The fabrication of silicon nanostructures by local gallium implantation and cryogenic deepreactive ion etching

Abstract

We show that gallium-ion-implanted silicon serves as an etch mask for fabrication of highaspect ratio nanostructures by cryogenic plasma etching (deep reactive ion etching). Thespeed of focused ion beam (FIB) patterning is greatly enhanced by the fact that only a thinapprox. 30 nm surface layer needs to be modified to create a mask for the etching step. Etchselectivity between gallium-doped and undoped material is at least 1000:1, greatlydecreasing the mask erosion problems. The resolution of the combined FIB-DRIE process is20 lines µm−1 with the smallest masked feature size of 40 nm. The maximum achieved aspect ratio is 15:1(e.g. 600 nm high pillars 40 nm in diameter).