Nano-electro-mechanical systems fabricated using tip-based nanofabrication

We present progress on fabricating silicon nano-electro-mechanical systems (NEMS) using tip based nanofabrication (TBN). A heated atomic force microscope (AFM) probe deposits molten polymer on the substrate to form nanopatterned polymer masks, which are transferred to silicon by etching. In our first approach, the polymer nanopatterns were deposited onto a 25 nm thick aluminum film on a single crystal silicon substrate. A wet aluminum etch transferred the polymer features into aluminum feature, which served as a mask for subsequent Bosch silicon etching. This approach produced an array of vertical silicon nanowires with diameters as small as 200 nm and heights of 5 μm. Various other structures such as rings and curved fin arrays were also demonstrated. In our second approach, we employed metal-assisted chemical etching (MacEtch) to transfer the polymer nanopatterns into silicon. This approach is capable of producing high aspect ratio silicon nanowires. Here, we deposited the polymer nanopatterns from a heated AFM tip and transferred the nanopatterns to a 35 nm thick gold film. In the next step, we used MacEtch to etch the silicon region that directly contacts the gold. Using this approach, we fabricated vertical silicon nanowires of height 18 μm and diameter 500 nm, achieving an aspect ratio of 36. The MacEtch process produced silicon nanostructures with smoother sidewalls compared with silicon nanostructures produced by Bosch etching.