Apertureless Beam Pen Lithography with Applications on Metallic Nano-Particles Array and Localized Surface Plasmon Resonance

Abstract

This dissertation presents a new type of apertureless beam pen near-field photolithography An array of polyurethane acrylate (PUA) pyramidal microstructures fully coated with a metal layer is illuminated by a traditional ultraviolet (UV) lamp to generate an array of UV beam pens over a large patterning area for realizing apertureless beam pen lithography Experimental results show that significant UV energy can pass through the apex of a fully metal-coated PUA pyramid even though the thickness of the metallic coating exceeded the penetration depth of UV light Both depth and the full-width-at-half-magnitude (FWHM) of patterned photoresist (PR) nanostructures increased with exposure dosage implying that the patterned PR profiles are created by UV exposure rather than by physical imprinting Finite-element simulation of the UV light intensity distribution near the apex of the pyramid and within the photoresist layer is carried out Simulation results show that the energy concentration within the pyramids is significantly increased by approximately an order of magnitude hence enhancing the UV energy passing through the fully metal-coated apex The advantage of apertureless beam pen lithography is its easy implementation for large-area patterning with a high resolution and high throughput However the topography of patterned photoresist is strongly related to the distribution of the UV field and therefore the patterned positive-tone photoresist structures are inverted-Gaussian-shaped rather than having a steep sidewall To resolve this issue a two-stage pattern transfer process is proposed and developed in this dissertation to produce vertical-sidewall photoresist nanostructures The basic concept is to use apertureless beam pen lithography to pattern a metallic hard mask which is then used in the subsequent deep reactive ion etching process to form high-aspect-ratio photoresist nanostructures The sub-micron feature size can be precisely controlled by optimizing the parameters of nanolithography and sputter-etching of metallic hard mask Photoresist nanostructures with a high aspect-ratio can be easily achieved This approach essentially overcomes the difficulties and limitation of Gaussian-shaped PR structures that are commonly encountered in near-field lithography and allows rapid prototyping and maskless micro/nano-fabrication at reasonable cost Finally a desktop 5-DOF nano-positioning system is built-up to achieve multi-steps exposure with apertureless beam pen lithography Following by two-stage pattern transfer and metal lift-off processes arrayed gold nano-particles (AuNPs) with a minimize diameter of 250 nm and a thickness of 40 nm are successfully achieved Several interparticle distances of AuNPs are achieved to demonstrate the ability of fabricating diversified arrangement of AuNPs by the developed exposure system over a large area Both experimental results and numerical simulations are carried out to analysis the localized surface plasmon resonance phenomenon of multi-dipole interaction appeared in various samples fabricated by the developed apertureless beam pen nanolithography system

Date of Award	2015 Aug 13
Original language	English
Supervisor	Yung-Chun Lee (Supervisor)