Proton beam writing using the high energy ion nanoprobe LIPSION

Abstract

Proton beam writing (PBW) is a very unique technique capable of the direct creation of three dimensional structures with a very high aspect ratio. Since the high energy ion nanoprobe LIPSION has a very high spatial resolution and is therefore well suited for the creation of structures in the micrometre range or below, it is planned to establish the PBW technique at the University of Leipzig. The results of the first proton beam writing experiments at the LIPSION nanoprobe are presented in this article. Structures with high aspect ratio and smooth side walls with an edge definition of ∼0.2μm were created in negative SU-8 photo resist using 2.25MeV protons. Furthermore, investigations were carried out concerning the mechanical stability of single free standing walls in order to collect information for the targeted production of samples with smaller feature sizes in the submicrometre range. Up to now, wall widths down to 1.5μm were achieved. However, smaller feature sizes could not be obtained due to beam spot fluctuations which enlarge the wall width by a factor of three. Self-supported structures were produced using 2.25MeV protons and subsequently 1.5MeV helium ions demonstrating the stability and accuracy of these real three dimensional structures. In addition, different methods for online dose normalization were tested showing that ionoluminescence is the most suitable method for this purpose.