Ion beam lithography for nano-scale pattern features

Abstract

With the expected availability of new tools for creating patterned ion beams containing few-nanometer sized features, it is important to examine the fidelity of registering such patterns in a receiving medium, such as the photoresist layer in a lithographic fabrication process. In this paper, we report experiments exploring the characteristics of ion beam patterning of polymethyl-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 atomic force microscopy (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. Reasonable feature profiles are readily obtained in fluence ranges around 1013 ions/cm2. Proximity effects are shown to be negligible except after over-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 feature geometries is clearly possible by appropriate selection of ion species, energy and fluence to suit the receiving medium. © 2007 Materials Research Society.