Proton beam writing: a platform technology for nanowire production

P-beam writing (proton beam writing) is a unique direct write 3D nano-lithographic technique which has been developed at the Centre for Ion Beam Applications (CIBA), in the Physics Department of the National University of Singapore. This technique employs a focused MeV proton beam which is scanned in a predetermined pattern over a resist (e.g. PMMA, SU-8 or HSQ), which is subsequently chemically developed. In e-beam writing as well as p-beam writing the energy loss of the primary beam is dominated by energy transfer to substrate electrons. Unlike the high energy secondary electrons generated during e-beam writing the secondary electrons induced by the primary proton beam have low energies (typically less than 100 eV) and therefore a limited range, resulting in minimal proximity effects. The low proximity effects exhibited by p-beam writing coupled with the straight trajectory and high penetration of the proton beam enables the production of high aspect ratio, high density 3D microand nano-structures with well defined smooth side walls to be directly written into resist materials. These structures can be used as templates to electroplate metallic nanowires.