists which are shown to be sensitive to single ions. A key issue is also the post-development imaging method.