Proton beam writing: A progress review

A new direct write 3D nano lithographic technique 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 or SU-8), which is subsequently chemically developed. The secondary electrons induced by the primary proton beam have low energy and therefore limited range, resulting in minimal proximity effects. Low proximity effects coupled with the straight trajectory and high penetration of the proton beam enables the production of 3D micro and nano structures with well-defined smooth side walls to be directly written into resist materials. In this review the current status of proton beam writing will be discussed; recent tests have shown this technique capable of writing high aspect ratio walls up to 160 and details down to 30 nm in width with sub-3 nm edge smoothness.