Fabrication of high-aspect ratio Si pillars for atom probe 'lift-out' and field ionization tips

A process for fabricating high-aspect ratio (∼1:20), micron-sized Si [0 0 1] pillars using mechanical and chemical size reduction is presented. A dicing saw was used for mechanically patterning an array of square pillars with side lengths of >20 μm. These pillars were then reduced in size using an aqueous NaOH and KOH solution heated to 100 °C. The chemical etch reduces the pillar size within the time range amenable for focus ion beam milling and/or attachment for atom probe 'lift-out' specimens. The pillars can be formed with either a flat top surface or into <100 nm tip points for direct field ionization.