Doctoral Defense - Novel advancements in nanofabrication for photonic crystal applications


Event Speaker: 

Lin Lee Cheong

Event Location: 


Event Date/Time: 

Monday, July 1, 2013 - 2:00pm


The progress of large-area 2D- and 3D-photonic crystals (PCs) at optical and
near infra-red frequencies has been limited by fabrication challenges. Periodic
nanostructures must be patterned in high-index and crystalline material such as silicon
over large areas (mm2 to cm2) with reasonable throughput. These patterns also must be
placed coherently over the entire area, and contain controlled defects. No single
conventional nanoscale patterning technique is able to fulfil all of these requirements

Pattern placement and throughput challenges for planar lithography can be
addressed by combining spatial-phase-locked electron-beam lithography (SPLEBL) with
lowenergy (sub-2keV) electrons. SPLEBL obtains feedback on the electron-beam position
using a reference grid placed on top of the resist. Combining low-energy
lithography with SPLEBL places strict requirements on the SPLEBL reference grid. A
systematic investigation on a suitable grid material is carried out, and a
self-assembled monolayers (SAMs) based grid is fabricated and characterized. Another method of
fabricating large area planar PCs is through interference lithography (IL). The key
challenge is the inability of IL to pattern defects or non-periodic structures and
thermal scanning probe lithography (TSPL) is proposed as a complementary technique to IL.
Integrating TSPL with IL requires capability to transfer TSPL-fabricated patterns into
underlying material and is challenging due to the thermal-mechanical nature of TSPL. A
robust pattern transfer process is designed and the effects of the lithography and etch
processes on resolution and line-edge roughness is studied.

The membrane-stacking approach, where large-area membranes are fabricated in
parallel and then stacked to form a 3D-PC, was proposed as a more efficient method of
fabricating 3D-photonic crystals (3D-PCs) compared to conventional
fabrication methods.  There exists a need to develop techniques capable of fabricating,
transferring and assembling these membranes. In this thesis, a membrane-on-carrier (MOC)
strategy based on the membrane-stacking approach is proposed. Membranes are
fabricated and floated on liquid, and then transferred onto a temporary rigid carrier. The
key challenge is in separating the membrane from the rigid carrier onto a receiving
substrate. A dissolvable separation layer is introduced between the membrane and
carrier, and two membranes are stacked on top of another as proof-of-concept. Finally,
azimuthal alignment is incorporated into the process.
Thesis Supervisor(s): Henry I. Smith