Fabrication of free standing resolution standards using proton beam writing

Abstract

The need for a smaller beam size has been driven by the goals of producing nanostructures using proton beam writing (PBW) and also improving the spatial resolution for ion beam applications (e.g. PIXE, RBS, IBIC, etc.) to nanodimensions. Thus, it is vital to have a resolution standard which has a high degree of side-wall straightness. PBW, as a true direct-write 3D micromachining process, is an ideal technique to produce free standing resolution standards with precise edges and straight side walls. This paper describes a process for fabricating free standing Ni resolution standards with a thickness of 2 μm. A large area support structure for the grid was fabricated in PMMA using deep ultraviolet (DUV) at 220–250 nm exposure, and at the centre of the support structure we used PBW to fabricate a microgrid. Ni Sulfamate electroplating was then performed to produce a 2 μm thick Ni grid from this polymer pattern. The combination of PBW and DUV allows a rapid fabrication of the resolution standard, which was observed to have a side-wall verticality of 89.4°, and an average side wall projection to the beam of around 20 nm on either side.