Challenges of fabricating plasmonic and photonic structures with Neon ion beam milling

The unique properties of surface plasmons permitting subwavelength confinement of light, ultrafast propagation, and highly localized sensing are the key features for combining broadband optics and nanoscale electronics. Potential applications of plasmon-based devices span both nanoscale structures in future on-chip communication, processing and sensing, and macroscopic optical devices, such as polarizers and filters.
For all these kind of devices a reliable technique to produce plasmonic structures with nanometer precision is required. So far fabrication has been mainly conducted with well-established electron beam lithography and focussed ion beam milling (FIB) using Gallium ions. These techniques, however, are to some extend limited in their resolution, and in addition Gallium and Carbon are implanted and deposited into the plasmonic structures during FIB process, potentially changing plasmonic properties.
We are currently studying the capabilities of focussed Helium and Neon ion beam milling for the fabricating of plasmonic and photonic devices. We found that Neon ion beam milling enables us to prepare plasmonic structures, such as trenches (see Fig. 1) and V-grooves without doping and alloying effects specific to Galium FIB. Neon FIB milling is superior to Helium FIB milling in terms of the processing speed and smaller levels of implanted ions. From our perspective it is the most promising technique for the fabrication of individual plasmonic devices with a few nanometers precision.
The main challenges of utilization of Ne FIB include: 1) Fabrication of metallic trenches with high depth/width aspect ratios. (such structures are predicted theoretically to have exceptional optical properties); 2) Low writing-speed in comparison to conventional electron beam lithography and Ga FIB milling.
In our presentation we show the current progress in Neon FIB milling of plasmonic structures. We compare different materials, in particular poly- and mono-crystalline gold as well as thin films of Titanium Nitride, which are commonly used for plasmonic applications.