High-Precision Fabrication of Single-Crystal Silicon Nanopores with Extremely Small Feature Sizes

Abstract

Silicon nanopores have emerged as the cornerstone of ionic and nanofluidic channels, enabling diverse applications such as biosensing, DNA-based information storage, and nanopore batteries. Their mechanical robustness, surface functionalization versatility, and seamless integration with nanofluidic devices make them highly adaptable to advanced technologies. The three-step wet etching (TSWE) method has shown great promise in fabricating silicon nanopores. However, precise control of silicon etching and achieving reliable etch-stop remain significant challenges. This thesis investigates the controllable fabrication of single-crystal solid-state silicon nanopores with extremely small dimensions using the TSWE method. Novel methodologies are introduced to address these challenges, exploring their applications in nano-mask lithography, biosensing, and ionic field-effect transistors (FETs). By analyzing nanopore formation principle at the atomic scale, the study establishes a quantitative relationship between nanopore size and the related ionic current, enabling the fabrication of nanoslits as small as 3 nm. The research integrates heavy boron doping and electrochemical passivation to regulate etching rates and achieve precise etch-stop, significantly enhancing fabrication controllability and scalability, with potential for large-scale production. The fabricated nanopores were further utilized in ionic FETs, demonstrating three-dimensional gating to modulate surface charge density. This enabled transitions between ohmic and diode-like regimes and enhanced ionic current rectification, as validated by COMSOL simulations. Additionally, the nanopores were successfully applied in biosensing, achieving high-sensitivity detection of biomolecular translocation events. Nano-mask lithography was also demonstrated, utilizing the nanopores as hard masks for focused ion beam (FIB) lithography to achieve precise and reproducible pattern transfer. These findings underscore the potential of single-crystal silicon nanopores for advanced applications in nanofabrication, biosensing, and ionic circuit development. This work establishes a foundation for future exploration in ion transport, nanofluidics, and scalable device manufacturing.