Focused ion beam (FIB) milling is a well established top-down fabrication approach. While being extremely accurate and flexible, the method suffers from a very low speed, making it virtually impossible to fabricate large arrays of structures.

In our approach, we create silicon nanostructures by combining FIB with cryogenic deep reactive ion etching (DRIE), which shortens the process time by several orders of magnitude. The trick is to use the FIB to create a thin masking layer measuring only 30 nm.

Another benefit is that the introduction of a separate etching step gives better control over the side-wall quality compared with direct milling. Holes and pillars with aspect ratios of up to 15 can be fabricated routinely using the combined procedure.

In our resolution determination experiments with a Helios Nanolab 600 dual-beam system (FEI Company) and a Plasmalab System 100 reactor (Oxford Instruments), we achieved the maximum resolution of 20 lines/µm, so structures with a size of 50 nm can be created.

Application areas include plasmonics and metamaterials as well as nanomechanical networks and quantum structures.

The researchers presented their work in Nanotechnology.