Unconventional lithographic fabrication of nanostructures using charged particles, laser interference and nanoimprint

Abstract

The research work presented in this thesis focuses on three topics: (1) the development of a novel lithographic approach to fabricate three-dimensional (3-D) nanostructures using focused helium ions based on deepened understanding of 3-D energy dissipation of helium ions; (2) the investigation of developing hybrid approaches using interference lithography, electrodeposition and imprint transfer for fabricating large-area regular nanostructures and demonstrating their applications in plasmonic sensing; (3) the studies on nanoimprint lithography (NIL) on unconventional substrates and durability of imprint patterns in sub-10 nm UV NIL. Based on these topics, the thesis is divided into three parts.

The first part presents the numerical and experimental investigations of helium ion beam lithography and the development of 3-D helium ion beam lithography. First, a model to simulate the volumetric energy dissipation of helium ions in materials is proposed and validated with experimental results. The model is based on a Monte Carlo method and has the capability to be tailored for various of resist materials by changing the parameters of resist. Moreover, by comparing the numerical and experimental results, critical energy density for sufficiently crosslinking hydrogen silsesquioxane (HSQ) by helium ion beam exposure is investigated. Second, a facile and controllable 3-D nanofabrication method relying on focused helium ion beam lithography is developed based on the model. Embedded nanochannels inside crosslinked HSQ structures, and free-standing nanosized grids have been fabricated as demonstrations of the method.

The second part describes a novel approach to fabricate large-area nanostructures on flexible plastic films using lithography, electrodeposition and imprint transfer (LEIT). A new type of plasmonic refractive index sensor featuring square gold-nanocheckerboard-embedded in a flexible plastic film is designed and fabricated. An excellent sensitivity of 435 nm RIU^(-1) has been demonstrated on the prototype sensor within the visible range, which is among the highest of all reported LSPR sensors in the visible range. Besides, because of the embedded nature of the gold nanostructures, excellent mechanical stability against repeated bending and peeling is observed.