Nanofabrication of Optofluidic Photonic Crystal Resonators for Biosensing

Abstract

Nanofabrication of Optofluidic Photonic Crystal Resonators for Biosensing Henry Andagana Advances in nanofabrication have made possible the development of novel nanophotonics based on Photonic Crystal (PhC) structures. Different types of biosensors have been proposed to take advantage of the unique optical properties of PhCs, which, when combined with microfluidics, provide an enabling approach for biomolecule analysis. In this thesis, nanofabrication of a new biosensor structure integrating a 2D PhC nanocavity resonator with an optofluidic channel is described. The recipes for e-beam lithography of PhC and PhC nanocavity patterns were optimized by carefully tuning the e-beam dose as well as control of the resist baking and development conditions. Two PhC fabrication processes based on pattern transfers by lift-off and etch-back were compared. The plasma etching of Si, GaN, and ITO were optimized to obtain fast etching rates, vertical profiles as well as high etch selectivities over different hard masks including Si 3 N 4 , SiO 2 , and Ni. Si, GaN and ITO PhC structures with airhole diameters in the range of 100-200 nm were fabricated using the developed processes. To facilitate the integration of the PhC structures with microfluidic channels, the PhC airholes were sealed with a SiO 2 thin film formed by glancing angle deposition. By gradually reducing the flux angle toward normal during deposition, we successfully deposited uniform SiO 2 capping layers with minimal material extended down into the PhC airholes. Finally, suspended Si PhC slabs were fabricated on a Si-on-Oxide substrate using an integrated procedure which consists of e-beam lithography, pattern transfer into Si by CF 4 plasma etching, and a selective etch of the underlying SiO 2 sacrificial layer in HF. The suspended PhC structure provides an important test bed for measuring resonant fluorescence of biomolecules in PhC nanocavities in the IR range.iii

Two-dimensional Polymer and Thin-Film Semiconductor-based Photonic Crystals for Biosensing Applications

“…Two methods will be explained in detail in the next two sections. The first is a recipe that is adapted from [43] to produce suspended photonic crystal lattices of air holes in Silicon by starting first with a negative tone e-beam resist, ma-N 2403. The second will be the opposite of the first, which is to create silicon rods (pillars) surrounded by air using a positive tone resist, PMMA 950K A3.…”

“…The second will be the opposite of the first, which is to create silicon rods (pillars) surrounded by air using a positive tone resist, PMMA 950K A3. Exposure and spin recipes have been already developed in [43]. However, optimizing these recipes to the Silicon-on-Insulator and regular Silicon samples will be discussed in detail.…”

“…When the lattice constant and the radius of a triangular photonic crystal lattice are known, a DesignCAD file can be created. In this section, a generic step by step procedure adapted and modified from [43] will be demonstrated to create a simple triangular lattice DesignCAD file that can be used to create a run file and therefore fabricate a PhC structure of either holes in PMMA or pillars of ma-N, depending on the desired final features and the type of resist that is used. Descriptive images of some the steps are explained after the step.…”

“…Process flow of a suspended PhC in silicon as adapted from[43]. (1)ma-N 2403 was first spun coated on the SOI sample and an EBL procedure was carried out to define a pattern in the resist.…”