Fabrication of a dense array of tall nanostructures over a large sample area with sidewall profile and tip sharpness control

We report a simple but efficient nanofabrication method to create a dense (nanoscale pitch) array of silicon nanostructures (post and grate) of varying height and shape over a large sample area. By coupling interference lithography with deep reactive ion etching (DRIE) in one process flow, we achieved silicon nanostructures of excellent regularity, currently with a pitch (i.e., period) of 230 nm, and uniform coverage, currently over 2 x 2 cm(2). The new nanofabrication practice of coupling interference lithography with DRIE not only simplified the nanofabrication process but also produced high-aspect-ratio (higher than 10) nanostructures. By regulating etching parameters, the nanoscopic scalloping problem typical in Bosch DRIE was not only controlled but also utilized to realize sophisticated sidewall profiles, such as tips with a pointed or a re-entrant profile. We showed the tips could be further sharpened by thermal oxidation and subsequent removal of the oxide. Well-defined nanostructures over a large area with controllable sidewall profiles and tip shapes open new application possibilities in areas beyond nanoelectronics, such as microfluidics and tissue engineering.