Reporting their results in the journal Nanotechnology, scientists in Finland have used a direct-write FIB implantation technique to pattern the thin (50 nm) surface layer of a silicon substrate. The patterned layer then acts as an etching mask in tetramethylammonium hydroxide (TMAH).

This simple, combined process allows accurate, predetermined control of the shape and dimensions of the nanostructure, and offers orders of magnitude improvements in writing speed compared with direct FIB milling of 3D structures. Thus, rather straightforward TMAH etching can be extended to nanoscale patterning of test samples without the use of any lithography masks.

Using the combined FIB implantation and TMAH etching process, the group has generated various types of 3D nanostructures, including high-resolution gratings (20 lines/µm), freestanding beams and bridges (widths from 25 nm), and nanochannels separated by vertical, high-aspect-ratio sidewalls (1:30).

The approach is applicable to true nanomechanical devices such as cantilever sensors and integrated optical components with subwavelength features. It is likely to be especially advantageous in future applications involving the integration of NEMS devices on the same substrate as semiconductor devices.

More details can be found in the journal Nanotechnology.