Silicon nano-fabrication by using silica nanosphere lithography technique for enhanced light management

We present a complete silicon (Si) nano-fabrication process to provide controlled shapes of nanostructures over large-scale Si surface area by combining our novel solvent controlled silica nanosphere (SNS) spin-coating method with reactive ion etching. Our novel spin-coating method shows that the introduction of N,N-dimethyl-formamide solvent for SNS spin-coating can greatly enhance the uniformity of spin-coated 2-dimensional SNS layer and its coverage with significantly less sensitivity to deposition area. The enhanced quality and coverage of SNS provided excellent nano-patterning for diverse etching applications. With our SNS lithography, reactive ion etching (RIE) has been applied with fluorine (F) and chlorine (Cl) based gases to provide (1) controlled etching selectivity between SNS (SiO₂) and Si substrate and (2) desired etching orientation depending on target shape of structure. Here we focus on the fabrication of Si nanopillar structures with various top diameters but fixed height which show significantly improved anti-reflection effect. In addition, computational optical modeling with rigorous coupled wave analysis (RCWA) shows that well-tapered nanocone structures can provide greatly reduced incident light angle dependence for surface reflection.