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

A process for fabricating high-aspect ratio ( approximately 1:20), micron-sized Si [001] 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 >20mum. These pillars were then reduced in size using an aqueous NaOH and KOH solution heated to 100 degrees 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 <100nm tip points for direct field ionization.