Fabrication of novel AFM probe with high-aspect-ratio ultra-sharp three-face silicon nitride tips

In this paper we present the wafer-scale fabrication of molded AFM probes with high aspect ratio ultra-sharp three-plane silicon nitride tips. Using $\langle$111$\rangle$ silicon wafers a dedicated process is developed to fabricate molds in the silicon wafer that have a flat triangular bottom surface enclosed by three \{111\} side planes. By conformally coating the mold with a sufficient thick layer, the mold is sharpened, removing the flat bottom surface in the silicon mold, leaving a mold ending in three \{111\} side planes, which always intersect in a point. This ultimately results in AFM probes with tetrahedral tips consisting of three planes, thus the tips have ultra sharp apexes. We used silicon nitride to mold the probes in order to obtain more wear resistant probes compared with commonly used silicon. Inspection of the fabricated tips shows a tip radius of less than 4 nm.