The fabrication of silicon nanostructures by focused-ion-beam implantation and TMAH wetetching

Abstract

Local gallium implantation of silicon by a focused ion beam (FIB) has been used to create a maskfor anisotropic tetramethylammonium hydroxide (TMAH) wet etching. The dependence of the etchstop properties of gallium-doped silicon on the implanted dose has been investigated and a dose of4 × 1013 ions cm − 2 has been determined to be the threshold value for achieving observable etchingresistance. Only a thin, approx. 50 nm, surface layer is found to be durableenough to serve as a mask with a high selectivity of at least 2000:1 betweenimplanted and non-implanted areas. The combined FIB–TMAH process has beenused to generate various types of 3D nanostructures including nanochannelsseparated by thin vertical sidewalls with aspect ratios up to 1:30, ultra-narrow(approx. 25 nm) freestanding bridges and cantilevers, and gratings with a resolution of20 lines µm − 1.