What question did this study set out to answer?

The aim is to develop a scalable method for fabricating 4 nm silicon nanopores with high reproducibility.

June 27, 2026Open Access

Scalable Fabrication of 4 nm Silicon Nanopores by Self-Limiting Metal-Assisted Chemical Etching Combined with Optical Process Control

FFFabio De FerrariKTH Royal Institute of Technology AEAlessandro EnricoUniversity of Pavia VLValentina LevaKTH Royal Institute of Technology

Key Points

The aim is to develop a scalable method for fabricating 4 nm silicon nanopores with high reproducibility.
Employed self-limiting metal-assisted chemical etching combined with optical process control.
Decoupled gold nanoparticle deposition from etching for independent optimization.
Mapped etching behavior by varying nanoparticle diameter and silicon layer thickness.
Achieved 4 ± 1 nm pore formation with a 50× reduction in diameter variability compared to catalyst size.
Established a predictive framework indicating that a d/t ratio of ≥0.8 conditions self-limiting behavior.
Successfully verified pore formation using bright-field microscopy, correlating undercut characterization to pore presence.

Abstract

High Resolution Image Download MS PowerPoint Slide Solid-state nanopores in ultrathin (<20 nm) membranes enable label-free single-molecule sensing, but their adoption as sensors is limited by the lack of scalable manufacturing methods that deliver nanopores with single-nanometer reproducibility. Self-limiting metal-assisted chemical etching (MACE) in silicon-on-insulator (SOI) membranes offers a parallel wet-chemical route for nanopore fabrication, yet prior demonstrations lacked a predictive design rule and required electron microscopy or electrical tests for confirming presence and number of pores. Here, we convert self-limiting MACE into a manufacturing-oriented workflow with optical process control to obtain and verify the formation of 4 nm nanopores in a scalable fashion. We decouple the deposition of 200 ± 10 nm gold (Au) nanoparticles from etching, enabling independent optimization of the two steps. The nanoparticle size allows for particle-per-membrane counting by dark-field optical microscopy, so that deposition can be repeated when counts are below target. We then map etching behavior across Au nanoparticle diameter d (10–200 nm) and silicon (Si) device-layer thickness t (5–18 nm), finding that d / t ≥ 0.8 ratio predicts self-limiting MACE behavior, where pore diameter becomes independent of particle size. In this regime, 200 ± 10 nm catalysts yield 4 ± 1 nm pores, corresponding to a reduction of ∼50× in pore diameter and ∼10× in pore-diameter variability compared to the catalyst diameter and related variability. Successful through-membrane pore formation produces undercuts in the buried oxide (typically ∼200–300 nm diameter) beneath each pore, which can be characterized for each membrane by bright-field microscopy and used as a proxy for the otherwise optically invisible 4 nm pores. Together, the predictive d / t framework and two-stage optical verification establish a scalable wet-chemical route to fabricate nanopores for biomolecular sensing and related nanofluidic devices.

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