With the expected availability of new tools for creating patterned ion beams, containing few-nanometer features, it is important to examine the fidelity of registering such patterns in the receiving medium, such as a photoresist layer in a lithographic fabrication process. In this paper, we report experiments exploring the characteristics of ion beam patterning of poly methyl methacrylate (PMMA) and polystyrene (PS) coatings on silicon substrates, with respect to their response as positive / negative resists to patterned low-energy H+, He+ and Ne+ beams. We examine by AFM the feature profiles thus created after solvent development of the polymer layers, and we examine the dependence of the polymer response upon ion species and fluence. Edge resolution ¡Ü20 nm is readily obtained, and broad process windows are identified in fluence ranges around 1013 ions/cm2. Proximity effects are shown to be negligible, except after exposure at very high ion fluences. Granularity within the final pattern features is shown to be a potential concern for high energy, light ion irradiations. Optimization of edge resolution is clearly possible, by appropriate selection of ion species, energy and fluence to suit the receiving medium.